Saline soluble inorganic fibers

[0001] This application is a continuation of U.S. Ser. No. 09/695,194 filed on Oct. 24, 2000 now abandoned, which is a divisional of U.S. Ser. No. 09/262,378 filed Mar. 4, 1999, now U.S. Pat. No. 6,180,546 issued on Jan. 30, 2001, which is a continuation of U.S. Ser. No. 08/899,005 filed Jul. 23, 1997, now U.S. Pat. No. 5,994,247 issued on Nov. 30, 1999, which is a continuation of U.S. Ser. No. 08/535,587 filed Sep. 28, 1995, now abandoned, which is a continuation of U.S. Ser. No. 08/039,086, filed Apr. 9, 1993, now abandoned, which claims priority to International Application No. PCT/GB93/00085, filed Jan. 15, 1993, which claims priority to GB 92 00993.5, filed Jan. 17, 1992 and GB 92 24612.3, filed Nov. 24, 1992.

[0002] This invention relates to saline soluble, non-metallic, amorphous, inorganic oxide, refractory fibrous materials.

[0003] Inorganic fibrous materials are well known and widely used for many purposes (e.g. as thermal or acoustic insulation in bulk, mat, or blanket form, as vacuum-formed shapes, as vacuum formed boards and papers, and as ropes, yarns or textiles; as a reinforcing fibre for building materials; as a constituent of brake blocks for vehicles). In most of these applications the properties for which inorganic fibrous materials are used require resistance to heat, and often resistance to aggressive chemical environments.

[0004] Inorganic fibrous materials can be either glassy or crystalline. Asbestos is an inorganic fibrous material one form of which has been strongly implicated in respiratory disease.

[0005] It is still not clear what the causative mechanism is that relates some asbestos with disease but some researchers believe that the mechanism is mechanical and size related. Asbestos of a critical size can pierce cells in the body and so, through long and repeated cell injury, have a bad effect on health.

[0006] Whether this mechanism is true or not regulatory agencies have indicated a desire to categorise any inorganic fibre product that has a respiratory fraction as ‘hazardous’, regardless of whether there is any evidence to support such categorisation. Unfortunately for many of the applications for which inorganic fibres are used, there are no realistic substitutes.

[0007] Accordingly there is a demand for inorganic fibres that will pose as little risk as possible (if any) and for which there are objective grounds to believe them safe.

[0008] A line of study has proposed that if inorganic fibres were made that were sufficiently soluble in physiological fluids that their residence time in the human body was short; then damage would not occur or at least be minimised. As the risk of asbestos-linked disease appears to depend very much on the length of exposure this idea appears reasonable. Asbestos is extremely insoluble.

[0009] As intercellular fluid is saline in nature the importance of fibre solubility in saline solution has long been recognised. If fibres are soluble in physiological saline solution then, provided the dissolved components are not toxic, the fibres should be safer than fibres which are not so soluble. The shorter the time a fibre is resident in the body the less damage it can do. H. Forster in ‘The behaviour of mineral fibres in physiological solutions’ (Proceedings of 1982 WHO IARC Conference, Copenhagen, Volume 2, pages 27-55(1988)) discussed the behaviour of commercially produced mineral fibres in physiological saline solutions. Fibres of widely varying solubility were discussed.

[0010] International Patent Application No. WO87/05007 disclosed that fibres comprising magnesia, silica, calcia and less than 10 wt % alumina are soluble in saline solution. The solubilities of the fibres disclosed were in terms of parts per million of silicon (extracted from the silica-containing material of the fibre) present in a saline solution after 5 hours of exposure. The highest value revealed in the examples had a silicon level of 67 ppm. In contrast, and adjusted to the same regime of measurement, the highest level disclosed in the Förster paper was equivalent to approximately 1 ppm. Conversely if the highest value revealed in the International Patent Application was converted to the same measurement regime as the Förster paper it would have an extraction rate of 901,500 mg Si/kg fibre—i.e. some 69 times higher than any of the fibres Förster tested, and the fibres that had the highest extraction rate in the Förster test were glass fibres which had high alkali contents and so would have a low melting point. This is convincingly better performance even taking into account factors such as differences in test solutions and duration of experiment.

[0011] International Patent Application No. WO89/12032 disclosed additional fibres soluble in saline solution and discusses some of the constituents that may be present in such fibres.

[0012] European Patent Application No. 0399320 disclosed glass fibres having a high physiological solubility.

[0013] Further patent specifications disclosing selection of fibres for their saline solubility are European 0412878 and 0459897, French 2662687 and 2662688, PCT WO86/04807 and WO90/02713.

[0014] The refractoriness of the fibres disclosed in these various prior art documents varies considerable. The maximum service temperature of any of these disclosed fibres (when used as refractory insulation) is up to 815° C. (1500° F.).

[0015] Service temperature for refractory insulation is definable in many ways but to be consistent with the above mentioned International Patent Applications this application shall mean by service temperature that temperature at which the fibre shows acceptable shrinkage (maximum of 5% linear shrinkage after exposure to temperature for 24 hours) and at which the fibre has not appreciably suffered through excessive sintering or softening.

[0016] There is a demand for physiologically soluble fibres having a service temperature of greater than 815° C., particularly for such fibres having a service temperature above 900° C.

[0017] Testing for physiological solubility and safety can be done by inhalation studies on, e.g. rats. However such studies are extremely time consuming and costly. A study can take of the order of 2½ years from start and can easily cost 1 million pounds per study. A cheaper alternative is to test for solubility in physiological or like fluids in vitro.

[0018] Testing of an inorganic fibre for solubility in physiological solutions is not so time consuming, but there is currently no way of predicting which systems will produce such soluble fibres. Therefore anyone seeking to find such soluble fibres has to work on a trial and error basis assisted by what is commonly known as ‘chemical intuition’ but is equally commonly known as ‘a hunch’. Such trial and error testing is laborious and time consuming. Further, once a fibre is found that is soluble there is no guarantee that it will be usable at useful service temperatures.

[0019] Accordingly there is a demand for a method of predicting whether a fibre will have a reasonable solubility in physiological solutions, and further there is a demand that such a test should preferably give an indication as to expected service temperature.

[0020] Shrinkage of inorganic refractory fibres occurs through two mechanisms; the first is viscous flow of the fibre material. Most inorganic refractory fibres are glasses and so may be defined as liquids having an exceedingly high viscosity (but still liable to flow). By their nature fibres are elongate and so have a high surface area per unit volume. As the reduction of surface area is a means of reducing the surface energy of a material, when the glass becomes fluid enough it will flow so as to reduce surface area. This flow results in a coarsening and shortening of the fibres and so to shrinkage, and in the extreme results in disruption of the fibres into separate particles.

[0021] The second mechanism leading to shrinkage is that at elevated temperatures glasses may crystallise to form one or more crystal phases. Usually these crystal phases have a smaller molar volume than the glasses from which they crystallise and so shrinkage results. Some fibres are known for which the molar volume of the crystalline form exceeds that of the glass (for example Al₂O₃/SiO₂ glassy fibres may crystallise to form mullite crystals). In these cases the expansion due to crystallisation may oppose the shrinkage caused by viscous flow.

[0022] If shrinkage through viscous flow occurs at a much lower temperature than crystallisation then the crystallisation may not be able to compensate for such shrinkage.

[0023] There is a demand for a fibre in which both viscous flow and crystallisation occur at as high and as similar a temperature as possible, and preferably in which the expansion due to crystallisation closely matches the shrinkage due to viscous flow so that the net effect is as close to zero shrinkage as possible.

[0024] When used as refractory insulation inorganic refractory fibres are used in several forms. The fibres may be supplied as a bulk material, but in this form the fibres are difficult to handle for many applications. Alternatively the fibre may be supplied as a blanket. Blanket fibre is generally made by a process of sucking fibre from air onto a conveyor to form a blanket. Because the fibres tend to be aligned parallel to the conveyor surface they can separate easily. Accordingly the blanket fibres are secured together by adding a binder to lock the fibres together, or by needling the blanket, or both. In needling needles are passed through the thickness of the blanket to push and draw fibres to lie transverse to the blanket and so tie the fibres together. Because binders are usually resins, such as phenolic resins, they burn off on first firing. There is a desire to reduce the amount of such binders used both because of possible health implications in handling, and because the combustion products may affect the strength of the fibres. Thus needled blanket is usually preferred.

[0025] The fibres may also be supplied as blocks, generally made from assembled layers of inorganic fibre blanket.

[0026] For some fibres needling is not possible. Crystalline fibres are generally too brittle to stand the stresses involved. For the fibres known in the industry as glass fibres (which are generally used for low temperature applications) the amount of ‘shot’ (unfiberised glass particles) present is generally too high to allow needling as the shot damages the needles. There is no needled blanket on the market that has a maximum service temperature in the range 900° C.-1200° C. There are needled blankets having a higher maximum service temperature but these use expensive fibres in comparison with other fibres usable (with the aid of binders) as blanket in the temperature range 900° C.-1200° C.

[0027] Accordingly there is a demand for needled fibre blanket formed from inexpensive materials, being soluble in saline solutions, and having a maximum service temperature in the range 900° C.-1200° C.

[0028] As stated previously refractory oxide fibres are made by several methods all of which involve the formation of a melt of oxides and the subsequent fiberisation of the melt by e.g. spinning or blowing.

[0029] The melt of oxide material is often formed by electrical discharge melting of the constituent raw materials. The applicants, in manufacture of a CaO/MgO/SiO₂ refractory oxide fibre encountered problems due to the necessity of handling CaO. These problems were discovered to be due to the moisture content of CaO as commercially available. One of the problems of use of CaO is the outgasing that results upon melting and this led at the least to a porous melt pool which caused fluctuations in the melt current; in the extreme the outgasing was explosive. Additionally use of CaO appeared to cause accelerated attack on the melt electrodes. Also CaO is a difficult and corrosive material to handle.

[0030] Accordingly there is a need for a process that minimises the use of CaO.

[0031] Accordingly the present invention provides the following features both independently and in combination:

[0032] A. Use of a vitreous inorganic fibre in the knowledge that it has a composition meeting the criteria either: that the calculated sum of the free energies of hydration of the compounds that would or could be present at equilibrium (on the basis of knowledge, informed belief or reasonable assumption) is more negative than −10 kcal/100 grams (−418.4 kJ/kg) of composition; or that the percentage of non-bridging oxygens is more than 30%. Such compositions tend to be saline soluble.

[0033] B. Use of such a vitreous inorganic fibre in the knowledge that it has a composition meeting the criterion that the ratio of glass modifiers to network formers is less than a critical value (for SiO₂ based compositions the critical value is 1). Such compositions tend to be glass formers.

[0034] C. The invention also encompasses fibres selected by adopting such criteria as a test for solubility and glass formation.

[0035] D. Use as saline soluble fibres having a shrinkage of less than 3.5% when exposed to 1000° C. for 24 hours and/or 800° C. for 24 hours, of vitreous fibres having a composition comprising (in weight %):

[0036]

SiO2	>58%	(for MgO =< 10%) and
SiO2	>58% + 0.5(% MgO − 10)	(for MgO >= 10%)
(SiO2 preferably
being below 70%)
CaO	0%–42%
MgO	0%–31.33%
Al2O3	0%–<3.97%

and being essentially free of fluxing components such as alkali metals and boron oxide.

[0037] E. In one such usage the first crystalline material resulting on crystallisation has the crystal structure of diopside and has the composition consisting essentially of:—

[0038]

		Composition A
	Component	Weight percent
	SiO2	59–64
	Al2O3	0–3.5
	CaO	19–23
	MgO	14–17

[0039] F. In a second such usage the first crystalline material resulting on crystallisation has the crystal structure of wollastonite/pseudowollastonite and has the composition consisting essentially of:—

[0040]

		Composition B
	Component	Weight percent
	SiO2	60–67
	Al2O3	0–3.5
	CaO	26–35
	MgO	4–6

[0041] G. The fibres used in such manner may further be used as needled blankets.

[0042] H. Preferably the fibres of the general composition and compositions A and B mentioned above have a SiO₂ content (expressed as a weight percentage of the constituents SiO₂, CaO and MgO) of greater than 60%.

[0043] I. The present invention further provides a method for the manufacture of refractory oxide fibres containing calcium and silicon by the formation of an oxide melt containing calcium and silicon characterised in that all or part of the calcium and all or part of silicon is provided by a calcium silicate.

[0050] A series of fibres were made of the compositions shown in Table 1. These fibres were melt spun by using a vertical spinning system of the type known for making inorganic fibres. Also shown in Table 1 are the compositions of some comparative commercially available inorganic oxide fibres and glass fibres.

[0051]

TABLE 1
	Al2O3	SiO2	CaO	MgO	ZrO2	MST
SW-A	3.3	59.3	20.5	15.5	—
SW-A1	1.1	63.7	20.5	15.2	—
SW-A2	0.8	60.8	21.4	15.4	—
SW-B1	2.3	65.3	26.8	5.7	—
SW-B2	1.3	66.9	27.5	5.2	—
SW-B3	1.0	60.0	34.0	4.4	—
COMPARATIVE EXAMPLES
CRBT	46.5	53	0.04	0.01	—	1260° C.
CWBT	40.6	49.5	5.50	4.00	—	870° C.
CHBT	49.7	35.1	0.04	0.01	14.7	1425° C.
Glass	15.2/	53.7/	21.1/	1.3/	— —	+5.9–6.2% B2O3
Fibre	15.5	57.5	21.8	1.6		0.11–0.12% TiO2
						0.46% Na2O
						0.32–0.33% K2O
Needled	3.7	60.5/	8.1	4.0	— —	+2.85–2.95% B2O3
Glass		60.0	7.9		—	13.5% Na2O
Fibre						1.0% K2O
[MST = Maximum Service Temperature (oxidising atmosphere)]

[0052] The fibres SW-A, SW-A1, SW-A2, SW-B1, SW-B2 and SW-B3 were tested for solubility by the following method.

[0053] The fibre was first chopped in the following manner. 2.5 g of fibre (deshotted by hand) was liquidised with 250 cm³ of distilled water in a domestic Moulinex (Trade Mark) food blender for 20 seconds. The suspension was then transferred to a 500 cm³ plastic beaker and allowed to settle after which as much liquid as possible was decanted and the remaining liquid removed by drying in an oven at 110° C.

[0054] The solubility test apparatus comprised a shaking incubator water bath, and the test solution had the following composition:—

[0055]

	Compound	Name	Grams
	NaCl	Sodium chloride	6.780
	NH4Cl	Ammonium chloride	0.540
	NaHCO3	Sodium bicarbonate	2.270
	Na2HPO4•H2O	Disodium hydrogen	0.170
		phosphate
	Na3C6H5O7P•2H2O	Sodium citrate	0.060
		dihydrate
	H2NCH2CO2H	Glycine	0.450
	H2SO4 s.g. 1.84	Sulphuric acid	0.050

The above materials were diluted to 1 litre with distilled water to form a physiological-like saline solution.

[0056] 0.500 grams±0.0003 grams of chopped fibre was weighed into a plastic centrifuge tube and 25 cm³ of the above saline solution added. The fibre and saline solution was shaken well and inserted into the shaking incubator water bath maintained at body temperature (37° C.±1° C.). The shaker speed was set at 20 cycles/minute.

[0057] After the desired period (usually 5 hours or 24 hours) the centrifuge tube was removed and centrifuged at ≈4500 revs/minute for approximately 5 minutes. Supernatant liquid was then drawn off using a syringe and hypodermic needle. The needle was then removed from the syringe, air expelled from the syringe, and the liquid passed through a filter (0.45 micron cellulose nitrate membrane filter paper [WCN type from Whatman Labsales Limited]) into a clean plastic bottle. The liquid was then analysed by atomic absorption using a Thermo Jarrell Ash Smith-Hiefje II machine.

[0058] The operating conditions were:—

[0059]

				FLAME
				(Nitrous
	WAVELENGTH	BAND	CURRENT	Oxide +
ELEMENT	(nm)	WIDTH	(MA)	Acetylene)
Al	309.3	1.0	8	Fuel Rich
SiO2	251.6	0.3	12	″
CaO	422.7	1.0	7	Fuel Lean
MgO	285.2	1.0	3	″

[0060] The procedure and standards adopted for determining the above elements were as set out below

[0061] SiO₂ can be determined without dilution up to 250 ppm concentration (1 ppm=1 mg/Litre). Above this concentration an appropriate dilution was made volumetrically. A 0.1% KCl solution (0.1 g in 100 cm³) was added to the final dilution to prevent ionic interference. NB If glass apparatus is used, prompt analysis is necessary.

[0062] From a stock solution of 1000 ppm pure ignited silica (99.999%) (fused with Na₂CO₃ at 1200° C. for 20 minutes in a platinum crucible (0.2500 g SiO₂/2 g Na₂CO₃) and dissolved in dilute hydrochloric acid (4 molar) made up to 250 cm³ with distilled water in a plastic volumetric flask) the following standards were produced:—

[0063]

	STANDARD (PPM SiO2)	STOCK SOLUTION (cm3)
	10.0	1.0
	20.0	2.0
	30.0	3.0
	50.0	5.0
	100.0	10.0
	250.0	25.0

[0064] Add 0.1% KCl to each standard before making to 100 cm³.

[0065] Aluminium may be measured directly from the sample without dilution. Standards of 1.0, 5.0 and 10.0 ppm Al may be used. For calibration readings are multiplied by 1.8895 to convert from A1 to Al₂O₃.

[0066] A standard Al atomic absorption solution (e.g. BDH 1000 ppm Al) was bought and diluted using an accurate pipette to the desired concentration. 0.1% KCl was added to prevent ionic interference.

[0067] Calcium may require dilutions on the sample before determination can be carried out (i.e. ×10 and ×20 dilutions). Dilutions must contain 0.1% KCl.

[0068] A standard Ca atomic absorption solution (e.g. BDH 1000 ppm Ca) was diluted with distilled water and an accurate pipette to give standards of 0.5, 4.0 and 10.0 ppm. 0.1% KCl is added to prevent ionic interference. To convert readings obtained from Ca to CaO a factor of 1.4 was used.

[0069] Magnesium may require dilutions on the sample before determinations can be made (i.e. ×10 and ×20). Add 0.1% KCl to each dilution. To convert Mg to MgO multiply by 1.658.

[0070] A standard Mg atomic absorption solution (e.g. BDH 1000 ppm Mg) was diluted with distilled water and an accurate pipette to give standards of 0.5, 1.0 and 10.0 ppm Mg. 0.1% KCl was added to prevent ionic interference.

[0071] All stock solutions were stored in plastic bottles

[0072] The results of the tests are indicated in Table 2.

[0073]

TABLE 2
BODY FLUIDS SOLUBILITY
(ppm)
	SiO2		CaO		MgO
	5 h	24 h	5 h	24 h	5 h	24 h
	SW-A	98	120	63	56	33	66
	SW-A1	83	141	32	70	21	70
	SW-A2	130	202	43	73	100	177
	SW-B1	58	77	10	38	5	9
	SW-B2	64	121	27	55	5	10
	SW-B3	138	192	80	46	8	21

[0074] Fibres with the best solubility (SW-A2 and SW-B3) were then tested, after annealing at varying temperatures, and compared with the comparative examples of Table 1. The results are shown in Table 3.

[0075] It can be seen that for the SW-A2 fibre, with increasing annealing temperature, the silica solubility drops progressively. In contrast the SW-B3 composition shows no loss in solubility up to 800° C. and although a reduction in solubility is shown above that temperature it is not as dramatic as for SW-A2. Despite this difference in solubility it is to be noted that only the needled GF fibre shows a comparable silica solubility and that material melts at 700° C.

[0076]

	TABLE 3
	Solubility Analyses
	CaO(ppm)	MgO(ppm)	SiO2(ppm)
Fibre	Condition	5 hrs	24 hrs	5 hrs	24 hrs	5 hrs	24 hrs
SW-A2	As received	58	37	37	3	89	130
SW-A2	600° C., 48 hrs	33	56	27	43	60	108
SW-A2	800° C., 48 hrs	35	53	17	30	43	87
SW-A2	1000° C., 48 hrs	7	3	3	2	11	21
SW-B3	As received	35	69	7	22	22	100
SW-B3	600° C., 48 hrs	61	150	12	22	55	130
SW-B3	800° C., 48 hrs	41	90	3	7	24	144
SW-B3	1000° C., 48 hrs	18	40	3	3	17	60
CRBT	As received	10	8	6	3	5	3
CHBT	As received	16	10	7	3	4	0.3
Glass Fibre	As received	14	17	5	3	5	7
Needled GF	As received	17	34	8	15	66	85
Needled GF	600° C., 48 hrs	11	26	7	10	19	37
Mineral Fibre	As received	16	16	7	6	8	9
[The Glass Fibre and Needled Glass Fibre had the compositions shown in Table 1.]

[0077] The user is primarily concerned with the solubility of the fibre as received as it is in this condition that most handling occurs; as received both SW-A2 and SW-B3 fibres have extremely high solubility. Even after exposure to 800° C. and 1000° C. these fibres have solubilities much higher than other high temperature use fibres.

[0078] To investigate the reasons underlying the difference in solubilities after high temperature annealing between the SW-A2 and SW-B3 fibres qualitative X-ray diffraction was done on the fibres. The results are indicated in Table 4 and it can be seen that the SW-B3 fibre forms pseudowollastonite and wollastonite, whereas the SW-A2 fibre forms diopside. It appears therefore that the crystalline diopside has a lower solubility in physiological saline solution than the crystalline pseudowollastonite and wollastonite material precipitated from the SW-B3 fibre.

[0079]

TABLE 4
Sample	Condition	Qualitative XRD
SW-A2	600° C., 48 hours	Amorphous
SW-A2	800° C., 48 hours	Amorphous with small amount Diopside
SW-A2	1000° C., 48 hours	Diopside
SW-B3	600° C., 48 hours	Amorphous
SW-B3	800° C., 48 hours	Amorphous
SW-B3	1000° C., 48 hours	Pseudowollastonite & Wollastonite

[0080] Various of the fibres were then tested for their shrinkage characteristics. Table 5 shows the results of Shrinkage tests on all the test fibres and on some of the comparative fibres. These results were obtained by proposed ISO standard ISO/TC33/SC2N220 (equivalent to British Standard BS 1920, part 6, 1986) with some modifications to account for small sample size. The method in summary comprises the manufacture of vacuum cast preforms, using 75 g of fibre in 500 cm³ of 0.2% starch solution, into a 120×65 mm tool. Platinum pins (approx 0.1-0.3 mm diameter) were placed 100×45 mm apart in the 4 corners. The longest lengths (L1 & L2) and the diagonals (L3 & L4) were measured to an accuracy of .±0.01 mm using a travelling microscope attached to a steel rule with a vernier scale. The samples were placed in a furnace at temperature and left for 24 hours. The shrinkage values are given as an average of the 4 measurements.

[0081]

TABLE 5
LINEAR SHRINKAGE (%)
(24 h at temperature)
Temp. ° C.	SW-A	SW-A1	SW-A2	SW-B1	SW-B2	SW-B3
730	1.45		1.43	1.02	0.22
870				0.41
900			1.07			1.07
1000		1.04	1.3	0.51	0.6	1.1
1100		0.71	1.8		0.73	2.2
Maximum	850	1050	1050	1050	1050	1000
Service
Temperature
° C.

[0082] It can be seen that in SW-A, SW-A1, SW-A2, SW-B1, SW-B2 and SW-B3, owing to the increase in molar volume on crystallisation, the linear shrinkage at the maximum service temperature is less than 3.5%.

[0083] Table 6 shows the results of a further series of shrinkage tests made in the same way.

[0084]

TABLE 6
	Measurement
	Direction	Test	Linear
	c.f. Roll	Temperatures	Shrinkages	%
Sample	Direction	° C.	Range	Mean
SW-A2	Parallel	850	1.1–1.4	1.2
SW-A2	Perpendicular	850	0.7–1.5	1.3
SW-A2	Parallel	900	0.5–1.1	0.9
SW-A2	Perpendicular	900	1.9–4.5	3.0
SW-A2	Parallel	1000	0.5–2.9	1.3
SW-A2	Perpendicular	1000	1.7–2.9	2.2
SW-A2	Parallel	1100	0.7–1.5	1.0
SW-A2	Perpendicular	1100	1.0–2.6	1.8
SW-B3	Parallel	900	1.6–1.8	1.7
SW-B3	Perpendicular	900	1.4–2.4	2.1
SW-B3	Parallel	1000	1.6–2.3	1.9
SW-B3	Perpendicular	1000	1.0–2.3	1.7
SW-B3	Parallel and	1100	Complete Melting
	Perpendicular		(Lantern type remnant)

[0085] To ascertain the applicability of these tests to long term usage a series of cyclic shrinkage tests were undertaken on the materials and the heating schedule used for these cyclic tests is shown in FIG. 3.

[0086] The results of the tests are shown in Tables 7 & 8 (the two figures given for SW-B3 are due to slight differences in chemical analysis [the fibre at the end of a production run of fibre tends to have slightly differing composition to that at the beginning of a production run of fibre]).

[0087] As a further comparison with the above discussed materials a melt was made comprising 55% SiO₂, 29.9% CaO and 18.6% MgO. Fibres made using this composition had a maximum service temperature of 700° C. and melted at 800° C.

[0088] As these results were encouraging the applicants conducted a further and extensive series of tests, concentrating on the SW-A2 and SW-B3 compositions, to ascertain the reproducibility of these results and the boundaries of the useful compositions.

[0089] Table 9 (three pages) below gives the compositions of a series of melts, ranked on silica content, and showing the shrinkage figure after exposure to 1000° C. for 24 hours (1st column) and 800° C. for 24 hours (2nd column). These shrinkages were measured by the same method as the shrinkages given above but measurements were made with a travelling microscope with a digital linear scale accurate to ±5 μm. It can clearly be seen that all fibres with a silica content of less than 58% have a shrinkage at 1000° C. of greater than 3.5% save two (B3-3 and 708). These fibres, together with some fibres with a silica content of greater than 58% although showing a reasonable figure at 1000° C., show a very poor figure at 800° C. Compositions with an SiO₂ content of greater than 70% appear to fiberise poorly. This may be because such compositions have two liquids in the melt as may be appreciated from FIG. 1.

[0090]

TABLE 7
CYCLIC SHRINKAGE (LINEAR)
(%)
	Product	1000° C.	1100° C.	24 h at
				1000° C.
	No. cycles	58	42
	CRBT	2.0	2.7	1.9
	CWBT	15.0	13.3	12.1
	SW-A2	0.33	2.0	1.3
	SW-B3	1.00	1.67	1.1
	SW-B3	0.33	0.67	1.1
	Accuracy: + or − 0.33%

[0091]

TABLE 8
CYCLIC SHRINKAGE
(%)
	LINEAR
	SHRINKAGE	THICKNESS
	24 h at	SHRINKAGE
PRODUCT	1000° C.	1100° C.	1000° C.	1000° C.	1100° C.
No. cycles	104	100		104	100
CRBT	1.47	3.1	1.9	0.47	11.19
CWBT	14.4	15.2	12.1	38.63	32.14
SW-A2	1.5	2.1	1.3	8.58	8.75
SW-B3	1.73	1.63	1.1	7.24	7.57
SW-B3	1.47	1.77	1.1	7.02	7.16
Accuracy: + or −0.3%(%)

[0092]

	TABLE 9
	Analysed Compositions	Shrinkage	Rationalised
	(Weight %)	at ° C.	Compositions
Melt	SiO2 %	CaO %	MgO %	Al2O3 %	Na2O %	K2O %	Fe2O3 %	ZrO2 %	1000	800	SiO2 %	CaO %	MgO %
A2-28	78.07	2.07	17.15	0.15	<0.05	<0.05	0.11	1.76	¶		80.3	2.1	17.6
A2-16	73.43	12.40	10.09	0.19	<0.05	<0.05	0.11	2.23	0.7	*	76.6	12.9	10.5
A2-32	73.09	6.36	19.60	0.23	0.05	<0.05	0.11	0.36	¶		73.8	6.4	19.8
B3-32	72.38	23.43	0.65	0.31	0.31	0.09	0.22	0.72	¶		75.0	24.3	0.7
A2-15	72.25	12.67	12.35	0.11	<0.05	<0.05	0.10	1.24	1.1	*	74.3	13.0	12.7
A2-22	71.48	9.36	16.34	0.33	0.10	<0.05	0.20	0.83	1.1	*	73.6	9.6	16.8
A2-29	71.24	4.46	22.31	0.19	<0.05	<0.05	0.13	1.23	1.8	*1.5	72.7	4.5	22.8
A2-27	71.14	6.77	19.64	0.24	0.08	<0.05	0.13	1.01	1.2	*1.2	72.9	7.0	20.3
B3-28	70.81	18.74	7.03	0.47	0.23	0.07	0.16	0.75	0.2	*	73.3	19.4	7.3
A2-17	70.43	11.58	14.52	0.15	<0.05	<0.05	0.13	1.58	1.3	*	73.0	12.0	15.0
A2-33	70.04	4.61	22.85	0.25	0.11	<0.05	0.12	1.01	¶		71.9	4.7	23.4
B3-18	69.42	23.27	3.76	0.43	0.37	0.06	0.12	0.47	0.4		72.0	24.1	3.9
A2-6	69.29	15.17	12.76	0.07	0.25	<0.05	0.11	1.13	1.5		71.3	15.6	13.3
B3-16	68.74	24.99	1.71	0.65	0.38	0.10	0.24	1.03	0.3	0.2	72.0	26.2	1.8
A2-26	68.65	8.12	19.26	0.29	<0.05	<0.05	0.21	0.98	1.5	1.5	71.5	8.4	20.1
B3-27	68.56	20.98	7.00	0.78	0.35	0.08	0.17	0.79	0.8	0.7	71.0	21.7	7.3
759	68.33	17.45	12.60	<0.05	0.11	<0.05	0.33	<0.05	1.7	1.1	69.5	17.7	12.8
A2-20	68.19	11.58	16.57	0.40	0.19	0.05	0.21	0.91	1.1	1.0	70.8	12.0	17.2
A2-31	67.62	8.45	21.72	0.32	0.09	<0.05	0.15	0.64	2.3	1.9	69.2	8.6	22.2
B3-31	67.59	27.76	0.49	0.40	0.40	0.11	0.22	1.01	0.7		70.5	29.0	0.5
B3-19	67.58	24.91	3.65	0.45	0.37	0.07	0.15	0.65	0.5		70.3	25.9	3.8
B3-17	67.25	26.68	1.86	0.70	0.45	0.10	0.23	0.57	0.3		70.2	27.9	1.9
A2-13	66.67	14.87	16.01	0.11	0.05	<0.05	0.10	0.92	1.6		68.4	15.2	16.4
B3-22	66.17	21.28	9.34	0.52	0.33	0.08	0.18	0.54	1.1	0.8	68.4	22.0	9.6
A2-10	66.17	16.22	15.80	0.49	0.06	<0.05	0.09	<0.05	2.2	1.9	67.4	16.5	16.1
B3-15	65.86	29.82	1.78	0.47	0.45	0.08	0.18	0.51	0.3		67.6	30.6	1.8
719	65.77	25.69	8.12	<0.05	0.24	<0.05	0.23	<0.05	0.5		66.0	25.8	8.2
A2-5	65.69	18.74	13.78	0.18	0.16	<0.05	0.10	0.14	1.9	1.0	66.9	19.1	14.0
B3-4A	65.50	25.81	4.88	2.05	0.28	0.12	0.16	0.24	1.4	1.0
A2-8	65.33	16.86	14.24	0.22	0.13	<0.05	0.14	1.17	1.5		67.7	17.5	14.8
718	65.23	27.14	6.95	<0.05	0.24	<0.05	0.20	0.49	0.4		65.7	27.3	7.0
B3-14	65.11	24.91	5.54	0.58	0.43	0.09	0.19	0.61	1.0		68.1	26.1	5.8
721	65.08	27.26	5.33	0.06	0.17	<0.05	0.08	<0.05	0.3	0.6	66.6	27.9	5.6
A2-34	64.85	6.63	26.20	0.23	0.06	<0.05	0.16	0.80	3.4	3.9	66.4	6.8	26.8
A2-21	64.16	13.74	19.98	0.34	0.17	<0.05	0.11	0.13	3.2	3.3	65.6	14.0	20.4
B3-30	64.13	31.93	0.37	0.64	0.45	0.09	0.14	0.28	0.6		66.5	33.1	0.4
A2-35	64.12	8.88	24.88	0.29	0.10	<0.05	0.13	0.47	7.3	7.1	65.5	9.1	25.4
B3-23	64.09	23.26	9.33	0.56	0.36	0.09	0.16	0.30	1.0		66.3	24.0	9.7
B3-5A	63.74	25.41	4.68	3.97	0.26	0.12	0.17	0.58	7.4	4.3
A2-30	63.68	16.06	18.21	0.40	0.11	0.07	0.15	<0.05	2.7	1.6	65.0	16.4	18.6
A2-9	63.66	21.44	12.96	1.49	0.32	0.10	0.11	<0.05	1.9	0.9	64.9	21.9	13.2
A2-12	63.56	16.55	18.00	0.33	0.11	<0.05	0.08	0.05	1.0	2.3	64.8	16.9	18.3
B3-6A	63.24	24.83	4.59	5.70	0.27	0.11	0.15	0.15	21.6	18.8
723	62.61	29.79	5.44	<0.05	0.17	<0.05	0.13	<0.05	0.4	0.5	64.0	30.4	5.6
757	62.60	20.92	15.22	0.20	<0.05	<0.05	0.16	<0.05	1.3	2.9	63.4	21.2	15.4
A2-25	62.36	10.99	24.18	0.33	0.10	0.05	0.16	0.07	6.1		63.9	11.3	24.8
B3-13	62.33	30.62	2.06	0.55	0.65	0.09	0.17	0.91	0.8	0.9	65.6	32.2	2.2
A2-7	61.98	23.37	11.98	0.44	0.25	<0.05	0.10	0.23	1.4		63.7	24.0	12.3
725	61.83	28.13	7.54	0.10	0.36	<0.05	0.17	<0.05	0.6		63.4	28.9	7.7
B3-11	61.71	33.25	2.33	0.69	0.52	0.12	0.25	0.59	0.9		63.4	34.2	2.4
B3-24	61.62	25.53	9.73	0.58	0.38	0.10	0.17	<0.05	1.8	1.2	63.6	26.4	10.0
A2-24	61.38	13.62	22.74	0.31	0.16	<0.05	0.14	0.08	3.3	12.3	62.8	13.9	23.3
722	61.33	31.08	5.25	0.05	0.20	<0.05	0.16	<0.05	1.3		62.8	31.8	5.4
924	61.32	19.78	14.54	2.57	<0.05	<0.05	0.09	0.66	0.3	3.0	64.1	20.7	15.2
B3-2A	60.83	32.30	0.48	4.15	0.35	0.15	0.19	0.12	7.5	3.3
A2-14	60.74	25.30	11.66	0.28	0.18	0.05	0.13	0.16	1.8		62.2	25.9	11.9
B3-1A	60.32	32.27	3.99	1.74	0.32	0.10	0.15	0.09	2.5	1.7
A2-11	60.32	24.28	13.24	0.25	0.18	<0.05	0.09	0.08	1.8	1.1	61.7	24.8	13.5
B3-9	60.28	34.49	2.50	0.76	0.50	0.13	0.28	0.49	1.6	1.7	62.0	35.4	2.6
A2-23	60.20	18.59	18.78	0.48	0.19	0.08	0.15	0.05	18.9	10.7	61.7	19.1	19.2
B3-1	60.11	32.56	3.80	0.79	0.54	0.12	0.23	0.82	0.5		62.3	33.8	3.9
932	59.85	21.60	15.65	1.50	0.06	<0.05	0.18	0.11	12.8		61.6	22.3	16.1
692	59.82	34.34	5.44	0.13	0.19	<0.05	0.08	0.17	2.1		60.0	34.5	5.5
B3-3A	59.54	31.64	0.67	5.91	0.33	0.15	0.21	0.41	43.3	15.3
B3-25	59.53	28.15	9.22	0.48	0.39	0.08	0.14	<0.05	2.3		61.4	29.1	9.5
B3-29	59.40	36.00	0.68	0.92	0.43	0.14	0.23	0.17	0.9		61.8	37.5	0.7
714	59.05	32.00	8.27	<0.05	0.27	<0.05	0.40	<0.05	0.7	1.2	59.5	32.2	8.3
696	58.81	30.91	6.15	0.21	0.18	<0.05	0.08	0.24	0.3	1.4	61.3	32.3	6.4
A2-19	58.71	18.48	19.74	0.54	0.20	0.07	0.19	<0.05	4.7		60.6	19.0	20.4
586	58.65	35.03	3.90	0.13	0.23	<0.05	0.16	<0.05	1.9	1.6	60.1	35.9	4.0
694	58.39	33.10	6.02	0.27	0.20	<0.05	0.10	0.17	1.6	1.9	59.9	33.9	6.2
765	57.78	3.90	35.07	2.12	<0.05	<0.05	0.23	<0.05	34.2		59.7	4.0	36.3
660	57.74	34.65	4.83	1.15	0.24	<0.05	0.19	<0.05	24.7		59.4	35.6	5.0
B3-20	57.57	32.70	6.07	0.91	0.57	0.13	0.22	<0.05	30.9		59.8	33.9	6.3
712	57.54	35.39	4.61	0.06	0.23	<0.05	0.12	<0.05	4.4	3.4	59.0	36.3	4.7
B3-21	57.38	36.62	2.43	0.73	0.52	0.11	0.16	0.08	30.3		59.5	38.0	2.5
B3-26	56.98	30.50	9.44	0.62	0.44	0.11	<0.05	<0.05	39.8	26.6	58.8	31.5	9.7
A2-18	56.96	26.29	13.01	0.66	0.51	0.10	0.19	<0.05	36.2		59.2	27.3	13.5
971	56.82	23.92	17.36	0.74	0.18	<0.05	0.14	0.05	41.7		57.9	24.4	17.7
734	56.58	23.62	17.05	1.00	0.06	<0.05	0.13	0.05	39.3		58.2	24.3	17.5
973	56.18	24.45	16.81	0.50	0.08	<0.05	0.14	0.05	34.9		57.7	25.1	17.2
B3-3	55.99	36.07	4.44	0.58	0.45	0.09	0.38	1.46	0.3	34.7	58.0	37.4	4.6
708	55.22	42.79	0.77	<0.05	0.31	<0.05	0.12	<0.05	1.1	8.7	55.9	43.3	0.8
71	54.68	24.04	19.66	0.20	0.17	<0.05	0.23	<0.05	51.7		55.6	24.4	20.0
*Poor fibres containing a lot of shot. All other constituents <0.1%.
¶ Too poor to test for solubility or shrinkage

[0093]

	TABLE 10
			Rationalised
	Analysed Compositions	Solubilities	Compositions
	(Weight %)	ppm			MgO
Melt	SiO2 %	CaO %	MgO %	Al2O3 %	Na2O %	K2O %	Fe2O3 %	ZrO2 %	SiO2	Cao	MgO	SiO2 %	CaO %	%
A2-28	78.07	2.07	17.15	0.15	<0.05	<0.05	0.11	1.76	¶			80.3	2.1	17.6
A2-16	73.43	12.40	10.09	0.19	<0.05	<0.05	0.11	2.23	113	45	55	76.6	12.9	10.5
A2-32	73.09	6.36	19.60	0.23	0.05	<0.05	0.11	0.36	¶			73.8	6.4	19.8
B3-32	72.38	23.43	0.65	0.31	0.31	0.09	0.22	0.72	¶			75.0	24.3	0.7
A2-15	72.25	12.67	12.35	0.11	<0.05	<0.05	0.10	1.24	105	35	48	74.3	13.0	12.7
A2-22	71.48	9.36	16.34	0.33	0.10	<0.05	0.20	0.83	126	36	75	73.6	9.6	16.8
A2-29	71.24	4.46	22.31	0.19	<0.05	<0.05	0.13	1.23	94	21	105	72.7	4.5	22.8
A2-27	71.14	6.77	19.64	0.24	0.08	<0.05	0.13	1.01	101	24	67	72.9	7.0	20.1
B3-28	70.81	18.74	7.03	0.47	0.23	0.07	0.16	0.75	108	49	31	73.3	19.4	7.3
A2-17	70.43	11.58	14.52	0.15	<0.05	<0.05	0.13	1.58	91	35	72	73.0	12.0	15.0
A2-33	70.04	4.61	22.85	0.25	0.11	<0.05	0.12	1.01	¶			71.9	4.7	23.4
B3-18	69.42	23.27	3.76	0.43	0.37	0.06	0.12	0.47	145	66	17	72.0	24.1	3.9
A2-6	69.29	15.17	12.76	0.07	0.25	<0.05	0.11	1.13	152	48	70	71.3	15.6	13.1
B3-16	68.74	24.99	1.71	0.65	0.38	0.10	0.24	2.03	132	72	10	72.0	26.2	1.8
A2-26	68.65	8.12	19.26	0.29	<0.05	<0.05	0.21	0.98	183	31	97	71.5	8.4	20.1
B3-27	68.56	20.98	7.00	0.78	0.35	0.08	0.17	0.79	122	54	20	71.0	21.7	7.3
759	68.33	17.45	12.60	<0.05	0.11	<0.05	0.33	<0.05	117	38	40	69.5	17.7	12.8
A2-20	68.19	11.58	16.57	0.40	0.19	0.05	0.21	0.91	162	31	69	70.8	12.0	17.2
A2-31	67.62	8.45	21.72	0.32	0.09	<0.05	0.15	0.64	103	26	72	69.2	8.6	22.2
B3-31	67.59	27.76	0.49	0.40	0.40	0.11	0.22	1.01	112	50	4	70.5	29.0	0.5
B3-19	67.58	24.91	3.65	0.45	0.37	0.07	0.15	0.65	163	44	21	70.3	25.9	3.8
B3-17	67.25	26.68	1.86	0.70	0.45	0.10	0.23	0.57	162	49	13	70.2	27.9	1.9
A2-13	66.67	14.87	16.01	0.11	0.05	<0.05	0.10	0.92	159	47	70	68.4	15.2	16.4
A2-10	66.17	16.22	15.80	0.49	0.06	<0.05	0.09	<0.05	122	42	52	67.4	16.5	16.1
B3-22	66.17	21.28	9.34	0.52	0.33	0.08	0.18	0.54	174	62	57	68.4	22.0	9.6
B3-15	65.86	29.82	1.78	0.47	0.45	0.08	0.18	0.51	156	38	7	67.6	30.6	1.8
719	65.77	25.69	8.12	<0.05	0.24	<0.05	0.23	<0.05	115	51	24	66.0	25.8	8.2
A2-5	65.69	18.74	13.78	0.18	0.16	<0.05	0.10	0.14	150	48	60	66.9	19.1	14.0
B3-4A	65.50	25.81	4.88	2.05	0.28	0.12	0.16	0.24	82	52	16
A2-8	65.33	16.86	14.24	0.22	0.13	<0.05	0.14	1.17	181	54	84	67.7	17.5	14.8
718	65.23	27.14	6.95	<0.05	0.24	<0.05	0.20	0.49	107	47	20	65.7	27.3	7.0
B3-14	65.11	24.91	5.54	0.58	0.43	0.09	0.19	0.61	158	67	27	68.1	26.1	5.8
721	65.08	27.26	5.33	0.06	0.17	<0.05	0.08	<0.05	158	68	20	66.6	27.9	5.5
A2-34	64.85	6.63	26.20	0.23	0.06	<0.05	0.16	0.80	39	11	119	66.4	6.8	26.8
A2-21	64.16	13.74	19.98	0.34	0.17	<0.05	0.11	0.13	160	28	56	65.6	14.0	20.4
B3-30	64.13	31.93	0.37	0.64	0.45	0.09	0.14	0.28	163	83	3	66.5	33.1	0.4
A2-35	64.12	8.88	24.88	0.29	0.10	<0.05	0.13	0.47	61	18	106	65.5	9.1	25.4
B3-23	64.09	23.26	9.33	0.56	0.36	0.09	0.16	0.30	101	44	31	66.3	24.0	9.7
B3-5A	63.74	25.41	4.68	3.97	0.26	0.12	0.17	0.58	48	43	11
A2-30	63.68	16.06	18.21	0.40	0.11	0.07	0.15	<0.05	102	33	52	65.0	16.4	18.6
A2-9	63.66	21.44	12.96	1.49	0.32	0.10	0.11	<0.05	195	67	66	64.9	21.9	13.2
A2-12	63.56	16.55	18.00	0.33	0.11	<0.05	0.08	0.05	160	47	66	64.8	16.9	18.3
B3-6A	63.24	24.83	4.59	5.70	0.27	0.11	0.15	0.15	26	7	26
723	62.61	29.79	5.44	<0.05	0.17	<0.05	0.13	<0.05	141	62	17	64.0	30.4	5.6
757	62.60	20.92	15.22	0.20	<0.05	<0.05	0.16	<0.05	187	62	73	63.4	21.2	15.4
A2-25	62.36	10.99	24.18	0.33	0.10	0.05	0.16	0.07	160	35	105	63.9	11.3	24.8
B3-13	62.33	30.62	2.06	0.55	0.65	0.09	0.17	0.91	151	41	7	65.6	32.2	2.2
A2-7	61.98	23.37	11.98	0.44	0.25	<0.05	0.10	0.23	178	59	63	63.7	24.0	12.3
725	61.83	28.13	7.54	0.10	0.36	<0.05	0.17	<0.05	186	76	35	63.4	28.9	7.7
B3-11	61.71	33.25	2.33	0.69	0.52	0.12	0.25	0.59	162	28	15	63.4	34.2	2.4
B3-24	61.62	25.53	9.73	0.58	0.38	0.10	0.17	<0.05	185	37	57	63.6	26.4	10.0
A2-24	61.38	13.62	22.74	0.31	0.16	<0.05	0.14	0.08	136	27	87	62.8	13.9	23.3
722	61.33	31.08	5.25	0.05	0.20	<0.05	0.16	<0.05	185	81	23	62.8	31.8	5.4
924	61.32	19.78	14.54	2.57	<0.05	<0.05	0.09	0.66	77	36	37	64.1	20.7	15.2
B3-2A	60.83	32.30	0.48	4.15	0.35	0.15	0.19	0.12	58	61	5
A2-14	60.74	25.30	11.66	0.28	0.18	0.05	0.13	0.16	127	57	43	62.2	25.9	11.9
B3-1A	60.32	32.27	3.99	1.74	0.32	0.10	0.15	0.09	119	72	16
A2-11	60.32	24.28	13.24	0.25	0.18	<0.05	0.09	0.08	149	54	51	61.7	24.8	13.5
B3-9	60.28	34.49	2.50	0.76	0.50	0.13	0.28	0.49	175	8	5	62.0	35.4	2.6
A2-23	60.20	18.59	18.78	0.48	0.19	0.08	0.15	0.05	192	35	47	61.7	19.1	19.2
B3-1	60.11	32.56	3.80	0.79	0.54	0.12	0.23	0.82	146	84	17	62.3	33.8	3.9
932	59.85	21.60	15.65	1.50	0.06	<0.05	0.18	0.11	92	41	43	61.6	22.3	16.1
692	59.82	34.34	5.44	0.13	0.19	<0.05	0.08	0.17	140	67	23	60.0	34.5	5.5
B3-3A	59.54	31.64	0.67	5.91	0.33	0.15	0.21	0.41	30	25	10
B3-25	59.53	28.15	9.22	0.48	0.39	0.08	0.14	<0.05	133	48	33	61.4	29.1	9.5
B3-29	59.40	36.00	0.68	0.92	0.43	0.14	0.23	0.17	201	29	5	61.8	37.5	0.7
714	59.05	32.00	8.27	<0.05	0.27	<0.05	0.40	<0.05	142	73	30	59.5	32.2	8.3
696	58.81	30.91	6.15	0.21	0.18	<0.05	0.08	0.24	163	48	37	61.3	32.3	6.4
A2-19	58.71	18.48	19.74	0.54	0.20	0.07	0.19	<0.05	125	42	66	60.6	19.0	20.4
586	58.65	35.03	3.90	0.13	0.23	<0.05	0.16	<0.05	182	54	19	60.1	35.9	4.0
694	58.39	33.10	6.02	0.27	0.20	<0.05	0.10	0.17	133	66	27	59.9	33.9	6.2
765	57.78	3.90	35.07	2.12	<0.05	<0.05	0.23	<0.05	100	16	169	59.7	4.0	36.3
660	57.74	34.65	4.83	1.15	0.24	<0.05	0.19	<0.05	152	69	23	59.4	35.6	5.0
B3-20	57.57	32.70	6.07	0.91	0.57	0.13	0.22	<0.05	181	29	40	59.8	33.9	6.3
712	57.54	35.39	4.61	0.06	0.23	<0.05	0.12	<0.05	160	24	22	59.0	36.3	4.7
B3-21	57.38	36.62	2.43	0.73	0.51	0.11	0.16	0.08	175	25	16	59.5	38.0	2.5
B3-26	56.98	30.50	9.44	0.62	0.44	0.11	<0.05	<0.05	149	64	41	58.8	31.5	9.7
A2-18	56.96	26.29	13.01	0.66	0.51	0.10	0.19	<0.05	161	47	57	59.2	27.3	13.5
971	56.82	23.92	17.36	0.74	0.18	<0.05	0.14	0.05	142	55	73	57.9	24.4	17.7
734	56.58	23.62	17.05	1.00	0.06	<0.05	0.13	0.05	135	52	66	58.2	24.3	17.5
973	56.18	24.45	16.81	0.50	0.08	<0.05	0.14	0.05	102	42	47	57.7	25.1	17.2
B3-3	55.99	36.07	4.44	0.58	0.45	0.09	0.38	1.46	185	14	18	58.0	37.4	4.6
708	55.22	42.79	0.77	<0.05	0.31	<0.05	0.12	<0.05	193	31	2	55.9	43.3	0.8
71	54.68	24.04	19.66	0.20	0.17	<0.05	0.23	<0.05	133	55	62	55.6	24.4	20.0

[0094] There are several anomalies, namely compositions B3-6A, A2-25, A2-24, A2-23, B3-2A, B3-3A, A2-19, and 932. All of these have an SiO₂ content of >58% but a high shrinkage.

[0095] On the assumption that the minimum silica level for satisfactory shrinkage varies with MgO content the applicants have determined that fibres with a silica content (in weight percent) that fail to meet the following expression do not have satisfactory shrinkages at either or both 800° C. and 1000° C.:—

[0096]

	SiO2	>58%	(for MgO =< 10%) and
	SiO2	>58% + 0.5 (%MgO − 10)	(for MgO >= 10%)

[0097] The applicants have further found that the Al₂O₃ content is important. From their studies it appears that the maximum Al₂O₃ content lies somewhere between 2.57% and 3.97%. The applicants have found that with increasing alumina levels the first material to crystallise is calcium aluminate and this possibly forms a liquid phase that assists flow and hence shrinkage.

[0098] Table 10 shows, for the same compositions as Table 9, 24 hour solubilities for each major constituent. It can be seen that all of the compositions have high solubilities.

[0099] As mentioned above use of CaO in forming calcium containing fibres is inconvenient and can be hazardous. The applicants investigated use of mixed oxide materials that would avoid the handling of CaO. A fibre was made by admixture of magnesia with silica and wollastonite (CaSiO₃).

[0100] The raw materials used to make the melt comprised:—

[0101] Pennine Darlington Heavy Magnesia (#200)

[0102]

	MgO	92.60%
	CaO	1.75%
	Fe2O3	0.04%
	SiO2	0.20%
	Cl	0.25%
	SO3	0.70%
	LOI	4.50%

[0103] Partek's Finnish Low Iron Wollastonite (#200)

[0104] (U.K. agent—Cornelius Chemical Co., Romford, Essex)

[0105]

	SiO2	51.80%
	CaO	44.50%
	MgO	0.80%
	Al2O3	0.60%
	Fe2O3	0.30%
	Na2O	0.10%
	K2O	0.05%
	TiO2	0.05%
	S	0.02%
	MnO	0.01%
	P	0.01%
	F	0.01%
	LOI	1.70%

[0106] Hepworth Mineral's Redhill T washed silica sand

[0107]

	SiO2	99.0% min.

[0108] These constituents were mixed as 78.65% Wollastonite; 19.25% SiO₂; and 3.6% MgO. This gave 0.4-0.5% of the final melt as Al₂O_3.

[0109] It was surprisingly found that in producing a melt using these constituents the current requirements were only two-thirds that for the use of the raw oxides.

[0110] Fibre was produced by blowing (although spinning and other methods can be used). 2 runs were performed with different blowing conditions.

[0111] Chemical analysis was undertaken by the Analytical Department at the applicant's subsidiary Morgan Materials Technology (hereinafter called M²T) using wet chemical techniques. Fibre diameters were measured using M²T's Galai particle analyser, with shape analysis software. Typically 40,000 fibres were analysed for each run.

[0112] The first result of note was the speed of melt reaction when using wollastonite as compared with lime. Also the current was seen to be very stable throughout the growth of the melt. If the current was lost whilst pulling the electrodes apart the current could be restored simply by pushing them back together again. This was not possible with the runs using lime.

[0113]

Chemical Analysis
	Others	CaO	MgO	Al2O3	SiO2	ZrO2	Na2O	Total
Run 1	0.7	32.6	3.8	0.8	60.1	0.8	0.5	99.3
Run 2	0.7	32.5	3.8	0.8	60.1	0.8	0.6	99.3

Runs 1 and 2 indicate the respective x-ray fluorescence analyses for each run.

[0114]

Shrinkage Results (1000° C. for 24 hours)
		L1	L2	L3	L4	Av.	Std. Dev.
	Run 1	0.9	0.2	0.4	0.6	0.5	0.3
	Run 2(A)	1.0	−0.2	0.7	0.6	0.5	0.5
	Run 2(b)	0.5	0.2	0.0	0.4	0.2	0.2

[0115]

Solubility Results (ppm)
	CaO	MgO	SiO2
	Run 1(5 hr)	67	10	95
	Run 1(24 hr)	84	17	146
	Run 2(5 hr)	39	7	72
	Run 2(24 hr)	73	17	186

[0116]

Fibre diameters
	Mean	Median	100%<	%>5 μm	%<1 μm
Run 1	5.1 μm	3.4 μm	30 μm	33%	13%
Run 2	4.1 μm	2.7 μm	25 μm	25%	19%

[0117] Accordingly it appears to be the case that by using what are cheaper ingredients than the pure oxides one can obtain a fibre that has as high a performance as using purer oxides and at much improved energy costs and safety. It is to be noted that this feature of the invention is not limited to saline soluble fibres and any oxide fibre that contains both calcium and silicon can advantageously be made with a calcium silicate, wollastonite being merely an example of such a silicate.

[0118] The previous description is directed towards high temperature usage of particular saline soluble fibres. The following is directed towards the prediction and use of saline soluble fibres. A series of fritted glass melts were made of the compositions shown in Tables 11A and 11B and quenched in water. Solubilities of the various components of the quenched melt were measured by the previously described method of atomic absorption. The solubilities were normalised to a specific surface area of 0.25 m²/gram of fibre.

[0119] The free energy of hydration was calculated by normalising the chemical analysis to 100 weight %; making the assumption that simple silicates (MSiO₃/M₂ SiO₃) are present and calculating the free energy of hydration contribution of each species; and summing to get the total free energy of hydration. The data in Tables 11A & 11B is also presented in FIG. 4. It can be seen that the fibres lie on a generally straight line bar four groups of materials that will be explained below.

[0120] Table 11 shows in each column the following:—

• • [0121] Fibre reference
  • [0122] Composition
  • [0123] Molar ratios
  • [0124] Moles/100 grams of melt
  • [0125] Species assumed (see below)
  • [0126] Calculated free energy of hydration of assumed species (kcal/100 grams)(see below)
  • [0127] Calculated free energy of hydration of assumed species (kJ/kg) (see below)
  • [0128] Solubility data (# indicates not measured [see below])
  • [0129] Specific surface area
  • [0130] Normalised solubility data
  • [0131] log normalised solubility

[0132] The base data on which calculation of the free energy of hydration was done is set out in Tables 12 which indicates free energies of hydration taken from the literature in the units kcal/mol and kJ/mol.

[0133]

TABLE 11
Table of Free Energy of Hydration Values for Silicate Melts
						Free
						Energy	Free
						of	Energy			Normal-
	Composition		Moles			Hydration	of			ized	Log
Melt		Wt.	Ration-		in		Moles	(kcal/	Hydration	Solubility	S.S.A	Solu-	(norm
Code	Oxide	%	alized	Moles	100 g	Species	in 1 kg	100 g)	(kj/kg)	Oxide	(ppm)	m2/g	bility	solub)
CAS10(B) -	CaO	47.2	47.8	0.852	0.451	CaSiO3	4.51	−7.3	−304.0	CaO	44	0.30	43	1.63
A	Al2O3	24.5	24.8	0.243	0.243	Al2O3	2.43	0.8	31.6	Al2O3	0
	SiO2	27.1	27.4	0.451	0.401	CaO	4.01	−5.3	−219.7	SiO2	7
	Total	98.8	100.0					−11.8	−492.1	Total	51
CAS10(B) -	CaO	46.5	47.2	0.842	0.479	CaSiO3	4.79	−7.7	−322.8	CaO	58	0.39	66	1.82
B	Al2O3	23.7	24.0	0.235	0.235	Al2O3	2.35	0.7	30.6	Al2O3	1
	SiO2	28.4	28.8	0.479	0.363	CaO	3.63	−4.8	−198.9	SiO2	44
	Total	98.6	100.0					−11.8	−491.1	Total	103
CAS10(B) -	CaO	47.8	48.4	0.863	0.456	CaSiO3	4.56	−7.3	−307.3	CaO	55	0.36	76	1.88
C	Al2O3	23.9	24.2	0.237	0.237	Al2O3	2.37	0.7	30.8	Al2O3	0
	SiO2	27.1	27.4	0.456	0.407	CaO	4.07	−5.3	−223.0	SiO2	55
	Total	98.8	100.0					−11.9	−499.5	Total	110
CIS(A)	CaO	42.7	44.3	0.790	0.707	CaSiO3	7.07	−11.4	−476.5	CaO	62	0.40	69	1.84
	TiO2	12.7	13.2	0.165	0.083	CaO	0.83	−1.1	−45.5	TiO2	0
	SiO2	41.0	42.5	0.707	0.165	TiO2	1.65	2.6	110.4	SiO2	49
	Total	96.4	100.0					−9.9	−411.6	Total	111
SrSiO3	SrO	63.1	64.4	0.622	0.592	SrSiO3	5.92	−14.4	−604.4	SrO	2	0.37	249	2.40
	SiO2	34.9	35.6	0.592	0.030	SiO	0.30	−0.5	−21.7	SrO2	367
	Total	98.0	100.0					−14.9	−626.1	Total	369
CaSiO3	CaO	46.1	46.9	0.836	0.836	CaSiO3	8.36	−13.5	−563.5	CaO	41	0.45	163	2.21
	SiO2	52.3	53.1	0.884	0.048	SiO2	0.48	0.3	11.2	SiO2	253
	Total	98.4	100.0					−13.2	−552.3	Total	294
MAS(A)	Na2O	18.8	18.9	0.305	0.305	Na2SiO3	3.05	−8.8	−367.5	Na2O	#	0.56	4	0.60
	Al2O3	39.7	39.8	0.390	0.390	Al2O3	3.90	1.2	50.7	Al2O3	4
	SiO2	41.1	41.3	0.687	0.382	SiO2	3.82	2.1	89.4	SiO2	5
	Total	99.6	100.0					−5.5	−227.4	Total	9
CAS4	CaO	21.0	20.9	0.373	0.373	CaSiO3	3.73	−6.0	−251.4	CaO	11	0.62	8	0.90
	Al2O3	35.4	35.2	0.345	0.345	Al2O3	3.45	1.1	44.9	Al2O3	4
	SiO2	44.2	43.9	0.731	0.358	SiO2	7.31	2.0	171.1	SiO2	5
	Total	100.6	100.0					−2.9	−35.4	Total	20
MAS(B)	MgO	10.0	10.3	0.256	0.256	MgSiO3	2.56	−3.6	−149.0	MgO	7	0.52	6	0.78
	Al2O3	33.7	34.9	0.342	0.342	Al2O3	3.42	1.1	44.5	Al2O3	2
	SiO2	53.0	54.8	0.912	0.656	SiO2	6.56	3.7	153.5	SiO2	4
	Total	96.7	100.0					1.2	49.0	Total	13
SAS(A)	SrO	29.8	30.5	0.294	0.294	SrSiO3	2.94	−7.2	−300.2	SrO	9	0.50	8	0.90
	Al2O3	31.1	31.8	0.312	0.312	Al2O3	3.12	1.0	40.6	Al2O3	2
	SiO2	36.8	37.7	0.627	0.333	SiO2	3.33	1.9	77.9	SiO2	5
	Total	97.7	100.0					−4.3	−181.7	Total	16
SCS(A)	SrO	35.0	35.1	0.339	0.339	SrSiO3	3.39	−8.3	−346.1	SrO	75	0.41	280	2.45
	CaO	21.0	21.1	0.376	0.376	CaSiO3	3.76	−6.1	−253.4	CaO	30
	SiO2	43.6	43.8	0.729	0.014	SiO2	0.14	0.1	3.3	SiO2	355
	Total	99.6	100.0					−14.3	−596.2	Total	460
SMAS(A)	SrO	55.0	56.6	0.546	0.296	SrSiO3	2.96	−7.2	−302.2	SrO	57	0.46	38	1.58
	MgO	1.2	1.2	0.030	0.030	MgO	0.30	−0.2	−8.2	MgO	2
	Al2O3	23.7	24.4	0.239	0.239	Al2O3	2.39	0.7	31.1	Al2O3	5
	SiO2	17.3	17.8	0.296	0.250	SrO	2.50	−4.3	−181.0	SiO2	5
	Total	97.2	100.0					−11.0	−460.3	Total	69
SMAS(B)	SrO	55.0	55.9	0.539	0.401	SrSiO3	4.01	−9.8	−409.4	SrO	110	0.39	95	1.98
	MgO	4.8	4.9	0.122	0.122	MgO	1.22	−0.8	−33.2	MgO	15
	Al2O3	14.8	15.1	0.148	0.148	Al2O3	1.48	0.5	19.2	Al2O3	1
	SiO2	23.7	24.1	0.401	0.138	SrO	1.38	−2.4	−99.9	SiO2	22
	Total	98.3	100.0					−12.5	−523.3	Total	148
SMS(A)	SrO	33.0	32.9	0.318	0.318	SrSiO3	3.18	−7.8	−324.7	SrO	147	0.39	212	2.33
	MgO	12.5	12.5	0.310	0.310	MgSiO3	3.10	−4.3	−180.4	MgO	61
	Al2O3	1.0	1.0	0.010	0.010	Al2O3	0.10	0.0	1.3	Al2O3	0
	SiO2	53.8	53.6	0.892	0.264	SiO2	2.64	1.5	61.8	SiO2	125
	Total	100.3	100.0					−10.6	−442.0	Total	331
SAS(C)	SrO	56.0	56.2	0.542	0.401	SrSiO3	4.01	−9.8	−409.4	SrO	70	0.38	52	1.72
	Al2O3	19.7	19.7	0.193	0.193	Al2O3	1.93	0.6	25.1	Al2O3	1
	SiO2	24.0	24.1	0.401	0.141	SrO	1.41	−2.4	−102.1	SiO2	8
	Total	99.7	100.0					−11.6	−486.4	Total	79
CMAS(A)	CaO	35.0	34.6	0.617	0.293	CaSiO3	2.93	−4.7	−197.5	CaO	11	0.30	24	1.38
	MgO	4.5	4.4	0.109	0.109	MgO	1.09	−0.7	−29.6	MgO	7
	Al2O3	44.0	43.4	0.426	0.426	Al2O3	4.26	1.3	55.4	Al2O3	3
	SiO2	17.8	17.6	0.293	0.324	CaO	3.24	−4.2	−177.6	SiO2	8
	Total	101.3	100.0					−8.3	−349.3	Total	29
SWA2	CaO	21.7	21.7	0.387	0.387	CaSiO3	3.87	−6.2	−260.8	CaO	53	0.48	119	2.08
	MgO	15.7	15.7	0.389	0.389	MgSiO3	3.89	−5.4	−226.4	MgO	57
	Al2O3	0.8	0.8	0.008	0.008	Al2O3	0.08	0.0	1.0	Al2O3	0
	SiO2	61.8	61.8	1.028	0.252	SiO2	2.52	1.4	59.0	SiO2	118
	Total	100.0	100.0					−10.2	−427.2	Total	228
SAS(D)	SrO	56.5	57.3	0.553	0.413	SrSiO3	4.13	−10.1	−421.7	SrO	107	0.40	92	1.96
	Al2O3	17.6	17.9	0.176	0.176	Al2O3	1.76	0.5	22.9	Al2O3	1
	SiO2	24.4	24.8	0.413	0.140	SrO	1.40	−2.4	−101.4	SiO2	39
	Total	98.5	100.0					−12.0	−500.2	Total	147
KMAS(A)	K2O	16.5	16.5	0.175	0.175	K2SiO3	1.75	−7.3	−305.4	K2O	#	0.36	14	1.15
	MgO	13.0	13.0	0.323	0.323	MgSiO3	3.23	−2.1	−188.0	MgO	8
	Al2O3	18.0	17.9	0.176	0.176	Al2O3	1.76	0.5	22.9	Al2O3	1
	SiO2	52.8	52.6	0.875	0.377	SiO2	8.75	2.1	204.8	SiO2	11
	Total	100.3	100.0					−6.8	−265.7	Total	20

[0134]

	TABLE 12
	Ghyd
	(kcal/mole)	(kJ/mol)
Relevant oxides
SiO2 + H2O → H2SiO3	5.6	23.4
(vitreous silica)
Al2O3 + 3H2O → 2Al(OH)3	3.1	13.0
MgO + H2O → Mg(OH)2	−6.5	−27.2
CaO + H2O → Ca(OH)2	−13.1	−54.8
SrO + H2O → Sr(OH)2	−17.3	−72.4
Na2O + H2O → 2NaOH	−33.5	−140.2
K2O + H2O → 2KOH	−46.1	−192.9
TiO2 + H2O → Ti(OH)2O	16.0	66.9
P2O5 + 3H2O → 2H3PO4	−55.9	−233.9
B2O3 + 3H2O → 2H3BO3	−9.8	−41.0
ZrO2 + H2O → Zr(OH)2O	−7.1	−29.7
Relevant Silicates
Na2SiO3 + 2H+(aq) → H2SiO3 + 2Na+(aq)	−28.8	−120.5
K2SiO3 + 2H+(aq) → H2SiO3 + 2K+(aq)	−41.7	−174.5
MgSiO3 + 2H+(aq) → H2SiO3 + Mg2+(aq)	−13.9	−58.2
CaSiO3 + 2H+(aq) → H2SiO3 + Ca2+(aq)	−16.1	−67.4
SrSiO3 + 2H+(aq) → H2SiO3 + Sr2+(aq)	−24.4	−102.1
BaSiO3 + 2H+(aq) → H2SiO3 + Ba2+(aq)	−37.3	−156.1
ZnSiO3 + 2H+(aq) → H2SiO3 + Zn2+(aq)	−2.4	−10.0
Disilicates
Ca2SiO4 + 3H+(aq) → H2SiO3 + 2Ca2++ OH−	−30.3	−126.8
Sr2SiO4 + 3H+(aq) → H2SiO3 + 2Sr2+ + OH−	−50.3	−210.5
Mg2SiO4 + 3H+(aq) → H2SiO3 + 2Mg2+ + OH−	−17.9	−74.9

[0135] Although calculations were undertaken assuming the presence of the simplest silicates choice of other silicates (such as disilicates) does not appear to change the calculations much. For example given below is the calculation for an assumed composition which shows only minor differences for the free energy of hydration calculated.

[0136]

Composition (moles/100 g)	0.767 CaO
	0.417 MgO
	0.669 SiO2
0.384 Ca2SiO4	=	−11.6	or	0.433 CaSiO3	=	−7.0
0.285 MgSiO3	=	−4.0		0.236 MgSiO3	=	−3.3
0.132 MgO	=	−0.9		0.334 CaO	=	−4.4
		−16.5		0.181 MgO	=	−1.2
						−15.9
			or	0.384 Ca2SiO4	=	−11.6
				0.132 Mg2SiO4	=	−2.4
				0.153 MgSiO3	=	−2.1
						−16.1

[0137] The applicants have found that when the free energy of hydration is more negative than −10 kcal/100 grams (−418.4 kJ/kg) of composition the composition showed high solubility. The compositions where this relationship broke down were those for which the total solubility was not available (for example those materials containing sodium, where any dissolved sodium would be swamped by the sodium in the saline solution) or where the free energy of hydration of the most likely species present was not available from the literature.

[0138] As a test of this technique the two examples of European Patent No. 0399320 were examined. The disclosed examples had the compositions:—

[0139]

		Composition 1	Composition 2
	Component	Weight percent	Weight percent
	SiO2	60.7	58.5
	Al2O3	—	5.8
	CaO	16.5	3.0
	MgO	3.2	—
	B2O3	3.3	11.0
	Na2O	15.4	9.8
	K2O	0.7	2.9
	Iron oxide	0.2	0.1
	BaO	—	5.0
	ZnO	—	3.9

[0140] Using the above method of calculation Composition 1 had a free energy of hydration of −11.6 kcal/100 grams (−485.3 kJ/kg) whereas Composition 2 had a free energy of hydration of −5.8 kcal/100 grams (−242.6 kJ/kg). This would suggest that composition 1 would be a saline soluble fibre, and hence physiologically safer than an insoluble fibre; whereas Composition 2 would be predicted to be a relatively insoluble fibre and hence less safe. This is what is disclosed in EP 0399320, the fibres of Composition 2 having a longer lifetime in studies in which the fibres were introduced interperitoneally into rats.

[0141] As mentioned above this predictive test can fail under some circumstances. To avoid these difficulties the applicants looked to a different predictive technique, namely the assessment of the amount of non-bridging oxygens present. This is calculated by normalising the chemical analysis to 100 weight %; calculating the molar percentage of each oxide; summing the oxygen-weighted contribution of each oxide to get the total number of oxygens; summing the weighted contribution of each oxide of non-bridging oxygens (see below); and taking the ratio of non-bridging oxygens to the total number of oxygens. The applicants have found that when this figure exceeds 30% the fibres are soluble.

[0142] To explain the term non-bridging oxygen one must look to the structure of glasses. Glasses are very stiff liquids and to form usually require the presence of a material that can form a network (usually an oxygen-bridged network). The network may be modified by constituents that contribute non-bridging parts to the network and open the structure of the network and so prevent crystallisation. These materials are usually referred to as network-formers and modifiers respectively.

[0143] The terms modifier and network former are well known in the glass industries. Network formers are materials such as SiO₂, P₂O₅, B₂O₃ and GeO₂ which can form an interconnected network to form the glassy phase. Modifiers are substances such as CaO, Na₂O, and K₂O which alter the network and have effects on such properties as viscosity and melting point. There are some intermediate materials (such as Al₂O₃, TiO₂, PbO, ZnO and BeO) which can act as both network formers and modifiers depending on the environment and on the amount present.

[0144] In the above mentioned test, for calculating the non-bridging oxygens, one ignores the network formers and calculates the contribution of each other oxide. The contribution of each oxide depends on the geometry and charge of each cation in the glass. As examples typical contributions are as follows:—

[0145] Ca²⁺, Mg²⁺, Sr²⁺ and other divalent network modifier cations contribute 2 non-bridging oxygens

[0146] K⁺, Na⁺ and other monovalent network modifier cations contribute 1 non-bridging oxygen

[0147] Al³⁺, Ti³⁺ and other intermediate cations contribute −1 non-bridging oxygen (i.e these oxides reduce the number of non-bridging oxygens)

[0148] (Ti⁴⁺ is reduced to Ti³⁺ in most glasses when present in relatively small quantities)

[0149]

	TABLE 13
	Composition		Mol.	Oxygen		%	Solubility	S.S.A	Normalized	Log
Melt Code	Oxide	Wt. %	Moles	%	Total	N.B.O	N.B.O	Oxide	(ppm)	m2/g	Solubility	(norm solub)
CAS10(B) -	CaO	47.2	0.842	54.9	160.8	78.4	48.8	CaO	44	0.30	43	1.63
A	Al2O3	24.5	0.240	15.7				Al2O3	0
	SiO2	27.1	0.451	29.4				SiO2	7
		Total	1.533	100.0				Total	51
CAS10(B) -	CaO	46.5	0.829	54.0	160.9	77.8	48.4	CaO	58	0.39	66	1.82
B	Al2O3	23.7	0.232	15.1				Al2O3	1
	SiO2	28.4	0.473	30.8				SiO2	44
		Total	1.534	100.0				Total	103
CAS10(B) -	CaO	47.8	0.852	55.4	159.6	80.4	50.4	CaO	55	0.36	76	1.88
C	Al2O3	23.9	0.234	15.2				Al2O3	0
	SiO2	21.1	0.451	29.3				SiO2	55
		Total	1.537	100.0				Total	110
CIS(A)	CaO	42.7	0.761	47.5	152.5	85.1	55.8	CaO	62	0.40	69	1.84
	TiO2	12.7	0.159	9.9				TiO2	0
	SiO2	41.0	0.682	42.6				SiO2	49
		Total	1.602	100.0				Total	111
SrSiO3	SrO	63.1	0.609	51.2	148.8	102.4	68.8	SrO	2	0.37	249	2.40
	SiO2	34.9	0.581	48.8				SiO2	367
		Total	1.190	100.0				Total	369
CaSiO3	CaO	46.1	0.822	48.6	151.4	97.2	64.2	CaO	41	0.45	163	2.21
	SiO2	52.3	0.870	51.4				SiO2	253
		Total	1.692	100.0				Total	294
NAS(A)	Na2O	18.8	0.303	22.0	228.3	−12.6	−5.5	Na2O	#	0.56	4	0.60
	Al2O3	39.7	0.389	28.3				Al2O3	4
	SiO2	41.1	0.684	49.7				SiO2	5
		Total	1.376	100.0				Total	9
CAS4	CaO	21.0	0.374	25.7	198.1	3.8	1.9	CaO	11	0.62	8	0.90
	Al2O3	35.4	0.347	23.8				Al2O3	4
	SiO2	44.2	0.736	50.5				SiO2	5
		Total	1.457	100.0				Total	20
MAS(B)	MgO	10.0	0.248	17.0	205.6	−11.2	−5.4	MgO	7	0.52	6	0.78
	Al2O3	33.7	0.331	22.6				Al2O3	2
	SiO2	53.0	0.882	60.4				SiO2	4
		Total	1.461	100.0				Total	13
SAS(A)	SrO	29.8	0.288	23.9	201.4	−2.6	−1.4	SrO	9	0.50	8	0.90
	Al2O3	31.1	0.305	25.3				Al2O3	2
	SiO2	36.8	0.612	50.8				SiO2	5
		Total	1.205	100.0				Total	16
SCS(A)	SrO	35.0	0.338	23.5	150.5	99.0	65.8	SrO	75	0.41	280	2.45
	CaO	21.0	0.374	26.0				CaO	30
	SiO2	43.6	0.726	50.5				SiO2	355
		Total	1.438	100.0				Total	460
SMAS(A)	SrO	55.0	0.531	49.1	169.6	60.8	35.8	SrO	57	0.46	38	1.58
	MgO	1.2	0.030	2.8				MgO	5
	Al2O3	23.7	0.232	21.5				Al2O3	2
	SiO2	17.3	0.288	26.6				SiO2	5
		Total	1.081	100.0				Total	69
SMAS(B)	SrO	55.0	0.531	44.6	157.6	84.8	53.8	SrO	110	0.39	95	1.98
	MgO	4.8	0.119	10.0				MgO	15
	Al2O3	14.8	0.145	12.2				Al2O3	1
	SiO2	23.7	0.394	33.2				SiO2	22
		Total	1.189	100.0				Total	148
SMS(A)	SrO	33.0	0.318	20.7	159.5	80.6	50.5	SrO	147	0.39	212	2.33
	MgO	12.5	0.310	20.2				MgO	61
	Al2O3	1.0	0.010	0.6				Al2O3	0
	SiO2	53.8	0.895	58.4				SiO2	123
		Total	1.533	100.0				Total	331
SAS(C)	SrO	56.0	0.540	47.7	169.3	61.4	36.3	SrO	70	0.38	52	1.72
	Al2O3	19.7	0.193	17.0				Al2O3	1
	SiO2	24.0	0.399	35.3				SiO2	8
		Total	1.132	100.0				Total	79
CMAS(A)	CaO	35.0	0.624	42.6	179.3	41.4	23.1	CaO	11	0.30	24	1.38
	MgO	4.5	0.112	7.6				MgO	7
	Al2O3	44.0	0.432	29.5				Al2O3	3
	SiO2	17.8	0.296	20.3				SiO2	8
		Total	1.464	100.0				Total	29
SWA2	CaO	21.7	0.387	21.4	157.5	85.0	54.0	CaO	53	0.48	119	2.08
	MgO	15.7	0.389	21.5				MgO	57
	Al2O3	0.8	0.008	0.4				Al2O3	0
	SiO2	61.8	1.028	56.7				SiO2	118
		Total	1.812	100.0				Total	228
SAS(D)	SrO	56.5	0.545	48.5	166.9	66.2	39.7	SrO	107	0.40	92	1.96
	Al2O3	17.6	0.173	15.4				Al2O3
	SiO2	24.4	0.406	36.1				SiO2	39
		Total	1.124	100.0				Total	147
KMAS(A)	K2O	16.5	0.175	11.3	179.5	41.4	23.1	K2O	#	0.36	14	1.15
	MgO	13.0	0.323	20.8				MgO	8
	Al2O3	18.0	0.177	11.4				Al2O3	1
	SiO2	52.8	0.879	56.6				SiO2	11
		Total	1.554	100.0				Total	20

[0150] Table 13 shows, for the compositions of Table 11, the calculated figure for non-bonding oxygens and these figures are reproduced in FIG. 5. It can be seen that the plot of FIG. 5 is more linear than that of FIG. 4. Compositions with greater than 30% non-bridging oxygens show high solubility.

[0151] To illustrate the method the calculation for one example (the first shown in Table 13) is given below:—

[0152]

	Mols/	Total	Non-bridging
	Mol	Oxygen	Oxygens
CaO	0.549	0.549	1.098 (2 * 0.549)
Al2O3	0.157	0.471 (0.157 * 3)	−0.314 (−1 * 0.157 * 2A1)
SiO2	0.294	0.588	0.000
	1.000	1.608	0.784
% non-bridging oxygens (0.784/1.608) * 100 = 48.8%

[0153] As an example one can look to European Patent Specification No. 0399320 referred to above. Using this method in relation to that specification Composition 1 has a non-bridging oxygen percentage of 48.2% whereas Composition 2 has a non-bridging oxygen percentage of 19.6%, again predicting that Composition 1 is more soluble than Composition 2.

[0154] There is a further criterion which a composition must meet for it to form vitreous fibres, namely that it be capable of forming a glass. The applicants have found a simple test. If the ratio of modifiers to network formers is less than a critical value (for SiO₂ based glasses, 1) the composition will generally form a glass. For the purpose of this test reasonable results are obtained if such intermediate materials are treated as networkers. Table 14 shows for a series of compositions in each column:—

• • [0155] Fibre reference (N.B. these are not the same fibres as shown in tables 9 & 10)
  • [0156] Composition
  • [0157] Molar ratios
  • [0158] Ratio of glass modifiers to network formers
  • [0159] Free energy of hydration of raw oxides
  • [0160] Melting Point
  • [0161] X-ray diffraction results
  • [0162] Solubility data (# indicates not measured)
  • [0163] Specific surface area
  • [0164] Normalised solubility data
  • [0165] Arbitrary ranking as to solubility and glass forming ability
  • [0166] Indication as to whether melting point above 1500° C.

[0167] It should be emphasised that this test is a screening one rather than a wholly predictive one as there are several circumstances that may lead to its failure. Among these circumstances are compound formation and inability to quench fast enough to form glass.

[0168] Having adopted these tests as a screening method there follows a further step to ascertain whether the composition will form a vitreous fibre. This last step is best examined experimentally as fibre forming ability is a complex function of many physical characteristics, e.g. viscosity, which are often difficult to measure.

[0169]

Key to FIG. 1
	CR Cristobalite	FO Forsterite
	TR Tridymite	PR Protoenstatite
	PS Pseudowollastonite	DI Diopside
	WO Wollastonite	AK Akermanite
	RA Rankinite	ME Merwinite
	LI Lime	MO Monticellite
	PE Periclase

[0170]

	TABLE 14
									Norm Solub	Criteria
	Composition		Modifier/				Solubility Data (ppm)	S.S.A.	(0.25 m2/g)	(0–10 Rating)	M. Pt.
Reference	(Wt. %)	Molar Ratios	Networker	Ghyd (kcal/mol)	M. Pt. (C.)	% RD Data	Species	1 day	Total	5 days	Total	(m2/g)	1 day	5 days	Solub	Glass	>1500 C.
CAS10(A)	49.4 CaO	3.8 CaO	0.97		1544	Amorphous * trace	CaO	62		48		0.25	124	187	10	9	T
No. 18	23.4 Al2O3	1.0 Al2O3		−4.6	(Eut.)	(3 small peaks)	Al2O3	7	124	10	182
	29.2 SiO2	1.9 SiO2					SiO2	55		124
CIS(A)	42.7 CaO	4.7 CaO	0.85		1425	Amorphous	CaO	100		88		0.56	83	88	7	10	W
No. 19	13.0 TiO2	1.0 TiO2		−1.3	(Eut.)	(No peaks)	TiO2	0	187	0	197
	43.6 SiO2	4.5 SiO2					SiO2	87		109
MAS(A)	12.4 MgO	1.2 MgO	0.2		1450	Amorphous * trace	MgO	63		248		0.57	40	116	4	9	W
No. 20	26.5 Al2O3	1.0 Al2O3		3.8	(1400 C.)	(2 small peaks)	Al2O3	5	92	1	264
	62.4 SiO2	40 SiO2					SiO2	24		15
MAS(A)	29.4 Na2O	1.2 Na2O	0.69		1475	Crystalline	Na2O	#		#		0.53	15	471	1	2	W
No. 21	39.2 Al2O3	1.0 Al2O3		−6.3	(Eut.)	(Glossy trace)	Al2O3	3	37	983	990
	33.7 SiO2	1.5 SiO2					SiO2	29		15
CPI(A)	53.3 CaO	2.7 CaO	1.35	−24.7	1565	Crystalline	CaO	47	47	17	17	0.68	17	6	1	0	T
No. 22	50.6 P2O5	1.0 P2O5			(Eut.)	(No glass)	P2O5	#		#
SAI(B)	68.0 SiO	1.1 SiO	1.1	−5.7	1545	Amorphous (strong) *	SiO	11	1247	5	729	0.88	346	203	10	5	T
No. 23	35.9 SiO2	1.0 SiO2			(Eut.)	some crystal. (strong)	SiO2	1236		724
CaSiO3	42.3 CaO	1.0 CaO	0.77	−3	1545	Amorphous * trace	CaO	19	1284	27	508	0.71	452	179	10	9	T
No. 24	57.2 SiO2	1.3 SiO2			(1460 C.)	(3 small peaks)	SiO2	1265		481
ASI(D)	37.3 MgO	1.0 MgO	0.91	0.6	1545	Crystalline (strong) *	MgO	62	216	249	362	0.83	65	127	5	6	T
No. 26	62.5 SiO2	1.1 SiO2			(Eut.)	some glass (strong)	SiO2	154		113
C612A17	47.7 CaO	11.2 CaO	0.8	−7.2	1400	Amorphous * trace	CaO	14	317	3	145	2.45	37	15	3	7	W
No. 28	53.9 Al2O3	7.0 Al2O3			(Eut.)	(Mod. cryst.)	Al2O3	298		142
CMS(A)	42.5 CaO	1.8 CaO	7		1575	Crystalline	CaO	42		21		0.47	158	118	10	0	T
No. 27	16.6 MgO	1.0 MgO		−4.3	(Eut.)	(No glass)	MgO	41	303	8	227
	39.7 SiO2	1.4 SiO2					SiO2	220		198
CTI(D)	15.4 CaO	1.0 CaO	4.570	9.5	1465	Crystalline	CaO	14	14	16	16	1.15	3	3	0	0	W
No. 25	77.5 TiO2	3.5 TiO2			(Eut.)	(No glass)	TiO2	0		0
NCS(A)	20.4 Na2O	1.0 Na2O	1.86		1425	Crystalline *	Na2O	#		#		0.99	204	95	10	4	W
Cryst.	35.8 CaO	1.9 CaO		−8.7	(Eut.)	some glass	CaO	595	806	333	375
No. 29	40.8 SiO2	2.1 SiO2				(Strong cryst.)	SiO2	211		42
NCS(A)	19.5 Na2O	1.0 Na2O	1.74		1425	Amorphous *	Na2O	#		#		1.36	123	49	10	7	W
Glassy	35.3 CaO	2.0 CaO		−8.1	(Eut.)	some crystal.	CaO	543	686	237	271
No. 30	42.7 SiO2	2.3 SiO2				(8 small peaks)	SiO2	143		34
CPI(A)Rpt	54.4 CaO	2.9 CaO	1.45	−24	1565	Crystalline	CaO	14	14	13	13	1.04	3	3	0	0	T
No. 31	48.2 P2O5	1.0 P2O5			(Eut.)	(No glass)	P2O5	#		#
NAS(A)	21.0 Na2O	1.0 Na2O	0.48		1475	Amorphous	Na2O	#		#		0.53	17	24	1	10	W
Apt.	40.1 Al2O3	1.2 Al2O3		−4	(Eut.)	(No peaks)	Al2O3	18	37	30	50
No. 32	38.7 SiO2	1.8 SiO2					SiO2	19		20
KAS(E)	20.0 K2O	1.0 K2O	0.31		1590	Amorphous	K2O	#		#		0.97	7	10	1	10	T
No. 33	30.4 Al2O3	1.4 Al2O3		−2.7	(Eut.)	(No peaks)	Al2O3	9	28	18	39
	46.1 SiO2	3.6 SiO2					SiO2	19		21
CAS4	21.2 CaO	1.1 CaO	0.26		1550	Amorphous	CaO	17		13		0.72	10	8	1	10	T
No. 34	34.0 Al2O3	1.0 Al2O3		1.1	(1500 C.)	(No peaks)	Al2O3	1	28	1	24
	44.6 SiO2	2.2 SiO2					SiO2	10		10
NAS(D)	14.9 MgO	2.7 MgO	0.24		1450	Amorphous	MgO	7		68		0.61	6	42	1	10	W
No. 35	35.9 Al2O3	2.0 Al2O3		3.4	(1400 C.)	(No peaks)	Al2O3	1	1.5	24	107
	51.6 SiO2	4.9 SiO2					SiO2	7	20
SAS(A)	32.5 SiO	1.0 SiO	0.25		1670	Amorphous	SiO	24		1		0.67	19	4	2	10	T
No. 36	32.4 Al2O3	1.0 Al2O3		0.1	(7)	(No peaks)	Al2O3	11	50	1	12
	38.1 SiO2	2.0 SiO2					SiO2	15		10
SCS(A)	17.1 SiO	1.1 SiO	0.91		1480	Amorphous * trace	SiO	57		3		0.57	177	258	10	10	W
No. 37	17.5 CaO	1.0 CaO		−3.6	(Eut)	(2 small peaks)	CaO	35	411	2	599
	43.4 SiO2	2.3 SiO2					SiO2	329		594
SCS(C)	19.5 SiO	0.5 SiO	0.9		1500	Amorphous	SiO	55		11		0.66	155	219	10	10	T
No. 38	29.4 CaO	1.4 CaO		−3.1	(Eut.)	(No peaks)	CaO	36	411	10	579
	47.1 SiO2	2.1 SiO2					SiO2	320		558
SCS(B)	51.4 SiO	1.7 SiO	0.96		1500	Amorphous * trace	SiO	5		45		0.66	161	219	10	10	T
No. 39	8.1 CaO	0.5 CaO		−4.6	(Eut.)	(1 small peak)	CaO	5	425	27	579
	39.7 SiO2	2.3 SiO2					SiO2	415		507
SAS(B)	65.9 SiO	5.2 SiO	0.96		1600	Crystalline (strong) *	SiO	102		5		0.99	114	65	10	5	T
No. 40	12.4 Al2O3	1.0 Al2O3		−6.6	(7)	some glass (strong)	Al2O3	1	453	1	256
	25.0 SiO2	3.4 SiO2					SiO2	350		250
SMAS(A)	58.0 SiO	2.7 SiO	0.76		1610	Amorphous * trace	SiO	87		61		0.65	48	31	4	10	T
No. 41	1.1 MgO	0.1 MgO		−6.7	(1560 C.)	(1 small peak)	MgO	7	104	4	81
	25.8 Al2O3	0.9 Al2O3					Al2O3	1		1
	18.4 SiO2	1.1 SiO2					SiO2	9		15
SMAS(B)	59.1 SiO	6.0 SiO	0.91		1610	Amorphous * trace	SiO	123		20		0.7	70	31	6	9	T
No. 42	3.8 MgO	1.0 MgO		−5.8	(1500 C.)	(3 small peaks)	MgO	32	197	29	86
	16.6 Al2O3	1.7 Al2O3					Al2O3	1		1
	24.6 SiO2	4.3 SiO2					SiO2	41		36
SMS(A)	35.9 SiO	1.1 SiO	0.78		1600	Amorphous	SiO	159		42		0.75	148	176	10	10	T
No. 43	0.8 Al2O3			−0.4	(1500 C.)	(No peaks)	MgO	100	444	129	348
	12.9 MgO	1.0 MgO					SiO2	185		177
	51.2 SiO2	2.7 SiO2
SAS(C)	60.6 SiO	2.9 SiO	0.74		1600	Amorphous	SiO	142		104		0.67	67	50	5	10	T
No. 44	20.7 Al2O3	1.0 Al2O3		−5.9	(7)	(No peaks)	Al2O3	7	167	7	133
	22.6 SiO2	1.9 SiO2					SiO2	18		22
ACPS(A)	16.6 Al2O3	1.5 Al2O3	0.74		1600	Crystalline	Al2O3	1		1		0.58	20	19	2	0	T
No. 45	39.0 CaO	6.2 CaO		−17.7	(Eut)	(No glass)	CaO	39	46	35	45
	35.6 P2O5	2.2 P2O5					P2O5	#		#
	6.7 SiO2	1.0 SiO2					SiO2	6		9
CMAS(A)	30.6 CaO	3.7 CaO	0.6		1530	Amorphous	CaO	24		21		0.54	19	18	2	10	T
No. 46	5.9 MgO	1.0 MgO		−3.2	(Eut)	(No peaks)	MgO	10	40	7	39
	41.6 Al2O3	2.8 Al2O3					Al2O3	2		2
	19.6 SiO2	2.2 SiO2					SiO2	4		9
SA	69.1 SiO	2.1 SiO	1.05	−10.7	1500	Crystalline (strong) *	SiO	49	1155	125	1257	0.62	466	507	10	4	T
No. 47	32.2 Al2O3	1.0 Al2O3			(Eut)	some glass (med)	Al2O3	1106		1132
SW2A	21.3 CaO	1.0 CaO	0.78		1360	Amorphous	CaO	70		65		0.66	127	140	10	10	W
No. 48	16.9 MgO	1.1 MgO		−0.2		(No peaks)	MgO	91	322	116	369
	1.1 Al2O3						Al2O3	10		1
	61.5 SiO2	2.7 SiO2					SiO2	151		187
MAS(C)	34.9 MgO	3.5 MgO	0.73		1600	Amorphous (strong) *	MgO	50		135		0.52	27	67	2	7	T
No. 49	25.5 Al2O3	1.0 Al2O3		0	(Eut)	some cryst. (weak)	Al2O3	2	58	2	144
	41.7 SiO2	2.3 SiO2					SiO2	7		7
SAS(D)	60.3 SiO	3.6 SiO	0.84		1600	Amorphous * trace	SiO	141		77		0.54	123	117	10	10	T
No. 50	16.5 Al2O3	1.0 Al2O3		−6.1	(7)	(2 peaks)	Al2O3	1	260	1	249
	22.4 SiO2	2.3 SiO2					SiO2	118		171
KMAS(A)	17.5 K2O	1.0 K2O	0.56		1500	Amorphous	K2O	#		#		0.94	6	7	1	10	T
No. 51	13.5 MgO	1.8 MgO		−2.4	(Eut)	(No peaks)	MgO	13	23	14	25
	18.6 Al2O3	1.0 Al2O3					Al2O3	1		1
	53.1 SiO2	4.8 SiO2					SiO2	9		10
KMAS(A)	20.0 K2O	1.5 K2O	0.54		1590	Amorphous	K2O	#		#	0.63	17	19	1	10	T
No. 52	9.0 Na2O	1.0 Na2O		−6.3	(Eut)	(No peaks)	Na2O	#	31	#	49
	33.8 Al2O3	2.3 Al2O3					Al2O3	14		32
	39.9 SiO2	4.6 SiO2					SiO2	17		17