HIGH TEMPERATURE RESISTANT SALINE SOLUBLE FIBRES

Abstract: A fibre is disclosed having a maximum use temperature of 1200 DEG C or more which comprises: SiO2 > 64.25 wt % CaO > 18 wt % MgO < 17 wt % and in which the amount of MgO in mol % is greater than the amount of CaO in mol %. Such fibres have high solubility and low dustiness.

Description: HlSHJEMPERATURF. RESISTANT SALINE SOLUBLE FIBRES This invention relates to high temperature resistant saline soluble fibres and particularly relates to calcium-magnesium-silicate fibres. Calcium-magnesium-silicate fibres are known for example from WO89/12032, WO93/15028 and WO94/15883. WO89/12032 first disclosed a broad class of fire-resistant saline soluble fibres. WO93/15028 showed that a class of the fibres of WO89/12032 were usable at temperatures up to 1000°C or more. WO94/15883 showed that some of the fibres of WO93/15028 had higher use temperatures still, of up to 1260°C or more, and indicated that such fibres needed a SiO 2 excess (defined as the amount of SiO 2 remaining after crystallisation of CaO, MgO and any ZrO 2 as silicates) of greater than 21.8mol%. WO97/16386 while falling in the general class of calcium-magnesium-silicate fibres looked to low calcium fibres to show use temperatures of 1260°C or more. It is apparent that there are regions of the CaO-MgO-SiO 2 and CaO-MgO-SiO 2 -Zrθ2 composition fields within which high temperature performance fibres can be made and other regions where they cannot. The applicants have now found a new and narrow range of compositions that are usable at temperatures of 1200°C or more and even 1250°C or 1260°C or more, and yet fall outside the scope of WO94/15883 and WO97/16386. These compositions preferably have little or no zirconia. Accordingly the present invention provides a fibre having a maximum use temperature of 1200°C or more in which the amount of MgO in mol% is greater than the amount of CaO in mol % and which comprises :- SiO 2 >64.25 wt% CaO >18 wl% MgO < 17 wt%. However, no claim is made to fibres having a SiO 2 excess as specified of greater than 21.8mol%. Further features of the invention are apparent from the appended claims. The excess SiO 2 figure is calculated by treating all of the CaO as being bound as CaO.MgO.2SiO 2 ; all of the ZrO 2 as being bound as ZrO 2 .SiO 2 ; and the remaining MgO as being bound as MgO.SiO 2 . The applicants also assume that any Al 2 O 3 crystallises as AI2O3.S1O2. Any remaining SiO 2 is called the excess SiO 2 . The invention is illustrated by way of example in the following description with reference to the drawings in which Fig 1 is a graph showing linear shrinkage with temperature for blankets comprising the fibres A4-2 and A4-3 of Table 1 below. Fig. 2 is a graph showing shrinkage through the height of blankets comprising the fibres A4-2 and A4-3 of Table 1 below. Fig. 3 is a graph showing shrinkage of preforms produced from fibres A4-1 , A4-2 and A4-3 of Table 1 below. Table 1 shows compositions extracted from WO89/12032, WO93/15028, WO94/15883, and WO97/16386 together with A4, a target composition fibre having the composition:- SiO 2 65 wt% CaO 19.5 wt% MgO 15.5 wt% and A4-1 , A4-2, and A4-3, which are analysed fibre samples. The fibres extracted from the data of WO89/12032 (referred to as Manville fibres), WO93/15028, WO94/15883, and WO97/16386 (referred to as Unifrax fibres) are those for which the SiO 2 excess as specified is less than than 21.8mol% and for which the amount of MgO in mol% is geater than the amount of CaO in mol%. A4-1 was produced as bulk fibre; A4-2 was produced as needled blanket having a density of approximately 96 kg.m "3 ; and A4-3 was produced as needled blanket having a density of approximately 128 kg.m "3 . In Table 1 shrinkages are indicated from the documents concerned or, for A4-1, A4-2, and A4-3, from measuring the shrinkage of vacuum formed preforms of the fibres concerned. rt § en H H 3 H W en W H w β W H in H H W n S w H It can be seen that the fibres according to the present invention show lower shrinkage at 1260°C than do the extracted fibres other than fibre Unifrax 42 which has a radically different composition. In Figs. 1-3, graphs show the shrinkage characteristics of the fibres A4-1, A4-2, and A4-3 after 24 hours exposure to the indicated temperatures, it can be seen that the fibres are readily usable at temperatures of 1200°C or more. Table 2 below shows the results of solubility tests on the fibres in physiological saline solution indicating mat the fibres are soluble in body fluids. (See WO94/15883 for a discussion of methods of measuring solubility). Pairs of results are indicated for separate tests on each sample as is a mean total solubility. A typical range of compositions for fibres of the present invention would be SiO 2 65 ±0.5 wt% CaO 20 ± 0.5 wt% MgO 15 ± 0.5 wt%. Further tests were made on fibres having the inventive composition of SiO 2 65%, CaO 19.5%, MgO 15.5% in comparison with Superwool 607™, a fibre having the nominal composition (by weight) of SiO 2 65%, CaO 29.5%, MgO 5.5%, and Al 2 O 3 <1% ; Superwool 612™, a fibre having the nominal composition (by weight) of SiO 2 64.5%, CaO 17%, MgO 13.5%, ZrO 2 5%; and refractory ceramic fibre having the nominal composition SiO 2 56%, Al 2 O 3 44%. The first test was aimed at indicating the amount of dust that might be released on handling. The test comprised the determination of the amount of dust present in a sample of blanket made from the respective fibres. The samples of blanket were vibrated on a Fritsch Analysette type 3010 vibratory sieve shaker, which was set for a frequency of 3000Hz and vertical amplitude of 0.5mm. The apparatus was equipped with a 1.6mm sieve and a pan. In the test method a sample of blanket 135mm x 135mm was placed on the sieve and vibrated for 10 minutes. The material collected in the pan was weighed and expressed as a percentage of the original weight of the sample. The results were as indicated below:- Fibre Material Percent dust released Superwool 607™ 0.16% Inventive material 0.18% Refractory ceramic fibre 0.25% Superwool 612™ 0.36% From this it can be seen that the inventive fibre is of comparable low dustiness to Superwool 607™. The second test made was to look to the shrinkage behaviour of blanket formed from the inventive fibre and the two Superwool™ fibres at high temperatures. Samples of blanket were exposed to specified temperatures for 24 hour periods and their linear shrinkage measured. The results are indicated in Table 3 below:- This shows that the inventive fibre is comparable in performance with both Superwool™ fibres up to 1200°C. At 1250°C the Superwool 607™ fibre shows a shrinkage of 4.8% (which would be considered as too high a shrinkage for most applications). At 1300°C the inventive fibre while still showing a high shrinkage of 4.2% is the best of the three fibres tested. A further series of tests were made to produce fibres on a production scale and the compositions of fibres obtained were as set out in Table 4 below. All showed low shrinkage at 1250°C (shrinkages were measured by different methods to Table 1 and are not directly comparable). In combination with the results of Table 1, this shows samples of usable characteristics having compositions consisting essentially of (in wt%) CaO 18.7 to 20.2 MgO 14.47 to 15.9 SiO 2 64.5 to 65.1 Al 2 O 3 0 to 0.56 The fibres of the present invention therefore have a high solubility (desired to permit fibres to be cleared from the body quickly); a low dustiness (desired to reduce the amount of fibre that can be inhaled); and good high temperature characteristics. cn H H H W 0\

Claims: CLAIMS 1. A fibre having a maximum use temperature of 1200°C or more which comprises: SiO 2 >64.25 wt% CaO >18 wt% MgO < 17 wt% and in which the amount of MgO in mol% is greater than the amount of CaO in mol % and in which the SiO 2 excess as specified is no greater than 21.8mol%.. 2. A fibre as claimed in claim 1 and comprising:- CaO <21 wt%. 3. A fibre as claimed in claim 2 and comprising:- CaO <20.5 wt%. 4. A fibre as claimed in any of claims 1 to 3 and comprising:- CaO >19 wt%. 5. A fibre as claimed in claim 4 and comprising:- CaO > 19.5 wt% 6. A fibre as claimed in any of claims 1 to 4 and comprising:- MgO > 14.25 wt %. 7. A fibre as claimed in claim 6 and comprising: - MgO > 14.75 wt %. 8. A fibre as claimed in claim 7 and comprising:- MgO> 15.25 wt%. 9. A fibre as claimed in any preceding claim and comprising:- MgO<16wt%. 10. A fibre as claimed in any preceding claim and comprising:- SiO 2 65 ± 0.5 wt% CaO 20 ±0.5wt% MgO15±0.5wt%. 11. A fibre as claimed in any of claims 1 to 9 and comprising:- SiO 2 64.5 - 64.7 wt% CaO 19.5- 20.2 wt% MgO 15.5- 15.6 wt%. 12. A fibre as claimed in any preceding claim and comprising: - SiO 2 about 65 wt% CaO about 19.5 wt% MgO about 15.5 wt%. 13. A fibre as claimed in any preceding claim and consisting essentially of:- CaO 18.7to20.2wt% MgO 14.47 to 15.9wt% SiO 2 64.5to65.1wt% Al 2 O 3 0to0.56wt%

Inventors: JUBB GARY ANTHONY, MARTIN JEAN-LOUIS, JUBB, GARY, ANTHONY, MARTIN, JEAN-LOUIS
Applicants: JUBB GARY ANTHONY, MARTIN JEAN LOUIS, MORGAN CRUCIBLE CO, JUBB, GARY, ANTHONY, MARTIN, JEAN-LOUIS, THE MORGAN CRUCIBLE COMPANY PLC
Application year: 2000
Main classification: C03C13
IPC codes: C03C13, D01F9