SALINE SOLUBLE INORGANIC FIBRES

Abstract: The use of P2O5 and/or B2O3 as a component to improve the refractoriness of inorganic fibres comprising SiO2, and CaO and/or MgO is described. The inorganic fibres have a composition such that SiO2 + P2O5-(58 + (if MgO > 10, 0.5 x (MgO-10) else 0)) > -2.4 wt.%.

Description: SALINE SOLUBLE INORGANIC FIBRES This invention relates to saline soluble inorganic fibres. Saline soluble inorganic fibres have been described in several patent specifications, see for example WO93/15028. Fibres are required to be soluble in saline solution so that inhaled or ingested fibres dissolve rather than providing a source of irritation or otherwise affecting health. WO93/15028 showed that fibres comprising S-O2, CaO and MgO and having a silica content of greater than 58% (or greater than 58% plus 0.5 times (wt%MgO - 10) if MgO > 10wt%) had suitable shrinkage characteristics at 800°C and 1000°C to be usable as refractory materials. A further feature of WO93/15028 was the use of the percentage of non-bridging oxygens present to predict the solubility of fibres in physiological saline solution. Various subsequent applications have described the effect of P 2 O 5 and B 2 O 3 on solubility - see for example W095/29135. P 2 O 5 is alleged to have a solubilising effect on such fibres. The German government have proposed a fibre classification which turns on a variable Ki which is defined as: K τ = Σ( Na,K,B,Ca,Mg,Ba -oxide) - 2* Al-oxide (the amounts of the oxides being expressed as weight %) According to the proposed fibre classification if Ki is greater than 40 the fibre requires no health warnings. If Ki lies between 30 and 40 the fibre requires health warnings to be made. If Ki is less than 30 more serious marking is required (it is labelled as a carcinogen). It is readily apparent that it is difficult to provide a high Ki fibre (Kι>40) while still providing a refractory fibre like that of WO93/15028 (Si0 2 >58wt%), there being a very narrow window of compositions to meet. As a result of investigating fibre compositions that may meet the fibre classification and yet still be refractory enough to meet the standard of WO93/15028 (slirinkage of less than 3.5% at both 800°C andl000°C) the applicants have found that addition of P2O5 to compositions allows a broader range of refractory fibres to be produced than had previously been appreciated. They have also found that B 2 0 3 , previously thought to be extremely detrimental to refractoriness, has a sirnilar, although lesser, effect and that both P 2 0 5 andB 2 0 3 may be used in the fibres of WO93/15028. The applicants have found that the refractoriness of the P 2 O5 and B 2 O3 containing fibres of the present invention is dependent on the sum of the amounts of Si0 2 and P 2 Os (expressed in wt%) It appears that a further factor that may be important in deternrining the refractoriness of a fibre is the percentage of non-bridging oxygens. If this percentage is 61.4% or more (calculated on the basis of the amounts of the components Si0 2 , CaO, MgO, P 2 0 5 , and B 2 0 3 ) the fibres tend to fail shrinkage tests at 800°C and 1000°C (failure being defined as a slirinkage of 3.5% or more). Accordingly the present invention provides the use of P 2 Os and/or B 2 0 3 as a component to improve the refractoriness of inorganic fibres comprising Si0 2 , and CaO and/or MgO, the inorganic fibres having a composition such that Siθ2 + P2θj- (58 + (if MgO > 10, 0.5 x (MgO - 10) else 0)) > - 2.4wt% The invention provides further such fibres in which the percentage of non- bridging oxygens is less than 61.4%. Further features of the invention are apparent from the claims in the Ught of the following description. The percentage of non-bridging oxygens (%N.B.O.) is calculated by converting the weight percentages of Si0 2 , CaO, MgO, P 2 O5, and B 2 0 3 to molar amounts and inserting these amounts into the equation:- The reason the amounts of CaO, MgO, P 2 O 5 , and B 2 O3 are doubled in the numerator to this equation is that each contributes two non-bridging oxygens. The reason terms are multiplied in the denominator to this equation is to reflect the number of oxygen atoms each molecular formula possesses. Table I shows the results of a first set of shrinkage and solubility tests on compositions comprising Si0 2 , CaO, MgO, P2O5, and B 2 0 3 as main ingredients. In this table the analysed compositions are normalised to 100%. It is clear from these compositions that where the percentage of non- bridging oxygens calculated on the basis of the amounts of the above named components is greater than 61.4% (those fibres lying above line A of Table I) the fibres fail the shrinkage tests, having shrinkages of greater than 3.5% at either or both of 800°C and 1000°C. WO93/15028 stressed the importance of alurnina content and the fibres lying between lines B and A of Table I show that alumina contents of greater than lwt% are damaging to the slirinkage properties of fibres. The applicants have also found that the combined amount of CaO and MgO is important. Those fibres lying between lines C and B have a combined CaO and MgO content of greater than 42wt% and also fail the shrinkage tests. The fibres below line C have a percentage of non-bridging oxygens less than 61.4%, an alumina content of less than lwt%, and a combined CaO and MgO content of less than 42wt%. All of these fibres pass the shrinkage tests. These fibres fall within the compositional ranges:- Si0 2 52.4 - 57.85wt% CaO 22.2 - 39.4wt% MgO 1.96 - 17.4wt% P2O 5 0.82 - 7.8wt% B 2 0 3 0 - 1.95wt% A1 2 0 3 <lwt% The solubility results presented in Table I were obtained by the methods described in WO93/15028 and show a high solubility for all of the fibres produced. It can be seen that all of the fibres below line C have a Ki of more than 35 and more than half have a Ki of more than 40. Further testing resulted in the data presented in Table II. The data presented are as in table I but an additional column entitled deviation shows the result of looking to the difference between the sum of the Si0 2 and P 2 Os contents and the Si0 2 amount predicted to be needed by WO93/15028 for a fibre to be refractory (shrinkage of less than 3.5% at both 800°C and 1000°C. The figure given is found by calculating the sum S.O- + P.OJ - (58 + (if MgO > 10, 0.5 x (MgO - 10) else 0)) If this is less than -2.4wt% the fibres fail. The fibres that failed are shown in plain text, those that passed in bold text, and those that were difficult to form in italics. More than 12.5wt% P2O5 is undesirable as it causes difficulties in making the fibres. While the above description and the claims refer to P 2 0 5 , B 2 θ 3 , Si0 2 , CaO and MgO it will be clear to the person skilled in the art that the pure materials need not be used and that provision of these components in combined form (e.g. provision of P 2 0 5 in the form of mixed oxide phosphates) is part of the invention.

Claims: CLAIMS 1. The use of P 2 O 5 or B 2 O3 as a component to improve the refractoriness of inorganic fibres comprising Si0 2 , and CaO and/or MgO, to produce inorganic fibres having a composition having a shrinkage of less than 3.5% when exposed to 1000°C for 24 hours and having a shrinkage of less than 3.5% when exposed to 800°C for 24 hours, the fibres having a composition such that SiO- + P2O5 - (58 + (if MgO > 10, 0.5 x (MgO - 10) else 0)) > - 2.4wt% 2. The use of P 2 O 5 or B2O3 as a component to improve the refractoriness of inorganic fibres as claimed in claim 1 in which the percentage of non-bridging oxygens is less than 61.4%. 3. The use of P 2 O 5 or B 2 O 3 as a component to improve the refractoriness of inorganic fibres as claimed in claim 1 or claim 2 in which the fibres fall within the compositional range:- Si0 2 44 or more CaO 20 - 40wt% MgO 0 - 18wt% P2O 5 0- 12.5wt% B 2 0 3 0 - 4wt% 4. The use of P 2 O 5 or B 2 O 3 as a component to improve the refractoriness of inorganic fibres as claimed in claim 3 in which the fibres fall within the compositional range:- Si0 2 52 - <58wt% [52 - <58+0.5'(MgO-10)wt% if MgO > 10wt%] CaO 22 - 40wt% MgO 0 - 17.5wt% MgO + CaO < 42wt% P 2 O s 0.5 - 10wt% B 2 O 3 0 - 2wt% 5. The use of P 2 O 5 or B 2 O3 as a component to improve the refractoriness of inorganic fibres as claimed in claim 3 in which the fibres fall within the compositional range:- Si0 2 44.34 - 62.48 CaO 20.36 - 39.4wt% MgO 0.62 - 21.16wt% P 2 0 5 0 - 12.01wt% B 2 0 3 0 - 3.54wt% 6. Saline soluble inorganic fibres having a shrinkage of less than 3.5% when exposed to 1000°C for 24 hours and having a shrinkage of less than 3.5% when exposed to 800°C for 24 hours, in which:- Siθ2 + P 2 OJ - (58 + (if MgO > 10, 0.5 x (MgO - 10) else 0)) > - 2.4wt% 7. Saline soluble inorganic fibres as claimed in claim 6 composing: - Si0 2 44 or more CaO 20 - 40wt% MgO 0 - 18wt% P 2 0 5 0- 12.5wt% B 2 0 3 0 - 4wt% 8. Saline soluble inorganic fibres as claimed in claim 7 comprising:- S1O 2 52 - <58wt% [52 - <58+0.5'(MgO-10)wt% if MgO > 10wt%] CaO 22 - 40wt% MgO 0 - 17.5wt% MgO + CaO < 42wt% P 2 0 5 0.5 - 10wt% B 2 0 3 0 - 2wt% and in which the percentage of non-bridging oxygens calculated on the basis of the amounts of the above named components is less than 61.4%. 9. Saline soluble inorganic fibres as claimed in claim 7 comprising - Si0 2 44.34 - 62.48 CaO 20.36 - 39.4wt% MgO 0.62 - 21.16wt% P 2 0 5 0 - 12.01wt% B 2 0 3 0 - 3.54wt% 10. Saline soluble inorganic fibres as claimed in claim 6 in which the fibres have a composition:- Si0 2 52.4 - 57.85wt% CaO 22.2 - 39.4wt% MgO 1.96 - 17.4wt% P2O 5 0.82 - 7.8wt% B2O3 0 - 1.95wt% A1 2 0 3 <lwt%

Inventors: CANTY PHILIP JOHN, EATON PAUL NIGEL, JUBB GARY ANTHONY, LOWE ALISON JANE, CANTY, PHILIP, JOHN, EATON, PAUL, NIGEL, JUBB, GARY, ANTHONY, LOWE, ALISON, JANE
Applicants: CANTY PHILIP JOHN, EATON PAUL NIGEL, JUBB GARY ANTHONY, LOWE ALISON JANE, MORGAN CRUCIBLE CO, CANTY, PHILIP, JOHN, EATON, PAUL, NIGEL, JUBB, GARY, ANTHONY, LOWE, ALISON, JANE, THE MORGAN CRUCIBLE COMPANY PLC
Application year: 1997
Main classification: C03C13
IPC codes: C03C13