Modification of alkaline earth silicate fibres

Abstract

A method of making refractory alkaline earth silicate fibres from a melt, including the use as an intended component of alkali metal to improve the mechanical properties of the fibre in comparison with a fibre free of alkali metal.

1 . A method of making refractory alkaline earth silicate fibres comprising less than 10 wt % alumina from a melt, comprising the inclusion as an intended melt component of alkali metal to improve the mechanical and/or thermal properties of the fibre. 
   
   
       2 . A method, as claimed in  claim 1 , in which the amount of alkali metal (M) expressed as the oxide M 2 O, is in the range 0.2 mol % to 2.5 mol %. 
   
   
       3 . A method, as claimed in  claim 1 , in which the alkali metal is included in an amount sufficient to increase the tensile strength of a blanket made using the fibre by >50% over the tensile strength of a blanket free of alkali metal, and less than an amount that will result in an excessive shrinkage at the intended maximum use temperature. 
   
   
       4 . A method, as claimed in  claim 1 , in which the composition of the alkaline earth silicate fibre and the alkali metal content is such that the shrinkage, as measured by the method of the description, of a vacuum cast preform of the fibres when exposed to 850° C. for 24 hours is no greater than 3.5%. 
   
   
       5 . A method, as claimed in  claim 4 , in which the composition of the alkaline earth silicate fibre and the alkali metal content is such that the shrinkage, as measured by the method of the description, of a vacuum cast preform of the fibres when exposed to 1000° C. for 24 hours is no greater than 3.5%. 
   
   
       6 . A method, as claimed as claimed in  claim 5 , in which the composition of the alkaline earth silicate fibre and the alkali metal content is such that the shrinkage, as measured by the method of the description, of a vacuum cast preform of the fibres when exposed to 1150° C. for 24 hours is no greater than 3.5%. 
   
   
       7 . A method, as claimed as claimed in  claim 6 , in which the composition of the alkaline earth silicate fibre and the alkali metal content is such that the shrinkage, as measured by the method of the description, of a vacuum cast preform of the fibres when exposed to 1250° C. for 24 hours is no greater than 3.5%. 
   
   
       8 . A method, as claimed as claimed in  claim 1 , in which the composition of the alkaline earth silicate fibre and the alkali metal content is such that the shrinkage, as measured by the method of the description, of a vacuum cast preform of the fibres when exposed to 1150° C. for 24 hours is no greater than 2 times the shrinkage of a fibre of the composition free of alkali metal. 
   
   
       9 . A method, as claimed in  claim 8 , in which the composition of the alkaline earth silicate fibre and the alkali metal content is such that the shrinkage, as measured by the method of the description, of a vacuum cast preform of the fibres when exposed to 1150° C. for 24 hours is no greater than 1.2 times the shrinkage of a fibre of the composition free of alkali metal. 
   
   
       10 . A method, as claimed in  claim 6 , in which the composition of the alkaline earth silicate fibre and the alkali metal content is such that the shrinkage, as measured by the method of the description, of a vacuum cast preform of the fibres when exposed to 1400° C. for 24 hours is no greater than 3.5%. 
   
   
       11 . A method, as claimed in  claim 1 , in which the inclusion as an intended melt component of the alkali metal results in a reduction in shot content. 
   
   
       12 . A method, as claimed in  claim 1 , in which the alkali metal (M) is present in an amount expressed as the oxide M 2 O less than 2 mol %. 
   
   
       13 . A method, as claimed in  claim 12 , in which the alkali metal is present in an amount less than 1.5 mol %. 
   
   
       14 . A method, as claimed in  claim 13 , in which the alkali metal is present in an amount less than 1 mol %. 
   
   
       15 . A method, as claimed in  claim 14 , in which the alkali metal is present in an amount less than 0.75 mol %. 
   
   
       16 . A method, as claimed in  claim 12 , in which the alkali metal is present in an amount greater than or equal to 0.3 mol %. 
   
   
       17 . A method, as claimed in  claim 16 , in which the alkali metal is present in an amount greater than or equal to 0.4 mol %. 
   
   
       18 . A method, as claimed in  claim 17 , in which the alkali metal is present in an amount greater than or equal to 0.5 mol %. 
   
   
       19 . A method, as claimed in  claim 18 , in which the alkali metal is present in an amount greater than or equal to 0.6 mol %. 
   
   
       20 . A method, as claimed in  claim 1 , in which the alkaline earth silicate fibre comprises <10 wt % MgO, and in which the alkali metal M comprises predominantly sodium, potassium, or a mixture thereof. 
   
   
       21 . A method, as claimed in  claim 20 , in which at least 75 mol % of the alkali metal is potassium. 
   
   
       22 . A method, as claimed in  claim 21 , in which at least 90 mol % of the alkali metal is potassium. 
   
   
       23 . A method, as claimed in  claim 21 , in which at least 95 mol % of the alkali metal is potassium. 
   
   
       24 . A method, as claimed in  claim 21 , in which at least 99 mol % of the alkali metal is potassium. 
   
   
       25 . A method, as claimed in  claim 1 , in which the alkaline earth silicate fibre comprises >15 wt % MgO, and in which the alkali metal M comprises predominantly lithium.