Barium lanthanum silicate glass-ceramics

Abstract

This invention relates to glass-ceramic materials in the BaO—La 2 O 3 —SiO 2 system, which are suitable for processing via a powder route, and which, after heat-treatment have a combination of high thermal expansion and excellent refractoriness. The precursor glass powders of the present invention have compositions on a weight percent basis of 10-55% BaO, 3-50% La 2 O 3 , 25-48% SiO 2 and optionally up to 30% in total of other compatible metal oxides. The powders are substantially free from alkali metal oxides and from boron oxide such that the refractoriness of the glass-ceramic materials is not compromised. The materials may be advantageously employed at high temperatures in direct combination with other materials of high expansion or may be used to join or hermetically seal components made of other materials having similarly high expansion.

1 . Glass-ceramic materials possessing high softening temperature (˜1000° C. or above) and a thermal expansion coefficient in excess of 10×10 −6 ° C. −1  (measured over the range 20-1000° C.),  
       characterised in that 
 said materials are prepared by controlled thermal treatment of precursor glass powders to a temperature in excess of 900° C., wherein said powders contain, on a weight percent basis, 10-55% BaO, 3-50% La 2 O 3  and 25-48% SiO 2 .  
 
     
     
         2 . Glass-ceramic materials according to  claim 1 ,  
       characterised in that 
 said precursor powders contain, on a weight percent basis, 10-55% BaO, 3-50% La 2 O 3 , 25-48% SiO 2  and up to 30% of another compatible metal oxide or mixture of metal oxides.  
 
     
     
         3 . Glass-ceramic materials according to  claim 1 ,  
       characterised in that 
 said precursor glass powders contain less than 5% aluminium oxide (Al 2 O 3 ) by weight.  
 
     
     
         4 . Glass-ceramic materials according to  claim 1 ,  
       characterised in that 
 the total content of alkali metal oxides in said precursor glass powders is less than 1% by weight.  
 
     
     
         5 . Glass-ceramic materials according to  claim 1 ,  
       characterised in that 
 said precursor glass powders contain less than 1% boron oxide (B 2 O 3 ) by weight.  
 
     
     
         6 . Use of the glass-ceramic materials according to claims  1 - 5  for joining or sealing components made of other materials.  
     
     
         7 . Use of the glass-ceramic materials according to claims  1 - 5  for direct combination at high temperatures with other materials of high expansion.