Manufacture of sintered silicon alloy

Abstract

Dehydration and drying of a silicon alloy argil which uses water as a principal binder are carried out by a freeze-drying process, a microwave irradiation process, or a combination thereof. In the freeze-drying process, the shaped compact is put into a cooling medium within 5 minutes after completion of shape forming, retained therein for at least 5 minutes to quick-freeze water within the compact while the water is still in a finely-dispersed condition. The compact is exposed to a pressure below the triple point pressure of water. In the microwave irradiation process, the shaped compact is put into a container exposed to continuous microwave irradiation at 2.450 GHz for at least 5 minutes while under a reduced pressure below atmospheric pressure.

What is claimed is: 
     
         1 . A method for manufacturing a sintered silicon alloy comprising the steps of:
 obtaining a raw material comprising a silicon alloy powder including 30-70 weight % silicon, 10-45 weight % nitrogen, 1-40 weight % aluminum, and 1-40 weight % oxygen;   kneading the raw material with the addition of 10-40 weight % water as a binder to form a kneaded silicon alloy argil;   shaping the kneaded argil to form a silicon alloy compact having a three-dimensional shape;   putting said compact in a cooling medium within 5 minutes after completion of the shaping step, and retaining the compact in said cooling medium for at least 5 minutes, thereby quick-freezing water contained within said compact in a finely-dispersed condition;   retaining the compact in a pressure-regulated container in which the pressure is maintained at a level below the triple point pressure of water; and   thereafter, sintering said compact.   
     
     
         2 . A method for manufacturing a sintered silicon alloy according to  claim 1 , in which at least one additive is added to the silicon alloy powder to form a mixture, the additive being from the group consisting of an inorganic binder and a sintering additive, the inorganic binder being composed mainly of silicon dioxide and aluminum, and, if present, constituting 0.5-10 weight % of the mixture, and the sintering additive, if present, constituting up to 5 weight % of the mixture. 
     
     
         3 . A method for manufacturing a sintered silicon alloy according to  claim 1 , in which at least one of the kneading step and the shape forming step are conducted in a reduced-pressure environment below atmospheric pressure. 
     
     
         4 . A method for manufacturing a sintered silicon alloy according to  claim 3 , in which at least one additive is added to the silicon alloy powder to form a mixture, the additive being from the group consisting of an inorganic binder and a sintering additive, the inorganic binder being composed mainly of silicon dioxide and aluminum, and, if present, constituting 0.5-10 weight % of the mixture, and the sintering additive, if present, constituting up to 5 weight % of the mixture. 
     
     
         5 . A method for manufacturing a sintered silicon alloy comprising the steps of:
 obtaining a raw material comprising a silicon alloy powder including 30-70 weight % silicon, 10-45 weight % nitrogen, 1-40 weight % aluminum, and 1-40 weight % oxygen;   kneading the raw material with the addition of 10-40 weight % water as a binder to form a kneaded silicon alloy argil;   shaping the kneaded argil to form a silicon alloy compact having a three-dimensional shape;   exposing said compact to continuous microwave radiation for at least 5 minutes; and   sintering said compact.   
     
     
         6 . A method for manufacturing a sintered silicon alloy according to  claim 5 , including the step of putting said compact in a container and exposing the compact to a reduced pressure below atmospheric pressure within 5 minutes following completion of the shaping step, wherein the step of exposing the compact to continuous microwave radiation is commenced within 5 minutes following completion of the shaping step, and wherein, over at least part of the time during which the compact is exposed to continuous microwave radiation, the compact is in said container and the pressure within said container is held at a pressure below 1 atmosphere. 
     
     
         7 . A method for manufacturing a sintered silicon alloy according to  claim 5 , including the step of putting said compact in a container and exposing the compact to a reduced pressure below atmospheric pressure within 5 minutes following completion of the shaping step, wherein the step of exposing the compact to continuous microwave radiation is commenced within 5 minutes following completion of the shaping step, and wherein, over substantially the entire time during which the compact is exposed to continuous microwave radiation, the compact is in said container and the pressure within said container is held at a pressure below 1 atmosphere. 
     
     
         8 . A method for manufacturing a sintered silicon alloy according to  claim 5 , wherein the frequency of said microwave radiation is within the range from about 0.9 GHz to 6 GHz. 
     
     
         9 . A method for manufacturing a sintered silicon alloy according to  claim 5 , wherein the frequency of said microwave radiation is 2.450 GHz. 
     
     
         10 . A method for manufacturing a sintered silicon alloy according to  claim 5 , in which at least one additive is added to the silicon alloy powder to form a mixture, the additive being from the group consisting of an inorganic binder and a sintering additive, the inorganic binder being composed mainly of silicon dioxide and aluminum, and, if present, constituting 0.5-10 weight % of the mixture, and the sintering additive, if present, constituting up to 5 weight % of the mixture. 
     
     
         11 . A method for manufacturing a sintered silicon alloy according to  claim 5 , in which at least one of the kneading step and the shape forming step are conducted in a reduced-pressure environment below atmospheric pressure. 
     
     
         12 . A method for manufacturing a sintered silicon alloy according to  claim 11 , in which at least one additive is added to the silicon alloy powder to form a mixture, the additive being from the group consisting of an inorganic binder and a sintering additive, the inorganic binder being composed mainly of silicon dioxide and aluminum, and, if present, constituting 0.5-10 weight % of the mixture, and the sintering additive, if present, constituting up to 5 weight % of the mixture. 
     
     
         13 . A method for manufacturing a sintered silicon alloy comprising the steps of:
 obtaining a raw material comprising a silicon alloy powder including 30-70 weight % silicon, 10-45 weight % nitrogen, 1-40 weight % aluminum, and 1-40 weight % oxygen;   kneading the raw material with the addition of 10-40 weight % water as a binder to form a kneaded silicon alloy argil;   shaping the kneaded argil to form a silicon alloy compact having a three-dimensional shape;   putting said compact in a cooling medium within 5 minutes after completion of the shaping step, and retaining the compact in said cooling medium for at least 5 minutes, thereby quick-freezing water contained within said compact in a finely-dispersed condition;   exposing said compact to continuous microwave radiation for at least 5 minutes; and   sintering said compact.   
     
     
         14 . A method for manufacturing a sintered silicon alloy according to  claim 13 , wherein said compact is exposed to a reduced pressure below atmospheric pressure following retention of the compact in the cooling medium, and wherein, over at least part of the time during which the compact is exposed to continuous microwave radiation, the compact is exposed to a pressure below 1 atmosphere. 
     
     
         15 . A method for manufacturing a sintered silicon alloy according to  claim 13 , wherein said compact is exposed to a reduced pressure below atmospheric pressure following retention of the compact in the cooling medium, and wherein, over substantially the entire time during which the compact is exposed to continuous microwave radiation, the compact is exposed to a pressure below 1 atmosphere. 
     
     
         16 . A method for manufacturing a sintered silicon alloy according to  claim 13 , wherein the frequency of said microwave radiation is within the range from about 0.9 GHz to 6 GHz. 
     
     
         17 . A method for manufacturing a sintered silicon alloy according to  claim 13 , wherein the frequency of said microwave radiation is 2.450 GHz. 
     
     
         18 . A method for manufacturing a sintered silicon alloy according to  claim 13 , in which at least one additive is added to the silicon alloy powder to form a mixture, the additive being from the group consisting of an inorganic binder and a sintering additive, the inorganic binder being composed mainly of silicon dioxide and aluminum, and, if present, constituting 0.5-10 weight % of the mixture, and the sintering additive, if present, constituting up to 5 weight % of the mixture. 
     
     
         19 . A method for manufacturing a sintered silicon alloy according to  claim 13 , in which at least one of the kneading step and the shape forming step are conducted in a reduced-pressure environment below atmospheric pressure. 
     
     
         20 . A method for manufacturing a sintered silicon alloy according to  claim 19 , in which at least one additive is added to the silicon alloy powder to form a mixture, the additive being from the group consisting of an inorganic binder and a sintering additive, the inorganic binder being composed mainly of silicon dioxide and aluminum, and, if present, constituting 0.5-10 weight % of the mixture, and the sintering additive, if present, constituting up to 5 weight % of the mixture.