Dense boron carbide ceramic and process for producing the same

Abstract

An aspect of the present invention is to provide an economical production technology for obtaining a dense boron carbide ceramic product without impairment to excellent mechanical properties, which boron carbide ceramics are inherently equipped with, by conducting heating under normal pressure without application of pressure and without needing addition of a large amount of a sintering additive to a raw material or needing any special additive or treatment. The present invention provides a production process in which, upon heating a boron carbide green body under normal pressure without application of pressure after pressing a boron carbide powder material to obtain the boron carbide green body, the boron carbide green body is heated with one of a powder, green body or sintered body, which contains at least one of aluminum and silicon, being disposed in a furnace.

1 . A dense boron carbide ceramic having a relative density of 89% or higher, wherein a content of boron carbide is 96 wt % or higher, and a content of aluminum is 0.03 wt % or higher but 1.0 wt % or lower. 
     
     
         2 . A dense boron carbide ceramic having a relative density of 89% or higher, wherein a content of boron carbide is 96 wt % or higher, a content of aluminum is 0.03 wt % or higher but 1.0 wt % or lower, and a content of silicon is 0.1 wt % or higher but 0.35 wt % or lower. 
     
     
         3 . A dense boron carbide ceramic having a relative density of 89% or higher, wherein a content of boron carbide is 96 wt % or higher, and a content of silicon carbide is 0.028 wt % or higher but lower than 0.5 wt %. 
     
     
         4 . A process for producing under normal pressure a dense boron carbide ceramic having a relative density of 89% or higher, which comprises, upon heating a boron carbide green body under normal pressure without application of pressure after pressing a boron carbide powder material to obtain the boron carbide green body, heating the boron carbide green body with one of a powder, green body or sintered body, which is comprised of at least one of aluminum and silicon, being disposed in a furnace. 
     
     
         5 . The process according to  claim 4 , wherein a temperature in the furnace is raised to have at least one gas, which is selected from an aluminum-containing gas, a silicon-containing carbide gas and a silicon-containing gas other than the silicon-containing carbide gas, produced from the one of the powder, green body or sintered body, which is comprised of the at least one of aluminum and silicon disposed in the furnace, such that the at least one gas is allowed to exist in an inert gas atmosphere inside the furnace; and then, the temperature in the furnace is raised further to conduct the heating of the boron carbide green body. 
     
     
         6 . A process for producing under normal pressure a dense boron carbide ceramic having a relative density of 89% or higher, which comprises, upon heating a boron carbide green body under normal pressure without application of pressure after pressing a raw material comprised of a boron carbide powder as a principal component to obtain the boron carbide green body, heating the boron carbide green body in an inert gas atmosphere with one of an aluminum-containing gas, a silicon-containing carbide gas or a silicon-containing gas other than the silicon-containing carbide gas being allowed to exist therein. 
     
     
         7 . The process according to  claim 4 , wherein a concentration of the aluminum-containing gas, silicon-containing gas or silicon-containing carbide gas in the inert gas atmosphere inside the furnace during the heating is 2×10 −6  g/cm 3  or higher but 2×10 −2  g/cm 3  or lower in terms of metal. 
     
     
         8 . The process according to  claim 4 , wherein the boron carbide green body is obtainable by pressing a boron carbide powder of 0.2 μm or greater but 2.0 μm or smaller in average particle size under a pressing pressure of 20 MPa or higher but 2,000 MPa or lower without heating. 
     
     
         9 . The process according to  claim 4 , wherein upon obtaining the boron carbide green body, the boron carbide powder material is pressed without addition of a sintering additive to the material such that the boron carbide green body is obtained. 
     
     
         10 . The process according to  claim 5 , wherein a concentration of the aluminum-containing gas, silicon-containing gas or silicon-containing carbide gas in the inert gas atmosphere inside the furnace during the heating is 2×10 −6  g/cm 3  or higher but 2×10 −2  g/cm 3  or lower in terms of metal. 
     
     
         11 . The process according to  claim 6 , wherein a concentration of the aluminum-containing gas, silicon-containing gas or silicon-containing carbide gas in the inert gas atmosphere inside the furnace during the heating is 2×10 −6  g/cm 3  or higher but 2×10 −2  g/cm 3  or lower in terms of metal. 
     
     
         12 . The process according to  claim 5 , wherein the boron carbide green body is obtainable by pressing a boron carbide powder of 0.2 μm or greater but 2.0 μm or smaller in average particle size under a pressing pressure of 20 MPa or higher but 2,000 MPa or lower without heating. 
     
     
         13 . The process according to  claim 6 , wherein the boron carbide green body is obtainable by pressing a boron carbide powder of 0.2 μm or greater but 2.0 μm or smaller in average particle size under a pressing pressure of 20 MPa or higher but 2,000 MPa or lower without heating. 
     
     
         14 . The process according to  claim 5 , wherein upon obtaining the boron carbide green body, the boron carbide powder material is pressed without addition of a sintering additive to the material such that the boron carbide green body is obtained. 
     
     
         15 . The process according to  claim 6 , wherein upon obtaining the boron carbide green body, the boron carbide powder material is pressed without addition of a sintering additive to the material such that the boron carbide green body is obtained.