Influence of gas pressure on the surface composition of capsule-free HIPed borosilicate glass

Abstract

Borosilicate glasses have been fabricated by capsule-free hot isostatic pressing. The oxidation reaction of carbon which come from graphite crucible and interfacial processes between carbon and borosilicate glass were important for carbon-rich layer formation on the surface of borosilicate glass material. It led to the evolution of color of glass surface. Effects of total gas pressure on HIP phase diagrams were considered to evaluate the difference of surface layer composition and melting behavior of borosilicate glasses at 1100°C under capsule-free HIPing. It was shown that, below total gas pressure of 40 MPa, CO gas was the most stable substance during glass melting and then carbon-rich layers were formed on the borosilicate glasses surface by precipitation-diffusion process during cooling when keeping high pressure, which led to the surface color change from black to gray under different pressure. When gas pressure was higher 40 MPa, the carbon was stable substance and the surface color was white.