Corrosion And Protection Of SiC In Borosilicate Glass

Si C-borosilicate glass composites are greatly used in mechanical, electrical, grinding and packaging areas. The added Si C could improve the wear-resisting property, hardness, thermal conductivity and decrease the thermal expansion coefficient of glass. However, the Si C would be corroded during sintering and the reaction releases gases, which will bring pores to the composites and reduce the strength and thermal conductivity of the composites. In this paper, a commercial borosilicate glass was used as binder and two methods including active additives and barier coatings were used to inhibit the oxidation of Si C.When sintered at 800 oC for 120 min, the borosilicate glass got best properties. Then the bending strength of borosilicate glass was 126 MPa, volume expansion ratio-32%, thermal expansion coefficient 8.76×10-6. The starting oxidation temperature of Si C in borosilicate glass was 630 oC. At first, the surface of Si C was oxidized into Si O2, then the Si O2 was solved by borosilicate glass. The Si C was constantly oxidized due to the effect of the oxygen and borosilicate glass. When 25-65 vol.% Si C was added into borosilicate glass, the maximum bending strength was 39 MPa, the minimum volume expansion ratio was 18.8%, the maximum relatice density was 48%, the maximum thermal conductivity was 0.13 W/(m·K), the minimum thermal expansion coefficient was 4.43×10-6.Active additive Ti, Al, Si and Zn were added into the borosilicate glass, they could absorb the oxygen in composites and inhibit the oxidation of Si C. The oxidation resultant of active additive could enter into and strengthen the glass network of borosilicate glass. When the content of active additive was excess, then Ti brought rutile, Al produced γ-Al2O3, Si took in cristalballite, Zn turned into gahnite and willmite. These compounds had different thermal expansion coefficient with borosilicate glass that they would creat cracks in composites. The best content of Ti, Al, Si, Zn were 4, 4, 6, 6 wt.%, respectively. The composites with 4 wt.% Si additive had best properties. When the content of Si C was 55 vol.%, the composites with 4 wt.% Si had best package properties, the thermal conductivity was 15.9 W/(m·K), the thermal expansion coefficient was 4.21×10-6. And the composites with Al, Si, Zn had thermal conductivity about 11.5, 13.5 and 12.9 W/(m·K), respectively, and their thermal expansion coefficient are 4.48, 4.56 and 4.53×10-6, respectively.A graded Ti C-Ti5Si3-Ti Si2 coating was deposited on Si C by vacuum thermal reaction method, which was heating a mix of Si C and Ti H2 at 750oC for 1h. The coating was about 200 nm and the compositions from the surface of coating to the surface of Si C were Ti Câ†'Ti5Si3+Ti Câ†'Ti Si2+Ti5Si3+Ti C. The interfacial bending strength between coating and Si C was at least 180.2 MPa. The composites with coated Si C got best properties when sintered at 800oC for 120 min. The composites with 55 vol.% coated Si C had best thernal properties. The bending strength was 57.3 MPa, the thermal conductivity was 14.2 W/(m·K) and the thermal expansion coefficient was 4.98×10-6. As compared, the properties of composites with uncoated Si C was 39 MPa, 0.13 W/(m·K) and 4.76×10-6.A Mn O2 layer was deposited on surface of Ti C-Ti5Si3-Ti Si2 coating by electrical deposition method. Ti C-Ti5Si3-Ti Si2-coated Si C particles were deposited in 1 mol/L KMn O4 solution with 5V, 0.2A, p H 5.5-7 conditions for 2 h, and then Si C particles with Ti C-Ti5Si3-Ti Si2/Mn O2 coating were prepared. Because there was no thermal stress during the deposition process that this Mn O2 coating had no cracks. The oxide Mn O2 could be dissolved by borosilicate glass that the Ti C-Ti5Si3-Ti Si2/Mn O2 coating had good interfacial bending strength with borosilicate glass. The Ti C-Ti5Si3-Ti Si2/Mn O2-coated Si C had betteranti-oxidation properties than Ti C-Ti5Si3-Ti Si2-coated Si C. When the content of Si C was 55 vol.%, the composites had the best package properties, the composites with Ti C-Ti5Si3-Ti Si2/Mn O2-coated Si C had bending strength 71 MPa, relative density 82%, thermal conductivity 15.6 W/(m·K) and thermal expansion coefficient 4.89×10-6, as compared, the properties of composites with Ti C-Ti5Si3-Ti Si2-coated Si C were 57.3 MPa, 78%,14.2 W/(m·K),4.98×10-6.