High-Temperature Oxidation of ZrB2–SiC and ZrB2–SiC–ZrSi2 Ceramics up to 1700 0С in Air

V.Lavrenko,
 
V.Lavrenko,
 
A.Panasyuk,
    

I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Krzhizhanovsky str., 3, Kyiv, 03142, Ukraine
Powder Metallurgy - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2012, #03/04
http://www.materials.kiev.ua/article/1015

Abstract

The high-temperature oxidation of ZrB2–SiC and ZrB2–SiC–ZrSi2 ceramics up to 1700 0С in air has shown their high corrosion resistance. A five-stage nonisothermal oxidation mechanism is established for the samples when heated at a rate of 20 deg/min: 1) oxygen adsorption–desorption; 2) formation of ZrО2 and B2О3 oxides; 3) formation of α-SіО2 cristobalite and ZrSiО4 zircon; 4) formation of amorphous SіО2; and 5) formation of upper protective borosilicate film with ZrSiО4 inclusions at less than 40 wt.% SіC. It is shown that small ZrSi2 admixtures (<6–8 wt.%) substantially slow down the oxidation of the ceramics in initial heating stages due to diffusion-hindered formation of ZrО2 and B2О3. The 67.3 wt.% ZrB2–26 wt.% SіC–6.7 wt.% ZrSi2 ceramics are characterized by the highest corrosion resistance since their upper scale layer represents borosilicate glass stabilized with ZrO2 (tetragonal) inclusions.


BOROSILICATE GLASS, CERAMICS, HIGH-TEMPERATURE OXIDATION, KINETICS AND MECHANISM OF PROCESS, OXIDATION PRODUCTS