Effect of Acid Etching Time and Concentration on Oxygen Content of Powder on the Microstructure and Elastic Properties of Silicon Carbide Densified by SPS

Zeynep Ayguzer Yasar,Richard Haber

doi:10.11648/j.ijmsa.20200901.12

Zeynep Ayguzer Yasar, Richard Haber

Open Access

https://doi.org/10.11648/j.ijmsa.20200901.12

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Abstract

In this current paper, oxygen content of a fine particle size SiC (H. C. Starck UF 25 Silicon Carbide) and coarser particle size SiC (Saint Gobain Silicon Carbide) were modified by using different concentrations of HF for etching. Fully dense silicon carbide ceramics (>99% th. density) were produced by the spark plasma sintering technique at 1950 °C under an applied pressure of 50 MPa for 5 min hold with boron carbide and carbon addition. Archimedes method, scanning electron microscopy, and the ultrasound analysis were used to examined density, microstructure, elastic (E), shear (G), and bulk (K) moduli of dense silicon carbide ceramics to investigate the effect of oxygen impurities on the densification and the properties of silicon carbide. The results showed that high oxygen content is detrimental to the final density of SPS silicon carbide. When the oxygen content increased from 0.60 to 5.92 wt.%, the relative density decreased from 99.99% to 96%. For both SiC powders, by increasing the etching time, the grain size of SiC decreased. It means that the high oxygen caused grain growth. Ultrasound analysis results showed that the high oxygen content affected the elastic properties. SiC samples with the high oxygen content had a lower elastic moduli, shear moduli and bulk moduli. It was clear that increasing the oxygen content decreased the elastic properties.

Highlights

Silicon carbide (SiC) has some outstanding physical and chemical properties, such as low theoretical density (3.21 g/cm3), a high hardness, a high elastic modulus, high thermal conductivity, good wear and oxidation resistance, and low coefficient of thermal expansion [1,2,3,4,5,6,7,8]
LECO TC 600 oxygen/nitrogen analyzer was used to measured oxygen content of both SiC powders
1 hour etching was more effective SiC powder etched for 1 hour with 50% HF was chosen despite the lower oxygen content in 50% HF for 4 and 24-hour etching

Summary

Introduction

Silicon carbide (SiC) has some outstanding physical and chemical properties, such as low theoretical density (3.21 g/cm3), a high hardness, a high elastic modulus, high thermal conductivity, good wear and oxidation resistance, and low coefficient of thermal expansion [1,2,3,4,5,6,7,8]. The other issue with the non-oxide high temperature ceramics such as SiC, B4C and TiB2 is that they tend to have an oxide layer on their surfaces It depends on particle size, moisture in the air, and additives. This oxide layer causes large grain coarsening and inhibits densification [12-15 ]

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