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Abstract Zirconium carbide (ZrC) powder, batched to a ratio of 0.98 C/Zr, was prepared by carbothermal reduction of ZrO₂with carbon black. Nominally phase‐pure ZrC powder had a mean particle size of 2.4 μm. The synthesized powder was hot‐pressed at 2150°C to a relative density of > 95%. The mean grain size was 2.7 ± 1.4 μm with a maximum observed grain size of 17.5 μm. The final hot‐pressed billets had a C/Zr ratio of 0.92, and oxygen content of 0.5 wt%, as determined by gas fusion analysis. The mechanical properties of ZrC_0.92O_0.03were measured at room temperature. Vickers’ hardness decreased from 19.5 GPa at a load of 0.5 kgf to 17.0 GPa at a load of 1 kgf. Flexural strength was 362.3 ± 46 MPa, Young's modulus was 397 ± 13 MPa, and fracture toughness was 2.9 ± 0.1 MPa•m^1/2. Analysis of mechanical behavior revealed that the largest ZrC grains were the strength‐limiting flaw in these ceramics. 

Abstract The melting temperatures of two different ZrB₂ceramics were studied using laser induced melting. ZrB₂having a low Hf content, produced by reaction hot pressing, had a melting temperature of 3546 K and a commercial grade ZrB₂had a melting temperature of 3553 K. Uncertainty of the temperature measurements was 1% of the absolute temperature, or ~35 K for both materials based upon 2‐sigma and a 95% confidence interval. While these values were consistent with the previously reported ZrB₂melting temperature of 3518 K, this study was able to measureT_mwith less uncertainty than previous studies (±45 K). Furthermore, this study assessed the effect of Hf content on melting temperature, finding that melting temperature did not change significantly for hafnium contents of 1.75 to 0.01 at%. This study also measured a normal spectral emissivity of 0.34 for ZrB₂at 3000 K. The emissivity decreased to 0.28 at the melting temperature, then, stabilized at 0.30 in a liquid phase. 

Abstract Ordered carbon vacancies were detected in zirconium carbide (ZrC_x) powders that were synthesized by direct reaction. Zirconium hydride (ZrH₂) and carbon black were used as starting powders with the molar ratio of ZrH₂:C = 1:0.6. Powders were reacted at 1300°C or 2000°C. The major phase detected by x‐ray diffraction (XRD) was ZrC_x. No excess carbon was observed by transmission electron microscopy (TEM) in powders synthesized at either temperature. Ordering of the carbon vacancies was identified by neutron powder diffraction (NPD) and further supported by selected area electron diffraction (SAED). The vacancies in carbon‐deficient ZrC_xexhibited diamond cubic symmetry with a supercell that consisted of eight (2 × 2 × 2) ZrC_xunit cells with the rock‐salt structure. Rietveld refinement of the neutron diffraction patterns revealed that the synthesis temperature did not have a significant effect on the degree of vacancy ordering in ZrC_xpowders. Direct synthesis of ZrC_0.6resulted in the partial ordering of carbon vacancies without the need for extended isothermal annealing as reported in previous experimental studies.