Microhardness studies on as-grown faces of NaClO3 and NaBrO3 crystals

Single crystals of NaClO₃ and NaBrO₃ are grown from their aqueous solutions at a constant temperature of 35°C by slow evaporation by using good quality seed crystals. Systematic microhardness studies are made on as-grown faces of these crystals at various loads. Typical cracks are observed at the corners of the impressions in NaClO₃ whereas in addition to the cracks at the corners microcracks also appeared in NaBrO₃ crystals around the impressions. The impressions formed in NaBrO₃ are not very clear as in NaClO₃, a possible mechanism for it is discussed. The work hardening index number(n) for both these crystals is around 1.6 suggesting that these are moderately harder samples. The hardness studies point out that NaBrO₃ is harder than NaClO₃ (ΔH ≈ 100 kg/mm ²,this could be due to strong inter ionic forces acting between Na-Br in NaBrO₃ crystals. Using Gilman’s empirical relation, hardness values are calculated from the values of elastic constants (C ₄₄) and are found to be close to the experimental results.