Chapter 45. Synthesis and Characterisation of TiB₂ Whiskers

Summary

Whiskers of TiB₂ have been synthesised via a carbotheimal vapour-liquid- solid (VLS) growth mechanism. In this VLS mechanism Ti and B in the form of gaseous chloride and oxochloride species are transported to a liquid-metal catalyst droplet that becomes supersaturated, resulting in the precipitation of TiB₂ as whiskers. The reaction terminates when the levels of reaction gases near the catalyst droplets have dropped below a certain limit. The synthesis was tested and optimised in the temperature region 1100–1800°C in argon. TiO₂ was used as precursor material for titanium, and both B₂O₃ and Na₂B₄O₇ were tested as sources of boron. Amorphous carbon was added to reduce the oxides. NaCl was used as Cl source for the gas-phase transportation. As metal catalysts Ni, Fe, Co, and Cu were evaluated. The best result was obtained with a mixture of TiO₂: B₂O₃ : C : NaCl : Ni in the molar ratios 1 : 1 : 6 : 0.25 : 0.1, at 1500°C. The obtained TiB₂. whiskers are −1 μm in diameter and −20 μm in length.