TRANSACTION PAPERS

The plasma manufacturing of titania pigment and nano-titania in a pilot plant

J.T. Nel^I; J.L. Havenga^I; J. Swanepoel^II; H. Bosman^II

^IThe South African Nuclear Energy Corporation Ltd, Pretoria, South Africa
^IIThermtron Plasma (Pty) Ltd, Pretoria, South Africa

SYNOPSIS

The establishment of a pilot plant for the continuous production of titania pigment and nano-titania is discussed. The plant was designed, constructed and operated on the Necsa site. The TiO₂ production capacity is 7-10 kg.h^-1 by the reaction of TiCl₄ and O₂ at >1000°C. Liquid TiCl₄ is sprayed under pressure into a plasma reactor where it evaporates and reacts with O₂ to form TiO₂. Process optimization has allowed for continuous production without any clogging or blockages. The primary advantage of the plasmaassisted process is the possibility to recover and recycle the chlorine values in high yield as Cl₂ for use in the manufacture of TiCl₄. The HCl formed in most conventional fossil-fuelled processes makes Cl₂ recovery and recycling much more difficult. Particle size distribution analysis of the fine, white product revealed a d₅₀ = 125 nm. The raw product consisted of 60% rutile that could be increased to 80-100% rutile by post-annealing. The specific surface area (SSA) of the pigment was 8-20 m²·^g-1(BET). According to the CIE colour index the 'whiteness' (L*>95) of the plasma-produced pigment was better than that of several commercially available pigments. The particle size could be manipulated by controlling the TiCl₄ feed rate, gas flow rates, and the particle quench rate and residence time. Nano-sized TiO₂ powders with a particles size (d₅₀) as small as 50 nm were also successfully produced in this way.

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References

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Paper received Mar. 2009
Revised paper received Dec. 2009