Abstract
Niobium and tantalum powders used in modern manufacturing are materials with nanostructure. The authors have studied and optimized the process of the production of niobium and tantalum nanopowders (adjusted in the range of the particle size of 20-150 nm) at pilot scale. The process is based on the reduction reaction of pentachlorides of tantalum and niobium with hydrogen in a plasma generator at about 3500 K. To stabilize the structure and adjust the granulometric composition of the produced nanopowders thermal treatment at 1373 K under vacuum was applied. The powders are characterized by very high purity with regard to oxygen and metallic admixtures and by low bulk density (0.1-0.3 g/cm 3 ). The specimens had a high specific surface area (10-30 m 2 /g). The process of compacting and sintering of powders was tested at temperatures from 1173 to 1373 K. The porosity of the specimens was 0.55-0.75 from the theoretical. The pore diameter was adjusted to 0.5-0.05 µm.
Highlights
Fast development of the electronic industry has highlighted the benefits of refractory metals as construction and functional materials
The process is based on the reduction reaction of pentachlorides of tantalum and niobium with hydrogen in a plasma generator at about 3500 K
Before 1991 pilot and fullscale tests of the production of niobium and tantalum nanopowders using the plasmochemical method in arc plasmatrons were carried out in Silmet JSC (Fig. 1a)
Summary
Fast development of the electronic industry has highlighted the benefits of refractory metals (niobium and tantalum) as construction and functional materials. Before 1991 pilot and fullscale tests of the production of niobium and tantalum nanopowders using the plasmochemical method in arc plasmatrons were carried out in Silmet JSC (Fig. 1a). These studies were supplemented by the results of pilot tests to install a plasma with a hollow tubular cathode with a capacity of 250 kW (Silmet JSC) [6]. The experimental studies and pilot scale tests of niobium and tantalum pentachlorides reduction were carried out in the heated up over 3000 K plasma stream from the arc plasmatron with a power of 15–100 kW. Adjusting the chemical composition of an already produced nanopowder is a very difficult task, the purity of the feedstock (niobium and tantalum pentachlorides) was no less than 99.95 mass%. For the thermodynamic modelling of the plasma process a licensed computer simulation program HSC Chemistry, elaborated by Outotec Oy, was applied [8]
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