Influence of non-vacuum electric arc synthesis energy on the product of tungsten ore concentrate processing

Relevance. Caused by the problem of developing methods for obtaining tungsten carbide, especially from tungsten-containing waste. As a solution, a non-vacuum electric arc method is proposed. It is easy to operate and cheap compared to a direct analogue (arc discharge method in inert gas atmosphere). The resulting product can be used as a catalyst carrier in hydrogen production reactions. Aim. To determine the current and the energy entered in the system, necessary to obtain a product with a largest proportion of the hexagonal phase of tungsten carbide WC from tungsten ore concentrate by a non-vacuum electric arc method and investigate a sample with the largest proportion of tungsten carbide phase. Object. Electric arc synthesis in open air from tungsten ore concentrate. Methods. Grinding in a SAMPLE SPEX 8000M ball mill, magnetic separation, non-vacuum electric arc method of synthesis, X-ray phase analysis on a Shimadzu XRD 7000s X-ray diffractometer (λ=1.54060 Å), scanning electron microscopy combined with X-ray fluorescence energy-dispersive analysis based on a TESCAN VEGA 3 microscope SBU with OXFORD X-Max prefix, transmission electron microscopy combined with energy dispersive spectroscopy and selected area electron diffraction based on the JEM-2100F microscope, scanning electron-ion microscopy based on the QUANTA 200 3D microscope. Results. The authors have built the dependence of the phase composition of the product of non-vacuum electric arc synthesis at current strengths from 50 to 220 A. Mass fraction of each of the identified phases in the synthesis product was determined using the reference intensity ratio. The current and the energy entered in the system, which provide the largest proportion of tungsten carbide WC in the synthesis product, are determined. The authors studied the product containing the largest proportion of tungsten carbide WC using scanning and transmission electron microscopy methods

Spark plasma sintering of SiC-based bulk materials from carbonaceous residue of rice husk thermal processing

Relevance. The search for a useful application of carbonaceous residues of rice husks thermal processing. These residues due to high silicon content in the inorganic part can potentially be used to produce silicon carbide – an important functional material for various fields of science and technology. Useful utilization of this waste will allow not only solving the environmental problem associated with their inefficient application and formal disposal, but also obtaining value-added products in the form of SiC-based ceramics. Aim. To obtain SiC-based bulk products from carbonaceous residues of rice husk thermal processing by spark plasma sintering with a minimum number of additional stages of feedstock processing. Objects. SiC-based bulk products obtained using carbonaceous residues of rice husk thermal processing. The samples were obtained by spark plasma sintering at 1800 °C, pressure of 60 MPa and holding time of 10 minutes. Methods. Spark plasma sintering; X-ray diffractometry (X-ray phase analysis); scanning electron microscopy; vacuumless arc discharge synthesis method. Results. The authors have carried out the experimental studies to assess the possibility of applying carbonaceous residue of rice husk thermal processing as a precursor for the synthesis of silicon carbide in bulk (ceramics) and dispersed (powder) forms. A series of experiments on spark plasma sintering of carbonaceous residue from rice husk thermal processing in the initial and milled form, with SiO2 silica sand additives, as well as with the use of silicon carbide powders synthesized from carbonaceous residue by vacuumless arc discharge method were implemented. The latter is performed within a one-stage fast-flowing process in an air environment and does not require the use of a vacuum system. Preliminary results demonstrated the possibility of obtaining bulk products and dispersed powders based on silicon carbide with a content of at least 50 and 60 wt %, respectively, and indicate the prospects of further increasing phase purity by optimizing spark plasma sintering and vacuumless arc discharge synthesis

Deposition of Cr films by hot target magnetron sputtering on biased substrates

The Cr films were deposited by hot target magnetron sputtering on grounded and biased substrates. The deposition modes with low and high deposition rates (different by 4 times) were selected. The sublimation of hot Cr target decreased the re-sputtering effect of the growing films under ion bombardment and reduced the losses of deposition rate from 28.7 to 13.4% (for −40 V bias and 1.9 kW discharge power). The calculations of energy flux density on the substrate revealed that the major contribution has a target radiation (56.2…85.5%) and kinetic energy of deposited particles and ions (4.8…34.3%) become a significant only with substrate biasing. The XRD measurements showed cubic structured (110) Cr films with compressive stresses (0.48…0.90 GPa), which is non-dependent from bias voltage for high-rate deposition modes. The Cr films mainly had a columnar structure and columnar width increased from 50 to 450 nm with rise of discharge power (W). The substrate biasing and high deposition rate resulted in the formation of irregular microstructure of the Cr films along their thickness from porous to columnar state. The indentation tests showed the strong dependence of film hardness and toughness (H/E) from W and different behavior of the mechanical properties of the Cr films for the deposition on biased substrates with low and high deposition rates