Ultrahigh Temperature Flash Sintering of Binder-Less Tungsten Carbide within 6 s

We report on an ultrarapid (6 s) consolidation of binder-less WC using a novel Ultrahigh temperature Flash Sintering (UFS) approach. The UFS technique bridges the gap between electric resistance sintering (≪1 s) and flash spark plasma sintering (20–60 s). Compared to the well-established spark plasma sintering, the proposed approach results in improved energy efficiency with massive energy and time savings while maintaining a comparable relative density (94.6%) and Vickers hardness of 2124 HV. The novelty of this work relies on (i) multiple steps current discharge profile to suit the rapid change of electrical conductivity experienced by the sintering powder, (ii) upgraded low thermal inertia CFC dies and (iii) ultra-high consolidation temperature approaching 2750 °C. Compared to SPS process, the UFS process is highly energy efficient (≈200 times faster and it consumes ≈95% less energy) and it holds the promise of energy efficient and ultrafast consolidation of several conductive refractory compounds.

Properties of Spark Plasma Sintered Compacts and Magnetron Sputtered Coatings Made from Cr, Mo, Re and Zr Alloyed Tungsten Diboride

To enhance the properties of tungsten diboride, we have synthesized and characterized solid solutions of this material with chromium, molybdenum, rhenium and zirconium. The obtained materials were subsequently deposited as coatings. Various concentrations of these transition metal elements, ranging from 0.0 to 24.0 at.%, on a metals basis, were made. Spark plasma sintering was used to synthesize these refractory compounds from the pure elements. Elemental and phase purity of both samples (sintered compacts and coatings) were examined using energy dispersive X-ray spectroscopy and X-ray diffraction. Microindentation was utilized to measure the Vickers hardness. X-ray diffraction results indicate that the solubility limit is below 8 at.% for Mo, Re and Zr and below 16 at.% for Cr. Above this limit both diborides (W,TM)B2 are created. Addition of transition metals caused decrease of density and increase of hardness and electrical conductivity of sintered compacts. Deposited coatings W1−xTMxBy (TM = Cr, Mo, Re, Zr; x = 0.2; y = 1.7–2) are homogenous, smooth and hard. The maximal hardness was measured for W-Cr-B films and under the load of 10 g was 50.4 ± 4.7 GPa. Deposited films possess relatively high fracture toughness and for WB2 coatings alloyed with zirconium it is K1c = 2.11 MPa m1/2.

Co-metabolic Effect of Glucose on Methane Production and Phenanthrene Removal in an Enriched Phenanthrene-Degrading Consortium Under Methanogenesis

Anaerobic digestion is used to treat diverse waste classes, and polycyclic aromatic hydrocarbons (PAHs) are a class of refractory compounds that common in wastes treated using anaerobic digestion. In this study, a microbial consortium with the ability to degrade phenanthrene under methanogenesis was enriched from paddy soil to investigate the cometabolic effect of glucose on methane (CH4) production and phenanthrene (a representative PAH) degradation under methanogenic conditions. The addition of glucose enhanced the CH4 production rate (from 0.37 to 2.25mg⋅L−1⋅d−1) but had no influence on the degradation rate of phenanthrene. Moreover, glucose addition significantly decreased the microbial α-diversity (from 2.59 to 1.30) of the enriched consortium but showed no significant effect on the microbial community (R2=0.39, p=0.10), archaeal community (R2=0.48, p=0.10), or functional profile (R2=0.48, p=0.10). The relative abundance of genes involved in the degradation of aromatic compounds showed a decreasing tendency with the addition of glucose, whereas that of genes related to CH4 synthesis was not affected. Additionally, the abundance of genes related to the acetate pathway was the highest among the four types of CH4 synthesis pathways detected in the enriched consortium, which averagely accounted for 48.24% of the total CH4 synthesis pathway, indicating that the acetate pathway is dominant in this phenanthrene-degrading system during methanogenesis. Our results reveal that achieving an ideal effect is diffcult via co-metabolism in a single-stage digestion system of PAH under methanogenesis; thus, other anaerobic systems with higher PAH removal efficiency should be combined with methanogenic digestion, assembling a multistage pattern to enhance the PAH removal rate and CH4 production in anaerobic digestion.

HEAT-RESISTANT COATINGS AND PROSPECTS OF THEIR USE FOR PROLONGATION OF THE RESOURCE OF POWER EQUIPMENT (Review).

An analysis of modern heat-resistant materials has been carried out, which contain refractory compounds of borides, nitrides, carbides with a limiting melting point of about 2000 °C. New approaches to obtaining heat-resistant materials and the results of studying their structure, phase composition, physical and mechanical properties are shown. For elements of power equipment, an effective and economically sound approach that has a significant effect is the use of heat-resistant coatings. Each heat-resistant covering and technology of its drawing is developed depending on conditions of its use, temperature modes of operation, ergonomic efficiency. The main method of increasing the operating temperature of the ceramic coating layer is to change the chemical composition of the ceramic by introducing an additional number of alloying rare earth elements. An important method of improving the quality of heat-resistant coatings is to optimize the thickness of the ceramic layer and the formation of a barrier microlayer at the interface.

Expedited Biodegradation of Organic Pollutants and Refractory Compounds Using Bio-Electrochemical Systems

Biodegradation of xenobiotics is often considered to be a slow process. This is especially true if the xenobiotic in question is polymeric in nature, contains many chemical substituent groups or generally exhibits high level of toxicity to environmental microbiota. Due to this observed slow kinetics of degradation, removal of many xenobiotics from contaminated environments using conventional bioremediation technologies is a difficult problem. To alleviate this, alternative technologies showing improved kinetics of biodegradation are sought by the scientific community. One such promising approach is the usage of the novel technology of bio-electrochemical systems for improved degradation of xenobiotics. Due to the newness of this technology and affiliated methods, not much information about its usage for biodegradation of xenobiotics is available in literature. Therefore, this chapter aims to address that gap and bring about a comprehensive analysis on the usage of bio-electrochemical systems for rapid removal of xenobiotic contaminants from the environment.

Diborides of transition metals: Properties, application and production. review. Part 2. Chromium and zirconium diborides

The second part of the review considers properties, application and methods for producing chromium and zirconium diborides. These diborides are oxygen-free refractory metal-like compounds. As a result, they are characterized by high values of thermal and electrical conductivity. Their hardness is relatively high. Chromium and zirconium diborides exhibit significant chemical resistance in aggressive environments. They have found application in modern technology because of these reasons. Chromium diboride is used as a sintering additive to improve the properties of ceramics based on boron carbide and titanium diboride. Zirconium diboride is a component of advanced ultra-high temperature ceramics (UHTC) ZrB2 –SiC used in supersonic aircrafts and in gas turbine assemblies. Ceramics B4C–CrB2 and B4C–ZrB2 have high-quality performance characteristics, in particular, increased crack resistance. The properties of refractory compounds depend on the content of impurities and dispersion. Therefore, to solve a specific problem associated with the use of refractory compounds, it is important to choose the method of their preparation correctly, to determine the admissible content of impurities in the starting components. This leads to the presence of different methods for the borides synthesis. The main methods for their preparation are: a) synthesis from elements; b) borothermal reduction of oxides; c) carbothermal reduction (reduction of mixtures of metal oxides and boron with carbon; d) metallothermal reduction of metal oxides and boron mixtures; e) boron-carbide reduction. Plasma-chemical synthesis (deposition from the vapor-gas phase) is also used to obtain diboride nanopowders. Each of these methods is described.

Treatment of Wastewaters from the Olive Mill Industry Wastewaters by Sonication Process at Different Conditions

In this study, the effects of increasing sonication time (60 min, 120 and 150 min), increasing temperatures (25oC, 30oC and 60oC), different Dissolved Oxygen (DO) concentrations (2 mg/l, 4 mg/l, 6 and 10 mg/l), different N2(g) sparging (15 and 30 min) and H2O2 concentrations (100 mg/l, 500 and 2000 mg/l) was investigated on Olive Mill Industry wastewaters (OMI ww) by sonication process. The maximum removal efficiencies were 60.91% CODdis, 59.28% TOC, 49.70% color, 58.25% total phenol, 63.27% total aromatic amines (TAAs), 37.51% total fatty acids (TFAs), at 25oC and 150 min, respectively. The maximum removal yields were 66.83% CODdis, 65.92% TOC, 83.77% color, 61.24% total phenol, 70.52% TAAs, 48.84% TFAs, at 60oC and 150 min, respectively. The maximum removal efficiencies were 88.73% CODdis, 93.79% color, 91.38% total phenol, 91.58% TAAs, 74.44% TFAs, at DO=10 mg/l, at 60oC and 150 min, respectively. The maximum removal efficiencies were 84.51% CODdis, 91.88% color, 78.98% total phenol, 74.56% TAAs, 80.18% TFAs, at 30 min N2(g) sparging, at 60oC and 150 min, respectively. The maximum removal yields were 91.13% CODdis, 93.59% color, 93.65% total phenol, 83.68% TAAs, 90.30% TFAs, at 2000 mg/l H2O2, at 60oC and 150 min, respectively. Sonication at 35 kHz proved to be a viable tool for the effective removal of COD, TOC, color, total phenol, TAAs and TFAs from OMI ww, providing a cost-effective alternative for destroying and detoxifying the refractory compounds in OMI ww.