Papers by Keyword: Molybdenum

Abstract: NiTi alloy has desired engineering properties with many applications, such as biomedical, aerospace, automotive, etc, where several researchers have investigated the development of ternary and quaternary alloying of NiTi to further enhance its performance for demanding technological applications. However, there are limited studies on the effects and synergy of Re and Mo on the nanomechanical properties of NiTi alloy, despite the highly recommended effect of Re on the mechanical properties of Ni-based superalloys. Therefore, this study bridged this gap by developing NiTi-Re-Mo alloy via the spark plasma sintering technique and investigating its nanomechanical properties in relation to NiTi, NiTi-Re, and NiTi-Mo alloys. It was noted that NiTi-Re-Mo has better nanomechanical responses than other developed NiTi-based alloys. For instance, the hardness and elastic modulus of NiTi-Mo-Re increased to about 28236.7 MPa and 483.4 GPa from 4460.7 MPa and 122.5 GPa for NiTi alloy, respectively. These significant increments were credited to the synergy effect of Re and Mo, the solution and hard phase precipitation strengthening of the NiTi system, which also contributed to the reduction of dislocations and improved mechanical locking of the NiTi system. This makes the alloy desirable for high mechanical strength applications.

Abstract: The present study was focused on the high-energy ball milling preparation of the oxide dispersed Mo-10 vol.%La₂O₃ composite powder by using two high-energy ball milling systems, including an attritor mill with a horizontally operating rotor and a planetary mill. Microstructural investigations using scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) found out that composite powders with a refined laminated microstructure can be obtained using both milling systems. Under selected milling conditions, Mo-La₂O₃ powder with better particle size homogeneity and more uniform and dispersed ceramic phase distribution was received in the planetary mill that can be connected with the more balanced contribution of breaking and cold welding processes during high energy milling.

Abstract: Pure niobium substrates were coated using laser cladding method. Pure molybdenum, Yttria Stabilized Zirkonia (YSZ) and corundum (Al₂O₃) powders were used as coating materials. Coatings were deposited on specimens as seperate paths with 3÷10mm width and 40mm of length. Two different laser power 3kW and 4kW were tested during deposition. In order to assess the quality of the Mo-YSZ and Mo-Al₂O₃ coatings, the light microscopy, Scanning Electron Microscopy (SEM), chemical analysis (EDS) and Vickers hardness test investigation were performed. The surface roughness and wear volume were also measured. As a result of YSZ-Mo powder cladding on the Nb substrate the composite layers were obtained without cracks and porosity not exceeding 1 μm. In addition, an increase in hardness of about 450 HV0.5 was revealed. As a result of Al₂O₃-Mo powder cladding on the Nb substrate the composite layers with many voids and cracks were obtained for each of the cladding variants.

Abstract: The effect of additives of P₂O₅ on the solubility of molybdenum in the amorphous part of glass and on the phase composition of the crystallized part of the highly alkaline glasses of the Li₂O–(Na₂O–K₂O)–B₂O₃-SiO₂ system was studied. The comparison of the phase composition of samples with or without phosphorus prior and after annealing allowed to determine the change of solubility of molybdenum in the amorphous part of the samples and to evaluate the thermal stability of the synthesized glass-ceramic materials. It was found, that for the compositions without phosphorus and the samples without lithium, when molybdenum is added at the synthesis stage, almost all of the molybdenum is included only in the crystalline molybdates. The study has shown an increase in the solubility of molybdenum only in the structure of lithium-containing glasses with phosphorus.

Abstract: The authors conducted the study at micro-scratching of titanium, zirconium, niobium and molybdenum alloys. The content of the main element in alloys was from 99.5 to 99.7 %. Micro-cutting was carried out by specially prepared indenters with silicon carbide mono-crystals of a given shape. The state of the relief and the chemical composition of the wear area were studied using a scanning two-beam electron microscope. The micro-scratching speed was 35 m/s without cooling. The condition of the contact surfaces of silicon carbide and metals was studied at a magnification up to 100,000 times with the rotation and tilt of the microscope slide. The content of chemical elements was determined at individual spots of an object by scanning along the line and area. The authors also studied the condition of the wear area after micro-scratching of metals and after removal of metal adhesions by chemical etching. The intensity of metal transfer was determined by the average concentration of metal atoms at the wear area. The article also gives a classification of metals according to the intensity of transfer immediately after grinding and removal of metal adhesions. The influence of metal and the depth of micro-scratching on the morphology of the wear site is shown. It was found that molybdenum, having a low adhesive activity to silicon carbide, is able to penetrate microcracks and other surface defects during micro-scratching. The width of microcracks and the depth of metal penetration were determined

Abstract: The present study considers various technological approaches to the processes of complex utilization of nickel slags with preliminary additional extraction of non-ferrous metals, iron, and ways of utilization of the obtained gangue. The valuable components are often produced from waste using the mineral acids or mixtures; the metals are extracted from acid solutions in a free form or in the form of compounds using electrochemical or chemical methods. Slag dumps have a heterogeneous structure and mineralization; the zone distribution of slag is clearly defined due to different cooling and solidification rates. The slag composition is mostly represented by dense low-porous varieties consisting of dark brown glass. The porous slag fragments are secondary. The third texture diversity in the composition of slag is represented by nodular and kidney-shaped particles. The diversity and size of the ore minerals is directly connected with the distribution of pores in slag. The major ways for utilization of nickel industrial waste are pyro-metallurgical and hydrometallurgical methods. In addition, each of the methods is usually preceded by the stage of mechanical preparation of the raw materials, where the techno-genic waste is crushed.

Abstract: In this work the wet etching of molybdenum thin films was investigated for applications requiring controlled recess without roughening or pattern loading. First, continuous etching of Mo in alkaline and oxidative peroxide solutions was studied. Then, additives like glycine and diethylenetriamine were used and their effect on etch rate and roughness was assessed. Finally, we evaluated if the requirements for a stepwise etching approach for Mo recess using peroxide or ozonated water as the oxidizing step and ammonia as the oxide dissolution agent were met.

Abstract: The article aims to comprehend the microstructural changes, in Plasma Transfer Arc (PTA) deposited M2 high speed steel (HSS) hardfacings upon incorporation of 10 wt% Mo alloying during deposition followed by laser surface melting. PTA deposited hardfacings were produced over 4140 steel. Then Mo alloyed and unalloyed PTA deposits were subjected to laser surface melting (LSM) process. A comprehensive microstructural characterization for all the resultant structures was carried out. Optical metallography using appropriate etching reagents and SEM microscopy in conjunction with XRD techniques were employed to ascertain the matrix structure and carbides morphology. The PTA microstructure was close to equilibrium structure of M2 HSS containing mixture of ferrite/austenite/martensite along with MC, M₂C and M₆C type carbides. While the LSM of M2 HSS caused higher fraction of martensite and finer grains in the structure resulting in increment in hardness. 10-wt% Mo addition changes the carbides from MC and rod like M₂C to fibrous M₂C and fishbone like M₆C carbides. The LSM of Mo alloyed M2 HSS PTA deposits led to an overall decrease in the fraction of M₆C carbides and fibrous M₂C carbides accompanied by a decrease in hardness.

Abstract: This article is dedicated to the questions of development of technological bases for the manufacturing blanks of friction disks with molybdenum gas-thermal coating applied by plasma spraying, for working in oil in the transmission units of transport machines. For ensure high performance indicators, there is has been offered a technological scheme for manufacturing friction disk blanks: short blasting preparation of the surface of the disk’s steel base, applying a molybdenum coating, that characterized by high adhesion to the ferrous metals, mechanical processing of the coating by grinding, monitoring the coating’s quality. The developed technological bases for manufacturing blanks of friction disks with molybdenum gas-thermal coating, applied by plasma spraying, for working in oil in transmission units of transport machines are contributed to the creation of efficient products with enhanced performance indicators for friction coefficient, wear resistance, reliability in modern conditions at the enterprises.

Abstract: The effect of different oxidants on extraction of uranium from low grade ore was studied. Leaching was performed using sulfuric acid solutions at a concentration of 10 to 30%. Ferric sulfate Fe₂(SO₄)₃, ammonium persulphate (NH₄)₂S₂O₈, and potassium permanganate KMnO₄ at different concentrations were used as oxidants in different variants of the experiment. In addition, solutions collected at Vostok deposit containing 6.86 g/L Fe³⁺ and 10⁶ cells/mL of the bacteria Acidithiobacillus ferrooxidans were used for leaching. The rate of uranium extraction with sulfuric acid solutions without oxidants was low and did not exceed 19.4%. Addition of oxidants made it possible to increase rate of uranium extraction. In the presence of ferric sulfate, ammonium persulphate, and potassium permanganate rates of uranium extraction were up to 68, 95.2, and 69.6%, respectively. The rate of uranium leaching in the experiments with the AMD sample was high and reached about 95%. Therefore, it can be concluded that using not only oxidizing agents, but AMD, which are formed during the natural oxidation of sulfide minerals contained in the ore of the deposit, can significantly increase the rate of uranium recovery.