Papers by Keyword: Mechanochemical Synthesis

Abstract: The paper presents a study of the formation process of cermet powders based on TiAl intermetallic with the addition of non-metallic refractory compounds. Non-metallic refractory compounds B4C, BN, SiC, and Si₃N4 were chosen as strengthening components, improving the mechanical properties and resistance to high-temperature oxidation of TiAl-type intermetallic coatings. The composition of the initial mixtures was selected based on thermodynamic analysis of the interaction between TiAl intermetallic and non-metallic refractory compounds. As a result of the mechanochemical synthesis of powder mixtures, 73TiAl-27B₄C, 69TiAl-31BN, 88TiAl-12SiC, and 83TiAl-17Si₃N4 (wt. %) cermet powders are formed, consisting of titanium aluminide (TiAl, Ti₃Al) phases and refractory compounds of aluminium (AlB2 and AlN) and titanium (TiB₂, TiC, TiN, Ti5Si₃). The conglomeration technology of produced cermet powders has been developed to enhance fluidity. Using conglomerated powders will provide their constant feed to the high-temperature jet and the formation of dense coatings during thermal spraying.

Abstract: Crystalline ZnO nanoparticles were synthesized by a mechanochemical method using zinc acetate dihydrate and sodium hydroxide as starting materials, and cetyl trimethylammonium bromide (CTAB) as a protective agent. Mechanochemical activation of the solid-state reaction was achieved at low temperatures in a rapid laboratory ball mill. A three-level full factorial experimental design was used to investigate the effect of milling time and surfactant ratio on ZnO crystallite size. The product powders were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The crystallite size of ZnO samples estimated from XRD is consistent with the SEM images and found to be less than 40 nm. The crystallite size of the ZnO decreased as the surfactant ratio increased. There is an optimal milling time of 60 minutes in order to obtain ZnO nanoparticles with the smallest average grain size. The antibacterial activity of the obtained products against Escherichia coli (E. coli) was examined, and the minimum inhibitory concentration value was 5 mg/mL. ZnO synthesized by this simple method can be considered potentially as an effective bactericidal agent.

Abstract: The phase composition, structural parameters, and basic magnetic characteristics of BaFe₁₂O₁₉ hexaferrites prepared by the mechanochemical synthesis with subsequent annealing at a temperature of 1000°С and 1100°С for 1 h are investigated. The influence of the annealing temperature on the properties of synthesized materials is analyzed. Values of the saturation magnetization and the anisotropy field are determined. It is established that annealing temperature in the interval 1000 - 1100 °C does not significantly affect on the phase composition and the size of nanoparticles. The value of the anisotropy field increases substantially with increasing temperature.

Abstract: In this study, the effect of mechanical alloying (MA) on the microstructural, mechanical and physical properties of vanadium boride particulate reinforced Al-7 wt. % Si matrix composites were investigated. VB-VB₂-V₃B₄ containing vanadium boride hybrid powders were mechanochemically synthesized for 5 h from the V₂O₅-B₂O₃-Mg powder blends and leached with hydrochloric acid (HCl) for purification. Laboratory-synthesized VB-VB₂-V₃B₄ powders were incorporated into the Al-7wt. % Si matrix powders with the amount of 2 wt.% via MA for 4h in a SpexTM Mixer/Mill using hardened steel vial/balls with a ball-to-powder weight ratio of 7/1. After the MA process, phase analysis (X-ray diffraction), particle size analysis (laser particle size measurement), surface area analysis (Brunauer-Emmett-Teller measurement) and microstructural characterization (scanning electron microscope (SEM) micrograph) and thermal analysis (differential scanning calorimetry (DSC)) of the non-milled/milled Al-7 wt.% Si-2wt.% (VB-VB₂-V₃B₄) powders were conducted. As-blended and MA’d powders were compacted at a uniaxial hydraulic press to obtain cylindrical compacts with a diameter of 12 mm under a pressure of 400 MPa. Green bodies were sintered at 570°C for 2 h under Ar gas flowing conditions. Microstructural characterizations of the sintered samples were carried out using XRD and optical microscope (OM). Physical and mechanical properties of the composites were investigated in terms of density (Archimedes method), Vickers microhardness and wear rate. The microhardness and wear rate of the 4h of MA’d and sintered sample respectively increased to 0.865±0.256 GPa and 0.0036 mm³/N.m as compared with those of as-blended and sintered sample.

Abstract: Structure of carbon modifications, obtained via pyrolysis of vegetable feed, and ash content of natural graphite are crucial factors during mechanochemical synthesis of titanium carbide under vibratory conditions. The possibility of synthesis of titanium carbide with minimal sulfur content has been shown.

Abstract: In this study, tungsten silicide powders mechanochemically synthesized using WO₃-SiO₂-Mg powder blends. Stoichiometric proportions and excess amounts of initial powders were used to indicate the effects of final composition of synthesized tungsten silicide powders. Since the initial powder compositions affect the reaction times, all compositions were mechanically alloyed for 1 hour. In addition, thermodynamic calculations of all compositions were theoretically conducted. The dominant phases are WSi₂ and MgO for all mechanically alloyed powders. Results show that the excess amount additions of initial powders directly effects the amount and formation of resultant phases in the synthesized powder compositions.

Abstract: In the present study the modeling of the HEBM process is presented. The impact velocity, impact angle, rotation speed, mass of balls, ball-to-powder weight ratio and time of milling have been taken into account in order to calculate the energy transferred from the balls to the powder. Two different systems, namely, TiN-AlN and polysalicylic acid were experimentally investigated in order to confirm the validity of the model. The calculation results are in a reasonable agreement with the results of experimental research.

Abstract: Solid state carbothermic reduction of tungsten oxide (WO₃) to nanosized tungsten carbide (WC) particles was achieved by heating mechanically activated mixture of tungsten oxide and graphite at different temperatures under vacuum condition. KCl and Ni were added to the mixture for some samples. The morphology and chemical composition of products, as well as particles size and their distribution were compared by X-ray diffraction and field emission scanning electron microscopy. Mechanical activation of WO₃-C powder mixture did not yield WC phase whereas it was possible to produce WC nanoparticles by heating at 1250 °C for 2 h. KCl additive caused fine and homogeneous particle and Ni additive assisted the growth of WC particles.

Abstract: The mechanochemical solid-state synthesis of Zn_xCd_1-xS nanoparticles from zinc acetate, cadmium acetate and sodium sulphide in a planetary laboratory mill is described. Through changing the molar ratio of the Zn and Cd precursors, Zn_xCd1_-xS nanoparticles of different composition were prepared. Structural, surface and morphological properties were investigated by XRD, XPS, SEM and UV-VIS. Diffusion structural diagnostics was characterised by the emanation thermal analysis (ETA) results measured on heating of the samples. The cubic phase was found to be stable under mechanochemical treatment, as determined by XRD. The mixed phases were found to have ideal solution behaviours. In addition, microstructural characterisation indicated that mechanochemical treatment resulted in a structural refinement with a surface weighted crystallite size about 2 nm. The additional information of microstructure development and transport properties of the samples on heating was obtained by ETA. The calculated lattice parameters of mixed crystals linearly depend on the composition of Zn_xCd_1-xS nanoparticles. The S(2p), Zn(2p) and Cd(3d) core levels of the Zn_xCd1_-xS nanocrystallites reveal two different types of sulphur, zinc and cadmium unlike bulk CdS and ZnS. The calculated results indicate that the quantum-size effect in the nanoparticles is not negligible. The differences in the absorption edge and the emission peak position of the nanoparticles depend not only composition. Applied high-energy milling is a facile, efficient, and scalable process that does not require a solvent and can be performed under ambient conditions. Therefore, it is a promising candidate for the production of nanocrystalline materials.

Abstract: Li₄Ti₅O₁₂ anode materials have been synthesized via mechnochemical method and subsequent sintering with nanosized TiO₂ and Li₂CO₃ as reagents. XRD measurements indicated that well crystallized Li₄Ti₅O₁₂ could be obtained above 800 °C. The sizes of Li₄Ti₅O₁₂ particles increased with sintered temperature augmenting. Various particle distribution and particle sizes are presented in SEM images. In electrochemical investigations, Li₄Ti₅O₁₂ sintered at 800 °C presented excellent discharge-charge performances and rate capability. The discharge capacity could achieve 168 mAh/g and 140 mAh/g at 0.1 C and 1.0 C rate, respectively, which was attributed to its uniform particle size distribution and relatively small particle size.