Inorganic Materials: Applied Research最新文献

The temperature and heating rate affecting the shrinkage kinetics are studied for cylindrical workpieces obtained from submicron and fine aluminum oxide powder. The studies involve the powder from three batches: (1) submicron (~0.15 µm) α-Al₂O₃ powder, (2) submicron (~0.2 µm) α-Al₂O₃ powder having an amorphous layer deposited on the particle surface, and (3) fine (~1 µm) α-Al₂O₃ powder. It is established that the powder particles in all batches has a monocrystalline structure. The powder workpieces are sintered using the electric pulse (spark) plasma sintering (SPS) technique. The shrinkage curves are analyzed using the Young–Cutler and the Coble models. The kinetics of sintering workpieces is shown to depend on diffusion developing between the powder particles. The sintering kinetics of workpieces made from submicron powder depends on intensity of the grain-boundary diffusion. In the sintering workpieces made of finely dispersed powder, the kinetics is additionally dependent on simultaneously developing volumetric and grain-boundary diffusion. It is established that the presence of an amorphous layer on the surface of particulate α-Al₂O₃ having submicron size affects the rate of migration of grain interfaces and the parameters of the Coble equation at the final SPS stage. It is assumed that the accelerated growth of grains and an increase in the microhardness of samples obtained through sintering workpieces made from submicron powder with an amorphous layer on the particle surface is caused by a higher density of defects at the grain interfaces. The elevated density of defects at grain interfaces can result from crystallization of the amorphous layer.

Abstract—The possibility of low-temperature in situ synthesis of (Ti, W)C using plasma-chemical WC nanopowders and industrial micron TiC powders is demonstrated. Sintering/synthesis of WC–(25, 50, and 75) wt % TiC is carried out by electric pulsed (“spark”) plasma sintering (SPS) by heating powders in a vacuum at a rate of 50°C/min to a temperature of more than 1200°C under conditions of applying a stress of 70 MPa. It is established that the synthesis proceeds most efficiently in nanopowders with an addition of 50 and 75 wt % TiC. It is shown that the joint use of plasma-chemical synthesis of nanopowders and SPS makes it possible to obtain fine-grained (with a grain size of less than 1 μm) samples with increased density and satisfactory mechanical properties (Vickers hardness is 17–18 GPa, and minimum Palmquist crack resistance coefficient is ~3 MPa m^1/2).

The effect of nitrogen and oxygen plasma on quasi-two-dimensional MoS₂ films is studied experimentally and theoretically in order to identify the main mechanisms of surface functionalization and the influence on the structure and on the properties of the films. Diagnostics of samples before and after treatment using radicals and ions is carried out ex situ using Raman spectroscopy, spectroscopic ellipsometry, X‑ray photoelectron spectroscopy, etc. It is shown that the effect of the nitrogen and oxygen plasma on ultrathin MoS₂ films results in modifying the near-surface layers of the samples due to removal of sulfur and incorporation of incident atoms into the resulting vacancies. The simulation of density functional theory is applied to reveal the main mechanisms of surface functionalization in MoS₂ monolayers and to explain the experimental results.

Abstract—The phase and structural state, parameters of the magnetic microstructure, and static and microwave magnetic properties of the Fe_81–74Zr_2–5N_17–21 films synthesized by reactive magnetron deposition have been studied. It has been established that, as the Zr and N contents increase, the film structure changes from the so-called mixed structure (amorphous and nanocrystalline represented by the Fe-based solid solution supersaturated with zirconium and nitrogen in the bcc modification and the fcc nitride phase) to the X-ray amorphous one. The interplay of the static magnetic properties and the parameters of the stochastic magnetic structure with the effective real permeability μ' at frequencies of up to 3 GHz has been examined. It is shown that the stochastic magnetic structure determines the dynamic magnetic properties.

Abstract—The review presents the parameters of magnetron sputtering of coatings based on cerium dioxide and their relationship to the structure and key properties of coatings. The influence of the type of target, the introduction of oxygen into the sputtering medium, changes in sputtering power, bias voltage, type of substrate, and its temperature on the structure, mechanical properties, and hydrophobicity of CeO₂-based coatings are considered.

Interaction of Pr/Dy with oxygen in nickel melts at P_Ar = 0.1 MPa and constant temperature was studied using the EMF instantaneous fixing method using a Mo[Cr/Cr₂O₃//ZrO₂(MgO)//O(Ni_l)]Mo cell and certified sensors. Dependences a_[O] = f[Pr/Dy, %] expressed in the form of logarithmic equations made it possible to compare them with each other in the concentration range of 0.001–0.2 wt % of each deoxidizer and determine that the deoxidizing ability of Pr is 1.7 times higher compared to Dy. The activity of oxygen a_[O] in Ni–O–Al–(Pr/Dy) melts was calculated in comparison with Al at a concentration of 0.05 wt % of elements and its sevenfold decrease was shown for the first deoxidizer and elevenfold for the second. The morphology of nonmetallic inclusions in metallographic sections of Ni–O–Pr/Dy alloys has been studied, indicating that the inclusions are located along grain boundaries and have different configurations and a complex heterophase composition. Analysis of nonmetallic inclusions with the maximum content of deoxidizing element proved the existence of Pr/Dy oxygen compounds, which confirmed the data of thermodynamic and mass spectrometric studies. The average content of Zr in nonmetallic inclusions during the deoxidation of Pr is two times higher than in experiments during the deoxidation of Dy, which indicates the interaction of Pr/Dy with the EMF ZrO₂ sensor and the preferential interaction of Pr compared to Dy and correlates with the data on the determination of a_[O].

Calculated and experimental mass spectra of gaseous tungstates of alkaline earth metals MgWO_4(g), CaWO_4(g), SrWO_4(g), and BaWO_4(g) in the temperature range from 1600 to 2000 K are presented. The partial vapor pressures are determined and equations are derived for the temperature dependences of the partial pressures of gaseous molecules of alkaline earth metal tungstates for liquids in the following form (P, atm):(log Pleft( {{text{MgW}}{{{text{O}}}_{4}}_{{left( {text{L}} right)}}} right) = - 28,737{text{/}}T + 7.95{text{ for the range from }}1600{text{ to }}1900{text{ K}};) (log Pleft( {{text{CaW}}{{{text{O}}}_{4}}_{{left( {text{L}} right)}}} right) = - 25,265{text{/}}T + 6.913{text{ for the range from }}1850{text{ to 20}}00{text{ K}};) (log Pleft( {{text{SrW}}{{{text{O}}}_{4}}_{{left( {text{L}} right)}}} right) = - 25,052{text{/}}T + 7.13{text{ for the range from }}1800{text{ to 19}}00{text{ K}};) (log Pleft( {{text{BaW}}{{{text{O}}}_{4}}_{{left( {text{L}} right)}}} right) = - 20570{text{/}}T + 4.58{text{ for the range from }}1770{text{ to 19}}00{text{ K}}{text{.}})On the basis of experimental data on vapor pressure, the enthalpies of evaporation ((Delta H_{{s,0}}^{0})), formation (( - Delta H_{{f,0}}^{0})), and atomization ((Delta H_{{{text{at}},0}}^{0})) of gaseous tungstates of alkaline earth metals are calculated, which, respectively, amount to (ΔH⁰, kJ/mol) 652, 890, and 2855 for MgWO₄; 644, 974, and 2968 for CaWO₄; 615, 1045, and 3056 for SrWO₄; and 548, 1045, and 3095 for BaWO₄. It is determined that the enthalpy of sublimation of alkaline earth metal tungstates decreases from magnesium to barium.

Abstract—The features of the method for generating gas-vapor plasma and the characteristics of a high-power ion beam (HPIB) obtained in a vacuum diode with a graphite cathode using a plasma-forming high-voltage nanosecond pulse are described. The cathode material and the two-pulse mode of operation of the TEMP-4 type diode make it possible to form a multicomponent nanosecond HPIB with a maximum ion energy of up to 1 MeV, a particle flux density on the surface of ~10¹³ ion/cm², and a power density on the sample surface of up to 10⁷ W/cm² to modify the surface properties of structural materials. Materials are published within the framework of scientific discussion. The authors invite researchers of the generation of high-power beams of non-gas ions and the processes of beam modification of solid-state materials to discuss the topics of this article.

Abstract—This paper presents the effect of hot gas extrusion (HGE) parameters on the phase composition and mechanical properties of composite rods composed of a core with reaction products of a Ni–Al powder mixture and a steel shell at room temperature. Composite rods are produced in three HGE modes depending on the initial extrusion temperature and the gas pressure in the chamber with parent materials. The phase composition of the produced materials is studied. It is found that the extent of the reaction of the powder mixture increases at higher temperatures of the initial HGE and, accordingly, low gas pressures, but unreacted nickel and aluminum particles remain at the lowest temperature of the initial HGE (at a higher gas pressure). Three-point bending tests show that the yield strength of the composite rod whose core contains plastic inclusions of the parent nickel and aluminum is higher than the yield strength of the steel rod. The rods with the maximum extent of the reaction are observed to have the highest microhardness.