Inorganic Materials: Applied Research最新文献

Abstract

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).

Abstract

The effect of implantation of argon, oxygen, and nitrogen ions on the physicochemical structure of the surface and the corrosion and electrochemical behavior of chromium-nickel steel 03Cr18Ni11 has been studied. Methods of electrochemical polarization (EP), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used. Ion implantation of argon, oxygen, and nitrogen leads to an increase in the corrosion resistance of steel 03Cr18Ni11 both in a neutral environment and in the presence of a corrosion activator (chloride anions), while irradiation with argon ions is most effective. It is found that, after implantation of argon ions, a partial etching of the steel surface occurs, i.e., an increase in the true surface. This, in turn, facilitates the onset of the passive state. At the same time, the use of oxygen and nitrogen ions leads to smoothing of the surface. AFM data indicate that the studied steel treated with argon ions exhibits the greatest resistance to local corrosion. The implantation of oxygen and argon ions reduces the overall corrosion to the greatest extent. It is important to note that deep craters and traces of pitting corrosion do not form on the surface of the steel. The XPS data show that after ion implantation, there is a change in the concentration of the elements that make up the steel in the near-surface layers of the material in the depth of the implanted layer compared with the unirradiated sample. It is established that the surface layers of steel are enriched in chromium atoms during ion implantation. This process occurs most intensively when samples are treated with argon ions. In this case, mixed chromium and iron oxides are formed, contributing to the passivation of the steel surface. Also, the process of ion implantation is accompanied by oxidation of the surface of the steel under study. This is confirmed by an increase in the oxygen content in the surface layers. To the greatest extent, this process occurs during the implantation of oxygen ions. After corrosion tests, an increased chromium content is also observed on the surface of steel treated with Ar⁺ ions, which confirms the formation in this case of stable chromium oxides that remain on the surface during the corrosion of steel. The analysis of the fine structure of the XPS spectra showed that, under the action of argon ions, the oxygen of surface oxides is redistributed in favor of chromium atoms and the formation of stable mixed iron and chromium oxides of the spinel type, including Fe²⁺, Fe³⁺, Cr³⁺, and Cr⁶⁺ compounds. It is important to note that, although chromium oxides are also formed during oxygen implantation and in the same quantities as during argon implantation, the protective properties of the resulting compounds are noticeably lower. Therefore, not only the chemical composition but also the structure of the resulting laye

Abstract—Experiments were carried out on the treatment of nanopowders of the W–C–Co system obtained by plasma-chemical synthesis in a microwave electromagnetic field with a frequency of 2.45 and 24 GHz in different gas media. The effect of treatment time, power input, and carbon content in the treated nanopowder on the yield of tungsten monocarbide WC was investigated.

Abstract

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

A two component Al–Ba system has been studied in which intermetallic compounds are formed that are stable at temperatures above the melting points of both barium and aluminum. This allows us to consider barium as a promising alloying element for aluminum alloys operating at high temperatures, which is also characterized by relatively high vapor pressure. Widespread use of aluminum–barium alloy in various fields of metallurgy for the preparation of alloys and complex modification of steels and cast irons, where aluminum improves the quality of steels, acting as a reducing agent for iron in its oxide compounds, and barium promotes the graphitization of cast irons, leads to improved structures of pearlitic and ferritic compounds. Taking into account the high vapor pressure of Ba in the aluminum–barium system is necessary when analyzing compositions in pressure–temperature–composition coordinates (p–T–x state diagrams), which can be used in the development of ternary or higher alloys containing aluminum and barium.

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

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].

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—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.