Effects of the porcelain-fused-to-metal firing process on the surface and corrosion of two Co–Cr dental alloys

The aim of this study was to evaluate the effects of a simulated porcelain-fused-to-metal (PFM) firing process on the surface, corrosion behavior, and cell culture response of two cobalt–chromium (Co–Cr) dental alloys. Two Co–Cr dental alloys were tested—a high and a low molybdenum (Mo)-containing alloys. Before PFM firing, as-cast alloy specimens were examined for their microstructure, surface composition, and hardness. Corrosion behavior was evaluated using electrochemical impedance spectroscopy tests. Mouse 3T3 fibroblasts were exposed indirectly to specimens and MTT cell proliferation assays were performed after 3 and 6 days. The cell culture medium exposed to specimens was analyzed for metal ion release. After firing, similar alloy specimens were examined for the same properties. The tests showed that the PFM firing changed both alloys’ microstructures and hardness values. After PFM firing, the corrosion resistance of the low Mo-containing Co–Cr alloy decreased statistically, which corresponded with a reduction of Cr and oxygen levels in the surface oxides via X-ray photoelectron spectroscopy. Also, the MTT assay of this alloy decreased significantly corresponding with an obvious increase of Co release after the firing. For the high Mo-containing Co–Cr alloy, the surface composition, corrosion resistance, and cell culture response were not significantly changed after PFM firing. The results suggested that the corrosion resistance and biocompatibility of the low Mo-containing Co–Cr alloy decreased after PFM firing, whereas the firing process had little effect on the same properties of the high Mo-containing Co–Cr alloy.     

Solving linear and nonlinear three-dimensional problems of fracture mechanics by a semi-analytic finite element method. Part 1. Theoretical background and a study of efficiency of fem procedure for solving three-dimensional problems of fracture mechanics

We present theoretical approaches and a procedure for the FEM computation of parameters of nonlinear fracture mechanics in prismatic bodies with a crack. The efficiency of the proposed approaches and the veracity of the results obtained have been analyzed.     

Emission from rare-earth ions in GaN wurtzite crystals

Intense studies of a wide-gap direct-zone semiconductor represented by GaN wurtzite crystals doped with rare-earth ions, namely, Eu, Er, Sm, and Tm, suggest the development of an alternative (compared to that with the use of InGaN layers) technology of fabrication of light-emitting diodes of white color. The opportunities of increasing the intensity of emission of intracenter 4f transitions are demonstrated for rare-earth ions in GaN wurtzite crystals by the optimization of doping technology, concentration of rareearth ions, and use of an additionally introduced impurity. The form of electroluminescence spectra of the GaN<RE<-based structures is similar to the form of photoluminescence spectra.     

X-ray photoelectron study of the MoCl2C30H30 composite

The surface of a MoCl₂C₃₀H₃₀ composite in the form of molybdenum nanoclusters in a polyacetylene matrix, produced by reacting MoCl₅ with C₂H₂ in benzene and toluene, has been studied by X-ray photoelectron spectroscopy before and after Ar⁺ ion milling. The composite actively reacts with atmospheric oxygen and moisture. As a result, the molybdenum clusters on its surface oxidize to molybdenum(V) or molybdenum(VI) oxides or oxychlorides (E _b(Mo 3d _5/2) = 232.3–232.5 eV) during the sample preparation process. The electron binding energy of molybdenum affter surface etching (E _b(Mo 3d _5/2) = 228.5 eV) suggests that the oxidation state of the molybdenum in the composite is 2⁺ or 3⁺. Analysis of the structure of the spectrum of the C 2s electrons of the inner valence molecular orbitals using the energy level diagram of the C₂ molecule suggests that the hydrocarbon matrix of the composite contains, in addition to-CH=CH-CH=CH- conjugate bonds, linear carbyne fragments: -HC=C=CH- or -C≡C-. After etching, the surface layer of the composite contained argon, which might be due to adsorption because of the small particle size of the composite or chemisorption on the surface of the polyacetylene matrix. The composite is stable in a high vacuum of 1.3 × 10⁻⁵ Pa up to 350°C and does not experience charging when exposed to X-rays, which indicates that it has weak dielectric properties.     

High-pressure volume magnetostriction in the diluted magnetic semiconductor Cd1 ? xMnxGeAs2 (x = 0.06–0.3)

The specific volume of the diluted magnetic semiconductor Cd_{1 − x} Mn _x GeAs₂ (x = 0.06–0.3) has been determined for the first time by strain measurements at pressures of up to 7 GPa. From the pressure dependences of the relative specific volume, we evaluated the volume magnetostriction (spontaneous magnetization coefficient). A scaling relation was used to estimate the bulk modulus of the magnetically ordered and disordered phases.     

Mechanochemical synthesis and hydrogen sorption properties of nanocrystalline TiFe

The equiatomic intermetallic compound TiFe has been prepared by elemental mechanochemical synthesis in a planetary ball mill from Fe and Ti powders. The structural and phase transformations during synthesis were followed using X-ray diffraction. The reaction of the synthesized compound with hydrogen was studied volumetrically. The results demonstrate that the hydrogen capacity of the mechanochemical TiFe is 1.2 wt % at 2.5 MPa. Its absorption isotherm has an extended plateau in the range 1.6–1.7 MPa at room temperature.     

Spray-drying of alumina powder for APS: effect of slurry properties and drying conditions upon particle size and morphology of feedstock

In this paper, effects of variables concerning slurry properties and drying conditions on the particle size and morphology of feedstock were discussed. The results indicated that, the increase of powder loading increased D ₅₀ and volume content but reduced recovery rate slightly. Other variables, such as inlet temperature, showed a maximum on the desired property. The particle size of resulting feedstock increased with the rise of feeding rate of slurry, however, decreased with the increase of atomization pressure based on the premise that atomization pressure was enough to force slurry to form the liquid membrane. For preparation of spherical feedstock, optimized variables were as follows: 60 wt.% powder in slurry, 2 wt.% PVA in slurry, inlet temperature of 60°C, atomization pressure of 13 × 10³ KPa and feeding rate of 12 ml min^?1. The volume content of feedstocks with 10–45 μm was above 65% and for D ₅₀ it was 15·42 μm. In addition, according to the heat and mass transfer equation, the drying mechanism was established, which was well in agreement with the experimental results.     

Analysis of the diametral compression method for determining the tensile strength of transparent magnesium aluminate spinel

Attempts were made to determine the inherent tensile strength of a coarse-grained, hot-pressed magnesium aluminate spinel (MgAl₂O₄) using the diametral compression test. Thick (9.6 mm) disk specimens were machined from a large (356 mm square) plate of spinel. Two pairs of tungsten carbide (WC) platens, one with flat surfaces and the other with a 20° half-arc and radius matched to the disk diameter, were used to transfer the applied load. Specimens tested using the platens with the matched radius had strength values almost 50% higher than those tested using flat platens. Images of the fracture process captured using a high-speed camera showed that irrespective of the type of platens used, fracture consistently initiated at the loading interface, resulting in an invalid test. These results show that the diametral compression test method is not appropriate for determining the tensile strength of this spinel and it raises concerns about the applicability of the method for any advanced ceramic.     

Regularizing the problem of monitoring the technical state of complex technical objects using program complexes for fuzzy conditional inference systems

Regularizing the problem of monitoring the technical state of complex technical objects in emergencies through drawing on additional semantic information is illustrated for a specific example.