Complex study of protective Cr3C2–NiAl coatings deposited by vacuum electro-spark alloying,pulsed cathodic arc evaporation,magnetron sputtering,and hybrid technology

Coatings were obtained by vacuum electro-spark alloying (VESA), pulsed cathodic arc evaporation (PCAE), magnetron sputtering (MS) techniques and VESA-PCAE-MS hybrid technology using Cr₃C₂–NiAl electrodes. The structure of the coatings was analyzed using scanning and transmission electron microscopy, X-ray diffraction and energy-dispersive spectroscopy. Mechanical properties were determined by nanoindentation, while tribological properties were assessed using pin-on-disk tribometer. Corrosion resistance was estimated by voltammetry in 1 N H₂SO₄ and 3.5%NaCl solutions. Oxidation resistance tests were performed at 800°С in air. The VESA coating had the highest thickness, low friction coefficient and high wear resistance. PCAE coating demonstrated the highest hardness (24 GPa) and elastic recovery (59%), oxidation resistance and superior corrosion resistance both in 1 N H₂SO₄ (i_corr = 70 μА/cm²) and 3.5%NaCl (i_corr = 0.74 μА/cm²) solutions. The MS coating had average mechanical properties and low corrosion current density (71 μА/cm²) in 1 N H₂SO₄. Deposition of coatings using VESA-PCAE-MS hybrid technology led to an increase in corrosion and oxidation resistance at least by 1.5 times in comparison with the VESA coating.     

Optimization of hydrogen enrichment via palladium membrane in vacuum environments using Taguchi method and normalized regression analysis

In this study, the separation of hydrogen from gas mixtures using a palladium membrane coupled with a vacuum environment on the permeate side was studied experimentally. The gas mixtures composed of H₂, N₂, and CO₂ were used as the feed. Hydrogen permeation fluxes were measured with membrane operating temperature in the range of 320–380 °C, pressures on the retentate side in the range of 2–5 atm, and vacuum pressures on the permeate side in the range of 15–51 kPa. The Taguchi method was used to design the operating conditions for the experiments based on an orthogonal array. Using the measured H₂ permeation fluxes from the Taguchi approach, the stepwise regression analysis was also employed for establishing the prediction models of H₂ permeation flux, followed by the analysis of variance (ANOVA) to identify the significance and suitability of operating conditions. Based on both the Taguchi approach and ANOVA, the H₂ permeation flux was mostly affected by the gas mixture composition, followed by the retentate side pressure, the vacuum degree, and the membrane temperature. The predicted optimal operating conditions were the gas mixture with 75% H₂ and 25% N₂, the membrane temperature of 320 °C, the retentate side pressure of 5 atm, and the vacuum degree of 51 kPa. Under these conditions, the H₂ permeation flux was 0.185 mol s^?1 m^?2. A second-order normalized regression model with a relative error of less than 7% was obtained based on the measured H₂ permeation flux.     

Fabrication and optical properties of transparent LaErZr2O7 ceramic with high excess contents of La and Er

In this study, transparent LaErZr₂O₇ ceramic with high excess La and Er contents (nominally La_1.28Er_1.28Zr₂O_7.84) was successfully prepared by vacuum sintering at 1850?°C for 6?h using nanosized powder. The XRD, SEM, EDX and TEM results reveal that the single pyrochlore phase in the powder sample transforms to the coexistence of La-rich pyrochlore phase and Er-rich defect fluorite phase after high temperature sintering. The high excess amounts of La and Er favor the formation of pyrochlore structure. Despite the coexistence of two phases, the sample with 1?mm thickness shows excellent in-line transmittance in the visible to mid-infrared region (as high as 81% at 1100?nm). The upconversion and infrared emission under 980?nm exciting were measured and discussed as well.     

Comparative analysis on performance of vertical drain improved clay deposit under vacuum or surcharge loading

This paper presents two well-instrumented large-scale field tests of PVD-improved soft soil with vacuum and surcharge preloading, respectively. The two large-scale field tests were conducted adjacent to each other with the same preload. A comparative analysis was performed to investigate the performance of subsoil (i.e., the ground settlement, the layered settlement, the lateral displacement of subsoil and pore water pressure) under vacuum preloading and equivalent surcharge preloading. Some design methods were verified based on the field data. Cone Penetration Tests (CPT) and Vane Shear Tests (VST) were conducted to assess the improvement effects on subsoil after preloading. The results showed that as compared with surcharge preloading, vacuum preloading mitigated the differential settlement of the ground. The vacuum pressure transmitted into the soil with a minor loss through the PVD length. From a practical point of view, the improvement effects by vacuum preloading and surcharge preloading were similar in terms of influence depth and soil strength based on the in-situ tests.     

Effect of PCL concentration on PCL/CaSiO3 porous composite scaffolds for bone engineering

Porous polycaprolactone (PCL)-coated calcium silicate (CaSiO₃) composite scaffolds were successfully prepared by 3D gel-printing (3DGP) and vacuum impregnation technology in this study. The effect of different PCL concentration on porous CaSiO₃ scaffolds prepared by 3DGP technology was studied. The composition and morphological characteristics of PCL/CaSiO₃ scaffolds were tested by using fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS) analysis. PCL coating amount on the scaffolds surface was calculated by thermogravimetric analysis (TGA). Compressive strength was tested by a universal testing machine, and degradability was tested by immersing the scaffolds in a simulated body fluid (SBF). The results show that PCL coating thickness increased from 7.29 μm to 12.2 μm, and the compressive strength of the corresponding composite scaffolds increased from 17.15 MPa to 24.12 MPa following with PCL concentration increasing from 7.5% to 12.5%. When the porous composite scaffolds were immersed in SBF for 28 days, the degradation ratio was 1.06% (CaSiO₃), 1.63% (CaSiO₃-7.5PCL), 1.81% (CaSiO₃-10PCL) and 1.55% (CaSiO₃-12.5PCL), respectively. It is obviously that PCL/CaSiO₃ composite scaffolds, which are suitable for bone growth in bone repair engineering, are beneficial to improve the mechanical properties and biodegradability of pure CaSiO₃ scaffolds.     

Effects of TiN addition on the properties of hot pressed TiN–Ti/Al2O3 composites

TiN–Ti/Al₂O₃ composites of varying TiN content (0–20?vol%) were prepared by vacuum hot-pressing sintering at different temperatures (1400?°C and 1500?°C) to investigate how TiN affected the mechanical properties and electrical conductivity of the composites. Sintered samples with added TiN exhibited better performance than those without it. The sample with 20?vol% TiN sintered 1500?°C had an optimal relative density of 99.49, Vickers hardness of 14.94?GPa, flexural strength of 321.55?MPa, and electrical resistivity of 1474.7?μΩ?cm. However, this increased temperature did not improve the best sample resistivity of 930.3?μΩ?cm, which was obtained at 1400?°C. Form SEM images and XRD patterns, the positive effect of TiN on composite mechanical properties may be ascribed to its good performance of high hardness and strength, a decrease of the brittle intermetallic phase, the form of AlTi₃N, and the impact of the fine-grained strength of the TiN phase.     

Influence of calcium concentration on formation of tetravalent chromium doped Y3Al5O12 ceramics

Yttrium Aluminium Garnet (YAG) ceramics doped with chromium were prepared by solid-state reactive sintering in a vacuum. The influence of the charge compensator Ca²⁺ concentration on microstructure, optical properties and efficacy of Cr³⁺ oxidation to Cr⁴⁺ under air annealing was investigated. A non-monotonic dependence of these features on the amount of CaO as an additive was found. The changes in ceramic transparency and microstructure were explained considering the interaction between CaO and Cr₂O₃ at the ceramic grain boundaries, which leads to a different pore evolution in distinct samples during sintering. The efficacy of the oxidation of Cr³⁺ to Cr⁴⁺ strongly depends on the concentration of Ca dissolved in the YAG. The calcium solubility decreases due to the higher oxygen partial pressure of the extra phases on the grain boundaries that decreases the amount of generated Cr⁴⁺ ions. Such phenomenon explains the lower concentration of Cr⁴⁺ ions in the sample with 0.8% of Ca against the one with 0.5%. The experiment shows that the ceramic with 0.5% of Ca has a better in-line transmission and a higher concentration of Cr⁴⁺ ions in comparison with samples with a different Ca concentration.     

Characterization of nickel manganite NTC thermistor films prepared by aerosol deposition at room temperature

NiMn₂O_4+δ thermistor thick films have been successfully deposited by the so-called Aerosol Deposition Method (ADM) at room temperature on alumina substrates, Si-wafers, as well as on special planar four-wire interdigital electrode structures for high-precision electrical characterization. The NTCR films are homogeneous, completely dense and scratch resistant. Both as-deposited and tempered, the NTCR films exhibit a cubic spinel structure. Between 25 °C and 90 °C, the NTCR film resistance behaves as it is typical for variable range hopping (VRH) with parabolic density of states. As a result of moderate film tempering, the thermistor constant B and the specific resistance at 25 °C (ρ₂₅) decrease from 4250 K to 4020 K and 65 Ω·m to 40 Ω·m respectively, and are close to bulk values. In combination with the excellent reproducibility of the ρ₂₅ and B values, AD processing of films appears to be a promising alternative for classical ceramic bulk processes.     

Effect of surcharge loading rate and mobilized load ratio on the performance of vacuum–surcharge preloading with PVDs

The results from three laboratory model tests performed under various vacuum and surcharge loads with PVDs are reported. Different SLRs were adopted to investigate the effect on the consolidation of dredged soil. To measure the lateral displacement, a refitted inclinometer was developed and tested. In the tests, the settlement, lateral displacement, and vane shear strength were measured, and the degree of consolidation (DOC), horizontal coefficient of consolidation (C_h), and bearing capacity were calculated. The results indicate that larger SLR values promote consolidation. The largest vane shear strength, settlement, and C_h values were all obtained under the highest SLR, and the bearing capacity under this SLR was more than double that under the lowest SLR. The DOC was found to increase with the growth of the SLR. However, considering the vacuum pressure was higher in Case-III, the influence of SLR on reinforcement effect may not be so significant.     

Enhancement of optical and electrical properties of SILAR deposited ZnO thin films through fluorine doping and vacuum annealing for photovoltaic applications

Undoped and fluorine doped ZnO thin films were deposited onto glass substrates using successive ionic layer adsorption and reaction (SILAR) technique and then annealed at 350 °C in vacuum ambience. The F doping level was varied from 0 to 15 at% in steps of 5 at%. The XRD analysis showed that all the films are polycrystalline with hexagonal wurtzite structure and preferentially oriented along the (002) plane. Crystallite sizes were found to increase when 5 at% of F is doped and then decreased with further doping. It was seen from the SEM images that the doping causes remarkable changes in the surface morphology and the annealing treatment results in well-defined grains with an improvement in the grain size irrespective of doping level. All the films exhibit good transparency (>70%) after vacuum annealing. Electrical resistivity of the film was found to be minimum (1.32×10⁻³ Ω cm) when the fluorine doping level was 5 at%.