A Metastable p-Type Semiconductor as a Defect-Tolerant Photoelectrode

A p-type Cu3Ta7O19 semiconductor was synthesized using a CuCl flux-based approach and investigated for its crystalline structure and photoelectrochemical properties. The semiconductor was found to be metastable, i.e., thermodynamically unstable, and to slowly oxidize at its surfaces upon heating in air, yielding CuO as nano-sized islands. However, the bulk crystalline structure was maintained, with up to 50% Cu(I)-vacancies and a concomitant oxidation of the Cu(I) to Cu(II) cations within the structure. Thermogravimetric and magnetic susceptibility measurements showed the formation of increasing amounts of Cu(II) cations, according to the following reaction: Cu3Ta7O19 + x/2 O2 → Cu(3−x)Ta7O19 + x CuO (surface) (x = 0 to ~0.8). With minor amounts of surface oxidation, the cathodic photocurrents of the polycrystalline films increase significantly, from <0.1 mA cm−2 up to >0.5 mA cm−2, under visible-light irradiation (pH = 6.3; irradiant powder density of ~500 mW cm−2) at an applied bias of −0.6 V vs. SCE. Electronic structure calculations revealed that its defect tolerance arises from the antibonding nature of its valence band edge, with the formation of defect states in resonance with the valence band, rather than as mid-gap states that function as recombination centers. Thus, the metastable Cu(I)-containing semiconductor was demonstrated to possess a high defect tolerance, which facilitates its high cathodic photocurrents.

Study and Computer-aided Design of Flux-cored Wire Rolling in Round Gauges

The mathematical model of the stress-strain state during flux-cored wire rolling in round gauges has been developed. Simulation was based on dividing the deformation zone into elementary volumes and simultaneous solution of the plasticity condition for porous materials and power static equilibrium equation inside the elementary volume. A distinctive feature of this model is taking into account the porous medium strain in the deformation zone. The experiments have confirmed the validity of the mathematical model for predicting the powder density and the energy-power characteristics of the process. Based on the developed mathematical model, the criteria and conditions for optimization were formulated, and the algorithm was developed for the automated design of technology for flux-cored wire rolling in round gauges. As an example of the obtained solutions implementation, the calculation of sintered copper flux-cored wire rolling technology was given.

The Analysis of The Process of Barley Grain Separation from Undesirable Particles

The article focuses on the intensification of raw barley grains initial purification and separation processes before the subsequentprocessing in the area of brewing. Above all, it deals with the physical and mechanical concepts of the purification and separationof qualitatively satisfactory grains from undesirable impurities, e.g. coarse impurities, as the prevention from the potential damageof milling and scrapping facilities. Four different cultivated barley species were tested within the study. Physical and mechanicalparameters were determined in all samples, for instance powder density, angle of internal friction and external friction angle withsteel contact material, particle size distribution and morphology. The first results of measuring revealed the difference in the qualityof initial entering component of barley grains before the purification process compared to the output quality of grains after machinepurification and separation processes in the facilities determined for the subsequent grain storage. As a result of the non-effectiveprocess of separation, the final quality of the product, i.e. the beer, may be affected by the qualitative parameters of partial processesinvolved in treating barley grains.

Influence of Machine Parameters on Ti-6Al-4V Small Sized Specimens Made by Laser Metal Powder Deposition

The present work is focused on one Additive Manufacturing (AM) process – Laser powder Metal Deposition (LMD-p) – and on one metallic alloy – Ti-6Al-4V. State of the art on LMD-p on Ti-6Al-4V alloy shows that three kinds of process parameters influence mechanical properties of building parts: raw materials (powder and substrate), machine parameters (Laser Power (P), Powder Flow (F) and Building Speed (V)), and building strategies (part orientation, waiting time between layers, etc.). Thus, this paper relates to first manufacturing investigations on small sized specimens (bead, wall and block) with the aim of providing a better knowledge about the first steps of manufacturing. Particularly, this paper is dedicated to the study of machine parameters (P, F and V). First, the influence of each machine parameter on 28 beads is studied separately. The geometrical aspect (high, width, dilution) of each bead is microscopically measured. Similarly, combinations of parameters (P/F, Energy Density and Powder Density) are introduced to increase parameters degree of freedom. First results show that P, V and F have a major influence on the beads’ geometry. In addition, a window process map is plotted and allows determining functional areas of machine parameters. From this map, walls (vertical superposition of one bead) are manufactured and microscopically observed. Functional sets of parameters from walls are selected and blocks can be built.

Determination of the Neck Size between Powders during Sintering Process Using Finite Element Methods

Today, sintering considers one of the significant processes that can be used in powder technology to produce a new solid product from powders using thermal energy. Many parameters can be successfully controlled by this process such as temperature, Particle size, process time, structure geometry, powder density, and powder composition. Study and analysis of the behavior of powder during the sintering process was carried out using finite element methods. The simulation provides two styles of discrete method and Qusi-static method. This research contributes to two types of processes in order to simulate the copper powder during the sintering process and to determine the variation by using contact and shrinkage ratios of powder behaviors. Finally, a comparison between the two styles of discrete element method explains how the selected parameters were impacted on the sintering process.

EFFECT OF MIX PROPORTIONS ON THE PROPERTIES OF CLSM CONTAINING RECYCLED GLASS

This research examined the effect of mix proportions namely, water to cementitious (w/c) ratio and glass content, on the flowability and compressive strength of controlled low-strength (CLSM) mixtures. A total of 20 mixes containing different proportions of cement, sand, class C fly ash, coarser glass, finer glass and water were prepared and tested. Results showed that both flowability and strength are dependent on w/c ratio and type and percent of glass content. Strength of mixes containing high volume of coarser glass was found more sensitive towards w/c ratio. Further strength was found to improve with increase in finer portion of the glass powder. Density was also found to correlate well with the moisture content of CLSM specimens. Specimens with lower moisture content produced denser CLSM structure. The results of this study would be useful in establishing mix proportions for CLSM incorporating recycled glass, fly ash, sand and cement for commercial applications

Determination of the conductivity of non-metallic powder materials by the eddy current method

A theoretical analysis of the interaction of the eddy current sensor field with powder particles makes it possible to calculate the particle conductivity using the measured value of the sensor added active resistance. Relative to its own reactance, the value of this resistance is proportional to powder density, frequency of the probing field, electrical conductivity of particles and square of their diameter. Particles of spherical shape and cylindrical shape, the height of which is equal to the diameter of the base, are considered. The analysis allows to explain the experimentally observed different character of the resistance frequency dependences for powder and corresponding solid material when measuring by the same sensor.

Optimization of the SiC Powder Source Size Distribution for the Sublimation Growth of Long Crystals Boules

The influence of four different SiC source powder size distributions on the sublimation behavior during physical vapor transport growth of SiC was studied. The growth processes were carried out in a 3 inch crystal growth setup and observed in situ using advanced 3D computed tomography X-ray visualization. The single modal D90 size distribution of two source powders was 50 μm and 200 μm, respectively, with a corresponding average powder density of 1.17 g/cm3. The third source powder consisted of a blend of the previously named powders and exhibited an average powder density of 1.66 g/cm3 with a bimodal particle size distribution. The last source was composed of a solid polycrystalline SiC cylinder. The bimodal powder source exhibited a smoother morphology change and material consumption during the growth run and led to a much more stable shape change of the growth interface compared to the single modal source powders. The solid source featured the least morphology change. Therefore, with a careful adaption of the source material stable growth conditions can be achieved.