Search

Useful silicone pressure-sensitive adhesives (PSAs) have been prepared from a high solid silicone resin. Platinum catalysts and crosslinking compounds were used to obtain new self-adhesive tapes. The influence of catalysts and crosslinking compounds on the basic properties of self-adhesive tapes was tested, taking into account the compatibility of silicone composition. The obtained systems showed good self-adhesive properties, and high thermal resistance over 225 °C. The low viscosity of the compositions obtained relatively increases the application potential of self-adhesive tapes based on it. Moreover, the prepared compositions show the potential for further modifications, especially physical ones e.g. silicon powder. The obtained new tapes showed good self-adhesive properties and kept high thermal resistance over 225 °C. It is well known that silicone pressure-sensitive adhesives are a group of silicone adhesives for special applications. Due to their unique resistance to environmental conditions, temperature and chemical resistance, they are difficult to modify. [ABSTRACT FROM AUTHOR]

Mechanical milling is a promising route for production of submicron and nano sized silicon powders, but it is challenging to predict and control the product properties. In this study a metallurgical grade silicon quality was milled in a planetary ball mill and the properties of the powder were investigated as a function of grinding time, grinding bead size (20 mm, 2 mm, 0.25 mm) and rotational speed based on the concepts presented in the stress model. The finest powder was characterized by a d50 of 0.62 μm. This powder was produced with the 2 mm grinding beads and 4 h of grinding (i.e. the highest specific energy input to the mill with this bead size). The largest BET specific surface area, the highest concentration of iron contamination and the smallest amount of crystalline silicon phase were characterized in the powder produced using the 0.25 mm grinding beads and 4 h of grinding (i.e. the highest stress number). Aggregates consisting of silicon and iron were formed. An acid wash to reduce the concentration of iron contaminant revealed that silicon did form an amorphous phase as well as the specific surface area increased. With a constant specific energy input to the mill, a reduction in rotational speed (i.e. reduced stress energy) produced similar powder properties with the exception of the particle size distribution. [ABSTRACT FROM AUTHOR]

The deposition characteristics of lead ions (Pb2+) in the presence of silicon powders (i.e., suspended particles, SPs) were investigated in water seepage in a long one-dimensional sand column experiment. The injected SPs possess a very wide particle-size distribution (PSD). The concentrations of deposited Pb2+ and SPs and the migration distance along the water flow direction were measured by sampling. The PSDs of the deposited SPs in different sections were obtained by laser diffraction after transport test completion, and microstructure photographs were also acquired through metallographic microscopy. The test results show that the presence of SPs may promote or inhibit Pb2+ migration, which is closely related to the concentration of the injected Pb2+, particle size and concentration of the injected SPs, seepage velocity, and change in the absolute zeta potential of the surface charge. The median diameter of the deposited SPs near the injection end is larger than that of the injected SPs and gradually decreases with increasing distance. Overall, the transport of SPs represents a clear particle-separation characteristic and significantly influences the migration progress of pollutants such as heavy metal ions such as Pb2+ due to their coupling effects. [ABSTRACT FROM AUTHOR]

This work investigates the surface modification of quenched and tempered AISI H13 tool steel, widely used in mold-making industry, by sinking EDM with very fine Si powder suspended in the dielectric. The output variable resultant friction coefficients, wear resistance, and hardness of recast layer were measured for different input variables. The 1 A/2.8 μs and 2 A/3.2 μs and 2 A/6.4 μs combinations of discharge current and discharge duration, respectively, produced high hardness, low friction coefficient, and high wear-resistant recast layers, after the formation of martensitic phases in the recast layer as well as C0.17, Fe0.81, Si0.02 carbide. Layer thickness tends to grow with machining time. PMEDM process produced variable amounts of Si in the resultant recast layers, forming iron-silicon carbide phases. Lower wear rates were measured for the high-quality recast layers tested favoring the lifetime of this tool steel in abrasive applications. Martensitic phase formation in the recast layers helps explaining the increased hardness. [ABSTRACT FROM AUTHOR]

A major challenge in recycling of silicon powder from kerf loss slurry waste is the complete removal of metal particles. The traditional acid leaching method is costly and not green. In this paper, a novel approach to recover high-purity Si from the kerf loss slurry waste of solar grade silicon was investigated. The metal impurities were removed with superconducting high gradient magnetic separation technology. The effects of process parameters such as magnetic flux density, slurry density, and slurry flow velocity on the removal efficiency were investigated, and the parameters were optimized. In one lot of control experiments, the silicon content was increased from 90.91 to 95.83%, iron content reduced from 3.24 to 0.57%, and aluminum content from 2.44 to 1.51% under the optimum conditions of magnetic flux density of 4.0 T, slurry density of 20 g/L, and slurry flow velocity of 500 mL/min. The result indicates that the superconducting high gradient magnetic separation technology is a feasible purifying method, and the magnetic separation concentrate could be used as an intermediate product for high-purity Si powder. [ABSTRACT FROM AUTHOR]

Rattan-based silicon carbide (R-SiC) ceramics, R-SiC and R-SiC, were successfully prepared from silica (SiO) sol and silicon (Si) powder, respectively. The rattan powder was impregnated, respectively, with SiO sol at ambient temperature and liquid melt-Si at high temperature. This was followed by one-step direct pyrolysis at 1500 °C under an argon (Ar) atmosphere. The final SiC samples were analyzed using mass analysis, X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX), and nitrogen (N) physisorption techniques. Experimental results showed that the mass residual of R-SiC (42.56 wt%) was almost equal to R-SiC (42.45 wt%). However, R-SiC had a higher yield of SiC, a higher specific surface area and a more intact porous morphology preserved from the rattan biomass. In addition, some rod-like SiC whiskers and tablet-like SiC particles were found in R-SiC. By comparison, R-SiC had a large amount of unreacted Si, as well as certain amount of SiC and unreacted C. Thus, it can be concluded that SiO sols are more appropriate for use in preparation of SiC from rattan, whatever the porous microstructure, yield, and purity of SiC. [ABSTRACT FROM AUTHOR]

In electrical discharge machining (EDM) process, one of the most important aspects is the surface quality of the workpiece. When a uniform and thick recast layer is achieved with characteristics of low roughness, high hardness, and the absence of pores and micro-cracks, it acts as a kind of coating. Such surface is required by mold-making industry, where the molds are subjected to chemical and abrasive wear, and the surface needs to present high resistance against corrosion and abrasive forces. The use of powder particles suspended in the dielectric is a way to provide such improvement and, at the same time, avoiding the need for subsequent polishing. This work investigated the influence of silicon and manganese powders with fine particle sizes, using two different concentrations, suspended in the dielectric when EDM machining AISI H13 tool steel. It evaluated the surface roughness, hardness, and the chemical composition and micro-structure of the recast layer; using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) techniques. The best results were obtained for silicon powder; presenting the surface roughness improved about five times, when compared to the conventional EDM process, as well as a thick and uniform recast layer without micro-cracks and pores. The silicon and the manganese powders also promoted an increase of the recast layer hardness of about 40 % when compared to the conventional EDM process. [ABSTRACT FROM AUTHOR]

Silicon nanopowders were prepared by hot-wire chemical vapour deposition (CVD) from monosilane. Wire materials including Hf, Nb, Ta, Mo, W, Rh, Re, Ir, Pd, and Pt were tested. The filament temperature was varied in the range of 400-2000 ℃ and pressures between 1.0-1.5 bar. Products were characterised by bulk elemental analysis and a laser granulometer. The powders were investigated by TG-DSC-MS under inert, O, and HO containing atmosphere, respectively, in a temperature range of 20-700 ℃. Hydrogen evolution occurred in three separate steps, depending on the applied gas atmosphere. The oxidation mechanism was explored by the characteristic OSi-H bands (x = 0-3) observed in ex situ DRIFT experiments. The oxidation of hydrogen terminated silicon surfaces was investigated employing oxygen (O), hydrogen peroxide (H O), permanganate (MnO $_{4}^{-}$), or peroxodisulfate $\left (\mathrm {S}_{2}\mathrm {O}_{8}^{2-}\right )$ in a temperature range of 0-120 ℃. The oxidation was stepwise and strongly enhanced after pretreatment by alkyl lithium salts or Grignard reagents. [ABSTRACT FROM AUTHOR]

In this work, we use a two-step metal-assisted chemical etching method to produce films of silicon nanowires shaped in micrograins from metallurgical-grade polycrystalline silicon powder. The first step is an electroless plating process where the powder was dipped for few minutes in an aqueous solution of silver nitrite and hydrofluoric acid to permit Ag plating of the Si micrograins. During the second step, corresponding to silicon dissolution, we add a small quantity of hydrogen peroxide to the plating solution and we leave the samples to be etched for three various duration (30, 60, and 90 min). We try elucidating the mechanisms leading to the formation of silver clusters and silicon nanowires obtained at the end of the silver plating step and the silver-assisted silicon dissolution step, respectively. Scanning electron microscopy (SEM) micrographs revealed that the processed Si micrograins were covered with densely packed films of self-organized silicon nanowires. Some of these nanowires stand vertically, and some others tilt to the silicon micrograin facets. The thickness of the nanowire films increases from 0.2 to 10 μm with increasing etching time. Based on SEM characterizations, laser scattering estimations, X-ray diffraction (XRD) patterns, and Raman spectroscopy, we present a correlative study dealing with the effect of the silver-assisted etching process on the morphological and structural properties of the processed silicon nanowire films. [ABSTRACT FROM AUTHOR]

The grain-size composition of silicon powder has been determined by optical microscopy, laser diffraction, photosedimentation, and differential high-velocity sedimentation. The results from the various methods are compared in regions of intersection of their ranges, and the advantages of each of the four methods are identified. [ABSTRACT FROM AUTHOR]

The addition of powder particles to the electrical discharge machining (EDM) dielectric fluid modifies some process variables and creates the conditions to achieve a higher surface quality in large machined areas. This paper presents a new research work that aims to study the improvement in the polishing performance of conventional EDM when used with a powder-mixed-dielectric (PMD-EDM). The analysis was carried out varying the silicon powder concentration and the flushing flow rate over a set of different processing areas and the effects in the final surface were evaluated. The evaluation was done by surface morphologic analysis and measured through some quality surface indicators. The results show the positive influence of the silicon powder in the reduction of crater dimensions, white-layer thickness and surface roughness. Moreover, it was demonstrated that an accurate control of the powder concentration and flushing flow is a requirement for achieving an improvement in the process polishing capability. [ABSTRACT FROM AUTHOR]