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The drying procedure is an important consideration for the silicon powder processing. Herein, a comparative investigation of the drying efficiency, drying performance, and energy consumption of silicon powder after separation and purification of monocrystal silicon cutting slurry by using the hot air, far‐infrared and microwave drying treatments. The results show that microwave drying of 30 g silicon powder takes only 12 min, which is much shorter than hot air drying of 200 min and far infrared drying of 40 min. The water evaporation energy consumption of microwave drying reached 73.5 g/kW·h, which was 3.3 times than that of far infrared drying and 16.5 times than that of hot air drying. For 1 kg of silicon powder, the power consumption of microwave drying was 8 kW·h, while the far‐infrared drying was 26.7 kW·h, and the hot air drying was 133.4 kW·h, respectively. Therefore, effects of microwave power, drying temperature and drying time on the dehydration rate of silicon powder were investigated and optimized by response surface method, demonstrating that the microwave drying dehydration rate of 30 g silicon powder could reach 97.65%, and the power consumption could be reduced to 6.7 kW·h/kg under the conditions of microwave power of 1000 W, drying temperature of 89°C and drying time of 12 min. The present study shows that microwave drying of silicon powder is an energy‐saving and efficient process with good industrial application prospects. [ABSTRACT FROM AUTHOR]

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]

Unburned magnesium aluminate spinel refractories were prepared using sintered magnesium aluminate spinel as the main raw material, phenolic resin as the binder, aluminum powder (2%, 4%, and 6% by mass) and silicon powder (when Al powder addition is 4%, Si powder addition varies: 1% and 2%, by mass) as additives. The effects of the Al powder and Si powder additions on the properties and microstructure of the refractories heat treated at different temperatures (1 000, 1 400, and 1 600 ℃ for 3 h) were studied. The results show that the Al powder addition can greatly enhance the cold modulus of rupture of the samples fired at 1 000 or 1 400 ℃, and meanwhile AlN reinforcement phase forms in the matrix, which greatly improves the hot modulus of rupture of the samples at 1 400 ℃; however, the heat treatment at 1 600 ℃ has little influence on the strength; the addition of Al powder and Si powder results in the formation of low melting point phases, greatly reducing the hot modulus of rupture. However, the low melting point phases promote sintering, which enhances the density and the cold modulus of rupture, and decreases the volume change during heating. The samples added with Al and Si all have higher cold modulus of rupture than those added with Al powder only. [ABSTRACT FROM AUTHOR]

In order to explore the repair characteristics of polymer modified silica powder mortar, an experimental study was conducted on the compressive, splitting and tensile properties of mortar mixed with acrylic emulsion (10%, 20% and 30%) and silica powder (5% and 10%) and its direct tensile bonding and bending bonding properties so as to provide a basis for the application of high-performance repair materials on concrete surface. The results show that, the addition of acrylic emulsion and silica powder can effectively improve the compressive strength and splitting tensile strength of mortar. When the addition of acrylic emulsion is 30% and the addition of silica powder is 10%, the compressive strength and splitting tensile strength of specimens at 28 d are increased by 15.24% and 46.90% respectively when compared with control samples. The addition of silicone powder and acrylic emulsion can effectively improve the bonding strength of mortar. The direct tensile bonding strength and flexural bonding strength of repair mortar using acrylic emulsion as the binder can reach 3.3-4.2 MPa and 7.5-11.4MPa,respectively. Acrylic emulsion modified silica mortar has excellent tensile and bonding properties and can be used as an ideal repair material for concrete, especially hydraulic concrete. [ABSTRACT FROM AUTHOR]

The Silicon on Dust Substrate (SDS) is a gas-to-wafer process that produces multicrystalline silicon ribbons directly from gaseous feedstock (silane), avoiding the standard industry steps of polysilicon deposition, crystal growth, and wafering. The SDS technique consists of three main steps: (i) micrometric-sized silicon powder production by grinding silicon chunks; (ii) chemical vapor deposition (CVD) of silicon over this silicon powder substrate; and (iii) zone-melting recrystallization (ZMR) of the nanocrystalline pre-ribbon obtained in the CVD step. Several samples were produced by this technique. During CVD, mechanically self-sustained nanocrystalline pre-ribbons were grown over silicon powder substrates, with growth rates in the order of 50 µm/min. The ZMR process performance is substantially impacted by the pre-ribbon physical characteristics. The best and largest recrystallizations were achieved on pre-ribbons grown over powder substrates with smaller particle sizes, which also have lower substrate powder incorporation ratios. Multicrystalline silicon ribbons with crystalline areas as large as 2 × 4 cm2 were successfully produced. These areas have visible columnar crystal growth with crystal lengths up to 1 cm. The SDS ribbons' measured resistivity confirmed the high powder content of the resulting material. The ability to produce solar cells on SDS multicrystalline silicon ribbons was demonstrated. [ABSTRACT FROM AUTHOR]

Copyright of Silicone Material is the property of Silicone Material Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Unburned magnesium aluminate spinel refractories were prepared using sintered magnesium aluminate spinel as the main raw material, phenolic resin as the binder, aluminum powder (2%, 4%, and 6%, by mass) and silicon powder (when Al powder addition is 4%, Si powder addition varies:1% and 2%, by mass) as additives. The effects of the aluminum powder and silicon powder addition on the properties and the microstructure of the refractories heat treated at different temperatures (1 000,1 400,and 1 600 °C for 3 h) were studied. The results show that the Al powder addiiion can greatly enhance the cold modulus of rupture of the samples fired at 1 000 or 1 400 °C,and meanwhile AlN reinforcement phase forms in the matrix, which greatly improves the hot modulus of rupture of the samples at 1 400 °C; however, the heat treatment at 1 600 °C has liitle influence on the strength; the addition of aluminum powder and silicon powder result in the formation of low melting point phases, greatly reducing the hot modulus of rupture. However, the low melting point phases promote sintering, which enhances the density and the cold modulus of rupture, and decreases the volume change during heating. The specimens added with aluminum and silicon all have higher cold modulus of rupture than those added with Al powder only. [ABSTRACT FROM AUTHOR]

The Silicon on Dust Substrate (SDS) is a gas-to-wafer process that produces multicrystalline silicon ribbons directly from gaseous feedstock (silane), avoiding the standard industry steps of polysilicon deposition, crystal growth, and wafering. The SDS technique consists of three main steps: (i) micrometric-sized silicon powder production by grinding silicon chunks; (ii) chemical vapor deposition (CVD) of silicon over this silicon powder substrate; and (iii) zone-melting recrystallization (ZMR) of the nanocrystalline pre-ribbon obtained in the CVD step. Several samples were produced by this technique. During CVD, mechanically self-sustained nanocrystalline pre-ribbons were grown over silicon powder substrates, with growth rates in the order of 50 µm/min. The ZMR process performance is substantially impacted by the pre-ribbon physical characteristics. The best and largest recrystallizations were achieved on pre-ribbons grown over powder substrates with smaller particle sizes, which also have lower substrate powder incorporation ratios. Multicrystalline silicon ribbons with crystalline areas as large as 2 × 4 cm2 were successfully produced. These areas have visible columnar crystal growth with crystal lengths up to 1 cm. The SDS ribbons’ measured resistivity confirmed the high powder content of the resulting material. The ability to produce solar cells on SDS multicrystalline silicon ribbons was demonstrated.

A cyclic adiabatic compression reactor is used for the Si powder fabrication by the monosilane decomposition in a gas mixture with argon. Along with arbitrary agglomerations of Si nanoparticles, this method allows synthesizing nanoparticle chains and nanowhiskers, as an outlet gas pressure in the reactor increases from about 2.0 to 5.0 MPa. The increase in pressure corresponds to an increase in temperature from ~450 to 1050 °C, which leads to a change in the particle structure from amorphous to crystalline and reduces the particle size distribution. The particle chain and nanowhisker formation is associated with an increase in the duration of the synthesis process. The optical properties of the synthesized Si powders were determined by Si/SiO 2 interfaces appeared by the oxidation in the air. The method is characterized by a relatively high production rate of Si powders of various morphologies, which may be of interest for various applications. [Display omitted] • Si powder was synthesized in adiabatic process using gas mixture of SiH 4 and Ar. • Amorphous Si nanoparticles became crystalline as gas pressure increases. • Si particles are agglomerated into chains or nanowhiskers depending on gas pressure. • Effects of gas pressure are associated with an increase in temperature. • Si/SiO 2 interface determines optical properties of Si powder after oxidation in air. [ABSTRACT FROM AUTHOR]

Metallic silicon powder has been widely used for the production of various industrial materials and parts such as refractory ceramics, solar cells, military parts and so on. Herein, we attempted to prepare pure silicon powder from SiO2 by a magnesium thermal reduction process. A mixed-phase, Mg2Si + MgO, was obtained by the reduction of SiO2 powder by magnesium gas at 1223K for 20 h. To extract pure silicon powder, Mg was separated by evaporation under vacuum through Mg2Si decomposition above 1073 K, leading to the formation of Si + MgO, and the MgO by-product was eliminated by dissolution in an aqueous hydrochloric acid solution. X-ray diffraction analysis confirmed the formation of pure Si powder and particle size shown in microstructure and oxygen content were analyzed to be 1~5 µm and 1.5~6 wt.%, respectively. [ABSTRACT FROM AUTHOR]

• SP could effectively increase the recovery of fluorine from 50.05% to 81.13%. • The addition of SP has negligible effect on the quality of WPA. • SP can significantly promote the conversion of liquid fluorine to SiF 4 gas. • The decreases of fluorine precipitates also play key roles in improving recovery. The recovery and utilization of fluorine resources from wet-process phosphoric acid (WPA) is of great importance in protecting environment and providing cheap raw materials for the fluorine chemical industry. Evaporation concentration method is widely used due to its simplicity and low operating expenses. However, the lack of effective reagents limits the further development. In this study, silicon powder (SP) was firstly used to enhance the fluorine recovery during the concentration process of WPA. The gasification performance and behavior in reaction system (SP dosage, stirring speed, and concentration temperature) and absorptive system (initial mass of absorptive water) were investigated in detail. The results showed that SP had an excellent performance for fluorine recovery, which was superior to traditional reagents like diatomite, white carbon black (WCB) and zeolite powder (ZP). Under the optimal conditions, the fluorine recovery could reach an impressively high percentage of 81.13%, exhibiting a significant increase of 31.08% compared with blank concentration. Furthermore, SP could selectively and efficiently recover fluorine without affecting the quality of WPA. Spillover kinetics suggested that the rate of reaction between SP and fluorine was slow, with an apparent reaction order of 0.56. During the concentration process of WPA, SP showed a better tendency to react with H 2 SiF 6 and HF. The addition of SP could increase the production of SiF 4 gas and reduce the formation of fluorine precipitates. These two pathways are responsible for the improvement of fluorine recovery. Overall, this research provides a valuable reference for the efficient recovery of fluorine from WPA. [ABSTRACT FROM AUTHOR]

The corundum-mullite bricks were prepared using brown corundum, α-AI2O3 powder, andalusite powder, and Guangxi white mud as raw materials. In order to improve the iron slag erosion and corrosion resistance of corundum-mullite bricks, 2 mass% Si powder was introduced into the corundum-mullite bricks, and the properties of the samples were compared before and after Si powder addition. The results show that compared with the corundum-mullite sample without Si powder, the sample with Si powder has uniform and small pores, and the apparent porosity decreases from 15.8% to 13.5%, the cold compressive strength increases obviously, the hot modulus of rupture increases by 5.6 times, the hot toughness and the iron slag corrosion resistance and the penetration resistance are obviously improved. [ABSTRACT FROM AUTHOR]

The coupled transport of heavy metals with suspended particles has been a topic of growing interest. The main purpose of this study is to experimentally investigate the seepage transport of heavy metal Pb2+ in the presence of silicon powders (SPs) through a sand column under different seepage velocities (v = 0.087–0.260 cm/s), injection Pb2+ concentrations (CP = 0–800 μg/ml) and SP sizes (D50 = 2.8–25.5 μm), which were likely to be encountered in practical engineering. The sand column was installed in a cylindrical chamber of 300 mm in length and 80 mm in internal diameter. The results clearly show that the increase in acidity results in a reduction of the repulsive interactions between SPs and the matrix, and consequently a decrease in the peak values in breakthrough curves (BTCs), especially for larger-sized SPs. The peak values and recovery rate of Pb2+ are obviously increased and an earlier breakthrough can be observed, due to the higher capacity of SPs with negative charge to adsorb heavy metal pollutants such as Pb2+ with positive charge. The adsorption of Pb2+ on SPs can reduce the repulsive forces between SPs and the matrix, thus resulting in the increase of the deposition possibility of SPs and the decrease of peak value and recovery rate.

In this work, silicon ink composing of silicon powder and zinc oxide solution was formulated and spin-coated on quartz and n/p-Si substrates followed by drying the films under atmosphere at the temperature of 550 ​°C. The results showed that this top-addition layer could be the highly promising layer for photo-generating carriers in third-generation photovoltaics to enhance blue-light absorption. X-ray diffraction and scanning electron microscopy techniques were used to study the presence of silicon and zinc oxide nano-crystallites. The thin films consisting of different energy bandgap of Si nanocrystals (~100 ​nm) with narrow bandgap and spherical ZnO:Bi nanocrystal (~20 ​nm) with wider bandgap could be obtained from the evidence of bandgap enlargement. The band gaps of the thin films were tunable by adjusting silicon dots density in ZnO:Bi film. Energy upshift of light absorption edge depended on the silicon dots density was observed in the range 1.6–3.3 ​eV related band gap enlargement by Tauc plot. Under illumination, a high photocurrent gain of the thin film comprised of low Si dots density coated on a quartz substrate was about 103 times higher compared with its dark current. This result is agreeably explained in terms of its lower superficial trap states at the interface between silicon and zinc oxide matrix. The composite layer can be applied to a third-generation solar cell with the efficiency 1.50% higher than that with a typical crystalline-Si solar cell. Fig. 3 (a) Patterned film on p-n junction, (b) cell structure, and (c) top-cell image with a multilayer of Si dots film.Fig 9 J–V curves, comparisons of V oc , J sc , FF, and efficiency values of solar cell samples with the different Si dots densities. [Display omitted] • The Si dots thin films composing of Si dots dispersed in ZnO:Bi matrix has been prepared by a spin coating method for optimizing their optoelectrical value. • The E g ​values of the Si dots films shift toward the higher photon energy from 1.1 eV to 2.2 eV for decreasing Si dot concentrations which implying the increase of blue-light absorption. • The Si dots multi-layers addition can be a promising approach for the efficiency improvement of third-generation solar cells. [ABSTRACT FROM AUTHOR]

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SiC-SiOx nanowires (NWs) with core-shell and chain-bead structures were synthesized via a catalyst-free chemical vapor deposition (CVD) route without Ar gas, using silicon and coal tar pitch powders as raw materials. The SiC-SiOx NWs with sharp tips formed by solid-vapor between Si (s) and CO (g) or C (s) and SiO (g), liquid-vapor between Si (l) and CO (g), and vapor-vapor between SiO (g) and CO (g) growth process along the [111] direction. The NWs were several millimeters in length, and the average diameters of the chains and beads were 40–90 nm and 325 nm, respectively. The obtained NWs had good blue-green photoluminescence property owing to the stacking faults and amorphous SiOx. This novel CVD route is simple, low cost and suitable for large-scale production. [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]

Copyright of Silicone Material is the property of Silicone Material Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

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SiO2 gel/alumina-silica fibers composites were prepared by impregnation method. Silicon powder with different mass fractions of 0%, 0.2%, 0.4%, 0.6% and 0.8% was added in the slurry, and the effects of silicon powder on the microstructure, bulk density, compression-resilience ratio and phase compositions of the SiO2 gel/alumina-silica fiber composites were investigated. The results show that when the mass fraction of the silicon powder is lower than 0.6%, the volume expansion of silicon resulting from the silicon oxidation fills the cracks between fibers and gel, the volume density of the composites increases from 0.468g/cm3 to 0.723g/cm3, and the resilience ratios increase from 43.1% to 59.6%. Besides, it is found that the mechanical property is improved and the degree of high-temperature damage for the composites is decreased by the silicon crystallization, which restrains the fibers crystallization and facilitates the generation of pyroxene. However, when the mass fraction of silicon powder is 0.8%,the compression-resilience ratio of the composites significantly declines to 44.5%, which is attributed to the big cracks generated from the excessive volume expansion of silicon powder at high temperature.

Copyright of Silicone Material is the property of Silicone Material Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

[Display omitted] • Closely packed silicon powder very facilely fabricated by pressing without sintering. • High ZT value, 0.112, potential for practical applications. • We propose an alternative TE materials designing architecture. We report TE properties of mesostructured closely packed silicon powder facilely fabricated by die-pressing without sintering. Seebeck coefficient of Si-FeSi 2 (13 wt% FeSi 2) composite powder was between 100 ∼ 148 μV/K, with maximum power factor (PF) ∼ 0.164 mW/m⋅K2 at 400 K (pure Si powder ∼ 0.03 mW/m⋅K2). Boosted by the very low thermal conductivity (0.58 W·m−1·K−1), the dimensionless figure of merit, ZT value of Si-FeSi 2 composite powder, ∼ 0.112, was obtained at 400 K, which is about 10 times higher than that of the bulk Si. [ABSTRACT FROM AUTHOR]

We successfully achieved the continuous melting of silicon powder in a vacuum electron beam melting system. The characteristic of electron beam melting of silicon powder was revealed by comparing the three different approaches to prefabricate the molten silicon pool. The application of silicon block can be regarded as the most efficient method to prefabricate a stable molten silicon pool. Afterward, the silicon powder was added into the molten silicon pool at different rates by a spiral silicon powder feeding device. Finally, all of the silicon powder was melted completely. Although the P removal efficiency decreases with increasing powder feeding rate during the powder feeding process, an appropriate increase in the powder feeding rate is not only beneficial to improve the melting efficiency of silicon powder but also conductive to the improvement in uniformity of the obtained silicon ingot. Therefore, the powder feeding rate of 10 g/min was the best option in this study. Compared with the melting of silicon block, which has been wildly applied, this continuous powder feeding process can be beneficial to saving smelting time and the total cost. [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]

With the rapid development of construction industry, improve the strength of concrete is the most common concern problem in today's civil construction circles of all countries in the world. The studies on the durability of the concrete with the mixture of silica powder are carried out. The results show that the concrete produced by using silica powder has very nice durability. All results show that the performance of the concrete with mixture of silica powder is higher than the standard concrete, and is increased significantly. This paper expounds origin and mechanism of concrete of freezing and thawing destroy. The test result validates that silicon powder have great impact on concrete frost resistance. [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]

We present the real and imaginary part of the dielectric permittivity of natural zeolite composites prepared by using zeolite and silicon powders. The dielectric response (DR) dependences on the frequency (3–300 GHz) of electric field and different Si concentrations (5–33%) are non-monotonic and a maximum peak is observed. This peak position is practically independent on the frequency and its maximum is observed in zeolite composites which included 9% of the Si-powder. Also the maximum peak is decreased by about an order of magnitude when frequency increases from 500 Hz to 5 kHz. Addition of the conductive Si-particles to zeolite-powder leads to two opposite effects. Firstly, the movement of electrons in the Si-particles provides increase of DR. Secondly, cations which leaving from zeolite pores can be neutralized by the particles of Si in the intercrystalline-space. Such a peculiar mechanism for recombination of Si electrons and cations from pores leads to a reduction of DR for large silicon concentrations. Due to the fact that the contribution of free carriers in the decreasing of the DR as the frequency increases, it is consistent with the suggestion that the maximum peak decreases with increasing frequency. [ABSTRACT FROM AUTHOR]

Alkali attack resistance of cement kiln refractories has become one of the key factors affecting their performance life. In this paper, the correlation between mean pore size, pore size distribution of bauxite–SiC composite refractories and their alkali attack resistance was investigated by means of mercury intrusion porosimetry, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Also, the percolation theory, as well as modeling prediction, was applied associated with thermodynamic calculations. The results showed that quartz phase was generated from the oxidation process of silicon filling in part of pores, which resulted in a significant decrease in both the mean pore size and permeability of the samples. The proposed alkali attack mechanism indicated that K 2 CO 3 was firstly reduced to K vapor and then infiltrated into the sample through the open pores. Consequently, the KAlSiO 4 phase was formed in the edge part of the samples. When the K vapor permeated into the center of the sample, the KAlSi 2 O 6 phase was first generated. Afterwards, the decomposition of KAlSi 2 O 6 in the K-rich atmosphere gave rise to the formation of quartz and KAlSiO 4 . The decrease of mean pore size and apparent porosity, especially the reduction of the proportion of large pores, helped to prevent the alkali vapor from infiltrating into the samples, bringing about a superior vapor attack resistance at high temperature. [ABSTRACT FROM AUTHOR]

The effect of sintering treatment on the amorphous silicon powders from monosilane pyrolysis was investigated to enhance polysilicon yield in the FBR-CVD process. The crystallite size, hydrogen bond structure and morphology of the powders were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Diffuse Reflection Fourier Transform Infrared Spectroscopy (DR-FT-IR) and Zeta Potential Analyzer (ZPA). The results showed that the higher sintering temperature and lower pressure were more favorable to the growth of silicon crystallites and the liberation of hydrogen from silicon hydrides. The crystallite size increased significantly with a critical low FWHM when the sintering temperature was at 750 °C, and the hydrogen releasing from polysilanes and OSiH took place remarkably with a relative flat IR spectrum when the vacuum condition was implemented. Moreover, the particle aggregation was strengthened with broad particle size distribution as long sintering duration or high temperature applied, and the fusion occurred as the temperature was high enough but still with good crystallinity. [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]