Fine Si Powder Research Articles

Preparation of undecanoic acid-terminated Si particles from rice husks

Luminescent fine Si powder was prepared by an Mg reduction process of SiO2 particles extracted from rice husks. The surface of the powder was terminated by the hydrophilic molecules of undecanoic acid via the hydrosilylation process. After the hydrosilylation of the fine Si powder obtained from rice husks, surface termination by undecanoic acid was confirmed to suppress natural surface oxidation. Transmission electron microscopy observations of the rice husk fine Si powder showed that the Si nanoparticles have a crystalline structure. Room temperature photoluminescence in the wavelength range of 500–1000 nm was observed in the samples taken at each step of the process, and the stability of the luminescence properties was improved via undecanoic acid surface termination. The observation of wavelength dependent microsecond-order photoluminescence indicates that the photoluminescence was due to quantum size effects. On the basis of time-transient light transmittance of rice husk Si colloid, the surface termination of undecanoic acid improved the dispersibility of Si particles in distilled water. The production of luminescent rice husk Si colloid is effective for the preparation of luminescent bio labels and will lead to high value-added recycling of rice husks.

Recast layer mechanical properties of tool steel after electrical discharge machining with silicon powder in the dielectric

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.

Reaction of SiF4 with Al Metal

The reaction of SiF4 gas with aluminum (Al) was studied at temperatures ranging from room temperature to 1723 K (1450 °C). Although thermochemical estimates indicate that reactions throughout the temperature range should be thermodynamically favorable, we found that no reaction takes place appreciably until Al is heated to around 1473 K (1200 °C). The reaction products consist of fine powders of Si, Al, and AlF3. Some of the reaction products were transported away from the reaction zone by strong convection currents resulting from the exothermic reaction. Even at approximately 1673 K (1400 °C), the reaction rate is slow and a significant amount of Al remains unreacted. When NaF powders were used to line the graphite reactor, NaAlF4, AlF3, and Si powders were observed on the upper cooler walls of the reactor, and Si whiskers were formed just above the Al-Si alloy globule on the bottom of the crucible. We found evidence of the formation of AlF and SiF2 vapor species in the reaction zone, which then disproportionated along the cooler walls of the reactor, generating powders of Al and Si and regenerating condensable AlF3 and SiF4 gas, respectively.

Effects of Silicon Particle Size on the Morphology of Rod-Like Si<sub>3</sub>N<sub>4 </sub>Crystals Prepared by SHS Method

Silicon nitride whiskers or rod-like crystals have a wide range application due to its excellent mechanical properties and high temperature performance. Two different silicon powders with different size (mesh 200 and mesh 300, respectively) were chosen to prepare rod-like Si3N4 crystals by SHS method and the effects of silicon particle size on the morphology of rod-like Si3N4 crystals were investigated. The results indicate that rod-like Si3N4 crystals could be formed with either kind of silicon powders when no more than 9wt% extra Y2O3 was introduced, which could effectively promote the growth of rod-like Si3N4 crystals. The residual free silicon was detected when using coarse silicon powders, while the silicon could be reacted completely with nitrogen gas when using fine silicon powders. The morphology of samples with coarse Si powders as starting materials is more uniform and regular than that of fine Si powders samples. Fine silicon powders are not ideal candidates for forming uniform and regular rod-like Si3N4 crystals.

Densification of Reaction Bonded Silicon Nitride with the Addition of Fine Si Powder - Effects on the Sinterability and Mechanical Properties

The densification behavior and strength of sintered reaction bonded silicon nitrides (SRBSN) that contain Lu 2 O3-SiO 2 additives were improved by the addition of fine Si powder. Dense specimens (relative density: 99.5%) were obtained by gas-pressure sintering (GPS) at 1850oC through the addition of fine Si. In contrast, the densification of conventional specimens did not complete at 1950℃. The fine Si decreased the onset temperature of shrinkage and increased the shrinkage rate because the additive helped the compaction of green bodies and induced the formation of fine Si 3 N 4 particles after nitridation and sintering at and above 1600℃. The amount of residual SiO 2 within the specimens was not strongly affected by adding fine Si powder because most of the SiO 2 layer that had formed on the fine Si particles decomposed during nitridation. The maximum strength and fracture toughness of the specimens were 991 MPa and 8.0 MPa?m 1/2 , respectively.

Reaction hot-pressing and property-composition relationships of modified sialon – boron nitride hetero-modulus ceramics

Hetero-modulus ceramics (HMC) present the combination of a ceramic matrix with inclusions of a dispersed phase with considerably lower values of Young's modulus, resulting in a material with significantly advanced properties. Densified ′-Si6−xAlxOxN8−x based HMC materials, with various volume contents of low-modulus α-BN phase and modifiers such as TiN or ZrO2 in sialon matrix, were prepared by high-temperature reaction hot-pressing in nitrogen atmosphere. The pristine blend composition for reaction hot-pressing consisted of mixed fine powders of Si, Al, B, Ti nitrides and Al, Zr oxides. Statistical design of 25−2 fractional factorial and third-order simplex-grid types was used for the experimental studies to estimate the effects of some technological factors on the densification of hot-pressed products and the property-composition relationships of modified HMC materials.

SHS of α-Si3N4 from fine Si powders in the presence of blowing agents

Explored was the effect of blowing agent (NH4Cl + NH4F mixtures) on the SHS of α-Si3N4 from a mixture of fine Si powder and α-Si3N4 used as an inert diluent. A prerequisite for a maximal specific surface of resultant Si3N4 powder was found to be perfect homogenization of starting Si-Si3N4 mixtures.

Porous Silicon Nitride Ceramics Fabricated by Carbothermal Reduction-Reaction Bonding

Porous Si3N4 ceramics with a fibrous interlocking microstructure were synthesized directly by carbothermal reduction between SiO2 and carbon and reaction bonding of Si, in the N2 atmosphere. X-ray diffractometry analysis demonstrated that β-Si3N4 was the major phase. The influences of content and powder size of the Si on the microstructure and properties of the samples were investigated. Scanning electron microscope (SEM) analysis exhibited that rod-like β-Si3N4 grains were formed in the samples prepared by using the fine Si powder. With an increase in the Si content, the porosity decreased, and the flexural strength increased accordingly.

폐실리콘의 고에너지 밀링 과정에서 초기 입자 크기가 분말의 미세화에 미치는 효과

Silfine. Co., LTD, 374-2, Shinsuri, Eumbongmyeon, AsanCity, Chungnam, 336-862, Korea(Received May 7, 2010, Revised May 27, 2010, Accepted June 8, 2010)Abstract In this research, the optimal manufacturing conditions of fine Si powders from Si scrap were inves-tigated as a function of different initial powder size using the high-energy ball milling equipment, which producesthe fine powder by means of an ultra high-energy within a short duration. The morphological change of the pow-ders according to the milling time was observed by Scanning electron microscopy (SEM). With the increasingmilling time, the size of Si powder was decreased. In addition, more energy and stress for milling were requiredwith the decreasing initial powder size. The refinement of Si scrap was rapidly carried out at 10min ball millingtime. However, the refined powder started to agglomerate at 30 min milling time, while the powder size becameuniform at 60 min milling time.Keywords : Microstructure, High energy milling, Si, Silicon scrap, Refinement

Binder-Free Pellet Fabrication of Ultra-Fine Poly-Si Powder for Economical Production of Solar Grade Si Ingot

The consolidation process of ultra fine Si powders, generated as by-product during the decomposition process of silane gases, was systematically investigated for use as economical solar-grade feedstock. Si powder compacts were tried to fabricate by a consolidation process without a binding agent and then their density ratio and strength were evaluated. The Si powders in as-received state were not pure enough to be used alone as solar grade feedstock material. After the adequate chemical treatments, a sufficiently high purity above solar-grade was able to be achieved.

Processing and properties of sintered reaction-bonded silicon nitride with Y 2O 3–MgSiN 2: Effects of Si powder and Li 2O addition

The effects of Si powder and Li 2O addition on the processing, thermal conductivity and mechanical properties of sintered reaction-bonded silicon nitride (SRBSN) with Y 2O 3–MgSiN 2 sintering aids were studied. Addition of Li 2O provides a less-viscous liquid phase that results in a more uniform and finer pore structure in RBSN with the coarser Si powders, but the pore structure plays a less important role in the densification of RBSN. The thermal conductivity of SRBSN without porosity decreases with increased Al impurity content and also decreases with the Li 2O addition regardless of the Si purity. The impurest coarse Si powder produces the lowest thermal conductivity (93 W m −1 K −1) but the highest four-point bending strength (∼700 MPa) and a higher fracture toughness (∼10 MPa m 1/2). However, the purer fine Si powder produces the highest thermal conductivity (119 W m −1 K −1) and highest toughness (∼11 MPa m 1/2) but the lowest strength (∼500 MPa).

Erosive Wear Behavior of Reaction Sintered Si<sub>3</sub>N<sub>4</sub>-SiCp Composite Ceramic in Liquid-Solid Flow

Si3N4-SiCp composites were prepared using fine Si powders as the starting materials for Si3N4, and SiCp as the aggregates. The erosive wear behavior of reaction sintered Si3N4-SiCp composite ceramic was investigated in liquid-solid flow. The results display that the composite ceramic hold a better capability of erosive wear resistance than 92 Al2O3 ceramics. The SEM pictures of the worn surface indicate that the main erosive wear mechanism of the composite ceramic is coexistence of micro-cutting and chisel-cutting.

Solid-State Synthesis of Mg<SUB>2</SUB>Si from Mg-Si Mixture Powder

The influence of the raw powder characteristics and cold compaction on the solid-state synthesis of Mg2Si from elemental Mg–Si mixture powder has been examined by thermal analysis using DSC thermogram. The Mg2Si synthesis progresses at the lower temperature range when employing the fine Si powder, because of the increase in the contacting area between the Mg and Si particles. MgO film, covering the Mg powder surface, prevents the Mg2Si synthesis due to its thermal stability, however SiO2 surface film is not so effective because of the deoxidization by Mg during heating. Concerning the effect of the compaction pressure, when the hard Si particles are embedded in the Mg powder after compacting the mixture powder, the mechanical breakage of the thermally stable MgO surface film occurs. Therefore, the enlargement of the contacting clean area between the particles causes the progress of the Mg2Si synthesis at the lower temperature. Based on these results, the bulk mechanically alloyed Mg–Si composite powder, in which the fine Si particles are distributed uniformly in the Mg matrix, shows a decrease of the reaction temperature by 350 K compared to the mixture powder.

Ｍｇ２Ｓｉの固相合成に及ぼす粉体特性および圧粉条件の影響

The influence of the raw powder characteristics and compacting condition on the solid-state synthesis of Mg2Si from elemental Mg-Si mixture powder has been examined by thermal analysis using DSC thermogram. The Mg2Si synthesis progresses at the lower temperature range when employing the fine Mg powder, because of the increase in the contacting area between the Mg and Si particles. In employing fine Si powder, the endothermic heat due to the appearance of liquid phase of Mg at 920 K decreases remarkably. MgO film, covering the Mg powder surface, prevents the Mg2Si synthesis due to its thermal stability, however SiO2 surface film is not so effective because of the deoxidization by Mg during heating. Concerning the effect of the compaction pressure, when the hard Si particles are embedded in the Mg powder after compacting the mixture powder, the mechanical breakage of the thermally stable MgO surface film occurs. Therefore, the enlargement of the contacting clean area between Mg and Si particles causes the progress of the Mg2Si synthesis at the lower temperature.

Nitridation behaviour of silicon with clay and oxide additions: Rate and phase development

Samples pressed from fine powders of Si, Si + SiO 2, Si + kaolinite and Si + SiO 2 + Al 2O 3 were nitrided by both the nitrogen demand method and a constant rate of heating using a graphite resistance furnace at temperatures of 1100 to 1450 °C. The nitridation rate for different compositions and input parameters were determined by continuously monitoring the time, temperature and pressure within the furnace. By comparing the different compositions, the effect of impurities, silica and particle size on nitriding rate, phase composition and percent theoretical weight gain were determined. Compositions containing high purity additives were found to nitride at higher temperatures and to be more susceptible to weight loss during nitridation. The prime cause for low weight gains was determined to be volatilization of silicon out of the samples. Si 2N 2O O ′ Sialon was formed in all compositions containing the as-used additives and acted to retain the oxygen within the sample.