Si Powder Research Articles

Enhanced thermoelectric performance of silicon powder arrays by remotely doping

We report improved thermoelectric (TE) properties of mesostructured silicon powder arrays simply prepared by die-pressing without sintering. In contrast to bromoethane's modest effect, the symmetric dibromoethane molecule coupling could significantly increase the conductivity of Si powder array TE device, from 12.7 S cm−1 of a silicon powder array to 62.3 S cm−1, which is possibly caused by the high electronic transmission probability of symmetric organic molecule–Si crystal coupling, and additionally enhanced by Si bandgap narrowing and defect states of an organic–inorganic interface identified by UV–vis absorption spectra and photoluminescence spectroscopy. Boosted by the very low thermal conductivity (0.58 W m−1 K−1), the dimensionless figure of merit, the ZT value of an Si powder array remotely doped by dibromoethane, ∼0.173, was obtained at 385 K, which is about 17 times higher than that of the bulk Si. An Si–organic hybrid TE device shows potentials to approach the threshold of practical applications with moderate ZT performance and low cost.

Microstructure and Mechanical Properties of Diamond–Ceramic Composites Fabricated via Reactive Spark Plasma Sintering

In order to prepare diamond composites with excellent mechanical properties under non-extreme conditions, in this study, a diamond–ceramic composite was successfully prepared via reactive spark plasma sintering using a diamond–Ti–Si powder mixture as the raw material. The microstructures and mechanical properties of the diamond–ceramic composite sintered at different temperatures were studied. When the sintering temperature was 1500 °C, the diamond–ceramic composite exhibited a volume density of 3.65 g/cm3, whereas the bending strength and fracture toughness were high at 366 MPa and 6.17 MPa·m1/2, respectively. In addition, variable-temperature sintering activated the chemical reaction at a higher temperature, whereas lowering the temperature prevented excessive graphitisation, which is conducive to optimising the microstructure and mechanical properties of the composite.

Selecting a target for obtaining films of higher manganese silicide using magnetron sputtering

A film of manganese silicides on mica was obtained using a magnetron sputter from three types of targets. Microstructure and elemental composition of targets and films studied by scanning electron microscopy and electron reflection diffraction methods. The phase composition and texture of films by thickness (cross sections) were controlled by scanning and transmission electron microscopy. It has been shown that when depositing films from a poly- and single-crystalline target of higher manganese silicide, in contrast to a target of sintered Mn and Si powders, after successive annealing at a temperature of 800 K and a temperature of 10–3 Pa for 1 hour, polycrystalline films of higher silicide can be obtained. manganese composition Mn4Si7.

A facile and effective strategy for modifying combustion of Zr/KClO4 via adding Si

As a commonly applied ignition composition, Zr/KClO4 has attracted various interests and plenty of efforts have been made to improve the combustion performance. In this study, Si nanoparticles were incorporated into Zr/KClO4 by sonication. Around 2.5× peak pressure and 9.2× reactivity were achieved by Si/50%Zr/KClO4 when compared to Zr/KClO4. In addition, the peak pressure and pressurization rate of Si/Zr/KClO4 ternary systems are all superior to ones of both Zr/KClO4 and Si/KClO4 binary systems. The synergetic effect of Si/Zr/KClO4 is a combination of shorter ignition delay of Zr/KClO4 and more gas production of Si/KClO4, which is also reflected on the higher flame propagation rate of Si/Zr-based thermites than composites with pure Si or Zr as the fuel. Meanwhile, the heat release during the redox reaction has been measured. The results show ∼700–1000 J/g higher energy release than Zr/KClO4, and higher combustion efficiency can be attained by ternary systems than binary ones. Thus, adding Si powders is an effective way to improve the energetic behavior of Zr/KClO4 ignition composition, and Si/Zr/KClO4 ternary composites can be a promising candidate for application in pyrotechnics.

Study on plasma modified silica powder epoxy resin composites

This work uses micrometer scale silicon powder as raw material, conducts plasma interface modification in a nitrogen atmosphere, and adds nitrogen elements to generate active groups such as amino groups on its surface to improve the dispersion of silicon powder, enhance the interface interaction between silicon powder and epoxy resin, and form Si–N bonds. To a certain extent, the absorption performance of silicon powder has been improved, which indicates the effectiveness of plasma modification of Si powder. The hardness of the modified composite material increased from 75.52 to 85.34 HA. Mechanical experiments have shown that the addition of 3% wt significantly improves the tensile strength of epoxy resin, increasing it from 16.47 to 22.67 Mpa. Further increase in dosage will lead to a decrease in tensile strength. After modification, the 3%, 5%, and 10% modified epoxy composite materials increased from 22.67, 9.94, and 5.67 Mpa before modification to 24.15, 14.52, and 12.75 Mpa, respectively. Using molecular dynamics simulation to verify the feasibility of plasma modification on epoxy composite materials, it was found that the simulation results were consistent with the experimental results, and the ultimate tensile strength of the modified composite materials was improved. The electrochemical impedance spectroscopy and salt spray test results show that the low-frequency impedance modulus of the composite coating modified by plasma interface is about one order of magnitude higher than that of the unmodified silicon powder composite coating. The coating containing 5 wt% plasma modified silicon powder exhibits the best corrosion resistance.

Fabrication of broadband wave-transparent porous Si3N4 ceramics by powder hybrid mechanism combined with binder jetting 3D technology

Binder jetting 3D printing is a novel methodology for fabricating broadband wave-transparent porous Si3N4 ceramics, but it faces challenges in low bending strength post-sintering, which impedes its broader application. This study proposed a hybrid mechanism by mixing Si and Si3N4 powders to surmount this challenge, and systematically scrutinized the mechanical and dielectric performance evolution of sintered samples at 1700–1800 °C after investigating nitride rules. Adding Si powder notably improved the bending strength, while retaining superior wave-transparent performance. When Si: Si3N4 was 50:50, at 1750 °C and 1800 °C, the bending strength was enhanced by 2.9 and 2.5 times compared to no Si powder addition. The real permittivity was consistently below 3.3. This work presented an effective methodology for modulating the overall performance of porous Si3N4 ceramics.

Preparation of silicon carbide reticulated porous ceramics with enhanced thermal shock resistance and high combustion efficiency

As the most prospective media material for porous media burners, silicon carbide reticulated porous ceramic (SiC RPC) is required to possess a high porosity to fulfill efficient combustion, as well as exceptional thermal shock resistance to withstand the thermal stress generated during the start-up and shutdown processes. To achieve the strengthening and toughening of highly porous SiC RPC, three-layered struts were constructed, and in-situ whiskers were formed in SiC RPC through vacuum infiltration and sintering under a nitrogen atmosphere in this work. The results indicated that the three-layered struts were formed after the preform was conducted with vacuum infiltration, encompassing a mullite coating, a silicon carbide layer and a mullite inner layer. When Si powder and flake graphite were incorporated into the SiC slurry, numerous SiC whiskers were formed in situ within the SiC skeleton. The formation of SiC whiskers was attributed to the enhancement of SiC RPC, resulting in an increase in CCS from 0.22 MPa to 0.55 MPa. Additionally, the residual strength retention rate after water quenching at 1100 °C was elevated from 41.6 % to 70.2 %. Moreover, the SiC RPC containing SiC whiskers exhibited an impressively high porosity of 83 %, leading to a surface temperature of 688 °C and a heating efficiency of 16.4 °C/min during the combustion process.

Experimental investigation on characterization of friction stir processed AZ31-based composite

Present study has been conducted to characterize the Mg alloy namely AZ31-based composite joined by Friction stir processing (FSP) technique. This study deals with the effect of single and double passes in FSP of AZ31 Mg alloy. The single pass run in FSP is followed at tool rotation speed (N) of 1000 to 1400 rpm. Also, the double pass run in FSP was followed at these speeds without using reinforcements. The feedstock particles namely SiC, Al2O3, Cr, and Si powders were used in fabrication process. The hardness, impact strength, and tensile strength characteristics were assessed in the stir region zone, and the results indicated significant improvement in these properties. The highest values of mechanical strength were seen in the FSPed area with N = 1000 rpm at a constant transverse speed (r) of 40 mm/min. Also, the tensile strength of the two passes FSPed plates is much higher than that of the single section without any reinforcement, as revealed in previous study also. The Scanning electron microscopy (SEM) analysis is done at two different magnifications for the Silicon carbide, Alumina, Chromium, and Silicon powder reinforced composites fabricated at speed of 1000 rpm. The microstructure shows that reinforced particles were uniform dispersed into FSPed region and agglomerated with Mg matrix. Si powder produces finer microstructure as compare to SiC, Al2O3, Cr. FSP decreases the grain size of processed material. Optical Microscopy results revealed that the reinforcement particle produced a homogenous microstructure and, a refined grain and equally dispersed in matrix material without split to the particle.

Smart Nanocomposite in the SiC-Si-Al-Al2O3-Geopolymer System

Goal-obtaining of composite in the SiC-Si-Al-Al2O3 (nanopowder)-geopolymer system with the metal-thermal method in the nitrogen medium. Method- In the present paper nanocomposite with SiALON was obtained through alum-thermal process in the nitrogen medium on the base of Geopolymer (kaolin and pology cley – Ukraine), SiC, alumina oxide nanopowder, aluminum nanopowder and Si powder with small additives of glas perlite (Aragatz, Armenia) by the reactive baking method. The advantage of this method is that compounds, which are newly formed thanks to interaction going on at thermal treatment: Si3N4, Si, AlN are active, which contributes to SiALON formation at relatively low temperature, at 1250-13000C. Results-ß-SiAlON was formed at the sintering of SiC-aluminium and silicium powder, geopolymer at 14500C. Porosity of carbide SiAlON composite obtained by reactive sintering, according to water absorption, equals to 13-15%. The samples were fragmented in a jaw-crusher and were powdered in attrition mill till micro-powder dispersion was obtained. Then samples were hot-pressed at 16200C under 30 MPa pressure. Hold-time at the final temperature was 8 min. Sample water absorption, according to porosity, was less than 0.4%. Further studies were continued on these samples. Conclusion-the paper offers processes of formation of SiC-SiAlON composites and their physical and technical properties. Phase composition of the composites was studied by X-ray diffraction method, while the structure was studied by the use of optic and electron microscope. Electric properties showed that the specimen A obtained by hot-compression is characterized by 2 signs lower resistance than the porous material B, which was used to receive this specimen. Probably this should be connected with transition of the reactively baked structure of the hot-compressed material into compact structure. Obtained materials are used in protecting jackets of thermo couples used for melted metal temperature measuring (18-20 measuring) and for constructions used for placing objects in factory furnaces.

Bimodal microstructural characterization of Si powder using X-ray diffraction: the role of peak shape

X-ray diffraction (XRD) characterization of Si powder was carried out using synchrotron and laboratory sources. Microstructural (size-strain) analyses of XRD patterns were carried out using the Rietveld refinement method. Experimentally observed super-Lorentzian shapes of the XRD peaks of Si powder were examined using multimodal profile fitting and bimodal model was found to be adequate. The two components obtained using a bimodal approach are referred as narrow and broad profiles based on their estimated relative peak widths. Peak shapes of crystallite size-dependent parts of narrow and broad profiles were found to be almost Gaussian and Lorentzian in nature, respectively. The simultaneous presence of such peak shapes corresponding to a bimodal microstructure is uncommon in literature. Therefore, in order to explore the role of different natures of XRD peak shapes (size dependent) of the bimodal profiles of Si, detailed microstructural analysis was carried out using the complementary method of whole powder pattern modeling (WPPM) and found to be related to the variance of crystallites' size distribution. Additionally, the effect of instrument resolution (laboratory and synchrotron sources) on the microstructural parameters was also studied. Scanning and transmission electron microscopy were used to characterize the morphology of Si powder and correlate with the microstructural findings of XRD methods.

Preparation of Si3N4 ceramic aerogel by foam-gelcasting combined concerted catalysis nitridation method

High-performance Si3N4 ceramic aerogel (CA) prepared by employing commercial Si powders containing impurity Fe as raw materials and Fe powders as catalyst through a simply Fe-concerted catalyzed nitridation technology, CS Si3N4 CAs, were synthesized at 1473 K for 5 h, and thoroughly characterized. It exhibited a porosity of 87.7 %, a compressive strength of 3.3 MPa and a specific strength of 8.7 MPa cm3 g−1, along with its outstanding low thermal conductivity (as low as 0.108 W m−1 K−1 at 373 K). Compared with the Si3N4 CA catalysis nitridation of concerted reactions by Fe(NO3)3·9H2O and in-situ catalytic nitridation by impurity Fe in commercial Si, and the specific strength of CS Si3N4 CA was about 14 % and 22 % higher than that of the former, respectively. This demonstrated that it may be more conducive to the preparation of Si3N4 CAs with high performance via catalysis nitridation of concerted reactions by Fe than Fe(NO3)3·9H2O. This work also provides an ideal method for the cost-effectiveness synthesis of high-performance Si3N4 and/or Si3N4 composites.

Depth-selective x-ray diffraction using energy-dispersive x-ray detector and straight capillary optics.

Depth-selective x-ray diffraction (XRD) technique was developed. In this technique, XRD spectra were measured using an energy dispersive (ED) x-ray detector at fixed angles. A straight capillary optic was used to define the incident x-ray beam, and a second straight capillary defined the beam path from the sample to detector. Thereby, only the XRD spectrum at the small intersection of two capillary optics could be obtained. A depth-selective XRD is possible by changing the sample position in depth. Many XRD peaks appear in a high-energy range more than 10keV in the ED spectrum. The detection of these peaks will be advantageous for depth analysis because of low absorption in the sample. Depth-selective measurement would be advantageous over general XRD. In this study, depth-selective and ED-XRD spectra are demonstrated for the layered sample, which consisted of film-like Si powder and a muscovite film.

Formation of skyrmion phase in the Fe–Co–Si system by mechanochemical activation

Fe, Co and Si powders were exposed to mechanochemical activation by high-energy ball milling for 0, 2, 4, 8 and 12 h. The samples were subsequently characterized by Mössbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflectance spectroscopy. The room temperature Mössbauer measurements were consistent with the occurrence of FeCo2Si and Fe0.5Co0.5Si crystalline phases. The low temperature Mössbauer spectra confirmed the absence of superparamagnetism up to 44 K in the milled system. XRPD patterns supported the phase sequence derived from Mössbauer spectroscopy. The coercive field was found to increase with the ball milling time (BMT). Zero-field-cooling-field-cooling (ZFC-FC) measurements performed at 200 Oe in the temperature range 5–300 K evidenced the transition to the skyrmion phase of the Fe0.5Co0.5Si material below the critical temperature of 44 K. The optical absorption in the UV–Vis–NIR region of the spectrum was found to increase with BMT.

Enhancing Charging Efficiency with Lithium Silicate in Silicon Composite Anode Materials Through Lithiothermic Reduction Reaction Synthesis

AbstractThis study synthesizes silicon (Si) powders with lithium silicates including lithium orthosilicate (Li4SiO4), lithium metasilicate (Li2SiO3), and lithium disilicate (Li2Si2O5), creating a composite structure of crystalline Si within a LixSiyOz matrix through the lithiothermic reduction reaction (LTRR) process. The reduction of Li‐ion consumption of the anode is investigated by 1) initial solid electrolyte interphase (SEI) layer formation, 2) SEI layer formation in response to Si expansion‐induced damage, 3) trapping of Li ions at Si defects, and 4) side reactions during initial charge and discharge cycles. Si/LixSiyOz electrode exhibits a specific capacity of 1522.2 mAh g−1 and an initial coulombic efficiency of 83.5%. The effect of the calendering process is observed, and a pressurization condition of 5000 kgf cm−2 or less is set, and the ICE is improved to 93.4%–96%. Si/LixSiyOz electrodes outperform pure crystalline Si electrodes in specific capacity (7.3%), ICE (42%), and retention characteristics (17%). The integration of the LixSiyOz matrix into Si anodes enhances Li‐ion transport and partially suppresses Si expansion. Additionally, the Si/LixSiyOz electrode exhibits superior rate capability in the 0.2–1.6 A g−1 range.

Flexible Janus Black Silicon Photothermal Conversion Membranes for Highly Efficient Solar-Driven Interfacial Water Purification.

Photothermal conversion materials are critical in the development of solar-driven interfacial evaporation techniques; however, achieving a high energy conversion efficiency remains challenging owing to the high cost and instability of light-absorbing materials, in addition to the difficulties of simultaneously improving light absorption while suppressing heat loss. A black silicon (Si) powder with a porous structure was prepared by chemical etching of a low-cost commercial micron-sized Al-Si alloy, and a flexible Janus black Si photothermal conversion membrane was constructed. The partially broken spherical particles and porous structure obtained after etching enhanced the refraction of light from the Si powder, imparting the prepared membrane with an average light absorption rate of 95.95% over the solar spectrum. Evaporation from the membrane increased the intermediate water content and reduced the equivalent evaporation enthalpy. The thermal conduction loss was inhibited through a one-dimensional water transport structure, and the membrane achieved a water evaporation rate of 2.17 kg m-2 h-1 and a photothermal efficiency of 94.95% under 1 sun illumination. Benefiting from the broadband absorption and high photothermal efficiency of black Si powder, surface modification of hydrophobic polydimethylsiloxane, and directional salt-out structure design, the evaporation rate of the Janus black Si membrane-based system in a 10% NaCl solution was maintained >2.10 kg m-2 h-1 after 7 days of continuous evaporation cycles. The removal rate of metal ions from simulated seawater and from practical wastewater containing complex heavy metals reached >99.9%, indicating the promising potential of black Si membrane for application in solar-driven interfacial water purification.

High performance and dense Si3N4 ceramic prepared by gelcasting combined with reaction re-sintering method

In this study, Si powder was used as raw material, Si3N4 powder as a diluent, Al2O3, MgO, Y2O3, and La2O3 as sintering additives to prepare Si3N4 ceramic with excellent properties using gelcasting and reaction re-sintering method. When the solid content of the slurry is 57.3 %, the viscosity is less than 1 Pa · s during the gelcasting process. After the reaction re-sintering, the sintered body of Si3N4 exhibited a bulk density of 3.15 ± 0.05 g/cm3, a relative density of 96 ± 1 %, open porosity of 5.7 %, bending strength of 610 ± 20 MPa, elastic modulus of 235 ± 10 GPa, thermal conductivity of 48 ± 5 W/(m·K), and a linear shrinkage rate of 12–13 %. These parameters indicate that Si3N4 ceramic possesses outstanding mechanical properties and thermal conductivity.

Inter-layer structures regulated by metallic Si powders in 3D printing of silica-based ceramic cores

3D printing is an excellent choice for manufacture of ceramic cores; however, the inter-layer structures in 3D printed sample leads to anisotropy in microstructure and properties. In this paper, silica-based ceramic cores were prepared by digital light processing, and metallic Si powder was employed as mineralizer to relieve the anisotropy. The metallic Si powder converts into SiO2 in oxidation reaction with significant volume expansion, which inhibits the shrinkage rate and partly fills the interlayer gaps of the ceramic core. Meanwhile, the metal Si powder leads to lower curing thickness in 3D printing, and thicken the interlayer gaps. Due to the cooperation of the oxidation reaction and decreased curing thickness by the metallic Si powder, the 0.4 wt% of metallic Si powder reduced the anisotropy in structure and mechanical property due to the alleviated inter-layer structure and the interlayer and intralayer strengths show optimal values of 11.4 MPa and 17.2 MPa at room temperature, respectively. This work inspires new guidance to 3D printing of ceramic cores with uniform microstructure and excellent mechanical properties.

Microstructure and properties of bilayered B4C-based composites prepared by hot-pressing

Bilayered B4C-based composites were prepared by hot-pressing method. One layer was a B4C ceramic layer using C and Ti powders as sintering assistants. The other layer was a B4C ductile layer named as BST layer, in which TiC, Si and Ti mixed powders were added to synthesize Ti3SiC2 phase to improve toughness of B4C. Although XRD results showed that no Ti3SiC2 was found in the BST layer, SEM and EDS analyses proved that trace amount of lamellar Ti3SiC2 structure was observed under high magnification fractographs in the BST layers with additive contents (x) equal to 30 and 40 wt%. Both the flexural strength and fracture toughness of the bilayered B4C-based composite increased with the increase in the amount of additions in the BST layer, reaching optimum values of 550 MPa and 6.6 MPa m1/2 at x = 40 wt%, respectively.

Microstructural development and oxidation resistance of MSi2-type multicomponent silicide coatings on Nb alloys by spark plasma sintering

MSi2-type multicomponent silicide coatings were prepared on Nb alloys by spark plasma sintering using mixed powders of Mo, Ta, W, Zr, Ti and Si. The coatings were composed of thick outer layers and thin inner layers (interdiffusion zone). A two-phase structure consisting of C11b (Mo,Ta,W,Ti)Si2 and C40 (Ti,Ta,Zr)Si2 was observed in the outer layers of all the coatings sintered for holding times ranging from 15 s to 5 min, but the distribution of these elements in each phase gradually became uniform with increasing holding time. The coatings demonstrated excellent protection during oxidation at 1300 °C for 100 h, and a continuous dense oxide scale mainly composed of ZrSiO4 and SiO2 was generated. The alternation of heating and cooling during oxidation caused cracks to appear at the interface between the outer layer and inner layer due to a mismatch of thermal expansion coefficients. However, crack extension was observed only along the inner layer toward the interior due to the multicomponent structure of the outer layer of the coating. The microstructural development and oxidation behavior of the coatings were discussed.

Macroencapsulated Al-Si phase change materials for high temperature latent thermal energy storage

This research investigated the encapsulation of Al-Si alloy phase change materials (PCMs) for efficient thermal storage at high temperature. Two strategies, the direct powder formation route and in situ powder alloying formation route, were employed successfully. In the direct powder formation route, Al-Si alloy powders were spheroidized into spheres and encapsulated within Al2O3 powder shells with the help of organic binder, which were finally sintered at high temperature, forming Al-Si@Al2O3 capsules with cavities. Isostatic pressing at 50 MPa and 200 MPa were applied to the Al-Si cores, in order to optimize the cavity size. In the in situ powder alloying formation route, Al and Si powders were used as raw materials, which could be in situ transferred to Al-Si alloy inside the capsule during the sintering formation process. With the powders as the raw materials, the final capsules obtained after sintering could provide a buffer cavity inside the capsules, which could accommodate the volumetric expansion of the PCMs during melting, thereby mitigating the potential leakage and rupture of the capsules. Investigations into the melting-solidification cycles revealed the remarkable durability of the Al-Si phase change capsules. Isostatic pressure treatment decreased internal ineffective cavities, improving the heat storage density of the capsules. The Al-12Si(Ar)-200 MPa capsule exhibited superior thermal storage performance, enduring up to 1300 cycles. The Al-12Si core had a melting enthalpy of 479 J/g, while the thermal storage density of the phase change capsule within the temperature range of 500 °C–700 °C reached 496 J/g. The results underscore the significant potential of macroencapsulated Al-Si PCM, positioning it as a promising candidate for high-temperature thermal storage applications.