A Simple Way to Prepare Silicon Carbide Reinforced Graphite Composite Lubricating Materials

SiC reinforced graphite composites were prepared via introducing carbide silicon into the natural graphite flakes（NGF） by hot-pressing process. Their physical and mechanical properties, including density, open porosity, flexural strength, and friction behavior were investigated. The addition of 30vol% Si C increased the bending strength of composites materials to 127 MPa, 2 times higher than 60 MPa of commercial pure graphite block. What was particularly interesting was that the as-obtained graphite composite with 30vol% Si C kept the same low friction coefficient of about 0.1 as pure graphite, and the wear resistance of composites increased.

A New Method for the Ultra-smooth Machining of the Silicon Based Materials

A New method,named atmospheric pressure plasma polishing,for the ultra-smooth machining of the silicon based materials is introduced.By inputting the CF4 gas into the atmospheric pressure plasma flame,high density reactive radicals will be generated,which will then react with the silicon based materials.The reaction product is the vaporization of the SiF4,which can be easily processed.In this way,the atomic scale material removal can be realized and the defect free ultra-smooth surface can be obtained.An experimental setup is built up,and the SiC polishing experiment is carried out.The AFM test result shows that the finished surface roughness (Ra) can be improved from 4.529 nm to 0.926 nm in 3 minutes.

Performance of n-type silicon/silver composite anode material in lithium ion batteries: A study on effect of work function matching degree

In this paper, two types of silicon（Si） particles ball-milled from n-type Si wafers, respectively, with resistivity values of 1 Ω·cm and 0.001 Ω·cm are deposited with silver（Ag）. The Ag-deposited n-type 1-Ω·cm Si particles（nl-Ag） and Ag-deposited n-type 0.001-Ω·cm Si particles（n0.001-Ag） are separately used as an anode material to assemble coin cells,of which the electrochemical performances are investigated. For the matching of work function between n-type 1-Ω·cm Si（nl） and Ag, nl-Ag shows discharge specific capacity of up to 683 mAh·g^-1 at a current density of 8.4 A·g^-1, which is40% higher than that of n0.001-Ag. Furthermore, the resistivity of nl-Ag is lower than half that of n0.001-Ag. Due to the mismatch of work function between n-type 0.001-Ω·cm Si（n0.001） and Ag, the discharge specific capacity of n0.001-Ag is 250.2 mAh·g^-1 lower than that of nl-Ag after 100 cycles.

Effects of Al-Si Addition on Thermomechanical Properties of Low-carbon MgO-C Materials

Effects of Al- Si addition on hot modulus of rup- ture ~ HMOR） . thermal shock resistance ~ TSR~ . phase composition and mierostructure of low-carbon MgO - C materials were investigated. The results show that： Al and Si addition to low-carbon MgO - C materials leads to dramatic increase in MOR at elevated temperatures; it increases from 4 MPa to 11 -21 MPa at 1 200 ℃ and from 2 MPa to 21 -29 MPa at 1 400 ℃. Al and Si addition to low-carbon MgO - C materials also improves TSR： residual strength ratio after thermal shock when △T = 1 200 ℃ is increased,from 44% to 73% - 77%. Al reacts with C and N2 to form, Al4C3 and AlN, Si reacts with C to form SiC. Ultimately. in-situ formed non- oxides increase appreciably with temperature rising and are well interlaced in periclase skeleton structure at 1 300 -1 400 ℃. which is beneficial to thermomechanical properties.

Recent Development of Metal and Non-oxide Refractory Raw Materials in China

The refractory raw materials used in recent years were introduced,including metal and intermetallic compounds（ aluminum,silicon,ferrosilicon,etc.）,nonoxide raw materials（ Si3N4 and ferrosilicon nitride）.The developmental tendency of China＇s raw refractories in the future was also discussed.

Preparation and Characterization of CA-MA Eutectic/Silicon Dioxide Nanoscale Composite Phase Change Material from Water Glass via Sol-Gel Method

This work mainly involved the preparation of a nano-scale form-stable phase change material（PCM） consisting of capric and myristic acid（CA-MA） binary eutectic acting as thermal absorbing material and nano silicon dioxide（nano-SiO_2） serving as the supporting material. Industrial water glass for preparation of the nano silicon dioxide matrix and CA-MA eutectic mixture were compounded by single-step sol-gel method with the silane coupling agent. The morphology, chemical characterization and form stability property of the composite PCM were investigated by transmission electron microscopy（TEM）, scanning electron microscopy（SEM）, Fourier-transform infrared（FT-IR） spectroscopy and polarizing microscopy（POM）. It was indicated that the average diameter of the composite PCM particle ranged from 30-100 nm. The CA-MA eutectic was immobilized in the network pores constructed by the Si-O bonds so that the composite PCM was allowed no liquid leakage above the melting temperature of the CA-MA eutectic. Differential scanning calorimetry（DSC） and thermogravimetric analysis（TGA） measurement were conducted to investigate the thermal properties and stability of the composite PCM. From the measurement results, the mass fraction of the CA-MA eutectic in the composite PCM was about 40%. The phase change temperature and latent heat of the composite were determined to be 21.15 ℃ and 55.67 J/g, respectively. Meanwhile, thermal conductivity of the composite was measured to be 0.208 W·m^（-1）·K^（-1） by using the transient hot-wire method. The composite PCM was able to maintain the surrounding temperature close to its phase change temperature and behaved well in thermalregulated performance which was verified by the heat storage-release experiment. This kind of form-stable PCM was supposed to complete thermal insulation even temperature regulation by the dual effect of relatively low thermal conductivity and phase change thermal storage-release properties. So it can be formulated that the nanoscale CA-MA/SiO_2 composite PCM with the form-stable property, good thermal storage capacity and relatively low thermal conductivity can be applied for energy conservation as a kind of thermal functional material.

Photoluminescence Properties of Er-doped SiC Thin Film

Hydrogenated amorphous silicon carbide （a-SixC1-x：H） films were grown on Si substrate by plasma-enhanced chemical vapor deposition. Fixed flow rate of H2 and different flow ratio of SiHJCH4 were used. Er-doped a-SixC1-x ： H （a-SixC1-x-H ：Er） films were prepared by implanting Er into the a- Si,C1-x-H host materials followed by annealing at different temperatures. The structure properties of the films were characterized by X-ray photoelectron spectroscopy （XPS）, Raman spectra. infrared absorption Photoluminescence spectra （IR） and （PL） intensities depending on flow rates and annealing temperatures were studied. High annealing temperature is not favorable for PL because of C-surface segregation. It is shown that thermal quenching of this material is small by comparing the PL intensities of a-SixC1-x-H： Er at room temperature and low temperature.

Properties and Microstructure Evolution of Al_2O_3-Si Material Fired in Different Atmospheres

A1203-Si composite specimens were prepared using fused corundum, ultra-fine α-A1203 and Si powder as starting materials and resin as binder. Effects of sintering atmospheres on properties, phase composition and microstructure of specimens after firing at 1 500 ℃ were investigated. The results show that： （ 1 ） after .firing in oxidizing or weak oxidizing atmosphere, there is some Si in the specimens and some glass phases containing mullite form on specimen surface, the density and strength at room temperature are relatively high, but hot modulus of rupture and thermal shock resistance are relatively poor; （2） after firing in, weak reducing or reducing atmosphere, Si reacts completely with CO or N2forming whisk-phere, Si reacts completely with CO or N2forming whisk-er-like SiC, granular Si2N20 or 0＇-SiAION, and the er-like SiC, granular Si2N20 or O＇-SiMON, and the thermo-mechanical properties of specimens are enhanced;（3） after firing in nitrogen atmosphere, Si reacts completely with N2, CO or G forming wbisker-like SiC and columnar β-SiA10N crystals, the hot modulus of rupture and thermal shock resistance of specimens are enhanced noticeably.

Injection molding of ultra-fine Si_3N_4 powder for gas-pressure sintering

The ceramic injection molding technique was used in the gas-pressure sintering of ultra-fine Si3N4 powder. The feedstock＇s flowability, debinding rate, defect evolution, and microstructural evolution during production were explored. The results show that the solid volume loading of less than 50vol% and the surfactant mass fraction of 6wt% result in a perfect flowability of feedstock; this feedstock is suitable for injection molding. When the debinding time is 8 h at 40°C, approximately 50% of the wax can be solvent debinded. Defects detected during the preparation are traced to improper injection parameters, mold design, debinding parameters, residual stress, or inhomogeneous composition distribution in the green body. The bulk density, Vickers hardness, and fracture toughness of the gas-pressure-sintered Si3N4 ceramic reach 3.2 g/cm^3, 16.5 GPa, and 7.2 MPa·m^1/2, respectively.

Synthesis and characterization of Fe_3O_4@SiO_2 magnetic composite nanoparticles by a one-pot process

Fe3O4@SiO2 core–shell composite nanoparticles were successfully prepared by a one-pot process. Tetraethyl-orthosilicate was used as a surfactant to synthesize Fe3O4@SiO2 core–shell structures from prepared Fe3O4 nanoparticles. The properties of the Fe3O4 and Fe3O4@SiO2 composite nanoparticles were studied by X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. The prepared Fe3O4 particles were approximately 12 nm in size, and the thickness of the SiO2 coating was approximately 4 nm. The magnetic properties were studied by vibrating sample magnetometry. The results show that the maximum saturation magnetization of the Fe3O4@SiO2 powder（34.85 A·m^2·kg^–1） was markedly lower than that of the Fe3O4 powder（79.55 A·m^2·kg^–1）, which demonstrates that Fe3O4 was successfully wrapped by SiO2. The Fe3O4@SiO2 composite nanoparticles have broad prospects in biomedical applications; thus, our next study will apply them in magnetic resonance imaging.

Progress on the Structures and Functions of Aerogels

Aerogel materials possess a wide variety of excellent functions,hence a striking number of applications have developed for them.In this paper,we present a historic review of the aerogel materials,showing the main concepts,research methods,important scientific problems,formation mechanism,structure characteristics and essence of aerogel.More applications are evolving as the scientific and engineering community,which becomes familiar with the unusual and exceptional physical properties of aerogels.In addition,we also discuss the huge development potential and prospect of polysaccharide aerogels as the research trend in the future.

Investigations of a nanostructured FeMnSi shape memory alloy produced via severe plastic deformation

Low-cost iron-based shape memory alloys（SMAs） show great potential for engineering applications. The developments of new processing techniques have recently enabled the production of nanocrystalline materials with improved properties. These developments have opened avenues for newer applications for SMAs. The influence of severe plastic deformation induced by the high-speed high-pressure torsion（HSHPT） process on the microstructural evolution of an Fe–Mn–Si–Cr alloy was investigated. Transmission electron microscopic analysis of the alloy revealed the existence of nanoscale grains with an abundance of stacking faults. The high density of dislocations characteristic of severe plastic deformation was not observed in this alloy. X-ray diffraction studies revealed the presence of ε-martensite with an HCP crystal structure and γ-phase with an FCC structure.

A strong and reversible adhesive fibrillar surface based on an advanced composite with high strength and strong adhesion

A material-structure integrated design method is proposed in this paper,with which micropillar and microwedge arrayed surfaces are fabricated based on a novel nanoparticlereinforced silicone rubber composite(NRSRC)with high mechanical strength and strong surface adhesion.It is found that the micropillar-arrayed surface and the microwedgearrayed surface show a normal adhesive strength of 50.9 kPa and a shear adhesive strength of 137.3 kPa,respectively,which are much higher than those of previously reported adhesive surfaces made by pure soft polymers.Furthermore,the micro-wedgearrayed surface shows not only strong and stable adhe-sion on rough and smooth substrates but also an obvious anisotropy in the adhesion property.The latter consequently leads to an easy control of the attachment/detachment switch,which is evidenced by a mechanical gripper with a microwedged surface.Therefore,firmly picking up and easily releasing a heavy glass plate can be realized.All these results demonstrate the apparent advantages of the present compo-sitebased fibrillar surfaces in achieving reliable and reversible adhesion and should have promising applications for manufac-turing advanced adhesive devices,such as mechanical fixtures,portable climbing equipment and space robots.