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In this experiment, silica sol was used as raw material, the mixture of ammonium chloride and ammonia was used as coagulant. After replacing the solvent with n-hexane, silica aerogel was obtained under the condition of normal pressure. The influence of sol pH and coagulating temperature on the gel time was studied. According to the SEM photographs, the influence of drying temperature from 30 °C to 60 °C on the microstructure of silica aerogel was analyzed. This study showed that when sol pH was 6.5, coagulating temperature was 80 °C and the concentration of ammonia was 0.4 mol/L, the gel time was the shortest. The average size of silica aerogel particles was 10-20 nm, the average size of apertures was 20-50 nm. When the drying temperature was 40 °C, the specific surface area was 402.41 m2/g, the pore volume was 2.33 cm3/g, the density was 0.18 g/cm3.

In this paper, using PCS and ZrB2 precursor as raw materials, we prepared Cf/SiC-ZrB2 composites by precursor infiltration and pyrolysis (PIP) process. We studied the solution of different solid content on the influence of porosity and weight gain，and also studied the effect of pressure and other conditions in the process of infiltration. The viscosity of the solution is tested with NDJ-8S digital rotational viscometer. We observed the microstructure of materials through the scanning electron microscope (SEM). The optimum technological parameter was determined by the experiment. The results showed that: a reasonable solution group in relation to the viscosity of the mixed solution，that is the main factor affecting on the performance of the impregnation; The method of vacuum and pressure impregnation can reduce the preparation period and improve material density rapidly. Under the experimental conditions, the best viscosity of the mixed solution is 54.8 mpa•s, the time of vacuum impregnation is 1.5h, and the optimum value of pressure impregnation is 7 MPa.

To improve the heat absorbed and scattered properties of quartz fiber tile, porous phenolic resin impregnated quartz fiber tile composite for ablator and thermal insulator was prepared by impregnating the quartz fiber tile with ethanol solution of phenolic resin, and then drying and cured. The phenolic resin impregnated quartz fiber tile ablative composite is a new heat protection composite material with lower density, lower heat conductivity and low mass ablation. It can be used as the widespread thermal protection system of the aero craft in the high heat flux, high temperature and extreme condition. The thermal property and ablation property of the composites were studied respectively. The ablation property of PICA was evaluated by the oxyacetylene ablation experiment. The microstructure morphology of specimen before and after ablation was viewed by SEM. The thermogravimetric analysis of the ablator was taken from room temperature to 800°C.

With the development of ultra high temperature rigid heat insulation materials in the space field, it is an important strategic significance to prepare and research insulation materials of 1500°C high temperature. In our paper, the material was achieved through the process of wet suction filter forming and high temperature heat treatment, during which the high temperature alumina fiber was used as main ingredient. The fiber binder directly influences the mechanical and thermal properties of the material, and our samples were prepared using boron carbide and silicon carbide (both), borosilicate glass, alumina sol and aluminum dihydrogen phosphate as binder, respectively. The results show that borosilicate glass was the best one. Coefficient of thermal conductivity at 1000°C, lift strength and plane direction compression strength (10% compression) of the high temperature material were 0.12 W/mK, 0.35 MPa, and 1.1 MPa, respectively.

Silicon carbide possess high performances such as high hardness and strength, oxidation and high temperature resistance, high thermal conductivity and low thermal expansion coefficient. Widely used methods of molding green body for sintered pressureless bonded silicon carbide comprise dry pressing molding and casting molding. The former fails in preparation of complex shapes, while those prepared by casting molding are prone to have defects such as nonuniformity of density and easy cracking. Gel-casting is a net-shape modeling technology caused by the polymerization of organic monomer (acrylamide). The green bodies molded by gel-casting have uniform structure, high density, high strength and machinability. In this study, gel casting molding and pressureless sintering were used to prepare silicon carbide. The effect of the parameters of gel casting and sintering on the microstructure of the obtained silicon carbide was examined

Mullite fiber-reinforced Al2O3-SiO2 aerogel composite was prepared through hybrid sol-gel process, vacuum pressure impregnation technology and ethanol supercritical drying technology using aluminum chloride hexahydrate (AlCl3·6H2O), tetraethoxysilane (TEOS) and mullite fiber as raw materials. The samples were characterized by XRD, SEM, BET, Hot Disk and Universal Testing Machine. The results showed that mullite fiber-reinforced Al2O3-SiO2 aerogel composite possessed excellent heat-insulation performance, high-temperature stability and mechanical property. The thermal conductivities of composite increased from 0.0186W/mK at 150°C to 0.1198W/mK at 1200°C. The surface area of Al2O3-SiO2 aerogel increased from 589m2/g at ambient temperature to 667m2/g at 600°C, and correspondingly the pore diameter increased from 21.47nm to 27.82nm. The phase of Al2O3-SiO2 aerogel was from boemite at ambient temperature to γ-Al2O3 at 600°C, and to mullite at 1200°C. The compressive strength was 1.8MPa, when the shape variables reached 10%, the tensile strength was 0.69MPa, the bending strength was 6.4MPa.

With the rapid development of advanced science and technology, the performance requirements of the PTFE fabric composite is rapidly increase. In this work, the dry friction tests of PTFE braided composites were carried out on high-speed Tribo-tester analysing the influence of different working conditions to the friction temperature and humidity in the measurement of friction characteristics experiments. Scanning electron microscopy (SEM) was utilized to examine composite microstructures and study modes of failure. Energy spectrometer analysis was also performed to study the wear surface and the ingredient of the debris in an effort to get the mechanism of the composites damage.

Continuous multi-filament boron nitride fibers have been prepared on a large scale using the melt drawn technique from a low-cost boracic acid. Boracic acid was heated to obtain the molten boric oxide in a melting tank. Molten boric oxide was melt spun in a conventional manner through an 200-tip bushing to produce a continuous multifilament yarn consisting of 200 filaments of boric oxide. Boric oxide fibers were nitrided in an ammonia and were annealed in an inert atmosphere while simultaneously subjecting the fibers to sufficient longitudinal tension as to at least prevent longitudinal shrinkage of the fibers. The resulting fibers, consisting essentially of boron nitride, were less than about 8 μm in diameter and greater than 500 m in length. It indicated that the boron nitride fibers has a sound mechanical function with tensile strength of 1.40 GPa. The continuous boron nitride fibers of high-performance were especially suitable for reinforcing plastic, ceramic or metal matrices in the preparation of fiber reinforced composites.

Cf/SiC composites were fabricated by chemical vapor infiltration with CH3SiCl3 as precursor and H2 as carrier gas. The carbon preform was noodled by continuous carbon fiber and network tires layer. The screws were processed with Cf/SiC composites by diamond tool. The mechanical properties of screws were studied in this paper. Results show that the tensile and double shear strength reach separately 128.15 Mpa and 58Mpa. The microstructure of fracture surfaces from tensile and shear test were analysized.

Zirconia fiber separator is one of the important materials of nickel-hydrogen battery .In this paper,we studied the factors affecting the properties of zirconia fiber separator used as nickel-hydrogen battery separator, which prepared by precursor process, including the precursor fibers,fibrous cloths,concentration of the precursor solution and the heating rate before 500oC.The results show that, because the gully structure copied the precursor fibers, as well as smaller diameter of the fiber has larger specific surface area, so the zirconia cloth has the higher absorption capacity and retention ability of alkal. In the same way as woven, the low fabric areal density is beneficial to the absorption ability. When the concentration of the precursor solution is 1.36g/ml, the properties of the zirconia fiber separator is the best. If the heating rate is too fast, will cause a decrease in performance of zirconia fiber separator. The diameter of the fibers in the zirconia fiber sepatator is about 4-5μm, the main phase of the separator is tetragonal zirconia.

A kind of new hollow silica microspheres were proposed in experiment, which are fabricatted by a fast hydrolysis and condensation of tetraethyl orthosilicate taking place around multi-lamellar octylamine vesicles. The morphology of the vesicles is then fixed by a quick gelation process, resulting in hollow organo-silica spheres. After the removal of the template by calcination, nanopores are formed in the hollow shells. The results show that the synthesized hollow silica microspheres have smooth surface and dispersed well£®There are bimodal nanopores in the hollow silica microspheres, with a diameter of 2.1 nm and 0.62nm for the mesopores and micropores respectively, giving a specific surface area of 1123m2/g and a pore volume of 0.6291mL/g£®

Cf/SiC-ZrB2 composites were fabricated by chemical vapor infiltration and precursor infiltration pyrolysis. Specimens were then tested for mechanical properties , thermo-physical properties and microstructure. Results show flexural strength, tensile strength and compressive strength reach 430MPa,120 MPa and 365 Mpa, respectively. The mechanical properties at high temperature were tested. And the fractograph and microstructure of composites were analysized.

To study the impacts of structural change of SiO2 aerogel on its insulating properties, the samples were treated in long time (0-12h) at 500°C, 600°C, 700°C and 800°C. The results show that with the time increased, the shrink extends in thickness, the weight loss and the density is basically unchanged under the 500°Cand 600°C. As for 700°C and 800°C, the results were treated with 0-12h, the shrink extends in thickness, the weight loss and density increases considerably. Besides, the structure and composition of SiO2 aerogel after the different temperature treaded with 0.5h were tested. The results show that when the heat treatment temperature is between 200-800°C, the small pores in SiO2 aerogel collapses and large pores increase, and the density is stil1 able to maintain the 1ow value due to the unbroken skeleton. When the heat temperature is between 800-1000°C, the secondary particle size increases and the rnutual integration of the secondary particles occurs, the density will be significantly increased.

Boron nitride(BN) fibres were synthesized by modified technique of Economy’s method. The products were characterized by X-ray diffraction (XRD), fourier transform infrared (FT-IR) absorption spectroscopy, field-emission scanning electron microscopy (FE-SEM), X-ray energy dispersive spectrum (EDS) and X-ray photoelectron spectroscopy (XPS). The results showed that BN fibers were mainly hexagonal boron nitride (h-BN) with diameters of 5-8 μm and the major compositions of BN fibers are B and N with a very small amount of O and C. At last, the chemical composition of samples were determined by the chemical analysis test method like GB/T 16555-2008 and GJB 507-1998.

ZrB2-20%volSiC ceramic composites with different volume of BN short fiber were fabricated by the hot-pressing sintering under 2000°C. The content of BN short fiber changed from 0 to 15vol%. The density, flexural strength, fracture toughness and thermal expansions coefficient were studied. The microstructures of the samples were observed by scanning electron microscopy. The results show that the introducing of BN short fiber into the ZrB2-20%volSiC lead to a serious of change to the mechanical properties of the ceramic. When the content of the BN short fiber is 10vol%, the flexural strength and fracture toughness reach 422.1MPa and 6.15 MPa•m 1/2 respectively. And the mechanism of the increasing toughness was studied.

The ZrB2-SiC composite ceramic was prepared using Al2O3 and Y2O3 as additives through pressureless sintering under 1800°C. The electrical and mechanical properties were studied with the different mass ratio of ZrB2 and SiC. The microstructure and phase transformation of the ZrB2-SiC composites ceramic were characterized by scanning electron microscopy. Results show that the densities of the samples are decreased with the decrease of the mass ratio of ZrB2 and SiC while the resistivities are increased. When the mass ratio of ZrB2 and SiC is 4 the resistivity reaches 14μΩ•mm while the density is 4.85g/cm3. When the mass ratio of ZrB2 and SiC is13:7, the flexural strength reaches the max value and toughness reaches the minimum value. The flexural strength reaches 233Mpa and the toughness reaches 4.51 Mpa• m 1/2. The changes of the properties of the ceramic were analyzed through the microstructure and the conduction mechanism was studied.

The hydrophobic aerogel heating-insulating composite ceramic was fabricated in the way of constant pressure. The properties of the ceramic were attributed through FT-IR and energy spectrum. The microstructure and phase transformation of the insulation composites ceramic was characterized by scanning electron microscopy. The results show that after compositing with aerogel the coefficient of heat conductivity of the heat-insulating ceramic decreases forty-sixty percent and the compressive strength increases a hundred percent. There is little change to the tensile-strength. The holes of the ceramic are full of aero gel particles whose grain size is ten-twenty μm and the distribution of pore size is ten-seventy nm. After heating at 400°C for 12 minutes by quartz lamp on the surface of the ceramic which the thick of it is 8mm, the temperature of the other side increases 10°C .When the thick of the ceramic is 16mm, the temperature of the other side remains unchanged. The ceramic has excellent heating-insulting property.

Stress gradient of a thin film along its thickness direction has important influence on performance of MEMS/NEMS devices. The measuring method based on curvature radius is a usual method for extracting film stress gradient. In this paper the error of the method has been analyzed using Finite Element Analysis software Coventorware, and the current theory has been modified according to FEA results to enhance its accuracy. Simulating results indicated that the accuracy of the method has been increased observably after correcting.

An oxidation kinetics model of hot-pressed ZrB2-SiC composites was established and then proved by experiments. The relationship between oxidation rate and temperature was attained by reaction activation energy and frequency factor at the different oxidation stages. Results showed that the relations between the oxidation gain of unit area and the oxidation time are linear, conic and parabolic, respectively, during the stage of the oxidation prophase, midterm and anaphase.