Cao Liyun

Preparation and phase composition optimization of yttrium silicates/SiC multilayer coating coated carbon/carbon composites

In order to optimize the phase composition and improve the oxidation resistance of yttrium silicates coating, Y2SiO5-Y2Si2O7-Y4Si3O12 coatings with different phase composition were deposited on the surface of SiC pre-coated carbon/carbon (C/C) composites using a hydrothermal electrophoretic deposition process. The as-prepared multilayer coatings were characterized by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The influence of phase composition on the morphologies and anti-oxidation properties of the multicomposition yttrium silicates coatings were investigated. The phase composition of the coating was optimized. Results show that Y2SiO5/Y2Si2O7/Y4Si3O12 mass ratio has strong effect on the morphology and oxidation resistance of yttrium silicates coatings. It is found that a low thermal expansion coefficient (CTE) district existed in the Y2SiO5-Y2Si2O7-Y4Si3O12 ternary phase diagram. When the optimized phase composition of Y2SiO5/Y2Si2O7/Y4Si3O12 in the low CTE district reaches Y2SiO5 = 20.1 wt%, Y2Si2O7 = 8.3 wt%, and Y4Si3O12 = 71.6 wt%, dense and homogenous yttrium silicates coatings with perfect oxidation resistance are achieved. After 80 h oxidation in 1773 K, weight loss of the coated C/C composites is only 2.17 × 10−3 g.cm−2.

Effect of Processing Factors on Flexural Properties of Cf-HA/PMMA Composites

Short carbon fiber (Cf) reinforced nano-hydroxyapatite (HA)/poly(methyl methacrylate) (PMMA) matrix bio-composites were prepared by an in situ processing and solution co-mixing process. The influence of carbon fiber content, initiator dosage, and nano-HA mass fraction on the flexural properties of the composites were particularly investigated. The flexural strength and modulus were tested by universal testing machine. The flexural fracture surface morphologies were characterized using scanning electron microscope. Results reveal that the as-prepared Cf/HA-PMMA composites have excellent flexural properties. With the increase of carbon fiber content, benzoyl peroxide (BPO) dosage, HA mass fraction and reaction temperature, the flexural strength, and modulus of Cf-HA/PMMA composites first increase to a maximum and then decrease. The flexural strength and flexural modulus will reach the maximum value of 129.56 MPa and 4.47 GPa when carbon fiber mass content, BPO dosage, and HA mass content arrive at 4, 1.6, and 8 wt%, respectively and reaction temperature is 80°C.Short carbon fiber (Cf) reinforced nano-hydroxyapatite (HA)/poly(methyl methacrylate) (PMMA) matrix bio-composites were prepared by an in situ processing and solution co-mixing process. The influence of carbon fiber content, initiator dosage, and nano-HA mass fraction on the flexural properties of the composites were particularly investigated. The flexural strength and modulus were tested by universal testing machine. The flexural fracture surface morphologies were characterized using scanning electron microscope. Results reveal that the as-prepared Cf/HA-PMMA composites have excellent flexural properties. With the increase of carbon fiber content, benzoyl peroxide (BPO) dosage, HA mass fraction and reaction temperature, the flexural strength, and modulus of Cf-HA/PMMA composites first increase to a maximum and then decrease. The flexural strength and flexural modulus will reach the maximum value of 129.56 MPa and 4.47 GPa when carbon fiber mass content, BPO dosage, and HA mass content arrive at 4, 1.6, a...

Structure and oxidation behavior of a plasma sprayed yttrium silicates coated SiC-C/C with a glass outer sealant from 1 573K to 1 873K

Different compositions of yttrium silicates coatings were deposited on SiC-C/C by plasma spraying and an outer borosilicate glass was applied on the yttrium silicates coatings surfaces. The structure of the multi-layer coatings was characterized by XRD and SEM analyses. High temperature oxidation behavior of the multi-layer coatings coated C/C composites was investigated. Results show that SiC/2SiO2·Y2O3/1.5SiO2·Y2O3/ SiO2·Y2O3/glass multi-layer coating has better high temperature oxidation resistance, protecting carbon/ carbon composites from oxidation at 1 773 K in air for 164 h with the weight loss of 1.65%. The oxidation weight loss of the coated C/C with time accorded with parabolic rule in the temperature range 1 573 K–1 873 K; and the corresponding oxidation activation energy of the coated carbon/carbon composites is 132.2 kJ/mol.

Effect of particle size on anti-oxidation property of mullite coating prepared by pulse arc discharge deposition

Mullite coatings with different particle sizes were prepared on carbon/carbon (C/C)–SiC composites surface by pulse arc discharge deposition (PADD). Phase compositions and microstructures of the as-prepared mullite coatings were characterized by XRD and SEM. The influence of particle size on the microstructures and oxidation resistance of the as-coated samples were investigated. Results indicate that the dense and homogeneous mullite coating was achieved when the size of mullite powder is about 1 μm, which could effectively protect C/C composites from oxidation at 1773 K in air for 156 h with a mass loss of 1.98%.

棒状ZnWO 4 纳米晶的合成及其光催化性能

以Na 2 WO 4 ·2H 2 O和Zn(COOCH 3 ) 2 ·2H 2 O为原料, 采用微波水热法, 制备具有光催化性能的黑钨矿型棒状ZnWO 4 纳米晶. 利用X射线衍射仪(XRD)、透射电子显微镜(TEM)、紫外–可见吸收光谱仪(UV-Vis)和光致发光谱仪(PL)分别对产物的物相、形貌和光学性能进行了表征. 结果表明: 采用微波水热法, 产物沿(100)晶面取向生长为棒状结构; 对其光学性能和光催化性能的研究显示, 所制备的ZnWO 4 具有蓝光发光特性, 其激发峰和发射峰分别为295和460 nm, 其还具有较强的紫外吸收特性; 棒长约为50~60 nm, (100)取向度为0.24的ZnWO 4 纳米晶具有最佳的光催化性能.以Na 2 WO 4 ·2H 2 O和Zn(COOCH 3 ) 2 ·2H 2 O为原料, 采用微波水热法, 制备具有光催化性能的黑钨矿型棒状ZnWO 4 纳米晶. 利用X射线衍射仪(XRD)、透射电子显微镜(TEM)、紫外–可见吸收光谱仪(UV-Vis)和光致发光谱仪(PL)分别对产物的物相、形貌和光学性能进行了表征. 结果表明: 采用微波水热法, 产物沿(100)晶面取向生长为棒状结构; 对其光学性能和光催化性能的研究显示, 所制备的ZnWO 4 具有蓝光发光特性, 其激发峰和发射峰分别为295和460 nm, 其还具有较强的紫外吸收特性; 棒长约为50~60 nm, (100)取向度为0.24的ZnWO 4 纳米晶具有最佳的光催化性能.

Synthesis Of Nanometer LiNiVO4 By A Wet Chemical Process Under Ultrasonic Irradiation

Experimental Analytical grade NH4 VOy LiCI2, NiCl2 and NH2CONH2 were selected for use in this work. A tool for irradiating ultrasound was an available commercial device (ultrasonic irradiator, Jiu Zhou, China) with a variable power of l00-300W. The sonic horn was made ofTi (tip diameter x length = <l>lOmmx 70mm) was driven by a PZT transducer. Firstly, NH4V03, LiCl2 and NiCl2 were weighed and mixed according to the mol ratio of Li/NiN= 1/1/1. The mixtures were dissolved in distilled water to form a homogenous solution. During the solution process, the solution was heated and maintained at 40°C. Then the NH2CONH2 was added into the solution under vigorous stirring to make a homogenous sol. The concentration of [Li+] and [NH2CONH2] in the solution was controlled at 0.664mol/L and 3.32mol/L respectively. During this process, the sonic horn was dipped into the solution around IOmm distance from the bottom of the flask and the ultrasonic sonic power and amplitude were adjusted to provide different power output of the generator (1oo-3OOW).After 6 hours reaction under ultrasonic irradiation, the sol was dry in 80°C for a sufficient time to make the sol into dry gel precursor. Next, the gel was dried at 100DCfor two hours and primrose yellow Li-Ni-V-O dry gel precursor was prepared. After that, the dry gel was heated slowly at 5°C/min up to 300-700°C in an electric furnace using alumina crucibles and maintained at the highest temperature for various times. After calcining, the powders were allowed to cool down to room temperature and ground up lightly with mortar and pestle. Finally, the powders were washed with de-ionized water 4 times to remove any dissoluble ion and then with alcohol twice to prevent the agglomeration of the particles. The as-prepared powders were characterized by X-ray diffractometry (XRD) using a high-resolution Seifert-FPM diffractometer operating with CuKa radiation at 40kV and 40mA, divergence slit of 1°, receiving slit width of 0.1 mm and a scan rate of 2°/min. Peak position and line width variation were controlled with the measurement of XRD lines of a standard silicon sample. The Debye-Scherrer equation, r = KAlBcosS, was used in order to determine the crystallite sizes of LiNiV04 along the (311) direction where; r is the crystallite size, K is a constant, Iv is the wavelength of the CuKu radiation and B is the line width of the XRD peak. Thermal studies of the gel precursor were carried out in air at a heating rate of IO°Cmin-L using a Simultaneous TG/DTA Thermal Analyzer, ranging from room temperature to 8000C (made by Dupont Company of USA). The crystallite morphologies of the samples were analyzed in a transmission electron microscope (TEM) operated at 200 kV.TEM specimens were prepared by depositing a few drops of LiNiV04 dispersed in acetone on a carbon-coated copper grid. 70 (I) (4)

Fabrication Of Samarium Monosulfide Thin Films By An Electrodeposition Process

Conclusions A new technique, called equal channel angular rolling (ECAR) was used to fabricate AZ31 magnesium alloy sheets. Compared with the as-received/annealed sheets the press formability of the AZ31 magnesium alloy sheets produced by this technique at room temperature was improved dramatically. This was seen to be very useful technique for application to the production of magnesium alloy structures.