Influence of nano-SiC on microstructure and property of MAO coating formed on AZ91D magnesium alloy

Ceramic coating incorporated with nano-SiC was obtained on AZ91D magnesium alloy during MAO by adding nano-SiC into the silicate-aluminate-based composite electrolyte. The microstructure, thickness, phase analysis, element composition and hardness of the coatings were respectively investigated by scanning electron microscopy（SEM）, film thickness meter, X-ray diffraction （XRD）, energy disperse spectroscopy（EDS） and Vickers hardness tester. The wear resistance of Mg alloy and coatings were evaluated by friction and wear apparatus, while the corrosion resistance of Mg alloy and coatings were evaluated by potentiodynamic polarization test and electrochemical impedance spectroscopy （EIS）. The results show that after adding nano-SiC into the electrolyte, both the striking voltage and final voltage decrease, the size and number of the micropore on the surface of the coating decrease, the thickness and hardness of the coating increase, both the wear resistance and corrosion resistance of the coating raise.

Nano-SiC薄膜在太阳能电池窗口表面的应用

由于环境的污染使空气中有泥土,太阳能电池在户外使用一段时间后,其窗口表面就会附着一些灰尘颗粒影响其进光量,进而影响太阳能电池的光电转换效率。采用溶胶凝胶法制备并通过热烧结过程,将Nano-SiC透明薄膜制备在太阳能电池窗口表面。通过实验测试了表面制备不同厚度的Nano-SiC薄膜对太阳能电池I-V特性的影响。实验结果表明Nano-SiC薄膜具有很好的光子透过性和自洁能力,能够提高太阳能电池的光电转换效率。

45#钢表面Ni-P-nano-SiC复合化学镀层的制备

在优化设计的化学镀基础镀液中通过添加不同含量的纳米SiC颗粒,研究在45#钢表面制备具有纳米SiC颗粒增强的复合镀层及形成机理.利用SEM,XRD和显微硬度计等方法对实验样品的组织结构、形貌、显微硬度及其镀层形成机理进行了研究,结果表明:实验制备的Ni-P,Ni-P-SiC镀层镀态时硬度分别为572 HV,649 HV,热处理后其表面硬度在400℃时达到最大值1 045 HV和1 341 HV.纳米SiC颗粒在镀液中不参与化学反应,只是与化学反应所产生的Ni和P共同沉积在镀层中起到了复合强化的作用.Ni-P-nano-SiC镀层的生长机理是按层状方式生长,生长方向垂直于钢基体表面.纳米SiC提高了复合化学镀层的生长速度,促进了复合镀层以较薄的分层方式生长.

硅烷偶联剂改性CE／nano-SiC静态力学性能的研究

采用模塑成型法制备CE/nano-S iC复合材料,分别考察了3种偶联剂表面处理nano-S iC后对其静态力学性能的影响,用透射电子显微镜(TEM)表征了材料的微观结构和形貌特征。结果表明:3种偶联剂的改性效果次序为:KH-560<SCA-3<SEA-171;当nano-S iC含量为1.00%时,相对于纯CE的冲击强度和弯曲强度,SEA-171的提高率分别为95.06%和34.69%。

KH-560改性CE/nano-SiC复合材料的韧性和耐热性

采用模塑成型法制备CE/nano-SiC复合材料,通过冲击强度测试、TGA分析和DMA分析,发现偶联剂KH-560表面处理nano-SiC后,对其韧性和耐热性具有显著的协同改性作用。相对纯CE,经KH-560表面处理后的CE、1.00%nano-SiC复合材料,冲击强度提高86.26%;玻璃化转变温度提高16.71%;失重5%时,热分解温度提高17.25%;450℃时,质量保持率提高59.67%。

丝网印刷nano-SiC薄膜阴极的电子特性的研究

研究了低成本大面积丝网印刷在玻璃衬底上均匀的纳米碳化硅(nano-SiC)薄膜的场致发射特性。提出了机械分散团聚的nano-SiC的方法,实验了适合导电玻璃衬底上制备nano-SiC薄膜的浆料配方,摸索导电玻璃衬底上nano-SiC薄膜的烧结工艺,研究了不同nano-SiC含量的薄膜的场发射特性,得到了最佳场致发射特性的配方比例。对样品进行微观分析和表征。具有稳定均匀场致发射性能的nano-SiC薄膜可作为显示器器件的阴极材料。

退火处理对Nano-SiC-Al_2O_3/TiC纳米陶瓷复合材料性能的影响

研究了退火工艺对纳米陶瓷复合材料力学性能的影响。研究表明，纳米陶瓷复合材料在适当退火工艺下，其抗弯强度和硬度可以提高４０％ ～５０ ％ ，但断裂韧度略有下降。

CE/nano-SiC复合材料的制备及其改性研究

采用模塑成型法制备了CE(氰酸酯)/nano-SiC复合材料,通过弯曲强度测定、TGA(热失重分析)法和DMA(动态力学分析)法对复合材料的性能进行了分析。研究结果表明:nano-SiC经硅烷偶联剂(SCA-3)表面处理后,对复合材料的力学性能和耐热性具有明显的协同改性作用;当w(nano-SiC)=1%(相对纯CE质量而言)时,nano-SiC经SCA-3表面处理前后,相应复合材料的弯曲强度分别提高了20.84%和32.84%,玻璃化转变温度分别提高了13.09%和18.29%,失重5%时的热分解温度分别提高了12.31%和13.87%,450℃时的质量保持率分别提高了26.24%和42.99%。

Al_2O_3-Coated Nano-SiC Particles Reinforced Al_2O_3 Matrix Composites

Properties of Al2O3-coated nano-SiC have been compared with those of as-received SiC. The isoelectric point (IEP) of SiC changed from pH3.4 to pH7.3 after coating with the alumina precursor, which is close to that of alumina. Because both surfaces of coated SiC and AI2O3 possess higher positive charge at pH=4.5-5.0, they are uniformly dispersed in the two-phase aqueous suspensions, Then a mixed powder containing nano-SiC dispersed homogeneously into the Al2O3 matrix was achieved from flocculating the two-phase suspension. Finally, Al2O3/SiC nanocomposites were obtained by coating nano-SiC with Al2O3, in which the majority of SiC particles were located within the AI2O3 grains. The observation by transmission electron microscopy (TEM) and the analysis by the X-ray photoelectron spectroscopy (XPS) showed that cracks propagated towards the intragranular SiC rather than along grain boundaries.

Nano-SiC薄膜对太阳能电板转换效率影响的研究

采用丝网印刷法在太阳能电板超白玻璃表面制备出不同厚度的Nano-SiC薄膜,研究了Nano-SiC薄膜厚度对光子透过率和户外太阳能电板转换效率的影响。结果表明,经过两层Nano-SiC薄膜处理后,超白玻璃的平均光子透过率提高了12%左右;同时Nano-SiC薄膜可以降低户外太阳能电板转换效率的降低速率,经过两层Nano-SiC薄膜处理后太阳能电板的转换效率降低速率约为未处理时的0.3倍。

Nano-SiC reinforced Zn biocomposites prepared via laser melting:Microstructure,mechanical properties and biodegradability

Zn has been regarded as new kind of potential implant biomaterials due to the desirable biodegradability and good biocompatibility,but the low strength and ductility limit its application in bone repairs.In the present study,nano-SiC was incorporated into Zn matrix via laser melting,aiming to improve the mechanical performance.The microstructure analysis showed that nano-SiC distributed along Zn grain boundaries.During the laser rapid solidification,nano-SiC particles acted as the sites for heterogeneous nucleation,which resulted in the reduction of Zn grain size from 250μm to 15μm with 2 wt%SiC(Zn-2 SiC).Meanwhile,nano-SiC acted as a reinforcer by virtue of Orowan strengthening and dispersion strengthening.As a consequence,the nanocomposites showed maximal compressive yield strength(121.8±5.3 MPa)and high microhardness(72.24±3.01 HV),which were increased by 441%and 78%,respectively,compared with pure Zn.Moreover,fracture analysis indicated a more ductile fracture of the nanocomposites after the incorporation of nano-SiC In addition,the nanocomposites presented favorable biocompatibility and accelerated degradation caused by intergranular corrosion.These findings suggested that the nano-SiC reinforced Zn biocomposites may be the potential candidates for orthopedic implants.

Aging Behavior of Nano-SiC/2014Al Composite Fabricated by Powder Metallurgy and Hot Extrusion Techniques

The aging-hardening kinetics of powder metallurgy processed 2014Al alloy and its composite have been studied. The existence of n-SiC particulates leads to the increase of peak hardness. Interestingly, the aginghardening peak of the composite takes place at earlier time than that of the unreinforced alloy. Transmission electron microscopy（TEM） studies indicated that the major precipitation phases are Al_5Cu_2Mn_3 and θ′（Al_2Cu）. Besides, Ω phase appeared in both specimens at peak hardening condition, which has been rarely observed previously in aluminum metal matrix composites without Ag. Accelerated aging kinetics and increased peak hardness may be attributed to the higher dislocation density resulted from the mismatch of coefficients of thermal expansion between n-SiC and 2014Al matrix. The results are beneficial to fabricating high performance composites for the application in automobile field such as pistons, driveshaft tubes, brake rotors, bicycle frames, railroad brakes.

Effect of Nano-SiC and Nano-Si Doping on Critical Current Density of MgB_2

The discovery of superconductivity in magnesium diboride (MgB2) has opened up a new field in materials science research. It offers a possibility of a new class of high performance superconducting materials for practical applications because of the relatively low cost of fabrication, high critical current densities (Jc) and fields, large coherence length, absence of weak links, higher Tc(TC = 39K) compared with Nb3Sn and Nb-Ti alloys (two or four times that of Nb,,Sn and Nb-Ti alloys). However, the weak flux pinning in the magnetic field remains a major challenge. This paper reports the most interesting results on nanomaterial (SiC and Si) doping in magnesium diboride. The high density of nano-scale defects introduced by doping is responsible for the enhanced pinning. The fabrication method, critical current density, microstructures, flux pinning and cost for magnesium diboride bulks, wires and tapes are also discussed. It is believed that high performance SiC doped MgB2 will have a great potential for many practical applications at 5K to 25K up to 5T.

Effect of Gr Content and Hot Extrusion on Tensile Properties of(Nano-SiCp+Gr)/Cu Composites Fabricated by Powder Metallurgy

Novel hybrid Cu matrix composites reinforced by graphite(Gr) particle with volume fraction of 5%- 15%and nano-SiC particle(nano-SiCp) with volume fraction of 3%have been prepared by powder metallurgy.The results show that Gr and nano-SiCp distribute uniformly in the Cu matrix.With increasing the volume fraction of Gr,the tensile strength of the composites decreases from 114 to 51 MPa and the elastic modulus decreases from 75 to 60 GPa.Compared with the sintered composites,the tensile properties including elastic modulus,tensile strength,yield strength and tensile elongation of the hot-extruded(nano-SiCp+Gr)/Cu composites are improved greatly due to higher relative density of the composites and more uniform distribution of Gr and nano-SiCp,in addition to finer grain size of the matrix as a result of dynamic recovery and recrystallization which occur during hot extrusion process.

Synthesis of Nano-sized Yttria via a Sol-Gel Process Based on Hydrated Yttrium Nitrate and Ethylene Glycol and Its Catalytic Performance for Thermal Decomposition of NH_4ClO_4

Nano-sized yttria particles were synthesized via a non-aqueous sol-gel process based on hydrated yttrium nitrate and ethylene glycol. The effects of the molar ratio of ethylene glycol to yttrium ion and calcination temperature on crystallite size of the products were studied. The catalytic performance of the as-prepared yttria for the ammonium perchlorate （AP） decomposition was investigated by differential scanning calorimetry （DSC）. The results indicate that the nano-sized cubic yttria particles with less than 20 nm in average crystallite size can be obtained after 2 h reflux at 70℃, dried at 90 ℃, forming xerogel, and followed by annealing of xerogel for 2 h, and that the addition of the nano-sized yttria to AP incorporates two small exothermic peaks of AP in the temperature ranges of 310 - 350 ℃ and 400 - 470 ℃ into a strong exothermic peak of AP and increases the apparent decomposition heat from 515 to over 1110 J·g^- 1. It is also clear that the temperature of AP decomposition exothermic peak decreases and the apparent decomposition heat of AP increases with the increase of the amount of nano-sized yttria. The fact that the addition of the 5 % nano-sized yttria to AP decreases the temperature of AP exothermic peak to 337.7℃ by reduction of 114.6℃ and increases the apparent decomposition heat from 515 to 1240 J·g^-1, reveals that nano-sized yttria shows strong catalytic property for AP thermal decomposition.

NiMo/Al_2O_3 catalyst containing nano-sized zeolite Y for deep hydrodesulfurization and hydrodenitrogenation of diesel

Two mixed-matrix NiMo/Al2O3 catalysts containing nano-and micro-sized zeolite Y have been prepared to explore the size effect of zeolite Y particle on the hydrodesulfurization（HDS）and hydrodenitrogenation（HDN）activities of fluid catalytic cracking（FCC）diesel.They were characterized by SEM,BET,XRD,H2-TPR,NH3-TPD and HRTEM.The results show that the catalyst containing nano-sized zeolite Y possesses larger average pore diameter,higher pore volume,weaker and lesser acid sites,more easily reducible metal phases,shorter MoS2 slabs and more slab layers than the catalyst containing micro-sized zeolite Y.The catalysts were also evaluated with a high-pressure fixed-bed reactor using real FCC diesel as feed.The results display that the catalyst containing nano-sized zeolite Y bears higher HDS and HDN activities and exhibits higher relative rate constant for the removal of total sulfur or nitrogen than the one containing micro-sized zeolite.

GELCASTING OF NANO-SIZE Y-TZP

The green specimens of nano-size Y-TZP are formed by gelcasting method. Using polymer electrolytes NaPAA and NH_4PAA, we have studied the rheological properties of slurry.The optimum pH range is between 8 to 10. The proper amount of dispersant changes with the solid content.The rheological measurements of suspension containing NH_4PAA show lower viscosity.The theoretical green density has been calculated.

Kinetics and Mechanism of Decomposition of Nano-sized Calcium Carbonate under Non-isothermal Condition

Experiments on thermal decomposition of nano-sized calcium carbonate were carried out in a thermo-gravimetric analyzer under non-isothermal condition of different heating rates (5 to 20K·min-1). The Coats and Redfern's equation was used to determine the apparent activation energy and the pre-exponential factors. The mechanism of thermal decomposition was evaluated using the master plots, Coats and Redfern's equation and the kinetic compensation law. It was found that the thermal decomposition property of nano-sized calcium carbonate was different from that of bulk calcite. Nano-sized calcium carbonate began to decompose at 640℃, which was 180℃lower than the reported value for calcite. The experimental results of kinetics were compatible with the mechanism of one-dimensional phase boundary movement. The apparent activation energy of nano-sized calcium carbonate was estimated to be 151kJ·mol-1 while the literature value for normal calcite was approximately 200kJ·mol-1. The order of magnitude of pre-exponential factors was estimated to be 10~9 s-1.

Synthesis and Characterization of Nano-sized Boron Powder Prepared by Plasma Torch

Hydrogen thermal plasma jet was employed to prepare nano-sized boron powder with hydrogen reduction of BCI3. The maximum yield of nano-sized boron powders was about 50% with the operational conditions of H2/BCl3 of 4.5：1, total feed of 4.9 m3/h, and plasma power of 25 kW. The samples were analyzed by X-ray diffraction （XRD）, field emission scanning electron microscopy （FE-SEM）, and inductively coupled plasma - mass spectrometry （ICP-MS）, inductively coupled plasma - atomic emission spectrometry （ICP-AES）, inductive combustion infrared absorption （ICIA） and infrared thermal conductivity of oxygen and nitrogen analyzer （ITCA）. The results show that the boron powders have different crystal structures with higher dispersion and purity. The average diameter is about 50 nm, and the purity is 90.29% or so. This new technology can use simple process to produce high quality boron powders, and is feasible for industrial production.