Thermoelectric properties for P-type (Bi2Te3)0.2(Sb2Te3)0.8 alloys fabricated by shear extrusion

P-type (Bi₂Te₃)_0.2(Sb₂Te₃)_0.8 compounds were synthesized via bulk mechanical alloying (BMA), and subsequently prepared by a shear extrusion process in order to create the developed texture. The shear extrusion process improved the preferred orientation factor of the anisotropic crystallographic structure. It was found by an electron backscattered diffraction pattern (EBSP) analysis that approximately 90% of the crystallographic orientations for shear-extruded sample are aligned in the range deviated from 60° to 90° from the c-axis. The electric resistivity is well controlled at 1.008×10⁻⁵Ωm, which is nearly equal to that of the unidirectionally grown sample. The maximum figure of merit for the (Bi₂Te₃)_0.2(Sb₂Te₃)_0.8 alloy was found to be z=3.03×10⁻³K⁻¹. The bending strength of the material produced is also improved to 120 MPa, six times larger than that of the unidirectionally grown sample.     

CNTs在PVDF熔体中导电网络形成的动力学

将不同长径比碳纳米管填充PVDF复合材料进行等温热处理,实时监测电阻率随时间的变化,研究了碳纳米管在PVDF熔体中导电网络形成的动力学过程。结果表明,电阻率-时间曲线在达到某一临界时间时电阻率迅速下降,随着热处理温度的升高和MWNTs含量的增加,渗流时间减小。渗流时间与温度的Arrhenius关系曲线表明,碳纳米管长径比对其导电网络形成具有重大影响。提出了一个修正的热力学渗流模型预测碳纳米管填充PVDF体系的渗流时间。     

西红花酸对晚期糖化终产物诱导内皮细胞晚期糖基化终产物受体表达的抑制作用

目的: 研究西红花酸对晚期糖基化终产物(AGE)诱导牛内皮细胞(BEC)中晚期糖基化终产物受体(RAGE)mRNA表达的抑制作用,并探讨其可能机制。方法: 不同浓度的西红花酸(1、0.1、0.01 μmol/L)预孵BEC细胞12h后,用AGE(100 mg/L)刺激细胞12h,RT-PCR法测定RAGEmRNA的表达水平;ELISA法测定细胞间黏附分子-1(ICAM-1)的表达;试剂盒分别检测胞外超氧阴离子和硫代巴比妥酸反应产物(TBARS)浓度;同时,还用2,7-二氯荧光素(DCFH)测定了胞内H2O2的浓度,并用罗丹明123(Rh123)荧光法及MTT法分别检测细胞线粒体膜电位(MMP)水平和其琥珀酸脱氢酶(MSDH)的活性。结果: 与AGE模型组相比,西红花酸能显著抑制RAGEmRNA的表达(P<0.05),降低胞外超氧阴离子和TBARS(P<0.01或P<0.05)及胞内H2O2水平;结果还显示,西红花酸能提高细胞MMP水平和MSDH活性。对ICAM-1蛋白表达也有抑制作用,且呈时间和剂量依赖性。结论: 西红花酸可能通过清除AGE与RAGE结合产生的活性氧(ROS)来抑制RAGEmRNA的高表达。提示西红花酸对糖尿病血管病变有潜在的治疗价值。     

微波测量氢氧化铝水分新方法的研究

微波技术可用于测量各种材料的水分，本文详细地介绍了微波技术测定物料水分的原理、技术特点、产品特性及其使用方法。并对该技术在氩氧化铝生产中的应用作了展望。     

CrAlYCN/CrCN nanoscale multilayer PVD coatings deposited by the combined High Power Impulse Magnetron Sputtering/Unbalanced Magnetron Sputtering (HIPIMS/UBM) technology

CrAlYCN/CrCN coating combining high hardness (H_p = 36 GPa) and low friction coefficient (µ = 0.42 against Al₂O₃) has been developed for machining of Si containing Al-alloys. The coating was deposited by the combined High Power Impulse Magnetron Sputtering/Unbalanced Magnetron sputtering, (HIPIMS/UBM) technology. Macroparticle free Cr⁺ ion flux was generated by HIPIMS discharge to sputter clean the substrates prior to the coating deposition. The use of HIPIMS for surface pre treatment resulted in excellent adhesion, scratch test adhesion critical load value of Lc = 55 N on HSS and Lc = 68 N due to the local epitaxial growth and extremely smooth coating surface, Ra = 0.012 μm due to the elimination of growth defects.The coating crystallised in fcc structure with a preferred {220} orientation. XTEM analysis revealed a nanoscale multilayer structure of the coating with carbon segregated at the column boundaries but also vertically to form a lateral phase at the interfaces between the individual nanolayers.Addition of C to CrAlYN/CrN increased the chemical inertness between cutting tool and workpiece material without deteriorating the oxidation resistance of the coating. Thermo gravimetric analysis showed that the temperature for the onset of rapid oxidation was as high as 940 °C.In dry milling of AlSi9Cu1 alloy, CrAlYCN/CrCN coated 8 mm diameter cemented carbide end mills outperformed non coated end mills by factor of 2.5 with effective hindered built up edge formation mechanism.     

A new apparatus for finishing large size/large batch silicon nitride (Si3N4) balls for hybrid bearing applications by magnetic float polishing (MFP)

A new apparatus was designed and built for the finishing of large size/large batch silicon nitride (Si₃N₄) balls by magnetic float polishing (MFP) technology for hybrid bearing applications. The polishing chamber is so designed that during polishing it can self-align with the upper part of the polishing chamber connected to the spindle. In situ machining of the upper part of the chamber is performed on the machine tool in which the apparatus is located, in order to achieve high accuracy and geometric alignment of the system. The finishing methodology consists of mechanical polishing followed by chemo-mechanical polishing. Boron carbide (B₄C), silicon carbide (SiC), and cerium oxide (CeO₂) are the three abrasives used in this investigation. Three stages are involved in polishing, namely, 1. a roughing stage to remove maximum material without imparting any damage to the surface, 2. an intermediate stage of semi-finishing to control the size and improve sphericity, and 3. a final finishing stage to obtain best surface finish and sphericity while maintaining the final diameter. Taguchi method was applied for the roughing stage to optimize the polishing conditions for the best material removal rate. Level average response analysis has indicated that a load of 1.5 N/ball, an abrasive concentration of 20%, and a speed of 400 rpm would give a high material removal rate using B₄C (500 grit) abrasive. A groove is formed on the bevel of the upper part of the chamber which plays different roles, some beneficial and other not so beneficial, in each stage. In the roughing stage, it is preferable, though not essential, to machine the groove after each run to maintain high material removal rates. It is, however, necessary to remove the groove formed at the end of the roughing stage. In the intermediate or semifinishing stage, sphericity can be significantly improved by not machining the groove. Thus groove, in this case, facilitates in the improvement of sphericity. Before the beginning of the final finishing stage, machining the groove is necessary for rapid improvement in the surface finish. A batch of 46, 3/4 in. Si₃N₄ balls was finished to a final diameter of 0.7500 in. with an average sphericity of 0.25 μm (best value of 0.15 μm) and an average surface finish, Ra of 8 nm (best value of 6.7 nm) with an actual polishing time of <30 h. This technology is easy to implement in industry and does not entile high capital investment.     

Angular measurement of acoustic reflection coefficient for substrate materials and layered structures by V(z) technique

An experimental method to evaluate the acoustic reflection coefficient as a function of the incident angle R(θ) for substrate materials or layered structures is presented. By measuring the acoustic material signature V(z) using a highly focused acoustic lens or transducer at normal incidence, the reflection coefficient R(θ) can be reconstructed from the FFT of the complex V(z) signal (amplitude and phase of the echo). This technique has a great simplicity for the experimental procedure of R(θ) measurement. It overcomes the disadvantages of the conventional method where the finite-aperture plane beam reduces the angular precision and causes the unexpected non-specular reflection at critical incident angles. Results are given for different substrate materials, single plates and a three-layered bonded joint, and are compared to theoretical predictions.     

Functional inorganic films fabricated by PIII(-D) for surface modification of blood contacting biomaterials: Fabrication parameters, characteristics and antithrombotic properties

One of the important considerations of antithrombotic biomaterial improvement is to control the response of blood cells and plasma proteins to the materials. Material surface characteristics can be suggested as the important factors that influence the response of blood to materials. Thus, modifying the surface characteristics of a material becomes an important way to endue it with the antithrombotic function of preventing blood cell/plasma protein activation. This article is going to summarize results from previous studies on functional inorganic films coated with blood contacting biomaterials, including fabricating condition, characteristics and antithrombotic function. The functional inorganic films of Ti-O, a-C:N:H and Si-N synthesized using PIII-D on the surface of a biomaterial can endue it with the antithrombotic function of preventing platelet adhesion/activation. The characteristics of the films changed with alteration of the fabrication condition and influenced their antithrombotic function strongly. The in vitro test results showed that improved biomaterial surfaces with special antithrombotic function can be obtained from the optimization of the fabrication condition according to the understanding of the blood-materials interaction.     

Destabilization of LiBH4 by (Ce, La)(Cl, F)3 for hydrogen storage

The mixtures of LiBH₄ with halides of Ce or La in a molar ratio of 3:1 were investigated to explore their hydrogen storage properties. The ball milling of LiBH₄ with chloride of Ce or La yielded Ce(BH₄)₃ and La(BH₄)₃, while fluoride of Ce or La did not react with LiBH₄ during extended ball milling at room temperature. The dehydrogenation temperatures of the ball-milled mixtures were reduced to 220-320 °C, which were much lower than that of pure LiBH₄. The diborane emission during hydrogen release was observed at a low level. The dehydrogenation temperature is found to be affected by the composition of rare earth halides, but less influenced by ball milling time. The endothermic dehydrogenation reactions produced lithium halides, hydrides and borides of the corresponding rare earth element. Moreover, the LiBH₄ + 1/3(Ce, La)(Cl, F)₃ showed partial reversibility through the formation of an unknown borohydride, allowing for a potential hydrogen storage system.     

Improvement of the electrochemical performance of LiMn2O4 cathode active material by lithium borosilicate (LBS) surface coating for lithium-ion batteries

The LBS coating on the surface of spinel LiMn₂O₄ powder was carried out using the solid-state method, followed by heating at 425 °C for 5 h in air. The powder X-ray diffraction pattern of the LBS-coated spinel LiMn₂O₄ showed that the LBS coating medium was not incorporated in the spinel bulk structure. The SEM result showed that the LBS coating particles were homogeneously distributed on the surface of the LiMn₂O₄ powder particles. The effect of the lithium borosilicate (LBS) coating on the charge-discharge cycling performance of spinel powder (LiMn₂O₄) was studied in the range of 3.5-4.5 V at 1C. The electrochemical results showed that LBS-coated spinel exhibited a more stable cycle performance than bare spinel. The capacity retention of LBS-coated spinel was more than 93.3% after 70 cycles at room temperature, which was maintained at 71.6% after 70 cycles at 55 °C. The improvement of electrochemical performance may be attributed to suppression of Mn²⁺ dissolution into the electrolyte via the LBS glass layer.