Adhesive and cohesive properties of nanostructured Zr02 coatings by the original Vickers Indentation Cracking technique

In order to characterize the adhesion of nanostructured plasma-sprayed Y₂O₃-ZrO₂ coatings presenting some geometrical specificities, it is here suggested to apply the Vickers Indentation Cracking (VIC) technique, which is capable of initiating a crack at the interface by performing the indentation test close to the interface within the substrate. This method renders it possible to overcome the difficulties concerning the characterization of the adhesion of nanostructured Y₂O₃-ZrO₂ (YSZ) coatings. It was suggested to calculate an adhesive stress parameter by employing two physical parameters, i.e., the critical load to initiate the crack and the indentation distance measured between the interface and the indent center. In addition, for the case of brittle coatings, the crack was found to deviate from the interface toward the coating. Under such conditions and on the basis of the critical point (given by the two parameters: load and indentation distance), a stress parameter representative of the cohesive properties of the coating was defined according to the crack deviation conditions.     

正辛基三乙氧基硅烷对白炭黑补强三元乙丙橡胶材料的影响

研究了正辛基三乙氧基硅烷、乙二醇对白炭黑填充三元乙丙橡胶的力学性能、硫化特性的影响,以及压缩蠕变特性与动态力学性能的影响。研究结果表明:添加正辛基三乙氧基硅烷可改善三元乙丙橡胶的蠕变性、降低压缩永久变形。随着硅烷用量的增加,三元乙丙橡胶的蠕变、压缩永久变形有所减小,在用量4~5份时效果较好。硅烷用量增加,使白炭黑填充三元乙丙橡胶的玻璃化转变温度上升、损耗因子增加。正辛基三乙氧基硅烷在EPDM/白炭黑中的效果优于KH-550和KH-792硅烷。     

Zn lactate as initiator of dl-lactide ring opening polymerization and comparison with Sn octoate

Summary Zn lactate, 3H₂O and dehydrated Zn lactate were used as initiator to polymerize DL-lactide under various conditions. It is shown that the latter does polymerize DL-lactide up to high molecular weight at a slower rate than Sn octoate. Zn lactate being formed when lactic acid is allowed to react with Zn metal, it is believed that the active species in Zn metal initiation is Zn lactate. Comparison was made of the two poly(DL-lactide) initiated with Zn metal and Sn octoate respectively and selected to have almost similar characteristics. It is shown that degradation characteristics of the two polymers are different, especially water uptake and rate of heterogeneous degradation. It is further shown that residual Sn concentrated within the matrix remnants whereas the content in Zn remained constant according to degradation controlled release.     

Crystalline oligomeric stereocomplex as an intermediate compound in racemic poly(DL-lactic acid) degradation

Hydrolytic degradation of intrinsically amorphous poly(DL -lactic acid) was re-examined in pH 7.4 isoosmolar phosphate buffer at 37°C. Size-exclusion chromatogarphy, X-ray scattering and differential scanning calorimetry were used to monitor molecular weight and morphology changes up to the ultimate degradation stage. It was found that heterogeneous degradation of poly(DL -lactic acid) yielded a crystalline residual material of low molecular weight. Comparison with a stereocomplex made of equimolar poly(L -lactic acid) and poly(D -lactic acid) showed that the poly(DL -lactic acid) degradation residue was actually an oligomeric stereocomplex. The formation of stereoregular oligomeric enantiomers agreed well with the predominantly isotactic structure of poly(DL -lactic acid) obtained by ring-opening polymerization of DL -lactide and argued in favour of the stereodependence of main chain ester bond cleavage.     

Synthesis and degradation of PLA-PCL-PLA triblock copolymer prepared by successive polymerization of ε-caprolactone and dl-lactide

A PLA-PCL-PLA triblock copolymer was synthesized by ring-opening polymerization of successively added ε-caprolactone and dl-lactide in the presence of ethylene glycol, using zinc powder as catalyst. The resulting copolymer was compression molded to yield circular films from which 10×10×0.4 mm³ square samples were cut. These samples were allowed to degrade in isoosmolar 0.13 M, pH 7.4 phosphate buffer at 37 °C. Various analytical techniques such as weighing, SEC, ¹H NMR, IR, DSC, X-ray, ESEM and CZE were used to monitor property changes during degradation such as water absorption, weight loss, molecular weight distribution, composition, bulk and surface morphologies, thermal behavior, and release of water-soluble oligomers into the aqueous phase. Comparison is made with a PCL homopolymer under similar ageing conditions. The presence of PLA sequences did not alter the ability of PCL segments to crystallize during degradation, in agreement with the microphase separation between PLA and PCL blocks. Large amounts of lactic acid-rich soluble degradation by-products were released into the solution between 18 and 25 weeks. Copolymer films cracked down under drying beyond 25 weeks' degradation, while the surface remained smooth. The copolymer exhibited faster degradation as compared with PCL homopolymer, a feature which is of great interest for temporary therapeutic applications.     

Optically active poly[thio-1-(N,N-diethylaminomethyl) ethylene]

Poly[thio-1-(N,N-diethylaminomethyl) ethylene] [poly(TDAE)] of different optical purities were prepared by stereoelective polymerization of racemic N,N-diethyl-N-(thiirane-2-ylmethyl) amine (TDAE) using a (1:1) $\text{ZnEt}{}_2\text{R}$ (?) 3,3-dimethyl 1,2-butanediol (R(?)DMBD) chiral initiator system. Optically enriched TDAE samples were isolated as residual monomers. These monomers were thermally polymerized to give optically active poly(TDAE) with randomly distributed R and S repeat units in various proportions. The configuration of the enantiomer preferentially incorporated into growing chains during the stereoelective polymerization was determined as R on the basis of the presence of a positive Cotton effect at 260 nm in the c.d. spectrum of residual monomers. This configuration agrees well with the known homosteric character of the $\text{ZnEt}{}_2\text{(?)}\text{DMBD}$ initiator system. ¹³C n.m.r. spectra of the different optically active poly(TDAE) samples and those of more or less stereoregular racemic ones were compared. It was found that the carbon atom of the main chain methine group is the only one which is stereosensitive. Observed triad effects were used to determine the degree of isotacticity of optically active poly(TDAE)s prepared by thermal polymerization of partly enriched monomers. The stereoelectivity of the initiator system and the optical activity of optically pure TDAE and poly(TDAE) were deduced. Side-chain nitrogen atoms did not show any competitive effect with sulphur atoms in the coordination process to the chiral initiator system.     

An A Priori Hot-Tearing Indicator Applied to Die-Cast Magnesium-Rare Earth Alloys

Hot-tearing susceptibility is an important consideration for alloy design. Based on a review of previous research, an a priori indicator for the prediction of an alloy’s hot-tearing susceptibility is proposed in this article and is applied to a range of magnesium-rare earth (RE)-based alloys. The indicator involves taking the integral over the solid fraction/temperature curve between the temperature when feeding becomes restricted (coherency) and that when a three-dimension network of solid is formed (coalescence). The hot-tearing propensity of Mg-RE alloys is found to vary greatly depending on which RE is primarily used, due to the difference in the solidification range. Mg-Nd alloys are the most susceptible to hot tearing, followed by Mg-Ce-based alloys, while Mg-La alloys show almost no hot tearing. The proposed indicator can be well applied to hot-tearing propensity of the Mg-RE alloys. It is expected that the indicator could be used as an estimation of the relative hot-tearing propensity in other alloy systems as well.     

飞机涂层材料美国军用规范MIL-PRF-85285D浅析

对飞机涂层材料美国军用规范MIL-PRF-85285D所引用的相关规范和标准、自身关键 技术指标以及测试方法等内容进行了简要的分析,并对该规范的技术特点以及该规范对飞机涂层材料配方设计的要求进行了探讨.     

城市综合公园更新中的文化保护策略探索——以威海环翠楼公园盆景园规划设计为例

城市综合公园具有社会、经济、文化和环境等多重功能,如何在保护与发展中取得双赢,成为城市综合公园在更新过程中面临的重要问题。威海环翠楼公园拥有深厚的历史文化底蕴。本文以环翠楼公园盆景园设计为例,探讨在新形势下的综合公园更新中的文化保护策略。     

A fully on-chip area-efficient CMOS low-dropout regulator with fast load regulation

Fully integrated voltage regulators with fast transient response and small area overhead are in high demand for on-chip power management in modern SoCs. A fully on-chip low-dropout regulator (LDO) comprised of multiple feedback loops to tackle fast load transients is proposed, designed and simulated in 90?nm CMOS technology. The LDO also adopts an active frequency compensation scheme that only needs a small amount of compensation capacitors to ensure stability. Simulation results show that, by the synergy of those loops, the LDO improves load regulation accuracy to 3???V/mA with a 1.2?V input and 1?V output. For a 100?mA load current step with the rise/fall time of 100?ps, the LDO achieves maximum output voltage drop and overshoot of less than 95?mV when loaded by a 600?pF decoupling capacitor and consumes an average bias current of 408???A. The LDO also features a magnitude notch in both its PSRR and output impedance that provides better suppression upon the spectral components of the supply ripple and the load variation around the notch frequency. Monte Carlo simulations are performed to show that the LDO is robust to process and temperature variations as well as device mismatches. The total area of the LDO excluding the decoupling capacitor is about 0.005?mm². Performance comparisons with existing solutions indicate significant improvements the proposed LDO achieves.