Kinetics and mechanism of ?-caprolactone and l,l-lactide polymerization coinitiated with zinc octoate or aluminum acetylacetonate: The next proofs for the general alkoxide mechanism and synthetic applications

Following our previous papers on mechanism of cyclic esters' polymerization coinitiated by tin(II) octoate [tin(II) bis-(2-ethylhexanoate), (Sn(Oct)₂)] in the presence of either the low molar mass coinitiator (an alcohol, hydroxy acid, or H₂O) or a macromolecule fitted with a hydroxy end group (ROH), the present work deals with ?-caprolactone (CL) and l,l-lactide (LA) polymerizations coinitiated with zinc octoate (Zn(Oct)₂) or aluminum acetylacetonate (Al(Acac)₃). A series of kinetic measurements revealed that similarly as in the Sn(Oct)₂ coinitiated process, these polymerizations proceed by simple monomer insertion into the …Mt-OR bond, reversibly formed in the reaction -Mt-L + ROH ? …-Mt-OR + LH (where Mt = Sn, Zn or Al; L = Oct or Acac), taking place throughout the whole polymerization process. MtL_n itself does not play an active role in the polymerization. Applicability of the commercially available Zn(Oct)₂ or Al(Acac)₃ for the aliphatic polyester (10³ ≤ M_n ≤ 4 × 10⁵) synthesis is also discussed.     

Effect of thermal insulation on microstructural homogeneity and onset temperature of flash sintered materials

The present work aimed to reduce the microstructure heterogeneity inherent to flash sintering by using alumina blankets as a thermal insulator around ZnO cylindrical samples during the sintering process, under different electric field conditions. Thermal insulation significantly reduced the flash onset temperature and the grain size heterogeneity. For higher electric fields, a temperature reduction as high as 480 °C was observed, which also led to lower densification. These findings were discussed in terms of changes in the heat loss dynamics coupled with the adsorbed water retention, both promoted by the applied thermal insulation. A model to estimate the temperature at stage III of flash sintering was proposed. The final temperature reached with thermal insulation did not differ significantly from the ones without it. Thus, thermal insulation could represent an alternative route to flash sinter materials with lower furnace temperatures with energy savings up to 78 % and a more homogeneous microstructure.     

La对ZA27合金组织,机械性能及摩擦磨损特性的影响

研究了Ｌａ对ＺＡ２７合金组织、常温机械性能的影响，并测定了ＺＡ２７（Ｌａ）合金的摩擦磨损特性。结果表明：Ｌａ可以细化合金初生ａ′相，改善共晶相的形貌与分布，提高合金的塑性和韧性指标；ＺＡ２７（Ｌａ）合金的摩擦磨损特性优于ＺＱＳｎ６－６－３     

烧结型钕铁硼电镀锌工艺研究

研究了不同前处理工艺对烧结型钕铁硼电镀锌层性能的影响，通过对镀层孔隙率、结合力、耐蚀性等性能的测试，确定了封孔、除油、除锈、活化、浸锌、电镀锌工艺，得到了光亮、孔隙率低、结合力和耐蚀性强的镀层。     

Effect of Fe-Zn alloy layer on the corrosion resistance of galvanized steel in chloride containing environments

In this study, the effect of Fe-Zn alloy layer that is formed during galvanizing process on the corrosion behavior of galvanized steel has been investigated. The galvanostatic dissolution of galvanized steel was carried out in 0.5 M NaCl solution to obtain the Fe-Zn alloy layer on the base steel. The alloy layer was characterized to be composed of FeZn₁₃, FeZn₇ and Fe₃Zn₁₀ intermetallic phases, which constitute the zeta, delta1 and gamma layers of galvanized steel, respectively. It was observed that the alloy layer has similar cathodic polarization behavior but different anodic polarization behavior compared to galvanized steel. The anodic current plateau of alloy layer was up to 100 times lower than that of galvanized coating. Corrosion test performed in wet-dry cyclic condition has shown that the alloy layer has lower corrosion rate as compared to galvanized steel. From the results of corrosion test of alloy layer and base steel, it was concluded that Zn²⁺ has positive effect on the protectiveness of the zinc corrosion products. The measurement of surface potential over the alloy/steel galvanic couple has confirmed the galvanic ability of alloy layer to protect both the alloy layer itself and the base iron during initial stage of atmospheric corrosion.     

硅锰稀土元素对铸态锌基合金组织性能的影响

采用正交组合回归设计实验方法，研究硅、锰元素对持态锌基合金力学性能的影响规律。结果表明，硅、锰元素对锌合金的室温硬度、100℃硬度、抗压强度和冲击韧性都有显著影响。适当控制硅、锰含量、并加入稀土元素进行变质处理，可得到具有较高强韧性的耐磨锌合金。     

Al、Cu含量对Zn-Al-Cu-Mg合金性能的影响

如何使铝铜含量良好匹配,是开发新型高性能Zn-Al-Cu-Mg模具合金的关键。研究了Al、Cu含量对Zn-Al-Cu-Mg模具合金力学性能和铸造流动性的影响。结果表明,铝含量从3%增加到14%,铜含量从3%增加到9%,合金力学性能明显增加,但铸造流动性下降。综合考虑各种因素,得出新型模具锌合金的建议成分w为：9%～11%Al,7%～9%Cu,0.04%～0.05%Mg。     

机械镀锌工艺在油箱体内表面的应用试验

采用机械镀锌工艺在热轧板焊接油箱内表面形成完整镀锌层，经中性盐雾腐蚀试验、耐油性试验、结合强度试验等检测表明，油箱内表面机械镀锌镀层完全合格。从而避免了传统电镀锌板直接焊接成型油箱内表面漏镀、焊缝及热影响区锌层烧损等缺陷。     

锌工业废渣次氧化锌的综合利用

我国冶金工业资源消耗高，二次资源利用率低，有相当大一部分可利用资源变成了污染物，炼锌工业废渣次氧化锌渣就是其中的一种。次氧化锌渣的主要成分是锌、铅、砷、锑、银、铟等元素的化合物。目前，从次氧化锌渣中综合回收铟、锑、砷、锌的工艺尚未成熟，在实际生产中的经济价值得不到体现；但随着近年来金属铟的使用范围不断扩大，需求量增长，导致市场紧俏，价格飚升，人们开始注重次氧化锌这种废渣资源。     

Preparation of self-healing protective films on a zinc electrode treated in a cerium(III) nitrate solution and modified with sodium phosphate and cerium(III) nitrate

Self-healing protective films were prepared on a zinc electrode previously treated in a Ce(NO₃)₃ solution by modification with Na₃PO₄ and Ce(NO₃)₃. The protective and self-healing abilities of the films were examined by polarization measurements and observation of pit formation after the electrode was scratched with a knife-edge crosswise and immersed in oxygenated 0.5 M NaCl at 30 °C for many hours. Mechanisms of the protective and self-healing activities were discussed using X-ray photoelectron spectroscopy and electron-probe microanalysis. The protective and self-healing abilities of the films prepared on the zinc electrode by treatment in the Ce(NO₃)₃ solution and modification with Na₃PO₄ plus Ca(NO₃)₂, Mg(NO₃)₂, Zn(NO₃)₂ or Ce(NO₃)₃ were summarized.