Synthesis and reaction path of Ti-Al-C MAX phases by reaction with Ti-Al intermetallic compounds and TiC

In this study, it was verified that the synthesis of Ti-Al-C MAX phases has advantages when using intermetallic compounds rather than using only elemental powders. The formation behavior of the MAX phases was presented through diffusion experiments. In the case of using elemental powder, Ti₂AlC is produced at 1300°C, and Ti₃AlC₂ is produced at 1400°C. When intermetallic compounds are used, Ti₂AlC is produced at 1000°C, and Ti₃AlC₂ is produced at 1300°C. In the case of the elemental powder, it is verified that Ti₃AlC₂ content is decreased and Ti₂AlC is increased when heat treatment is performed at 1400°C for 3 h. Rather Ti₃AlC₂ content is increased when intermetallic compounds are used. When an intermetallic compound is used, synthesis occurs more actively at high temperatures, and the tendency to be thermally decomposed can be prevented. When TiAl and TiC are heat treated, Al of the intermetallic compound is diffused into TiC, and C of TiC is diffused into the intermetallic compound. Furthermore, there are many two-dimensional defects in TiAl, which act as a C diffusion channel. C diffuses into TiAl to produce TiC_X, and the MAX phases is generated by the short-range diffusion of Al. At the region of TiC, TiC transforms into TiC_X after C diffuses into TiAl, which consequently structure of TiC changes from cubic to hexagonal. This is the same crystal structure as the MAX phases, and it is confirmed that the (110) surface is maintained. A Ti-C layer structure of the (110) surface is maintained, and it was determined that Al is diffused during this time to generate the MAX phases.     

Realization of diversity in physical properties of Zr2Se(B1-xSex) MAX phases through DFT approach

The discovery of a series of MAX phases, Zr₂Se(B_1-xSe_x), with Se at both A- and X-sites, drives a new chemical diversity to the MAX family. Here, we employed the density functional theory (DFT) approach to realize the diversity in physical properties of Zr₂Se(B_1-xSe_x). All compositions of Zr₂Se(B_1-xSe_x) are mechanically stable and the dynamical stability of the end member Zr₂SeSe is confirmed. The elastic constant C₃₃ and bulk moduli B show a decrease almost monotonically with Se-content x while other constants and moduli change irregularly. All elastic constants and moduli except C₁₂ and C₁₃ are highest for the end member Zr₂SeB. Additionally, the Vickers hardness, Debye temperature, minimum thermal conductivity, and lattice thermal conductivity are highest for Zr₂SeB. The increase of Se-content x at X-site reduces most of the properties of Zr₂Se(B_1-xSe_x). The electronic band structures change drastically with increasing Se-content x. This diversity in electronic band structures is mainly the reason for the diversity in physical properties of Zr₂Se(B_1-xSe_x). All compositions of Zr₂Se(B_1-xSe_x) have the potential to be thermal barrier coating materials, and Zr₂SeB has the potential to be etched into 2D MXene, Zr₂B.     

Synthesis of low-oxygen Ti3AlC2 powders by hydrogenation–dehydrogenation and deoxidation from titanium scraps

The MAX phase is a material with excellent electrical and thermal conductivity and thermal shock and oxidation resistance owing to its metallike bonding properties. The impurities in the Ti₃AlC₂ MAX phase must be controlled because the oxides and TiC derived from the synthesis process remain in MXene and markedly affect the electrical conductivity and chemical stability. This study investigated whether the Ti₃AlC₂ MAX phase can be synthesized from titanium powder prepared from low-cost titanium scrap by hydrogenation–dehydrogenation (HDH) and deoxidation in the solid-state (DOSS) processes. Almost single-phase Ti₃AlC₂ MAX phase was obtained by synthesis at 1450°C for 5 h. The oxygen concentrations of the HDH-MAX and DOSS-MAX powders (25–45 μm) were 7215 and 3875 ppm, respectively. Oxygen reduction of titanium powder through DOSS can help improve the purity of Ti₃AlC₂ MAX phase by minimizing the imbalance in the stoichiometric ratio during synthesis. The HDH-MAX and DOSS-MAX powders prepared from titanium scrap displayed a higher Ti₃AlC₂ phase fraction and lower oxygen concentration than those of commercial Ti₃AlC₂ MAX phase powders. This cost reduction and purity improvement will increase the accessibility of the Ti₃AlC₂ MAX phase, supporting further research into its applications.     

Synthesis of new lead-containing MAX phases of Zr3PbC2 and Hf3PbC2

In this work, two new 312 MAX phases of Zr₃PbC₂ and Hf₃PbC₂ were successfully synthesized by spark plasma sintering. It is the first discovery of lead-containing 312 MAX phases, which together with M₂PbC (M = Ti, Zr, Hf) form the lead-containing MAX phase family. Considering the extremely low electrical conductivity of Hf₂PbC, these two new compounds are of great research value. Based on the Rietveld refinement results, their lattice parameters and atomic positions were well determined, as a = 3.3771(5) Å, c = 20.0070(9) Å for Zr₃PbC₂ and a = 3.3357(1) Å, c = 19.7659(8) Å for Hf₃PbC₂, where M atoms are located at (0, 0, 0) and (1/3, 2/3, 0.1258(6)[Zr]; 0.1255(2)[Hf]), Pb atoms are located at (0, 0, 1/4), and C atoms are located at (1/3, 2/3, 0.0663(2)[Zr]; 0.0641(3)[Hf]), respectively. Additionally, the typical laminar microstructure of Zr₃PbC₂ and Hf₃PbC₂ grains was observed.     

50%虎蛙等几种杀虫剂对稻纵卷叶螟的防治效果

田间试验示范结果表明:虎蛙EC对稻纵卷叶螟有良好的防治效果。2龄幼虫高峰期用80ml/667m2,药后3、7d杀虫效果分别为90.2%和94.1%,保叶效果分别为82.0%和87.7%,优于30%螟服EC70ml/667m2和40%三唑磷EC80ml/667m2。3龄幼虫高峰期用100ml/667m2,药后4、6d杀虫效果仍达80.1%以上。     

3-(2-对甲苯基苯并呋喃-3-基)环己-2-烯酮的合成

以N,N-二甲基甲酰胺作溶剂,2-对甲苯乙炔基苯酚和α-环己烯酮在氯化钯和四丁基碘化铵的作用下,可以顺利发生分子内环化反应一步合成3-(2-对甲苯基苯并呋喃-3-基)环己-2-烯酮。反应最佳条件为:n(2-对甲苯乙炔基苯酚)∶n(α-环己烯酮)∶n(氯化钯)∶n(四丁基碘化铵)=1∶5∶0.05∶1,反应温度为100℃,反应时间为24h,反应最佳产率82.0%。产物经1 H NMR、13 CNMR和GC-MS确征。     

离子液体催化氧化2,3,6-三甲基苯酚合成2,3,5-三甲基苯醌

研究了离子液体作为助催化剂催化氧化2,3,6-三甲基苯酚合成2,3,5-三甲基苯醌的反应。催化剂CuCl₂和MnCl₂的用量分别为2,3,6-三甲基苯酚物质的量的10%,助催化剂离子液体1-丁基-3-甲基咪唑四氟硼酸盐用量为2,3,6-三甲基苯酚物质的量的20%,空气中的氧气为氧化剂, 80 ℃反应4 h,转化率100%,选择性92.60%。在后处理过程中,离子液体易于分离和回收利用,为工业合成2,3,5-三甲基苯醌提供了一种较好的选择。     

行动导向教学在高职塑料模具1+N课程包中的应用探索与实践

行动导向是从德国职业教育中发展起来的一种有效教学方法。对目前高职塑料模具教育的现状进行了深入分析,提出了适合现代教育理念的行动导向教学模式,并对高职塑料模具课程进行了应用探索与实践,取得了一定的成效。     

DQ+T工艺在800MPa级高强钢开发中的研究与应用

本文以莱钢4300mm宽厚板生产线MULPIC冷却系统生产Q890D高强钢为研究对象,通过对DQ冷却策略、水处理系统、生产组织及水比参数等进行优化,成功开发出800MPa级高强高韧钢。检验结果表明,采用在线淬火+离线回火工艺生产Q890D钢板,其组织为回火马氏体和回火索氏体,钢板力学性能优良,组织、性能均匀性好。     

差分脉冲伏安法对生物冶金中铜(II)的在线检测(英文)

采用差分脉冲阳极伏安法实现生物冶金中铜(II)浓度的在线检测。结果表明,当体系中仅有铜(II)存在且其浓度范围为1μmol/L～1 mmol/L时,差分脉冲阳极伏安法所测阳极氧化峰电流与浓度间有很好的线性度。当此体系中含有0.2 mol/L KCl时,铜离子检测的线性范围从1 mmol/L(64 mg/L)扩展到100 mmol/L(6.4 g/L)。在此条件下,二价铜离子的还原分为两步连续的单电子转移过程,中间态为Cu+的络合物CuCl-。此外,在铜的生物冶金体系中,经常会有铁离子存在,因此对铜离子检测的铁离子干扰也进行了研究,结果表明,当铁离子浓度低于100 mmol/L(5.6 g/L)时,其对铜离子检测的干扰可忽略。