Dielectric and EMW absorbing properties of PDCs-SiBCN annealed at different temperatures

Polymer derived SiBCN ceramics (PDCs-SiBCN) were prepared from polyborosilazane and then annealed at 1200–1800 °C in N₂. Effects of annealing temperature on the microstructure, phase composition, dielectric and wave-absorbing properties of ceramics were investigated. Results showed that nano-sized SiC grains were formed in amorphous SiBCN after annealing and the content and crystallization degree of SiC gradually intensified with annealing temperature increasing. The permittivity, dielectric loss and electrical conductivity of PDCs-SiBCN gradually increased as the temperature rose due to the formation of conductivity network of SiC grains and the increase of nano-grain boundary. The increased content of SiC (as the dipole) and interface between SiC nano-grains and amorphous SiBCN phase led to a higher polarization ability and higher dielectric loss. The RC gradually decreased with the annealing temperature increasing, demonstrating the annealed ceramics had the superior wave-absorbing ability and high annealing temperature was conducive to the improvement of wave-absorbing property.     

Catalytic dechlorination of C5 compounds over metal-oxide/ZSM-5 catalysts

In this research, the dechlorination of 2-chloro-2-butene in C5 oil from the fluid catalytic cracking (FCC) process was performed through a catalytic reaction. Metal oxides were used as active materials and ZSM-5 was used as the supporting material for the catalysts; the metal was cobalt, iron, or manganese. After the preparation of three types of metal-oxide/ZSM-5 catalysts through the ion-exchange method, the activities and characteristics of each catalyst were evaluated. Through screening tests, the Co₃O₄/ZSM-5 catalyst was selected as the dechlorination catalyst, and the performance of catalysts containing different amounts of Co₃O₄ relative to ZSM-5 were tested.     

Enantioselective Additions of Aryltitanium Tris(isopropoxide) to Ketones: Structure of [(i‐PrO)2Ti{μ‐(S)‐BINOLate}(μ‐O‐i‐Pr)TiPh(O‐i‐Pr)2], Study of Mechanistic and Stereochemical Insights

Aryl addition reactions of ArTi(O‐i‐Pr)₃ to aromatic, heteroaromatic, or α,β‐unsaturated ketones are described, producing tertiary alcohols in good to excellent enantioselectivities of up to 97% ee. The structure of the dititanium complex [(i‐PrO)₂Ti{μ‐(S)‐BINOLate}(μ‐O‐i‐Pr)TiPh(O‐i‐Pr)₂] [(S)‐ 4 ] that simultaneously bears a chiral directing ligand and a nucleophile is reported. Complex (S)‐ 4 possesses a pocket structure and has been illustrated as the key active species for addition reactions of both aldehydes and ketones. Mechanistic and stereochemical insights concerning addition reactions of organometallic reagents to organic carbonyls are rationalized based on the pocket structure and pocket size of (S)‐ 4 .     

Rhodium‐Catalyzed C?H Olefination of Aryl Weinreb Amides

A rhodium(III)‐catalyzed oxidative C H olefination directed by Weinreb amides, a class of well developed versatile building blocks in organic synthesis, has been developed with air as the terminal oxidant. The reactions proceed with excellent reactivity, good functional group tolerance and high yields.     

2012年ABS树脂生产与市场分析

综述了2012年国内外ABS(丙烯腈-丁二烯-苯乙烯)树脂生产商的生产能力和实际产量、国内外ABS市场和价格,对国内ABS树脂技术现状及其市场发展趋势进行了分析和预测。另外,还介绍了国内外科研开发、技术进展以及新产品开发情况,并针对国内ABS树脂装置提出了几点建议。     

抗肿瘤药物来那度胺的合成方法

2-甲基-3-硝基苯甲酸甲酯(1)与卤化剂反应,制得2-卤甲基-3-硝基苯甲酸甲酯(2)。L-谷氨酰胺(3)经酯化反应制得谷氨酰胺甲酯(4),在Boc试剂、偶联剂和催化剂的作用下,进行分子内关环,制得Boc保护的3-氨基哌啶-2,6-二酮(7),与2-卤甲基-3-硝基苯甲酸甲酯(2)在弱碱的条件下合环,经硝基还原反应,得到来那度胺(9)。本方法反应条件较温和,反应步骤简单易行,降低了生产成本,并且提高了产率,总收率约为40%。     

提高复合肥水溶性的技术措施

介绍了普通复合肥的水溶性情况,并通过采取养分形态、原料选择、原料配比、生产管理等技术优化措施,提高了复合肥产品的水溶性。改进后,复合肥中的水不溶物质量分数由20．8％下降至10．5％,且密度小、易漂浮。     

芳纶浆粕对丁腈橡胶性能的影响

研究预处理芳纶浆粕对丁腈橡胶(NBR)性能的影响。结果表明:随着芳纶浆粕用量的增大,NBR胶料的焦烧时间呈缩短趋势,M H逐渐增大,硫化胶的硬度和50%定伸应力增大,拉断伸长率减小,撕裂强度先增大后减小,耐油性能提高,剪切储能模量增大;加入芳纶浆粕的硫化胶热稳定性优于未加芳纶浆粕的硫化胶;预处理芳纶浆粕在NBR中分散均匀。     

Effect of rotation extrusion and molecular weight on ductile failure of polyethylene pipes under hydrostatic pressure

ABSTRACT

In this study, two kinds of polyethylene (PE) with different molecular weight were processed into the pipes via rotation extrusion and the failure behaviours under hydrostatic pressure as well as molecular relaxation were investigated. The experimental results showed that the high molecular weight PE exhibited slower relaxation behaviour with higher relaxation activation energy to facilitate the formation of shish-kebab under flow field, while for the low molecular weight one, the stretching molecules easily relaxed back coil state and spherulites were prone to form. Therefore, the low molecular weight PE pipes via convention and rotation extrusions had similar isotropic spherulite morphology and short failure times. In the case of high molecular weight PE, during the convention extrusion, polymer melts flowed along the axial direction to induce the alignment of shish-kebab accordingly, which went against to the hoop stress in hydrostatic pressure. With the rotation of mandrel and die, the direction deviated from the axis so that PE pipe exhibited better resistance to the hoop stress. The failure time was 182?h, 264% longer than the convention-extruded one. Accordingly, a new strategy to prepare high hydrostatic pressure PE pipe under cooperative effects of rotation extrusion and long molecular relaxation time was proposed.     

Effect of nonstoichiometry on the microstructure and microwave dielectric properties of Ba(Mg1/2W1/2)O3 ceramics

Effects of nonstoichiometry on crystal structure and the microstructure of double perovskite Ba(Mg_1/2W_1/2)O₃ ceramics have been investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Raman spectrometry in this paper. The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 8–11 GHz. The results show that small deviation from stoichiometric composition has little influence on the crystal structure such as B-site 1:1 ordering degree. Evaporation of BaO was confirmed during the sintering of BMW ceramics, which in turn produce more BaWO₄ phase. Ba-deficiency or W-excess in BMW could improve the sinterability and Q×f value, while Ba-excess or W-deficiency could suppress the formation of BaWO₄ at the expense of increase in sintering temperature and decrease in Q×f value. Mg nonstoichiometry has little effect on the variation of BaWO₄ content and Q×f value. Maximum Q×f value of about 140,000 GHz could be obtained for the Ba-deficient or W-excessive samples after sintering at 1500 °C/2 h or 1550 °C/2 h, respectively. All Mg-nonstoichiometric compositions exhibit high Q×f value of about 120,000 GHz after sintering at 1550 °C/2 h. All well-densified samples have dielectric permittivity of about 19–20 and τ_f value varied within the range of ?21～?28 ppm/°C.