On the influence of molecular weight and crystallisation condition on the development of defect in highly drawn polyethylene

Longitudinal morphology of highly drawn high density polyethylenes has been investigated. Three grades of HDPEs with different molecular weights were used. Two different initial morphologies were obtained by quenching and slow cooling from the melt. The samples were drawn at 75 °C close to their breaking points and their longitudinal morphologies examined under SEM after etching. Two types of defects were observed. These are the structure containing a large number of parallel longitudinal etched pockets laid in the regions between almost parallel continuous transverse bands or ‘Pisa’ structure recently reported and transverse cracks. The appearance of these defects was found to correlate with molecular weight and thermal history of the samples. For all quenched samples, both Pisa structure and transverse cracks were observed. The number of transverse cracks was found to increase with increasing molecular weight. Apparently, the transverse cracks, which thought to limit the drawing to high draw ratios, can be retarded by drawing at higher temperature (100 °C). This suggests that the formation of transverse cracks relates to chain mobility and drawability of the materials. The Pisa structure was found to disappear from slowly cooled low molecular weight samples. For slowly cooled high molecular weight sample, the Pisa structure became less salient. It is suggested that the formation of Pisa structure is determined by molecular entanglement. Analysis of the band separation of the Pisa structure shows that there seems to be a characteristic value which depends on drawing temperature.     

Effect of nano-titania (η-TiO2) content on the mechano-physical properties of a magnesia refractory composite

The mechano-physical properties of a sintered magnesia matrix containing 0–8 wt% nano-titania (η-TiO₂) have been investigated. The crystalline phases and microstructure characteristics of the refractory specimens sintered by solid state at 1500 °C for 4 h in an electric furnace were studied by X-ray diffraction (XRD), and scanning electron microscopy (SEM) with microanalysis (EDS), respectively. The physical properties are reported in terms of density and porosity. The mechanical behavior was evaluated by a cold crushing strength (CCS) test. As a result, it was found that the presence of η-TiO₂ in the magnesia matrix induced titanates formation (Mg₂TiO₄ and CaTiO₃), which improved the sintering process. Nano-titania also produced a fine-grained microstructure with intergranular second phase particles, which remain at the boundary and exert a pinning effect. In general, the addition of 5 wt% of η-TiO₂ contributed to reach a maximum increment in physical and mechanical properties.     

纳米碳酸钙的制备、表面改性及应用进展

纳米碳酸钙是一种新型的无机纳米材料,可应用于塑料、橡胶、油墨、造纸、日用化工、胶黏剂和密封材料、医药、食品等许多领域。笔者概述了纳米碳酸钙常用的制备方法。列出了纳米碳酸钙表面改性的途径以及纳米碳酸钙在应用过程中所表现出的与普通轻质碳酸钙所不同的、反常的物理化学特性以及各方面特性的应用领域。对进一步拓展纳米碳酸钙的应用、不断优化其性能、突出其纳米特性、提升其潜在的价值等提出展望．具有一定的指导意义。     

Hydrogen and carbon dioxide adsorption with tetra‐n‐butyl ammonium semi‐clathrate hydrates for gas separations

Gas adsorption rates of H₂, CO₂, and H₂‐CO₂ gas mixture (H₂/CO₂ = 3.4) with tetra‐n‐butyl ammonium salt (bromide, chloride, and fluoride) semi‐clathrate hydrate particles were measured at 269 K to assess their properties for gas separation. Equilibrium gas occupancies in the S‐cages of the particles were in order of (high to low) for hexagonal structure‐I, tetragonal structure‐I, and superlattice of cubic structure‐I structures with the maximum fractional occupancy by CO₂ being about 40%. The CO₂ diffusion rate depended on the anion size of the salt, which is attributed to distortion of the S‐cage that is close to the molecular size of CO₂. Simulations of semi‐clathrate hydrate particles with theory showed that H₂/CO₂ selectivities could be as high as 36 (3.0 mol% TBAF) and that selectivities for an ideal membrane (3.3 mol% TBAF) could be >100 (269 K, 0.3–4.5 MPa). Semi‐clathrate hydrates have wide application as separation media for gas mixtures. © 2014 American Institute of Chemical Engineers AIChE J, 61: 992–1003, 2015     

Phase formation in Al2O3-C refractories with Al addition

Depending on the recipe and the firing conditions, several non-oxides can be formed in Al₂O₃-C refractories. In this paper, the effect of the purity of the recipe components on the phase formation in Al₂O₃-C refractories with Al addition was investigated. Two test series were sintered from 800 °C to 1600 °C under air embedded in coke breeze. One test series was with brown fused alumina, and the other was with tabular alumina. At temperatures of up to 1200 °C the phase formation was the same for both recipes. For temperatures greater than 1400 °C, the impurities of brown fused alumina enhanced the formation of a polytype, while Al₄O₄C and Al₂₈O₂₁C₆N₆ were formed in the other series. The findings explain the occurrence of several non-oxides in disequilibrium at the chosen temperatures. The occurrence of Al₄C₃ was of particular interest due to its low hydration resistance. It was formed at 1200 °C.     

Selective formation of 2-methyl-2-butene and 2-methyl-1-butene: Operating conditions and kinetic analysis

The effect of linear gas velocity, catalyst particle size, reaction temperature, space time, etc. on the dehydration of amyl alcohols (from fusel oil) was studied, using as catalyst a pre-treated bentonite. The analysis of the kinetic data, using Hougen-Watson type models, gives as the best model one in which amyl alcohol is absorbed on two active sites, the reaction rate being determined by the surface reaction of absorbed species.     

固态配料和硝酸盐共沉淀配料制备Bi(Pb)—Sr—Ca—Cu—O系高温超导相的工艺比较

用固态配料和硝酸盐共沉淀配料制备了各组份为(Bi_(1.85)Pb_(0.40))Sr_(1.95)Ca_(2.05)Cu_(8.10)的超导材料,研究了两种不同制备工艺对Bi系超导相形成过程、超导电磁性能和显微结构的影响.实验发现,由共沉淀制备的样品T_(c(zero))稳定性好,T_(c(zero))均在107.5K以上.SEM观察表明:共沉淀法制备的样品中超导相颗粒比固态配料制备的要细小、均匀,颗粒间连结紧密,与T_(c(zero))结果相符.但XRD相分析结果显示:固态配料样品中高温相含量高于共沉淀配料,共沉淀配料制备作品中高、低温相同时存在,但其交流磁化率—温度曲线上仅在120K附近出现相应于高温相的抗磁信号.研究认为,这是由于共沉淀配料烧成时,高温相容易在部分液相参与下,在低温相表面通过反应成核生长,导致在形成的高温相内部包裹有残余低温相的“内芯”.依此包裹模型可自洽地解释X射线相分析与电、磁性能测定结果间的矛盾,讨论了Bi系高温相的形成机理,为选择合理的制备工艺提供了依据.     

安塞油田候市地区长61油层沉积微相研究

候市地区是安塞油田的一个主力区块,区域构造是平缓的西倾单斜,长61油层为其主力产层。根据岩心、粒度、薄片及测井曲线等资料,运用沉积学理论将研究区长61油层确定为三角洲前缘亚相沉积环境,进一步识别出水下分流河道、河口砂坝、远砂坝、前缘席状砂以及水下分流河道间等五种微相。在此基础上结合物性以及试油成果,确定物性及含油性最好是水下分流河道,河口砂坝次之,前缘席状砂相对较差。     

镁渣配料煅烧熟料形成过程的试验研究

对不同镁渣掺量的生料在不同温度下进行煅烧试验，分析了煅烧料的游离氧化钙，利用XRD分析了煅烧料的矿物组成，并进行了岩相分析。结果表明：掺镁渣生料易烧性较好，熟料矿物岩相结构及形貌正常，熟料矿物形成过程与采用天然原料的基本相同。     

陕甘宁盆地姬塬地区长2油层组沉积相特征研究

长2油层组是姬塬地区延长组的重要含油层之一,以岩心,测井和地质资料为基础,研究了姬塬地区曲流河三角洲的沉积特征,总结出两种亚相,五种微相的沉积类型。其识别标志是以水下分流河道、河口砂坝和远砂坝三种沉积微相沉积构造特征为主导的多种微相组合形式。进一步编制沉积微相平面分布图,分析其展布特点和演化规律,对研究区的油气富集因素探讨以及今后的勘探开发具有重要的意义。