Polymeric positive-temperature-coefficient materials: dynamic curing effect

The object of this work was to prepare high-density polyethylene (HDPE)/ethylene–propylene–diene terpolymer (EPDM)/conductive carbon black (CB) composites by dynamic curing and to characterize the positive-temperature-coefficient (PTC) performances of the composites.EPDM and dicumyl peroxide were preblended in a research mill. The roll-milled strands were blended with HDPE and CB in a Haake mixer. The sheet resistivity and morphology of the HDPE/EPDM/CB composites with or without the dynamic curing process were investigated. It was concluded that the dynamically cured blends exhibit better PTC performance than the simple blends without dynamic curing. The effects of shear intensity and dicumyl peroxide content during the dynamic curing process were discussed for the PTC characteristics of the HDPE/EPDM/CB composites.     

氟代乙烯阳离子的理论研究

用B3LYP和MP2方法及6-31G(d, p)、6-31＋G(d, p)、6-311G(d, p)和6-311＋G(d, p) 基组，对六种氟代乙烯阳离子做了理论研究，优化了它们的基电子态的结构，计算了对应分子的垂直电离势（VIP）和绝热电离势(AIP).结果表明，与具有非平面结构的乙烯阳离子不同，六种氟代乙烯阳离子都只具有平面结构；与分子结构相比，离子结构的C－C键增长， C－F键缩短， CCF键角变小. 自然布居分析计算表明，这些离子的正电荷主要分布在与F原子相连的C原子和各H原子上. B3LYP/6-311＋G(d, p) 级别上计算的各分子的VIP和AIP值和实验值符合得很好. 使用含弥散基函数的基集可以明显提高这类分子的电离势的计算精度.     

纳米Y2O3/钴基合金激光熔覆层的组织

利用5 kW CO2激光器,在Ni基高温合金表面,熔覆纳米稀土氧化物(Y2O3)/钴基合金复合材料,制备了涂层.利用光学显微镜、扫描电镜及透射电镜分析了熔覆层的组织结构.结果表明: 熔覆层的主要相组成为γ-Co,ε-Co,Cr23C6和Y2O3;加入纳米Y2O3,凝固组织由细长的柱状树枝晶转变为较短的树枝晶;纳米Y2O3含量增大至1%时整个断面获得等轴晶组织;纳米Y2O3作为异质形核的核心,细化了组织;纳米Y2O3在熔覆层中分布不均匀,促进了γ-Co向ε-Co的转变;熔覆层的亚结构为堆跺层错.对熔覆层等轴组织形成机制进行了分析.     

Three-dimensional configurations of organic/inorganic hybrid nanostructural blocks (I). A quantum mechanical investigation for ladder-like structure of vinylsilsesquioxane

Silsesquioxanes (SSO) or polyhedral oligomericsilsesquioxanes (POSS) are generally prepared frommolecular precursors using the hydrolytic condensa-tion of trialkoxysilane, RSi(OR')3. They are organic/inorganic hybrid nanostructural blocks with theircomplete general formula Tn(T = RSiO1.5, n = 1,2, …), and the incomplete generic formula is Tn-(OH)x(OR')y[x, y = 0, 1, 2, …, T= RSiO1.5 ?(x+y)/2n][1,2].Each VSSO, possessing a certain structural formulaand molecular weight, may h…     

希土季铵盐配合物的研究——Ⅴ.[(n-C4H9)4N]3Nd(NCS)6的晶体结构研究

合成了硫氰酸合希土酸四丁基季铵盐配合物,测定了它们的远红外光谱及部分配合物的中红外光谱,结果表明,配合物中的NCS^-是以氮原子与Ln³⁺配位。用X射线单晶衍射法测定了[(n-C₄H₉)₄N]₃Nd(NCS)₆晶体的结构,结果表明,该晶体属单斜晶系,C_c空间群,晶胞参数为:a=25.188(8)Å,b=13.320(6)Å,c=25.322(8)Å,β=121.30(2)°,晶胞体积V=7258.9ų,每一晶胞中有四个配合物分子,中心离子Nd³⁺与六个来自NCS^-的氮原子配位,这六个氮位于配位正八面体的六个顶角上,构成配阴离子Nd(NCS)₆^3-,它与三个[(n-C₄H₉)₄N]⁺以静电引力结合成中心分子,所以晶体为离子型晶体。     

Molecular weight distribution studies. I. Radiation-induced polymerization of liquid α-methylstyrene

The concentration of water in purified and BaO-dried α-methylstyrene was found to be 1.1 × 10^?4M. The radiation-induced bulk polymerization of the α-methylstyrene thus prepared was studied in the temperature range of ?20°C to 35°C. The polymerization rate varied as the 0.55 power of the dose rate. The theoretical molecular weights and molecular weight distribution were calculated from a proposed kinetic scheme and these values were then compared with those found experimentally. The agreement between these two was reasonably close, and therefore it was concluded that, from the molecular weight distribution point of view, the proposed kinetic scheme for the cationic polymerization of α-methylstyrene is an acceptable one. The rate constant for chain transfer to monomer k_f changed with temperature and was found to be responsible for the decrease in the molecular weight of the polymer with increase in temperature. k_f and k_p at 20°C were found to be 0.95 × 10⁴ l./mole-sec and 0.99 × 10⁶ l./mole-sec, respectively.     

Electrochemical vapor generation of selenium species after online photolysis and reduction by UV-irradiation under nano TiO<Subscript>2</Subscript> photocatalysis and its application to selenium speciation by HPLC coupled with atomic fluorescence spectrometry

An online UV photolysis and UV/TiO₂ photocatalysis reduction device (UV–UV/TiO₂ PCRD) and an electrochemical vapor generation (ECVG) cell have been used for the first time as an interface between high-performance liquid chromatography (HPLC) and atomic fluorescence spectrometry (AFS) for selenium speciation. The newly designed ECVG cell of approximately 115 L dead volume consists of a carbon fiber cathode and a platinum loop anode; the atomic hydrogen generated on the cathode was used to reduce selenium to vapor species for AFS determination. The noise was greatly reduced compared with that obtained by use of the UV–UV/TiO₂ PCRD–KBH₄–acid interface. The detection limits obtained for seleno-DL-cystine (SeCys), selenite (Se^IV), seleno-DL-methionine (SeMet), and selenate (Se^VI) were 2.1, 2.9, 4.3, and 3.5 ng mL^–1, respectively. The proposed method was successfully applied to the speciation of selenium in water-soluble extracts of garlic shoots cultured with different selenium species. The results obtained suggested that UV–UV/TiO₂ PCRD–ECVG should be an effective interface between HPLC and AFS for the speciation of elements amenable to vapor generation, and is superior to methods involving KBH₄.     

Trace lead measurement and on-line removal of matrix interference in seawater by isotope dilution coupled with flow injection and ICP-MS

Isotope dilution analysis method coupled with flow injection and inductively coupled plasma mass spectrometry (ID-FI-ICP-MS), enabled trace lead concentration in seawater to be determined and the high salt concentration in the matrix, such as Na⁺, Ca²⁺ and Mg²⁺, to be removed on-line. The operational parameters of the FI system including pH for the chelating reaction, concentration of 8-hydroxyquinoline-5-sulfonic acid (8-HQS), sample loading time and injection speed, washing time and speed, eluting acid concentration and eluting speed, and instrumental parameters for ICP-MS were optimized and selected. Accurate results could be achieved because the isotope ratios required can be precisely measured in the range of the eluting peak by means of ID-FI-ICP-MS. The 3σ detection limit was 0.204 ng ml⁻¹. The trace lead concentration of seawater in south Xiamen, China was 0.988 ± 0.039 ng ml⁻¹. The recoveries of spiked Pb standard in seawater and standard reference water (GBW 08607) were 97.9 and 101.0%, respectively, with a relative standard deviation of 0.98%. This method can be used to determine trace lead concentration in high salt matrix samples, and is especially useful when the eluting peaks do not have a Gaussian-distribution.     

Determinations of geniposide using LC/MS/MS methods via forming ammonium and acetate adducts

In this paper, we report method development work to determine geniposide using LC/MS/MS via the formation of positive and negative ion adducts. Geniposide, which has been recognized to have choleretic effects, is the major iridoid glycoside component of Gardenia herbs. To enhance the sensitivity of LC/MS detection of geniposide, a small amount of volatile additives such as ammonium acetate and acetic acid are added into mobile phase solvents to form positive and negative adducts, which can then ionize via electrospray processes. The formation of positive adducts is due to the complexation between geniposide and ammonium ions ([M + NH₄]⁺). The formation of anionic adducts [M + CH₃COO]⁻ is believed to occur via hydrogen bonds bridging acetate ions and glucose groups on the geniposide molecule. Mobile phase solvents containing acetonitrile and aqueous solution (0.2 mM ammonium acetate or 0.1% acetic acid) at the ratio 15: 85 are employed to elute geniposide using C8 reverse phase liquid chromatography columns with electrospray tandem mass spectrometry determinations. Using geniposide standards, the methods are validated at the concentration ranges of 5 to 1000 ng/mL and 20 to 5000 ng/mL using ammonium and acetate adducts respectively. The correlation coefficients of the standard curves are 0.9999 using both ammonium and acetate adducts. The detection limits of using ammonium and acetate adducts are 1 and 5 ng/mL respectively. The measurement accuracy and precision of using ammonium adducts are within 12% and 3% respectively, whereas the accuracy and precision are within 6 and 11% respectively using acetate adducts. When the validated calibration curves of the ammonium adduct of geniposide are used to determine spiked control samples in rat blood dialysates, the determination errors of accuracy and precision are within 12% and 10% respectively.     

Monte Carlo simulation of adsorption of binary and quaternary alkane isomers mixtures in zeolites: Effect of pore size and structure

Grand canonical Monte Carlo and configurational bias Monte Carlo techniques were employed to simulate the adsorption of binary mixtures of butane isomers and quaternary mixtures in nine zeolites at 300 K. For binary mixtures the results show there is a critical pore size, which is 10-membered-ring about 5.6 Å. The channel sizes of BEA, ISV, MOR and CFI are larger than this critical pore size, they prefer i-butane than n-butane, whereas TON with smaller channel size than critical pore size prefers n-butane than i-butane, but its selectivity decreases with pressure increasing. MFI, MEL and TER prefer i-butane than n-butane at low pressure, but with pressure increasing, the selectivity is reversed. BOG prefers i-butane than n-butane but the selectivity decreased with pressure increasing. It demonstrates that the adsorption and selectivity are controlled by both pore size and pore structure. The n-butane–i-butane–n-pentane–2-methylbutane quaternary mixtures adsorbed in these nine zeolites were studied, and the results show alkane chain length dependence at low pressure, but the adsorption is controlled by pore size and structure with pressure increasing in all the zeolites except for TON and BOG.