Some aspects for sintering of β-rhombohedral boron

The investigation of sintering conditions for magnesiothermic amorphous boron (Mg_mB_n) powder is presented. The results of chemical and X-ray analyses of magnesiothermic boron (Mg_mB_n) indicate that it consists of amorphous boron MgB₁₂ and a lesser amount of β-rhombohedral boron. The Mg_mB_n-sintering process is determined by the conditions of amorphous boron transformation into β-boron (crystallization), such as the process of decomposition of MgB₁₂ followed by formation of the “new” centers of active elementary boron. As a result of the experimental investigations of this process the following three stages—thermal decompositions, crystallization and Mg_mB_n sintering—were combined into one sintering process with the sintered bodies as a result of it.     

结晶／结晶共混体系聚苯硫酸／聚醚醚酮中聚醚醚酮组分的结晶熔融行为──熔融温度的影响

结晶／结晶共混体系聚苯硫酸／聚醚醚酮中聚醚醚酮组分的结晶熔融行为──熔融温度的影响麦堪成，许家瑞，梅震，曾汉民（中山大学材料科学研究所，广州，５１０２７５）关键词聚醚醚酮，聚苯硫醚，结晶／结晶共混物，结晶熔融行为近年来，高性能聚合物共混物如聚砜（ＰＳ...     

CRYSTALLIZATION AND MELTING OF NYLON 610

Differential scanning calorimetry was used to study the crystallization andmelting of nylon 610. For nylon 610 crystallized from the melt state (260℃), the overall rateof bulk crystallization can be described by a simple Avrami equation with Avrami exponentn ≈ 2, independent of crystallization temperature. With the experimentally obtainedT_m~0 (235℃ ～ 255℃) of nylon 610, the fold surface free energy σ_e was determined to be35 ～38 erg/cm~2. The effects of annealing temperature and time on the melting of quenchednylon 610 were also investigated. For nylon 610 quenched at room temperature there isonly one DSC endotherm peak DSC scans on annealed samples exhibited an endothermpeak at approximately 10℃ above the annealing temperature. The size and position of theendothermic peak is strongly related to annealing temperature and time. An additionalthird melting was observed when quenched nylon 610 was annealed at high temperaturefor a sufficiently long residence time. The existence of the third melting peak suggests thatmore than one kind of distribution of lamella thickness may occur when quenched nylon610 is annealed. The implications of these results in terms of crystal thickening mechanismwere discussed.     

嵌段共聚物/均聚物共混体系的结晶行为 I. 非球状共聚物胶束的作用

将Leibler, Whitmore和Mayes等近期关于非晶嵌段共聚物“稀固体溶液”的理论应用于嵌段聚共聚物结晶型“稀固体溶液”结晶行为的研究。发现球状共聚物胶束既可起成核剂作用, 也可起抑制成核作用。报导了当共聚物胶束由球形变为非球形时, 共聚物胶束的上述作用都会发生较大的变化, 并根据Leibler和Mayes分别提出的球形和非球形胶束理论解释了这一实验现象。     

环己烷催化氧化制取顺酐和醋酸的催化剂研究

为研究气态环己烷催化氧化制取顺酐及醋酸的新反应，采取不同的方法制备了系列固体VPO催化剂.借助XRD、FT-IR对催化剂进行了主体晶相确定，用氧化还原滴定方法测定了不同晶相催化剂中钒的平均氧化数.结合催化反应的活性评价，发现催化剂主体晶相、结晶度、活化气氛和催化剂的V4＋/V5＋比均对目标反应的催化活性产生影响，5种催化剂中以(VO)2P2O7晶相催化剂的活性为最高.     

Co-crystallizing coordination compounds

Crystallization of an equimolar mixture of 1,10-dimethylphenanthroline (DMP) and manganese(II) chloride from N,N-dimethylformamide (DMF) has been studied. Rather than a useful route to a well-defined product, it was found that identical solutions could deposit crystals of three different compounds. The most common outcome was the formation of crystals of [MnCl₂(dmp)(dmf)], 1, or co-crystallization of [MnCl₂(dmp)(dmf)] and [{MnCl₂(dmp)}₂]. The co-crystals, 2, were always found to dissolve as crystals of 1 started to grow. Crystals of a third compound, [MnCl₂(dmp)₂], 3, were also isolated once.     

Higher Aliphatic Aldehyde Polymers. V. Cyclic Trimers of C9 to C12, Normal Aliphatic Aldehydes

Cyclic trimers of n-nonaldehyde (NA), n-decaldehyde (DA), n-undecaldehyde, (UA) and n-dodecaldehyde (DDA) were prepared by reacting the individual aldehydes with protic or Lewis acids. Higher aliphatic aldehydes whose long paraffinic chains dominate the general properties of these compounds do not trimerize readily the trimers, when formed, are purified with difficulty. The cyclic trimers, characterized by IR and NMR spectroscopy, are exclusively the cis isomers and commonly exist in all equatorial conformations. The melting behavior of the cyclic trimers was studied by DSC. The melting endotherms and the enthalpies of fusion increase with increasing chain length. Although the melting temperatures of the cyclic trimers are similar to the melting range of the side-chain crystallization of the corresponding crystalline isotactic polyaldehydes, the transition peaks of the trimers are single peaks and much sharper than the corresponding polymer peaks.     

Isothermal-crystallization kinetics and spherulite growth of aliphatic polyketone/polyamide-6 blends

In this research,the morphologies,isothermal-crystallization kinetics,and spherulite growth of aliphatic polyketone/polyamide-6 blends were studied.A single glass-transition temperature (Tg) was determined,and the composition dependence of Tg for these blends was well described by the Kwei equation.The strong intermolecular interaction between the two polymer components was confirmed by melting-point depression.The isothermal-crystallization kinetics were analyzed on the basis of the Avrami approach.A linear increase in the radii of the spherulites with time was observed for all compositions.All the spherulites continued to grow at nearly identical growth rates.With increasing polyamide-6 content,the size of the spherulites in the polyketone/polyamide-6 blends gradually decreased,and the number of spherulites in the blends increased.     

Improved Photovoltaic Performance from High Quality Perovskite Thin Film Grown with the Assistance of PC71BM

The strategy of sequentially spin-coating a perovskite film from the perovskite precursor and an electron transporting layer of [6,6]-phenyl-C_(71)-butyric acid methyl ester(PC_(71)BM) is developed to simplify the fabrication procedure of perovskite solar cells. X-ray diffraction and scanning electron microscopy indicate that PC_(71)BM film on perovskite layer can retard the evaporation of dimethyl sulfoxide(DMSO) efficiently, thus prolonging the transformation of intermediate phase to perovskite crystals, leading to a high quality perovskite thin film. The solar cells with the structure of indium tin oxides(ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)/CH_3NH_3PbI_3/PC_(71)BM/bathocuproine(BCP)/Ag made from this simplified method exhibit a higher efficiency(12.68%) than those from the conventional one-step method(9.49%).     

Effect of partial crosslinking on morphology and properties of the poly(β-hydroxybutyrate)/poly(d,l-lactic acid) blends

Poly(β-hydroxybutyrate) (PHB) is a bio-based and biodegradable aliphatic polyester, however its application is limited by some disadvantages such as high price, brittleness, poor processability and low melt-strength due to serious thermal degradation. Partial crosslinking initiated by dicumyl peroxide (DCP) was applied in this work to improve the performance of poly(β-hydroxybutyrate)/poly(d,l-lactic acid) (PHB/PDLLA) blends. The partial crosslinking of the blends and its effect on the properties, morphology, rheology and thermal behavior of the blends were investigated. The tensile strength and impact toughness of the PHB were increased by incorporation of the PDLLA, which were improved further after the partial crosslinking because of an increased compatibility between the PHB and the PDLLA phases. The rheological study revealed that the storage modulus (G′) and complex viscosity (η*) of the blends were increased after addition of the DCP. On the other hand, the crystallization of PHB in the blends was restricted to a certain extent by the formation of partially crosslinked network while its crystal form was not modified.