VDC－MA悬浮共聚树脂分子量及其分布的研究

联用宽分布ＶＤＣ－ＭＡ悬浮共聚物试样的［η］和ＧＰＣ谱图数据，确定了此共聚物在四氢呋喃溶剂中、３０℃下的Ｍａｒｋ－Ｈｏｕｗｉｎｋ常数：Ｋ＝２．５４×１０－２，α＝０．６７５７。进一步研究了单体配比、转化率、引发剂浓度以及聚合温度等因素对于分子量及其分布的影响，并建立了分子量模型。     

GPC测定环氧端基聚芳醚腈(E-PCE)的分子量

联用窄分布环氧端基聚芳醚腈试样的和ＧＰＣ谱图数据,确定了环氧端基聚芳醚腈在四氢呋喃溶剂中,３０℃下的Ｍａｒｋ－Ｈｏｕｗｉｎｋ常数为Ｋ＝５．５２＊１０＾－６,ａ＝１．３２２６,就分子量对性能的影响进行了讨论。     

二甲基 - 二苯基聚硅氧烷与二甲基 - 甲基乙烯基聚硅氧烷嵌段共聚研究

利用聚二甲基－二苯基硅氧烷二醇（Ａ）与聚二甲基－甲基乙烯基硅氧烷二醇（Ｂ），在辛酸己胺催化下缩合聚合、形成（ＡＢ）ｎ、（ＡＢ）ｎＡ及（ＢＡ）ｎＢ型嵌段共聚物。该类聚合物经１ＨＮＭＲ、ＵＶ、ＩＲ及特性粘数测定，研究了催化剂用量、反应时间及反应温度对分子量的影响。利用分步沉淀分级得出了分子量分布。     

二甲基—二苯基聚硅氧烷与二甲基—甲基乙烯基聚硅氧？…

利用聚二甲基－二苯基硅氧烷二醇（Ａ）与聚二甲基－甲基乙烯基硅氧烷二醇（Ｂ），在辛酸己胺催化下缩合聚合、形成（ＡＢ）ｎ、（ＡＢ）ｎＡ及（ＢＡ）ｎＢ型嵌段共聚物。该类聚合物经＾１ＨＮＭＲ、ＵＶ、ＩＲ及特性粘数测定，研究了催化剂用量、反应时间及反应温度对分子量的影响。利用分步沉淀分级得出了分子量分布。     

高温燃料电池阴极材料La（Sr）MnO3的电导性能研究

用固相合成法合成了（Ｌａ１－ｘＳｒｘ）１－ｙＭｎＯ３（ｘ＝０～５，ｙ＝０～０．１）单纯相化合物。在空气中用直流四探针法测定了各组成的电导率。测试温度范围为１００～９５０℃。其中（Ｌａ０．７Ｓｒ０．３）０．９５ＭｎＯ３具有最大的电导率。讨论了Ｌａ（Ｓｒ）ＭｎＯ３的电导机理。     

高分子熔体和浓溶液的流变性能研究Ⅲ．高聚物的起始分子量及其分布对其线性粘弹性的依赖性

以理论同实验相结合的方法，证明了高分子熔体的粘弹性是由高分子的起始分子量与其分布、高分子链间缠结链组数和其两种缠结链组（末端和环绕缠结链组）在高分子链空间的序列分布三重效应所决定。其三者的统一物理量即是两种链组在高分子远近缠结限制空间中的平均维数υ，又称之为标度指数。根据多重缠结模型和多重蠕动耗能机理，我们推导出了标度指数υ与起始分子量及其分布和测试试样个数间的定量关系式，并建议了一种相应测试标度指数的新方法。又以统计法计算出了高分子熔体的线性粘弹性参数（η０、ψ１０、η０ｅｘｔ和Ｊ０ｅ），与起始分子量（Ｍｗ）和其分布宽度指数（Ｍｗ／Ｍｎ）间的定量关系式，并对它们以大量实验数据加以证实。结果表明，它们能很好地预测高聚物熔体的线性粘弹性行为。并首次证实了标度指数υ＝３．３３～３．７７和其会因高聚物品种、分子量范围和被测试样个数而稍有改变的事实。     

原子转移自由基聚合制备ABA型嵌段共聚物

以α，α’－二溴代二甲苯为引发剂，CuBr/2,2‘－联吡啶为催化体系，制备了双溴端基的分子量分布窄的聚苯乙烯（MWD＝1．21）。再以此作为大分子引发剂，实现了甲基丙烯酸甲酯的原子转移自由基聚合，制得了分子量可控且分子量分布窄的ABA型嵌段共聚物，即聚甲基丙烯酸甲酯－b－聚苯乙烯－b－聚甲基丙烯酸甲酯。     

钙钛矿型复合氧化物LaM_yM_（1－y）~＇O_3的氧化还原性能的研究

用ＴＰＲ、ＸＲＤ和ＸＰＳ手段研究了Ｂ位二元复合钙钛矿型复合氧化物ＬａＭｙＭＯ３（Ｍ、Ｍ’＝Ｍｎ、Ｆｅ、Ｃｏ；ｙ＝０．０～１．０）中过渡金属离子的氧化还原性能和还原过程·ＬａＭｎＯ３和ＬａＣｏＯ３及富Ｍｎ和富Ｃｏ样品的还原分为两步：第一步对应于高价过渡金属离子的还原，且不破坏钙钛矿的骨架结构，但可使晶体的对称性及缺陷浓度发生改变；第二步还原使钙钛矿结构破坏，还原产物中出现单元氧化物和金属单质如Ｌａ２Ｏ３、ＭｎＯ、Ｃｏ．ＬａＦｅＯ３和富铁样品的还原过程比较复杂，温度低于１１２３Ｋ时结构基本保持不变，此温度范围内的还原主要是缺陷浓度的变化和高价金属离子数量的减少，第二种离子的加入及其之间的相互作用对样品的还原温度和氧化还原性能有明显的影响，这种影响的程度与样品的结构有关．Ｍｎ、Ｆｅ、Ｃｏ离子的氧化还原性能的强弱可用如下的反应表示：     

分子量对聚丙烯拉伸微孔膜结构的影响

以重均分子量和分子量分布不同的三种聚丙烯树脂为原料,采用熔融挤出-退火-室温拉伸-热拉伸的方法制备了聚丙烯微孔膜.采用凝胶渗透色谱(GPC)、松弛时间谱、差示扫描量热(DSC)、扫描电镜(SEM)等测试手段表征了分子量对最终微孔膜结构的影响.结果表明,重均分子量为587.0 kg/mol、特征松弛时间最长的T30S粒料...     

高级胶印油墨树脂的合成与改性研究Ⅰ．甲阶酚醛缩合物的合成与表征

研究了叔丁酚和甲醛在碱催化下合成羟甲基缩合物的反应机理，得出醛酚摩尔比为２．５，ＮａＯＨ浓度为６％，滴加甲醛于６５℃反应４ｈ的合成工艺。此时，制备酚醛浆表观粘度为１２００ＭＰａｓ／２５℃，数均分子量Ｍｎ＝３６５，其主要结构为两个羟甲基酚之间连１个亚甲基桥的缩合物。该缩合物经松香改性后具有较高的溶液粘度和矿油容纳度，是一种性能优异的高级胶印油墨树脂连接料。     

Mn_2Sb_(0.95)Bi_(0.05)化合物的磁性和电输运性能

通过首先熔炼Sb0.95Bi0.05固溶体,然后再把该固溶体和Mn一起熔炼的多步骤熔炼法,成功地制备了Mn2Sb0.95Bi0.05化合物。样品的热磁曲线测量表明在亚铁磁的Mn2Sb基体中,通过Bi对Sb的替代可以在90K附近诱发亚铁磁到反铁磁转变。与这个一级变磁转变相对应,随着温度的降低,该化合物的电阻曲线在90K附近呈现异常的向上跳跃。电阻异常变化的机理可以被归结为反铁磁态下的超级布里渊区带隙的形成。     

A study on dental nonprecious cast alloys

The ternary nickel-copper-manganese (Ni-Cu-Mn) cast alloys were studied on hardening by the addition of elements such as aluminium and indium to the ternary alloys. Tensile tests showed that both the 20 Ni-40 Cu-40 Mn (which has the lowest melting temperature of all the Ni-Cu-Mn ternary alloys investigated) and the 50 Ni-30 Cu-20 Mn (with the highest melting temperature) exhibited a ductile behaviour. Dendritic structures seen by optical microscopy were constituted of ternary alloys containing aluminium and indium and the amount of dendritic structures increased in the indium-containing alloys rather than in the aluminium containing alloys, and as a result the hardness (VHN) had larger values in the latter alloy than in the former alloy.     

窄分子量分布端羟基聚四氢呋喃的合成与表征

以高氯酸为催化剂,乙酸酐为促进剂及分子量调节剂,通过四氢呋喃阳离子开环聚合合成了分子量可控且分子量分布较窄(Mw/Mn1.2)的聚四氢呋喃,聚合产物端部含有乙酸酯基,经醇解后得到端羟基聚四氢呋喃(PTMEG)。探讨了聚合时间、高氯酸用量、乙酸酐用量、溶剂对聚四氢呋喃分子量(Mn)及分子量分布(Mw/Mn)的影响。研究表明,延长聚合时间、增加高氯酸及乙酸酐的用量均会造成Mn先升后降,但只有聚合时间对Mw/Mn会造成显著的影响,聚合时间为4h时Mw/Mn最小;加入CH2Cl2溶剂会降低聚四氢呋喃的Mn及Mw/Mn。采用凝胶渗透色谱-多角度激光散射联用仪(SEC-MALLS)对聚合产物的Mn及Mw/Mn进行了准确地测定,应用FT-IR、1 H-NMR表征了端羟基聚四氢呋喃大分子结构,利用DSC及TG研究了其热性能,结果表明,端羟基聚四氢呋喃的熔点及分解温度随着Mn的增加略有升高。     

Formation mechanism of silicide nanoparticles by induction thermal plasmas

The condensation mechanism of metal mixture in thermal plasmas was investigated experimentally and numerically to prepare nanoparticles of silicon base intermetallic compounds. Silicon powder premixed with metal powder (Mo, Ti, Co, Fe, Cr, or Mn) was introduced into the plasma. The nanoparticles were prepared on condition that metal vapor was quickly quenched by the water-cooled copper coil. The nucleation rate expression was used for the estimation of critical saturation ratio. The nucleation temperature of the metal almost corresponds to the melting temperature, while silicon has wide liquid range between the nucleation and melting temperature, resulting in better preparation of silicide. For Mo–Si system, nucleation position of Mo is different from that of Si. Therefore, quenching position has strong effect on the particle composition of molybdenum silicide nanoparticles.     

Formation mechanism of silicide nanoparticles by induction thermal plasmas

The condensation mechanism of metal mixture in thermal plasmas was investigated experimentally and numerically to prepare nanoparticles of silicon base intermetallic compounds. Silicon powder premixed with metal powder (Mo, Ti, Co, Fe, Cr, or Mn) was introduced into the plasma. The nanoparticles were prepared on condition that metal vapor was quickly quenched by the water-cooled copper coil. The nucleation rate expression was used for the estimation of critical saturation ratio. The nucleation temperature of the metal almost corresponds to the melting temperature, while silicon has wide liquid range between the nucleation and melting temperature, resulting in better preparation of silicide. For Mo–Si system, nucleation position of Mo is different from that of Si. Therefore, quenching position has strong effect on the particle composition of molybdenum silicide nanoparticles.     

Structural, Optical and Magnetic Properties of Mn-doped CdS Diluted Magnetic Semiconductor Nanoparticles

Diluted magnetic CdS:Mn nanoparticles were synthesized by the aqueous solution method with different manganese (Mn²⁺) concentrations (x=7?C10?atom?%) at room temperature in nitrogen atmosphere and capped with Thiogelycerol. The X-ray diffraction patterns of CdS nanoparticles with different Mn doping concentration indicated that samples have hexagonal structure at room temperature. Energy dispersive X-ray spectroscopy confirmed incorporative of Mn ions in CdS nanoparticles. UV-Visible spectroscopy is used to investigate optical absorption of Mn-doped CdS. From photoluminescence measurement it was found that the intensity of the luminescence spectra decreases by increasing Mn²⁺ dopant ions at high precursor concentration. Also, the room temperature ferromagnetic behavior of Mn-doped CdS nanoparticles is discussed by using hysteresis measurement results.     

Refining effect of hydrogen plasma arc melting on titanium sponges

Hydrogen plasma arc melting (HPAM) of commercial Ti sponges (> 99.7%) was examined. Ti sponges had main impurities such as Fe, Al, Cl and Mn. These main impurities could be reduced more efficiently by HPAM than by Ar PAM. Other small amount of impurities also had a tendency of reduction by HPAM. In addition, it was found that each removal degree is attributable to a differential refining effect caused by the difference of initial impurity concentration. For the unique refining effect of HPAM, dissociated and activated hydrogen atoms involved in the high temperature plasma arc are considered to play an important role in the melting process.     

Simultaneous Contact and Non-contact Measurements of the Melting Temperature of a Ni–C Fixed-Point Cell

A novel fixed-point cell design that allows simultaneous measurements using contact and non-contact thermometers was developed and investigated at PTB to realize the nickel-carbon (Ni–C) fixed-point. The melting temperature indicated by the LP3 radiation thermometer amounted to (1328.86 ± 0.52)°C (k = 2). The melting temperature of the Ni–C fixed-point cell was also calculated by extrapolating the emf-temperature characteristics of two Pt/Pd thermocouples based on their calibrations at conventional fixed points of the ITS-90. The melting temperature of the Ni–C eutectic amounts to (1328.44 ± 0.45)°C using thermocouple Pt/Pd 01/04, and to (1328.53 ± 0.46)°C using thermocouple Pt/Pd 01/05, with uncertainties for k = 2. The contact and non-contact thermometers agree well within the combined uncertainties.     

Melting of Krypton Layers Adsorbed in Cylindrical Pores

The mechanism of melting and its correlation to adsorption on cylindrical surfaces of silica-like cylindrical nanopores has been studied for the first time. The size of the pores has been defined by its diameter (4 nm in this work). As an example, we have analyzed krypton atoms as adsorbed system. We have shown, that the layer adsorbed on the surface of the pore has much lower melting temperature (T = 77.5 K) than both the filled pore (T = 90 K) and the bulk system (T = 118 K). The mechanism of melting in the layer is a continuous transition and depends on the vacancy formation. The layering transition changes its character with temperature from a sharp transition below the melting temperature into a continuous one above it.     

An investigation into the melting of silicon nanoclusters using molecular dynamics simulations

Using the Stillinger-Weber?(SW) potential model, we have performed molecular dynamics?(MD) simulations to investigate the melting of silicon nanoclusters comprising a maximum of 9041 atoms. This study investigates the size, surface energy and root mean square displacement?(RMSD) characteristics of the silicon nanoclusters as they undergo a heating process. The numerical results reveal that an intermediate nanocrystal regime exists for clusters with more than 357?atoms. Within this regime, a linear relationship exists between the cluster size and its melting temperature. It is found that melting of the silicon nanoclusters commences at the surface and that T(m,N) = T(m,Bulk)-αN(-1/3). Therefore, the extrapolated melting temperature of the bulk with a surface decreases from T(m,Bulk) = 1821?K to a value of T(m,357) = 1380?K at the lower limit of the intermediate nanocrystal regime.