碳酸氢钠苛化的平衡和速率

一般条件下,碳酸氢钠与氢氧化钙以1:1(摩尔比)苛化。灰碱比低于0.5时,苛化液中没有大量OH~-生成,可认为反应先生成CO_3~(2-),再苛化成氢氧化钠。只在高温和高浓度时才有少量碳酸氲钠分解反应发生。苛化时随碳酸氢钠初始浓度增大,平衡苛化率下降。温度对平衡苛化率有影响,但不显著。温度可显著影响苛化速率,90℃反应两小时已趋近平衡。宏观动力学测定表明,反应属于二级,活化能不失,相当于扩散控制或控散—反应控制。     

钨、镍、钴混合氧化物氢还原研究

本文用X-射线衍射与扫描电镜分析研究了在700～1000℃范围内钨、镍、钴混合氧化物的氢还原。也研究了添加少量镍、钴的钨的低温烧结特性。研究结果表明,采用混合氧化物氢还原取得了满意的结果。     

20Cr钢回火马氏体疲劳时的再回火效应

通过研究不同回火温度的马氏体在疲劳前后的组织变化,发现在疲劳过程发生了碳化物的析出或聚集现象;以及相应的位错结构的回复。其变化方向与回火过程一致。提出变化的本质就是疲劳载荷协助的再回火效应。用这一观点统一解释了不同回火温度下马氏体的疲劳软化机制,以及400℃回火可获得最大软化量的原因。此外,根据对400℃回火马氏体疲劳前后碳化物特征参数的测定,表明微细碳化物的聚集是该温度回火态试样疲劳软化的主要机制。     

双相钢冷拔钢丝的自然时效

研究了09Mn2Si热轧态双相钢冷拔钢丝经6个月自然时效后的力学性能和显微组织的变化。结果发现,无论是冷拔态钢丝还是冷拔-回复态钢丝,均呈现明显的自然时效现象。冷拔态钢丝经6个月自然时效后,强度提高而塑性降低。但是,对于冷拔-回复态钢,不仅强度提高,而且塑性也有明显改善。用透射电镜对钢丝金属薄膜进行了组织观察,并对两种不同的自然时效特性进行了讨论。     

Experimental investigations in combining primal dual interior point method and simplex based LP solvers

The use of a primal dual interior point method (PD) based optimizer as a robust linear programming (LP) solver is now well established. Instead of replacing the sparse simplex algorithm (SSX), the PD is increasingly seen as complementing it. The progress of PD iterations is not hindered by the degeneracy or stalling problem of SSX, indeed it reaches the near optimum solution very quickly. The SSX algorithm, in contrast, is not affected by the numeral instabilities which slow down the convergence of the PD near the optimal face. If the solution to the LP problem is non-unique, the PD algorithm converges to an interior point of the solution set while the SSX algorithm finds an extreme point solution. To take advantage of the attractive properties of both the PD and the SSX, we have designed a hybrid framework whereby crossover from PD to SSX can take place at any stage of the PD optimization run. The crossover to SSX involves the partition of the PD solution set to active and dormant variables. In this paper we examine the practical difficulties in partitioning the solution set, we discuss the reliability of predicting the solution set partition before optimality is reached and report the results of combining exact and inexact prediction with SSX basis recovery.     

Determination of tungsten with pyrocatechol violet by first-derivative solid-phase spectrophotometry

Derivative spectrophotometry was applied to solid-phase spectrophotometry in order to enhance its sensitivity and remove the large background caused by the absorbance of the resin layer. Determination of micro-amounts of tungsten with pyrocatechol violet to form a 21 green complex in acid medium which is fixed on a dextran-type anion-exchange resin (Sephadex QAEA-25) is described as an example for the application of this technique. The absorbance of the resin packed in a 1-mm spectrophotometric cell, was measured directly. The characteristic peak amplitude of the signal at 674 nm in the first-derivative spectrum is useful for quantitative determination of tungsten (3–16 g 1^–1; RSD 5.8%) in natural and industrial water samples.     

Dilatometric studies of physical aging of polyetherimide

Physical aging of polyetherimide (PEI) was studied using a bellows dilatometer based on Zoller's design. A linear variable differential transformer (LVDT) is used to measure the displacement of the bellows. The voltage output of the LVDT is interfaced to a computer for automated data collection. Isothermal aging experiments were carried out at temperatures near the glass temperature (206–209 C) using a constant temperature oil bath maintained at the desired aging temperature. The time required to reach equilibrium and the reduced curve produced by aging time-temperature superposition are given. The results compare well with data obtained by capillary dilatometry for the same material.     

A green route for microwave synthesis of sodium tungsten bronzes NaxWO3 (0<x<1)

A green route has been developed for microwave synthesis of sodium tungsten bronzes Na_xWO₃ (0<x<1) from Na₂WO₄, WO₃ and tungsten powder. The hybrid microwave synthesis was carried out in argon atmosphere using CuO powder as the heating medium. Tungsten powder is used as the reducing agent instead of the alkali metal iodides previously used for the microwave synthesis of oxide bronzes. The prepared samples were characterized by powder X-ray diffraction, energy-dispersive X-ray analysis and scanning electron microscopy, and their phase constitutions, crystal structures and morphologies are in consistence with that in the literature. This synthesis method is simple, green and atom economic, and promising for preparation of other oxide bronzes and related compounds.     

Übergangsmetall-Carben-Komplexe,CXXXVII Darstellung zweikerniger Gold(I)-Biscarben-Komplexe durch Carbenübertragungen von Wolfram auf Gold

The binuclear tungsten(0) biscarbene complexes3 and4 react with tetrachloroauric acid (stöchiometric ratio 1 : 2) to give the corresponding gold(I) complexes5 and6 involving the transfer of biscarbene ligands from two tungsten to two gold fragments. Preparation and spectroscopic data are described.

Herrn Prof. Dr.K. Schlögl zum 60. Geburtstag gewidmet.