Laser-pulse photocurrent transient measurements at oxygen evolving n-PtS2

Laser-pulse transient measurements have been performed at single crystalline n-PtS₂ electrodes with the aim of understanding light-induced hydroxide, oxide and oxygen formation. Different detected time constants permit the identification of distinct reaction products. They form surface states which function both as centers for recombination and charge accumulation in the interface. The rate constants determined are influenced by the RC-constant of the measuring circuit and can be interpreted only qualitatively. In the presence of recombination processes time constants faster than R_LC_SC are found. Evidence is given that the reaction step leading to oxygen evolution is dependent on the building-up of an electric field in the Helmholtz layer. This result may be of importance for the development of materials for the photoelectrolysis of water.     

Analytical applications of picolinealdehyde salicyloylhydrazone: Spectrophotometric determination of nickel and zinc

With a view to the use of picolinealdehyde salicyloylhydrazone as analytical reagent, a study of the physical properties and chemical reactions of this substance has been carried out. It reacts with nickel (λ_max = 375 nm, ? = 3.9 × 10⁴M^?1cm^?1) or zinc (λ_max = 365 nm, ? = 4.8 × 10⁴M^?1cm^?1) to produce a yellow 1:2 complex in both cases. Spectrophotometric determinations of trace amounts of nickel and zinc have been established.     

NaBr对C12-s-C12•2Br/氯仿体系中反胶团增溶水能力的影响

近红外(NIR)光谱技术可用于表征氯仿体系中反胶团增溶水的能力. 对于C12-s-C12•2Br (s=2, 3, 4, 5, 6, 8)系列, 不论体系是否含有NaBr电解质, 由于具有较短联接链的表面活性剂易形成较大的反胶团, 其增溶水的能力随着联接链长度增加而降低. 与未含NaBr电解质的体系相比, 当体系中存在NaBr电解质时所形成的反胶团增溶水能力降低.     

Structure of H(D)TaO3 determined by powder X-ray and neutron diffraction

Pure crystalline samples of HTaO₃ and DTaO₃ have been prepared. The crystal structure has been solved using powder X-ray and neutron diffraction (at 2 K and room temperature) and has been shown to consist of Ta(O,OH)₆ octahedra sharing vertices with the oxygen atoms displaced toward the vacant perovskite A sites. The compound is isomorphous with HNbO₃, D_xWO₃, and D_xReO₃ and contains hydrogen atoms as hydroxide groups.     

Decomposition of vegetables for determination of Zn,Cd, Pb and Cu by stripping voltammetry

A simple and accurate digestion method using nitric acid, perchloric acid and hydrogen peroxide has been developed for use in trace analysis for heavy metals in vegetables by differential pulse anodic stripping voltammetry. The recovery of the metals from the samples is lower if the hydrogen peroxide is omitted from the digestion mixture. Standard reference materials have been analysed satisfactorily by this method.     

Correlation of the position of the bond functions in H-X with electronegativity

S type Gaussian bond functions are optimized for HF, H₂O, NH₃, and CH₄. The optimization is carried out with respect to the exponent and position in the H-X bond. The position is found to correlate well with the electronegativity of Pauling and Allred-Rochow.     

The intermolecular potential function of Smith–Thakkar type for C60

The intermolecular potential function of Smith–Thakkar type for C₆₀ has been proposed, and its expression is as follows

The unit of u(r) is J/mol, r is the distance between two C₆₀ molecules center and the unit is nm. Some properties of C₆₀ in the gas and crystal have been studied using the interaction potential of Smith–Thakkar type, such as stability of C₆₀ crystals, virial coefficient and lattice dynamics.     

Subtractive differential pulse voltammetry following adsorptive accumulation of organic compounds

Subtractive differential pulse voltammetry following adsorptive preconcentration of organic compounds at solid electrodes is described. Different preconcentration periods are used, and the difference between the oxidation (stripping) currents is recorded. Background currents which are independent of the preconcentration period cancel out. Combining the enhanced peak current, due to the preconcentration step, with the background current correction of the subtractive mode, gives improved sensitivity and/or allows the use of shorter preconcentration periods. Chlorpromazine and dopamine have been used as test systems. A detection limit of around 1 x 10(-9)M has been obtained for chlorpromazine with a 10-min preconcentration period. Applicability to clinical samples is illustrated by the determination of chlorpromazine in whole blood and urine.     

Application of heat conduction calorimetry to high explosives

This paper describes some thermal analysis experiments conducted on high explosive samples. These employ differential scanning calorimetry to monitor thermal effects at elevated temperatures (around 200 °C) and heat conduction calorimetry to record thermal effects at much lower temperatures (below 100 °C).The work shows that, due to the generally high thermal stability of many high explosive compositions, heat generation rates are very low, if detectable at all, at normal storage temperatures, even when using a very sensitive instrument. The sensitivity and reproducibility of this technique has been investigated in detail by Wilker et al. [S. Wilker, U. Ticmanis, G. Pantel, Detailed investigation of sensitivity and reproducibility of heat flow calorimetry, in: Proceedings of the 11th Symposium on Chemical Problems Connected with the Stability of Explosives, Sweden, 1998] and shown to be capable of recording heat generation rates of less than a microwatt. This allows continuous measurement of decomposition processes in nitrate ester based propellants at temperatures as low as 40 °C. However, the measurement of very low levels of heat generation is difficult, time consuming and therefore expensive. If the assumption is made that the life limiting process is invariably the slow decomposition of the energetic component, this will frequently lead to very long service lifetime predictions.A number of possible complications are identified. Firstly, due to its low detection threshold, a heat conduction calorimeter may detect other reactions which will not lead to failure, but which may still dominate the heat flow signal. Secondly, the true failure process may generate little energy and be overlooked. In view of these considerations, at present it seems unwise to rely on heat conduction microcalorimetry as the only tool for the assessment of the life of high explosive energetic systems.Based on examples of life terminating processes in high explosives during storage and use, it is clear that decomposition of the energetic material is not invariably the cause of system failure. It is also by no means the only reaction that may take place in, and be observed by, a heat conduction calorimeter.     

双马来酰亚胺增韧研究Ⅱ.链扩展双马来酰亚胺及其树脂的合成及表征

合成了一系列结构不同和链长短不一的双马来酰亚胺，并对其结构和性能作了表征，同时研究了它们的固化反应和固化产物的性能。用双马来酰亚胺和二烯丙基化合物反应制造了增韧树脂，研究了该树脂的固化和热稳定性。