Chronocoulometric study of the electrochemistry of Prussian blue

During the electrochemical oxidation of Prussian blue (PB) to Prussian yellow (PY), an electrocatalytic oxygen production proceeds at the electrode when aqueous electrolyte solutions are used. The formed oxygen is scavenged by the PY, probably by absorption, and it is consumed during the electrochemical reduction of PY to PB by a heterogeneous chemical reaction of PB with oxygen to PY and hydrogen peroxide. Because of this catalytic regeneration of PY, it is impossible to determine the amount of low-spin iron by chronocoulometry using a potential program in which PB is first oxidized to PY and then the charge is measured to reduce PY to PB. The latter charge is biased by the electrocatalytic PY regeneration.     

几种建筑材料的氡射气系数研究

通过天然γ能谱测量方法测定建材样品中的镭含量,计算理论上衰变产生的氡密度,以及用硫化锌闪烁法测定由样品释放到空气中的氡密度的方法来计算氡的射气系数。通过改变样品的颗粒度大小,以及改变样品的灼烧温度等条件,来研究氡射气系数的变化规律。结果表明,土坯砖射气系数在8.5%~29.4%,红砖射气系数在0.031%~3.5%之间,瓷砖射气系数在0.74%~4.5%之间;建筑材料的氡射气系数随着其自身颗粒度的增大而减小,随加工(灼烧)温度升高而减小。     

Mechanism of action of a fire retardant chloroparaffin

The mechanism by which a typical fire retardant chloroparaffin imparts fire retardant characteristics to high density polyethylene, polypropylene and polystyrene is studied by comparing the oxygen indices of these mixtures measured before and after dehydrochlorination. It is shown that flame poisoning by HCl evolved from the chloroparaffin is negligible in polystyrene and high density polyethylene, whereas it is noticeable in polypropylene. The results obtained are related to previous data on the thermal degradation of these mixtures. It is concluded that the chloroparaffin acts mainly by modifying the mechanism of pyrolysis of these polymers in the burning process. Only in the case of polypropylene is there an appreciable contribution by flame poisoning.     

Advances in the field of the synthesis of amino derivatives of terpenoids

Information on the synthesis of amino derivatives of monoterpenes by the reduction of oximes by the Leuckart reaction, and by the reductive amination of ketones by amines and nitriles is generalized. The stereochemistry of the amines formed as the result of the above-mentioned reactions is discussed.     

The effect of dissolved oxygen on the rate of pulsed electrodeposition of copper and bismuth nanowires under the conditions of template synthesis

The effect of dissolved oxygen on the electrodeposition under the conditions of template synthesis (the fabrication of arrays of meso- and nanowires by the electrochemical deposition into the aluminum oxide membranes with pore diameter of 20 to 200 nm, which were coated with a conducting metal on one side) is studied. It is shown that, when the deposition rate is controlled by mass transfer, it can be raised by using the pulsed electrolysis due to additional delivery of electroactive substance during a pause. However, the method is limited by the material corrosion during the pause (this is shown by the examples of copper deposition from the pyrophosphate solution and bismuth deposition from the nitrate solution). By the example of copper deposition from the pyrophosphate electrolyte, it is shown that corrosion proceeds with oxygen depolarization. The electrodeposition in the inert gas atmosphere gives the possibility to raise the deposition rate by several times, and the rate becomes close to the Faradaic one.     

Emulation of racemase activity by employing a pair of stereocomplementary biocatalysts

Racemization is the key step to turn a kinetic resolution process into dynamic resolution. A general strategy for racemization under mild reaction conditions by employing stereoselective biocatalysts is presented, in which racemization is achieved by employing a pair of stereocomplementary biocatalysts that reversibly interconvert an sp3 to a sp2 center. The formal interconversion of the enantiomers proceeds via a prochiral sp2 intermediate the formation of which is catalyzed either by two stereocomplementary enzymes or by a single enzyme with low stereoselectivity. By choosing appropriate reaction conditions, the amount of the prochiral intermediate is kept to a minimum. This general strategy, which is applicable to redox enzymes (e.g., by acting on R2CHOH and R2CHNHR groups) and lyase-catalyzed addition-elimination reactions, was proven for the racemization of secondary alcohols by employing alcohol dehydrogenases. Thus, enantiopure chiral alcohols were used as model substrates and were racemized either with highly stereoselective biocatalysts or by using (rarely found) non-selective enzymes.     

Sorption and desorption of water vapor by grains of native starch of some crops

The sorption-desorption of water vapor by grains of potato, corn, and wheat native starch is studied. It is shown that water vapor is mainly sorbed inside starch grains. A model is proposed for water vapor sorption by starch grains. Constructed sorption isotherm is shown to adequately describe the process in a wide humidity range. The kinetics of the sorption and desorption of water vapor by starch grains is shown to have an abnormal character.     

Kinetics and mechanisms of the oxidation by permanganate of L-Phenylalanine

The oxidation of L-Phenylalanine by permanganate ion in aqueous phosphate buffers is autocatalized by the inorganic reaction product, which is stabilized in solution by adsorption of phosphate ions on its surface. This product is a soluble form of colloidal manganese dioxide. The rate of the noncatalytic reaction pathway is first-order in both the oxidizing and reducing agent. It is not affected by potassium chloride addition to the solution, but by phosphate addition. The rate increases with the pH of the medium. The autocatalytic pathway is first-order in both permanganate ion and colloidal manganese dioxide, (the permanganate ion according to the Langmuir isotherm). The autocatalytic rate increases with reductant concentration (follows the Langmuir adsorption isotherm). It is not affected by potassium chloride addition to the solution, whereas an increase in the phosphate concentration results in an increase in the rate with the same pH of the medium. Mechanisms consistent with the experimental data are proposed.     

Synthesis and kinetics of non-isothermal degradation of acetylene terminated silazane

Novel acetylene terminated silazane compounds,with three types of substituent,were synthesized by the aminolysis of dichlorosilane with 3-aminophenylacetylene(3-APA).Thermal property of the compounds is studied by thermogravimetry analysis (TGA).It shows that the acetylene terminated silazane has high temperature resistance.The char yield at 1000℃is 77.6,81.9 and 68.7 wt%for methyl,vinyl,and phenyl substituted silazane,respectively.The pyrolysis kinetics of the silazane is investigated by non-isothermal thermogravimetric measurement.The pyrolysis undergoes three stages,which is resolved by PEAKFTT.The kinetic parameters are calculated by the Kissinger method.The role of functionalities on the thermal resistance is discussed.The vinyl-silazane exhibits higher thermal stability because of higher cross-linking density.     

Selectivity of catalytic methods of determination

By means of catalytic analytical methods, extremely low levels can be determined at low cost and with a high sensitivity that is equal to that of physical methods of trace analysis. The selectivity of the catalytic determinations, is, however, usually rather lower than that of other methods of trace analysis. The selectivity can sometimes be improved by modification of the indicator reaction through variation of the reagents and their concentrations, or by use of masking reagents or activators, or by combination with a separation method. Modification of the indicator reaction can be exemplified by the selective determination of osmium and ruthenium by their catalysis of the nitrate oxidation of 1-naphthylamine. By variation of the nitrate concentration and the use of 1,10-phenanthroline and 8-hydroxyquinoline as complexing agents it is possible to determine these two elements simultaneously. An especially significant increase in the selectivity is made possible by use of a preliminary separation step. If the ion to be determined is separated by solvent extraction and then catalytically determined directly in the extract, a very specific determination is possible; this technique has been called "extractive catalytic determination". This method has been used for determination of molybdenum (0.5 ng/ml) in sea-water, iron (5 ng/ml) in heavy metal salts, and copper (3 ng/ml) in the presence of numerous elements.     

The Role of Viscoelastic Adhesive Contact in the Sintering of Polymeric Particles

The sintering of polymeric particles is analyzed by considering the growth of contact between viscoelastic spheres driven by adhesive intersurface forces. This process is dominant during the initial phase of sintering and is succeeded by a viscous sintering step that is driven by surface tension and accommodated by viscous flow. The intersurface forces in this work are described by a cohesive zone model. A new formulation of adhesive contact that does not require the cohesive zone to be smaller than the contact radius, together with finite element simulations is used to study the growth of contact. The results of this paper establish conditions that determine the dominant mechanism of contact growth during sintering. These conditions are described using a "deformation map". For a Maxwell material, if particle radius R(max),相似文献   

Application of competitive reaction systems to catalytic kinetic analysis-determination of phosphate

A technique is described for the determination of catalytically active substances, in which a slow catalysed reaction is coupled to a fast competitive reaction. One reactant, which at the same time serves as the indicator substance, is removed by the slow reaction as well as by the competitor added to the system from outside. Under suitable conditions the time for the complete removal of the indicator substance is dependent only on the rate of the catalysed reaction and consequently on the catalyst concentration. The technique is illustrated by means of the phosphate-catalysed reduction of Mo(VI) by ascorbic acid.     

N-硬脂酰基亮氨酸的合成

采用酰氯化反应与缩合反应两步法合成N -硬脂酰基亮氨酸。以硬脂酸和亚硫酰氯为原料 ,n(硬脂酸 )∶n(亚硫酰氯 ) =1∶1 .5 ,在 80℃下冷凝回流 6h酰氯化反应合成硬脂酰氯 ,硬脂酰氯经减压蒸馏收集 1 70～2 0 0℃的馏分得到。硬脂酰氯收率为 65 %。硬脂酰氯再与亮氨酸的氢氧化钠溶液在冰水浴中进行Schotten -Baumann缩合反应制得N -硬脂酰基亮氨酸。缩合反应最佳工艺条件是反应溶液pH值控制为 9.0。反应后滴加1mol/L盐酸至pH =5 .0～ 6.0 ,加入正己烷使N -硬脂酰基亮氨酸处于水层中 ,分离并蒸干水层溶液得含NaCl的混合物。用无水乙醇萃取混合物 ,萃取液蒸干得产物。N -硬脂酰基亮氨酸收率为 75 %     

Problems encountered with the routine application of HPLC to the analysis of carbamate pesticides

Summary This paper describes the determination of all carbamate pesticides mentioned in the Austrian regulations for pesticides and of some other carbamates commonly used in the EEC. Clean-up procedure is carried out by ethyl acetate extraction. Purification is by a liquid-liquid extraction step followed by use of a florisil column. Final detection of the carbamates is carried out by HPLC on silica gel and GLC respectively The method works well for all carbamates under consideration. Only benzimidazolamine-2, the decomposition product of benomyl and carbendazime cannot be determined by the method described. Therefore determination of benomyl, carbendazime and benzimidazolamine-2 was by hydrolysis of benomyl and carbendazime to benzimidazolamine-2, which is then determined by reversed-phase chromatography.     

Kinetics of thermoelectric signals under nanosecond laser heating of mercury in aqueous electrolyte solutions

Acetaldehyde oxidation to form acetic acid is enhanced by oxygen adsorbing ad-atoms to a great extent. At the same time, the oxidation is enhanced by the S_hole control by Bi, Te, Se and S ad-atoms, which do not adsorb oxygen. The number of unoccupied Pt sites isolated by these inactive ad-atoms (S_hole), which is available for reactions, is less than that required for the formation of poisoning species but equal to that required for the oxidation, resulting in the inhibition of the poison formation reaction and the enhancement of the oxidation. The same type of enhancement, that is, the enhancement both by the S_hole control by ad-atoms and by oxygen adsorbing ad-atoms, was previously found in the enhancement of formaldehyde oxidation by ad-atoms.     

Influence of the polarity of the microenvironment of pyrene on the intensity of its solid-phase luminescence

The sorption of pyrene by a filter paper modified with lead acetate is studied by luminescence methods. Based on changes in the vibrational structure of fluorescence spectra of pyrene, it was found that the polarity of the microenvironment of pyrene adsorbed from solutions in ethanol increases with the concentration of acetic or hydrochloric acid in these solutions. It was revealed that, when an acid is added, pyrene fluoresces and phosphoresces more intensely at room temperature. It is shown that this is associated with a more efficient sorption of pyrene by the filter paper from acid solutions in ethanol.     

用废电池锌片制备硫酸锌的实验改进

用废电池锌片制备硫酸锌的学生实验,因锌的酸溶解过程所需时间太长而影响实验教学质量。本文采取加热、加入稀CuSO4溶液"催化"并实施锌的"部分溶解"等措施较好地解决了这一问题。     

有机化合物血卟啉及其衍生物被物理因素--超声激活机理研究

利用1,3-二苯基异苯并呋喃(DPBF)作为单线态氧捕获剂,研究了超声激活血卟啉的机理,通过用紫外-可见分光光度计测量了超声辐照配制好的血卟啉和DPBF溶液后的DPBF相对消耗量,表明了单线态氧的存在量．实验结果显示了DPBF的消耗量随超声照射时间和强度的增加而增加．从而支持了超声激活血卟啉产生单线态氧的说法．并提出了采用各向同性集光球把声致发光和声场分开的方法,进一步研究了是超声空化产生的荧光,还是高温热点激活血卟啉产生单线态氧．与白光对比结果表明,声致发光虽能使照相底版感光,但不足以激活血卟啉产生单线态氧．     

Fundamental aspects of oxidation of electroexplosive nickel nanopowder

Fundamental aspects of the process in which a nickel nanopowder produced by an electric explosion of conductors is oxidized under heating in air at a linearly increasing temperature and in the isothermal mode were studied. It is shown that the dispersion composition of the powder, structure of the metallic core of nickel particles, and characteristics of the oxide shell affect the kinetic parameters of the process. An explanation is suggested for specific features of the macrokinetic reaction mode caused by the joint influence exerted by the relative amounts of fractions of different-size particles in the powder and by the characteristic of the oxide layer. The reaction kinetics is simulated, with the size distribution function of nickel particles taken into account.     

Kinetics of Neutralization of Weak Electrolyte Ion-Exchange Resins

The adsorption of acids and alkalis by weak electrolyte resins is described by diffusion of the ions through the resin bead, with an accompanying neutralization reaction. A model proposed by Helfferich has been extended to account for the situation where the solution concentration of the reagent is changing during the rate experiment. Two mechanisms are necessary, depending on the concentration of the reagent. The rate expression for systems where the reagent concentration is greater than 0.01 M is given. It predicts that the adsorption rate is dependent on the solution hydrogen ion concentration in the case of weakly basic resins, and that it varies inversely with the square of the particle radius. The rate should also be unchanged by the resin of added salt.

Experimental evidence in the form of rate data for the uptake of hydrochloric acid by a commercial weakly basic resin support the derived equation, which can be modified further to account for the diffusional resistance of the liquid film around the resin particle.