Stability of granules of solid solutions of poly-pehnyleneterephthalamide

Conclusions Studies of starting solutions of PPTA in sulfuric acid and of granules obtained under pressrue at low temperature, and of granules stored in a hermetic package, have been carried out by the methods of differential thermal analysis, turbidity spectrum and viscometry.On granulation of a solidified PPTA solution, short-term storage of the granules in a hermetic package, or short contanct of the granulated mass with air, no appreciable change in melting point or of the intrinsic viscosity of the system takes place.Long storage of a granulated solution, even in hermetic packages, can lead to a considerable decrease in the melting point of the crystal solvates, caused by an increase in defectiveness of crystal structure under the effect of moisture.Translated from Khimicheskie Volokna, No. 3, pp. 25–26, May–June, 1986.     

Rate of propagation and of damping of ultrasound in polycaproamide fibres of elastics

Conclusions The change in propagation rate and in damping of ultrasound in elastic polycaproamide yarns has been studied. It has been found that the change in these figures is determined by the same mechanism as in yarns from the press chamber method of preparation.A region of high values of the damping coefficient (25–33) has been found for elastic yarns.Texturizing yarns by the false twist method exerts a more intense action on the polymer than the compression and bending deformation in chamber pressing.The dependence between the rate of propagation of ultrasonic waves and the damping coefficient for elastic yarns reflects the effect of molecular orientation in the polymer itself and the geometric orientation of sections of the crimp relative to the sonication direction.Translated from Khimicheskie Volokna, No. 3, pp. 46–48, May–June, 1984.     

预中和度对磷酸二铵产品氮含量的影响分析

针对预中和反应槽-管式反应器混合工艺生产磷酸二铵(DAP)产品时产品氮含量时常波动的现象进行了分析.由实际生产情况分析可知,进入预中和槽洗涤液及预中和槽料浆中和度的大小及波动是造成产品氮含量波动的原因之一,预中和槽的中和度应控制在1.45～1.58.     

水泥水化热测定方法综述

水泥水化热是中、低热水泥和核电工程用水泥的一项关键的技术指标。全球范围内测定水泥水化热的方法有溶解法、直接法/半绝热法、等温传导量热法三种。本文总结了中、美、欧相关方法标准,对其测试原理、仪器设备、试验过程等方面进行了比对,并对其在领域的应用做了简单的概括。     

Photoinduced changes of the rate of dissolution of bilayer films of chalcogenide glasses

The change of the rate of dissolution upon the exposure of bilayer As₃₉S₆₁/As₃₆S₄₄Se₂₀ films to light of wavelength 380 nm and more than 470 nm from the sulfo-selenide layer side has been investigated. Although light of wavelength 380 nm is absorbed in the first layer, in the second layer photoinduced structural changes are observed, which are assumed to occur as a result of the diffusion of electron-hole pairs from the illuminated selenium-containing layer to the nonexposed arsenic sulfide in contact. The excess charge carriers induce structural changes in the As₃₉S₆₁ film that are registered as dissolution rate changes. The calculated value of the drift mobility of the slowest charge carriers (electrons) of 10^?11 cm²/(V s) is in agreement with the literature data. Studies of the Raman spectra of the films of interest confirmed that the diffusion of excess electrons and holes into the sulfide layer resulted in structural changes that manifested themselves in a decrease in the intensities and widths of the bands corresponding to vibrations of structural groups containing homopolar bonds.     

阿司匹林系列综合性实验的教学改革

将以往实验教学中分散的、孤立的关于阿司匹林方面的实验加以总结和进一步延伸,使其系列实验内容涉及知识面较广、较深,涵盖的基本技能操作较全面,使之达到培养学生的综合能力、创新能力及提高综合素质的一项综合性实验。     

Analysis of products of high-temperature pyrolysis of various hydrocarbons

Ethane, ethylene, acetylene, propane and neopentane have been pyrolyzed at 1173 K, and methane at 1372 K in a flow system, and the volatile pyrolysis products analyzed. Eleven aromatic hydrocarbons, containing 14 or fewer carbon atoms, accounted for 98 + % of the liquid products recovered in each case. Benzene was the main product, followed by naphthalene. No compounds with branched chains or multiple substituents were present, and compounds containing even numbers of carbons comprised 93–99% of each mixture. Acetylene was a major component of the gaseous effluent from each of the initial hydrocarbons. The effect of temperature on the composition of the gaseous effluent during pyrolysis of methane, ethane and ethylene was determined. Carbon film deposition from methane commenced at about 1273 K; from ethane at 1015 K and from ethylene at 1100 K, in each instance coinciding with the appearance of acetylene in the effluent. As the temperature was raised, at first the increase in the rate of carbon deposition closely followed the increase in the concentration of acetylene in the effluent. It is proposed that acetylene may be a common factor in the pyrolysis of aliphatic hydrocarbons, perhaps acting as the precursor of both surface carbon and aromatic hydrocarbons by a process of head-to-tail linkage of two-carbon units at active surface sites to form chains that then undergo dehydrogenation to carbon or cyclization and desorption as aromatic species.     

Model of Cellular Instability of Flames of Ternary Mixtures

A simple phenomenological diffusive-thermal model of cellular instability of premixed flames of ternary mixtures is developed and presented. The model shows that preferential diffusion can alter stoichiometry of the mixture, i.e., the ratio of the fuel and oxidizer concentrations, and also its effective dilution by an inert. Key parameters of the model are estimated using numerical modeling of burning velocities. Laminar burning velocities are calculated for hydrogen-oxygen-nitrogen, methane-oxygen-nitrogen, and propane-oxygen-nitrogen mixtures. Conditions for the appearance of cellular instability in ternary mixtures are determined and compared with experiments. In good agreement with experimental observations, the diffusive-thermal instability is predicted in hydrogen flames with equivalence ratios φ ≲ 1.45, in lean methane flames with φ ≲ 1.02, and in rich propane flames with φ ≳ 1.03. The magnitude of the change in the local flame velocity due to preferential diffusion is evaluated. It is demonstrated that nitrogen diffuses faster than oxygen in hydrogen-air and methane-air flames, while oxygen diffuses faster than nitrogen in flames of propane and other heavier hydrocarbons. In mixtures of air with propane or heavier hydrocarbons, the transition between stable and unstable regimes is predicted in mixtures that are leaner than the mixture corresponding to the peak of the burning velocity curve, in agreement with experimental observations. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 14–22, September–October, 2005.     

3种肠杆菌科细菌的耐药性变迁

目的研究大肠埃希菌、肺炎克雷伯菌、阴沟肠杆菌的耐药性变迁。方法对2007～2009年临床分离的大肠埃希菌(645株)、肺炎克雷伯菌(260株)和阴沟肠杆菌(150株),采用纸片扩散法进行体外药敏测定,并依据美国临床实验室标准化协会(Clinical and Laboratory Standards Institute,CLSI)规定的标准,分析3种肠杆菌科细菌的耐药性变迁。结果大肠埃希菌、肺炎克雷伯菌、阴沟肠杆菌对氨苄西林的耐药率均较高;对头孢他啶的耐药率低于头孢噻肟;与2007年比较,2008年和2009年对头孢吡肟的耐药率明显增长;未发现对亚胺培南耐药菌株的产生。结论细菌耐药性不断增强已成为临床治疗面临的重要难题,应从耐药监测、医院感染控制、合理使用抗生素等多方面努力,减少细菌耐药性的产生。     

降冰片二烯光敏异构反应动力学

以降冰片二烯为原料,四乙基米氏酮为光敏剂,在无溶剂条件下,采用循环式反应器研究了降冰片二烯光敏异构反应动力学。结果表明,反应前期降冰片二烯的浓度下降较快,反应后期降冰片二烯的浓度下降变缓。反应速率可用一级反应动力学方程表达,反应活化能为29 173 J/mol,指前因子为1026 min-1。     

Studies of Early Stages of Paste Hydration of Different Types of Portland Cements

The early stages of hydration of four different types of portland cements were studied by electron-optical and X-ray diffraction techniques. It was observed that, except for low-heat cement, very little ettringite formed up to 3 hours of hydration and that the alite present in the cements was more reactive than the laboratory form. Ettringite formed earlier in the low-heat cement than in other cements. Ettringite was found to be the stable sulfate-bearing phase in sulfateresistant cement, at least up to 30 months, although in other cements ettringite began to change to monosulfate by 14 days. Direct evidence was found for the formation of gypsum from either CaSO₄±0.5H₂O or soluble anhydrite in some cements.     

Kinetics of Crystallization of Binary Melts of Eutectic-Forming Substances

The crystal nucleation and growth rates in eutectic-forming melts are experimentally determined using a universal technique for finding the kinetic parameters of processes involving phase transformations. It is shown that, with an increase in the concentration of the impurity component, the crystal nucleation and growth rates gradually decrease and reach a minimum at a eutectic point. It is confirmed that inter- and extrapolation equations known in the theory of crystallization of one-component melts can be used to obtain reliable values of the kinetic parameters in the crystallization of binary melts at large supercoolings.     

Synthesis of fine powders of KTP-group compounds of stoichiometric composition

Precipitation of crystalline monophase nanopowders (50-100 nm in diameter) of stoichiometric binary orthophosphates of titanyl and alkaline metal in aqueous solutions has been studied. It has been shown that, in the formation of those powders, titanyl hydrophosphate can be used as a precursor. Rising temperature and alkaline ion concentration in the solution decrease the size of the powder grains, while elongating the exposure of the synthesized solid phase in the suspension increases grain sizes. An effective technique to synthesize fine-dispersed powders of monophase stoichiometric binary orthophosphates of titanyl and alkaline metal has been developed.     

A study of the rate of formation of polysulfides of tetramethylthiuram disulfide

The rate of formation of tetramethylthiuram polysulfides (TMTP), that play an important role in vulcanization, was studied. After a short induction period (<30 s), tetramethylthiuram disulfide (TMTD) and TMTD-sulfur mixes, heated to 130–150°C in the absence of rubber, rapidly form a series of TMTPs. The concentrations of TMTPs of lower sulfur rank increase most rapidly, indicating that sulfur atoms are added to the accelerator sequentially. The incorporation of sulfur molecules to give TMTPs, which subsequently desulfurate, does not occur. Equilibrium concentrations of the various TMTPs are achieved in about 2 min. Little tetramethylthiourea is formed below 200°C. Tetramethylthiuram monosulfide (TMTM) is stable, but TMTM-sulfur mixes form TMTPs. A mechanism is proposed to account for the large amount of TMTM formed on heating TMTD in the absence of sulfur and the correspondingly higher TMTP concentrations in the presence of sulfur. © 1995 John Wiley Sons, Inc.     

Strategic Planning of Production of New Types of Chemical Fibres

Strategic plans for production of new types of chemical fibres selected for implementation should be taken into account in strategic planning of the development of the concrete enterprise and should be flexibly incorporated in its overall strategic program, which usually includes a complex combination of several innovative strategies. We hope that the material in the article will draw the attention of specialists who are developing innovative programs for the enterprises in the industry.     

Effect of reactivity of different types of hydroxyl groups of HTPB on mechanical properties of the cured product

The amount of three types of hydroxyl functional groups (G_OH, H_OH, and V_OH) in hydroxyl terminated polybutadiene (HTPB), remaining in samples acetylated to the same extent under two different conditions, viz., fast acetylation using acetyl chloride in presence of N-methyl imidazole catalyst and slow acetylation by acetic anhydride, differed significantly. For the fast acetylation there is a uniform reduction in all the three types of hydroxyls, probably because the reaction becomes random at rapid rates and the reactivity of the different types of hydroxyls does not play a major role. However, in the slow reaction, the reduction of G-type hydroxyls was 30% more than the expected value and there was a corresponding increase in the amount of V-type hydroxyls remaining in the acetylated product, showing reactivity of OH in the order of G > H > V. When the reaction is slow, it becomes selective and the change in reactivity of the three types of OH groups is reflected in the extent of conversion. The mechanical properties and the crosslink density data show a reduction in the samples containing lesser amounts of G_OH, confirming the branching nature of G_OH, which is involved in the crosslinking reaction. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1313–1320, 1997     

Abuse of megadoses of vitamins

There is no evidence of any nutritional benefit derived from the consumption of vitamin supplements in excess of the daily intakes recommended by the various international and national expert committees. Furthermore, in the case of certain of the vitamins such as vitamin A and vitamin D, excessive intakes result in toxic effects. To a lesser extent this is also the case for vitamin C and nicotinic acid. In addition, the use of high supplements or megadoses of any vitamin results in a wasteful misuse of economic resources. This reduces the capacity to acquire foods which would have clear nutritional benefits for the whole family. Consequently, the indiscriminate use of these megadoses must be discouraged. Their application is exclusively justified in clinical situations under direct medical supervision.     

The effect of deterioration of nanofiltration membrane on retention of pharmaceuticals

The retention of 8 acidic and 2 neutral pharmaceuticals in nanofiltration (NF) was investigated by a loose NF membrane and a tight NF membrane. The retention change due to the exposure to chlorine was studied. The retention of pharmaceuticals was affected by the electric repulsion effect in addition to the size exclusion effect. In the case of the loose NF membrane, the retention of pharmaceuticals was more sensitive to the exposure to chlorine than salt retention because both the decrease in electric repulsion effect and the increase in pore size affected the permeation of pharmaceuticals. On the other hand, in the case of the tight NF membrane, the retention of acidic pharmaceuticals were maintained at higher range at neutral pH range even after exposure to chlorine, though the increase in the pore size was obvious judging from the decrease in the retention of pharmaceuticals in the acidic solution environment.     

Effect of addition of dyes to brightening-lubricating compositions of properties of viscose fibres

Conclusions It has been found that a content of certain dyes in the brightening-finishing composition exerts and important effect on phenomena which take place during the drying of the freshly spun fibres.The introduction of additives in dyeing ensures obtained fibres of increased strength.The analogy in action of dyes and some organic and inorganic substances which we have previously investigated indicates a large role for the addition of such substances in the course of the process of drying freshly spun fibres, regardless of features in their structure.Translated from Khimicheskie Volokna, No. 4, pp. 54–56, July–August, 1989.     

Rheokinetics of polymerization of N-laurylmethacrylate

The free radical polymerization of n-laurylmethacrylate has been studied using a combination of rheological and kinetic methods. In addition to classical dilatometry, the extent of reaction of a polymerization was followed in a cone and plate rheometer by measuring the change in the diffraction of a laser beam shone through the polymerizing sample parallel to the plate of the rheometer. The change in diffraction was caused by the change in index of refraction of the monomer becoming polymer, which was related to the extent of reaction. Simultaneous measurements of loss and storage moduli and dynamic viscosity at 1 Hz provided the data necessary for correlating changes in the kinetics with changes in the rheology of the polymerizing system.