Synthesis of deuterobutadiene-butadiene AB2 and AB3 miktoarm star copolymers

The synthesis of well-defined, monodisperse AB₂ and AB₃ miktoarm star copolymers, in which A is polydeuterobutadiene and B is polybutadiene, is described. The synthetic procedure involved reacting living polydeuterobutadiene with a large excess of either methyltrichlorosilane or tetrachlorosilane to yield a ‘one-arm star’. SEC traces of this ‘one-arm star’ are indistinguishable from that of the uncoupled polydeuterobutadiene indicating no further coupling to form multi-arm stars occurs. Unreacted chlorosilane was removed by distillation and the introduction of an excess of living polybutadiene generates the star. The star polymer was isolated from the precursor polybutadiene by fractionation. Received: 27 April 1998/Revised version: 15 June 1998/Accepted: 16 June 1998     

Comparison of the group V and VI transition metal carbides for methane dry reforming and thermodynamic prediction of their relative stabilities

The DME‐SCR activity was suppressed upon exposure of a γ-alumina catalyst to SO₂, in contrast to methanol‐SCR, which remains active at the same surface sulphate coverage. This difference in behaviour is attributed to the limited availability of surface methoxy, which may be regarded as a prerequisite for NOx- reduction over γ-alumina under lean conditions, in the case of dimethyl ether in the presence of SO₂. This revised version was published online in July 2006 with corrections to the Cover Date.     

Special features of the mineral composition of magnesite from deep horizons of the Satkinskoe deposit

Some special features of the mineral composition of magnesite from deep horizons of the Satkinskoe group of deposits is considered. Minerals that are paragenetically connected with magnesite and affect substantially the production process and quality of refractory products are described. It is established that the concentration of SiO₂ in the magnesites increases regularly with increase in the depth of the horizon. Ways to solve the problem of fabricating quality magnesite for roasting are suggested.     

Studies on the respiratory health of primary school children in urban communities of Hong Kong

The first stage of a 2-year survey of respiratory morbidity in primary school children was conducted in two districts of Hong Kong in April/May 1989. One group (2009) of children was from Kwai Tsing District, which had high levels of exhaust emission from factories. The other group (1837) was from Southern District where atmospheric pollution was considered to be relatively low. After adjustment for gender, age, socioeconomic factors, child smoking and exposure to parental smoking, the prevalence ratios of sore throat, evening cough, cough for more than 3 months, morning phlegm and wheezing were found to be significantly higher in Kwai Tsing. The difference between the districts is likely to be related to the environmental air quality. The study, which is continuing, will provide the basis for an evaluation of the impact of new low sulphur fuel regulations introduced in July 1990.     

A Novel Processing Route to Control Grain Growth in Submicrometer Alumina Compacts

A novel processing procedure for significantly suppressing grain growth in submicrometer alumina compacts has been developed and implemented with the intent of ultimately using the same processing route to control grain size in nanophase alumina compacts. In this study, partially sintered alumina pellets made from 0.5 µm starting powders are altered by the chemical infiltration of Si₃N₄. The control and infiltrated pellets are then heated to 1650°C for 4 h. The fully sintered pellets are approximately 97% dense. Suppressed grain growth is observed in the infiltrated pellets. The average grain size in the control pellets after densification is 4.2 and 1.2 µm in the infiltrated pellets. Depth of infiltration is measured using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Depending on the specific infiltration conditions used, the outer 15-50% of the infiltrated pellets exhibit a graded microstructure consisting of a region of abnormal grain growth and a region of suppressed grain growth. Abnormal grain growth is visible on the outer surfaces of the infiltrated pellets where a relatively high ratio of Si to N is present. Further into the pellet, after some depletion of the Si source gas has occurred, regions of suppressed grain growth are apparent. Based on these results, an infiltration profile is determined. A mathematical model is developed to describe the infiltration process and to determine optimal infiltration conditions. High-resolution electron microscopy (HREM), energy dispersive spectroscopy (EDS), electron energy loss spectroscopy (EELS), and X-ray photoelectron spectroscopy (XPS) are used to study the infiltrated samples.     

Graft polymerization of hydroxyethyl methacrylate to polycaproamide using a heat-treated solution of monomer

A method of modifying the polycaproamide fibre Megalon is proposed; it consists of introducing a stage of preliminary heat treatment of a solution of the monomer in the graft polymerization process. The basic characteristics of the kinetics of graft polymerization of heat-treated hydroxyethyl methacrylate to PCA were investigated. The induction period decreased to 15 min, the reaction rate increased by 2-2.5 times, and the activation energy decreased by 1.6 times. It was found that the modified PCA fibre prepared by the new method has satisfactory strength and hygienic properties. Volgograd State Technical University. Translated fromKhimicheskie Volokna, No. 6, pp. 11–13, November–December, 1999.     

Electrochemical reduction of chromate ions from dilute artificial solutions in a GBC-reactor

Reduction of chromate in very low concentration (20 ppm) has been carried out in a GBC reactor. Final concentrations below 0.5 ppm have been achieved at reasonable reaction rates. Spontaneous reduction of chromate by hydrogen in a GBC reactor without an external power source requires careful selection of cathode material. Chemically stable materials such as titanium and RVC tend to passivate when in contact with chromate solution and are unsuitable for use as cathode materials. Graphite, active carbon and graphite felt show no obvious passivation. Reduction of oxidized groups and oxygen are the major side reactions. These occur significantly, especially when using an activated carbon bed as a cathode.