摘要:

AbstractA new translucent cement, the product of the reaction between ion‐leachable glass and an aqueous solution of polyacrylic acid, is described. Its properties, with particular reference to dental applications, are reported and a proposed setting mechanism is advance

ISSN:0375-9210    

DOI:10.1002/jctb.5020211101

出版商:John Wiley&Sons, Ltd    

年代:1971

数据来源: WILEY

摘要:

AbstractHeating gypsum below 100°c gives rise to limiting values of weight loss around that of the hemihydrate formation whatever is the time of heating. Calcination at 100°c and above, on the other hand, causes a continuous loss in weight as the time is prolonged, leading to γ‐anhydrite when adequate time is given. In most of the examined samples a resistant state, with trace amounts of residual water, is reached towards the end of the dehydration process. Such residual water is driven off completely below the transformation temperature of γ‐ to

ISSN:0375-9210    

DOI:10.1002/jctb.5020211102

出版商:John Wiley&Sons, Ltd    

年代:1971

数据来源: WILEY

摘要:

AbstractThe preparation of tetraisopropoxysilane by the liquid phase reaction between tetrachlorosilane and isopropanol is described, together with the preparation of ‘isopropyl silicate’ by treating tetrachlorosilane or crude tetraisopropoxysilane with a mixture of isopropanol and water in which the molar ratio SiCl4: H2O is less than 1:1. This ‘isopropyl silicate’ is a mixture of tetraisopropoxysilane and isopropoxypolysiloxanes. The formation of isopropoxypolysiloxanes from pure tetraisopropoxysilane saturated with hydrogen chloride is also described. The hydrolysis of silicon isopropoxides is discussed. Under suitable conditions, hydrolysates which may be used to bind powdered refractories can be o

ISSN:0375-9210    

DOI:10.1002/jctb.5020211103

出版商:John Wiley&Sons, Ltd    

年代:1971

数据来源: WILEY

摘要:

AbstractThe reaction between BaCO3and Fe2O3in the proportions necessary for the formation of the hexaferrite has been studied in air. The decarbonation reaction was followed by measuring weight loss isothermally, the formation of hexaferrite by measurement of saturation magnetisation and by X‐ray diffractometry.The only kinetically important intermediate found was the monoferrite and its rate of formation could be correlated with the rate of decarbonation. An unexpected feature of this process was the rapid apparent disintegration of the barium carbonate lattice: this was far more rapid than the weight loss suggested.An examination of the pseudobinary system BaO‐Fe2O3in air at 1000°C using the electron micro‐probe analyser on reaction products at an interface between partly reacted Fe2O3and BaCO3revealed the high barium ferrites 2BaO.Fe2O3; 3BaO.Fe2O3; 5BaO.Fe2O3but no compound intermediate in composition between mono‐ and hexaferrite, nor any solid solution of Fe2O3in monoferrite.With powdered reactants the high barium phases were not formed in sufficient concentration and or crystallinity to be revealed by X‐ray diffraction. But their presence could be inferred, because of their reaction with water vapour and/or carbon dioxide, from infrared (i.r.) absorption in the range 700–900 cm−1. An absorption peak at 880 cm−1appeared to be associated with a very small amount of incompletely reacted material as saturation magnetisation approached the maximum achievable.In the presence of only 0.5% lithium fluoride both decarbonation and the conversion of mono‐ to hexaferrite were greatly accelerated; scanning electron microscopy revealed a big change in crystal size and the form suggested a mechanism involv

ISSN:0375-9210    

DOI:10.1002/jctb.5020211104

出版商:John Wiley&Sons, Ltd    

年代:1971

数据来源: WILEY

摘要:

AbstractGoethite, pure and doped with silica by co‐precipitation, was calcined at temperatures up to 900°c. The textures of the goethites and derived iron oxides were examined by nitrogen adsorption and electron, microscopy. With the latter the progressive elimination at higher temperatures of the porosity created by dehydroxylation at 300°c was followed. A sample of iron oxide produced by calcination of pure goethite at 900°c was found to possess the simplest texture. The dimensionless adsorption isotherm for this sample, which is similar to that reported in the literature for alumina, provided the reference data used in the interpretation of the isotherms for the other samples. A number of features of the pore size data derived could be satisfactorily correlated with observations made in the electron microscope. Doping with silica caused the goethite needles to grow in spherulite‐like aggregates. This texture inhibited interparticle sintering at high temperatures but did not influence the behaviour of the pore system produced in the needles by dehydroxy

ISSN:0375-9210    

DOI:10.1002/jctb.5020211105

出版商:John Wiley&Sons, Ltd    

年代:1971

数据来源: WILEY

摘要:

AbstractSatisfactory growth of Bacillus macerans and high activities of cyclodextrin glycosyltransferase (CGT) were obtained in media containing potato extract. The appearance of CGT in culture supernatant fluids during the stationary phase of growth was not due to autolysis, since intracellular levels of the enzyme were very low throughout the cultivation. When cell growth was limited by the starch concentration in the medium, CGT activity remained low during the logarithmic phase of growth but high activities appeared suddenly in the supernatant fluid when growth ceased. Negligible activities were produced by cultures growing in a nitrogen‐deficient medium in which starch was present in excess. CGT therefore appears to be a true extracellular enzyme, produced in response to exhaustion of the starch from the medium. A simple fractionaltion procedure was developed for concentrating the CGT from culture supernatant fluids. This enzyme preparation was used to convert 20% (w/v) starch solutions to cyclodextrins in 24 h and the cyclodextrins recovered were equivalent to 55% of the original starc

ISSN:0375-9210    

DOI:10.1002/jctb.5020211106

出版商:John Wiley&Sons, Ltd    

年代:1971

数据来源: WILEY

摘要:

AbstractSamples of Kenya diatomite were washed with dilute hydrochloric acid and both untreated and acid‐treated samples then heated to various temperatures. Benzene adsorption isotherm on each sample was determined at 25°c. Hysteresis occurred in all the isotherms except isotherms on diatomite preheated at 1000°c. The suitability of these isotherms for BET surface area calculation has been examined. For the untreated and acid‐treated samples which were not preheated, the pore‐size distribution and pore‐volumes have also been calculated from the

ISSN:0375-9210    

DOI:10.1002/jctb.5020211107

出版商:John Wiley&Sons, Ltd    

年代:1971

数据来源: WILEY

ISSN:0375-9210    

DOI:10.1002/jctb.5020211108

出版商:John Wiley&Sons, Ltd    

年代:1971

数据来源: WILEY