摘要:

AbstractA method for the determination of degree of branching, much faster than the one previously used, is described. A sample cell designed for fast introduction and removal of samples is used and the method for measuring band intensities has been adapted to computer use.It is shown how the degree of branching decreases from the first member of a series of extract waxes to the residue, because of the higher solubility of isoparaffins compared with that of n‐paraffins. A linear relationship between crystallinity and degree of branching was found to exist for the series. Fischer‐Tropsch ‘medium wax’ exhibits an abnormally low crystallinity. Possible causes for this are the fact that it has a much lower average molecular weight than the extract waxes, which were derived from ‘hard wax’, and that there can be differences in chain‐length distribution.The extract waxes were found to contain 4–6% more amorphous material than isoparaffins, as determined by urea adduction. This difference is explained in terms of the tendency of the urea method to give too low values, the fact that some normal molecules can be present in amorphous regions and the uncertainty of the significance of infra‐red crystallinity

ISSN:0021-8871    

DOI:10.1002/jctb.5010200701

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe oxidation of high‐purity aluminium sheet in dry oxygen, moist oxygen, carbon dioxide and carbon monoxide (at total pressure 1.333 × 103Nm−2) was studied in the range 673–923°K, using a vacuum microbalance to follow weight gains.14CO2and14CO were used to elucidate the mechanism of the oxidation in these gases and to estimate the extent of carbon deposition in the oxide layer.The rate of oxidation in moist oxygen was similar to that in dry oxygen, the principle reaction being 2Al + 3H2O ← Al2O3+ 3H2.It is suggested that there are three steps in the reaction in CO2, viz. 2Al+3CO2← Al2O3+ 3CO, followed by 2Al + 3CO ← Al2O3+ 3C, and about 10% of the deposited carbon reacting further by 4Al + 3C ← Al4C3. Only the last two reactions are operative in carbon monoxide.The Arrhenius plots show a distinct break in the region 773–823°K for both carbon monoxide and carbon dioxide, but not for dry or moist oxygen. This is tentatively explained by a change in the rate‐determining process from diffusion via grain boundaries or cracks in the oxide, to lattice diffusion. It is suggested that carbon may become mobile in the oxide film between 773 and 823°K and may tend to congregate in the grain boundaries and cracks.The oxide film remained protective throughout the duration of the experim

ISSN:0021-8871    

DOI:10.1002/jctb.5010200702

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe electro‐winning of chromium from chromic oxide after chlorination in a carbon‐containing fused sodium chloride flux is described. Only low values of current efficiency (based on the reaction Cr3++ 3e← Cr) can be attained. The effects of concentration of chromic and chromous chlorides in the melt, of current density and of melt temperature are reported. The conclusion is reached that the major factor responsible for the low current efficiency is the re‐solution of deposited metal by anodic c

ISSN:0021-8871    

DOI:10.1002/jctb.5010200703

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractWater vapour isotherms at 35° were measured on two samples of thorium dioxide, one crystalline and the other an amorphous gel. Specific surface areas and pore size distributions were estimated and compared with those obtained from nitrogen adsorption at −196°. The effect of thermal treatment on both samples was also investigated at 35–500°. It was shown that the adsorption of water vapour on thoria gel is purely physical in nature, and that the gel surface is characterised by the existence of pores of very particular sizes, namely of hydraulic radii 4–6 Ǎ. On the other hand, water seems to interact chemically with the surface of the crystalline sample. In this case the specific surface area could not be evaluated from the adsorption branch of the isotherm, but was successfully evaluated through the application of the ‘corrected modelless’ method to the desorption branch of the water isotherms. This gave the surface area of the total pore system which was found to be in good agreement with the B.E.T.

ISSN:0021-8871    

DOI:10.1002/jctb.5010200704

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractAdsorption‐desorption isotherms of nitrogen at −196°, and of methanol and cyclohexane vapours at 35°, were determined on a sample of microcrystalline hydrated ceria and its products of dehydration formed in air at temperatures up to 1000°. The nitrogen adsorption isotherms were analysed by the de Boert‐method. In one particular sample, theVa‐tplot gave a straight line passing through the origin, which continued until near the saturation pressure. This sample is known to be porous, and its pore size distribution curve gave a most probable hydraulic radius of 35 Ǎ. In analysing the pore structure, the corrected modelless method was used, and there is an indication that the pores are most likely to be cylindrical in shape. Sintering seems to take place through material transport from wider pores to fill narrower ones, where the total number of pores is reduced. Adsorption of larger molecules than nitrogen, namely methanol and cyclohexane, gave surface area values which are slightly lower than those calculated from nitrogen adsorption. It seems that slight persorption effects can take place in minor fractions of micropores present. However, the remainder of pores present in all samples investigated are accessible to the three adsorbat

ISSN:0021-8871    

DOI:10.1002/jctb.5010200705

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe sorption of sulphur dioxide by untreated wood samples has been investigated at a concentration of 90 μg/m3by use of35SO2. The softwoods sorbed less sulphur dioxide than the hardwoods and the sites of sorption were different in each class. Most of the sorbed sulphur dioxide was found in the outermost 0.05 mm of each sample and a large portion of it was water‐soluble. The possible role of sulphur dioxide in the weathering of woods is discuss

ISSN:0021-8871    

DOI:10.1002/jctb.5010200706

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY

ISSN:0021-8871    

DOI:10.1002/jctb.5010200707

出版商:John Wiley&Sons, Ltd    

年代:1970

数据来源: WILEY