Combined infra-red and X-ray studies of β-silicon nitride and β′-sialons

Previous investigations of the replacement of silicon by aluminium and nitrogen by oxygen in -silicon nitride have been based primarily on X-ray powder diffraction studies. In the present work this technique is coupled with parallel infra-red studies. X-ray analyses of sialons over a wide composition range confirm previous observations that increasing substitution of aluminium for silicon and nitrogen for oxygen in -silicon nitride is accompanied by an increase in cell size, with no evidence of any other structural modification. Parallel infra-red analyses show shifts in certain of the infra-red absorption bands to lower wavenumbers as the degree of substitution increases. Changes in the infrared spectra at the composition Si₂Al₄N₄O₄ indicate structural modifications which are not apparent from the X-ray investigations. It is suggested that these changes are a result of the ordering of the different atom types at this composition.     

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Ergonomics in the design and evaluation of a system for "postal video letter coding"

In co-operation with the German Central Post Office for Technological Development, the authors designed and investigated the task of and workplace for "Postal video-letter-coding". Experiments including measures of performance, errors, heart rate, arrhythmia, EMG's, and EOG's were used to experiment with variations in the design of displays, codes, keyboards, shifts and rest pauses. As a result of this work the following recommendations have been made by the authors and accepted by the authorities: An optimal display configuration has been developed with two vertically arranged tv displays. Coding-rules are to be simplified by modifications of the postcode. The usual flat keyboard has been replaced by an inclined and angular keyboard. Night-shifts must be avoided because of the tedious nature of the task. A work-rest-schedule of 50 min work and 10 min rest is proposed. In 1978 the complete work-system-design will be introduced in the standard postal service.     

Graphit als Werkstoff im Apparatebau. Graphite for the Construction of Chemical Equipment

The growing interest in the use of graphite as a material for chemical equipment is occasioned by the highly corrosion resistant properties of this low-cost material. Economic and safety specifications require a thorough knowledge of the material's properties and performance and also of the effect of these factors on a particular unit. It is to be considered for instance that the material's compressive strength is 3 to 5 times higher than its tensile strength. Another important characteristic is its static strength: the smaller the stressed volume, the higher the breaking strength. This comparatively good performance is of advantage in cases of high voltage gradients as encountered as edge stresses at the openings of tube plates and nozzles. In such cases the breaking strength may reach twice the value of the rupturing strength. A third characteristic to be mentioned is the high dependence of strength on the parameters of production; the strength decreases, for technological reasons, with increasing size. The following design principles are based on the specific properties and performance of the material:

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Conductivity measurements on liquid sulphur

The electrical conductivity of liquid sulphur has been measured from the melting point to 900° C, evaporation of the sulphur being prevented by use of an atmosphere of argon at elevated pressure. With rise in temperature, the conductivity increases except at the polymerization maximum near 170° C where a minimum in the conductivity is confirmed. Above 400° C the plot of log versus 1/T is linear, and on the assumption that the conductivity at these temperatures is intrinsic, a value of 3.1 eV is obtained for the energy gap. Although the rise in conductivity above 400° C is accompanied by a decrease in mean chain length in the liquid, there is no simple relationship between the two properties. The behaviour of sulphur is compared with that of liquid selenium.