A high-temperature Debye-Scherrer camera, and its application to the study of the lattice spacing of silver

A Debye-Scherrer camera capable of giving accurate results at high temperatures is of great value in metallurgical research work. In Part I of the present paper a camera is described which has been designed primarily for accurate measurements of lattice spacings at temperatures up to 1000º C. In Part II results are given for the lattice spacing of silver at temperatures up to 943º C., and an equation is described which gives the coefficient of expansion of silver from the absolute zero to the melting-point. Part I In a previous publication (Hume-Rothery and Reynolds 1937) the authors have described the precautions which are necessary if the composition of annealed filings is to be determined accurately, and in high temperature work these difficulties are accentuated. At 1000º C. most metals are volatile to some extent in a vacuum, whilst many re appreciably volatile at atmospheric pressure. For precision work on alloys it is therefore usually undesirable to use any type of camera in which a small quantity of filings is heated in a relatively large space, particularly if the design is such that distillation from a hot to a cold region can occur. In the present camera these difficulties are avoided by enclosing the filings in a very thin-walled silica capillary tube which may be sealed off in a vacuum, or with an inert gas at a suitable pressure. The preparation and handling of these thin tubes requires special methods which are described on p. 29.