David Harker

Preferred Orientation Determination Using a Geiger Counter X‐Ray Diffraction Goniometer

A simple and accurate method of determining pole figures by using a special sample mount with a Geiger counter x‐ray diffraction goniometer is described and examples given. Also, a correction formula is derived which takes into account absorption change and change in diffracting volume as the sample changes position with respect to the x‐ray beam.

Phases of Fourier coefficients directly from crystal diffraction data

It is shown that the application of Schwarzs and Cauchys Inequalities to the formulas for calculating Fa** from, respectively, the density of scattering matter and the atomic positions in a crystal leads to relations between the magnitudes of some Fa~,s and the signs or phases of others. These relations are in the form of inequalities, which vary with the symmetry of the crystal under consideration. A table of the simplest inequalities applicable to crystals possessing each of the simple symmetry elements is included. Examples of the inequalities arising from the presence of combinations of symmetry elements are presented.

Surface Replicas for Use in the Electron Microscope

A simple method is described for making replicas of surfaces for study in the electron microscope. The surface to be studied is cleaned and then coated with a very thin slightly wedge‐shaped film of polyvinyl formal having a range in thickness from about 500 to 750A in 2.5 cm. This film is formed by dipping the prepared surface into a 0.5‐percent solution of the resin dissolved in dioxane or ethylene dichloride and permitting the solvent to evaporate while the surface is held in a vertical position. The replica film is removed by placing the coated surface under water and peeling the film from it. A description of this technique is given in detail. A graph is presented which shows the thickness of resin films obtainable from various concentrations of resin in dioxane, and a table gives the interference effects which may be used for determining approximate thicknesses of thin resin films. Several easy procedures are described for checking the thickness of such films. A technique is described for preparing ...

The Crystal Structure of Ni4Mo

A nickel‐molybdenum alloy containing about 20 atom percent of molybdenum exists above 900°C as a cubic close‐packed structure. If this alloy is quenched and then held at temperatures below 840°C, an ordering reaction occurs which results in a slight tetragonal distortion of the cubic structure. This ordered structure requires for its description a tetragonal cell with 2.5 times the volume of the distorted face‐centered cubic cell. The completely ordered structure can be described analytically as follows: space group: C4h5—I4/m; dimensions of unit cell: a0=5.720A, c0=3.564A, c/a=0.6231; atomic positions: 2 Mo in 2(a), 8 Ni in 8(h), x=0.200. y=0.400.

An X‐Ray Microscope Using Mirrors of Adjustable Curvature

An x‐ray microscope is described in which the mirrors are thin optical flats. These flats are mechanically bent to obtain the radius of curvature necessary to focus the image. The adjustable curvature increases the flexibility of the microscope and the ease of focusing the image. The difficulties of grinding and polishing concave cylindrical surfaces are avoided.The degree of smoothness of reflecting surfaces was studied, and the anelastic properties of various mirror materials were investigated to find a material suitable for bending. Highly polished tungsten carbide was found to be an excellent mirror material and does not require an evaporated surface coating of high density metal.The x‐ray microscope promises to be a valuable research instrument.

Activation energy for recrystallization in rolled copper

The recrystallization reaction in OFHC and spectroscopically pure copper has been followed by X ray diffraction determinations of the amount of material with the cold-worked and recrystallized textures in specimens which had been given various heat treatments. The heats of activation for recrystallization are found to be: 29.9 kcal per mol for OFHC copper and 22.4 kcal per mol for spectroscopic copper.

Recrystallization reaction kinetics and texture studies of a 50 iron 50 nickel alloy

Recrystallization rate curves for a 50 iron 50 nickel alloy are plotted from data obtained using an X-ray spectrometer, and an activation energy is calculated for the reaction. A multiple crystal orientation is found for the as-rolled material, and the cube texture when recrystallized in the range of 500° to 600°C. It is well established that the directions of easiest magnetization in a single crystal of alpha iron are of the form , while for nickel the corresponding directions are of the form . However, when iron is added to nickel the directions persist as the easiest for magnetization until about 25 pct iron has been reached. In alloys containing more than 25 pct iron the directions of easiest magnetization change from to .