The solubility of hydrogen in zirconium has been determined as a function of temperature and hydrogen pressure in the temperature range 6000 to 9000C. The solubilities obtained for a hydrogen pressure of one atmosphere are about ten per cent higher than those obtained by Hall, Martin, and Rees. 9 A partial binary phase diagram is presented and correlated insofar as possible with previous x-ray work. In particular, we have indicated existence of a new phase, ' , in the composition range 59.4 to about 61 atom per cent bydrogen. The zirconium-rich boundary of this phase is invariant with temperature. This phase is apparently separated frvm the C phase (which includes the composition ZrH 2 ) by a very narrow twophase field which has generally escaped detection and was only indirectly established in this paper.
I. lntroductionAn accurate interpretation of the microstructures, however, cam be made only if suitable specimen preparation has been achieved.EASUREMENTS of grain size, grain orientation, and porosity and the identification of the phases present can be important "tools" for coordinating the fabrication techniques with the electrical characteristics of ferrite materials. II. Preparation of Ferrite Specimens M ( I ) Grinding and PolishingThe method of grinding and polishing a ferrite specimen may vary slightly with the particular ferrite. However, the following procedure, or a modification of it, worked successfully in all instances. Rough grind on a silicon carbide cloth (grit 400) and then silicon carbide cloth (grit 600) and Microcut paper. All the grinding operations were done on a horizontal wheel at 550 r.p.m. using a 25% alcohol-water solution.For the more friable samples, an intermediate step between the fine grinding and the usual polishing may be necessary. This consists of polishing on a silk wheel lightly charged with 1200-grit lapping compound.Most surfaces obtained with wet-grinding techniques were easily polished with 1 p Diamet-Hyprez paste on kitten-ear broadcloth or with aluminum oxide (1 p ) or chromic oxide ( l p ) on a heavily loaded silk wheel at 550 r.p.m. For the final polishing 0.5p chromic oxide was used on a silk wheel a t 160 r.p.m. (2) EtchingSince ferrite materials are prepared in a wide range of compositions, their etching properties may vary considerably. Grain boundaries were clearly delineated with the following etches: etch No. 1, 50% aqueous HCl; etch No. 2, 50% concentrated H2S04, 50% saturated oxalic acid.The time necessary to bring out the grain boundaries varies from 4 to 15 minutes in Fig. 1. Typical microstructure of a nickel ferrite (bright field, 550 mp).Etch No, 1 is used on manganese ferrites. Fig. 3. Inter-and trans-crystalline cracking in a nickel ferrite (bright fleld, 550 mpl. Fig. 2. Etch flgures in a zinc-nickel ferrite (bright field, 550 mp). the temperature range 85" to 90°C. Etch No. 2 is used on nickel and zinc ferrites (Fig. 1). The etching time is approximately 1 hour a t 110°C. The condition of the etched surface, as might be expected, is a function of time and temperature. At higher temperatures the grains are more likely to be attacked, whereas a t lower temperatures only the grain boundaries are attacked. An optimum combination of temperature, timp, and etchants can be used to produce specific results in any given ferrite. 111. ( I ) Cryrfolline OrientofionOn etching, once an atom is removed from the crystal surface, dissolution will start quite readily near this void; an etch pit will then be formed. The development of etch figures depends on lattice imperfections as well as on mechanical stresses and ruptures on the surface of a crystal plane. In the study and analysis of mature etch figures, the most useful information is derived from the geometry of the etch patterns produced on planes of high atomic density. Each crystallographic plane has its own ...
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