In the course of an X-ray study of the iron-palladium system (1) we have made a rigorous determination of the crystal structures of the FePd and FePd3 superlattices. Since our results do not agree with the reported structure of FePd, and the FePd3 structure has not been reported, we think it worth while to publish our full structure determinations. Jellinghaus(2) has found that annealing at 500° C. profoundly affects the coercive magnetic properties of an alloy of the composition FePd. From De bye patterns, he concluded that the annealed alloy possessed an ordered, tetragonal structure like AuGu with c/α = 1.03 and a0 = 3.80 A. The same alloy quenched from higher temperatures was face-centered-cubic, a0 = 3.78 A, and was not ordered. He listed the following lines as being present in his pattern: (, and (004). The determination is not satisfactory, however, since the lines (011), (012), (230), and (123) have h + k odd, which is forbidden for an AuCu structure. Hocart and Fallot (3) found anomalous magnetic properties at the compositionFePd and also at FePd3. They took X-ray diffraction photographs which showed the disordered face-centered cubic phase predominating in both cases with a few weak lines of another phase present. Presumably the alloys were not sufficiently annealed. Grigorjew (4) reports a probable compound or superlattice at the compositionFePd3 on the basis of thermal measurements, hardness, and electrical conductivity. We prepared a number of alloys of pure palladium and carbonyl iron by pressing together the filings and melting them in alumina crucibles in a vacuum. A flush of hydrogen during heating with immediate reevacuation reduced possible oxides. The resulting ingots were homogenized by long anneals near the melting point combined with cold work. When filings mixed from several parts of the ingot gave sharp lines on back-rcflection photographs, the sample was considered to te homogeneous.The Debye patterns of a sample containing 51.9 atomic per cent palladium are shown in the figure. Samples quenched from above 700° C. show a face-centered-cubic structure with atoms distributed at random. At 650° C. and below, the tetragonal structure shown in the second picture was found. At intermediate temperatures, a mixture of the two patterns was present.The interplanar spacings of the lines cannot be fitted to a tetragonal
The effects of hydrogen as functions of time, temperature, and impurities in steel are described and experimentally demonstrated. Experimental evidence is presented to show that the blistering and boiling action over carbide areas in steel are due principally to hydrogen that associates with the carbon. Steel enameling stock contains quantities of hydrogea which may effuse during firing to cause or aggravate such phenomena as "boiling," "primary boiling," "reboiling," "blistering," and "bubbling." Low-temperature effusion of hydrogen contributes to other defects, including "fishscaling," "delayed fishscaling," and possibly "pop-offs," "jumping," "shiners," and some caws of "chipping" and, perhaps, "bursting" of enamel on cooking utensils. These defects have seldom been identified with hydrogen evolution. An indirect effect of hydrogen on "copperheads" and "black specks" is also identified.An exhaustive review of both English and German literature on enameling defects is included. Many observations recorded in the literature are shown to agree with the hydrogen theory. Certain types of inclusions in steel are shown to react with occluded hydrogen to form compounds that will not dissociate appreciably at some enamel-firing temperatures, and critical quantities of the hydrogen are therefore prevented from reaching the enamel coating during firing to cause blistering and related defects.
No abstract
The confusion in identifying hydrogen as the predominating cause of certain defects in enamel on cast iron has been due largely to the close association of carbon and hydrogen in cast iron and steel. The principal relation of carbide and graphite to enameling defects is the release of hydrogen from the carbon during enamel firing. The much-discussed "chill layer" therefore is important chiefly because this layer often contains hydrogen that is bound to the carbon in the cementite. Experiments show that when hydrogen is absent, regardless of the depth or nature of the surface chill, no pinholing or blistering results during firing at 725°C.Sources of the hydrogen that causes the defacement are found chiefly in melting and in casting. The low oxygen pressure of molten cast iron favors hydrogen absorption. Moisture in the atmosphere, in the charge, or chemically combined in the rust on scrap provides thegreatest quantities of thegas,>nd moisture and organic materials in the mold are also prolific sources of hydrogen for absorption by the iron. At ordinary temperatures, rusting is often harmful.Flushing the melt with a dry, hydrogen-free gas, such as nitrogen, removes the dissolved hydrogen, and defects during subsequent enameling will not occur unless hydrogen is obtained later from other sources.Chipping phenomena probably are caused chiefly by hydrogen effusion, just as are analogous defects in sheet-steel enameling.
The technique of fractography is applied to the cleavage surfaces of an ammonium dihydrogen phosphate synthetic single crystal, using both dark-field and oblique illumination. Excellent hackle patterns are observed; and other markings are also found which relate to crystallographic deformation mechanisms and to crystal imperfection. These latter are: (a) lamellar and blocklike markings suggesting fine-scale crystallographic weakness of a micellar type, (b) dendritic formations of unknown origin, (c) inclusions of foreign phases, and (d) thin textural effects on the cleavage surface. Fractography is accordingly proposed as a tool for studying the perfection of such crystals, also the manner in which they respond to deformation and cleavage.
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