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By Howard Martens, Pol Duwez

XPERIMENTS were performed on a Cr-Fc alloy Econtaining 44.7 pet Cr in order to determine the heat evolved during the transformation of the a solid solution into the s phase, and the change in volume accompanying the transformation. Since previous measurements on the rate of formation of a from s indicated that the reaction was quite fast as soon as the equilibrium temperature of 820°C was exceeded by some 50°, standard thermal analysis experiments were performed on heating specimens of s at the rate of approximately 40°C per sec. A definite thermal arrest was observed at 870"C, Fig. 1. This result indicates that the reverse seaction of into a is exothermic. From the heating curve of Fig. 1, taking 15°C per sec as the heating rate in the neighborhood of the transformation, 2.4 sec as the time for transformation, and assuming that the specific heat of the alloy at 850°C is an average between iron and chromium, namely 9.5 cal per mol per "C, the latent heat of transformation is approximately 342 cal per mol. The order of magnitude of this latent heat was also obtained by comparing the heating curve of Fig. 1 with a similar curve obtained with pure iron under identical experimental conditions. It was found that the length of the thermal arrest for s was about 1.8 times as long as that for iron. Since the latent heat of the a to 7 iron transformation is 203 cal per mol1, 2 the latent heat of it to a would be 365 cal per mol, which is in relatively good agreement with the value determined from the heating curve. For the determination of volume change, thermal expansion curves were recorded using a specimen containing 44.7 pet Cr and completely transformed to cr by previous treatment. The curves were recorded at a rate of heating of about 4°C per min and at approximately 840°C a sharr, increase in length of about 0.08 pet took place. Fig. 2. It is therefore established that the specific volume of a near the transformation temperature is about 0.24 pet smaller than that of a, and consequently, when the s phase forms in an a matrix, it would tend to shrink away from the matrix. Since the s phase is known to be extremely brittle, these results offer an explanation for the microscopic cracks often observed in the a phase under the microscope. The results of this study are in qualitative agreement with previously published data on stainless steel 19-9DLa and on a Cr-Fe alloy containing 45 pet Cr.' The increase in density due to the transformation from n to s given in ref. 4 is 0.90 pet. These measurements, however, were made at room temperature. whereas the presently reported 0.24 pet is the change at the temperature at which the transformation takes place during heating. In the graph of Fig. 2, the percentage change in length that would be observed at room temperature is given by the length X, which is about 0.27 pet. This would correspond to 0.81 pet in volume change. Acknowledgment This work was done at the Jet Propulsion Laboratory, California Institute of Technology, under Contract No. DA-04-495-ORD-18 with the Army Ordnance Corps, Washington, D. C. The authors wish to thank this agency for permission to publish the results of this investigation. References I H. Klinkhardt: Measurements of True Specific Heats at High Temperatures. Annalen der Physik (1927) 84, pp. 167-200. - H. Esser and W. Runghardt: Influence of the Method, of Dctcrmination on the Measured Heat Content of Iron. Archtvo ffur Dct Eisenhiittenwesen 11934) 8, pp. 37-38. J. J. Gilman, P. K. Koh, and 0. Zmeskal. Delta Ferrite Formation and its influence on the Formation of Sigma in a Wrought Heat Resisting Steel. Trans. ASM 1 1949) 11, pp. 1371-1388. 1 J. M. Thomas: Discussion of ref. 3. Trans. ASM (1949) 41, pp. 3 390-1392.

Jan 1, 1957

By L. D. Jaffe

THE data recently published1-" on heat treatment of titanium alloys have not been readily systematized into an overall picture. When the ß titanium phase transforms isothermally at low temperatures, the hardness follows a typical age-hardening pattern, going through a peak as schematized by the "hardness" vs "time of isothermal transformation" coordinates of Fig. 1. As the temperature is raised, the peak will decrease in height and occur at shorter times; slowing must however take place as the /3 transus is approached. The brittle microconstituent in the region of peak hardness has been termed /3'. Its structure is still undetermined but it is clearly a transition stage from soft /3 to the £ + a that is found at the right of the peak. On continuous cooling, high cooling rates correspond to short times on Fig. 1; abscissa labeling has been added accordingly. Extremely rapid cooling will retain soft /3; very slow cooling will precipitate soft a; intermediate rates give hard 8'. Increasing distance from the water-quenched end of a Jominy hardenability bar corresponds to slower cooling (right on Fig. I), but the range of cooling rates covered by a Jominy bar is only a small portion of that shown in the figure. The p-stabilizing alloying elements retard the transformation process, moving the material to the left on Fig. 1. A lean alloy is harder water-quenched (P') than air-cooled (/3 +a); a rich alloy is harder air-cooled (/3') than water-quenched (/3). Examples of the position of various compositions with respect to the curve, based on limited data in the literature, are given at the top of the figure. Oxygen and carbon accelerate the transformation process, moving the material to the right on Fig. 1. If an alloy quenched quickly enough to retain soft /3 is reheated below the £ transus (tempered), it ages, going through a hardness maximum as time increases (moving right on Fig. 1). Material which after cooling from the /3 range lies on or right of the hardness peak, will move still further right on tempering, and so soften. Since the rate of the tempering (aging) reaction increases with temperature, the figure also may be used to represent the variation in properties with tempering temperature, at short tempering times. The simple picture given here neglects martensite transformation, as well as differences between decomposition products of /3 formed by direct isothermal transformation and those formed by quenching and tempering. It may nevertheless be of use as a guide for practical heat treatment and for further research.

Jan 1, 1955

By H. J. Oberson, J. H. Brown

Comminution devices such as rod or ball mills are characteristically nonselective in their operation in that all material fed to a mill is ground to some extent. This is unfortunate when the object of comminution is liberation, for not only is energy expended in breaking pure gangue particles wasted, but, since gangue is frequently the predominant phase, the opportunity for such loss is great. Ideally, in this application a comminuting device should develop fracture only in locked particles. In the present investigation an attempt was made to use the large density difference which may exist between minerals to prevent comminution of one while grinding the other. EXPERIMENTAL MATERIALS AND EQUIPMENT The two minerals used in this work were -8-mesh galena and -8+ 20-mesh quartz. All tests were made on 2000-g charges containing 50 pct by weight of each mineral. Heavy media suspensions consisted of -100-mesh ferrosilicon in water. For grinding, a laboratory mill 10 in. diam by 12 in. long was filled to about 30 pct of its volume with either a ball or a rod charge. The balls ranged in size from 3/8 to 1 1/8 in. in diam; the rods ranged from 5/8 to 1 1/4 in. diam by 11 in. long. EXPERIMENTAL PROCEDURE In all tests employing heavy media, the ground pulps were treated as follows: 1) After recovering the ground charge from the mill but before drying, the pulp was wet screened on 200 mesh. 2) After drying the + 200-mesh product from step 1, the ferrosilicon was removed magnetically. 3) The nonmagnetic quartz and galena product from step 2 was sized on 10-mesh through 200-mesh screens. 4) The mineralogical composition of each screen fraction was determined by measuring its specific gravity. The specific gravity was related to the weight of galena in the fraction through the relationship

Jan 1, 1961

By V. F. Zackay, J. F. Carlson

CURRENT experimental work on the development of gas turbine engines in the automobile industry has emphasized the need for a relatively low cost nonstrategic castable alloy for service in the 1200" to 1400°F temperature range. Ferritic steels

Jan 1, 1956

By J. R. Spencer

When supplies of high pressure mercury or other liquids are required in analytical work, it is convenient to have the source of supply at a relatively constant pressure and available in sufficient volume to satisfy the requirements of the apparatus in use. It is also desirable that the pressuring device be as simple and as inexpensive as possible and convenient to operate. This pump combined with a small storage reservoir containing gas under pressure has the attributes of (1) positive control of the maximum output pressure through the use of a regulator in the low pressure air supply; (2) an increasing capacity as the rate of withdrawal of mercury from the pressured system is increased; and (3) simplicity, requiring only the use of a lathe, drill press, and welding unit in its construction. DESCRIPTION Essential parts of the pump are shown in Fig. 1. In appearance the unlt is similar to the usual steam pump in common use in industrial applications although considerably smaller in size. The main differences lie in the area ratio of the air and mercury pistons and in the design of the air valve mechanism. Approximate diameters of these pistons are 4.25 in. to 0.375 in. respectively, giving an area ratio of about 130 to 1. The air piston (2) is attached to the end of shaft (4), with the mercury piston being merely a reduced extension of the shaft. Mercury intake and discharge to the pump are controlled by high pressure check valves that screw into the ports indicated at (6). Air supply is controlled by the valve assembly mounted on top of the

Jan 1, 1950

By L. Thomassen, N. Spooner, J. M. Thomas

NI-CR and some Ni-Cr-Fc alloys, when used as electrical resistance heating elements in reducing atmospheres, at times suffer rapid breakdowns due to so-called "green rot." These reducing atmospheres are most frequently used in bright annealing and heat-treating furnaces which are kept for long periods of time at 1500' to 1800°F. The green rot is a preferential oxidation of the chromium in the alloy to such an extent that the remaining metal frequently becomes ferromagnetic. The Curie point (magnetic transition point) at room temperature for a pure Ni-Cr alloy is known to be at about 7 pct Cr.¹ This represents a severe loss in chromium for one popular grade of resistance alloy, which is nominally 80 pct Ni-20 pct Cr. The formation of oxides along the grain boundaries makes the ribbon brittle and gives the fracture a green, earthy appearance—hence the name. The authors have studied this phenomenon, simulating the industrial conditions by heating resistance ribbons in various reducing atmospheres, such as moist hydrogen or the atmosphere specified in the ASTM test.² This atmosphere contains 16 pct H2, 10 pct CO, 4 pct C02, 1 pct CH1, 1.5 to 2.5 pct H2O, balance N2. Little success was had in producing severe corrosion with the commercial 80 pct Ni-20 pct Cr alloys. It had been noticed, however, that 90 pct Ni-10 pct Cr alloy wires deteriorated very rapidly when placed in the bottom of narrow thermocouple protection tubes. The bottoms of the tubes with the wires were heated in air. This took place both in porcelain tubes and in Inconel* tubes either with the cold end open or loosely stoppered with asbestos. On examination the wires showed microstructures which would be classified as green-rot corrosion. Subsequent investigations with various alloy wires confirmed the observation that corrosion occurred in some wires, including 80 pct Ni-20 pct Cr alloys, much more rapidly in such tubes than had occurred previously in test atmospheres mentioned above. When 90 pct Ni-10 pct Cr alloys are oxidized with an abundant air supply, the oxide coat consists of both nickel and chromium oxides. In this case thermodynamic equilibrium between the oxides is not established. However, when oxidized 90 pct Ni-10 pct Cr alloy specimens were heated to 1500" to 1800°F inside small diameter tubes, the oxide coat transformed to a bright metallic outer layer of nickel or nickel-rich alloy, beneath which appeared a green oxide, followed by intergranularly attacked metal. The obvious explanation is that in the narrow tubes, thermodynamic equilibrium is being established according to the equation NiO + Cr (in alloy) ? Ni + Cr2O3 This reaction is favored due to the fact that the oxygen pressure over nickel oxide is more than 10"' times the oxygen pressure over the green chromium oxide. The initial oxygen in the tubes is depleted very rapidly by oxidation of the wire and of the tube, if it is metallic. A confirmation of the occurrence of the reaction, reduction of NiO by the chromium in the alloy, was obtained by putting oxidized nickel foil into an evacuated quartz tube along with a piece of bright 90 pct Ni-10 pct Cr alloy ribbon, and heating the tube at 1820°F for a number of hours. The nickel oxide on the foil was completely reduced to pure nickel, leaving a bright foil. The 90 pct Ni-10 pct Cr alloy became strongly magnetic and showed the typical green-rot structure. Weights of the samples before and after testing showed the weight loss of the foil to approximately equal the weight gain of the ribbon. Evidently the bottom of long, narrow protection tubes, stoppered or not, may under certain conditions act just as the sealed quartz tubes in respect to being a confined space in which oxygen is not freely replenished. This condition of oxygen depletion can be prevented by introducing a small amount of air into the bottom of the tube. Many conditions becloud the green-rot phenomenon, such as carburization, sulphidization, and the presence of other corrosive agents. However, these experiments have shown that the basic reaction is a case of internal oxidation which can occur simply by adjusting the oxygen pressure to a low enough level so that the atmosphere will leave the nickel intact and oxidize the chromium. The action of the other agents in commercial atmospheres can then be taken up as individual cases. From these and numerous other tests completed to date or still in progress, it is believed that a more critical evaluation of electrical resistance alloys for their resistance to green-rot corrosion can be made. A much better understanding of the mechanism for this type of corrosion should also result. A more complete report on these experiments will be published later. In the May 1953 issue: TP 35213 Discussion: Solubility of Carbon and Oxygen in Molybdenum by W. E. Few and G. K. Manning, discussion by N. A. Gokcen: p. 747, first column, the fifth, sixth, and seventh lines should be the first, second, and third lines, followed by the present first, second, third, fourth, eighth, ninth, and tenth lines.

Jan 1, 1954

By B. W. Levinger

THE system Ti-CI- has been studied by several investigators." ' Though titanium and chromium are completely miscible at high temperatures, an intermediate phase of the approximate atomic proportions TiCr, has been identified at various compositions between 60 and 68 wt pct Cr. The structure of this phase was established as the cubic C15 (MgCu2) type with 24 atoms per unit cell and a lattice parameter 6.929 kX.2 During a study of the ternary system, Ti-Mo-Cr,5 the existence of a high temperature modification of the TiCr, phase was discovered. In a series of alloys annealed at 1300°C and containing from 60 to 70 wt pct Cr and 5 pct Mo, a new phase was present which did not correspond to either ß solid solution or TiCr,. By trial, the new phase was identified to be of the hexagonal C14 (MgZn2) structure with 12 atoms per unit cell. Further work showed that the hexagonal structure was. in fact, also present in binary Ti-Cr alloys quenched from high temperatures. To make the identification more certain, the intensities of the various reflections were calculated assuming a composition TiCr2 and C14 structure. Table I lists reflection planes, interplanar distances, calculated intensities, and a comparison of these values with the lines of a binary Ti-Cr alloy (66 pct Cr) annealed for 20 min at 1385°C and water quenched. Since high angle lines were more diffuse, the correspondence between visually observed and calculated intensities was not as good at these angles. Lattice parameters were computed to be a = 4.922 kX, c = 7.945, c/a :- 1.614. The corresponding interatomic distances are: titanium to titanium distance, 3.00:, kx, chromium to chromium distance, 2.43, kX, titanium to chromium distance, 2.88,, kX. These compare to 3.00, 2.45, and 2.87 kX in the cubic phase, respectively.' The atomic positions in the C14 structure are as follows: Titanium 1/3, 2/3, Z; 1/3, 2/3, 1/2: 2/3, 1/3, i; 2/3, 1/3, (1/2-z); Chromium 0, 0, 0: 0, 0, 1/2; 2x, 2, 1/4; 232, x, %; X, 22, 1/4; X, 2x, 3/4; x. x, 1/4; x, x, 3/4; The values of x and z were calculated for the alloy mentioned and found as follows: z — 0.061, x = 0.165. The values assumed in the intensity calculations were those for an ideal close-packed lattice or z = 1/16, x = 1/6. Work in the Ti-Mo-Cr system indicates that y2 the hexagonal modification of TiCr2, is the stable phase above 1300°C, while y1 with the cubic structure is stable below 1000°C. X-ray examination of a number of alloys annealed at intermediate temperatures showed that the hexagonal and cubic phases can coexist. Alloys quenched from 1000°C and annealed at 1100" and 1200°C showed small amounts of y2 at the higher temperature. A considerable amount of y, seemed present, however, in cast alloys annealed at 1100°C. It further appears that there is a small but definite solubility range for both phases in the ternary system. Acknowledgment The results of this paper represent work carried out in conjunction with a project sponsored by Watertown Arsenal, Contract No. DA-11-022-ORD-272. References 'M. K. McQuillan: Journal Inst. Metals (1951) 79, p. 379. 2 P. Duwez and J. L. Taylor: Trans. ASM (1952) 44, p. 495. W. J. Van Thyne,. H.. D. Kessler, and M. Hansen: Trans. ASM (1952) 44, p. 974. 1 F. B. Cuff, N. J. Grant, and C. F. Floe: Trans. AIME (1952) 194, p. 848; Journal of Metals (August 1952). Unpublished Research, Armour Research Foundation. "H. J. Wallbaum: Ztsch. Krist. 103, p. 391.

Jan 1, 1954

By W. M. Baldwin, C. R. Johns

Cobalt is reported1,2 to scale in accordance with the Pilling and Bed-worth3 parabolic law: where w = weight increase per unit surface area K = constant l = time The reported values of the parabolic oxidation constant, K, in the temperature range 600 to 1100°C follow an Arrhenius type of equation as inspection of Fig 1 shows. According to Valensi's theory5 on the scaling of metals where multiple-layered scales (for example, MeX, MeX2, and others) are possible, this fact could be construed as indicating that a single oxide only is formed on cobalt in this temperature range. Since the single straight line extends above 920°C where only CoO is stable in air (see Fig 2) it might be inferred that this is the only oxide formed on scaling. Arkharov and Voroshilova10 have studied the scales formed when cobalt is heated in air in the temperature range 385 to 800°C and report that CoO is indeed found in the scale but that CoO4 is also found as an overlay and in increasing amounts in the lower temperature ranges. No quantitative data regarding the relative proportions of the two oxides were reported. Again in the light of Valensi's theory this would indicate that the straight line in Fig 1 would be expected to undergo an inflection at some point in the temperature range 385 to 800°C. Chauvenet2 has studied the oxidation rates of CoO to Co3O4 and has found this reaction to proceed parabolically with time but reports parabolic scaling rates which are considerably (about ten times) larger than the scaling rates of cobalt metal itself. This is difficult to explain in terms of Valensi's theory although a full discussion of the possible discrepancy cannot be made in view of the lack of sufficient data. These points made an investigation of the scaling behavior of cobalt in air an attractive study. Discussion of Results Relatively large (approximately 95 sq cm of surface area) samples of 0.020 in. thick electrolytic cobalt strip,* sanded with 2/0 paper, were heated in air in a cyclone type furnace. The samples were weighed before and after the scaling treatment. The weight increases so observed obeyed the Pilling and Bedworth parabolic law at all temperatures studied. The parabolic scaling constants when plotted on a logarithmic scale as a function of absolute temperature are reproduced

Jan 1, 1950

By W. D. Bennett

AN interesting effect has been observed in the vacuum etching of titanium in the high temperature ß phase. Using a high vacuum annealing furnace, operating at less than 2x10-6 mm with a tubular titanium liner, it has been found possible to etch polished metallographic specimens at different temperatures between room temperature and 1000°C without contamination or increase in hardness.' Heat etching of titanium has been reported by other workers,' but the following example is of interest as an experiment under high vacuum in the absence of any contamination. Two polished specimens of iodide-processed titanium are placed at different positions along the axis of the furnace corresponding to temperatures of 900" and 800°C above and below the a-ß transus. The specimens are then raised to these temperatures and annealed simultaneously for 3 hr under the same high vacuum conditions. After cooling and withdrawing the specimens, their surfaces are photographed without further treatment. Figs. 1 and 2 show the results for the 800" and 900°C specimens, respectively. Fig. 1, corresponding to a vacuum etch in the a region, shows a typical equiaxed structure with what appears to be a slight shift of grain boundaries. Fig. 2, corresponding to a vacuum etch in the ß region, shows an equiaxed type of structure with the growth of striations in certain grains. The striations are only superficial, as a light polish and chemical etch restores the clean equiaxed structure. The vacuum etch, occurring as it does above the a-ß transus, records the state of the metal in the ß phase by means of the surface relief produced by the selective evaporation of metal from different grains; the metal itself reverts to the equiaxed a on cooling. The nature of the ß etch" (Fig. 2) suggests that, in transforming from the close-packed-hexagonal a to the body-centered-cubic ß lenticular-shaped laminae are formed parallel to common planes of the two structures. This would explain why some grains appear to be unaffected by the etch. The technique has interesting possibilities in the investigation of the mechanics of high temperature transformation. Acknowledgment This note is published by permission of the Deputy Minister, Dept. of Mines and Technical Surveys, Ottawa, Ont., Canada.

Jan 1, 1956

By J. P. Hammond, C. J. McHargue, J. R. Holland

IT has been reported that both berylliumL and zirconium&apos; developed the same basic textures during rolling at temperatures up to 1475 °F as at room temperature, differing only by an increase in the spread of basal planes toward the transverse direction as the temperature of deformation was increased. Iodide titanium&apos;&apos; rolled at 1050°F has a texture similar to the cold-rolled texture, {000l}, 25° to 30" from the rolling plane toward the transverse direction, <1010>, Rolling iodide titanium at 1450°F produced a more random condition with the basal planes parallel to the rolling plane and no direction strongly aligned with the rolling direction.

Jan 1, 1957

By C. E. Sims

IN an earlier paper by Sims, Moore, and Williams: data were given to show that hydrogen contents of 0.3 relative volume (0.00033 wt pct), existing at the center of 4-in.-square cast-steel coupons, could be removed by aging at 400°F for 125 hr. At the end of that time, complete restoration of normal ductility for the steel was obtained. Replicate specimens of the same steel were aged at room temperature up to 555 days or .18 1/2 months. At the end of that time, the hydrogen content at the center had fallen to 0.13 relative volume or 0.00015 wt pet, but there was no perceptible change in the ductility. On the basis of experience with accelerated aging of 1-in. and 4-in. coupons and room temperature aging of 1-in. coupons, it was predicted that, some time after two years and when the hydrogen content has been reduced to about 0.10 relative volume, there would be some recovery of ductility. One set of three bars remained, and these were held for 1310 days, or more than three years. Then tensile test bars were cut from the center, and these bars were sampled for hydrogen analysis at the time they were broken. The sample specimens were cylinders % in. in diam x 1 1/4 in. in length. The data showed that in this time the average hydrogen content had fallen to 0.096 relative volume or 0.00011 wt pct, and the ductility had increased sharply. Elongation had risen from 10 to 17.3 pct, while reduction of area increased from about 16 to 27.5 pct. On the basis of these data, fig. 1 was drawn to replace fig. 15 of the earlier paper. Extrapolation of the curves of fig. 1 indicates that it would require a period of about 2200 days or approximately six years at room tem- perature to reduce the hydrogen to the minimum value and to recover full ductility in the center of the coupons. The aging process apparently involves the movement of hydrogen from the interior to the surface of the bar and evaporation at the surface. This flux of gas presumably follows some diffusion mechanism, and an effort was made to use the aging data, obtained at room temperature and at 400°F, to calcu-late coefficients of diffusion, in the hope that they might indicate the nature of the diffusion. The conclusion was reached. however. that the data were inadequate for such a purpose.

Jan 1, 1951

By H. F. Silver

Although the literature indicated that a hydrogen-ated coal bitumen might be used as a substitute for petroleum asphalt and road tar, no work could be found in which the material was actually used or evaluated as a road binder.&apos; Therefore, a study was initiated to investigate the production and properties of a road binder made by hydrogenating coal in the presence of a solvent at elevated temperatures and pressures. HYDROGENATlON PROCEDURE Four different samples of sub-bituminous Wyoming coals and three samples of coals from other states, ranking from lignite to a low-volatile bituminous coal,

Jan 1, 1969

By N. Arbiter, C. C. Harris

In 1961, a research program started at Columbia into the mechanical aspects of flotation,* and certain ends are now in view. The purpose of this note is to explain these tentative conclusions in the hope of stimulating discussion and eliciting new data, especially industrial data, with which to test the views expressed. The variables presently under consideration are impeller rotational speed, N, volumetric air rate, Q, and impeller diameter, D, the latter being the parameter chosen to designate cell size. The most favorable *The latest work 1 references all previous publications. chemical environment is not under discussion since the procedures for establishing it are better understood than those for optimizing N and Q by virtue of a longer history of more intensive investigation. THE GRADE AND RECOVERY SURFACES With a given ore, chemical treatment, and flotation machine, both grade, G, and recovery, R, are functions of N and Q. The GNQ and RNQ relationships are best viewed in terms of three-dimensional surfaces (Fig. 1) which are experimentally determinate.2 TO maintain grade at an acceptably high level, it is necessary for N and Q to lie within certain limits, and similarly with recovery. However, the ranges of N and Q for grade on the one hand and recovery on the other are rarely the same. Selecting the single N

Jan 1, 1970

By M. Metzger, J. Intrater

IN the large number of important studies on high-purity aluminum (e.g., recrystallization and grain growth, creep, internal friction), it does not seem to have been generally recognized that the iron content, despite its very low figure, has a strong influence on a number of properties. In part, its influence is due to the very low solubility of the Fe-A1 6 phase. For aluminum of about 99.99 pct purity, the iron content may be 0.001 to 0.004 pct. For values in this range, a second phase will be present below 410" to 480 °C. This was determined by extrapolation of a log solubility vs inverse temperature plot of the solid solubility data of Edgar.&apos; One consequence is the inhibition of grain coarsening below the solubility limit. This is shown in Table I, which gives, for three iron contents, the annealing temperature required for the absence of grains smaller than 1/2 mm average diameter together with the minimum temperature for the presence of some grains larger than 2 mm diameter. The specimens were 1/4x 1 1/2-in. strips cut from hard-rolled 1/16-in. sheet supplied by the Aluminum Co. of America.

Jan 1, 1954

By J. B. Gayle

PRESENT flotation processes depend almost entirely on the buoyant properties of air bubbles to effect separations of mineral and gangue, but there is no convenient method for measuring aeration in flotation cells. Consequently the relation between aeration and cell performance has not been definitely established. In connection with a comparative study of kerosene and froth flotation processes, a modification of the displacement method&apos; was developed in which air escaping from the cell surface is measured with a wet-test meter. The arrangement shown in Fig. 1 is satisfactory for use with a number of cells and is not critical, except that care must be taken to use connections and tubing large enough to avoid excessive back pressures. Attempts to use smaller tubing resulted in back pressures that caused displacement of the liquid level in the receiver, so that some air was lost around the sides, an occurrence readily visible when measurements were taken with only water passing through the cell. With the arrangement shown, the manometer indicated an average reading of about 1/2-in. water pressure. No loss of air was evident. Fig. 2 presents typical data for a standard Denver sub-A 24x24-in. unit cell operated at impeller speeds from 0 to 710 rpm. Each plotted point represents the average for five readings distributed over the entire cell surface. Readings were taken with only water passing through the cell. Results of this type have been used in a study of the influence of operating variables on cell performance and in detecting inherent differences in the operating characteristics of cells of various kinds. Although the information presented in Fig. 2 resulted only with water passing through the cell, the apparatus is suitable for use during flotation of coal when various reagents are present. Possible modi- fications that might prove convenient under special circumstances include varying the size and shape of the receiver and substituting a calibrated, inverted, water-filled carboy or other gas-measuring device for the wet-test meter. If such modifications result in excessive back pressures, some form of draft should be applied at the discharge end of the measuring system.

Jan 1, 1959

By C. D. Haynes, S. C. Gambrell

The practice of roof bolting in WORLD-WIDE mining activities is very well-known, having been used extensively for over 50 years. The theory of roof bolting, however, is extremely complicated, and only recently have investigators attempted to explain the theory. Various means of stress analysis have been utilized in rock mechanics, most of which reduce rock to an isotropic, homogeneous medium that can be easily analyzed. One of the indirect research methods is the photo-elastic technique, the theory of which is widely known and needs no elaboration. This technique has been used extensively to examine the state of stress around underground openings of various shapes in certain types of strata, and under various loading configurations.&apos;-" In-Situ Mine Roof Trusses The photoelastic technique was employed here to evaluate the state of stress above a mine opening where support is provided by the in-situ mine roof truss. This support configuration, shown in Fig. 1, has gained popularity in recent years, particularly in mines with bad roof conditions." To the authors&apos; knowledge, no scientific determination has been made of the advantages roof trusses may offer over conventional bolting configurations comparable to roof trusses. Ordinary mine roofs usually sag or bulge downward soon after mining. Normally, after some movement the roof begins to stabilize, but the face of this bulging mine rock is usually in tension and will almost always fail unless supported. Because rock fails easily in tension, it is desirable to "preload" the roof, that is, to impress a compressive force on the mine roof to prevent bulging and subsequent tensile failure. Ordinary rock bolting installations, particularly if the bolting is perpendicular to the mine roof plane, do not produce a preloading effect. Although bolting installations squeeze the strata together and produce a beam effect desirable for support, they do not have the advantage of actual uplift. They pull down at the anchorage point with a force equal to the bolt tension which sometimes causes a separation in the plane of the anchorage detrimental to roof strength. In-situ mine roof trusses require the installation of steel tension rods in the roof of the mine much the same as conventional roof bolts, except that the rods are arranged to produce a stress pattern above the upper surface of the opening similar to that of a prestressed beam. The roof rock acts to transmit the compression force. The simplest form of truss consists of two steel rods anchored to the back of holes drilled at an angle of approximately 45 over the mine pillars. These rods are collared near the middle of the room, and the lower ends of the rods are connected by tie rods and turn-buckles. Used in this manner, a small-diameter steel rod can provide essentially the same support as a wide-flange steel beam. By tightening the turnbuckles, an uplift on the roof can be produced. Objective of the Investigation The objective of this investigation was to determine qualitatively the state of stress that exists above a mine roof after the installation of the in-situ mine roof truss vs. that of two angle roof bolts, hereafter referred to as "roof bolts," drilled and placed in the same configuration, that is, 45" above each pillar and connected together in the middle of the room by a bearing member such as a steel beam. Each state of stress was to be identified, insofar as possible, as compression or tension above the mine opening. Model Construction A photoelastic model of a mine opening was coil-structed from -in. thick PLM-4B birefringent plastic and was machined to specification shown in Fig. 2. The dimensions of the opening were chosen to simulate a width-to-depth ratio of 3 to 1. Two % -in. holes were drilled at 45" angles, as shown, to provide for the loading devices. After construction, the model was annealed at 240°F to remove stresses produced during machining.

Jan 1, 1971

By H. E. Stauss, G. Sandoz

AN increase in the value of magnetostriction1 * is known to result from the annealing of some ferromagnetic alloys in a magnetic field. Similar increases may be anticipated in the value of the magnetostriction of alloys that are of interest because of their normal high values. Two were selected for trial, 87 pct Fe-13 pct Al(Fe,Al) and 69 pct Co-31 pct Fe, the latter being used as a representative of the Co-Fe alloy series. The influence of a magnetic field present during annealing is explained by the domain theory of magnetism." The field orients the domain vectors in its own direction when the alloy is at or below the Curie temperature, and holds them there until the metal is cold. During cooling the interaction stresses between neighboring grains are largely relaxed. Interaction stresses will reappear, however, if the state of magnetization of the specimen is changed in any way, and will be larger the more the new state of magnetization differs from the one existing during the magnetic anneal. In this connection the 180" reversal of a magnetization vector is not considered a change because a simple reversal does not tend to produce a change in shape of a magnetized region. When the field existing during the anneal is removed after the metal is cold, the domain vectors can turn back only to the nearest crystallographic directions of easy magnetization because return to random

Jan 1, 1953

By William A. Mitchell

AN X-ray diffraction pattern for "calcined cold precipitated ferric oxide" is reproduced dia-grammatically along with data for other iron oxides by R. C. Mackenzie.1&apos; This pattern, which shows spacings higher than those for any other form of iron oxide, was obtained from material prepared and photographed at several different times over a period of weeks, but later attempts to reproduce the results were unsuccessful, the pattern of hematite being obtained every time.2 In an attempt to solve this problem, the original photographs showing the strange diffraction pattern were examined and a marked similarity to the hematite pattern was noticed, suggesting that the pattern was in fact due to hematite but corresponded to a shorter wavelength of X-rays than the Cu Ka which was assumed to have .been used. The eight strongest lines were provisionally identified with the strongest hematite lines and, by means of the corresponding hematite spacings, the X-ray wavelength was calculated for each line. This gave an almost constant value, with the exception of the innermost line which was somewhat diffuse, and confirmed the presence of hematite. The value obtained, 0.703 ± 0.015Å, corresponds to the molybdenum Ka wavelength. The X-ray tube used was a four-filament demountable tube with a copper target. Other photographs, mostly of soil clays, taken during the same period gave normal patterns of Cu Ka radiation with one exception. This was a calcined soil clay with a high iron content and also showed Mo Ka lines of the hematite structure. The explanation is almost certainly that the copper target was contaminated with molybdenum, but it is not known how this occurred. Specimens of alumino-silicates gave their normal Cu Ka pattern, but as the K absorption edge of iron is a little longer than the Cu Ka wavelength, specimens with a high iron content greatly reduced the intensity of the Cu Ka diffraction lines relative to that of the lines due to the shorter Mo Ka wavelength. The formation of hematite on calcining cold precipitated hydrated ferric oxide3 is thus confirmed. References R. C. Mackenzie: Investigations on Cold-precipi-tated Hydrated Ferric Oxide and its Origin in Clays. Problems of Clay and Laterite Genesis, p. 69, Fig. 4, F. AIME Symposium, St. Louis, Mo. Feb. 19-22, 1951. Published 1952. &apos;R. C. Mackenzie: Ref. 1. Note added on proof. V. C. Hansen and L. T. Brownmiller: Equilibrium Studies on Alumina and Ferric Oxide and on Combinations of These with Magnesia and Calcium Oxide. American Journal of Science (1928) 5, No. 15, pp. 225-242.

Jan 1, 1954

By J. C. Fisher

THE following facts are reasonably well established concerning the influence of boron on the hardenability of steel:1-4 1—Boron does not appreciably influence the ther-

Jan 1, 1955

By T. lkeda, R. S. Montgomery. A. Hara

Actual test specimens used in the previous laboratory wear investigation,&apos; were fully characterized and the data is given in Table 1. Most of the carbides tested could be placed into groups of similar mean grain size. When the wear rates of the members of these groups were plotted as functions of their hardnesses, a family of curves resulted; curves for groups containing data from larger grained composites were at lower wear rates at the same hardnesses. Most specimens tested showed only A-1 porosity (ASTM Standard designa-

Jan 1, 1971