Search Documents

AVING started to tell you of working potter's clay for making crucibles and shells, the wish came to me to tell you of the practice of this art also. Although it may seem at first glance to be outside the order and purpose of my writing, he who considers well will see that it is not unrelated to it but proper, since it is wholly dependent on the agency and power of fire if it is to be brought to its perfection. Moreover, the potter's glazes and colors are all substances of various metals or impure minerals and therefore belong to fire. Since it is my intention to treat of fire, minerals, and metals for you, I surely should not have omitted this, particularly because it is a necessary art which enriches and is greatly praised both for its ingenuity and its beauty. The art of the potter has two sources as its principal basis. One comes from the art of design, the other from various alchemical secrets and elemental mixtures. In regard to these, I find that, in my opinion, all this art depends in the last analysis on four things: on good judgment in general, and on the art of design so as to be able to make the vessels beautiful and of good shape, as well as to ornament them with painting; after baking them well the first and second times, the next thing is to know how to make and apply the glaze well and to paint them with varied and appropriate colors. The fourth is to see that you have good, fine clay without small stones or lumps-indeed this is to be considered as the first thing. Now this that I have called clay is what many call cretaceous earth and some call argil. It is found and dug up when the masters wish to make use of it and is put in a container to be moistened. When it is moistened, it is beaten on a bench with an iron rod and very well prepared. Mixing it carefully, every small stone, lump, or other hardness that it contains is removed and cleaned away. Then a shaft [145V] of iron is fitted as the journal in a large wheel. On the other end of the journal a small wheel is made which forms an instrument for working that is called a lathe. Having put some clay on this, it is made to rotate by pushing with one foot, and, by rotating it, vessels are worked into a pleasing shape and size. Then they are taken off and put on a board to dry. After drying artificially or naturally they are painted red,

Jan 1, 1942

By R. L. Rickett, W. C. Leslie

The influence of deoxidation practice, prior thermal history, and aging time and temperature on the strain-aging behavior of low-carbon open-hearth steels was investigated. The criterion of aging employed was the increase in yield strength in the tensile test, after straining and aging. Composition, prior heat treatment, and aging conditions were all found to be important in governing the strain-aging characteristics of these steels. THAT deoxidation changes the strain-aging propensities of low-carbon steels has been known for a long time, but there has been little agreement, and even contradiction, between results obtained by different investigators and between results obtained in the laboratory and in the mill. This investigation was begun in the hope that some of the uncertainties connected with the strain aging of commercial steels could be eliminated. In considering this problem, it was necessary to define strain aging and to examine the methods used to measure this property. Strain aging can be defined as the changes in properties of a metal or alloy with time, after cold working. The rate at which these changes occur increases as the temperature is raised above atmospheric. The requisite plastic strain is the principal distinction between strain aging and quench aging, the latter being due to precipitation from supersaturated solid solution. Strain aging is also characterized by rapid attainment of maximum hardness at high aging temperatures and lack of softening (overaging) at low aging temperatures. Several possible criteria of strain aging have been listed by Sachsl and by Davenport and Bain.' Because changes in mechanical properties are the most easily measured and the most commonly used, consideration of methods to be used in this investigation was confined to three tests: tensile, notch-impact, and hardness. Hardness tests are the most economical and easiest to perform, but produce only one measure of strain aging. Also, as pointed out by Felmly, Hartbower, and Pellini,³ hardness changes due to aging are not pronounced for steels containing more than 0.15 pct C. Notch-impact tests require careful preparation of large numbers of specimens. Above and below the transition temperature the test lacks sensitivity; furthermore, it is extremely difficult to impart a uniform strain to the specimens, followed quickly by aging and final testing; machining must generally take place after straining. For these reasons, the tensile test was selected for use. Although this test requires a considerable expenditure of time, labor, and money in preparation of the specimens and performance of the test, more information can be gained than from any other single mechanical test, information which includes upper and lower yield points, yield-point elongation, tensile strength, strain-hardening exponent, reduction of area, and elongation. Low and Gensamer' and Schwartzbart and Low5 lso used the tensile test, taking the increase in flow stress after straining in tension and aging as a measure of strain aging. In our work, as in theirs, each specimen was strained an arbitrary amount, sufficient to pass through the

Jan 1, 1954

By C. M. Romanowitz, H. A. Sawin

PLACER dredging as we know it today, especially gold dredging, is an industry about 40 years old, dating from the beginning of this century, when a few mining men in California saw the possibilities in adapting earlier dredging methods to California placer fields in and immediately adjacent to streams. At first it was thought that dredges must be operated in existing stream beds, but experience soon pointed the way to dredging alluvial deposits of old stream beds, operating on landlocked dredging ponds. Within the first five or six years of modern dredging, experience was gained so rapidly that dredges to dig 60 ft. below water level were designed and built. This depth was believed by many operators to be the maximum at which successful dredging could be carried on. Alluvial deposits of gold, suitable for dredging, were readily handled by equipment available and developed early in the industry's history. Much of the gravel was easily dug and if deposits were cemented, contained large boulders, or for some other reason could not be handled by a dredge, the ground was abandoned in favor of other deposits that could be handled easily. Many failures, adversely affecting the dredging industry, resulted from attempts at that time to extend the scope of placer dredging with equipment not suited to the formation being dredged. Dredging ground suited to early equipment was exhausted eventually, but many supposedly undredgeable alluvial fields containing gold in commercial quantities were found and became known to dredgemen. Improved equipment was needed to work deposits known to exist at great depths or associated with unusual obstructions. Operating companies looked to dredge manufacturers and metallurgists, particularly manganese-steel foundries, for improved designs and materials. Experience developed in California has spread throughout the world, and dredges of improved types have been adapted to the mining of platinum and tin as well as gold. Space will not permit a description of all the improvements in dredging since the early days, but a few of the recent developments are worthy of note, because they make possible the dredging of placer deposits of great depth, those having hard, irregular bedrock or containing large boulders in great quantities, and compacted or cemented gravel deposits. DEEP DREDGING At Hammonton, Calif., Yuba Consolidated Gold Fields has, within the past two years, built its dredge No. 20. The company has operated continuously in that field since 1904, digging successively at maximum depths of 60 ft., 80 ft., 112 ft., and now 124 ft. below water level. The first dredges were equipped with buckets of 6 and 7 1/2-cu. ft. capacity; six dredges operating in the field today have 18-cu. ft. buckets, digging now 65 to 124 ft. below water level. Some ground near Hammonton has been dug for the third time, owing to the devel-

Jan 1, 1941

By William Metcalf

William Metcalf, Pittsburgh, Pa. : In rising to discuss Dr. Dadley's paper, I feel somewhat as I did at the Baltimore meeting —that a "crucible" man has no right to interfere in a "Bessenier" discussion; yet having read the paper very carefully, I feel impelled to say something, for two reasons: First, because I believe Dr. Dudley is entirely on the right and having undertaken and partly accomplished a great work, he .is entitled to the help of all who have experience in these matters; and second, because the data given force me to colicur in Captain Jones's opinion that the analyses are incomplete, since they ignore sulphur, copper, nitrogen, and possibly other injurious elements. In an experience of fourteen years, and with probably more than a hontlwl tests, we have never found the chemistry and the of crucible steel to disagree. If in any cave a disagreement tins sp- . peared, it has been our invariable custom to go over all our physirtal testa with great care, and if we found no error, then to refer the matter back to the cherubt, who has invariably found some unexjmted element to account for the trouble. It is only just to the chemist to say here, that ordinarily be is only expected to determine phosphorus, silicon, sulphnr. Generally the metals, with the exception of manganese, are not looked for, although a watch is usually kept for copper and arsenic. Further, in most cases we have found our own work more liable to be faulty than the chemist's. Having arrived then at such a degree of experience that we can preJict the analysis from our tests, or our tests from the analysis, with almost absolute certainty, I can see no reason why the same results map not be attained in the Bessemer practice. But two things are essential, neither of which we have here; first, cornplete analyses; and second, a record of the nature of the blow, the heat at which the ingots were bloomed, and the mile finished,—in short, a complete history of the This latter is quite as essential as accurate and complete analyses. Dr. Duclley ignores sulphur and copper on fair enough grounds commercially speaking, bnt when he announces so gmve a conclusion as he has reached, in a scientific way, the omission of any elementn that, may affect the conclusion is hardly justifiable. His diEerenvcs of phosphorus units, which I milst term units of rottenness 83 fr os phosphorus is concerned, and which I am sorry be did not llama wnits of alloys,—are very small, and if eulphur and copper hod been inclurlid they might havo upset hie conclusions sitogether, The

Jan 1, 1881

By C. S. Yust, C. S. Morgan

ThIS note reports the observation of masses of dislocation etch pits around the weld necks of small single-crystal particles of calcium fluoride sintered to a cleaved face of a larger CaFz crystal. Crystal particles in the -50 +I00 mesh size range were placed on freshly cleaved CaFz surfaces and heated at 1250°C for 30 min in a tantalum container in an argon atmosphere. The sintered specimens were then etched at room temperature for 40 to 50 min in a 2 pct sulfamic acid solution which is a selective etch for dislocations in caF2.' Figs. 1 through 3 show the masses of dislocation etch pits observed around weld necks after etching. In some cases, particles were gone after removal of the specimens from the furnace although weld necks were readily visible. In other instances, no etch pits formed around a weld neck. A possible cause of concentrations of dislocations on the crystal surface is mechanical deformation of the base crystal when particles are dropped on it. If such a deformation does occur, it would be much smaller than that caused by the light punching of a crystal with a sharp instrument which results in large concentrations of etch pits. However, crystals deformed by punching with the sharp instrument and annealed at the conditions of these experiments (1250°C for 30 min) before etching showed no concentrations of dislocation etch pits. It is obvious that dislocations from the much smaller deformations, possibly created when particles are placed on the surface, would also anneal out. Etching of large crystals which had particles placed on them in the usual manner but which were not heated showed no dislocation concentrations such as shown in Fig. 1. The magnitude of dislocation etch-pit concentrations did not vary with extensive variation of the cooling rate. The appearance of many of the etch-pit clusters is typical of a well-annealed condition, indicating that the dislocation concentrations formed before the specimen temperature was lowered. Therefore, it is evident that thermal stresses in the neck area did not create the deformation indicated by the presence of the dislocations. The possibility exists that the etch-pit concentrations at places where particles had been removed may be the result of deformation accompanying the fracture of the sintered bond. That this is not so was demonstrated by breaking off particles around which no etch pits occurred. Re-etching never resulted in the large concentrations observed at sintering sites. The stress available to effect material movement during sintering of two particles will depend on the geometry at the contact point but can easily exceed the macroscopic yield stress in CaFz systems. It appears that the plastic deformation observed results from sintering or simply from the weight of the small particles. It has been previously argued that plastic flow makes an important contribution to the initial densification of oxides having the fluorite crystal structure.2p3 If plastic deformation occurs, it would begin as soon as the temperature is sufficiently high

Jan 1, 1967

By P. Niessen, S. J. Bercovici

RECENTLY Aust et al.&apos; proposed a model of non-equilibrium grain boundary segregation based on a vacancy gradient induced uphill diffusion process of solute to grain boundaries. According to their proposal, solute atoms which are attracted to vacancies would, during the cooling of a sample, migrate with vacancies toward grain boundaries (vacancy sinks) and thereby enhance the solute concentration in boundary regions. For solute atoms which are not attracted to vacancies no such boundary solute enrichment would be expected. These concepts were given experimental support by boundary and bulk mi-crohardness measurements of various thermally treated dilute zinc and lead alloys and also doped aluminum oxide. The underlying assumption in their work was that solute enrichment in boundary regions is indicated by higher microhardness values. From thermodynamic considerations1&apos;2 it appears that the solid-liquid solute distribution coefficient (K), defined as the concentration of solute in the solid to the concentration of solute in the liquid at equilibrium, indicates whether attractive or repulsive forces exist between vacancies and solute atoms. K < 1 indicates a solute-vacancy attractions, K > 1 indicates no, or a repulsive, vacancy-solute interaction. This note is to report on observations of different grain boundary etching phenomena in high purity zinc alloys. These phenomena appear to depend on whether a K < 1 or K > 1 solute is present. In experiments designed to measure directly the solute enrichment in grain boundary regions, samples of zone refined zinc with 0.1 at. pct solute additions were cooled from 380°C at a rate of 3°C per min. A surface layer of approximately 50 was then removed from the samples by chemical polishing. The samples&apos; surfaces were then protected by a chromating treatment such that in a subsequent etch only grain boundary regions were dissolved. The dissolved regions were approximately semicircular troughs, 10 µ in width. The grain boundaries were usually in the middle, i.e., at the bottom, of this trough. For zinc containing the K < 1 solutes cadmium and aluminum, the grain boundary was always indicated by a ridge as shown in Fig. 1. For pure zinc, and zinc containing the K > 1 solutes copper and gold, a groove at the bottom of the trough indicated the boundary position, Fig. 2., To test if these different grain boundary etching behaviors were possibly connected with the segregation process discussed above, the Zn-Cd alloy was again heated to 380°C and quenched into brine. After surface protection and etching it was found that this specimen no longer exhibited the grain boundary ridges but rather grain boundary grooves as shown in Fig. 2. It would appear, therefore, that the boundary ridge is a consequence of a process occurring during the slow cooling of the samples. From absorption spectrophotometric analysis it was found that for slowly cooled samples containing K < 1 solutes, the solute/zinc ratios of the material from the boundary trough were consistently considerably higher than the solute/zinc ratios of the bulk alloys. This boundary region solute enrichment was not observed in quenched samples. It is concluded therefore, that the boundary ridge shown in Fig. 1 is directly or indirectly connected with nonequilibrium solute segregation.

Jan 1, 1970

By M. M. Slotnick

IT was once aptly said that a sign of approaching senility is ceasing work on a subject and beginning to talk about it. Perhaps that explains why, after many years in which part of my duties has been the training of college men in various branches of petroleum exploration geophysics, I have now begun to talk about it. In making an outline of what I believe ought to be discussed under the general heading of the title, I found it almost impossible to subdivide the ideas into an ordered set of discrete subjects. Rather, the pertinent remarks seemed to interlock almost everywhere. The consequence is that it will be necessary to start with the conclusions and then try to justify them by jumping back and forth. However, based on the types of men with whom I have had to deal, the subject naturally divides itself into two parts. In the first part, I should like to deal with the case of those undergraduates whose natural bent is toward the physical sciences and who may decide to enter the geophysical fold as a career. The other part will deal with those many men, geologists and engineers for the most part, who have drifted into exploration geophysics by one means or another, and whom it is necessary to train for geophysical work while they are occupied in their routine jobs. Here it may be in point to remark that most men in exploration geophysics at present have been developed from precisely the latter group, and that the problem of training here is of great importance even though, in this paper, it will perforce occupy the secondary place. TRAINING OF A GEOPHYSICIST The outstanding reason for the perplexing problem on the training of a geophysicist is that ideas differ on the answer to the question: "What is a geophysicist?" In any of the scientific "specialties," like physics, for example, it is relatively simple to pigeonhole a man as being qualified to call himself a physicist. That appellation applied to an individual does not mean that he has mastered only the branches of intellectual endeavor usually associated under the broad name of "physics." We expect him also to have a more than mere acquaintance with mathematics and chemistry and some understanding of most of the other sciences. But note this important point-we expect our physicist, whom we have chosen as an example, to be intelligently trained so that, if necessary, he can and will know how and where he can get the proper information on a subject in which he is not a specialist; he will know how to absorb that information and turn it to his uses. It seems to me that this is the outstanding characteristic of a man who can truly call himself a scientist: that he is a specialist in one of the broad branches of science and that he has enough training and discipline in the scientific approach so that, when called upon to do so, he can intelligently absorb knowledge from another bordering science (and all sciences not only border upon one another to some extent, but more often, overlap one another), and

Jan 1, 1941

By Norikazu Hashimoto

SILICIDE coatings on refractory metals are often applied by transporting a silicon halide vapor to a hot metal surface . The coatings are usually grown by solid-state diffusion reaction. The diffusion is often slower than the vapor transport and hence may become rate-controlling.

Jan 1, 1968

By R. E. Hoffman, R. A. Ward

The self-diffusion coefficient in high purity nickel has been measured over the temperature range 870&apos; to 1248°C. The results are described by the relation D = 1.27 exp[—-66,800/RT 1cm2ec-1. The measured activation energy correlates satisfactorily with absolute melting point, heat of fusion, and heat of sublimation. KNOWING the rates of self-diffusion is important in the understanding of many metallurgical reactions. However, in spite of the rather widespread interest in nickel, both commercially and in fundamental investigations, no measurement of the self-diffusion in solid nickel has previously been re- ported." In connection with a program of measuring rates of diffusion in some nickel alloys, self-diffusion in pure nickel has been investigated over a rather wide temperature range by combining a sectioning technique and a surface counting technique.

Jan 1, 1957

Jan 1, 1894

Jan 1, 1889

Jan 1, 1932

The attached tables show that in 1935 production of crude oil in Poland slightly decreased (minus 14,450 tons) and that gas production

Jan 1, 1936

Jan 1, 1946

The attached tables show that in 1935 production of crude oil in Poland slightly decreased (minus 14,450 tons) and that gas production

Jan 1, 1936

Mining Methods LUCIEN EATON, Chairman S. R. ELLIOTT, Vice-chairman CHARLES W. WRIGHT, Secretary Alluvial Mining CLINTON BERNARD CHARLES JANIN O. J. EGGLESTON CHARLES H. MUNRO N. L. WIMMLER Open-cut Mining Iron MAX H. BARBER J. A. MACKILLICAN KENNETH DUNCAN W. R. VAN SLYKE

Jan 1, 1932

Jan 1, 1948

Jan 1, 1911

By H. M. Zoerb

Based on the belief that operating details are a definite contributing factor to major economies, this paper traces the development of crushing cavity design in Symons cone crushers to attain maximum liner utilization. Wear rates are analyzed and compared in this presentation and drawings illustrate succeeding design changes.

Jan 6, 1953

[ ]

Jan 1, 1938