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By S. Amira

In the last two decades, many new creep-resistant magnesium alloys have been developed for high temperatures applications. Their mechanical performance and corrosion behaviour were reported for various experimental conditions. However, these conditions often led to uneven comparison basis. In the present study the microstructure, mechanical properties and corrosion performance of four of these newly developed creep-resistant magnesium alloys were systematically compared. Specimens were obtained from experimental box-like components that were die-cast and thixocast in comparable conditions. Their mechanical and corrosion properties were compared using similar testing conditions. Results show that the creep resistance, strength and impact resistance of specimens are comparable but systematically lower compared to specimens cast under optimized conditions. The reduced concentration of elements such as Al, Ca, Sr and Ce lead to a decrease of the corrosion resistance of the magnesium alloys in 3.5% NaCI solution.

Jan 1, 2007

By Thomas B. Douglas

INSTRUMENTATION in the process industries can no longer be regarded as a convenience, but rather an absolute necessity. Although many chemical processes must already be conducted with instruments, every properly designed application of automatic process control will improve operation: 1) the product will be more uniform and of higher quality; 2) the manual labor saved will reduce cost; 3) uniformity of flow and uniform control of process will increase production; and 4) surges will be eliminated, making it possible to operate equipment near ultimate capacity at all times. Industrial instruments fall into two general classifications—those that measure and those that measure and control. The cement industry has been using instruments for a number of years, particularly in the burning process, primarily for indicatlng and recording. Automatic process control makes additional use of these instruments, and others, to control variables. Assisted by the instrument manufacturers, engineers at Ideal Cement Co. achieved considerable progress in determining how well the usual recording instruments could be made to control various phases of cement-making. The results of these experiments were used to make the new plant at Houston as wholly automatic as possible. The original Houston plant, built in 1937 by Gulf Portland Cement Co., consisted of only one 8 x 220-ft kiln and the necessary grinding mills and accessory equipment and had a capacity of 900 bbl per day (300,000 bbl annually). Ideal Cement Co. purchased this plant in 1940 and almost immediately started plans to increase its production. In 1941 a 9 x 220-ft kiln was installed and grinding and storage capacity were increased. The growing demand for cement in the Houston area necessitated a third kiln (9 ft 6 in. x 250 ft) in 1947. This brought the plant up to its present capacity of about 1.3 million bbl per year. Calcium silicates in cement are produced in a burning operation at high temperatures from raw mix of argillaceous and calcareous materials that have been crushed, mixed, and ground to a fine powder. The composition of this mixture must be kept consistent within narrow limits. Raw mixing and grinding may be done either wet or dry, but in both instances the materials must be correctly proportioned, finely ground, and thoroughly intermixed before entering the kiln. As the raw mix passes through a long horizontal rotary

Jan 1, 1959

By J. E. Hawley

Introduction The Siscoe gold mine is the most easterly producer of gold from deposits lying in the belt of Keewatin and Timiskaniing rocks which extends east from Kirkland Lake, Ontario, and on through the Rouyn copper area. Unlike many of the deposits in this belt, those of Siscoe are contained almost entirely in a stock of much-altered granodiorite which intrudes Keewatin lavas. They are situated on an island of about one square mile in area, lying in lake De Montigny, Dubuisson township, 40 miles south of Amos, on the Transcontinental branch of the Canadian National railways, and 52 miles east, and slightly south, of Noranda. Geographically, the deposits are favour-ably situated with respect to transportation facilities, a through water-route being available from Amos, along the Harricana river and its lake expansions. The deposits consist of auriferous quartz-tourmaline veins of the fissure-filled type and are of particular interest because of their geological structure and genesis. Furthermore, deposits of a similar type occur both in the Keewatin and in granodiorite bodies to the east, in Dubuisson, Bourlamaque, Pascalis, and Louvicourt townships, and it is hoped that the following discussion may be of some aid in the exploration work now being carried on throughout this general area.

Jan 1, 1932

By Hughes J. C

THE smelting plant consists of five large furnaces operating in the treatment of current flintered material, and one small furnace operating periodically in the treatment of copper dross and antimonial slag produced in the lead-refining process.he following table supplies the leading dimensions and details of the large furnaces:-(a) Crucible - Dimensions 17 ft. 2 in. long x 4 ft. wide x 2 ft. 3 in deep. Capacity - 30 tons lead. Class of lining - firebrick. No. firebricks required - 3000.(b) Crucible Tank - Dimensions 20 ft. 6in. long x 10 it. 6 in. Wide x 4 ft. 3 in. deep. Material - 1/2 in. mild steel.(0) Jackets - Dimensions 6 ft. long x 19 in. wide x 6in. thick. Material - Cast-iron. Average life - 2 years. Number per side - 11, with 13-in. bosh. Number per end - 3, with 9-in. bosh.

Jan 1, 1922

By L. Price, R. Hortie

Movement of ore and waste from the Hilton Mines pit is accomplished by truck haulage. With the aim of reducing costs, a study of truck fleet replacement was initiated. The study included on-site short-term tests and longer-term rental purchase agreements for haulage trucks. The operation and maintenance characteristics of different trucks, along with projected haulage conditions, were used to prepare cash flows, from which the most advantageous trucks were selected. The results of the study and implementation of the recommendations gave a cost saving greater than had been estimated. The study also indicated areas where improvements could be made, and resulted in much more attention being paid to road conditions, the training of operators and mechanics, and the development of a practical preventative maintenance scheme.

Jan 1, 1971

By D. Chakravarty, D. Dutta, B. Samanta, S. Patteti

"This paper presents the mixed spectral behaviour of iron ores from deposits in Gua, India. Spectral signatures of powder samples and their two-component mixtures were generated by spectro - radiometry. Spectra were divided into continuum and absorption components. A modified Gaussian model was used to extract subtle features from the absorption components of the spectra. A linear unmixing model (LUM) applied to estimate minerals from the spectra of mixed powder samples indicated that this model achieved an R2 value of 0.88. The LUM was then applied to estimate the abundance of ores from a hyperspectral satellite image of the deposit area.RÉSUMÉ Le présent article montre le comportement spectral mixte de minerais de fer de gisements à Gua, en Inde. Les signatures spectrales d’échantillons de poudres et leurs mélanges à deux composantes ont été générés par spectroradiométrie. Les spectres ont été divisés en composantes de continuum et d’absorption. Un modèle gaussien modifié a été utilisé pour extraire des caractéristiques subtiles des composantes d’absorption des spectres. Un modèle de démélange linéaire, appliqué pour estimer les minéraux dans le spectre des échantillons de poudres mixtes, indique que ce modèle a atteint une valeur R2 de 0,88. Le modèle de démélange linéaire a ensuite été appliqué pour estimer la quantité de minerai à partir d’une image satellite hyperspectrale du secteur du gisement."

Jan 1, 2015

By Jozef Zmik, Sergey Dobatkin, Martin Fujda, George Raab, Libor Kraus

"The present work, likewise, deals with grain refinement of medium carbon steel AISI 1045 having different initial microstructure resulting from thermal and/or thermomechanical treatment (TM) applied prior severe plastic deformation. In case of TM treated steel, structure refinement was conducted in two steps. Preliminary structure refinement has been achieved due to multistep open die forging process which provided total strain Eef ~ 3. Uniform and fine recrystallized ferrite structure with grain size of the order of 2-5 µm and with nest-like pearlite colonies was obtained. The further grain refinement of steel samples having different initial structure was accomplished during warm Equal Channel Angular Pressing (ECAP) at 400°C. The microstructure development was analyzed in dependence of effective strain introduced ( Eef ~ 2.5 - 4). Employment of this processing route resulted in extensive deformation of ferrite grains where mixture of subgrains and ultrafine grain was found regardless the preliminary treatment of steel. As straining increases the dynamic polygonization and recrystallization became active to form mixture of polygonized subgrains and submicrocrystalline grains having high angle boundaries. The intensive straining and moderate ECAP temperature caused the partial cementite lamellae fragmentation and spheroidization as straining increased. The lamellae cementite spheroidization was more extensive in TM treated steel samples. The deformation behavior of for both steel structural state confirm the strength increase; however the work hardening behavior was modified with respect to initial structure of steel prior SPD processing.IntroductionIn the last years, ultrafine grained materials have attracted considerable research interest because they tend to possess high strength without sacrificing toughness and ductility. Microstructural refinement of steel is usually achieved by alloying and/or by thermomechanical treatment process, which modifies phase transformation. Recently, advancement of severe plastic deformation (SPD) techniques provides another efficient access for grain refinement of metals and alloys. The fabrication of bulk materials with ultrafine grain sizes has attracted a great deal of attention over the past two decades because of the materials' enhanced properties [ 1, 2]. In last decade a worldwide effort in manufacturing process to obtain ultrafine grain structures in steels is persisting."

Jan 1, 2011

By Giuseppe Pintaude

This study aims to evaluate the effect of specimen preparation on the dry sliding wear behavior of CA-6 NM stainless steel. Two different surface finishing manufacturing processes were applied: lapping and metallographic polishing. The wear tests were conducted in reciprocating ball-on-flat system, performed for two loads: 5 or 8 N. For all test conditions, hardmetal ball was employed as counterbody. The surfaces were evaluated using 3D interferometry technique to determine their surface roughness, including texture analysis regarding isotropy. Surface characterization results indicated the presence of texturing and preferential orientation, since the parameter Str was smaller than 0.5 for samples of both the studied conditions. Two distinct levels of isotropy evaluated through Str parameter were achieved: 0.13 for lapping and 0.3 for metallographic polishing process. It is clear from wear tests that the variation of average surface roughness is the key point for tribological behavior of CA-6 NM stainless steel.

Jul 31, 2018

By Z. B. Moukhametshina

The process of various zirconium alloys iodination by the iodine vapor was investigated. The nature of impurities, conditions of iodination, iodine flow rate, and zirconium tetraiodide condensation rate effect on the metal impurities transfer process was analyzed, both qualitative and quantitative correlations were established. Impurities were classified according their transfer extent. Another classification of impurities transport dependence on iodination process temperature was also offered. Obtained results were compared with impurities transport data in the process of iodide refining available in literature. Some impurities transport mechanisins and iodide-refined metals improvement possibility by means of iodination conditions control were discussed.

Jan 1, 1997

By S. G. Shabestari

Thermal analysis is a tool that is generally employed to predict the structure of the alloy before the actual casting is carried out. By cooling a sample of the molten alloy and recording the temperature-time curve, important solidification events may be analyzed by using the first derivative-cooling curve. In this research, strontium is added to (AS5U3G) 319 aluminum alloy and its influence on the formation of intermetallic compounds e.g. Al15(Mn,Fe)3Si2, Al2Cu, Al5Mg8Cu2Si6 formed during pre- and post-eutectic reaction have been investigated. Also any changes in solidification parameters such as temperature of Al-Si eutectic under cooling and temperatures of nucleation and growth of each phases caused by strontium addition, have been determined via the first derivative cooling curves. The effect of strontium on the formation of various intermetallic compounds has been studied by using very accurate thermal analysis equipment and the microstructures were analyzed using an optical microscope. The various phases reported in this paper were identified using Scanning Electron Microscopy (SEM) and linked to Energy Dispersive Spectroscopy (EDS). Formation of all pre- and post-eutectic phases was interpreted by comparing the phases formed in the microstructure and the reactions detected by using cooling curves. The results of this research indicate that thermal analysis technique can be used as an on-line process control in the production lines in aluminum casting industries.

Jan 1, 2004

By J. A. Ruppert, P. M. Sullivan

A study was made of filtration techniques for recovering the major part of the tin contained in iron - tin alloys known as hardhead . Special smallscale filtering apparatus and a three - stage cyclic process were developed . Eighty- seven percent of the tin contained in an alloy of 82 percent tin and 17 percent iron was recovered as pure metal by pressing at 975° C followed by a second pressing at 800 ° C and a final filtering at 250 ° C. Small amounts of Sb , Cu , and Fe impurities were removed by adding Al to the molten product and performing another filtration at 250 ° C.

Jan 1, 1964

By Arthur W. Cooper

This paper contains a review of the development of blast furnace? slag handling and processing technology in the Ironmaking industry over the past 30 years, with an emphasis on economic and environmental factors. The requirements and practice of air-cooling slag for use as aggregate and of pelletizing and granulating slag for use in cement manufacture are described. The operation of slag pits, slag pots or ladles, the slag pelletizer and early granulation systems are compared with the new continuous .granulation, dewatering and handling systems developed in the past decade.

Jan 1, 1992

By B. E. Halbert, K. T. Himbeault, S. L. Fernandes, R. L. J. Phillips, B. J. Topp

The Beaverlodge uranium mining and milling facilities operated from 1952 to 1981 with about 94% of the ore extracted from the main underground mine and 6% from smaller satellite deposits. Decommissioning work occurred from 1982 to 1985 involving periods of shutdown, salvage and reclamation. Transition phase monitoring, leading to eventual delicencing commenced in July 1985. Over the last 15 years, discharge from the tailings management facility (TMF) and a fresh water stream, impacted during the operational phase by tailings spills, has improved in water quality for most parameters of concern. Loadings to the environment of three key contaminants (radium-226, total dissolved solids, and uranium) have consistently been less than during the operational phase with radium-226 having the greatest variability. Outstanding environmental issues associated with the recovering drainage system formerly used for tailings disposal, are being addressed in an enhanced environmental monitoring program to commence in 2000. Changes in water chemistry and the natural re-introduction of aquatic organisms are issues of concern. In the meantime, application for release from selected satellite areas commenced in 1999. This paper reviews the issues which have arisen during the transition phase, outlines how they have and are being addressed, and provides a comparison of original and current predictions of the recovery process under way at the former Beaverlodge mine site.

Jan 1, 2000

By Qiang Zhong, Bin Xu, Qian Li, Yongbin Yang, Tao Jiang

Viscosity of slag determines the production efficiency, energy consumption and distribution of elements between metal and slag, which is very important for pyrometallurgy. Slag of goldantimony ore blast furnace smelting has seldom been studied. In this paper, the viscosities of gold-antimony ore smelting slags of different composition have been studied by the rotating cylinder method. The results showed that, for a slag of 38.95% SiO2, 16.17% CaO, 25.97% FeO, 10.25% Al2O3, 5.17% MgO, the viscosity can be decreased by reducing 3.24%-8.5% SiO2 or increasing 3.31%-9.56% CaO content. Complex SixOy z- from SiO2 acts as the main cause for the high viscosity in a slag of high SiO2. The increasing of CaO causes the decreasing of the amount of SixOy z- and the O2- dissociated from CaO breaks the complex SixOy z-, which can decrease the viscosity. Viscosity of different composition slag in the appropriate range temperature can be calculated from the Arrhenius equation.

Jan 1, 2015

CONTENTS PAGE East Texas, except the Gulf Coast-H. Vance 3 Gulf Coast-L. P. Teas 8 Texas Panhandle-C. C. Rae 16 North Central Texas-H. F. Smiley 23 North Louisiana, South Arkansas and Mississippi-B. C. Craft 25 Oklahoma-C. H. Pishny, Raymond M. Carr and E. J. Dickinson 31 Kansas-E. A. Koester 35 Rocky Mountain District-C. D. Johnson 46 Illinois and Indiana-T. Wasson 49 Michigan-T. Wasson 52 Eastern States-P. D. Torrey and W. H. Young, Jr 58 West Texas and New Mexico-W. V. Vietti. Published as a Supplement.

Jan 1, 1933

By J. Noll, C. DeGennaro, C. Zhou, J. Srednicki

"The personal dust monitor (PDM) (model PDM3700), as well as other electronic devices, can cause electromagnetic interference (EMI) which can disrupt the operation of some proximity detection systems (PDSs). A 15 cm (6 inch) minimum separation distance between the miner-wearable component (MWC) of the PDS and the electronic device usually avoids these disruptions, but due to the amount of equipment on a miner’s belt and the method of wearing the PDM in some situations, this distance can be difficult to always reliably maintain. Another method of reducing EMI effects is utilizing magnetic field shielding. The shielding capability of several different materials was investigated by surrounding the PDM with the material and quantifying the EMI. A copper mesh pouch reduced the EMI from a PDM3700, allowing a minimum separation distance of 10 cm (4 inches) instead of 15 cm (6 inches) as shown in a previous study for an unshielded PDM. A MU-metal box had a better shielding effectiveness, as it further reduced the minimum separation distance to less than 7 cm (2.8 inches). Shielding reduced the EMI of the PDM with MU-metal providing better results than the copper mesh. These materials may be beneficial for shielding individual components of the PDM or for constructing a shielded pouch. However, before the advantages of a shielded pouch can be determined, the effects of just the shielding material (metal) on the PDS needs to be quantified. INTRODUCTION According to statistics from the Mine Safety and Health Administration (MSHA), 43 miners have been fatally struck or pinned by a continuous mining machine (CMM) since 1984. In an effort to prevent future striking and pinning fatalities from occurring, proximity detection systems (PDSs) have been developed and are required on all operating CMMs in underground coal mines, with the exception of full-face CMMs, by 2018 (MSHA, 2015)."

Jan 1, 2018

By Philip W. Simmons

THE Colorado Plateau uranium province is in a mining boom rivaling the most colorful days of the early West. The application of scientific skills and the use of modern and novel mechanical equipment, however, is unique. No metal has ever received such concentrated effort from geologists and mining engineers. Moreover, no other metal has had the variety of tools available for finding and mining ores. Radiation detection equipment, bull- dozers, truck-mounted wagon and core drills, jeeps, airplanes, helicopters, tractor loaders, self -propelled 3-wheeled dump cars, front-end loaders and fleets of modern trucks are some of the present-day tools of the uranium prospector and miner. Because uranium is so vital to our national defense, the Atomic Energy Commission has offered many incentives for its mining. Through a series of circulars, the AEC has established base price schedules and various incentive payments. The incentive payments for acceptable ores from domestic mines are: (1) a guaranteed base price of $3.50 per Ib for ores assaying 0.20 pct U3O8 and more; (2) premiums based on grades above 0.20 pct U3O8 as for example, ores assaying above 0.50 pct U3O8 receive $1.00 per lb premium; (3) a development allowance of 506 per Ib of U3O8 contained in ores assaying over 0.10 pct U3O8 (4) an ore haulage allowance of 64 a ton mile for a maximum of 100 miles; and (5) an initial production bonus which may amount to as much as $35,000 in addition to all other payments. The producers have been guaranteed this policy until Feb. 28, 1957. The other four will continue until April 1962.

Jan 4, 1954

By Sahin Furkan Sahiner, Onur Golbasi

Effective maintenance planning is vital for coal mining operations, where haul truck fleets directly determine production continuity. This study presents a discrete event simulation (DES) model for evaluating maintenance strategies under multiple failure modes and their interdependencies. The model integrates corrective, periodic preventive, and opportunistic maintenance, dynamically updating equipment lifetimes through probabilistic time-betweenfailure and time-to-repair distributions. Applied to a fivetruck coal haulage fleet over a one-year horizon, results show that periodic preventive maintenance delivers the highest availability (76%) under unconstrained conditions, slightly outperforming corrective-only maintenance (75%). Opportunistic and integrated approaches performed worse (68% and 69%), reflecting redundancy from overlapping interventions. These findings suggest that structured preventive programs provide the most reliable outcomes when costs and resources are not limiting. The DES framework serves as a baseline for future models incorporating cost, spare parts logistics, and workforce availability, supporting robust maintenance planning in coal mining operations.

Feb 22, 2026

By C. A. Siebert, D. J. Girardi

PRACTICALLY every metallurgical process in-volves, at some stage or another, the contact of a metal with a gas. Because of this, gas-metal re-actions are of great practical importance and have been subjected to numerous investigations. It has long been recognized that the presence of cuprous oxide in liquid copper has an important effect on its casting characteristics and .physical properties. This has led to the desirability of determining the quantitative relationships between cuprous oxide in the liquid copper and the usual gases present during processing. Such data are not only of practical importance but also of a theoretical interest in that they provide a means of applying the principles of physical chemistry to problems in applied metallurgy. The object of this investigation was to determine the quantitative relationship at equilibrium between the gases carbon monoxide and carbon dioxide and the cuprous oxide content of liquid copper. The reaction and its equilibrium constant may be expressed as follows: 2 Cu (liq) + CO2 (g) = Cu2O + CO (g) acu2o X aco/a2 cu X aco2 Here the underlined symbol Cu2O designates cuprous oxide dissolved in liquid copper and (a), the activity of the various constituents. The activities of carbon monoxide and carbon dioxide are assumed to be directly proportional to their re- spective partial pressures and the activities of cuprous oxide and copper are taken to be proportional to their respective mol fractions. The equilibrium constant may then be expressed as follows: K2 = Ncu2o X Pco [Ncu]2 X Pco2 where N = mol fraction The solubility of carbon monoxide and carbon dioxide in liquid copper is a rather controversial subject.'-' A review of the literature is given by 0. W. Ellis.' It appears that carbon monoxide and carbon dioxide are both only very slightly, if at all, soluble in liquid copper. Volskii and Slobodskoi5 determined the equilibrium between carbon monoxide, carbon dioxide, and liquid copper at 1100°C. Their results show a higher cuprous oxide content for a given CO/CO2 ratio than found in the present work. The system hydrogen, water vapor, and liquid copper was investigated by Allen and Hewitt8 over the temperature range of 1090" to 1350°C. Equilibrium values for the system carbon monoxide, carbon dioxide, and liquid copper calculated from these data agree reasonably well with the present work. Materials and Procedure The copper used was oxygen free, designated as OF and analyzed as 99.98 pct copper with no appreciable amount of any one impurity based upon spectrographic determinations. The carbon dioxide was cylinder gas averaging about 99.95 pct CO2 with air as the major impurity. The carbon monoxide was produced by passing carbon dioxide over heated charcoal. Alundum combustion boats were used as containers for the liquid copper. No appreciable reaction took place between the copper and the alumina. This was evident from the fact that the copper sample after a run did not ordinarily adhere to the bottom of the boat and that the

Jan 1, 1951

By Allan T. Gwathmey, J. Bruce Wagner, Kenneth R. Lawless

Between 250°and 550°C in oxygen pressures of 10 to 760 mm Hg, the relative oxide thicknesses formed per unit time on the (100), (111), (110), and (320), decreased in this order. The predominant oxide orientation was (001)Fe3O4 and [110] Fe304 A small amount of a-Fe2O3 which exhibited a fiber pattern was observed in all oxides except those formed at 250°c in low oxygen pressures. IN order to understand the properties and behavior of thin films, particularly their role in oxidation reactions, there is needed more experimental information on their structure, composition, and kinetics of formation on clean surfaces of known geometry. The present study was undertaken to obtain such information for thin oxide films formed on single crystals of a body centered cubic metal, iron. Crystals in the form of spheres were used in order to expose all possible crystal planes to the reactant gases simultaneously. Using this procedure the relative rates of oxidation of all planes could be estimated, and those exhibiting, maximum or minimum oxidation rates could be selected for a more intensive study of composition and expitaxy. Since the three types of information were obtained from the same experiment using a single crystal substrate, any differences between rate, composition, and expitaxy on the several planes may be attributed to the influence of the substrate structure. EXPERIMENTAL The starting material for this study was Armco iron rods, 6 in. long and 3/8 or 1/2 in. in diam. The analysis was reported to be 99.8 pct Fe, with major impurities listed as carbon 0.018 pct, manganese 0.027 pct, phosphorous 0.005 pct, sulfur 0.029 pct, silicon 0.005 pct, and copper 0.11 pct. These rods were cleaned with ether and heated in an atmosphere of moist hydrogen at 950°C for three days. The purpose of this treatment was to decarburize the iron and to provide a consistent, uniform grain size for the growth of single crystals. Crystals in the form of rods, up to 1/2 in. in diam and 2 in. long, were prepared by a method similar to that reported by Leidheiser and Buck.2 Spherical crystals, 3/8 and 1/2 in. in diam and having a handle about 1/4 in. in diam by 112 in. long, were machined from the single-crystal rods. After machining, each crystal was etched in aqueous nitric acid to remove the cold-worked metal at the surface. Before each experiment, the crystal was polished mechanically with metallographic papers through number 4/0, and electropolished in a perchloric acid-acetic anhydride mixture by the method of Jacquet and Rocquet.3 The crystal was washed in running distilled water for at least 5 min. The excess water was blotted with a soft paper tissue, and the crystal was placed in an all-glass reaction vessel (See Fig. 1). The crystal was heated at 550°C in hydrogen for at least 8 hr prior to the oxidation in order to reduce any surface oxides and to help relieve any stresses in the metal. For the structure and composition studies, flat faces were cut parallel to (loo), (111), and (110) planes on the iron crystal spheres. The orientation of these faces was checked by a back-reflection X-ray diffraction technique. The faces were within 2 deg of the desired orientation. The flat faces were treated as described above except that prior to electropolishing they were given an additional polish on metallographic felt saturated with twenty-minute levigated alumina. After the crystal was heated in hydrogen for at least 8 hr, the temperature was adjusted to the desired value, and the hydrogen was evacuated. Commercial oxygen which had been purified by successively passing through tubes containing magnesium perchlorate, Ascarite and magnesium perchlorate was admitted to the desired pressure as measured by a mercury manometer. A resistance-wound furnace surrounded the oxidation chamber, and a temperature controller maintained the temperature within ±3°C. The furnace was provided with a small window for observing the crystal. The changes in thickness of the oxide films were followed by observing the interference colors. The oxidation was allowed to proceed until the desired oxide thickness was attained on a given crystal plane. The experiment was terminated by evacuating the oxidation

Jan 1, 1962