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By Wen H. Su

Multiple seam mining and its associated problems are very serious in Southern West Virginia where poor planning or lack of knowledge in seam interaction often results in complete loss of coal properties. Several measures have been proposed to alleviate the interaction problems under various multiple seam conditions, but few of them are specific in terms of mining plan. Two parallel approaches are adopted for this paper. One is field investigation which consists mainly of mine site visits and gathering of data. The other is the two-dimensional finite element simulation of mine workings using the data gathered as input. Two typical cases which represent the past and present multiple seam mining practice in West Virginia were investigated. Much attention is focused on the interaction problems experienced and the important parameters controlling interaction. Several key parameters controlling interaction in multiple seam mining were analyzed. Proper mining plans, by which the interaction problems can be minimized, are proposed for the individual cases after a better understanding of the interaction mechanism was realized through finite element analyses.

Jan 1, 1984

By Harry C. Swanson

TRANSPORTING concrete from mixer to forms has always been a problem. Twenty-five years ago this task was generally accomplished by means of wheelbarrow or concrete buggy. On large dam jobs, as the number of these projects increased, the gantry crane or highline came into use. Today several methods of handling concrete are employed on smaller surface construction jobs, for example, transit-mix trucks or dumpcrete trucks, which have crawler cranes with buckets for placing concrete into forms. In 1944, during early stages of developing Mather mine A shaft, several large underground concrete jobs were necessary. At this time the Cleveland-Cliffs Iron Co. purchased the first pumpcrete machine, introduced by the Chain Belt Co. of Milwaukee. The machine was used to pour approximately 200 cu yd of concrete for a dam, or bulkhead, located 400 ft from the shaft. Concrete was mixed on surface, lowered down the shaft 1000 ft in a 2-cu yd bucket hung under one skip, spouted into the bowl of the pumpcrete machine from the bucket, and pumped directly into the forms.

Jan 4, 1954

By Chase Palmer

INTRODUCTION. WHILE the reducing action of organic matter, of ferrous sulphate, and of hydrogen sulphide has frequently been invoked to account for the deposition of native gold and silver from ore-forming solutions, the high efficiency in this respect of certain of the metallic minerals which form the ore itself has not been sufficiently recognized. If a little finely powdered chalcocite is placed. in a test-tube and 2 or 3 cc. of a dilute solution of gold chloride are poured over it, two or three shakes of the tube suffice to remove all the gold from the solution. The color of the solution changes from yellow to pale green, showing that copper is dissolved simultaneously with the precipitation of metallic gold. If a piece of chalcocite is hung in a dilute aqueous solution of silver sulphate (1 normal), a coating of silver begins immediately to form on the mineral, and within a few moments a beautiful silver tree has developed, similar to that formed when metallic zinc is immersed in a similar solution.

Jan 5, 1913

By G. Adel, J. Richard Lucas, C. Haycocks

This paper describes over sixteen computer programs developed at Virginia Polytechnic Institute and State University during the past twenty years to assist in the design of coal operations. Overall development concepts in the construction of the programs are outlined, commencing with those used in the exploration phase of mining and extending through economic analysis and into the design of specific engineering systems such as belt, rail and power networks, scheduling, rock mechanics problems and simulation of face systems. Summarized information is given for the use of the major programs including user restrictions, input data, typical output and industrial applications and case studies. Analysis has been made of the programs' applications by industry throughout the world. Such analysis is facilitating development of new programs as well as a refinement of existing ones. To date programs have been constructed in four categories: exploration, ground control, economic and simulation. Face production simulations are stochastic in nature and require the use of time study data obtained at sites underground. Future programming efforts currently under development are aimed at interactive programs for use with minicomputers and, where advantageous, with graphical displays.

Jan 1, 1983

By Chikaosa Tanimoto

INTRODUCTION The committee on Rock Mechanics, Japanese Society for Civil Engineers, has been discussing 'soft rock engineering in Japan' and presented several papers concerning dam, tunnel, bridge and slope constructions to International Symposium on Weak Rock, Tokyo 1981. This is the summarized paper based on References of Okamoto et a1 (1981), Iida et a1 (1981), Working Group on Tunneling-JSCE (1981), Working Group on Bridge Foundations-JSCE (1951) and Kikuchi et a1 (1981), which can convey general view on engineering experiences with weak rocks in Japan. From the point of view to the origin and/or distinctive physical properties, weak rocks in Japan may be classified into (1) sedimentary, (2) weathered, (3) low welded-pyroclastic and (4) fractured ones. Their typical characteristics are summarized in the following section. Concerning dam foundations on soft rock, several hundreds have already been constructed and, at present, nearly one hundred are under construction or at planning stage. These dams, almost without exception, have some problems such as site selection, material selection for fill-type and concrete dams, design of dam and its foundation, and construction procedures, requiring special ingeneous and cautious measures to cope with the local geotechnical difficult situations. In tunneling, for the decade of 1970s, the number of tunnels in soft rock either completed or under construction was at least 160, including Seikan Tunnel of 53.9 km long, Nakayama Tunnel of 14.8 km long and so on. Most of these tunnels are distributed in the northern half of Mainland, consisting of a basement of Paleozoic strata and Plutonic rocks, overlayed by Neogene Tertiary formations which include large

Jan 1, 1982

By David D. Rabb

Under the auspices of the Atomic Energy Commission, the Lawrence Radiation Laboratory of the University of California analyzed an experiment to provide information as to whether the chimney of broken rock produced by a deeply buried nuclear explosive could be "drawn" by conventional techniques. Since many low-grade disseminated ore-bodies occur in a granite media, the experiment took place in a granodiorite-quartz monzonite intrusive porphyry in the Nevada Test Site as a follow-up to the Department of Defense's Hardhat detonation in February 1962. For emplacement of the nuclear device, a 12 ¼ - in. pilot hole was reamed to a diameter of 44 in. and a depth of 950 ft in one pass using a Hughes multiple-cluster rotary bit. It was then cased to 36 in. ID. The center of the explosive device was located 938.85 ft below the collar. The yield of the device was predicted to be 5 kilotons, or an equivalent of 5000 tons of TNT; the yield was later confirmed by chemical means to be 5.4 kilotons.

Jan 3, 1964

By Melvin H. Podwysocki

Lineament and fracture analysis have enjoyed a resurgence of interest over the last several years, particularly since the advent of the Landsat series of Earth resources satellites. Some applications for lineament analysis include mineral, petroleum and ground- water exploration, engineering studies such as highway routing, mine roof stability, dam and power plant siting and general tectonic studies. The needs of each study may be different, but the general problem of large masses of data is common to all. Methods for efficient handling of the information and some statistical methods for its evaluation are discussed. These include comparing the lengths of the fracture population against known distributions, trend surface analysis of fracture lengths and number per unit area and multivariate analysis of rose diagrams. Examples are shown in an experimental program for predicting the presence of reef structures, areas of potential petroleum production.

Jan 1, 1977

By Edward B. Walker, Michel Grosmangin

The geological and economic conditions peculiar to the Greater Oficina area are presented to demonstrate the necessity of a low-cost, well-site method of distinguishing gas-bearing formations. The method of gas detection with the neutron log is briefly discussed and its limitations are explained. A new method is described which consists in running a second neutron log with a larger source-to-detector spacing. Field data indicate that under favorable conditions the larger spacing response is proportionately more influenced by the virgin gas zone than is the shorter spacing response. One important condition is that the gas sands be invaded, with a diameter of invasion equal to about two to three times the hole diameter. The calibration of the longer spacing log is made so that the two logs read the same deflection in shale and in a known water or oil sand. Under such conditions, gas is indicated by a positive separation, i.e., the curve for the longer device is displaced to the right of the curve for the shorter device. Because of the non-linearity of the long spacing response, low porosity formations also show positive separations. In sands with large porosity variations, the gas sands can no longer he located visually. They can be detected on a plot of shorter spacing vs longer spac-ing deflections. INTRODUCTION In the Greater Oficina area of Eastern Venezuela, the rapid and accurate detection of gas from well logs is of primary importance because of a combination of economic, geologic, and operational conditions. Briefly, these conditions are: economic—there is no market for gas at the present time; geologic—a single well may contain as many as 30 or more oil or gas sands for which intervals -to be tested must be selected; opera-tional—first, once opened to the casing through perforations, gas sands are extremely difficult and expensive to squeeze off, and second, gas detection must be rapid because the geologist must decide immediately, at the well, which sand to perforate. During the early period of exploitation in Greater Ofi-cina, when clay base muds were used, sidewall samples, together with electric logs, gave fairly good distinction between oil and gas sands. When exploitation became concentrated on deep fields of poorer sidewall sample recovery, and after the advent of oil emulsion muds, now the standard drilling fluid in Greater Oficina, the regular neutron log became the most reliable indicator of gas. In 1953, R. Norelius devised the dual-spacing neutron technique for gas detection. The dual-spacing neutron log has proved to be highly successful in detecting gas and has been adopted as a regular survey by all of the oil companies of the area. Several hundred dual-spacing neutron logs have been run in Eastern Venezuela and several tests per well are available for positive evaluation of the logs. The findings outlined below are based upon this extensive field experience. GEOLOGICAL CONDITIONS OF THE GREATER OFICINA AREA The Greater Oficina area lies on the south flank of the Eastern Venezuela Basin (Fig. 1). Nearly all accumulations of oil and gas in the area are trapped, in whole or in part, against normal faults. All known oil and gas reservoirs in Greater Oficina occur in the Ofi-cina formation (Miocene-Oligocene) or in the "U" sands. The U sands are the lithologic equivalent of the Merecure group (Otigocene-Eocene), which contains oil in many fields north of Greater Oficina. Most of the petroleum produced in Eastern Venezuela is from the Oficina formation.

Jan 1, 1958

By D. G. Westlake

THE structure observed in thin foils by transmission electron microscopy is not necessarily representative of the initial bulk material. We have shown that hydrogen, originally present in a specimen of vanadium, niobium, or tantalum, can be concentrated by the thinning operation used to prepare foils from the bulk materials.' These foils exhibited domain walls indicative of a tetragonal distortion of the bcc unit cells, probably caused by ordering of the hydrogen in preferred interstitial sites. We believe this ordering does not occur at room temperature in the bulk material which contains less than 1 at. pct H. In a continued effort to prepare metal foils whose hydrogen concentrations remain constant during preparation, we have developed some new chemical and electrothinning techniques for vanadium. Each of the procedures presented in Table I produced foils that were thin enough for transmission electron microscopy. The experiments described below were performed to test the effect of each thinning procedure on hydro-

Jan 1, 1968

By Wm Price

THE object of this paper is to present a survey of some of the physical properties of sheet nickel silver when subjected to cold rolling and when annealed at temperatures extending from 350° C. throughout the commercial annealing range. A number of alloys were taken from stock and analyzed. Four of these, representing low nickel and high nickel both with and without lead, were chosen for the tests. The analyses were as follows: ALLOY COPPER, LEAD, IRON, NICKEL, MANGANESE, ZINC, PER CENT. PER CENT. PER CENT. PER CENT. PER CENT. PER CENT A 64.68 Trace 0.194 - 6.73 0.06 remainder B 65.82 1.27 0.227 6.17 0.06 remainder C 65.44 Trace 0.345 17.83 0.08 remainder D 65.60 1.08 0.238 17.77 0.06 remainder These alloys were rolled in accordance with regular mill practice to approximately No. 6 B. & S. gage. The bars (which were then coiled) were annealed together in a mill muffle and afterwards pickled in a 10 per cent. sulfuric-acid solution and cold rolled in stages of approximately .one number (B. & S.) at a time to No. 18 B. & S. gage. After each stage, suitable samples were set aside for physical tests. Additional samples were chosen for tests after the bars were rolled to Nos. 8, 10, 12, and 14 gage. These samples were annealed together in the mill muffle and, after pickling, were finished on 0.050-in. gage, yielding a series of specimens 2, 4, 6, and 8 numbers hard for the subsequent annealing tests. Tensile test pieces 9 by 1 in. (22.9 by 2.5 cm.) were cut from both lots and the central portion was milled to give a test section 2 ½ in. long by ;Z in. wide. A distance of 2 in. was marked off on the edge of each specimen with light punch marks. In the case of the annealed alloys, Erichsen test pieces 4 by 2 1/2 in. were also taken.

Jan 10, 1920

By William H. Shockley

[SECRETARY'S ]NOTE.-The following notes, arranged and edited in this office, but not yet revised by the author, were placed at my disposal with much modest hesitation (due to their incomplete and fragmentary character), upon my earnest request, and my argument that such recent and trustworthy data concerning a new and important mining industry ought not to be withheld from our Transactions, simply because they are not sufficient to constitute a, complete academic treatise on the subject. This argument is recommended to the attention of many other members, who are waiting for the opportunity to contribute something "monumental" to our Transactions. In a number of instances, death has nulli¬fied this ambition, and the intended "monumental" contribution has turned out to be an obituary notice by the Secretary, instead of a valuable record of the professional experience thus hopelessly lost to the world.-R. W. R.] The official publications of the the Russian Government give fairly complete statistics of the dredges operated in the Empire; and in a recent English bluebook, Mr. Cook's report on Siberian Trade presents a brief account of dredging in Siberia. The data in Table I. (not given by Mr. Cook) have been taken from the Gold Mining Messenger (Russian) for July, 1905. These interesting statistics, though incomplete, show that the Yenisei dredges are working on poor ground and yield small returns. According to report, but few yield a profit exceeding 10 per cent. per annum on the capital invested. In the summers of 1904 and 1905, I traveled in the Urals as far north as lat. 61° N., long. 61° E., on the the Lozva river, a part of the vast system of the 01) river. This clear-water stream starts from the summits of the Urals at an altitude of 4,000 ft., and flows through a flat country, densely wooded with larch, spruce, pine, fir, birch and poplar. The river is full of fish, and is navigable for good-sized steamers as far as Ivdell. Winter lasts from early November to late April, the temperature rang¬ing from -60° F. to a summer maximum of 90° F. The rain¬fall is 20 in.. The climate is healthy, although mosquitoes,

Jul 1, 1906

By Richard Dunmore

Tests of the MRDE firedamp prediction method have been carried out in a number of longwall districts with different conditions. The method itself and its development have been described previously At many test sites the prediction has been good, i.e. the calculated gas emission levels have agreed with measured values, averaged over a period of many weeks, within a few percent. In other cases, where there have been larger discrepancies between calculation and measurement, investigations have shown that these may be attributed to particular conditions of mining or geology. Recognition of these conditions in advance of mining is clearly desirable to improve the accuracy of the initial prediction. It has been shown that variations in gas emission rates depend largely on coal production in terms of the weekly advance of the coal face. Although there appears to be a random element present, variations in gas emission levels calculated from changing face advances agree well with measurement. The accuracy of prediction therefore depends on how well face advance can be forecast and needs to be updated as the working proceeds in the light of the face performance actually achieved. Continuous monitoring of the mine environment provides the information necessary to compare actual gas emission with predicted levels, and computerised systems make it possible to carry this out in real time. Predictions can thus be adjusted to take account of emission levels measured in previous weeks These adjustments, whether they are made after the first few weeks or subsequently during the district life, would also be used to alert management to particular abnormalities or significant changes in gas emission.

Jan 1, 1982

By P. D. Proctor, M. P. Nackowski

Quantification in recording geologic phenomena and application of well-known geologic principles to engineering works continued at an increasing rate during the year. Highway departments, water resources agencies, private firms and governmental agencies involved in tunnel excavations, dam site locations and construction, consultants and government experts in subsurface liquid-waste disposal, designers of underground storage facilities and city and regional planners all confirmed greater use of applied geology in their planning and implementation of plans. Applications of quantified geologic data to highway locations, slope control of cuts, raw material sources, water sources and water run- off showed a striking increase in number. Environmental geology and geologic hazards became part of the jargon of the geologic profession, and the American public began to realize more fully the significance of where they live, and on what and near what geologic phenomena which might effect their well-being. Tunnel work for water projects of almost dream-like magnitude kept geologic engineers busily engaged in predicting and testing local geologic conditions for construction projects. Disposal of industrial and radioactive liquid wastes continued as problems, but use of stratigraphic data, fluid flow rates and direction of flow helped solve some critical waste disposal problems. Unusual applications of seismic networks, remote sensing methods and X-ray techniques in geological engineering applications added other tools to this increasingly important profession.

Jan 2, 1968

By Walter W. Lilly, Issa S. Oweis

Application of rock engineering in geotechnial consulting practice considered herein is in areas of: (a) bedrock verification for foundation support, (b) bearing capacity and settlements, and (c) excavations. A routine geotechnical investigation usually provides data on depth to rock, rock classification, and rock quality. In cases of rock outcrop, such outcrops are mapped for geologic structures and rock mass description. In addition, the regional geology and the general aspects of the groundwater regime are usually known from either published literature or previous experience. The predominant technique for ground and site investigation are usually drilling and geologic reconnaissance. Other techniques involving seismic and geophysical soundings, borehole camera, and oriented cores are used by by no means routine. Performing laboratory strength and compressibility tests is often made to be considered as routine. The use of the point load test is gaining increasing use in the United States and would, perhaps, become a routine field or laboratory test due to its simplicity and, more importantly, its relatively low cost. The purpose of this paper is to describe cases where mostly routine investigation and testing were used to arrive at engineering decisions. Bearing Capacity and Settlements The allowable bearing values for foundation support on rock is usually dictated by local building codes which presumably should reflect local experience. The interpretation of the code, however, can present a problem, especially if the interpretation is made by a designer under the delusion of knowledge in rock engineering. For

Jan 1, 1982

By J. E. Lawrence

Copper-decorated lattice disorders in silicon have been analyzed by electron transmission microscopy, chemical etching, and P-N junction reverse current measurements before and following different gettering treatments. Lattice disorders acted as the nucleating sites for copper precipitation. Copper precipitates in silicon resist chemical etching, absorb electron beams more than silicon, and cause excess reverse currents. Totally gettered disorders will chemically etch rapidly, be transparent to electron beams at extinction contrast, and not contribute to excess reverse currents. Three different gettering procedures were performed to determine the effectiveness of different EXTRANEOUS metal contamination can alter the minority carrier lifetime and resistivity of bulk silicon as well as cause excessive reverse currents in semiconductor devices. Previous workers have reported such activity for gold,1,2 copper,'-* iron,' and rnanganese.2,5 Gettering is a method employed to render these impurities electrically inactive. However, some property of the junction-degrading metals prevents gettering procedures from being wholly reliable. The comparative effectiveness of gettering with different agents has been the topic of earlier publications.2,3,6-11 Two mechanisms for gettering metallic impurities have been proposed: the distribution coefficient mechanism by Thurmond and Logan7 and the compound formation mechanism by Goetzberger and Shockley.2 Both of these models evolved from data gettering mechanisms. First, phosphorus was allowed to enter a protective SiO2 film but remain away from the Si-SiO2 interface to test the effectiveness of the compound formation gettering mechanism. Second, phosphorus was allowed to enter the backside of silicon wafers to test the effectiveness of the lattice strain gettering mechanism. Finally, nickel was diffused into the backside of silicon wafers to test the effectiveness of the distribution coefficient gettering mechanism. In each case, copper precipitates dissolved as a result of the gettering treatment. Tightly packed precipitates will resist gettering more than loosely packed copper precipitates. acquired by the electrical analyses of gettered semiconductor materials. An electrical analysis, however, cannot identify the fate of the gettered metals. The radiotracer technique has recently been applied to determine the redistribution of metals following different gettering treatments.3,9,10 The spatial resolu tion of the radiotracer technique prevented the analysis of metal precipitates which contribute to the excessive reverse currents of P-N junctions. The gettering processes employed by the earlier workers, almost without exception, allowed the gettering agent to enter the silicon lattice. This procedure makes it quite difficult to differentiate between the distribution coefficient and the compound formation mechanisms. The metallographic analysis of gettered copper precipitates discussed in this work supplements the earlier work by obtaining direct evidence of silicon lattice defects decorated with copper before and following different gettering treatments. The effectiveness of a process which restricts the gettering agent, phosphorus, to a dielectric film and thus away from the silicon lattice is discussed in addition to the ef-

Jan 1, 1969

By J. M. Clark

(Wilkes-Barre Meeting, June, 1911.) For some years past, those interested in the development of the increasingly important mining industry of Canada, have urged the adoption by the Dominion Parliament of a federal mining-law, which would have the force and stability of statutory enactment. At present, placer-mining in the Yukon Territory, is governed by the Yukon Placer Mining Act. All other mining under federal jurisdiction is governed by 'Orders in Council and Ministerial Regulations. In the earlier stages of development, it is perhaps a matter of necessity that these important matters should be so dealt with; but it is now felt that the time has come when mining-rights in the extensive regions under federal control should be put on a permanent basis, -and that any changes required from time to time should be made only after full and open discussion in Parliament. A short sketch will suffice to indicate how vast and varied the interests affected really are. When the Dominion of Canada was constituted by the Imperial Statute known as the British North America Act of 1867 (which came into force by proclamation on July 1 of that year), it comprised only the present Provinces of Ontario, Quebec, Nova Scotia, and New Brunswick; but provision was made for the inclusion of Newfoundland, Prince Edward Island, British Columbia, Rupert's Land, and the North West Territories. Subsequently Rupert's Land and the North West Territories were acquired, the 'Crown Colonies of British Columbia and * SECRETARY'S NOTE.-Mr. Clark, an eminent Canadian lawyer, and joint author of the treatise on "The Law of Mines in Canada," has been requested by the Do¬minion Government to prepare a Federal mining-law, and presents this paper, by invitation of the Council, in order to obtain, if possible, useful suggestions from members of the Institute.-R. W. R.

Apr 1, 1911

By Robert W. Thompson, Darry A. Ferguson

In August, 1977 the United States Congress passed Public Law 95-87 which has been commonly referred to as the Surface Mining Control and Reclamation Act (or SMCRA). This title is somewhat misleading in that the act creates as many regulatory requirements for underground coal mines as for surface coal mines. How- ever, this paper will concentrate on the effects of SMCRA on designs and stability for various activities of surface coal mines, specifically those concerning "Disposal of Excess Spoil". In the past, the objective of most laws and regulations applicable to the mining industry has been to achieve goals of safety or environmental concerns for all types of mining. However, SMCRA is unique in that it sought to regulate-all-activities of coal mining from initial data gathering, exploration, mine design and facilities design to reclamation activities and design. More specific to the stability of the activities of surface coal mining, special criteria for design and construction performance standards have been promulgated for the construction and maintenance of roads, dams and embankments, coal processing waste, ex- cess spoil piles, backfilled reclamation and pit slides. The criteria for design for the previously mentioned facilities has been enumerated by regulations and in many ways restrict the use of site specific design parameters. The restrictions imposed by regulations significantly inhibit the engineer's ability to develop the best practical and economical design and in some cases may re-

Jan 1, 1983

By E. C. Dominguez

INTRODUCTION The first commercial plant in the world to successfully produce pellets from manganese ore fines is the ICOMI pelletizing facility in northern Brazil. The main purpose of this paper is to describe the manganese pelletizing process that was developed through a cooperative R & D program by the Bethlehem Steel Corporation and ICOMI, i.e., Industria e Commercio de Minerios, S. A. The process combines heavy- media and gravity separation, reduction roasting, magnetic separation, and pelletizing on a straight-grate indurating machine. It produces high-grade manganese pellets from reviously unsalable low-grade ore fines at a rate of 20,000 tonnes (1) per month. The physical properties of the manganese pellets are comparable to those of iron ore pellets. The pelletizing plant, built at a cost of about 18 million dollars, is part of an ICOMI complex that includes manganese ore mining, an ore-washing plant, and railroad and port facilities, as well as two town sites. These two towns, one at the mine and the other at the port, each with complete community services, were built by ICOMI to serve the needs of over 1500 employees that operate the industrial complex. To give an idea of the magnitude of the investment represented by this complex, the cost up to 1957 to develop the mine and supporting services and social infrastructure was over 100 million dollars. It should be borne in mind that the above capital cost figures are in dollars of the years during which the respective projects were initiated and completed.

Jan 1, 1977

By J. M. Blank, V. A. Russell

When the nucleation of silicon on a sapphire substrate is accomplished by gradually decreasing the substrate temperature while subjecting it to a constant impingement rate of hydrogen and silicon tetrachloride, the resulting deposit is characterized by widely separated islands of silicon scattered over an "open sea" of sapphire. Analysis shows that nucleation takes place mainly on sites of large adsorption energy, about 85 kcal per mole, and small surface concentration, about 108 cm-2. Crystal growth proceeds rapidly on these nuclei and results in enough depletion of Sicl4 from the ambient gas to suppress further nucleation. The technological importance of single-crystal films on dielectric substrates has prompted considerable work on the deposition of silicon on sapphire. This paper is concerned with the deposition of silicon, by the reduction of silicon tetrachloride with hydrogen, onto heated sapphire substrates. The apparatus consisted of a temperature-controlled container for the silicon tetrachloride along with gas lines and flow meters necessary to convey a hydrogen-silicon tetrachloride mixture to a reaction chamber constructed of quartz tubing. Heat for the substrate was provided by means of an inductively heated graphite susceptor. The observations pertinent to the present discussion were made with an American Optical Co. high-temperature microscope which allowed us to make motion pictures of the deposition process at a magnification of approximately 50 times. Two main categories of experiments were carried out: one on determination of critical condensation temperatures and the other on the deposition of epitaxial silicon films on the sapphire substrates. Critical condensation temperatures were determined in the traditional way by raising the substrate temperature well above that at which condensation could be expected at the impingement rates being studied and then gradually lowering the temperature until the condensation of the first silicon was observed. This was done initially with ellipsometry-type detection but it was soon discovered that the deposits were occurring as widely separated islands and groups of islands scattered over an "open sea" of sapphire. We have called these archipelago formations. They were most easily detected by optical microscopy. Data gathered from experiments of this type have been collected in Table I. Motion pictures of the formation of archipelago patterns show that the nucleation period lasts about 10 sec if the substrate temperature and impingement rate are kept constant. Essentially all of the nuclei are formed in a few seconds and all subsequent silicon deposition merely adds to the size of the established nuclei. After an archipelago formation has matured at a given substrate temperature and impingement rate, it is very difficult to stimulate any further nucleation in the open space between islands. Lowering the substrate temperature will occasionally stimulate nucleation but increasing the impingement rate hardly ever produces any more new nuclei. It should also be emphasized that the nucleation rates appear to be very small, about 104 cm-2 sec-1. They will receive special attention in the analysis section. Another series of experiments was performed employing a systematic variation of substrate temperatures and impingement rates approximating those expected to produce epitaxy. Sapphire substrates with surfaces normal to the 2233 direction were used. In contrast to the procedure that produces archipelago patterns, these films were deposited by raising the substrate temperature to a desired value at which time the silicon tetrachloride and hydrogen flow was begun. Of course, these depositions produced mainly films that were continuous. After removal from the deposition chamber, the substrate and silicon film were examined microscopically to determine the nature of the deposit and by X-ray diffraction to determine the extent to which a single-crystal film had been achieved. Results of these experiments are summarized in Table 11. Of interest for the present analysis is the fact that epitaxy appears to be confined to a fairly narrow temperature range between about 1050" and 1150°C. This also will be discussed in the analysis section. ANALYSIS In this section we shall apply nucleation theory to the data presented above with the objective of testing

Jan 1, 1967

By Frederick G. Tickell

GEOLOGISTS have been quick to adopt new methods in locating new oil fields and in finding the extensions, laterally or at depth, of the old fields. For most of these new methods he is indebted to the physicist, the engineer, and the chemist, although he has also drawn from such ordinarily unrelated sciences as bacteriology and protozoölogy. These last-named sciences have been of help in problems dealing with the origin of petroleum and, although not of direct application to oil finding, have furnished evidence of value in learning what oil is made from and what are the natural agencies involved in its formation.

Jan 1, 1932