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By J. R. Low

The brittle fracture of a Tic-lnconel cermet at room temperature is shown to occur primarily as a result of the cracking of the larger carbide particles (at a tensile strain of approximately 0.3 pct), followed by cracking of adjacent, smaller carbides and, finally, by the rupture of the lnconel matrix between cracked carbides (at a strain of-1.2 pct). No evidence was found for separation at the interface between carbide and matrix at any point in the fracture process. MATERIAL used in this study was a Tic-Inconel cermet prepared by infiltration (50 pct Tic, 50 pct Inconel: designated as TC66-I). A thin section of this material was brazed to a piece of low carbon steel and then mounted in lucite for metal-lographic preparation." After grinding, polishing, Deformation and fracture of the specimen was accomplished by bending the specimen as a simply supported, centrally loaded beam, in a bending fixture which could be placed in the stage of a microscope, with the tension side of the bend specimen under the microscope objective.? This method of deformation and observation has the advantage that the surface under examination is the most severely deformed portion of the specimen. The procedure followed was to deform the specimen a small amount, scan the surface at Xl OOO for any evidence of deformation or cracking, deform another small increment, scan the surface again, and so on until a

Jan 1, 1957

By W. S. Owen, A. R. Rosenfield

The measured changes in the yield stress of a poly crystalline Ta-O alloy after strain aging at 100°C have been separated into two components; the change inflow stress and the change in dislocation locking parameter. These two components vary independently indicating that at least two separate recovery processes take place during strain-aging. Variations in the locking parameter can be accounted for by segregation of oxygen atoms to dislocations, but variations inflow stress cannot be explained by current theories. STRAIN-AGING in Fe-C and Fe-N alloys has been studied extensively.' The kinetics of the removal of the interstitial solute from solution appear to agree with the predictions of the cottrell-bilby2 model or a variation of it proposed by harper.3 Solute segregates to the dislocations under the influence of the elastic strain field of the dislocation and the rate of depletion of the solute can be measured by following the change in electrical resistivity4 or internal friction.5 On reloading a prestrained specimen, plastic flow starts at Fig. 1, but after aging the reloaded specimen yields discontinuously at a higher stress The aging index reflects the extent to which the yield has returned. Until recently it was usual to assume that ? is a result solely of the pinning of dislocations by the segregated solute atoms, that is, that op and oj coincide and the strain hardening curves AB and CD are continuous. Thomas

Jan 1, 1963

By Frank D. Hoyt

BY far the most conspicuous of the Pennsylvania slate districts is that extending from the New Jersey line at the Delaware Water Gap westward almost to the Schuylkill River. This covers parts of three counties in east-central Pennsylvania: Northampton, Lehigh, and Berks. The most important development, both in geographic size and product importance, is in Lehigh and Northampton counties. The greater part of the region is underlain by only one formation-the Martinsburg, consisting of slates, clay slates, and sandy shales, all of the Ordovician period. The slate-bearing Martinsburg formation is underlain by Cambro-Ordovician limestones. Immediately overlying the Martinsburg formation is the Tuscarora quartzite of the Silurian period. The Martinsburg formation itself is divided into three distinct divisions, termed simply: the upper, the middle, and the lower members. Commercial slate has been extracted from all of these members, but the formation of greatest importance is the upper member, representing 2600 ft of the total formation thickness of nearly 11,000 ft. The upper member is commonly referred to as the "soft slate" and consists of three facies: 1) beds of blue-gray, very sandy, almost quartzitic slate, in many places, approximately a medium-coarse sand- stone with calcareous cement; 2) blue-gray sericitic slat-the dominant rock type of this member-with occasional chloritic beds; and 3) dark gray or virtually black, highly carbonaceous beds, referred to locally as "ribbons."

Jan 8, 1958

Professor Somasundaran has given an excellent presentation of the numerous problems which remain to be solved before the selective aggregation of fine particulates is likely to see broad commercial application in the beneficiation of mineral fines. However it is useful, I think, to reiterate some of the major problem areas. The over-riding factor which has limited the development of selective aggregation techniques is that processes such as coagulation and flocculation tend to be inherently non-selective. Conditions which favor the aggregation of one kind of fine particles usually favor the aggregation of all kinds of particles. As Professor Somasundaran has pointed out, the state of aggregation of a fine-particle dispersion is primarily determined by the forces of interaction between the individual particles. In most systems, the dominant forces are: 1. van der Waals - London Dispersion forces between the particles themselves 2. electrical double layer forces 3. steric forces between adsorbed layers on the surfaces of the particles. The London Dispersion forces between like particles are always attractive, but for dissimilar particles dispersed in a fluid medium can, in some cases, lead to a net repulsion. Electrical double layer forces always lead to repulsion between like particles but can, again, cause either attraction or repulsion for dissimilar materials. The steric forces, which are by far the least understood of the three types, can also lead to attraction or repulsion depending on condi-

Jan 1, 1979

By Frederic P. Dewey

Having shown1 the difficulty of assaying so-called cyanide bullion and the extreme variations often found in the results, an investigation was undertaken to discover, if possible, the causes of these variations by a series of tests upon the specific action of various metals during cupellation. Zinc.—In order to test the effect of zinc, 48 assays were made in sets of 6, 2 rows of 3. The charge for the middle cupels consisted of 500+ mg. Au, 1,125 mg. Ag, 10 mg. Cu. To the end cupels 50, 75, 100 and 125 mg. Zn were added, and a set of each proportion was cupelled with 4 and 8 grams Pb. The cupels were assayed and showed the following gold contents in milligrams, the figures being arranged as the cupels stood in the muffle: In many instances the zinc does not appear to affect the cupel gold, but various exceptions are apparent, generally in the cupels in the back row. With 100 and 125 mg. Zn, in some cases the Zn burned with its characteristic flame' before it could alloy with the other metals. Also, less fusible oxidized lumps were observed during the cupellation and some cupels showed a scum. In order to lessen the premature burning out of the Zn, an alloy of 2 parts Ag to 1 part Zn was used. A uniform charge of 500+ mg. Au,

Jan 1, 1918

By H. O. Hofman

Lime-roasting is a term proposed by Ingalls' for the operation of forcing air under pressure through a mixture of galena and lime at the kindling-temperature with the object of oxidizing lead and sulphur and of fritting or fusing the charge. If finely-divided galena were treated in this manner without the addition of lime, the heat set free by the oxidation of part of the lead and the sulphur would be sufficiently great to fuse un-decomposed sulphide, and thus stop desulphurization. Besides the chemical action that the addition of lime, limestone or gypsum to the charge may have, the admixture has the physical effect that it keeps the particles of galena separated from one another and accessible to the oxidizing effect of the air. At present, three methods of lime-roasting are carried out on a working-scale,—the Huntington-Heberlein, the Carmichael-Bradford and the Savelsberg2 processes. In the last, which interests us here, an 8-ton charge is made up of galena, limestone and perhaps some siliceous or ferruginous flux; the whole is crushed to pass a screen with 3-mm. holes and moistened with 5 per cent. of water. It is fed gradually into a bowl-shaped converter, 6.56 ft. in diameter, supported by trunnions attached to a truck. On the bottom the converter has a grate with blast-inlet beneath. In starting, the truck with the converter

Jan 1, 1908

By V. R. Garflas, J. W. Ristori, R. V. Whetshel

Preliminary estimates indicate that world consumption of petroleum products and related fuels in 1937 shattered previous records with a figure of 1,920,000,000 bbl.; that is, 124,000,000 bbl. more than the 1936 total. The writers, as in previous years, have been unable to account for all the available supply in 1937. This "unaccounted-for" supply, which formerly was thought to go largely into storage in foreign countries, was close to 53,000,000 bbl. in 1933; 93,000,000 in 1934; 111,000,000 in 1935; 75,000,000 in 1936 and 148,000,000 in 1937. As this discrepancy between supply and demand continued year after year, it became evident that other reasons than additional foreign stocks were responsible for it. It can now be stated that the "unaccounted-for" supply (see Table 1) goes to take care of: (1) consumption of petroleum products and related fuels for military purposes, the figures of which have been and are kept confidential by foreign countries, (2) additions to stocks to be consumed for military and nonmilitary purposes in foreign countries on which likewise no information is available, (3) errors incurred in the conversion of figures of production of crude oil, its products and related fuels from "weight" units, as used in Russia, for instance, to their American or "volume" equivalents and vice versa, and (4) to the lack of reliable statistics on production and consumption, particularly from Russia, the

Jan 1, 1938

By J. Douglas Gibson

In Canada, the economic climate for mining is still warm, but a noticeable chill set in last November when the Government published a White Paper on tax reform known as the Carter Report. Moreover, this chill could drop to a freeze injurious to the whole Canadian economy if two of the proposals in the Carter Report are adopted. The offending suggestions call for an end to (1) the depletion allowance and (2) the three-year tax holiday for new mines. Both of these tax incentives have played a major role in the postwar development of the Canadian economy and will, if undisturbed, play an even more important role in the future. The fact that they have worked and worked well is evident from the record. Fruits of an Industrial Beanstalk Excluding fuels, the value of Canadian mineral production was just under $3 billion in 1968-almost nine times as much as in 1946. With fuels included, the figure is $4.25 billion, or almost ten times as much as in 1946. Proportionately, this growth far exceeds that of Canada's manufacturers or of her economy as a whole. Table I traces the overall mineral production growth by principal products. Of particular interest here are petroleum, iron ore, natural gas, sulfur and potash, the combined production of which has grown from little or nil to a point where it now accounts for more than 40% of Canada's mineral output.

Jan 1, 1970

By Dol Duwez, R. H. Willens

A technique is described by which metastable alloy phases can be obtained by very rapid cooling from the liquid state. The results obtained so far have lead to; 1) extension of solubility limits beyond their equilibrium values, 2) new phases not found under equilibrium conditions, and 3) amorphous alloys. MANY new nonequilibrium phases have been found in alloys rapidly cooled from the liquid state. The technique used in these investigations essentially consisted of propelling a small molten globule of an alloy against the inside surface of a rotating copper cylinder. Since these original experiments were performed, the technique has been greatly improved. The purpose of this paper is to describe in detail, for the first time, a simple and efficient apparatus for producing foils of alloys which are rapidly cooled from the melt and to summarize some of the observations made on these alloys. I) FAST COOLING APPARATUS In the original fast cooling apparatus used by Duwez, Willens, and Klement,' the alloy was melted in a graphite container having the shape shown schematically in Fig. 1. A shock tube was attached to one end of the graphite part to supply the pressure for ejecting the molten globule. The globule was received on the inside of a rotating cylinder located about 0.5 in. from the exit of the graphite container. The globule trajectory made an angle of about 15 to 25 deg with the tangent to the cylinder at the point of

Jan 1, 1963

By Arthur W. Sheafer

MR. ECKLEY B. COXE, in his able and interesting paper on " The Preparation of Small Sizes of Anthracite,"* read and discussed at the Glen Summit Meeting, October, 1891, refers to the reputed immense amount of coal contained in the culm-banks, which are the unsightly accompaniment of every mining operation in the anthracite coal-regions. Mr. Coxe thinks the available amount and value greatly exaggerated, giving among his reasons (1) the spoiling of the culm by mixing with other refuse; (2) its deterioration; (3) its destruction by fire ; and (4) frequent failures to realize expectations as to the size of the banks. These points are undoubtedly important factors in determining the advisability of working any individual bank, but they have a varying influence in the several regions, some prevailing more in one than in another. Although the amount of fuel lying waste in these banks is still an uncertain and undetermined quantity, yet no one can visit the Schuylkill region without being impressed with the fact that a considerable amount of culm, too valuable to be left merely to the mercy of the elements, surrounds and encumbers each site of an old or present colliery operation. The rapid increase in the number of washeries, and the demand for leases on old culm-banks, shows that, in the Schuylkill region at least, the question of deterioration doès not play an important part. The proportion of coal to refuse, the relative percentage of the sev-

Jan 1, 1895

By Blamey Stevens

The object of this paper is to present a theory of the formation of fissures, which seems to be supported by all available data. The investigation is, in the main, an exact one, and irregularities of the rock-structure are generalized. From the conclusions drawn a general classification of fissures is made, and this should be of practical use in the comparison of mineral deposits. The theory also throws some light on the equilibrium of the earth's crust and the depth of action of surface-waters. Incidentally, additions are made to the theory of earthquake-slips. Former Theory. It has been previously pointed out that the "jointing" of homogeneous rocks occurs in two sets of planes, at right angles to one another, and making angles of 450 with the directions of greatest and least principal stress.' The theory by which this fact is explained does not, however, account for fissures and faults, because normal faults are usually more vertically, and reverse faults more horizontally, inclined than 450. The "jointing law" is based on the following axiom: In a homogeneous mass under pressure, rupture must take place on the lines of maximum tangential stress."2 This law applies, with fair approximation, to the tests on jointing which can be made in the laboratory, and as nearly as can be expected to the natural jointing-planes in rock-masses, where the stresses are not very great; but it entirely fails to account for fissure-fractures.3

Jan 1, 1910

By Emile Hiertz

THE first press was installed in June, 1910, and the second in March,1911. They produce 1,000 briquettes per hour, weighing 5 kg. (11.05 1b.) each, under a pressure of about 400 kg. per square centimeter (5,689.2 lb. per square inch). The chloride of magnesium is received from the potash mines at Hanover in tank cars in approximately a 35 per cent. solution. The quantity of solution added to the flue dust varies between 2 and 3 per cent., so that the briquettes contain about 1 per cent of MgCl2. To fresh dust as much as 10 per cent. of coke breeze may be added and bri¬quettes made that still have a crushing strength of from 25 to 30 kg. (377 to 426.6 lb. per square inch) after 36 hr., and 45 kg. (639.9 lb. per square inch) after six days. After having treated 140,000 tons of the material, the reports of the blast furnaces show that the briquettes improved the action of a furnace and produced less dust than did Minette ore. As much as 35 per cent. of briquettes is added to the furnace charge without bad effects on operations. The presence of chlorine did not produce any corrosion in the furnace, downtakes or other piping. The presence of a certain amount of chlorine in the dust reduces the amount of chloride of magnesium which it is necessary to add for briquetting.

Jan 12, 1913

By A. A. Venghiattis

This paper is discussed not because of its intrinsic value but because it has been related by its authors to the oilwell gun perforators. It is well known that conditions almost ever present in oilwell perforations are the overburden and the presence of the casing. Because of the lack of information in the paper on the dimensions or confinement of the target rocks, one is led to guess that they were not confined at all and, particularly, that no steel front plates were used on the impact face of the rocks to materialize the presence of the cemented casing. This situation, plus the fact that small steel balls have been used as projectiles instead of actual bullets, makes the whole thing unapplicable to oilwell perforation. When shooting is performed against target rocks confined (as shown on Fig. 1) in such a way as to give a fair image of the overburden applied to the formation to be perforated, as well as of the cemented casing, the following are found. 1. There is no cratering worthy of mention, even with bullets having 10 times higher impact energy per unit projected area than the steel balls mentioned in the article. This has been confirmed with sandstone as well as with other rocks (granite, limestone and chalk). See Figs. 2 and 3. 2. Penetrations vary closely as the logarithm of the impact velocity. On this matter I have established the relation

DESPITE strikes, domestic production of copper and zinc in 1951 rose about 3 pct and 10 pct, respectively. Lead output fell only about 7 pct. Primary refined, including processed scrap and imported concentrates, was somewhat higher for zinc, and slightly lower for copper and lead. Prospects are for moderately larger mine and refined production in 1952 according to Standard & Poor's analysis of nonferrous metals. The survey goes on to report domestic copper prices averaged 14 pct higher in 1951, lead prices 30 pct higher, and zinc prices 32 pct higher. The 2¢ rise in zinc and lead ceilings in October will lift the average price in 1952 over 8 pet, assuming no further price change. Currently, OPS appears opposed to raising the 24 ½ ¢ copper ceiling to the 24 ½ ¢ maximum on imported metal. The steep premiums in world markets are likely to be reduced in 1952. Sales in 1951 were at new peaks. A further moderate rise is indicated for 1952. Earnings of the industry were at a new high in 1951. The increase for companies covered in the survey was perhaps 25 pet, despite a tax rate of about 53 pet, against about 40 pct. in 1950. Relatively maintained to moderately higher earnings are currently indicated for 1952. About two thirds of the companies covered in the survey raised dividends, including extras, in 1951. In general, maintained payments appear probable in 1952.

Jan 1, 1952

By P. H. Royster

IN a study of the blast-furnace process, the Bureau of Mines has made many experiments for the purpose of determining the exact nature of the combustion of coke in the neighborhood of the tuyeres. Two papers1 presented at a meeting of this Institute discussed somewhat the practical aspects of coke combustibility in its relation to the operation of the blast furnace. In a later paper,2 Sherman and Kinney discussed the possible effect of variations in the combustibility of cokes on the furnace operation, and find that the "reoxidation theory" of Koppers and the "heat concentration theory" of Brassert3 are insufficient to explain the variation in the conduct of different cokes that has been observed by furnace operators. In their report to the D-5 Committee of the American Society for Testing Materials, with which the Bureau of Mines has been cooperating, Perrott and Fieldner4 seem to agree with Sherman and Kinney that, for practical purposes, the nature of the combustion of coke at the tuyeres of any furnace is constant and is affected neither by the physical properties of the coke nor by the nature of the furnace operation. They omit as unimportant any tests on the combustibility of coke from their proposed methods for standard tests on coke. In the last two papers, it is pointed out that performance tests, in which all other factors except coke quality are kept constant, are to be desired and

Jan 3, 1924

By H. C. Rolseth, R. H. Kohler

Jet channeling made its entry into the granite industry in 1955 and quickly gained acceptance as an economical method of quarrying. Developed by the Linde Division of Union Carbide Corp., this method employs a small rocket-jet burner with a high-temperature, high-velocity exhaust flame that causes granite to disintegrate. It can thus make continuous vertical cuts to free large blocks from granite formations. The Thermal Spalling Process The effect of a thermal device on rock depends upon the rock's spallability. In simplest terms, spalling is the decrepitation resulting from differential expansion of rock crystals due to thermally induced stresses.1 the individual rock properties influencing the spalling characteristic are so numerous and their interaction is so complex that it has so far been impossible to predict with accuracy the reaction of any particular rock to a high-temperature source of heat. Perhaps computers will eventually make such predictions possible, but for the present it is necessary to impose the thermal shock conditions on a sample of the rock to establish its spalling characteristics. The properties most favorable to a high degree of spallability are: (1) Large linear thermal expansion at temperatures below 700º C. (2) High thermal diffusivity at temperatures below 400º C. (3) Equigranular interlocking structure with little or no fine-grained clay or mica alteration products. (4) No significant amounts of soft, low-melting, or elastic minerals or materials which yield after thermal decomposition.

Jan 7, 1969

By Beverley S. Randolph

The coal-measures of George's Creek coal-region, in Maryland, lie in a comparatively flat synclinal basin, about 4 miles wide. The dip of the measures is, in places near the edge of the basin, as much as 20 feet in 100. The Pittsburgh seam, known locally as the " Big Vein," is the only seam worked at the present time. Ocean No. 3, one of the large mines of the Consolidation Coal Company, has its opening on the outcrop of the Pittsburgh seam, in a ravine which cuts into this seam to such an extent as to bring this opening to within a mile of the axis of the basin. After working all the coal to the rise of this point, the mine was further developed by extending a slope down the dip of the seam, making such an angle with the line of greatest dip as to give a grade varying from 1 to 10 per cent., down which the empty cars carry a rope from a single-drum winding-engine. The coal was worked from each side of this slope in successive Iifts during its progress. From the top of the slope, for a distance of 4000 feet to the fourth lift, the " make " of water is drained by gravity through a heading into the adjoining mine. Below this point the water was pumped into this same heading, at the fourth lift, from which point, as before mentioned, it flowed by gravity.

Jan 1, 1895

By D. L. Harris, A. M. Gaudin

THE following results, presented here in condensed form,1 were obtained in a preliminary study of the adsorption of n-hexane thiol, hexyl mercaptan, on sphalerite, zincite, willemite, and quartz, from aqueous solution and from a gas. Interest in this subject was aroused by a Belgian report2 of effective use of hexyl mercaptan for flotation collection of oxidized zinc minerals. The relatively low boiling point, 149°C, of the mercaptan3 suggested the desirability of extending the usual measurements of partition of collector between aqueous solution and gas and between gas and mineral. It is believed that this paper presents the first measurements of this type on a flotation system. Attempts were made to carry out the measurements at equilibrium, but as the work progressed it became increasingly doubtful that this desirable condition had been achieved. To control composition and extent of the gas phase, the apparatus was a wholly-enclosed thermally-controlled glass system. Because of these constraints and the desirability of dealing with pure minerals, a scale of operations was chosen in which a few grams of deslimed mineral were used in each test. It was also necessary to choose a particularly sensitive method for mercaptan analysis, and in fact a method that would permit the experimenters to follow the approach to equilibrium. For these reasons mercaptan marked by radiosulphur 35 was used. An analysis was made for the radiosulphur by a modification of the method of Gaudin and Carr.4

Jan 9, 1954

By C. L. Dake

Iron is much more soluble in the ferrous than in the ferric form. Where, as in the case of the ferrous silicates and. the sulphides, the iron is already in the ferrous form, it may go at once into solution and be removed, upon the breaking down of the parent rock. If in the ferric form, it must first be reduced; usually by the decay of organic matter, the demand of the decaying carbonaceous matter for oxygen being so great that the latter is abstracted from the ferric compounds and the iron is thereby reduced and rendered soluble. The iron may go into solution as the sulphate, or in the presence of excess CO2 as ferrous carbonate. It is probably soluble as salts of the organic acids.' Recent work indicates that these are important in the formation of bog ores.2 There is considerable variety of opinion concerning the behavior of these organic compounds.3 The secretions about the roots of plants and trees also cause the solution and removal of iron and a consequent bleaching of the soil,4 While the matter is not yet well understood, we can probably say definitely that the so-called organic acids are a group of colloids which possess slightly acid properties, and the salts of which are partly soluble and partly insoluble.5 Their iron salts readily change from the ferrous to the ferric form, and their solubility is greatly modified by the presence of ammonia.

Jan 1, 1916

By W. M. Yim

Experimental results are presented which indicate that transverse striations in horizontal zone-leveled Bi-Sb alloy crystals are due to irregular growth rate resulting from thermal fluctuations in the melt (Iring gowth. Thc thermal fluctutations arose from two different sources. The first type was brought about by periodic fluctuations in the furnace temperature. The second type can be attributed to turbulent therrrol conlcclion in the trzelt near the solid-liquid inteyace. Tile arrzplitlcde ond fvequency of the tetiperaticre fluctlrations vesultity from llle lhevnal con1,ecrrell. The striation spacings in Lhe crystals covvelale well with the periodicity 0.f the tempevature flueluatiors. Altliough the strialiors represenl corrlpositiozul inhoiHogeneity oh a rzicroscule, less than f.z cil. be1 S6 in Best's as deterrirzed by electron-pro be chalq'sis, the slriations roerre fbund to ILUL' no rrleusuanble effect on electical vesistirity rwr on weak field macgnetoresistance of. the Bi-Sb a1lu.y in the ternpevutue ),unge 4.Polo 300°K. DURING the course of an investigation on the horizontal growth of semimetals,' it was found that crystals of Bi-Sb alloys contained many closely spaced parallel arrays of striations. These striations occurred perpendicular to the growth direction and parallel to the solid-liquid interface. We shall refer to them as transverse striations, or just striations'', to distinguish them from lineage substructures or longitudinal striations which form parallel to the growth direction and have been known to be associated with cellular structures.' Similar transverse striations have been reported previously to occur in other materials prepared by horizontal growth: metals,4 semiconductors,5 as well as their alls. - Various methods of crystal preparation have apparently little effect on the occurrence of the transverse striations. They form whether the crystals were grown by the vertical Czochralski technique, withe1' or without'3- rotation, or by the horizontal zoning methd.- Thus, the transverse striations are not limited to any one class of materials, nor to any particular method of preparation. It is likely, therefore, that all of the observed transverse striations may have some common cause. Previously, workers agreed that periodic changes in the growth rate bring about the striations. However, no agreement exists as to the origin of the growth-rate fluctuations. Some attributed the discontinuous growth to a purely external cause, such as fluctuations in the furnace temperature, jerky motions in the crystal pulling mechanism, or a nonsymmetrical temperature distribution in the melt (in the case of crystals grown by the Czochralski technique with rtation). Others looked for the cause in some fundamental property of the growth process itself. For instance, a certain degree of supercooling is required to initiate growth from the melt. But, with further growth, the degree of supercooling decreases because of the liberation of the heat of solidification at the solid-liquid interface. Thus, crystal growth would be brought to a halt until sufficient supercooling is resotred and the cycle begins again.3'11 According to this model, periodic fluctuations in the melt temperature should exist at the solid-liquid interface. Since the periodic fluctuations in growth rate would result in changes in the segregation coefficient of solute atoms, crystals containing the transverse striations may, in some cases, show a periodic impurity fluctuation along the length, resulting in a degradation of electrical properties. The resistivity striations in doped germanium'9-10 or lnsbB are well-known examples of this microsegregation. The present work was undertaken to explain the exact origin of the transverse striations, and to assess the extent of their effect on chemical homogeneity as well as on electrical properties of Bi-Sb alloy crystals. Results from our previous study of the crystal growth of Bi-Sb alloys1 indicated that the transverse striations may arise from the temperature fluctuations in the melt during growth. This paper will show that the melt temperature fluctuations are indeed responsible for the occurrence of the transverse striations. I) EXPERIMENTAL Although the transverse striations have been observed in all slow-grown Bi-Sb alloys across the entire compositional range, we selected a composition, Big3Sbs, for the present study in view of the extensive data available on the crystal growth of this alloy from a previous study.' High-purity bismuth and antimony, both a 6-nine grade by the manufacturer's emission spectrographic analysis, were used throughout. Independent mass-spectrographic analysis showed, however, that the starting materials were more nearly a 5-nine grade. each containing metallic impurities of approximately 10 ppm atomic. In zone-leveled Big5Sb5 alloys, the total metallic-impurity content was slightly lower, about 7 ppm atomic, indicating that some degree of purification was achieved during the growth. None of the electrically active impurities, such as tin and lead (acceptors) and tellurium and selenium (donors), were present in significant quantity in undoped Bi95Sb5. Typical analysis of the undoped Bi95Sb5 alloy is shown in Table I. Nonmetallic impurities, such as carbon and oxygen, were detected, sometimes as much as 100 ppm, in both the starting materials and the zone-leveled alloys: but the data were only qualitative. Temperature fluctuations in the melt were monitored over 1 or more days by means of a 5-mil chromel-

Jan 1, 1967