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By M. Khorouzan, L. Thomas

Designers of semiconductor devices have been strivi,ng to resolve problems associated with Au-A1 alloys in bonded in.tercomzeclions. One approach now being- used is that of waintaining a physical seyav-atioz between the two metals in bond areas. This is accolrzplished by alunzincnz-plating a bonding area on the tips oJ the kovar leads and using alcminurn wires to join the senzicondictor device to the leads. The portion of the kovar lead which is on the externul side of the sealed package is gold-plated to provide an oxide-free surface for soldering or welding. A discoloration condition originally thought to be sinilar to purple plague, occuving in the yluled uluninur bonding area after package sealing, has been investigated to determine its efiects ipm bond integrity. Electron-micro-probe analysis determined that no1 only gold, but lead, zinc, and silicon were also present in the discolored area. A series of samples conlaining' conkrolled umonts of these inzpitrities weve prepared and subjected to a sil.zuluted sealing process. The investigations swcued that, of the contawiinants, only zinc toas detrinenlul to Lhe bond integily. The discoloration condition itself was found not to be detrimental to the bond integrity. DESIGNERS of semiconductor devices have been striving to resolve problems associated with Au-A1 alloys in bonded interconnections. One approach now being used is that of maintaining a physical separation between the two metals in bond areas. This is accomplished by aluminum plating a bonding area on the tips of the kovar leads and using aluminum wires to join the semiconductor device to the kovar leads. The portion of the kovar lead which is on the external side of the sealed package is gold-plated to provide an oxide-free surface for soldering or welding. Contamination as evidenced by discoloration of the aluminum-plated area was observed in a number of integrated circuits undergoing examination for defect characteristics which cause electrical failures.' This paper contains the results of an investigation to determine the nature of this discoloration, its cause, and its effect upon the integrity of the interconnection bond. I) THE NATURE AND EXTENT OF ALUMINUM-BOND CONTAMINATION The initial hypothesis in the investigation was that the discoloration was caused by reaction of the aluminum film with some unknown contaminants during the sealing of the hermetically sealed integrated-circuit flat package. The package is a rectangular ceramic container sealed with glass which surrounds the kovar leads as well as joining the top to the bottom. The seal is made hermetic by heating and cooling the package to devitrify the glass. In the case of the packages under investigation, the hermetic sealing had been accomplished with dry air as internal atmosphere. The apparent effect of contaminations as observed by microscopic examination was the formation of surface oxides having variations in color encompassing the whole spectrum of visible light. The contamination appeared to be related to one of the more notorious examples of these colorations, the so called purple plague.' In addition to purple plague, Fig. 1 shows the tarnish in the luster of the aluminized surface in the bond area which had been observed in many of the integrated circuits. To identify the contaminant in the bond area electron-probe microanalysis techniques were used.3 Fig. 2 shows the result of this analysis. The contaminants identified were gold, aluminum, zinc, lead, silicon, and cobalt. Fig. 2(a) is a back-scatter display of the area under study. The back-scattered electrons provide a general indication of the distribution of elements in the specimen surface. Elements with higher atomic number scatter more electrons back from the surface and are seen as light areas in the picture. The sample current, Fig. 2(b), is the amount of current conducted by the specimen as a result of electron-beam striking it and is an indication of element distribution. The Sample current is the reverse of back-scatter and complements it. Other pictures in Fig. 2 are produced by characteristic X-rays generated by the elements, allowing the isolation of the element of interest. The isolated element appears white and all other elements are dark. In this manner a comparative study provides a correlation between different surface areas and the elements which are in these areas. The area covered by the gold film, Fig. 2(c), shows that the boundary between the gold film and the kovar is not sharp as expected and that some sort of diffusion has taken place. Fig. 2(c) shows that some gold particles have been carried to the bond area and are in the proximity of the bonded wire in spite of the presence of a physical barrier in the form of the un-

Jan 1, 1967

By W. O. Philbrook, L. D. Kirkbride

IN the normal operation of the iron blast furnace, reduction of the iron oxides is accomplished almost entirely above the tuyeres.' Blast furnace slags usually contain less than 0.5 pct FeO, although higher values may occur with abnormal operation. There is reason to conjecture, however, that incompletely reduced ore may sometimes reach the hearth and enter the slag as a result of heavy slips or, perhaps, even from cores of excessively large lumps of a charge material of poor reducibility. The possibility of reoxidation of iron droplets falling in front of the tuyeres has been considered by several writers. It would be of interest, to know how rapidly iron oxides reaching the slag for any of these reasons could be reduced by reaction with coke or with the high carbon liquid iron in the hearth. In comparison with the hundreds of papers that have appeared on various aspects of the reduction of solid iron oxides by gases and in the presence of several forms of carbon, little work has been published on the reductioin of liquid oxides or slags. Dancey measured rates of reaction of the pure liquid oxides, both FeO and Fe,O,, with molten iron containing about 4.3 pct C. The oxide was dropped into the cup formed in the upper surface of the iron by rotating the crucible and melt. Under these conditions, reduction of either FeO or Fe,O., was completed in less than 10 sec. The present study was concerned with the reduction of FeO from blast furnace-type slags containing less than 5 pct FeO and melted over carbon-saturated iron in stationary graphite crucibles. The results were considerably different from those found by Dancey, as will be discussed later. Although this work is of interest in relation to hearth reactions in the blast furnace, interpretations must be made with caution because the experimental conditions do not duplicate those within a furnace and may not even lead to the same reaction mechanism. The authors were motivated in undertaking this work by an additional interest—the part played by FeO reduction in the mechanism of de-sulphurization of iron by slags under similar experimental conditions. Derge, Philbrook, and Goldman eveloped detailed experimental evidence to support a three-step mechanism for desulphurization like that originally proposed by Holbrook and Joseph' (These reactions are written in molecular form for convenience, but this is not intended to imply the existence of molecules of FeS in the bulk metal phase nor to deny the likelihood of ionic reactions in the slag.) Earlier work by Chang and Goldman" had shown that the overall reaction follows first-order kinetics with respect to sulphur and that the rate of reaction is proportional to the slag-metal interface area, which observations have been confirmed by subsequent work. Later studiese,' have established the influence of al.loying elements on the first and last steps of the reaction. This paper reports a study of step 3 alone, uncomplicated by the simultaneous process of sulphur transfer. Apparatus and Procedure The experiments were made in a conventional high frequency induction furnace powered by a 35 kva Hg spark gap converter. The graphite crucibles used for most of the runs were 14 cm (5.5 in.) deep and 4.8 cm (1.9 in.) ID with 0.75 cm (0.3 in.) wall. An insulating cover with a small opening for withdrawing samples was used to minimize heat loss and infiltration of air into the furnace. The crucible was charged with 300 g of carbon-saturated iron and either 65 or 100 g of prefused slag analyzing 38.0 pct SiO,, 15.4 pct A10 and 47.1 pct CaO. To obtain the cleanest possible interface at the start of the reaction, the metal and slag were brought to temperature together to prevent the rejection of kish graphite that would have been caused by the chilling effect of a large addition of cold slag to carbon-saturated iron. After temperature control had been established, the desired amount of iron oxide was added in the form of a prefused slag of composition 73.6 pct FeO, 7.7 pct AWX and 19.0 pct SiOl. This slag addition was observed to be molten in somewhat less than 1 min, and a very vigorous reaction proceeded for 1 to 2 min after its introduction. Zero time was taken as 2 min after the ferrous silicate slag addition. Slag samples weighing about 0.5 g each were taken periodically by a copper chill sampler." The weight of the initial slag was large relative to the weight of samples removed, so that the slag weight never varied by more than 5 pct during any run. Temperature was measured by a calibrated W/Mo thermocouple immersed in the metal, with a graphite tip cemented over the fused silica protection tube to prevent attack by slag and metal. After some difficulties with uncertain temperatures during the first two runs, the practice adopted to position the thermocouple for reproducible results was to lower the protection tube to touch the bottom of the crucible and then raise it 0.5 cm. The apparent temperature gradient between the bottom of the crucible and the top of the slag was found to be 15°C (27°F). but much of this spread was probably the result of inadequate immersion of the protection tube to off-set conduction losses along the graphite tip when the thermocouple was inserted only into the slag. The temperature of the bath was controlled within 25°C (9°F) during a run.

Jan 1, 1957

By M. G. Driessen, H. E. Criner

Possible applications of cyclone thickeners for: (1) clarification of the washery water and, (2) recovery of fine coal from the plant bleed. The paper shows: (1) that it is possible to remove all particles including the very finest, from the circulating water, thus obtaining a closed water system and, (2) that reduction of the ash content of the solids of the plant bleed is feasible by means of cyclone thickeners. Performance data for different size cyclones is given in the form of graphs.

Jan 1, 1950

By P. Ramachandraraa, T. R. Anantharaman

THE technique developed by Duwez, Willens and Kle-ment' for rapid solidification of molten alloys in small quantities by ejecting them on to a highly conducting substrate with the aid of a shock wave has come to be known as "liquid quenching" or "splat cooling" in literature and has already been applied to alloys of many binary systems.' The very high cooling rates of the order of l060 to 1080 per sec obtained in this technique and the consequent drastic undercooling of the melt have led to such striking results as formation of new amorphous and crystalline metastable phases and extension of solid-solubility limits in many alloy systems. The cooling rates in these experiments can, however, be neither accurately measured nor effectively controlled and hence the occurrence of either more than one metastable phase or appreciable differences in constitution in splat-cooled alloys of the same composition cannot be ruled out.3 In fact, workers in two laboratories have reported formation of two different cubic metastable phases in liquid-quenched Au-Si alloys containing 17 to 20 at. pct si.4,5 The present note deals with some new and interesting results obtained in a Ag-21 at. pct Ge alloy and a Au-27 at. pct Ge alloy subjected to the liquid-quenching treatment at different cooling rates. Two alloys of nearly the same composition had earlier been rapidly solidified by the standard "gun technique" in the same laboratory and shown to solidify in nonequilibrium structures, viz., an hcp phase (a = 2.987Å;c =4.718Å) in the Ag-Ge system6,7 and both hcp (a = 2.885Å; c = 4.754Å) and tetragonal (a = 11.627A; c = 22.491Å) phases in the Au-Ge system.3 Apart from different substrates (copper and stainless steel), different melt temperatures (50º to 500°C above the liquidus), and different capillary sizes (0.4 to 1.5 mm diam) in the "gun technique", slower cooling rates of the order of l050C per sec were also obtained in the present work by replacing the substrate by water at room temperature in a modification of the technique due to Olsen and Hultgren.8 No attempt was made to measure the cooling rate in any experiment. The products varied from fine powder (>40 pct by wt—200 mesh) obtained by quenching in water to thin flakes and foils (11.0 sq mm to 4.0 sq cm) produced by splat cooling. They were subjected to the Debye-Scherrer method of X-ray examination in each case. In case of the Ag-Ge alloy, in addition to the expected metastable hcp phase,6 a coexistent tetragonal phase (a = 5.093,Å; c = 7.009Å) was detected in some experiments. Eight weak X-ray reflections from this phase could be identified, two of them being the same as reported earlier.7 With increase in the cooling rate, the dominant hcp phase seems to be first accompanied by traces of silver or germanium and then either homogeneous or mixed with traces of this new tetragonal phase. The splat-cooled Au-Ge alloy showed generally the expected hcp and tetragonal phases,3 but sometimes traces of germanium were also present. Further, two new tetragonal phases with the following lattice param ters could be clearly identified in samples quenched

Jan 1, 1970

By V. C. Allen

THE Tri-State Zinc, Inc., Galena, Ill., was confronted with the problem of securing ore from a deposit because the hoisting shaft was several thousand feet from the mill. The orebody is several thousand feet long, averaging 200 ft in width and 60 ft in height and opened up by vertical shafts some 300 ft deep. Mining is by the room-and-pillar method. During the initial operation the ore was loaded by conventional electric 1/2-yd boom-and-dipper shovels and hauled to the shaft by 8-ton diesel trucks. This underground ore loading and hauling was well adapted to the conditions and productive of low costs per ton. However, with the mill situated as mentioned, a triple handling of all broken rock was necessary: l—from the stope to the shaft by truck, 2—up the shaft by skip br can into the surface hopper, and 3—by truck from the surface hopper to the crushing plant at the mill. In addition to the repeated handling, serious troubles were encountered during the winter because of freezing in the shaft hopper. Consideration was given to either moving the mill to the new orebody or to the construction of a second mill. The presence of other orebodies to be mined at a later date made the first alternative impractical while the capital outlay for a second mill, when the present plant of approximately 850 tons per day was deemed sufficiently large for the total reserves, made the second alternative also unwise. It was decided to retain the mill in the originals location and continue to move the ore to it. The idea of driving an inclined adit from the surface to the bottom of the orebody suitable for truck haulage and big enough to allow the passage of all mechanical equipment was conceived. Among the apparent advantages of such an incline were: 1— Direct haulage from the stope to the mill without rehandling. 2—Elimination of virtually all grizzlies. Trucking from underground to the mill would do away with all hoppers, chutes, gates, and skips and make the maximum rock size dependent solely on the size of the shovel dipper at the mine and the crusher opening at the mill. 3—Less secondary blasting would be needed. 4—Ease of transporting equipment and supplies underground. Shovels and trucks could be taken through the incline intact. 5—Equipment could be brought to the surface for repairs and servicing without loss of time. The same advantages of ease in moving would be present in the handling of men, steel, powder, and supplies. 6—There would be far less difficulty in increasing the amount of tonnage that could be moved by truck up an incline than would be found in attempting to increase the capacity of a shaft. 7—All the broken ore in the stopes would serve as bin capacity, as it would take the breakdown of all of the loading and hauling equipment to have the same effect as a delay in shaft hoisting. 8—All danger of men being trapped in the mine as a result of shaft fire or power stoppage would be eliminated. 9— Virtually all trouble from severe winter conditions would be eliminated by the direct haul underground to the mill. The decision was made to proceed with the driving of an inclined adit. The topography of the surface between the orebody and the mill was such that it was possible to locate the portal at a point 170 ft above the mine floor and 1800 ft horizontally from the central point of the orebody to the south and 2500 ft from the mill to the north. A grade of 10 pct was found to be optimum for continuous truck haulage when the various factors of speed, safety, and truck maintenance were all considered. The incline as driven was consequently 1700 ft long on 10 pct grade and 12 ft high by 17 ft wide in cross section. The tunnel-driving equipment was chosen so that it could be used in mining after the completion of the tunnel. Drilling was done with a jumbo with two Joy jibs mounting 3-in. drills, loading with an Allis-Chalmers diesel-powered, front-end loader of approximately 11/4-yd capacity, and hauling by Koehring Dumptor trucks of 8-ton capacity, diesel-powered. The width of the tunnel allowed the end loader and Dumptor to be placed abreast. Since the Dumptors can be driven either forward or backward with equal facility, loading was accomplished without turning around either machine throughout the loading operation. The crew in addition to the tunnel foreman was comprised of three men per shift at the start and in the later work, four men. Each crew could perform any part of the working cycle. If the drilling was completed and the round blasted in the middle of a shift, the same men would proceed with the loading and hauling. Since the mine already had been drained to the bottom levels, no water was encountered. At the halfway point the tunnel was widened for approximately 100 ft to permit trucks to pass. The total cost of the tunnel excluding the capital outlay for equipment, which was all continued in use in the subsequent mine operation, was $60,363.00 or $35.50 per ft. The tunnel was completed at the end of June, 1949 and has been in continuous use since that time. In the five months from July to November inclusive, 106,049 tons have been transported to the mill or an average of 835 tons per day. No unforeseen disadvantages have been encountered and the advantages which had been predicated before the adit's construction have been more than realized. As previously mentioned, the deposit is worked by the room-and-pillar system with occasional faces up to 125 ft high. Except in driving development drifts when diesel-powered, front-end loaders such as were used in the tunnel are employed, all shoveling is done by Yz-yd boom-dipper type shovels electrically driven. These units need a width of 25 ft and a height of 14 ft in which to operate. All hauling is by diesel trucks, mainly Koehring Dump-tors. Roads are maintained with caterpillar tractors and a road grader. The tonnage output from the

Jan 1, 1952

By Dodge, C. E.

ONE of the first mining areas to be developed in Arizona was that in the district centering about Clifton and Morenci. Traces of metals were first noticed by Henry Clifton on an expedition in 1864. Definite copper outcroppings were also reported in the following year by General J. H. Carleton when he led his troops into the district on an Indian raid. Actual mining operations were started in the early seventies. and the first smelter was finished in 1873. Two adequately financed companies acquired most of the property, and both commenced production about 1882. These were the Arizona Copper Co.. owned by a group of Scotch investors, and the Detroit Copper Mining Co., afterwards purchased by the firm of Phelps, Dodge & Co. Later the Shannon Copper Co. acquired and operated a number of claims in the northern part of the district. These three companies all operated underground, mines independently for many years.

Jan 1, 1942

By Edward Martinez

Although the copper segregation process has been known as a method for treating oxide copper ores since the 1920's, the reactions involved in this process are still a matter of conjecture. However, the evidence turned up in a recent series of experiments at Asarco's Central Research Laboratories strongly indicates that some of the proposed reactions may not be occurring. Experimental work on oxide copper ores from the Sagasca mines in Chile led to the discovery of the copper segregation process in 1923. It was found that the reduction of the copper with coal at about 700°C occurred on the surface of the coal instead of remaining disseminated in the ore. The unusual behavior of the copper, which caused it to migrate from the ore particles to the coal, was traced to the presence of a small quantity of sodium chloride occurring in the ore. Further experiments with oxide copper ores proved that the presence of a halide, either occurring naturally or admixed with the ore, caused the copper to migrate from the ore particles and to segregate in the charge.

Jan 8, 1966

By C. H. Samans, G. F. Tisinai, J. K. Stanley

The addition of nitrogen (0.10 to 0.20 pct) to Fe-Cr-Ni alloys of simulated commercial purity results in a real displacement of the u phase boundaries to higher chromium contents. The effect is small for the (Y + s)? boundary, but is pronounced for the (y + a +s)/(y + a) boundary. Although there is an indication of an exceptionally large shift of the n boundaries to higher chromium contents, especially in steels with nitrogen over 0.2 pct, the major portion of this apparent shift results from the fact that carbide and nitride precipitation cause "chromium impoverishment" of the matrices. The effect of combined additions of nitrogen and silicon to the Fe-Cr-Ni phase diagram is demonstrated also. Nitrogen can nullify the effect of about 1 pct Si in shifting the (y + o)/? phase boundary to lower values of chromium at all nickel levels from 8 to 20 pct. NItrogen can nullify this U-forming effect of about 2 pct Si at the 8 pct Ni level, but not at the 20 pct Ni level. The alloys studied were in both the cast and the wrought conditions. There are indications that the u phase forms more slowly in the cast alloys than in the wrought alloys if both are in the completely austenitic state. The presence of 6 ferrite in the cast alloys accelerates the formation of U. Cold working increases the rate of o formation in both cast and wrought alloys. THE major improvement in Fe-Cr-Ni austenitic alloys in recent years has been in the addition or removal of minor alloying elements to facilitate better control of corrosion resistance, sensitization, and heat resistance. One shortcoming of the austenitic Fe-Cr-Ni alloys, which never has been completely circumvented, is their propensity toward u formation. In the AISI-type 310 (25 pct Cr-20 pct Ni) and type 309 (25 pct Cr-12 pct Ni) steels, sufficient amounts of u phase can form, if service or treatment is in a suitable temperature range, to cause severe embrittlement. Also, there is a growing conviction that this phase may be contributory to some unexpected decreases in the corrosion resistance of certain of the 18 pct Cr-8 pct Ni-type steels. The present paper discusses the effect of nitrogen additions on the location of the (r+u)/d and the (y+a+u)/(y+a) phase boundaries in the ternary Fe-Cr-Ni system, for cast and wrought alloys of simulated commercial purity, and in similar alloys containing up to about 2.5 pct Si. The objective is to define compositional limits for alloys which will not be susceptible to u formation when used near 1200°F (650°C). An excellent review of the early studies of the u phase in the Fe-Cr-Ni system has been compiled by Foley.1 Rees, Burns, and Cook2 have determined a high purity phase diagram for the ternary system, whereas Nicholson, Samans, and Shortsleeve3 are- stricted themselves to a portion of the simulated commercial-purity phase diagram. Both groups of investigators show almost an identical position for the commercially significant (y+u)/y phase boundary. Further comparison of the work of the two groups indicates that, below the 8 pct Ni level, the commercial alloys have a decidedly greater propensity toward u formation than the high purity alloys. The two groups of workers agreed that both the AISI-type 310 (25 pct Cr-20 pct Ni) and the type 309 (25 pct Cr-12 pct Ni) steels are well within the (y+~) region and that the 18 pct Cr-8 pct Ni-type alloys straddle the U-forming phase boundaries. Nicholson et al.3 showed, in addition, that these boundaries shift toward lower chromium contents if greater than nominal amounts of silicon or molybdenum are added. The effect of nitrogen on the location of the s phase boundaries in the Fe-Cr-Ni system has not been known with any certainty. In 1942, an approach to this problem was made by Krainer and Leoville-Nowak,' but at that time they apparently were unaware of the slow rate of s formation in strain-free samples and aged their samples for insufficient times, e.g., 100 hr at 650°C (1200°F) and 800°C (1470°F). For this reason, it would be expected that their (y+ u) /y boundary would be shifted toward lower chromium contents (restricted ?-field) when equilibrium conditions were approximated more closely. Procedure for Studying the Alloys The alloys used were prepared in the following way: Heats of 200 lb each were melted in an induction furnace. A 5 lb portion of each heat was poured into a ladle containing an aluminum slug for de-

Jan 1, 1955

By Chester O. Ensign

Many publications to date have advocated under- seas mining operations, optimistically overlooking the paucity of information on mineral distribution and the ocean environments in which minerals occur. Such articles (smattered with opinion, as is this article) are herein tempered by my more conservative views on the economics of mining under the seas. For purposes of this paper, underseas mining refers only to the deeper surficial deposits of the continental shelf and the deep sea floor, i.e., the deposits of phosphorite and manganese nodules.

Jan 9, 1966

By Howard Scott, Henry S. Rawdon

The method of demonstrating the structure existing in a metal or alloy at high temperatures, by etching a polished sample after it has been heated to the desired temperature, is quite familiar to metallog-raphists. The usual procedure1 2 is to heat the specimen, previously polished for microscopic examination, to the desired temperature, in a neutral atmosphere (hydrogen or nitrogen), then admit the etching gas (chlorine, hydrochloric acid or similar gas) for a few seconds, and finally, after flushing out the etching gas with the neutral one, cool the specimen in the neutral atmosphere. The pattern produced by etching at a definite temperature is usually taken as a record of the microstructure prevailing at that temperature. It has frequently been pointed out that changes in composition of the surface metal occur during the preliminary heating in the neutral atmosphere, so that the appearance produced by the etching at high temperature may not exactly represent the condition of the interior of the specimen. To overcome this uncertainty, the heating has sometimes been done in vacuo,3 the etching gas being admitted when the desired temperature was reached, then pumped out and the specimen cooled in vacuo. The studies of Rosenhain, Humfrey, and other workers 4, 5, 6, 7, 8 dem-

Jan 1, 1922

By Howard Scott, Henry S. Rawdon

The method of demonstrating the structure existing in a metal or alloy at high temperatures, by etching a polished sample after it has been heated to the desired temperature, is quite familiar to metallog-raphists. The usual procedure1 2 is to heat the specimen, previously polished for microscopic examination, to the desired temperature, in a neutral atmosphere (hydrogen or nitrogen), then admit the etching gas (chlorine, hydrochloric acid or similar gas) for a few seconds, and finally, after flushing out the etching gas with the neutral one, cool the specimen in the neutral atmosphere. The pattern produced by etching at a definite temperature is usually taken as a record of the microstructure prevailing at that temperature. It has frequently been pointed out that changes in composition of the surface metal occur during the preliminary heating in the neutral atmosphere, so that the appearance produced by the etching at high temperature may not exactly represent the condition of the interior of the specimen. To overcome this uncertainty, the heating has sometimes been done in vacuo,3 the etching gas being admitted when the desired temperature was reached, then pumped out and the specimen cooled in vacuo. The studies of Rosenhain, Humfrey, and other workers 4, 5, 6, 7, 8 dem-

Jan 1, 1922

By E. S. Bardwell

THE reverberatory copper-refining furnaces at the Great Falls Reduction Dept. of the Anaconda Copper Mining Co. have used successively, as fuel, lump coal on grates, pulverized coal, oil and natural gas. In no other plant, so far as can be ascertained, has such a variety of fuels been used. This fact affords a unique opportunity for comparing the relative efficiency obtained with these several fuels under nearly identical conditions. FURNACES The present furnace refinery at Great Falls was placed in operation in April, 1916. The original installation consisted of two furnaces, each with hearths 36 by 14 ft. and provided with fire boxes 10 by 12 ft. for firing lump coal on grates. These furnaces had air-cooled sand bottoms and chrome-brick side walls both above and below the metal line. The roofs were of 12-in. silica brick. Each furnace was provided with a waste-heat boiler of approximately 400 boiler-hp. capacity. We soon found that chrome brick was very unsatisfactory as sidewall material because of its excessive spalling. At the first opportunity the furnaces were rebuilt, using magnesite brick below the metal line and silica brick from the metal line to the roof. At the same time the thickness of the side walls was increased, thus decreasing the width of the hearth to 13 ft. At about this time also, the thickness of the furnace roofs was increased from 12 to 15 in. No further changes occurred in furnace design until 1922, when the use of lump coal on grates was abandoned in favor of pulverized coal.

Jan 1, 1932

By P. M. Robinson, M. B. Bever

THE heats of formation at 273°K of the compounds InBi, In2Bi, and TIBi2 have been determined by metal solution calorimetry with bismuth as solvent. The published information on the thermody-namic properties of these compounds is limited. The structure of the compound InBi (mp, 383°K) is tetragonal of the PbO (B10) type.1 The compounds In2Bi (mp, 362°K) and TIBi2 (mp of highest-melting composition, 486°K) are now believed to have structures of the NizIn (B8) type273 and not the A1B2 (C32) structures reported earlier.4, 5 The compounds In2Bi and TIBi2 have limited homogeneity ranges at room temperature, while the compound InBi has no detectable homogeneity range.' Samples of the compounds were prepared from 99.99 pet Bi (Mallinckrodt Chemical Works), 99.999 pet in (American Smelting and Refining Co.), and 99.99 pet Tl (Amend Drug and Chemical Co.) by melting the components in sealed, evacuated Vycor tubes. The compounds InBi and in2Bi were of the stoichiometric compositions. The compound TIBi2 contained 40 pet T1; this composition was chosen because at room temperature the alloy of stoichiometric composition does not lie within the homogeneity range.' The melts were held approximately 50°C above the liquidus for 8 hr and then quenched into iced brine. The samples were homogenized for 48 hr at temperatures 20°C below the temperature of complete solidification. Metallographic examination of sections taken from the center and the ends of the ingots did not reveal second phases or segregation . The heats of formation were determined as the difference in the heat effects on solution of a compound and of a mechanical mixture of its components added from the reference temperature of 273°K to liquid bismuth at 623°K. The details of the calori-metric procedure and method of calculation have been described elsewhere? The calorimeter was calibrated by adding bismuth at 273°K to the bismuth bath at 623°K. The calculated values of the heats of formation of the compounds, listed in Table I, are based on a value of 4.96 keal per g-atom for the difference between the heat contents of bismuth at 273" and 623oK7 No published values are available for the heats of formation of the compounds InBi and In2Bi. Hultgren et a1.7 have calculated a value of -0.50 i 0.10 keal per g-atom for the heat of formation at 423°K of the compound TIBi2 containing 40 at. pet T1 from heat-content measurements in the range from 398" to 700°K and the heats of formation of the liquid alloy. The difference between this value and the value of -0.66 * 0.01 keal per g-atom at 273°K is too large to be attributed to a difference between the heat capacities of the compound and the components over the temperature range 273o to 423oK7 However, the direct determination of the heat of formation by a calorimetric method should give a more accurate value. The heats of formation at 273°K of the compounds InBi and In2Bi lie on a straight line when plotted as a function of composition, Fig. 1. The compound In2Bi, therefore, appears to be barely stable with respect to its neighboring phases. In order for the free energy vs composition curve to be concave towards the composition axis, the entropy change on formation of In2Bi must be more positive than that on formation of InBi. As the compounds are ordered,2, 3, 8 there is no configurational entropy change on formation. The difference between the entropy changes on formation of the two compounds, therefore, is probably associated with the vibrational entropies. In view of the low heats of formation, the changes in vibrational entropy, due to changes in bond strength on formation of the two compounds, are likely to be small. Owing to the volume contractions on formation of the two compounds,5 the vibrational entropies probably decrease slightly but the decrease of the vibrational entropy of InBi is expected to be larger than that of In2Bi.

Jan 1, 1965

By M. S. Rashid, C. J. Altstetter

Allotropic transformations in cerium have been studied by dilatometric, resistometric, X-ray diffraction, and metallographic techniques. The dilatometric study indicated that, on cooling below O°C, the high-temperature fcc phase, y, transforms partly to the hexagonal phase, ß, and, on further cooling, to the collapsed fcc phase, a. The amount of $ phase present at room temperature is increased by repeated cycling through the a-y transformation. It has been shown metallograPhically that the y-ß transformation has many characteristics of a martensitic transformation. In contrast to the y-ß transformation the ?-a transformation does not give the manifestation of a shear transformation. Small cellular ? domains of random shape and size collapse to a in a short time with no apparent coordination with neighboring domains. The considerable confusion in the literature over the existence of more than one high-temperature fcc phase is discussed. Two such phases have been reported in the literature and an attempt is made in this study to clarify the situation. Twelve fcc and two hcp structures have been shown to be easily reproduced or eliminated. It is proposed that the two "additional" allotropes reported in the literature and fourteen of the phases detected here are not allotropes of cerium but are due to contamination. CERIUM exists in several allotropic forms, but there is some disagreement over what the forms are. Furthermore, the conditions favoring the presence of a particular allotrope and the nature of the transformations from one form to another are uncertain. The objectives of this research were 1) to ascertain the allotropic forms of cerium, 2) to establish the conditions under which the allotropes exist, 3) to study the effects of annealing and thermal cycling on the allotropic transformations, and 4) to study the transformation mechanisms. Dilatometric, resistometric, metallographic, and X-ray diffraction techniques were employed. The form of cerium commonly found at room temperature is fcc and is designated ?. A complex hexagonal phase, 8, forms when y is cooled to slightly below room temperature. At still lower temperatures the y fcc structure transforms to an fcc form with a much smaller lattice parameter, termed a cerium. A bcc form, 6, which exists just below the melting point (800°C), will not be considered further in this work. There is a substantial body of experimental evidence (reviewed by Gschneidnerl) which favors the acceptance of these four allotropes, though some investigators have tried unsuccessfully to observe the ß hexagonal form.'-' There is disagreement, however, over the phase-transformation temperatures, due, in part, to broad hysteresis and overlapping of the transformations between the a, ß, and ? forms. The transformations are also sensitive to prior thermal and mechanical treatment. The differing purity of cerium used by different investigators is undoubtedly a factor. Cerium is difficult to separate from other elements and is quite reactive, igniting spontaneously when it is filed in air. The highest purity of cerium to date is reported to contain several hundred parts per million by weight of impurities, and early investigations were carried out on cerium containing several percent of impurities. There have been reports of more than one fcc allotrope at room temperature. Gschneidner, Elliott, and McDonald5 obtained diffraction patterns of an fcc phase with a lattice parameter about 1 pct less than that of the ? phase, instead of the y phase, on slowly cooling cerium filings from 23° to -198°C and warming them back to room temperature. However, when the sample was heated to 447°C and cooled to room temperature it consisted of only the ? phase. They have designated this new fcc phase "a-? intermediate", and say it is quite sensitive to impurities. After prolonged high-temperature treatment of a powder specimen, Weiner and Raynor2 obtained a diffraction pattern of an fcc phase of lattice parameter about 1 pct less than the ? phase. This they called the y' phase. It could not be reconverted to the y phase and is claimed to be different from the a-? intermediate phase.5,6 Dialer and Rothe3 reported two fcc phases* after cycling their powder specimens between room temperature and -192°C. Gschneidner, Elliott, and McDonald5 suggested that one of the fcc structures obtained by Dialer and Rothe was equivalent to their "a-? intermediate" phase. Table I presents some pertinent data on the proposed allotropes. For the ?(fcc)-ß(hexagonal) transformation

Jan 1, 1967

By G. S. Scott, G. W. Jones

ECONOMIC waste caused by mine fires may become considerable,15 especially if a fire is allowed to spread or temporarily to get beyond control. It is important, therefore, to act promptly whenever a fire is suspected and to make every action count. To contribute toward its extinction effectively it is necessary to know at the earliest possible moment, and continuously thereafter, what is happening at the seat of the fire, which may be in a remote or inaccessible area, and also to recognize what may be expected as a result of any proposed combative measure. In combatting a fire the mining engineer and the chemist should cooperate, first deciding upon the course of action to be taken and then drawing upon the mining engineer's intimate knowledge of the physical structure of the fire area, the cost and time required to carry out proposed operations, and the probable efficiency with which these operations could be performed, and upon the chemist's knowledge for the results to be expected therefrom. After the initial steps to be taken have been decided, it devolves upon the mining engineer to see that they are carried out and upon the chemist to evaluate the results and to keep the mining engineer continuously informed in regard to a variety of matters-such as the composition and toxic or asphyxiating properties of the atmosphere in which the men may be working, whether the fire is increasing or decreasing in intensity and its probable temperature, the quantity of air leakage and the explosion hazards of the fire area. The purpose of this paper is to discuss what the chemist can and cannot contribute as a member of the fire-fighting personnel. The technical literature contains several hundred papers relating directly and indirectly to mine fires, and this fact alone is testimony to the complex nature of the phenomena involved in the birth, life, and final demise of a fire. A fire may be stopped (I) by preventing oxygen from reaching the coal or (2) by removing the conditions necessary for the rapid reaction of coal with oxygen; i.e., decreasing the temperature. All methods of prevention or control. necessarily must be based upon one or the other, or both, of these two principles. . The chemistry of a fire may be understood readily if the low-temperature oxidation of coal is considered as a starting point; then oxidation at higher temperatures (or combustion) ; and with these, the composition of the solid and gaseous products resulting from the oxidation or from the effects of the heat liberated. This discussion refers particularly to Pennsylvania anthracite, although much of the material applies equally well to coals of lower rank. OXIDATION OF COAL Oxidation of coal fundamentally is confined to the surface; that is, the rate at which oxygen penetrates into the interior of a solid block of coal is so slow that it may be ignored.6,16 Oxidation starts when a fresh surface is exposed, and the rate is

Jan 1, 1942

By R. L. Fleischer, W. F. Hosford

Tensile data for coarse grained aluminum Polycrystals suggest that the "grain size" effect is not due to dislocations piled up at grain boundaries but rather is primarily a relative size effect due to surface crystals being weaker and less confined. STUDIES directed at interpreting hardening of poly-crystalline metals normally identify their strain hardening properties with those in some particular type of single crystal.1"4 The recent recognition in face centered-cubic metals of a nearly linear stage with rapid hardening occuring at comparable rates for both polycrystals and single crystals, suggested that the same process or processes determine both cases and hence that there exists some justification for the use of single crystals to understand polycrystals. Further evidence for the above view may be found by an approach initiated by Chalmers:5 By using bicrystals of controlled orientation it is possible to begin to assemble a polycrystal and also to study grain boundary effects in detail. In this way it has been found that a single grain boundary affects easy glide but not the subsequent stage II hardening.6 This result suggests that a sensitive way to observe grain boundary effects in polycrystals would be to vary grain size and measure easy glide. As will be seen, easy glide is only possible for coarse-grained samples, and hence the results will serve to fill in the gap in measurements between single crystals and bicrystals on one hand and fine-grained polycrystals on the other. One problem inherent in comparing single crystals with polycrystals is the uncertainty as to what slip systems are acting in a polycrystal. To compare the two types of samples, rates of shear hardeninn---L. on the acting -planes are needed. and these may be computed only if it is known what particular systems are active. The acting systems were examined for a coarse-grained polycrystal and it will be shown that the systems supplying the preponderance of slip can be determined with little ambiguity. EXPERIMENTAL PROCEDURE Twelve samples of aluminum were prepared by chill casting into a heated graphite mold, followed by annealing at 635° ± 5°C for 24 hr with an 8-hr fur- nace cool, and finally either etching7 or electropol-ishing.' The samples, with a 7 to 10 cm length between grips and 4.4 by 6.6 mm in cross section, were deformed at a strain rate of about 3 10 -3 . per min in a tensile device which has been described elsewhere.5 The composition was reported by Alcoa as 99.992 pct Al, 0.004 pct Zn, 0.002 pct Cu, 0.001 pct Fe, and 0.001 pct Si; nine samples were deformed while immersed in liquid helium and three in air at room temperature. The stress-strain curve for one of the samples (P-1) deformed at 4.2 "K has been reported previ~usl~.~ This sample was selected for determination of active slip systems. Eighteen of the crystals were examined by optical microscopy to determine the angles of slip line traces and by X-ray back reflection to determine orientation. By this means the slip planes were determined and the resolved shear stress factors for possible slip systems could be computed. Finally each sample was sectioned so that after etching, the number of crystals could be counted for each of ten newly exposed surfaces. The average of these ten values will be termed n, the number of crystals per cross section. Values of 11, varied from 1.9 (nearly bamboo structure) to 12.7. Sketches of typical cross sections appear in Fig. 1. RESULTS AND DISCUSSION: SLIP SYSTEMS 1) Determination of Acting Slip Planes—The stress axis orientation and operative slip planes in eighteen crystals of sample P-1, as determined by slip line traces and crystal orientation, are summarized in Fig. 2. For one of the crystals two planes had a common trace. so that the traces alone did not distinguish which plane or planes were slipping. However it was found that the stress resolving factor for the primary system was 0.386, .while that for the most stressed system in the other plane (indicated bv the dotted arrow) is 0.138. It will be assumed tgerefore that only the primary plane acted. Since the orientations were determined after extending the samples 4 pct, the stress axes may be rotated from their original value by as much as 2 deg in some cases. It is interesting to note that in five crystals only one slip plane acted, in eight two acted, and in five three planes were observed—an average of two slip

Jan 1, 1962

Jan 1, 1880

By K. Prins

ONE of the more pressing problems faced by the coal industry today is the development of adequate means for meeting conservation laws, particularly those involving stream pollution, in various parts of the country. Discharge of dirty coal washery water into streams and rivers is almost universally frowned upon. Many states have enacted laws carrying heavy fines to curb the practice. The Prins stream-cleaner is one of the latest machines to enter the market. It is closely related to the cyclone thickener in principle. Eleven stream-cleaners are currently operating, ranging in size from 4 to 16 in. diam. In more recent installations the water enters directly in line and on a tangent with the impeller. The impeller consists of a vertical shaft up through a packing gland and bearings, and a V-belt pulley. The lower part is a tubing fastened to the shaft above, extending through the water intake compartment and provided with six vertical flat bars welded to the tubing. Portholes are situated in the upper end of the tubing, immediately below the point where shaft and tubing join together. The portholes are placed so that they are in open communication with the upper compartment of the stream-cleaner from which the processed water is discharged. The impeller is motor driven with a wide range vari-pitch drive employed between motor and impeller. The motor is mounted vertically, and the mounting provided with a vertical hinge allowing for needed adjustment of the wide range vari-pitch drive. The dirty coal washery water entering the machine under 20 lb psi pressure, flows from the compartment above the impeller, between the impeller blades, and is whirled around in the vertical section of the impeller enclosure. The speed of the impeller supplies centrifugal force and velocity required for separating suspended solids from water. The lower part of the machine consists of a cone, whose action is similar to other machines of the same type. The underflow discharge orifice is a cold rolled steel block machined to correspond with the cone angle and allows insertion of steel tubes of different diam. On 16 in. machines a 1 ¾ in. ID vertical discharge pipe is used. Provision is made for attaching a curved section of the same diam to the vertical pipe, to which, in turn, different lengths of horizontal pipe can be connected. Curved Pipe Advantageous It has been found that a curved pipe offers resistance to discharged material flow. In addition, the rotary motion of the underflow can be easily arrested in a curved pipe. Impeller speed of the 16 in. diam machine is provided from 400 to 800 rpm. A speed of about 474 rpm is suitable for maintenance of a constant underflow in coal slurry. In one installation 5x ¼ in. coal is cleaned in a Jeffrey Baum type washer at a 225 tons per hr rate. Washer installation is of the conventional type and a drag type sludge tank is used for water clarification purposes. Capacity of the water system, including the Baum washer, is about 40,000 gal. Before placing the stream-cleaner in operation, it was necessary to flush out the entire system every five days of two shift operations. The only time the system is drained now is for repair work on the sludge conveyor or the rig. The suction line of the stream-cleaner pump terminates in a number of small branch lines located at a depth of about 4 ft above the sludge conveyor. Each branch line extends the full width of the tank and is provided with four intake ports, each one with a funnel shaped inlet projecting downward. The arrangement provides an extensive pick-up area, for dirty water, and the inlets are arranged for a low rim velocity, preventing the taking in of coarse particles. The funnels are also arranged to extend up or down in the tank. They are set to pick up -60 mesh material exclusively.' The material is a high ash and high sulphur product and thus has to be disposed in the refuse conveyor. The underflow of the stream-cleaner is discharged on top of the washery refuse which is carried in a drag type horizontal conveyor, discharging into another refuse conveyor inclined at 30º with a short horizontal loading section. Some Disadvantages The impeller inherits certain disadvantages because of the nature of its construction. Additional moving parts make it subject to wear and maintenance costs. The advantage of being able to maintain a constant speed, however, to produce desired water velocity in the machine outweighs the drawbacks. Better separation between water and solids can be obtained by regulating time of residence of water through adjustment of valves in the intake and discharge lines. The amount of fines encountered during plant operation will vary because of higher or lower moisture in coal passing over fine coal vibrating screens. Even the amount of fines picked up by underground loading machines will be inconstant. Consequently, the percentage of solids will vary in water to be processed. The velocity in the feedlines to the slurry thickeners will fluctuate, with the required water velocity lacking. Another advantage advanced for the machine is its ability to operate on 15 to 25 lb line pressures at the water intake, reducing pump power required and pump maintenance.

Jan 1, 1952

GEORGE F. COMSTOCK (author's reply to discussion*).-Mr. Thum's description of the effects of butt welding and spot welding on the micro-structure of steel are interesting and timely. The speed with which the changes noted by Mr. Thum must take place is indeed remarkable, but the writer has noted a similar very rapid diffusion of carbide in annealing a t a rather high temperature certain samples of soft sheet steel containing massive cementite segregated on a small scale. The massive cementite in such steel can be dissolved and distributed very quickly if the proper temperature is attained. Mr. Thum's explanation of the structure he found in the spot welds seems entirely reasonable, but the mystery of the decarburized material in the butt weld is one that might well be the subject of further research. The possibility of decarburization by air ,might perhaps be worthy of a little more consideration than he gives it, for the oxides formed would be gaseous on account of the presence of carbon, and hence not visible in the microscope, and the effect of the pressure might be to squeeze the carbon oxides, which would normally form blow-holes, out of the metal or possibly into such small volumes as not to be noticed The removal of carbon by liquation and squeezing into the fin would be an effect similar to the "bleeding" of a steel ingot that is rolled while the center is still liquid, giving a soft low-carbon interior in the finished section while the segregate was removed in cropping the pipe. This effect in Mr. Thum's butt welds could, however, only be obtained if the weld was heated to near the melting point of the steel, and if the carbon was considerably segregated in the bars at the start, for the first effect of the high temperature would be to promote diffusion rather than the contrary segregation and Equation. It is gratifying to learn from Dr. Ruder's remarks that his researches have resulted in no disagreement with the few points brought out by the writer's experiments. In addition to the three forms in which nitrogen may occur in iron that he mentions, it would seem that a fourth form is often found; This is apparently a eutectoid, like pearlite, and sometimes almost as coarse as the massive cementite seen in soft steel sheets that have been annealed for a long time. One of the things needed in the metallographic study of steel is an etching reagent that will distinguish definitely between nitride in this form and the more common pearlite or cementite.

Jan 6, 1919

By Robert E. Ogilvie, Zvonimir Ban

Oxidation experiments were conducted above 600°C to investigate the oxidation products formed on the surface of MoSi2. Results are presented which indicate that minor iron impurities play a key role in the oxidation behavior of MoSi2 above 600 °C. Based on considerations of the crystal chemistry of the oxidation products, MoSi2 with rhenium and iron additions was found to be resistant to oxidation in the pesting temperature range. AS early as 1914, Honigschmidtl observed that some silicides of molybdenum exhibited high resistance to oxidation at elevated temperatures. This fact did not arouse much interest until 1950, when Kieffer and cerwenka2 examined this property in more detail. They found that Mo-Si alloys with approximately 70 pct Mo (by weight) could be heated to 1600°C in an oxidizing atmosphere without any significant damage. The surface was found to be protected by the formation of an extremely thin silica glass layer which had no tendency to spa11 during subsequent thermal cycling. In 1955, Fitzer3 discovered that even solid bodies made of MoSi2 completely oxidized within a relatively short time when exposed to the air in the temperature range from 300° to 600°C. To describe this phenomenon he proposed the name "molybdenum disilicide 'pest' ", clearly analogous to the previously observed "tin plague" ("tin pest") which, however, arises as the result of a phase transformation. Studies performed by Fitzer and, in particular, one published recently by Berkowitz, Blackburn, and Fel-ten,' comprise the most extensive research to date on the pest phenomenon in MoSi2, as far as the fundamen- tal mechanism of the process is concerned. The first of these studies revealed the existence of a crystalline phase which appeared at the surface at 750°C and dissolved in the glassy silica layer at 1150°C. The logical assumption was that this phase was some reaction product of MOO3 and SiO2. The formation of a reaction product of this type seemed probable since it had been mentioned by Glemser and Lutz6 in a paper describing their studies of molybdenum oxides; however, this assumption was later disproved.8 It is our belief that information concerning the exact nature of this crystalline phase may be important for a better understanding of both pesting and the protection mechanism. Therefore, since the only available general description of the pest phenomenon was that of Fitzer, it was decided to reproduce his experiments. These experiments established that, in addition to the "pest" and "nonpest" temperature range, an intermediate region exists between 600" and approximately 650°C. This region is characterized by the appearance of a variable amount of yellow to orange colored crystals. The electron-beam microanalyzer was used to qualitatively determine their composition. Iron and molybdenum were found to be major constituents. This result can be explained based on the following facts: 1) iron, according to literature data,* is the most common impurity in molybdenum powder, and its content can be as high as 0.25 pct; 2) technical silicon powder usually contains iron; 3) steel ball mills are often used for the crushing and grinding of MoSi2. In order to clarify the exact role of iron, it was deliberately added to a stoichiometric mixture of molybdenum and silicon. The observed results corroborated the previous experiment, proving that iron (probably as some silicide phase) concentrates along the grain boundaries. I) EXPERIMENTAL PROCEDURE A) Oxidation of MoSi2 with Iron Additions. 1) Specimen Preparation. Specimens were prepared by both

Jan 1, 1967