Showing papers by "Michigan Technological University published in 1972"

A debate on the bainite reaction

Abstract: The authors debate three topics central to the controversies which have enveloped the bainite reaction ever since it was first recognized as a distinctive mode of austenite decomposition. These include: “what is bainite?”, “the growth mechanism of the ferritic component of bainite”, and “the sources of bainitic carbide precipitation.” RFH concludes that bainite is the product of a shear transformation. Individual bainite plates are suggested to grow substantially more rapidly than volume diffusion-control allows, but a constraint such as the build-up of volume strain energy limits the extent of their growth. This mechanism of growth ensures extensive supersaturation of bainitic ferrite with respect to carbon. Whether or not carbides precipitate in association with bainite plates and whether the carbide is cementite ore, however, is a complex question in competitive reaction kinetics. New experimental evidence is presented to demonstrate thate carbide precipitated in lower bainite dissolves upon heating above the kinetic-B stemperature in an alloy steel containing 1.5 pct Si. This result is taken to support the existence of the metastable eutectoid reactionγ ⇌ α + e atca 350°C. HIA and KRK define bainite as the product of a nonlamellar eutectoid reaction. On this view, carbide precipitation thus plays an essential, rather than an ancillary role. Development of the Widmanstatten morphology by the ferritic component of bainite is shown to be inessential to the classification of a eutectoid structure as bainite. When this morphology is present, however, it is concluded to grow by the ledge mechanism, without the participation of shear, at rates of the order of or less than those allowed by volume diffusion-control. New experimental evidence is presented to show that the lengthening and thickening kinetics of individual plates within sheaves of upper bainite are consistent with this description. The results of a new calculation indicate that the initial carbon content of bainite plates lies between theα/α + Fe3C) and the extrapolatedα/(α+ γ) phase boundaries, in agreement with expectation from the ledge mechanism of growth.

Santiaguito Volcanic Dome, Guatemala

Abstract: The Santiaguito volcanic dome insouthwestern Guatemala is a multiple extrusive dome that has shown constant volcanic activity since its birth in 1922. Fourteen extrusive units are mapped. Five of these are volcanic domes; the remaining nine are lava flows which generally cling to the sides of the domes. The volume of material extruded at Santiaguito since 1922 (0.7 km 3 ) is a small fraction of the volume of pyroclastic debris from the 1902 eruption of Santa Maria (5.5 km 3 ), Santiaguito9s parent composite cone. Extrusion of the dome began in the center of the explosion crater created by Santa Maria9s 1902 activity. This crater was volumetrically much smaller (0.5 km 3 ) than the amount of material erupted during the 1902 event, and local slumping near the crater has occurred and is continuing along a series of east-trending faults. The general westward growth of the dome complex and many of the structural featureson Santiaguito are controlled by these near-vertical faults. The domes are studded with Pelean spines. Twenty-five new chemical analyses are presented, showing Santiaguito9s eruptive products to be soda-rich dacite of the calc-alkaline suite. The dome lava has differentiated quite significantly from the overwhelmingly abundant pyroxene andesite magma which makes up Santa Maria and the older volcanic rocks in the area. Trace element analyses of the lavas, along with major element data suggest a differentiation by fractional crystallization under constant or increasing PO 2 . Sr isotope determinations could not detect contamination of the lavas by radiogenic crustal material; the Sr 87 /Sr 86 ratio in Santiaguito rock averages .7043. The Santiaguito lavas are tridymite-bearing hypersthene dacites, characterized by strongly zoned plagioclase phenocrysts and oxyhornblende. Compositional and petrographic comparisons are made with other modern volcanic domes and other Central American lavas.

Notes on the 1902 eruption of Santa María volcano, Guatemala

Abstract: The first historic activity of Santa Maria volcano, Guatemala constituted one of the ten largest historic eruptions in the world, producing 5.5 km3 of debris. In hindsight, the six-month period before the October 1902 eruption was one of extremely abnormal seismicity in all of western Guatemala. The pyroclastis from the eruption were scattered widely over Western Guatemala and Southern Mexico and also caused world-wide atmospheric effects. The volcanics produced were of andesitic-dacitic composition, but there was wide variation from place to place in the sampled material — a fact apparently chiefly attributable to atmospheric-fractionation. There was apparently a change in chemistry of ash during the two-day eruption as well, the first, most voluminous ash was pumicious and white; later ash was finer, denser, darker, and slightly less silicious. The kinetic energy/thermal energy partition is determined to be similar to the value derived for Krakatoa,E k/E th ≅ 5.0 %. The thermal energy of the eruption was estimated at 4.2×1025 ergs. The explosion crater left on Santa Maria’s southwest flank after the eruption had a volume equal to less than 0.5 km3, a small fraction of the volume of material erupted. The two-day 1902 blast has greatly overshadowed subsequent activity; extrusion of the Santiaguito dome, which has occurred since 1922 in the explosion crater, has produced about 0.7 km3 of dacite lava and 1.6×1025 ergs of thermal energy in 48 years of activity.

Lead Content of Human Hair (1871-1971)

Abstract: Samples of antique and contemporary human hair were analyzed for lead by atomic absorption spectroscopy. Antique hair contained a significantly greater amount of lead than did contemporary hair.

The initial stages of the cellular reaction

Abstract: Both the nucleation process per se and the organization of nearby nuclei or precipitates formed at a given disordered grain boundary into a viable cell structure are considered. When the critical nucleus is modeled in simple fashion, based upon a rectangular parallelepiped, the rate of nucleation by the “conventional” mechanism, in which the grain boundary is essentially immobile during the nucleation process, far exceeds that by the Tu-Turnbull “pucker” mechanism, in which the grain boundary is deflected so that its plane is parallel to the habit plane of the nucleus. A more rigorous model of the critical nucleus, based upon the somewhat specialized assumption that an energy cusp facet forms at only one boundary orientation but developed without a preconceived view of the nucleus morphology, leads to this result only when the facet energy is greater than one-half the energy of a disordered grain boundary. In the reverse energetic situation, the nucleus morphology is effectively that supposed by the pucker mechanism. The initial stage of cellular growth is examined in the framework of the question: why do allotriomorphs form at disordered grain boundaries under some conditions of alloy composition and temperature and cells develop under other conditions? The conditions for the two reaction paths are established on the basis of two key ideas: the direction in which the torque term associated with a facet deflects a grain boundary meeting the edge of the facet (deduced from the considerations of Hoffman and Cahn), and the existence of a driving force for the breakaway of a grain boundary from such a junction resulting from the requirement of continuity of path to another junction located nearby.

Treatment of zinc rich steel mill dusts for reuse in steel making processes

Abstract: Crush-resistant, metallized agglomerates, containing substantially no zinc or lead and capable of being charged to various steel-making furnaces, are produced from dust recovered from the fumes of a basic oxygen or open hearth steel-making furnace by forming a moistened mixture of (a) the dust (b) finely divided solid carbonaceous material containing sufficient carbon to make the total equivalent fixed carbon content of the mixture about 5 to about 25 weight percent, based on the dry weight of the mixture, (e) a bonding agent in the range of about 5 to about 25 weight percent, based on the dry weight of the mixture, and (d) one or more additional strengthening agents in minor amounts; forming the resultant mixture into green agglomerates; hydrothermally hardening partially dried or dried agglomerates at a temperature substantially below the combustion or decomposition temperature of the carbonaceous material; and then heating the hardened agglomerates at an elevated temperature for a sufficient time to reduce the iron oxide to metallic iron and to reduce and volatilize the zinc, lead and other reducible impurities therein.

Film Boiling on Vertical Surfaces

Abstract: Film boiling of a saturated liquid on a vertical surface is analyzed to determine the local heat-transfer rates as a function of height and heater-surface superheat. Experiments show that the laminar-flow model is inadequate. A turbulent-vapor-flow model is used, and the influence of the interfacial oscillations is incorporated on a semiempirical basis. Measurements of local film boiling were obtained with a transient technique using saturated liquid nitrogen.

Discontinuous precipitation in aluminum-base zinc alloys

Abstract: The kinetics of discontinuous precipitation in Al-21.6 at. pct. Zn and Al-22 at. pct. Zn-0.01 at. pct Sn alloys was determined by quantitative metallographic measurements on solution-treated and aged specimens. The growth rate of the discontinuous precipitate appears to be controlled by interfacial diffusion. It was found that the addition of a small amount of tin reduced the overall reaction rate. Nucleation of the discontinuous precipitate was confined to grain edges or boundaries, filling the available sites (site saturation) at a very early stage in the reaction. It was observed that a variation in quench rate markedly affected the growth rate of the precipitate and the site-saturating-dimensionality during a room-temperature aging treatment.

Method for agglomerating steel plant waste dusts

Abstract: Highly crush-resistant hardened agglomerates are produced from steel plant waste dusts by forming a moistened mixture including (a) one or more of such dusts, (b) about 2 to about 20 weight percent of a bonding agent, such as lime or calcium hydroxide, and (c) about 0.5 to about 5 weight percent of a siliceous material, such as silica; aging the moistened mixture at an elevated temperature for a sufficient time to hydrate the overburned lime and/or slag contained therein; forming the aged mixture in discrete, green agglomerates; adjusting the moisture content of the green agglomerates to about 5 weight percent or less; and then hydrothermally hardening the green agglomerates to a hardened form. The crushing or compressive strength of the hardened agglomerates can be further increased by subjecting them to a drying step to remove at least a portion of the moisture contained therein immediately after the hydrothermal hardening step.

A diffraction study of the annealing of cold-worked Cu 3 Au

Abstract: X-ray diffraction was used to study the recrystallization and ordering behavior of cold-worked Cu3Au annealed below the critical temperature Samples of the alloy initially disordered by quenching and then cold-worked by filing were found to establish a high degree of long-range order very rapidly at temperatures in the range 300° to 375°C The kinetics of antiphase domain growth were found to be essentially the same as previously established for the alloy having no cold work after thermal disordering However, for a given annealing treatment, the average antiphase domain size in the initially cold-worked samples waslarger than that in initially disordered samples which had not been cold-worked This observation is contrary to results of previous investigators and the reasons for their incorrect conclusions are discussed Measurements of the particle size and rms microstrains established that recrystallization is retarded as the annealing temperature approaches the critical temperature

Experimental determination of stress-concentration factors in thick-walled cylinders with crossholes and sideholes

Abstract: In a companion paper1 submitted to ASME, the theoretical determination of stress-concentration factors in thick-walled cylinders was reported. The present paper reports the results of experiments conducted to check the predictions of the theory. The configuration is a thick-walled cylinder with crossholes or sideholes oriented perpendicular to the bore. Stress concentrations occur at the “tee” intersections of the holes with the bore. The loadings considered are internal pressure and external pressure. Both steel and plastic models were tested. Experiments were also conducted to determine the reduction of the stress-concentration factor by intersection radii at the crosshole intersection. Experimental results were found to agree well with theory. The best configuration was found to be one with crosshole (or sidehole) diameter equal to the bore diameter, and with an intersection radius at the tee intersection equal to the bore radius.

Electrolytic electrical field mapping device

Abstract: The device includes a plotting board which overlies an electrolyte tank and on top of which a sheet of graph paper is positioned for plotting the electrical field distribution between electrodes immersed in the electrolyte. A movable, exploratory probe assembly, including a stylus extending into the electrolyte, is slidably mounted on a pair of perpendicularly crossing guide rods located beneath the plotting board. The guide rods are connected to correspondingly corssing arms, which are positioned above the plotting board and are slidably mounted thereto so that movement of the arms in the x and y directions produces corresponding movement of the exploratory stylus. Each arm has an elongated slot which always intersect directly above the exploratory stylus as the arms (and thus the exploratory stylus) are moved to locate a null point. When a null point is detected, its location can be recorded directly onto the graph paper by inserting a pencil, ball point or the like through the opening provided by the intersecting slots. In a preferred embodiment, the arms and guide rods are connected at their opposite ends to guide members which slide along the inside edges of elongated slots provided in the plotting board adjacent the edges of the graph paper. These guide members are connected together via a cable and pulley arrangement to insure easy, smooth, and accurate movement of the arms and rods while searching for null points.

Effect of Geometric Characteristics of Aggregates on the Fatigue Response of Bituminous Paving Mixtures

Abstract: THREE COARSE AGGREGATES AND TWO FINE AGGREGATES, REPRESENTING BOTH NATURAL AND CRUSHED MATERIALS, WERE TESTED TO MEASURE THE EFFECTS OF THE GEOMETRIC CHARACTERISTICS OF AGGREGATES ON THE FATIGUE RESPONSE OF BITUMINOUS PAVING MIXTURES. RESULTS OF THE INVESTIGATION SHOW THAT THE FATIGUE LIFE OF THE MIXTURE INCREASED WITH THE VALUE OF THE PARTICLE INDEX OF THE FINE AGGREGATE. THE FATIGUE BEHAVIOR OF THE MIXTURES TESTED WAS NOT SIGNIFICANTLY AFFECTED BY THE GEOMETRIC CHARACTERISTICS OF THE COARSE AGGREGATE, NOR WAS IT AFFECTED BY THE GRADATION OF THE AGGREGATES IN THESE MIXTURES. /AUTHOR/

An Iterative Technique for Determining the Minimal Number of Variables for a Totally Symmetric Function with Repeated Variables

Abstract: Several analytic procedures exist for transforming a partially symmetric switching function to a totally symmetric switching function by judiciously repeating certain variables. Presumably the best totally symmetric representation for a given function would be the one having the fewest variables. This note presents an iterative technique for finding the totally symmetric realization for a given function that has the absolute minimum number of variables.

The Relation of Ceramics Processing to Materials Properties for Electronic Applications

Abstract: General properties of electronic ceramics are examined, noting especially their influence upon fabrication economics and quality. Particular emphasis is placed upon the preparation of sinterable powders to attain high densification. The effects of fabrication technique and powder preparation upon ceramic quality and dimensional control are pointed out. Recent developments and possible future trends in electronic ceramic materials are discussed briefly.