Showing papers by "Michigan Technological University published in 1975"

Thickening kinetics of proeutectoid ferrite plates in Fe-C alloys

Abstract: Thermionic electron emission microscopy was used to measure directly the thickening kinetics of proeutectoid ferrite sideplates in Fe-C alloys. These kinetics were found to be exceedingly irregular. During the first few seconds of growth, the thickening rate is 5 xl0-5±1 cm/s; afterwards it usually diminishes to 1 - 30 × 10-6 cm/s. As predicted by a general theory of precipitate morphology, thickening was shown to occur only by the ledge mechanism, despite the relatively poor matching of the austenite and the ferrite lattices. Ledges were observed to lengthen at rates controlled by the diffusion of carbon in austenite. Tent-shaped and other more complex surface relief effects, rather than the invariant plane strain relief, were found to predominate. These features are shown to be the expected result of a diffusional transformation occurring by means of a ledge mechanism.

Influence of crystallography on aspects of solid-solid nucleation theory

Abstract: Expressions for the major variables in the general rate equation for solid-solid nucleation were developed on the basis of various models of the critical nucleus shape during homogeneous and heterogeneous nucleation. These models are based upon spheres, but in some a facet was incorporated at one boundary orientation to represent the presence of a partially or fully coherent structure. Gibbs’ relationship for the critical radius is applicable to all of the models. The other variables in the nucleation rate equation are affected by the model and by faceting. Reduction of AG* by faceting is concluded to be the primary cause for the presence of reproducible lattice orientation relationships and for the existence of transition phases during precipitation from solid solutions.

Additive and Impurity Distributions at Grain Boundaries in Sintered Alumina

Abstract: Additive and impurity distributions at grain boundaries in sintered Al2O3 were determined using a scanning Auger microprobe, transmission electron microscopy, metallography, and electron probe analysis. The results indicated that Ca was present uniformly at the boundaries as a segregant, whereas the Mg or Ni levels observed resulted from nonequilibrium spinel particles. The Ca concentrations were consistent with equilibrium segregation theory and followed an equilibrium segregation isotherm.

Intermolecular interactions and excess thermodynamic properties of argon-krypton and krypton-xenon mixtures

Abstract: Recently, reliable pair-potentials have been obtained for argon, krypton and xenon. Pair-potentials of similar form are obtained for the argon-krypton and krypton-xenon interactions. Three parameters are adjusted to give experimental values for the long-range r -6 term and the excess free energy and excess volume for an equimolar liquid mixture at zero pressure and a specified temperature. The excess thermodynamic properties are calculated from the Barker-Henderson perturbation theory, which has been shown to give good values for the excess thermodynamic properties of mixtures of 6:12 molecules, with the contributions of three-body forces and quantum effects included. Excellent agreement with the excess properties of argon-krypton and krypton-xenon mixtures is found at all concentrations.

Sequences of precipitate nucleation

Abstract: Solid-solid nucleation theory, as recently extended to faceted nuclei, is applied to several problems in understanding experimentally observed sequences of precipitate nucleation involving transtion phases during isothermal ageing Transition precipitates form due to a low interfacial energy resulting from a greater structural similarity to the matrix than the equilibrium phase or succeeding transition phases and in spite of a usually smaller driving force, ¦ΔG v ¦, for nucleation than any of these competing phases Transition phases formed after the first one are predicted to nucleate preferentially at the interphase boundaries of their predecessors, also on the basis of interfacial energy, rather than ΔG v considerations Most examples of precipitation sequences cited from the literature are in agreement with this prediction; the few exceptions found are noted and discussed The preference of equilibrium phases for nucleating at high-energy grain boundaries and of transition precipitates for nucleation at dislocations and other lower energy sites is explained on the following basis The high-energy boundaries reduce the net interfacial free energy needed for nucleation of either phase so much that the higher ¦ΔG v ¦ for the equilibrium phase becomes dominant At the lower energy sites, the smaller reduction in ΔG *, the free energy of activation for nucleation, provided makes the lower interfacial energy of the transition phases the dominant factor in causing such phases to nucleate more rapidly

Chemical and isotopic constraints on the origin of low-silica latite and andesite from the Andes of central Peru

Abstract: Low-silica latite highly enriched in large-ion-lithophile elements and moderately potassic low-Si andesite were erupted in central Peru during late Cenozoic time. FeO*/MgO ratios of 0.93 to 1.25 at 53 wt percent SiO/sub 2/ indicate a definitely calcalkalic character. The combination of low FeO*/MgO ratios, low SiO/sub 2/, and high Cr, Co, and Ni with large-ion-lithophile and light rare-earth elements makes it very unlikely that the parent magmas were produced by high-pressure partial melting of subducted ocean-floor basalt (eclogite). The data are more compatible with small degrees of partial melting of ultramafic material or mixtures of basalt and ultramafic mantle. The initial melts probably contained 52 to 53 percent SiO/sub 2/ and had a content of large-ion-lithophile elements nearly as high as that of the rocks. /sup 87/Sr//sup 86/Sr ratios of from 0.7042 to 0.7051 and low to very low Rb/Sr ratios indicate an isotopically variable source region that, at least in part, had earlier been depleted in Rb relative to Sr.

Decomposition in Al-Zn alloys: Part I. Isothermal decomposition in an Al-22 at. pct Zn-0.1 at. pct Mg alloy

Abstract: A small-angle X-ray scattering (SAS) study has been made on solution treated and isothermally annealed specimens of an Al-22 at. pct Zn-0.1 at. pct Mg alloy. The changes in peak position and integrated area of the SAS spectra with time and temperature indicate that de composition is nearly complete immediately after quenching, in agreement with the earlier interpretation that Gerold and Merz placed on the results of Rundman and Hilliard in the binary Al-22 at. pct Zn alloy. Furthermore, structural changes occurring during annealing are consistent with a coarsening or maturation of the fluctuations in the solution. The domi nant wavelength varies ast 1/3 over a large time span and the temperature dependence of the coarsening process yields an activation energy of 94.2 kJ/mole. The effect of Mg is to re tard the formation of the equilibrium phases while having a small effect on the growth of the composition fluctuations during the coarsening process.

Stress corrosion cracking of alpha brass in a tarnishing ammoniacal environment: Fractography and chemical analysis

Abstract: Alloy 260 brass specimens under stress were exposed at room temperature to 15 N aqueous ammonia solution with 8 g/1 of cupric copper predissolved. This environment causes tarnishing of the brass surface and intergranular stress corrosion cracking. Scanning electron microscopy, energy dispersive X-ray analysis, and Auger electron spectroscopy were employed to study fractography, corrosion product composition and distribution within the stress corrosion crack, and fracture surface chemistry characteristic of stress corrosion cracking in this system. A thin oxidized film was detected by Auger spectroscopy at the leading edge of the propagating crack. With continued exposure to the corrosive environment, deposits form on the fracture surface, then coalesce to form a continuous tarnish film that is depleted of zinc. No bulk depletion of zinc was detected in the alloy at the stress corrosion crack leading edge. No evidence of noncrystallographic crack arrest marks was found on the intergranular fracture surface.

Chemistry and Mineralogy of Precambrian Paleosols in Northern Michigan

Abstract: Paleosol profiles can be recognized on a basement terrain of granodiorite, peridotite, and diabase that underlie the upper Keweenawan (?) Jacobsville sandstone. The main characteristics of the granodiorite and peridotite profiles are a substantial loss in SiO 2 , Al 2 O 3 , and alkaline earths; a smaller loss in Fe 2 O 3 and NiO; the concentration of dolomite and quartz in paleocaliche horizons; and the strong pigmentation of some of the primary minerals at the lower fringe of weathering. The granodiorite paleosol consists of a mixture of secondary and primary minerals: sericite, chlorite, vermiculite, biotite, muscovite, K-feldspar, dolomite, quartz, hematite, and rutile. The paleosol on peridotite contains chlorite, vermiculite, dolomite, quartz, hematite, and talc. The paleosol profiles resemble present-day ones developed under semi-arid to arid conditions.

Considerations on the Kaufman approach to binary phase diagram calculation

Abstract: The Kaufman approach to phase equilibria involving primarily the fcc, bcc and hcp phases was examined outside the Group Nos. 4 to 10 range where it is customarily employed. The “stability parameters” (ΔH and ΔS of transformation) for most elements in the Group Nos. 1 to 3 region were found to fit satisfactorily the correlation curves of stability parametervs group no.; some of the parameters for Al, Be, Mg and Ti, however, did not. The rare earth parameters fit well in the Group No. 3.5 position they were expected to occupy. A sample phase diagram calculated between two Group 1 elements was in good agreement with experiment. Phase boundaries of fcc +bcc regions adjacent to terminal solid solutions in several Group 1/Group 2 and Group 1/Group 3 systems, on the other hand, were quite unsatisfactory. This difficulty was traced to the high, positive regular solution constants calculated for both phases. Such constants were shown to result from the downward concavity of a plot of enthalpy of vaporizationvs Group No. in the Nos. 1 to 3 region; in the Nos. 4 to 10 range this plot is concave upward.

Effect of excess Au on antiphase domain growth in Cu 3 Au

Abstract: The kinetics of antiphase domain growth have been studied in three nonstoichiometric Cu/sub 3/Au alloys containing nominally 26, 28, and 31.5 at. percent Au. During isothermal annealing of disordered samples below the critical temperatures, the domain growth in all of the alloys initially followed the same t/sup 1/2/ dependence found previously for stoichiometric Cu/sub 3/Au. At long times, the two alloys furthest off stoichiometry reached limiting domain sizes which decreased with increasing Au content. Although the role of the excess Au in determining these limiting sizes is not clear, it is evident that most of the excess Au is accommodated within the domains. The antiphase domain size distributions in the alloys agree with those found for the stoichiometric alloy. (auth)

Thermally activated electrochemical cell including an alkali metal salt solvate electrolyte

Abstract: The thermally activated electrochemical cell includes a cathode, an anode and a solid electrolyte which is non-conductive at ambient temperatures and is capable of becoming an ionically conductive liquid upon being heated above its melting point. The electrolyte is an organic solvent solvate of certain alkali metal salts which is formed by coordinating the salt with a polar organic solvent preferably having a Gutmann donor number greater than 18 and a dielectric constant of at least 20.

Circadian activity of the red squirrel, Tamiasciurus hudsonicus, in continuous darkness and continuous illumination.

Abstract: In order to examine the effects of constant conditions on wheelrunning activity, 58 red squirrels (Tamiasciurus hudsonicus ) were taken directly from the field and placed in either total darkness (DD) or continuous illumination (LL) 500 lux, for up to 70 days. The squirrels were sampled at various times of the year so that seasonal changes in the endogenous rhythm could be examined. The initial phasing of activity correlated with the photoperiod in the field and had a free-running period (τ) close to 24 hours. However,τ increased in a nearly linear fashion, averaging about 0.19 min/day for squirrels in DD and about 0.87 min/day for squirrels in LL. All animals in LL had rhythms which eventually became dissociated into two or more components. On the other hand, squirrels kept in DD had running patterns which usually remained intact. After being in constant conditions for between 20 and 70 days, 28 squirrels were subjected to step transitions in illumination from DD to LL (500, 350 or 200 lux) or vice versa. An increase in illumination level generally resulted in a phase advance and a decreasedτ. A decrease in illumination level generally resulted in a phase delay and increasedτ. The maximum amount of activity occurred at some critical intensity between 200 and 350 lux. The free-running period was directly correlated with the entrainment phase-angle difference. This relationship was compared to the red squirrel's light-pulse response curve. These data support Pittendrigh's (1965) entrainment model.

Decomposition in Al-Zn alloys: Part II. Decomposition during continuous cooling

Abstract: A small angle X-ray scattering study (SAS) has been made of decomposition during contin uous cooling in four binary Al-Zn alloys with compositions spanning the miscibility gap and in two ternary alloys, each containing 22 at. pct Zn plus small amounts of Sn and Mg. Plots of logλm (wavelength receiving maximum amplification during the quench)vs logQ (quench rate) yield slopes of approximately -1/3 for all alloys, indicating that coarsening plays an important role during the quench. In addition, measurements of integrated area under the SAS spectra indicate that decomposition is essentially complete in the quenched condition for all of the alloys studied.

Recovery of silver and terephthalic acid components from light sensitive film material

Abstract: OF THE DISCLOSURE The process for the recovery of silver and tere-phthalic acid component from scrap film of a light sensitive silver compound on a Mylar substrate in which the film is subjected to at least a partial wet oxidation in an aqueous alkaline medium at elevated temperature and pressure whereby the Mylar substrate is depolymerized into components which remain soluble in the liquid reactant while the silver com-ponent remains insoluble therein to enable separation of the silver component and the subsequent recovery of terephthalic acid component by acidification of the liquid phase.

Survey of Electrical Engineering and Computer Science Departments in the U. S.

Abstract: As a part of a major curriculum study undertaken by the IEEE Computer Society Education Committee in the fall of 1974, a subcommittee surveyed existing curriculum and equipment in both computer science and electrical engineering departments to assess the current situation. The survey was also intended to update the COSINE survey of electrical engineering departments conducted in the fall of 1972. 1

On Work and Authority: Issues in Job Enlargement, Job Enrichment, Worker Participation and Shared Authority

Abstract: . Continued debate over the nature of work is adding to an existing vast literature in labor economics, business and personnel administration, industrial sociology and social psychology. Both theory and experience indicate that the authoritarian workplace results in social costs through reduced labor productivity and increased worker dissatisfaction. But progress toward shared authority and worker participation in the administration of the production process promises to be slow. Management generally preserves a legitimized authority, defending it with the misplaced rationale of elitism, i.e., the presumed functional superiority of managers. Unions will not press for shared authority, for to do so would undermine their basic and formal function of organizational restraint of managerial authority. Thus, while management and union logically protect their traditional roles, the worker and society are denied the potential benefits of basic changes in work and authority.