John Chipman

Bio: John Chipman is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Slag & Oxygen. The author has an hindex of 24, co-authored 72 publications receiving 1926 citations.

Thermodynamics and phase diagram of the Fe-C system

Abstract: A critical review of published data provides a fairly accurate knowledge of the thermodynamic properties of all of the phases of the system Fe-C that are stable or metastable at atmospheric pressure. Selected data are shown as tables and equations. A proposed phase diagram differs only slightly from others recently published but has the following features. Peritectic compositions and the α-γ equilibrium are shown to agree with measured values of the activity of iron in the solid and liquid solutions and the thermodynamic properties of pure iron. Of all the reported carbides of iron only two may be studied under equilibrium conditions. The solubilities of cementite and of χ-carbide in α-Fe are deduced from measured equilibria. Both are metastable at all temperatures with respect to graphite and its saturated solution in iron. The χ-carbide becomes more stable than cementite below about 230° Certain published data on e-carbide permit an estimate of its free energy as a precipitate during the aging process.

Thermodynamics of the Fcc Fe−Ni−C and Ni−C alloys

Abstract: The activity of carbon in the fcc solid solution of the Fe−Ni−C system has been measured at 800°, 1000°, and 1200°C by comparison with observed values in the Fe−C binary by equilibration with methane-hydrogen mixtures. Defining the lattice ratioz C≡n C/(n Fe+n Ni−n C), the activity coefficient ΨC≡a C/z C has been determined as a function of temperature and composition. At infinite dilution log ΨC goes through a maximum at about 70 pct Ni in agreement with Smith. The partial molar free energy of carbon in the dilute solution referred to graphite is not a linear function of the base alloy composition, but has a large deviation with maximum at about 60 pct Ni. Similar maxima occur in both ΔH C ° and ΔS C ° . Linear equations are derived for the activity coefficient of carbon in three composition ranges of Fe−Ni−C alloys; a simplified equation applicable to nickel steels is included. The solubility of graphite in nickel has been determined. The marked deviation from linearity is ascribed to the existence of iron atoms in two electronic states, γ1 and γ2 which differ in energy and are antiferromagnetic and ferromagnetic, respectively.

Thermodynamics of austenitic Fe-C alloys

Abstract: New data on the activity of carbon in austenite have been obtained by CO2/CO equilibration of Fe-C alloys in the temperature range 900° to 1400°C. Equations for the thermodynamic properties of carbon and iron in austenite are obtained from the data combined with selected data from the literature. A slightly modified phase diagram is presented. The stability of cementite is also determined from data published earlier and the results of the present study. Parameters of the various models of the behavior of carbon in austenite taken from the literature are also calculated from the data.

Activity of carbon and solubility of carbides in the FCC Fe-Mo-C, Fe-Cr-C, and Fe-V-C alloys

Abstract: The activity of carbon in austenitic Fe-Mo-C, Fe-Cr-C, and Fe-V-C alloys has been studied by equilibration with controlled CH4-H2 atmospheres at temperatures in the range 850° to 1200°C. The observations included a number of compositions in the two-phase fields, γ + carbide. Equations are given for the activity coefficient of carbon as a function of temperature and composition in the austenite field and from these the other thermodynamic properties of the solution may be computed as desired. The phase boundaries γ/γ + carbide were determined by breaks in the isoactivity lines. This was supplemented in the case of Fe-Mo-C alloys by metallographic linear analysis of equilibrated samples. The results confirm certain published phase diagrams and discredit others.

Job strain, work place social support, and cardiovascular disease: a cross-sectional study of a random sample of the Swedish working population.

Abstract: This cross-sectional study investigates the relationship between the psychosocial work environment and cardiovascular disease (CVD) prevalence in a randomly selected, representative sample of 13,779 Swedish male and female workers. It was found that self-reported psychological job demands, work control, and co-worker social support combined greater then multiplicatively in relation to CVD prevalence. An age-adjusted prevalence ratio (PR) of 2.17 (95% CI-1.32, 3.56) was observed among workers with high demands, low control, and low social support compared to a low demand, high control, and high social support reference group. PRs of approximately 2.00 were observed in this group after consecutively controlling for the effects of age together with 11 other potential confounding factors. The magnitude of the age-adjusted PRs was greatest for blue collar males. Due to the cross-sectional nature of the study design, causal inferences cannot be made. The limitations of design and measurement are discussed in th...

Electrons in disordered structures

Abstract: (1967). Electrons in disordered structures. Advances in Physics: Vol. 16, No. 61, pp. 49-144.

Carbon Deposition in Steam Reforming and Methanation

Abstract: Deactivation of supported metal catalysts by carbon or coke formation is a problem of serious magnitude in steam reforming, methanation, and other important catalytic processes. Its causes are generally threefold: (1) fouling of the metal surface, (2) blockage of catalysts pores and voids, and/or (3) actual physical disintegration of the catalyst support. Since loss of catalytic activity and physical destruction of the catalyst by carbon deposits can occur rapidly (within hours or days) under unfavorable conditions, understanding and control of these effects are of major technological and economical importance.