Application of an adiabatic calomimeter to the determination of the heats of fusion and heats of formation of several metallic compounds
High temperature thermodynamic properties of metal alloys and refractory materials are important in both research and engineering. Reliable and precise measurements are difficult to make and require rather elaborate equipment. In recent years a commercial adiabatic calorimeter has been made available by the Rigaku Denki Company, Ltd., of Tokyo, Japan. The general operating principles of this apparatus are summarized; its application to the measurement of heats of fusion and transformation of materials, and heats of formation of intermetallic phases is described. The results of the heat of formation experiments are: MgZn2 @863° K, -4. 30 kcal/ g-atom; CaMg2 @532° K, -3. 12 kcal/ g-atom; and CeZn @623° K, -10. 6 kcal/ g-atom. The results of the heat of fusion of the materials are: MgZn2, 9. 687 kcal/mole; CaMg2, 11. 744 kcal/mole; CeZn, 7. 826 kcal/mole. The average values for the heats of fusion are accurate to ±2 pct. Disciplines Ceramic Materials | Metallurgy This report is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/ameslab_isreports/99
Thermodynamic modelling of the Mg–Ca, Mg–Sr, Ca–Sr and Mg–Ca–Sr systems using the modified quasichemical model
In this work, a thermodynamic description of the Mg‐Ca‐Sr system is carried out using the modified quasichemical model. The three binary systems Mg‐Ca, Mg‐Sr and Ca‐Sr have been reoptimized based on the experimental phase equilibria and thermodynamic properties available in the literature. Good agreement was obtained among the calculated phase diagrams, thermodynamic properties and the corresponding experimental data from the literature. Using the established database, the Mg‐Ca‐Sr phase diagram is calculated. Also, a comparison between the liquidus projection calculated using random solution model and the modified quasichemical model is presented. Since experimental data on the mutual solubility between Mg2Ca and Mg2Sr could not be found in the literature, the Mg‐Ca‐Sr phase diagram is calculated and compared for the two cases of limited and complete solubility between these two compounds. c 2007 Elsevier Ltd. All rights reserved.
An Ultrasensitive Analytical Method Based on Chemiluminescence Sensing Electrochemical Parallel Catalytic Reaction Event
An ultrasensitive electrochemiluminescence (ECL) method on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed for improving ECL analytical characteristics using vanadate(V) as a representative. Vanadate(V) could be electrochemically reduced to generate vanadate(II) which could be chemically oxidized by potassium periodate to regenerate vanadate(V) and give parallel catalytic wave effect. Then, the reduced product of potassium periodate could react with butyl-rhodamine B to emit a sensitive chemiluminescence signal. The chemiluminescence intensity was correlative with vanadate(V) concentration. The investigation on the electrochemical reaction rate constant (k0) confirmed that the speed of electrochemical reaction was faster than that of the subsequent chemiluminescence reaction. The possibility of the combination of electrochemical parallel catalytic reaction with chemiluminescence signal sensing was proved. The similar ECL behaviors could be observed at zirconia nanowires-Nafion modified electrode. Because of the separation and enrichment effect of the modified electrode on vanadate(V), the selectivity and sensitivity was further improved greatly. Based on these findings, a new concept on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed and an ultrasensitive ECL method for the determination of vanadate(V) was developed at zirconia nanowires-Nafion modified electrode. Under the optimum experimental conditions, the ECL intensity was linear with the concentration of vanadate(V) in the range of 2.0×10−12 mol/L–2.0×10−10 mol/L. The detection limit was 8.0×10−13 mol/L, which was more than 6 orders of magnitude lower than that observed by electrochemical current transduction for electrochemical parallel catalytic reaction at zirconia nanowires-Nafion modified electrode.