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 modeling and experimental investigation of the Mg-Al-Ca-Sr system
In this work, a self-consistent thermodynamic database for the Mg-Al-Ca-Sr system using the modified quasichemical model has been constructed. The thermodynamic description of the quaternary system was established by combining the thermodynamic descriptions of the constituent binary and ternary sub-systems. The Mg-Al-Ca and Mg-Al-Sr systems were investigated by combining thermodynamic modeling and experimental investigation. The experimental investigation has been performed using DSC, XRD, SEM and EPMA. Also, isothermal sections at 300°C and 400°C were constructed for the Mg-Al-Ca and Mg-Al-Sr systems. In the Mg-Al-Sr system, six ternary solubilities of the binary compounds extended into the ternary system have been found and denoted as (Mg 17 Sr 2 ), (Mg 23 Sr 6 ), (Mg 38 Sr 9 ), (Mg 2 Sr), (Al 4 Sr) and (Al 2 Sr). The reported ternary compound in the literature (Mg 58 Al 38 Sr 4 ) has been observed in this work. In the Mg-Al-Ca system, three binary compounds were found to dissolve the third component in the ternary system and were denoted as (Al 2 Ca), (Al 3 Ca 8 ), and (Mg 2 Ca). The ternary compound (C36) reported in the literature has been confirmed. A comparison between the calculated liquidus projection of the Mg-Ca-Sr system using the modified quasichemical model and random solution model has been presented. It was found that while the random solution model agrees well with the experimental phase diagram, the modified quasichemical model gives better agreement with the experimental thermodynamic data and the experimental phase diagram. Liquidus projection of the Al-Ca-Sr system was calculated using the modified quasichemical model and combined with the other three ternaries in one database for the Mg-Al-Ca-Sr system.
Electrochemical detection of copper(II) at a gold electrode modified with a self-assembled monolayer of penicillamine
A penicillamine (PCA) self-assembled monolayer (SAM) was prepared on a gold electrode. It has been found that the modified electrode exhibited a selective response to copper ions. As demonstrated by cyclic voltammetric experiments, the SAM-based electrode showed an attractive ability to preconcentrate efficiently traces of copper(II) from solutions. Under optimum conditions, the anodic peak current was proportional to the concentration of Cu(II) in the range from 8.0 × 10−7 to 1.0 × 10−4 M with a detection limit of 4.0 × 10−7 M. Moreover, this modified gold electrode is also characterized by excellent repeatability, showing a relative standard deviation of 3.2% for nine successive measurements of 1.0 × 10−5 M Cu(II). The PCA/Au SAM gold electrode was used for the determination of Cu(II) in a tap water sample and the results showed a good agreement with the data obtained by atomic emission spectrometry.