Miscellaneous Category

In this chapter the calorimetric-equilibrium technique based on the combination of the two techniques has been discussed. The technique has been successfully exploited in the direct and simultaneous measurement of partial molar enthalpy and the corresponding partial molar free energy of hydrogen in the alloys of palladium with silver, gold, copper, iron, nickel, cobalt and manganese. The important conclusions based on these studies are (i) The more exothermic heat of solution of hydrogen in Pd–Au, Pd–Ag and Pd–Mn (upto 33 at % Mn) is in conformity with the expansion of palladium lattice on alloying with gold, silver and manganese and the negative values of the interaction parameters, \( {\varepsilon}_H^{Au} \) , \( {\varepsilon}_H^{Ag} \) and \( {\varepsilon}_H^{Mn} \) , (ii) the less exothermic or endothermic values of the heat of solution of hydrogen in Pd – Cu, Pd – Ni, Pd – Co and Pd – Fe alloys are in conformity with the contraction of palladium lattice on alloying with copper, nickel, cobalt or iron and the positive values of the \( {\varepsilon}_H^{Cu} \) , \( {\varepsilon}_H^{Ni},{\varepsilon}_H^{Co} \) and \( {\varepsilon}_H^{Fe} \) interaction parameters (iii) the hydrogen–hydrogen interaction in Pd–Au, Pd–Ag and Pd–Mn alloys changes from attractive to repulsive at around 30–40 at % Au, Ag and Mn. The nature of interaction in Pd – Mn alloys is more complex due to the order-disorder transformation in the system. In the other section, combination of vapor pressure and electrical conductivity has been demonstrated to measure the electrical conductivity of polycrystalline CdTe in the very low ambient tellurium pressure ranges varying from 1.0 × 10−15 to 2.0 × 10−5 atm in the temperature range 675–975 K by constructing an especially designed experimental assembly. At all the temperatures the conductivity increases with the increase in tellurium pressure up to a critical pressure. After attaining the maximum, it started decreasing with further increase in tellurium pressure. The abrupt change in conductivity occurs in the pressure range of 1.3 × 10−9 − 1.3 × 10−6 atm with the minimum around 4.2 × 10−8 atm. From the thermo-emf measurements of CdTe it is concluded that the conduction in CdTe is p type in the low tellurium pressure region and n type in the high tellurium pressure region. However, doping with monovalent silver and trivalent indium has shown different effects. The conduction in all of the samples was found to be n type at the tellurium pressure of 1.7 × 10−6 whereas substitution of cadmium with indium in the low pressure region changes the conductivity of CdTe from p to n type.