Thermodynamic measurements on Ag - 28% Cu nanopowders processed by mechanical alloying route

A correlation between thermodynamic properties, thermal expansion and electrical resistivity of Ag–28% Cu nanopowders processed by the mechanical alloying route

“…This effect due to the larger strain energy accumulated after longer milling times has been previously reported by Spassov 14 on the DSC curves of Cu-Ag alloys milled for 12 and 20 h and has also been observed on the DSC curves of the 20 and 80 hour milled samples which were discussed in our recent paper. 22 As we were expecting, this effect is followed by a steadily decrease of heat capacity at an interval of about 75 K. The clear inflection observed between 548 and 573 K is followed by an interval of about 50 K in which both the enthalpy increments and the heat capacity values are almost constant. After 623 K, the enthalpy exhibits a gradual increase up to about 1048 K, even though, in spite of the increasing character of enthalpy, the presence of some other features is also noticed around 848, 898 and 948 K. The heat capacity also increases from 623 K, but the C p weaker temperature dependence has to be noted.…”

“…3, inset B) can be due to cumulative effects of thermal expansion and Cu segregation from the solid solution. 22 Also, the narrowing of the diffraction line is a measure of increasing the crystallite size with temperature, indicating an apparent grain growth in the sample.…”

“…The procedure was described in detail in our previous paper. 22 In situ XRD measurements were performed using the same equipment and parameters, in continuous mode, from 323 to 973 K, in an open air atmosphere. The crystallite size was estimated by the Scherrer equation from broadening of the (111) diffraction line of Ag-Cu ss , using the formula: 27…”

“…To experimentally investigate the thermal behaviour of the Ag-Cu nanoalloys produced by mechanical alloying, differential scanning calorimetry has been generally used. Except our recent work, 22 the previous publications on thermal behaviour cover only restricted temperature ranges, generally until approximately 673-773 K. 14,16,20,23 By combining the modeling approach with differential scanning calorimetry, some information has been obtained regarding the enthalpy-composition curves for metastable phases over a limited composition domain. 5,16,24,25 Despite the amount of research being conducted on this area, the experimental information on the relevant functions suitable for thermodynamic evaluations of chemical processes of phase formation associated with a specific processing technique is still scarce and needs to be investigated.…”

“…It has been a goal of our recent work 22 to identify the characteristic system parameters that favour stable nanostructured systems in Ag-28% Cu powders synthesized by the mechanical alloying route. By a critical comparison of the isothermal enthalpy (obtained by drop calorimetric measurements) with dynamic DSC results and in situ controlled annealing XRD experiments, a key output of our prior work 22 was a preliminary understanding of the thermodynamic stability correlation with the effect of the milling time and particle size in a large temperature range from room temperature to 1073 K.…”