Formation of value-added materials has been demanded in materials science and engineering. “Exergy” is used to evaluate how valuable a target material is. Exergy is defined as (Enthalpy)-(Room Temp.)*(Entropy). When the exergy is evaluated to be large, the target material is recognized to be valuable. For example, it is required to recycle waste slag and glass to make some value-added materials. Since slag and glass are mixture of various stable oxides which consist of many cations and anions, they have low enthalpy compared to metals and large mixing entropy. In other words, slag and glass have very low exergy which means that it is very difficult to recycle them to make a value-added material. However, the concept of surface and interface in a material is not considered in the above explanation on the exergy. If some interfaces would be introduced in slag and glass, we could make new materials even from slag and glass. Here, a porous material is one of the candidates to introduce interfaces in materials. In this presentation, two examples are shown firstly on porous materials made from metals and glass. One of them is a surface porous metal obtained from oxidation and reduction of metallic materials. The other one is fabrication of porous glass by hydrothermal reaction under high pressure and thermal expansion under normal pressure.
When we try to design a new material added with surface properties, we need to understand the surface properties of the materials. The authors have tried to develop a system to predict various surface properties on the basis of thermodynamic databases, which are usually used to calculate phase equilibria, chemical reactions and so on. On the surface properties of metals and alloys, we can estimate, for example, the surface tension of liquid metals and alloys. Based on those trials, we have calculated phase diagrams in nano-sized alloys by considering the effect of the surface properties on phase equilibria. On the other hand, it is difficult to estimate even the surface tension of molten ionic mixtures consisting of an alkali-halide binary mixture which is the simplest system of ionic mixtures. For those materials, we found that we need additional information on ionic radii to evaluate the surface tension of molten ionic mixtures. However, we can not evaluate exactly the surface tension of molten slag or glass systems containing H2O which is one of the target materials for making the above porous glass. In this presentation, some examples will be described on our trials of the evaluation of surface / interfacial properties referring to some problems.