Study Of The Boundary Theory Of Phase Diagram And Its Application

Phase diagram is very important in science and technology. It is also a most usefultool in the field of material science. In brief, the research on the theory of phasediagrams can be divided into two categories: the first is the research for thenecessary conditions which all the phase diagrams must satisfy. To be morespecifically, one abstracts different concepts, such as the physical parameters likethe number of phases, the number of independent components or the degrees offreedom etc, and then studies the relation among them. The research for all phasediagrams is based on such theories. The second category studies the sufficientconditions necessary for a concrete phase diagram. Explained in detail, they studythe quantitative functional relation between thermodynamic properties of eachcomponent of the specific phase equilibrium system and temperature, compositionetc. And based on this relation, a complete specific phase diagram is to beconstructed. The combination of the two categories constructs the whole theory ofphase diagrams.The great thermodynamic and statistical physicist, J.W. Gibbs, is the founder ofthe theory of the first category. The phase rule deduced by him is the mostimportant classical work in this field. The great physical chemist, the founder ofsolid state chemistry, Carl Wagner, is the pioneer of the theory of the secondcategory.Gibbs' phase equilibrium theory, especially the phase rule, is the foundation forthe phase theory, but the phase rule cannot solve the problems regarding therelation between neighboring phase regions (abbreviated to NPRs) and theirboundaries. Therefore, several empirical rules concerning this relation have beenproposed, such as Schreinemakers' rule, Vogel-Masing's rule and Rhines' rules etc.Palatnik-Landau puts forward the well known Palatnik-Landau's contact rule ofphase regions and makes an important contribution to the phase theory. Rhinesdeduces ten rules which must be obeyed by constructing a complicated ternaryphase diagram. Gupta et al. suggests a concept of ZPF (Zero Phase Fraction) line,and applies this concept to constructing complicated multicomponent isothermalsections based on limited information. Muyu Zhao after years of work proposes asystematic boundary theory of phase diagrams. The researcher of the presentthesis finds that in dealing with the relations between NPRs, the boundary theoryis superior to Palatnik-Landau's theory in some aspects. For constructingmulticomponent isothermal sections with limited information, the method ofboundary theory also shows some merits in comparison to Gupta's method. So,the researcher of the present thesis compares these three theories and gets thefollowing conclusions:1. With the concept of phase boundary, the problem, which the Palatnik-Landau'scontact rule can not solve well could be solved. The phase boundary theory candeduce the contact rule theoretically, but the contact rule can not deduce any oneof the important formulas of the phase boundary theory.2. In constructing the isothermal section of a multicomponent system with limitedinformation with the phase boundary theory, it is easy to draw boundary lineswithout any arbitrariness. But the Gupta's method does have this demerit. In somecases, when more than one topologically valid section may be drawn, it can not bejudged which one is right by the Gupta's method and additional samples in thevicinity of the controversial region must be studied. But the phase boundarytheory can only theoretically judge which one is right.The researcher of the present thesis also studies the principle of the variation ofthe phase composition with the variation of the system composition. With theseprinciples, many problems of phase diagrams can be solved.The researcher of the present thesis also designs a new method to determine aquinary isothermal section based on the phase boundary theory. And a lot of theexperimental work had been done, but for some reasons, it has not been finished.