Research On The Selective Crystallization Technology And Recovery Process Of Sulfur In The Pressure Leaching Residue Of High Iron Zinc Concentrat

Nanocrystalline materials have been the focus of material research in recent years.Because of its nanometer scaled grains and microstructure,nanocrystalline materials have unique and superior mechanical properties,such as higher strength and hardness compared with ordinary coarse grain materials.On the other hand,high grain boundary volume fractionand grain boundary energy caused by nanometer scaled grains make the driving force for grain growing much higher than coarse grain materials.So nano-scaled grain is thermal unstable and easy to coarsen when heating or even at room temperature,which leads to the loss in mechanical properties and limits its processing and application.Therefore,nanocrystalline materials thermal stability research is of great theory and application value.There are two basic ways to enhance thermal stability of nanocrystalline metals and alloys,i.e.thermodynamics stabilization and kinetics stabilization.Thermodynamics stabilization is achieved by reducing grain boundary energy through solute atoms segregating at grain boundary,so driving force for grain growth is reduced(or even eliminated).While for kinetics Stabilization,grain boundary migration is impeded by solute atom dragging and the second phase pining,then grain boundary mobility decreases and grain growth is suppressed.Our research is focused on the thermodynamics stabilization of nanocrystalline materials.At present,Trelewicz/Schuh(TS)model,Saber’s work based on the modification of TS model by Lagrange multiplier method and Modified Wynblatt-Ku(WK)Model used by C C Koch are in a leading position in the field of nanometer grains thermodynamic stability research.The first two aim to the relationship between solute atom segregation at grain boundaries and Gibbs free energy change of alloying system,while the latter focuses on influence of solute atom segregation on grain boundary energy.Contraposing the questions needed to be studied further in above models(such as the definition of "transitional region",accurate calculation of elastic strain energy released when solute atom segregation at grain boundaries,judgment method of thermodynamic stabilization tendency).In this article,some modifications are made on TS model and Saber’s model on condition of regular solution,changes in elastic strain energy and Gibbs free energy when solute atom segregating at grain boundaries are calculated,and a practical method to judge thermodynamic stabilization tendency of binary/ternary nanocrystalline alloys is put forword,i.e.Whether a binary/ternary nanocrystalline alloy is thermodynamic stable or not is depended on whether or not its Gibbs free energy decrease when solute atom segregating at grain boundaries.In this paper,calculation program is wrote with MATLAB software and relevant thermodynamic parameters(such as elastic strain energy,Gibbs free energy,mixing enthalpy,segregation enthalpy and grain boundary energy etc)of twenty-eight Cu based binary nanocrystalline alloys and twelve W based binary nanocrystalline alloys are calculated.Thermodynamics stabilization possibilities of these alloys and influence of elastic strain energy,mixing enthalpy,segregation enthalpy,grain boundary energy are studied and discussed in detail.During the course of solute atoms segregating at grain boundary,changes in segregation enthalpy,grain boundary energy and Gibbs free energy of forty alloy systems above are calcualted.Change tendencies and patterns are summarized based on calculation results.Interaction and influence of interaction parameter,mixing enthalpy,segregation enthalpy and grain boundary energy on the Gibbs free energy change are studied and discussed in detail.Thermodynamics stabilization model of ternary alloying system is deduced based on the model of binary alloying system.Inner connection between ternary system model and binary system model is studied,and the the way of deducing binary system model from ternary system model is provided.This work paves the way for the research of thermodynamics stabilization model of multicomponent alloying system.Thermodynamics stabilization posibilities of some Cu based ternary alloying system are calculated with ternary system model,and influence of the second solute on thermodynamics stabilization posibility of primary binary system is studied.Modificated binary system/ternary alloying system thermodynamics stabilization model has some characters as follows:a.Ignoring the "transitional bonding" in calculation and take the whole volume of mixing system as a two-phase material with bulk "phase" and intergranular "phase",introducing effective bonding coefficient a to distinguish the bonding energy in intergranular region and bulk region.This way simplifies calculation model,avoides the problem that total bonds number in intergranular region will be zero when multiplier v is taken as 1/2 in TS model and Saber’s model;Third,and make two nonstandard thermodynamics parameters i.e.interaction parameterωig and bonding energy Eig in intergranular region can be defined and calculated explicitly.b.Mixing enthalpies of every alloys are accurately calculated according to solute and its content by Miedema model,then interaction parameters ω and(α·ω)are defined,which improves calculation accuracy.c.Gibbs free energy before and after solute atoms segregating at grain boundaries are calculated,and thermodynamic stabilization tendency of binary/ternary nanocrystalline alloys can be judged by Gibbs free energy difference before and after solute atoms segregating at grain boundaries..d.Change patterns of Gibbs free energy of binary alloying system during solute atoms segregating at grain boundary are summarized.Interaction and impaction of interaction parameter,elastic strain energy,mixing enthalpy,segregation enthalpy,grain boundary energy on Gibbs free energy change are studied and discussed in detail.Totally eight different binary nanocrystalline alloys(Cu-Sn、Cu-Nb、Cu-Zr and Cu-Sb,four alloying systems)were prepared by mechanical alloying and annealed at different temperature under vacuum condition.Thermodynamic stabilization tendencies of these alloys were study by XRD analysis and microhardness test.Experiment results of Cu-Sn、Cu-Nb and Cu-Zr alloying systems proved initially the correctness and availability of modified model.