The Improvement Of MIVM And Its Application In Liquid Alloys And Organic Solutions

Thermodynamic models,as one of the important approaches for the research of the thermodynamic properties,are greatly concerned due to its convenient use,low cost and good accuracy in prediction.But in some fields,especially in metallurgy field(like liquid alloys),the complicated and changeful intermolecular interaction directly leads to the complexity and the diversity of the deviation types of systems in this solution.In addition to the common regular systems including negative deviation systems(NDS)and positive deviation systems(PDS),the deviation types of systems also contains irregular systems including strong negative deviation systems(SNDS),both negative and positive deviation systems(BNAPDS)and low concentration saturated solution(LCSS).The general local composition models,like the Wilson model,nonrandom two liquid formula(NRTL),molecular interaction volume model(MIVM),etc,are well known for their convenient use and the accuracy of prediction in the regular systems.But unfortunately,they are quite incapable of handling the thermodynamic calculation of the both negative and positive deviation systems(Ag-Sn,etc.)and the low concentration saturated solution(Cr-C,etc.),which greatly limits these models' accuracy of prediction in irregular systems and their scope of application.And this unadaptability of these models has bothered the metallurgical thermodynamic researchers for the past decades.Therefore,building a model which can well handle all these deviation types of systems would give fresh impetus to the basic research of metallurgical thermodynamics and even to the study of solution model.(1)According to the analysis and induction on the data fitting results of 103 binary liquid alloys calculated by five different models,a fresh idea for new model building was found out.Then,based on the configurational partition function of MIVM,combined with Scott's two-fluid theory as well as Scatchard-Hildebrand theory,a model with two forms for excess Gibbs free energy of liquid mixture,Modified-MIVM,is derived from statistical thermodynamics.Then the validity of M-MIVM and its application range is assessed by comparing it with the other four competitive models(including Wilson,NRTL,MIVM and SRSM).The results show that the average relative error of M-MIVM in activity prediction of seven regular systems is below 4%,while that of seven BNAPDS is 8.72%.This means in BNAPDS,the predicting accuracy of M-MIVM improved more than 30% in comparison with other four models(Wilson: 12.52%,NRTL: 14.26%,MIVM: 13.74% and SRSM: 18.83%).In addition,in strong negative deviation systems,the average relative error of M-MIVM is 21.08%,and the increase in predicting accuracy is more that 50% compared to MIVM(41.51%).More importantly,in low concentration saturated solution(Cr-Fe-C),the M-MIVM has similar and good predicting effect with united interaction parameter formula(UIPF),and meanwhile a noticeable improvement can be found when compared with MIVM.The relative errors of these three models are 22.99%,25.51% and 47.23% in turn.All these illustrate M-MIVM can both handle the regular systems(PDS and NDS)as well as the irregular systems(SNDS,BNAPDS and LCSS),showing strong adaptability.(2)According to the significant advantages of M-MIVM in low concentration saturated solution and strong negative deviation systems,this model was used for thermodynamic calculations of liquid alloys containing non-metal like C,B,Si or P,and its results were compared with that of MIVM and UIPF.The results demonstrate that in contrast with MIVM,M-MIVM has stronger adaptability.The fitting precision in Cr-C binary systems increases approximately 60% due to the use of M-MIVM.In comparison with UIPF,M-MIVM has better accuracy and satisfying stability,and the improvement of predicting accuracy varies from 0.95% to 30%.This illustrate that M-MIVM may have certain potential in the application of the thermodynamic calculation of liquid alloys.(3)M-MIVM was applied for the thermodynamic calculation in vacuum metallurgy,including vapor-liquid equilibrium calculation and the separation coefficient prediction,the predicting effect of which is similar to that of Wilson model and MIVM in symmetric systems.The difference is that the M-MIVM is of distinct advantage in dealing with the asymmetric systems in comparison with the other two models,and the improvement of fitting precision varies from 2.31% to 30% compared with other two models.On one hand,these advantages give the M-MIVM better capability to descript the feature of the asymmetric systems that the MIVM and Wilson model are not suitable for.On the other hand,these advantages also lay a foundation for more accurate activity prediction of multicomponent systems containing binary asymmetric systems in vacuum metallurgy.Therefore,from the perspective of accuracy and applicable scope,the M-MIVM may have good applying prospect in vacuum metallurgy.(4)Another main result in this article is the first verification that MIVM-type models can be used as an effective calculating tool for organic mixtures.In contrast with NRTL and MIVM,the M-MIVM has superiority in the detail processing capability and the accurate description to special systems' feature(such as the description of phase split phenomenon).This illustrates the reliability and accuracy of M-MIVM both exist in liquid alloys and organic mixtures.(5)A segment-based molecular interaction volume model,polymer-MIVM,is proposed for correlating and predicting the thermodynamic properties of polymer solutions.In contrast with the ‘combined models',MIVM has many differences.In form,MIVM can be conveniently used for excess Gibbs free energy of polymer solutions without big modification,just like UNIQUAC equation,while combined models adopt cooperative combinations of two different models;in working mechanisms,combined models are unilateral adjustment,while MIVM is bilateral synergistic adjustment.