Thermodynamic Database MALT Omega / Basic

MALT Omega database has been widely enlarged and aqueous species have been added. --->The list of compounds (7890 species)
MALT Basic database remains with the same compounds as MALT for Windows (excluding New items in above list : 4930 species).
A part of the data are revised. --->List of Updated Compounds in Old MALT Database
Help documents of both versions are fully supplied (on-line/PC local). You can read them as a whole or on-demand articles.

Chemical Potential Diagram (CHD) and Gibbs Energy Minimizer (gem) are in common in Omega and Basic versions.
They have been enhanced to handle the system including aqueous species.
For example, in Omega, CHD can draw Pourbaix Diagram. Example diagrams of CHD
Also in Omega, gem can calculate the equilibrium of the system including gas, condensed, and aqueous phases. An example of gem calculation

1. to provide thermodynamic data with a good quality to those who need to make thermodynamic analyses;
2. to facilitate the utilization of thermodynamics in the research and development associated with materials science, new process development, etc.

For those purposes, the followings can be made:

1. Preparation of thermodyanmic data for the compound system
2. Analysis based on one chemical reaction
3. Analysis based on the Gibbs energy minimization method
4. Analysis based on the Chemical potential diagram
5. MALTDirect-User's Program

(1) Preparation of thermodyanmic data for the compound system

(2) Analysis based on one chemical reaction

(3) Analysis based on the Gibbs energy minimization method

The MALT related software, muti-element chemical equilibrium calculation programgem is based on the Gibbs energy minimization technique.

When temperature, pressure and the initial amount of chemical reactions are given, the corresponding equilibrium amount and associated chemical potential are given for respective species involved in equilibrium. This is parrticularly convenience for the multicomponent system in which several chemical reactions can proceed simultanesouly.

The Gibbs energy minimization under the constant pressure or the Helmholtz energy minimization under the fixed volume can be made in a series. The latter makes it possible to make calculations for the system under the selected conditions characterized by the constant chemical potentials. For example, equilibria in air are quite important in many industrial processes. The equilibria as a function of oxygen potential are also important in high temperature fuel cells.

In a series of calculations, the amounts of reactants can be determined from the reaction products in the previous calculation. This makes it possible to calculation the time dependent change in composition of those materials which are exposed under a flow of gases containing some reactive impurities.
In a long reaction tube, the changes in substances in the tube can be evaluated by the condition that the gases are in equilibrium with the substance in a point and then equilibriated gases flows to the next point to react with substance at the point.

This is the strong tool in the themodyanmic analyses for the practical situations of materials science or chemical processes. Since the unique solution can be given for the specified conditions, results are quite understandable and are easily applied for other further considerations. It is therefore crucial to be familiar with handling gem software in the thermodynamic considerations. As described above, it is also essential to extract the most important chemical reaction out of a huge amount of results produced by this software. This makes it useful for users to understand the phenomena occuring on materials or chemical processes from the physicochemical reasons.



gem in Omega : The main points of treating aqueous species in gem are as follows: Default setting: Default setting wil be made for treating the aqueous ideal solution which consists of the water solvent and the aqueous solvent species. Specification of activity: Commands are available to specifiy the (logarithmic) activity of aqueous species in an analogous way to the gaseous species for which the partial pressure can be specified. In additio, pH can be also specified as -log a(H+). Restriction: A new function is introduced to indicate whether the temperature region of calculation is beyond the valid temperature region of respective species. Particularly, this is important for the aqueous species having no high temperature heat capacity. Batch process is now possible by gem (common in both Omega and Basic : See gem batch process).

(4) Analysis based on the Chemcial potential diagram   See What is Chemical Potential Diagram? for further details.

The chemical potential diagram is constructed on the basis of the Gibbs phase rule. In the ternary system at fixed temperature and pressure, three phase coexistence gives no freedom so that the chemical potentials of all elements are uniquely fixed and as a result, the chemical potential of other species/compound can be quique determined.
This state corresponds to the point in the chemical potential space. From this equilibrium point, three lines are extended; those are the two-phase coexistence equilibrium. Those geometric feature can be plotted to construct the chemical potential diagram having two axis values. Usually, those axis values are selected among the environmentally controllable properties such as temperature, log p(O2), log p(CO2) etc. Even so, more general variables can be adopted as the variables. This is so called generalized chemical potential diagram.

CHD is a strong tool of constructing the generalized chemcial potential diagrams using the powerful polyhedron algorithm.
This makes it possible to construct the high temperature stability diagrams as well as the Pourbaix diagrams by the same software. In addition, the profile diagram is also constructed to show the variation of the partial pressure of the gaseous species or of the logarithmic activities of the aquoues species along the fixed line in the diagram.

The Pourbaix diagram is newly prepared in the recent verion up procedure. Since the special treatments are needed to construct the Pourbaix diagram, the default setting are widely adopted when CHD is run for the chemical system which contains aqueous species. For example, tempearrture is fixed at 298.15 K since the availability of aqueous data is best at 298.15 K. The fixation of H2O(l) at activity of unity is adopted together with the adoption of pH and E/V as axes.In the multicomponent O-H-X-M system, the element of M is selected as target element according to the order of NBS table, when the NBS order of M is higher than that of X. In the <O,H,S,Fe> or <O,H,P,Fe> system, the element Fe is selected as target, while in the <O,H,Fe,Ti> or <O,H,Fe,Na> system, the element Fe will not selected as target.





CHD in Omega : The main feature of treating the aqueous species in CHD are given below. Default setting for Pourbaix diagram: The chemical potential diagrams for the aqueous systems are well recognized as the Pourbaix diagrams, and have been widely utilized in various fields so that the present setting is adopted so as to provide the Pourbaix diagrams as default setting. Even so, where the aqueous solutions are not identified from the selected species to be used in construction of the diagrams, such default settings will not be adopted and the normal settings will be validated as nor mal functions in CHD. Normal diagram, Predominance area diagram, Profile diagram: There can be seen several different diagrams for the well known Pourbaix diagrams. Mostpopular diagrams are those given in the pH-pE(or E/V) plot to indicate what kind of the chemical state is stable for the selected element such as Fe or Mn. Those diagram which exludes the solid or other condensed phase and contains only aqueous species is called the Predominance area diagram. Furthermore, this analysis deals with a mixture consisting of many species so that the profile diagram is also widely utilized to show the concentration or activity of such species as a function of selected variable such as pH. Pourbaix diagram for Multicomponent systems: The Pourbaix diagrams for the multicomponent systems can be also constructed by following the strategy of generalized chemical potential diagrams and well developped way of representating the stability diagram for the systems containing two target elements such as Fe and S. Normally, the stability regions of the Fe containing compound/species are preferentially selected to be visualized. This can be done in the generalized chemical potential diagrams by adopting the method of unvisualizing the polygons for which do not contain the Fe component. This can be manually operated by changing the transparency of polygons for such items to be shown.

(5) MALT Direct - User's Program

MALT suggests users to write their own programs and to make their own analyses on their problems. For this purpose, several sample programs written in Delphi are prepared to show how user programs can be written to utilize the MALT supplied procedures for handling thermodynamic data. In order to transfer the thermodynamic data in the MALT to the User's propgrams, the special function of "MALT Direct" is prepared. In the MALT related software, gem and CHD make use of the same MALT Direct function to recieve the data from the MALT Data management System.



---

Detailed Explanation of Data

Considered matters:

• Some difficulties were encountered during the optimization of their themodynamic properties in view of consistency with phase diagram behavior and other sources derived from the plausible kinetic effects behind the observed thermodynamic behaviors.
  
• Special remark should be needed for a particular compound with controvercial discussions.
  
• Special treatment was adopted for better understanding the behavior of a family of compounds such as perovskite compounds and related Ruddlesden-Popper phases.
  
• Special treatment was adopted for high temperature heat capacities of gaseous or aqueous species to expand the usability of compound data.
  

Focused Compounds/Properties

1. Perovskite Related Ruddlesden-Popper Phases
   • Those oxide compounds in the perovskite-type structure or related Ruddlesden-Popper phases exhibit the extensive solid solution behaviors among the family of compounds.
   • This makes attractive to treat this type of families as the ideal associated solutions. For such a purpose, chemical formula has been changed like A1.5BO3.5 instead of A3B2O7 and AB0.75O2.5 instead of A4B3O10.
   • This is due to the fact that the mixing entropy in the ideal associated solutions strongly depends on the atom numbers in one molecule (the hypothetical component in the solution).
   
   
2. About La2Zr2O7
   No change has been made, in spite of recent many investigations on the thermodynamic data of La2Zr2O7 after the first thermodaynamic evaluation was made in early 1990's. Detailed explanation was reported.
   
   
3. NaSiCon and related Phases in the Na-Zr-Si-P-O system
   Old data for Nasicon was based on the electrochemical investigations (ref 162). New calorimetric inverstigation as well as the phase relation have been made extensively. Thus, attempts were made to evalute the thermodynamic data which are consistent with the experimental phase relations.
   
   
4. Li-Mn-O system
   This system is famous in the technological field associated with the Li batteries. The materials behavior and electrochemical behaviors have been well investigated in the vicinity of room temperature, whereas the high temperature phase behaviors have been also extensively investigated. There can be some inconsistency among related information. The compiled thermodynamic data have been derived with understanding that the room temperature electrochemical characteristics are not necessarily in consistent with the most stable behaviors among compounds.
   
   
5. Li-Fe-P-O system
   This system is also important in the Li battery technology. In this sense, new features appear in utilization of thermodynamic data in materials science. This is the deep utilization of the first principle energy calculations. In the Li-Fe-P-O system, a systematic approach has been adopted to make clear the phase stability in the multicomponent systems. In such a multicomponent system, experimental investigations have been focused on clarifying the high temperature phase relations. On the other hand, the calorimetric investigations are few and therefore not systematic. In view of this, this system provides important examples concerning how to harmonize the experimental and theoretical efforts. In the Example diagram 9a and 9b in CHD manuals, this is partly shown.
   
   
6. High Temperature Heat Capacity of Aqueous Species
   Recently, the heat capacities of aqueous species related with the geology have been evaluated using a specialized heat capacity equation which is not consistent with the MALT adopted equations. Description is given to show how those coefficients of such equations can be transfered to those adopted in MALT database.
   
   
7. High Temperature Heat Capacity of Gaseous Species
   A large number of thermodynamic data for gaseous species have been determined by the high temprature Mass Spectrometry. However, in many cases, only the enthalpy of formaiton at 298 K or 0K are given withuot entropy or heat capacity information. Some attempts have been made to provide estimated values by simple considerations.
   
   
8. High Temperature Alloys
   Only a limited number of alloys are stored in the MALT database. This is beause that the MALT system has the strategy that the nonideal solutions are not treated and therefore only the intermetallic compounds are stored. In a particular composition of alloy solution phase can be given to provide rough idea about the stability of the target alloy solutions.

---