MTDATA – Phase Diagram Software from the National Physical Laboratory







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The calculation of temperature/composition sections through multicomponents systems

This application is used for calculating temperature / composition vertical sections through multicomponent phase diagrams for a fixed pressure but with varying temperatures and (constrained) compositions. Graphical output is produced as the calculations proceed showing the phase boundaries calculated by MTDATA. Two different algorithms for calculating isopleths are available within MTDATA. In the first algorithm (ISOPLETH), the graph displayed consists of a series of discrete points ie not joined up. Options are available to perform more calculations within a given area and to label individual phase fields. Following the calculations the graph may be plotted with all the calculated points joined up.

In the second algorithm (NEW_ISOPLETH), the calculation follows each line corresponding to a particular phase boundary across the phase diagram using the concept of zero phase fraction. Again options are available to label individual phase fields. For each algorithm the macro provides prompts to help the user to decide what to type in next.

Before asking for the isopleth to be calculated it is necessary to define a datafile, to classify any phases required to be absent or identified as giving rise to miscibility gaps, to specify the range of temperatures to be considered and the temperature tolerance (typically 0.1). Also the range of compositions must be defined by setting start and final composition groups and specifying the number of compositions to be examined between them. All this can be set up using the normal APPLICATION commands within MTDATA.

Various other parameters need to be defined, the composition tolerance (typically 0.0001), the number of temperature intervals (perhaps 30). These will be prompted for.

Extra options are available ie to plot liquidus or solidus curves or to ignore designated phases, these are invoked by setting the user variable Defn_Method to 2 (the default value is 0).

SET USER_VARIABLE(Defn_Method) = 2 !

Further user variables, Liq_Solidus, liq_phs_nos and ign_phs_nos provide the extra control.

The user variable Liq_Solidus allows a resticted set of the available lines to be calculated and plotted, liq_phs_nos allow a particular phase (or phases) to be assigned as the liquid phase and ign_phs_nos allows certain phases to ignored in terms of the definition of the phase boundaries although still present in the calculations.

0   just the liquidus curve is calculated defined as the highest temperature at which a solid is still present or at which a liquid miscibility gap is still present
1   just the liquidus curve is required defined as the highest temperature at which a solid is still present
2   just the solidus curve is required defined as the highest temperature at which no liquid is present.
3   all boundaries are required except those corresponding to those phases that are to be ignored, defined by the user variable ign_phs_nos

The user variables liq_phs_nos and ign_phs_nos should be entered within quotes. If a list of numbers is given they be separated by + signs. Multiple numbers for liq_phs_nos allows both liquid and gas phases to be assigned as high temperature phases eg '2+4'.


Updated 7 May 2010