About this tool
GibbScope Application
GibbScope computes a binary phase diagram from a thermodynamic
(.tdb) database and redraws it as the assessed parameters are
changed. It also overlays experimental data on the diagram and fits the
parameters to these data. The engine is written in Rust and compiled to
WebAssembly, so every calculation runs and stays in the browser.
A database can be loaded from Example system,
from a file on disk (Drop a .tdb file or
browse), or by choosing a pair of elements in
the Systems tab, which lists every assessment
of that pair in the SGTE collection of binary datasets.
Figures
GibbScope plots the phase diagram and, when
Gibbs energy curves is on, the Gibbs energy
curves at a selected temperature below it, on a shared composition axis.
The features of the two plots are as follows.
-
Isotherm. The horizontal lime line marks the temperature
at which the energy curves are drawn, and its markers are the
common-tangent compositions at that temperature. It moves with the
at T slider, by clicking or dragging on the
diagram, and with the arrow keys.
-
Crosshair. The readout gives x and T under the pointer,
the tie line through that point, and the phase amounts from the lever
rule (in moles). When the pointer is in the same phase field as the
isotherm at that composition, the lower panel highlights the matching
tangent or curve.
-
Invariant reactions are solid horizontal lines through
the coexisting compositions. The table beside the figure lists the type,
temperature, and phases of each reaction.
-
Line styles. The crosshair, the top of the assessed
range, and the tangents are dashed, whereas boundary curves, invariant
lines, and the isotherm are solid. Once a parameter is changed, the
original diagram is drawn underneath in gray.
-
Hatching covers temperatures above the range for which
the database declares its functions, where the diagram is an
extrapolation. When a solid remains stable above that range, a button on
the plot extends the axis to include it.
-
Fills. Two-phase fields have muted fills.
Labels writes the phase names into the
fields, and Raster turns the fills on and
off; with the fills off, an exported SVG is fully vector.
-
Caption. The caption in the corner names the database
and any phases that are missing or drawn with physics dropped. It is part of
the figure and is therefore included in exports.
-
Zoom and pan. Scrolling zooms and dragging pans;
double-clicking or pressing Reset view fits
the axes again. Light figure draws the
figure on a white background for publication.
Changing Parameters and Fitting
R-K Parameters has one slider for the
A coefficient (in J/mol) of each Redlich–Kister term
and one for the Gibbs energy (in J per formula unit) of each line compound.
Each slider shows the change from the assessed value, so 0 corresponds to
the published database, and Reset returns all
sliders to 0. An interaction slider spans ±25 % of the assessed
coefficient (at least ±5000 J/mol), and a compound slider
spans ±10 000 J. An exact value can be typed into the box
beside a slider. The diagram is recomputed in the background, typically
within a second, so the page stays responsive while a slider is dragged.
Compare with draws another assessment of the
same system in gray beneath the current one, in place of the original
diagram. The comparison can be a database from the collection or a dropped
.tdb file, and a database that lists the same elements in the
opposite order is mirrored. Loading a comparison closes the energy panel.
Drop experimental data loads measured points
from a file in the format described below. The points are drawn with error
bars, and Misfit reports the weighted RMS
distance between the points and the diagram, in units of each point's
uncertainty. Color: Source switches the
coloring of the points between their source and their residual, which
shows the direction in which each point pulls the model.
Points hides the markers without changing the
misfit, whereas unticking a source in the data list removes it from both the
misfit and the fit.
Experimental data loaded for one system stays with that system. When
another database is loaded for the same pair, the data is kept; for the same
pair in the opposite order, it is mirrored; and for a different pair, it is
set aside, neither drawn nor scored, until Remove or Keep is chosen.
To fit, tick fit beside each parameter to be
freed and press Fit unlocked parameters. A
Nelder–Mead search then minimizes the misfit over these parameters,
starting from the current slider values and staying within the slider
ranges. The misfit covers the entire temperature range regardless of the
zoom. The result can be reviewed and then kept with
Accept or discarded with
Revert.
Experimental Data File
GibbScope reads experimental data from .csv, .tsv, or
.json files with a header row and one row per measurement. Columns
can appear in any order, and only x and T are
required. Comma, tab, and semicolon delimiters are detected, and lines
starting with # or $ are comments. A row that
cannot be read is reported with its row number and the reason, while the
rest of the file still loads.
| Column | Meaning |
|---|
x (required) | Mole fraction of the second element the database names, e.g., Cu in an Ag–Cu file. A header of x (at%) or x (wt%) converts the values on import; wt% needs the database loaded first, for the atomic masses. A header of x(Ag) names the element: values for the first element are mirrored onto the second, and an element not in the database is refused. Also accepted: composition, x_B, mole_fraction. |
T (required) | Temperature in kelvin, or in Celsius with the header T (C) or T_C. Also accepted: temp, temperature. |
kind | The type of measurement: boundary (default), tie_left, tie_right, invariant, or single_phase. liquidus, solidus, and solvus are read as boundary, and each reaction name in the table below (eutectic, monotectic, metatectic, monotectoid, eutectoid, syntectic, peritectic, peritectoid, polymorphic, allotropic, other) as invariant. The kind sets the marker shape and the misfit row. An invariant point is measured to the composition of the nearest participating phase at the reaction temperature, not to the reaction line, so a thermal arrest recorded at the overall composition of an alloy appears off in x even when its temperature matches. |
x_err | Uncertainty in composition, in the unit of the x column (e.g., 0.5 under x (at%) is 0.005). It is drawn as an error bar and scales the misfit. Default 0.01. Also accepted: dx, sigma_x. |
T_err | Uncertainty in temperature. Default 10 K. Also accepted: dT, sigma_T. |
phase | The phase to which the point belongs, e.g., FCC_A1. The point is then scored against that phase only. |
weight | Relative weight in the misfit. Default 1. |
source | Dataset label, used for colors and for showing or hiding points, so that one file can hold several studies. Default: the file name. |
# Ag-Cu, digitized from Smith 1985
x,T,kind,x_err,T_err,phase,source
0.399,1052.2,invariant,0.005,1.0,LIQUID,Smith 1985
0.141,1052.2,tie_left,0.006,1.0,FCC_A1,Smith 1985
0.950,1052.2,tie_right,0.006,1.0,FCC_A1,Smith 1985
A JSON file holds the same records, either as an array or as
{"points": […]}.
Thermo-Calc .pop
GibbScope reads a PARROT .pop file directly. Load the
database first: the element names and phase abbreviations in the file are
matched against it, so X(FCC,CR) becomes x(Ni) on a
Cr–Ni axis and LIQ becomes LIQUID. Rows of
TABLE-HEAD blocks that give one composition and one
temperature become points, with the :σ value as the
error bar and the SET-WEIGHT lines providing the weights and,
through their trailing comments, the sources.
Everything else is refused with a reason and line numbers. In a typical
PARROT file, this is most of the file, since enthalpies (HMR),
activities (ACR), and chemical potentials are not points on a
phase diagram.
ESPEI ZPF datasets
ESPEI datasets with output ZPF are also read
directly, again with the database loaded first. In each
values row, a single measured composition is a boundary point,
and two measured compositions are the ends of a tie line; a
null marks a phase that was present but not measured. The
dataset's reference becomes the source and its
weight the weight. Since ZPF datasets carry no uncertainties,
the defaults (0.01 and 10 K) apply. Other outputs, such as
HM_FORM and HM_MIX, are refused, as is a dataset
marked disabled, and a phase name that is not in the database
is reported.
Thermo-Calc .EXP (DATAPLOT) is not read and has to be converted
to the columns above.
Exporting and Sharing
-
Figure (PNG) and
Figure (SVG) save the figure as shown on
screen, including the caption.
-
Data (CSV) saves the boundary curves, and
Data (JSON) also saves the invariant
reactions, the phase changes that the engine could not classify, and the
provenance. Both use mole fraction and kelvin, whatever units the axes
show.
-
Download .tdb saves the database with the
changed parameters; all other parameters are copied byte for byte.
-
Save session and
Load session store and restore the
parameters, the set of unlocked parameters, the view, the temperature, and
the experimental data. A session does not include the database, so the
database has to be loaded before the session.
-
Cite gives the citations for GibbScope and its
paper. The databases and experimental data that GibbScope uses are
credited in Acknowledgments below.
The address bar records the current view, so a copied link reproduces it.
Experimental data is not part of the link; a session file stores it.
Keyboard Shortcuts
After clicking a plot or moving to it with Tab, the following keys are
available.
| Key | Action |
|---|
| ↑ ↓ | move the isotherm one slider step (energy panel open) |
| Page Up / Page Down | move it ten steps |
| ← → | move the crosshair along the isotherm by 1 % of the visible range |
| Home / End | move the crosshair to the edge of the window |
| Shift + arrow | pan |
| + / − | zoom about the crosshair, or the center of the window |
| 0 | reset the view |
| Escape | clear the crosshair |
With the energy panel closed, the temperature cannot be changed: the slider
and the isotherm are hidden, and ↑ / ↓ scroll the page.
Thermodynamic Model
Each solution phase φ is a substitutional solution of the two elements,
described by SGTE unary reference energies, a Redlich–Kister excess
term, and the Inden–Hillert–Jarl magnetic term:
Gφ(x,T) = xA °GAφ
+ xB °GBφ
+ RT(xAln xA + xBln xB)
+ xAxB Σν Lνφ(xA−xB)ν
+ Gmagφ(x,T)
A and B are the two elements in alphabetical order, regardless of the
order in which a parameter is written. This order sets the sign of the
odd-order terms and follows the convention of pycalphad and Thermo-Calc. A
line compound has a fixed composition and a single Gibbs energy per formula
unit.
At each temperature, GibbScope constructs the lower convex hull of the G(x)
curves of all phases, each solution phase sampled at 1001 compositions and
refined around common tangents. It scans the temperature range in 200 equal
steps and, wherever the set of stable phases changes within a step, bisects
the step to 0.5 K and reports an invariant reaction. The temperature axis
extends from the bottom of the database's declared range to just above the
highest temperature at which a solid is stable within that range.
A reaction is named after the phase that disappears or forms on cooling and
the two phases on either side of it. L stands for any phase that the
database calls a liquid, and a subscript marks one phase at two
compositions. A reaction is tagged extrapolated when one of its
phases is beyond the temperature range declared for it in the database.
| Name | On cooling |
|---|
| eutectic | L → α + β |
| monotectic | L1 → α + L2 |
| metatectic | β → α + L |
| monotectoid | α1 → α2 + β |
| eutectoid | γ → α + β |
| syntectic | L1 + L2 → α |
| peritectic | L + α → β |
| peritectoid | α + β → γ |
| polymorphic | a compound changes its structure at a fixed composition, between two neighboring phases |
| allotropic | an element changes its structure at the edge of the axis, and neither form dissolves more of the other element than the other form does. Otherwise, the reaction takes one of the names above; e.g., in Ga–Pu, the β → α transformation of plutonium is a peritectoid because only α dissolves gallium |
| other | none of the above, such as a liquid forming on cooling. Such a reaction is often, but not always, an extrapolation, so its tag is worth checking |
Phase Grades
GibbScope grades every phase declared in a database, and a database takes
the grade of its worst phase. The grade appears in the figure caption, in
the fidelity panel, and in the Systems table.
- Modeled in full: every term given in the database is
evaluated.
- Physics dropped: the phase is drawn without a term given in
the database. Since the diagram still looks complete, this grade
deserves the most attention.
- Phase missing: the phase is left off the diagram and so its
field is absent.
A phase is drawn with physics dropped for one of the following reasons.
| Reason | What is missing |
|---|
| associate species | a compound species, such as an associate. The phase is computed as a plain substitutional solution without it |
| unreadable terms | part of the phase's energy, given in a form that the parser does not implement or as a call to a function that the database does not define |
| parameter type | a PARAMETER type that the engine does not implement. At present, this is the third-generation Einstein heat capacity (THETA, LNTHETAn, THETAFn, GD), which carries most of the phase's temperature dependence |
| magnetic setup | magnetic data that cannot be evaluated: a Curie temperature without a MAGNETIC type definition, a third-generation Néel model, or a parameter given twice |
A phase is left off the diagram for one of the following reasons.
| Reason | Why |
|---|
| gas | the engine does not model a gas phase |
| multiple sublattices | the phase requires the compound energy formalism. This includes ordered phases such as B2_BCC and L12_FCC, and the ionic liquid |
| interstitial sublattice | the phase mixes an element with vacancies on a separate sublattice, which two mole fractions cannot describe |
| non-element species | the constituents of the phase are not the two elements, so its composition is not a mole fraction of them |
| no end members | the database does not give the Gibbs energy of the phase at both pure elements |
Phases that the database excludes with REJECT_PHASE are listed
separately. A term that the engine cannot evaluate is always reported and
never treated as zero.
Accuracy and Limitations
The known limitations are as follows.
-
Binary substitutional models only. GibbScope does not
implement the compound energy formalism or order–disorder models,
the ionic liquid, or the gas phase, and phases that need them are left
off the diagram. Associate species and third-generation parameters are
left out, and the phases that have them are drawn with physics dropped.
-
Narrow miscibility gaps. A gap narrower than 0.004 in x
is drawn as one phase. A gap that closes gradually is therefore cut
below its true top, and its critical point is drawn at the cut and
marked “narrowed below” in Data (JSON).
-
Thin fields. A phase field narrower in temperature than
one sweep step can be missed. Tie line ends are accurate to about
6×10−7 in x, and a solubility below about
10−8 reads as 0.
-
Many fields of one phase. The fourth and later fields of
the same phase share one shade and the bare phase name, so a gap between
two of them can look like a gap within a single field.
-
Unnamed changes. When two reactions fall within one
temperature bracket, the engine cannot name them and lists the change as
a warning. This is rare.
-
Fitting is geometric. The misfit is a distance in units
of each point's uncertainty, and
tie_left and
tie_right points are scored in the same way as
boundary points. GibbScope offers neither a driving-force
(ZPF) objective nor uncertainty estimates for the fitted parameters; a
full assessment calls for PARROT or ESPEI.
Acknowledgments
SGTE binary databases
Each file begins with a $ comment block that gives the
reference for the assessment and often the assessor's notes on it, such
as “the hcp interaction could be problematic”. GibbScope shows
these lines in the Database section of the
interface.
Experimental data
The experimental data loaded with four of the preloaded examples are
from the following sources.
-
Cr–Ni: adopted from Tang and Hallstedt
(Calphad 55, 2016), which compiles measurements
from the original studies cited therein.
-
Ag–Cu: liquidus temperatures from Heycock and
Neville (Phil. Trans. R. Soc. A 189,
1897) and from six thermal-analysis studies compiled by
Subramanian and Perepezko
(J. Phase Equilib. 14, 1993), which cites the
original studies; the Ag-rich solidus and solvus from Bienzle et al.
(Mater. Trans. JIM 33, 1992).
-
Fe–Ni: liquidus, solidus, and δ/γ
arrests from Hellawell and Hume-Rothery
(Phil. Trans. R. Soc. A 249, 1957), as
transcribed in
ESPEI-datasets (CC BY 4.0, with the
phase names changed to those of the database),
and solid–liquid tie lines at 1500 °C from Chabot et
al. (Meteorit. Planet. Sci. 52, 2017).
-
Al–Si: adopted from Murray and McAlister
(Bull. Alloy Phase Diagrams 5, 1984), which
compiles measurements from the original studies cited therein.
The header of each data file lists the tables the points were taken
from and the points that were left out.
License
Application code © 2026 Arizona Board of Regents
on behalf of the University of Arizona. Licensed for non-commercial
educational and research use only; commercial use requires a license from
the University — inquiries to
Tech Launch Arizona.
This is a summary; see the full LICENSE in the repository.
The WebAssembly module contains open-source Rust libraries under
permissive licenses, mostly MIT and Apache 2.0. Their notices are in
LICENSES.md.