Ternary compositions and tie-triangle accounting
Three-component compositions occupy a normalized triangle: x_A+x_B+x_C=1 with nonnegative fractions.
Key knowledge
Three-component compositions occupy a normalized triangle: x_A+x_B+x_C=1 with nonnegative fractions. In a three-phase equilibrium, the bulk composition is x₀=f₁x₁+f₂x₂+f₃x₃ with f₁+f₂+f₃=1. Nonnegative phase fractions express the bulk point as barycentric coordinates of the tie triangle. Two-phase mixtures lie on their tie line.
Values and equations
x_A+x_B+x_C=1; x₀=Σᵢfᵢxᵢ; Σᵢfᵢ=1; fᵢ≥0
- x₀,xᵢ
- bulk and equilibrium phase three-component composition vectors 1
- fᵢ
- phase fraction on the matching basis 1
Conditions and scope
- All vectors and phase fractions use one matching mass or component-mole basis at the same temperature and pressure; the tie triangle must have independent vertices for a unique three-phase solution.
- A liquidus projection shows primary crystallization fields and boundary paths but omits a full temperature dimension. Additional components, reactions, fractionation or projected compositions can require different accounting.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read actual three-component/eutectic, boundary-curve and lever-balance body. The barycentric vector equation is explicitly derived from the source's component conservation and lever construction; no contradictory source-example temperatures or full petrological pseudosection claim.
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Entry details
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- uni-earth-ternary-phase-accounting
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- core.1
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- University core expansion