Phase relations within mixtures of n-paraffins have such principal significance as toreveal the crystallochemical nature of hydrocarbonminerals. Phase equilibrium diagrams of three binaryparaffin systems C21H44-C23H48 C19H40-C21H44 andC17H36-C19H40 were plotted by results of themo-X-raystudy of phase transitions of these components andtheir mixtures with various molar ratios (by 10-15variants of composition for each system). The thermo-X-ray method application has allowed for the firsttime to take at these diagrams into account fivecondensed phase states of n-paraffins: orthorhombiccrystalline (Orcrysi), low temperature orthorhombicrotator-crystalline (Orrot.i), intermediateorthorhombic rotator-crystalline (Orroi.l+2), hightemperature hexagonal rotator-crystalline (Hrot.2) andliquid (L). Such a result could not be obtained by theusage of only conventional methods of physicalchemistry analysis. Components C17H36 and C19H40 arein the Orrot.l state even at room tempereture. Thepolymor- phic transition Orrot.l→ Hrot.2 is onlyobserved for the homolog C23H48. Because of thesereasons, at the C21H44- C23H48 diagram five single-phase fields are distinguishible pratically for allthe studied compositions (except only one); at theC19H40-C21H44 diasram these fields are typical onlyfor a part of the compositions, and at the C17H36-C19H40 diagram only four phase fields appear but notfor all the compositions. Every one among the detectedstates is characterized by its own form of the thermalmovement of chain moleculae within crystals of n-paraffins as typical representatives of the rotatorsubstance. Individual features of studied diagrams aredetermined by the length and phase state of the rotator homolog-components.
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