Solid Phase Transition Temperature Research Articles

Dissolved water in jet fuels: a low-temperature quality and water solubility study

While undesirable, water contamination of jet fuels is unavoidable. It is essential to understand the impacts of dissolved water on the fuel properties and the water-fuel interactions. In this study, the impacts of dissolved water on low-temperature qualities of aviation fuels were determined. The liquid–solid phase transition temperature was found to increase with the jet fuels saturated with dissolved water under increased temperatures owing to the increase of fuel water solubility. The conductor-like screening model for realistic solvation (COSMO-RS) method was employed to predict the water solubility in petroleum and sustainable aviation fuels (PAFs and SAFs) over a temperature range of −40 to 50 °C based on fuel composition data obtained by comprehensive GC × GC chromatography. The calculation results are in good agreement with experimental values at temperatures below 20 °C, with RMSE = 17.1 and 17.7 ppm for PAFs and SAFs, respectively. Results calculated for these complex fuel chemistries predicted experimental values more closely than calculations performed for simpler PAF and SAF surrogates. COSMO-RS was also employed to calculate water solubility in PAF and SAF blends (RMSE = 18.3 ppm). Results demonstrate that the COSMO-RS method has potential as a tool in new SAF certification.

Structural, Thermal, and Electrical Properties of Poly(Ethylene Oxide)-Tetramethyl Succinonitrile Blend for Redox Mediators.

An all-solid–state dye-sensitized solar cell is one of the non-fossil fuel-based electrochemical devices for electricity generation in a high-temperature region. This device utilizes a redox mediator, which is a fast ion-conducting solid polymer electrolyte (SPE). The SPE makes the device economical, thinner, and safer in high-temperature regions. The SPE generally has a form of matrix−plasticizer−redox salts. Succinonitrile (SN) is generally employed as a plasticizer for reducing the crystallinity of poly(ethylene oxide), abbreviated as PEO, a common polymeric matrix. In the present paper, the structural and thermal properties of tetramethyl succinonitrile (TMSN) were compared with SN for its application as a solid plasticizer. TMSN and SN both are plastic crystals. TMSN has four methyl groups by replacing the hydrogen of the SN, resulting in higher molecular weight, solid–solid phase transition temperature, and melting temperature. We thoroughly studied the structural, thermal, and electrical properties of the [(1−x)PEO: xTMSN] blend for utilizing it as a matrix, where x = 0–0.25 in mole fraction. The FT-IR spectra and XRD patterns of the blends exhibited PEO-alike up to x = 0.15 mole and TMSN-alike for x > 0.15 mole. Differential scanning calorimetry revealed formation of a eutectic phase from x = 0.1 mole and phase separation from x = 0.15 mole. The blends with x = 0.1–0.15 mole had a low value of PEO crystallinity. Thermogravimetric analysis showed thermal stability of the blends up to 75 °C. The blends exhibited electrical conductivity, σ25°C more than 10−9 S cm−1, and Arrhenius behavior (activation energy, ~0.8 eV) in a temperature region, 25–50 °C.

Tetramethyl Succinonitrile as a Solid Plasticizer in a Poly(ethylene oxide)8 -LiI-I2 Solid Polymer Electrolyte.

Dye-sensitized solar cell (DSSC) is a promising alternative to the commercially available amorphous silicon-based solar cell because of several advantageous properties. A DSSC with a fast ion conducting solid polymer electrolyte is required for the arid atmosphere of Gulf countries. In this work, a new matrix, poly(ethylene oxide)-tetramethyl succinonitrile blend to synthesize a blend-LiI-I2 solid polymer electrolyte for the DSSC application has been proposed. The tetramethyl succinonitrile is a member of plastic crystal with a solid-solid phase transition temperature (Tpc ) of ≈71°C and melting temperature (Tm ) of ≈170.5°C. Its molar fraction, 0.1-0.15 is sufficient enough for synthesizing a polymer electrolyte with electrical conductivity of >10-4 S cm-1 at room temperature. This electrolyte shows Vogel-Tamman-Fulcher type behavior with a low value (≈0.083eV) of pseudo-activation energy for easy ion transport. The results of Fourier-transform infrared spectroscopy, X-ray diffractometry, and differential scanning calorimetry studies reveal the plasticizing effect of tetramethyl succinonitrile to form an amorphous phase. This electrolyte results in a ≈661% gain in short-circuit current density and thereby a ≈552% gain in the cell efficiency (≈3.5%) with respect to the DSSC prepared with the tetramethyl succinonitrile-free electrolyte.

MOF‐Directed Synthesis of Crystalline Ionic Liquids with Enhanced Proton Conduction

AbstractArranging ionic liquids (ILs) with long‐range order can not only enhance their performance in a desired application, but can also help elucidate the vital between structure and properties. However, this is still a challenge and no example has been reported to date. Herein, we report a feasible strategy to achieve a crystalline IL via coordination self‐assembly based reticular chemistry. IL1MOF, was prepared by designing an IL bridging ligand and then connecting them with metal clusters. IL1MOF has a unique structure, where the IL ligands are arranged on a long‐range ordered framework but have a labile ionic center. This structure enables IL1MOF to break through the typical limitation where the solid ILs have lower proton conductivity than their counterpart bulk ILs. IL1MOF shows 2–4 orders of magnitude higher proton conductivity than its counterpart IL monomer across a wide temperature range. Moreover, by confining the IL within ultramicropores (<1 nm), IL1MOF suppresses the liquid–solid phase transition temperatures to lower than −150 °C, allowing it to function with high conductivity in a subzero temperature range.

Effects of phase transition temperature and preheating on residual stress in multi-pass & multi-layer laser metal deposition

To investigate the influences of phase transition temperature and preheating on the residual stress of multi-layer and multi-pass laser metal deposition (LMD), the multi-layer and multi-pass LMD, with and without preheating, were performed using five kinds of alloy with different phase transition features, and their residual stresses were measured using the hole drilling method. A finite-element (FE) model incorporating the phase transition was developed based on experimentally obtained physical property data. The results demonstrated that the low-temperature solid phase transition has a tensile stress relaxation effect, which leads to the formation of a compressive stress area. This relaxation effect was observed to decrease with the increase of the phase transition temperature. The high-temperature solid phase transition has no significant tensile stress relaxation effect during the multi-layer and multi-pass LMD process, which is different from the single track LMD. when the solid phase transition temperature is low, the preheating can improve the uniformity of the stress field only to a certain extent. However, when the preheating increases the lowest temperature of the thermal cycle and makes it higher than the starting point temperature of the solid phase transition, the tensile stress relaxation effect of the solid phase transition can be brought into full play.

Pentaerythritol with alumina nano additives for thermal energy storage applications

Pentaerythritol is a poly alcohol with high solid–solid phase change enthalpy that makes it suited for thermal energy storage applications. At solid–solid phase transition temperature, pentaerythritol change from body centered tetrahedral molecular structure into a homogeneous face-centered cubic crystalline structure accompanied with the absorption of the hydrogen bond energy. The present work investigates the effect of adding alumina (Al2O3) nanoparticles to pentaerythritol on thermal and chemical stability by performing thermal cycling test. Dispersion stability and aggregation of nanoparticles during thermal cycling were studied with FESEM and EDX analysis. The thermal and chemical stability of pentaerythritol samples added with alumina nanoparticles in the weight proportions 0.1%, 0.5% and 1% were tested using the characterization methods such as TGA, DSC and FTIR. The change in the specific heat and thermal conductivity of pentaerythritol was studied by the T-history method. The experimental results showed good thermal and chemical stability for alumina enhanced pentaerythritol subjected to 100 thermal cycles along with a negligible change in specific heat and thermal conductivity values. Non-isothermal crystallization kinetics of the PE added with alumina nanoparticles were also studied in this experimental work.

Bis-imidazolium iodide organic ionic plastic crystals and their applications to solid state dye-sensitized solar cells

Novel dicationic bis-imidazolium iodide salts have been discovered as new organic ionic plastic crystalline materials. Most of them show multiple solid-solid phase transitions below their melting temperatures. Their phase transition temperatures are dependent on the imidazolium cation structure. According to Timmermans' definition of plastic crystals, bis-imidazolium iodide salts with either n-heptyl or n-octyl side arms can be classified as “true plastic crystals” because of their low ΔSf values (<20 J mol−1 K−1). The bis-imidazolium iodide salts are stable up to 260 °C under thermal gravimetric analysis. The ionic conductivities, investigated using dielectric relaxation spectroscopy, follow the Arrhenius temperature dependence with discontinuities and changes in slopes at the observed solid–solid phase transition temperature. Dye-sensitized solar cells (DSSCs) fabricated by a whole solid-state electrolyte consisting of n-hexyl side-armed bis-imidazolium iodide (BII-6) show a 4.93% power conversion efficiency (η): a remarkable result for the solid-state electrolyte system compared to that obtained using an liquid electrolyte with 1-butyl-3-methylimidazolium iodide (η = 8.00%) as a reference composition.

Confinement Effects for Lithium Borohydride: Comparing Silica and Carbon Scaffolds.

LiBH4 is a promising material for hydrogen storage and as a solid-state electrolyte for Li ion batteries. Confining LiBH4 in porous scaffolds improves its hydrogen desorption kinetics, reversibility, and Li+ conductivity, but little is known about the influence of the chemical nature of the scaffold. Here, quasielastic neutron scattering and calorimetric measurements were used to study support effects for LiBH4 confined in nanoporous silica and carbon scaffolds. Pore radii were varied from 8 Å to 20 nm, with increasing confinement effects observed with decreasing pore size. For similar pore sizes, the confinement effects were more pronounced for silica than for carbon scaffolds. The shift in the solid–solid phase transition temperature is much larger in silica than in carbon scaffolds with similar pore sizes. A LiBH4 layer near the pore walls shows profoundly different phase behavior than crystalline LiBH4. This layer thickness was 1.94 ± 0.13 nm for the silica and 1.41 ± 0.16 nm for the carbon scaffolds. Quasi-elastic neutron scattering confirmed that the fraction of LiBH4 with high hydrogen mobility is larger for the silica than for the carbon nanoscaffold. These results clearly show that in addition to the pore size the chemical nature of the scaffold also plays a significant role in determining the hydrogen mobility and interfacial layer thickness in nanoconfined metal hydrides.

Spectral analysis and clustering of large stochastic networks. Application to the Lennard-Jones-75 cluster

We consider stochastic networks with pairwise transition rates of the form where the temperature T is a small parameter. Such networks arise in physics and chemistry and serve as mathematically tractable models of complex systems. Typically, such networks contain large numbers of states and widely varying pairwise transition rates. We present a methodology for spectral analysis and clustering of such networks that takes advance of the small parameter T and consists of two steps: (1) computing zero-temperature asymptotics for eigenvalues and the collection of quasi-invariant sets, and (2) finite temperature continuation. Step (1) is reducible to a sequence of optimisation problems on graphs. A novel single-sweep algorithm for solving them is introduced. Its mathematical justification is provided. This algorithm is valid for both time-reversible and time-irreversible networks. For time-reversible networks, a finite temperature continuation technique combining lumping and truncation with Rayleigh quotient iteration is developed. The proposed methodology is applied to the network representing the energy landscape of the Lennard-Jones-75 cluster containing 169523 states and 226377 edges. The transition process between its two major funnels is analysed. The corresponding eigenvalue is shown to have a kink at the solid–solid phase transition temperature.

Synthesis and thermal properties of poly(styrene-co-acrylonitrile)-graft-polyethylene glycol copolymers as novel solid–solid phase change materials for thermal energy storage

A novel poly(styrene-co-acrylonitrile)-graft-polyethylene glycol (SAN-g-PEG) copolymer was synthesized as new solid–solid phase change materials (SSPCMs) by grafting PEG to the main chain of poly(styrene-co-acrylonitrile). The chemical structure of the SAN-g-PEG was confirmed by the Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy techniques. The thermal energy storage properties and the storage durability of the SAN-g-PEG were investigated by differential scanning calorimetry (DSC). The SAN-g-PEG was endowed with the solid–solid phase transition temperatures within the range of 23–36 °C and the latent heat enthalpy ranged from 66.8 kJ/kg to 68.3 kJ/kg. Thermal cycling tests revealed that the SAN-g-PEG kept great heat storage durability after 1000 thermal cycles. The thermal stability was evaluated by a thermal gravity analysis (TGA), and the initial decomposition temperature (Td) of SAN-g-PEG is 350 °C, which proves that the SAN-g-PEG possessed good thermal stability.

Confinement effects of graphene oxide nanosheets on liquid–solid phase transition of water

In this work, the liquid–solid phase transition temperature of water confined between two graphene oxide (GO) sheets is investigated using molecular dynamics simulations.

Formation of single-walled bimetallic coinage alloy nanotubes in confined carbon nanotubes: molecular dynamics simulations

The growth of single-walled bimetallic Au-Ag, Au-Cu and Ag-Cu alloy nanotubes (NTs) and nanowires (NWs) in confined carbon nanotubes (CNTs) has been investigated by using the classical molecular dynamics (MD) method. It is found that three kinds of single-walled gold-silver, gold-copper and silver-copper alloy NTs could indeed be formed in confined CNTs at any alloy concentration, whose geometric structures are less sensitive to the alloy concentration. And an extra nearly pure Au (Cu) chain will exist at the center of Au-Ag (Au-Cu and Ag-Cu) NTs when the diameters of the outside CNTs are big enough, thus producing a new type of tube-like alloy NWs. The bonding energy differences between the mono- and hetero-elements of the coinage metal atoms and the quasi-one-dimensional confinement from the CNT play important roles in suppressing effectively the "self-purification" effects, leading to formation of these coinage alloy NTs. In addition, the fluid-solid phase transition temperatures of the bimetallic alloy NTs are found to locate between those of the corresponding pure metal tubes. Finally, the dependences of the radial breathing mode (RBM) frequencies and the tube diameters of the alloy NTs on the alloying concentration were obtained, which will be very helpful for identifying both the alloying concentration and the alloy tube diameters in future experiments.

Fiber-optic threshold temperature sensor

This paper describes the principles of the operation and design of a fiber-optic threshold temperature sensor that is insensitive to the influence of strong electric and magnetic fields and is intended for use in the test-and-measurement apparatus of electric-power systems. The operation of the sensor is based on the change of the light scattering of organic materials close to the liquid–solid phase-transition temperature. The results of calculations of the optical transmission and the experimental development of the sensor are presented.

Synthesis and thermal properties of poly(styrene-co-ally alcohol)-graft-stearic acid copolymers as novel solid–solid PCMs for thermal energy storage

A series of poly(styrene-co-allyalcohol)-graft-stearic acid copolymers were synthesized as novel polymeric solid–solid phase change materials (SSPCMs). The graft copolymerization reactions between poly(styrene-co-allyalcohol) and stearoyl chloride were verified by Fourier transform infrared (FT-IR) and Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy techniques. The crystal morphology of the SSPCMs was investigated using polarized optical microscopy (POM) technique. Thermal energy storage properties of the synthesized SSPCMs were measured using differential scanning calorimetry (DSC) analysis. The POM results showed that the crystalline phase of the copolymers transformed to amorphous phase above their phase transition temperatures. Thermal energy storage properties of the synthesized SSPCMs were investigated by differential scanning calorimetry (DSC) and found that they had typical solid–solid phase transition temperatures in the range of 27–30°C and high latent heat enthalpy between 34 and 74J/g. Especially, the copolymer with the mole ratio of 1/1 (poly(styrene-co-allyalcohol)/stearoyl chloride) is the most attractive one due to the highest latent heat storage capacity among them. The results of DSC and FT-IR analysis indicated that the synthesized SSPCMs had good thermal reliability and chemical stability after 5000 thermal cycles. Thermogravimetric (TG) analysis results suggested that the synthesized SSPCMs had high thermal resistance. In addition, thermal conductivity measurements signified that the synthesized PCMs had higher thermal conductivity compared to that of poly(styrene-co-allyalcohol). The synthesized copolymers as novel SSPCMs have considerable potential for thermal energy storage applications such as solar space heating and cooling in buildings and greenhouses.

Synthesis and thermal properties of polystyrene-graft-PEG copolymers as new kinds of solid–solid phase change materials for thermal energy storage

A series of polystyrene-graft-PEG6000 copolymers were synthesized as new kinds of polymeric solid–solid phase change materials (SSPCMs). The synthesized SSPCMs storage latent heat as the soft segments PEG6000 of the copolymers transform from crystalline phase to amorphous phase and therefore they can keep its solid state during the phase transition processing. The graft copolymerization reaction between polystyrene and PEG was verified by Fourier transform infrared (FT-IR) and 1H NMR spectroscopy techniques. The morphology of the synthesized SSPCMs was characterized by polarization optical microscopy (POM). Thermal energy storage properties, thermal reliability and thermal stability of the synthesized SSPCMs were investigated by differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis methods. The DSC results showed that the synthesized SSPCMs had typical solid–solid phase transition temperatures in the range of 55–58°C and high latent heat enthalpy in the range of 116–174Jg−1. The TG analysis findings showed that the synthesized SSPCMs had high thermal durability above their working temperatures. Also, thermal conductivity measurements indicated that the synthesized PCMs had higher thermal conductivity compared to that of polystyrene. The synthesized polystyrene-graft-PEG6000 copolymers as new kinds of SSPCMs could be used for thermal energy storage.

Confinement-induced structural changes of water studied by Raman scattering

The temperature dependence of water confined in the ordered cylindrical nanopores of MCM-41 and SBA-15 materials is studied by means of Raman scattering for different pore sizes covering a diameter range from 2.0 to 8.9 nm. The liquid--solid phase transition temperature of water in confinement can be determined by the analysis of the mode contribution in the OH-stretching region. For pore sizes down to 3 nm, the freezing/melting point depression with decreasing pore size can be consistently described by a modified Gibbs-Thomson equation, with a nonfreezable water layer of 0.6 nm (about two monolayers) close to the pore walls. When the pore size is 2.5 nm or smaller, indication for a first-order phase transition can no longer be found that is in agreement with previously reported differential scanning calorimetry measurements on the same samples. The Raman data further suggest that two spatially separated water phases exist in the smallest pores, i.e., the nonfreezable wall layer and a structurally different water phase in the core of the pores. A distinct tetrahedral hydrogen-bonded network of water molecules is found only in the core part of the pores. In the weakest confinement (8.9-nm pore diameter), the core water is shown to be compatible with crystalline ice with a spectral fingerprint similar to bulk ice. In strong confinement (2.0-nm pore diameter), the core water shows a spectral fingerprint identical to low-density amorphous ice, and there is a gradual transition between these two extremes. These findings suggest that the core part of confined water undergoes considerable structural changes with decreasing pore size, leading us to question recent proposals that aim to extract information about the state of bulk liquid water in the ``no man's land'' from water in confinement.

Phase behaviour of 1-butyl-1-methylpyrrolidinium thiocyanate ionic liquid

The phase diagrams for the binary systems of {1-butyl-1-methylpyrrolidinium thiocyanate [BMPYR][SCN] + an alcohol (1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, 1-undecanol, 1-dodecanol), or + water, or + aliphatic hydrocarbons ( n-hexane, n-heptane, n-octane), or + cyclohexane, or + cycloheptane, or + aromatic hydrocarbons (benzene, toluene, ethylbenzene)} have been determined at atmospheric pressure using a dynamic method. The basic thermal properties of pure ILs, i.e. melting temperature and the enthalpy of fusion, the solid–solid phase transition temperature and enthalpy have been measured using a differential scanning microcalorimetry technique. The decomposition of [BMPYR][SCN] was detected. The density and viscosity of the IL at 298.15 K were measured. (Solid + liquid) phase equilibrium diagrams with complete miscibility in the liquid phase region were observed for the systems involving alcohols and water. A decrease in the solubility of [BMPYR][SCN] in alcohols was observed with an increase of the alkyl chain length of an alcohol. (Solid + liquid) phase equilibrium diagrams with immiscibility in the liquid phase region were observed for the systems involving hydrocarbons. As for all ionic liquids (ILs) solubility decreases with an increase of number of carbon atoms in n-alkanes, cyclohydrocarbons, or of substituents at the benzene ring. The correlation of the experimental data has been carried out using the NRTL equation. The data presented here have been compared to the systems published earlier for the thiocyanate based ILs and for ILs with 1-butyl-1-methylpyrrolidinium cation. The influence of the cation and anion on the phase behaviour has been discussed.

Physico-chemical properties and phase behaviour of piperidinium-based ionic liquids

The sufficient review of the existing literature of the 1-alkyl-1-methylppiperidinium-based ionic liquids has been presented. The phase diagrams for the binary systems of {1-butyl-1-methylpiperidinium thiocyanate [BMPIP][SCN] + an alcohol (1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, 1-dodecanol), or + water, or + aliphatic hydrocarbons ( n-hexane, n-heptane, n-octane), or + cyclohexane, or, + cycloheptane, or + aromatic hydrocarbons (benzene, toluene, ethylbenzene)} and for the binary systems of {1-ethyl-1-methylpiperidinium bis{(trifluoromethyl)sulfonyl}imide [EMPIP][NTf 2] + an alcohol (ethanol, 1-propanol, 1-butanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol), or + water} have been determined at atmospheric pressure using a dynamic method. The influence of an alcohol chain length was discussed for these ionic liquids. A systematic decrease in the solubility was observed with an increase of the alkyl chain length of an alcohol. (Solid + liquid) phase equilibria with complete miscibility in the liquid phase region were observed for the systems involving water and the alcohols for the thiocyanate-based ionic liquid. Opposite, the bis{(trifluoromethyl)sulfonyl}imide-based ionic liquid reveal the immiscibility gap in the liquid phase. The correlation of the experimental data has been carried out using the NRTL equation. The phase diagrams reported here have been compared to the systems published earlier with the 1-alkyl-1-methylpiperidinium-based ionic liquids. The influence of the cation and anion on the phase behaviour has been discussed. The basic thermal properties of pure ILs, i.e. melting temperature and the enthalpy of fusion, the solid–solid phase transition temperature and enthalpy have been measured using a differential scanning microcalorimetry technique.

Experimental solid–liquid phase equilibria of {cholesterol + binary solvent mixture: 1-Alcohol (C 4–C 10) + cyclohexane}

Solid–liquid phase diagrams (SLE) have been determined for {cholesterol + 1-alcohol (1-heptanol, 1-octanol, 1-nonanol, 1-decanol}, or binary solvent mixture {1-alcohol (1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol) + cyclohexane} using a dynamic method at ambient pressure. Simple eutectic systems with complete miscibility in the liquid phase were observed. The solubility increases with an increase in the number of carbon atoms in the 1-alcohol chain length. The temperature of the eutectic points shifts to the lower cholesterol mole fractions as the alkyl chain length of the 1-alcohol decreases. The higher cross-intermolecular interaction was observed for the longer length of an alcohol, especially with 1-decanol. The solubility data in 1-alcohols were compared with values calculated by means of the Wilson, UNIQUAC and UNIQUAC ASM equations utilizing parameters derived from the SLE results. The existence of a solid–solid first order phase transition in cholesterol has been taken into consideration in calculations. The average root–mean–square deviation for the correlation of the solubility data in alcohols and cyclohexane has been on the level of σ T = 2.8 K. Solid–liquid equilibria, for the ternary systems (cholesterol + binary solvent) have been discussed as a function of the mole fraction of a second named component in the solute-free mixed solvent ( x C 0 ). The experimental results have shown the influence of the solvent or binary solvent mixture on the temperature of the solid–solid phase transition ( T tr). The addition of cyclohexane to the binary solvent mixture causes in general an increasing the solid–solid phase transition temperature of the cholesterol. The synergistic effect of solubility was observed in binary solvent mixtures with maximum at x C 0 = 0.6 – 0.8 . Isotherms reveal decreasing effect of the enhanced solubility with an increase in temperature. SLE curves for two ternary systems were correlated with the Wilson model as an example.

The Ternary System (n-Heptane + Docosane + Tetracosane): The Solubility of Mixtures of Docosane and Tetracosane in Heptane and Data on Solid−Liquid and Solid−Solid Equilibria in the Binary Subsystem (Docosane + Tetracosane)

In this paper experimental data on the solid−liquid and solid−solid equilibria in the binary system (docosane + tetracosane) and solid solubility data in the ternary system (heptane + docosane + tetracosane) are presented. For 14 binary mixtures of the two heavy alkanes, DSC measurements were performed to detect the solid−liquid and solid−solid phase transition temperatures. Solid disappearance temperatures were measured for 14 mixtures of docosane and tetracosane dissolved in various quantities of heptane. The experimental results reveal that the solubility curves found in the ternary system correspond to the phase behavior of the binary subsystem studied. At low concentrations of heptane, probably almost ideally mixed crystals are in equilibrium with the liquid phase, while at high heptane concentrations, the solid−liquid equilibrium involves most likely different nonideal solid phases.