Endothermic Phase Transition Research Articles

Ferric oxide/ammonium nitrate nanocomposite: novel catalyzed eco-friendly oxidizer with advanced decomposition kinetics

ABSTRACT Ammonium nitrate (AN) could serve as a green substitute for ammonium perchlorate (AP) in halogen-free oxidizers. However, AN faces issues with endothermic phase transitions, melting, and sublimation. Ferric oxide, a common catalyst for solid propellants, was used to catalyze AN. This study reports the synthesis of 5 nm colloidal ferric oxide particles, integrated into the AN matrix through co-precipitation. Energy dispersive analysis by X-rays (EDAX) confirmed the proper dispersion of the ferric oxide catalyst. The impact of ferric oxide on AN decomposition enthalpy was assessed using differential scanning calorimetry DSC. Virgin AN showed an endothermic decomposition enthalpy of +1708 J/g, while catalyzed AN showed exothermic decomposition of −732 J/g. Ferric oxide nanocatalyst offered a decrease in AN main decomposition temperature by 83°C using thermogravimetric analysis (TGA). Activation energy dropped significantly, from 87.3 to 16.8 KJ/mol (Kissinger model), due to ferric oxide’s catalytic effect involving ferric and ferrous ion reactions.

Customized Green Energetic Tetra(Imidazole)Copper(II) Nitrate (Cu-Im) Complex/Ammonium Nitrate Co-crystal: A Novel Reactive Halogen-Free Oxidizer with Superior Stability and Decomposition Kinetics

AbstractAmmonium nitrate (AN) is the most promising affordable green oxidizer for solid propellants; however, its endothermic phase transitions and endothermic decomposition restrict its applications. This work shaded the light on multifunctional energetic complex tetra(imidazole)copper (II) nitrate (Cu-Im) with combustion enthalpy of 15.57 KJ/g as a high energy dense material, phase stabilizer, and catalyst for AN-based propellant. The Cu-Im complex was synthesized via a green simple solvent-free melt-assisting technique. As-synthesized Cu-Im complex demonstrated a highly pure crystalline structure with thermal stability up to 200 °C. Cu-Im complex was integrated into AN via an evaporative crystallization technique. The phase transitions and the thermal behavior of the developed Cu-Im complex/AN cocrystal were investigated via DSC and TGA. The Cu-Im complex stabilized the phase transition of AN up to 88.48 °C via an evolved strong hydrogen bonding system within the Cu-Im complex/AN cocrystal. Moreover, the energetic Cu-Im complex offered a significant decrease in the endothermic phase transition peaks associated with IV↔II, and II↔I by 38.81%, and 25.28% respectively. Additionally, AN strong endothermic melting was decreased by 45.32%. The Cu-Im complex converts the AN endothermic thermal decomposition peak with + 1400 J/g into an intensive exothermic peak with the release of -2241 J/g. The Cu-Im complex exhibited a superior catalytic effect via the decrease in AN decomposition temperature by 48.85 °C. Cu-Im complex offered a remarkable reduction in apparent activation energy of AN decomposition by 56.24% and 48.12% via Kissinger’s model and integral iso-conversional nonlinear Vyazovkin method (VYA) respectively. The superior catalytic performance of the Cu-Im complex was attributed to the evolution of CuO nanoparticles during its decomposition. The electron-deficient Lewis acid copper ions have a large affinity to electron lone pair of nitrogen; this effect could support the conversion of NH3 to N2 and H2. This catalytic action could boost the decomposition enthalpy of AN. Consequently, the developed Cu-Im/AN cocrystal could be considered a potential green substitute for perchlorate-based oxidizers.

Local thermal non-equilibrium effects on phase transition of fiber reinforced thermoplastic composites with temperature-dependent heat generation

Under the excitation of external fields, fiber reinforced thermoplastic (FRTP) composites can be thermally processed due to the internal heat generation, in which the local thermal non-equilibrium (LTNE) can be significant during the phase transition. In this study, a representative elementary volume scale Lattice Boltzmann model was developed to simulate the phase transition process of FRTP composites with the temperature-dependent internal heat source. The results from LTNE model and local thermal equilibrium (LTE) model were compared in terms of the phase interface evolution and the local temperature difference between fibers and matrix, so that the LTNE effects on phase transition behaviors were examined with different material properties and internal heat sources. It is found that the LTNE effects cannot be ignored in FRTP composites, and the main mechanisms include the dynamic local heat generation, endothermic phase transition of matrix, and relatively high thermal conductivity of fiber. A small heat exchange between the fibers and matrix results in a large local temperature difference and a slow phase transition. A high internal heat generation enhances the phase transition and LTNE effects, but an increase in the temperature range for heat generation leads to a slow phase transition with slight change in LTNE effects. With the increase of matrix fraction, LTNE effects first increase and then decrease due to the combined results of the more internal heat generation and the increase of endothermic mass of matrix and the less heat loss through fibers. This study is significant for guiding the reliable thermal processing of FRTP composites in emerging industrial applications.

Regulatable endothermic behavior of one-chain-tethered sliding graft copolymers as novel solid-solid phase change materials

Sliding graft copolymer (SGC) is a polyrotaxane (PR) composed of a poly(ethyelene glycol) (PEG) axle and α-cyclodextrins (α-CDs) substituted with polymer graft-chains. We have previously reported a sharp-endothermic phase transition of SGCs, which was expected due to the high mobility of graft chains by the mechanical linkage of PRs. To examine this hypothesis, SGCs with well-defined structures were prepared. PRs consisting of monoazidated α-CD and PEG were grafted with monomethoxy poly(ethylene glycos)s (mPEGs) via click chemistry. The SGC bearing shortest graft chains (mPEG750) did not exhibit endotherm, whereas those with side chains of mPEG2000 and mPEG4000 underwent endothermic phase transition. However, values of the transition temperatures and those of melting enthalpies were lower than those of unmodified mPEGs. Unlike our previous report, the SGCs synthesized here contained densely-packed α-CDs, which were capable of rotational movement but not translational movement. The endothermic peak observed for the present SGC is relatively broader than that observed for our previous SGC, which suggests that the mobility of α-CDs were critical to induce sharp-endothermic phase transition.

Phase Transitions in Boron Carbide.

The idealized rhombohedral unit cell of boron carbide is formed by a 12-atom icosahedron and a 3-atom linear chain. Phase transitions are second order and caused by the exchange of B and C sites or by vacancies in the structure. Nevertheless, the impact of such minimal structural changes on the properties can be significant. As the X-ray scattering cross sections of B and C isotopes are very similar, the capability of X-ray fine structure investigation is substantially restricted. Phonon spectroscopy helps close this gap as the frequency and strength of phonons sensitively depend on the bonding force and mass of the vibrating atoms concerned. Phase transitions known to date have been identified due to significant changes of properties: (1) The phase transition near the chemical composition B8C by clear change of the electronic structure; (2) the endothermic temperature-dependent phase transition at 712 K according to the change of specific heat; (3) the high-pressure phase transition at 33.2 GPa by the drastic change of optical appearance from opacity to transparency. These phase transitions affect IR- and Raman-active phonons and other solid-state properties. The phase transitions at B~8C and 712 K mean that a well-defined distorted structure is converted into another one. In the high-pressure phase transition, an apparently well-defined distorted structure changes into a highly ordered one. In all these cases, the distribution of polar C atoms in the icosahedra plays a crucial role.

2D stress rotation in the Tonga subduction region

Despite their enigmatic origins, deep earthquakes provide unique information about the stress distribution in slabs. Down-dip compression is expected at depth, due to resistance from endothermic phase transition near 660 km and increasing viscosity. Focal mechanisms for ordinary deep (620-680 km) earthquakes in the Tonga subduction zone exhibit down-dip compressional stresses in agreement with this expectation, but unusually deep (≥ 680 km) earthquakes exhibit vertical tension and horizontal compression. Here we present a numerical modelling study of the Tonga slab focused on stress patterns in the transition zone. The subducting Pacific plate is one of the oldest and thus coldest plates in the world, so our parametric study tests the effects of rheology and phase transitions on stress evolution for an exceptionally cold subducting plate. Our results suggest that direct buoyancy effects from the endothermic phase transition at 660 km depth are overprinted by bending-related forces. A stress pattern best fitting seismogenic stresses is found for the coldest tested subducting plate (150 Myr old) and a viscosity interface decoupled from the 660-km phase transition and shifted to 1000-km depth. An abrupt change of stress orientations is observed when the slab, temporarily deflected by the phase transition, penetrates to the shallow lower mantle and the fold of the flat-lying part is tightening.

Preparation and characterization of graphene antibacterial phase change energy storage viscose fibers

In this work, viscose fiber with antibacterial and phase change energy storage was made by microcapsule technology and wet spinning. Graphene oxide was used to enhance the thermal conductivity and antimicrobial properties. The heat preservation performance of graphene antibacterial phase change energy storage viscose fiber was determined by flat type fabric temperature protector and differential scanning calorimetry. The result of heat preservation test shows that the fiber has a good heat preservation property The antibacterial property, far-infrared property, mechanical properties, and the structures were also characterized. The enthalpy of exothermic & endothermic phase transition reached about 10 mJ/mg. According to the result of antibacterial test, the fiber had good antibacterial properties. The distribution of phase change microcapsules and graphene in fibers was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The strength and elongation of antibacterial phase change viscose fiber were found suitable for underwear garments fabrics and filling storage sheet. Combined with the electron microscope photograph and strength test results, the addition of graphene and phase change microcapsules has little effect on the mechanical properties of fibers, and can be used for industrial production.

Hybrid Rendering for Interactive Visualization of Mantle Convection.

In this article, we describe our system for visualizing convection in the Earth's mantle using hybrid rendering-a combination of interactive raytracing, raycasting, and conventional rasterization graphics. The dataset for the SciVis 2021 contest includes a velocity vector field and multiple scalar fields, such as temperature and thermal conductivity anomalies, which we display using isosurface raycasting, streamlines, and line integral convolution, among other techniques. We demonstrate how these methods can be used to explore the dataset, identify slabs, plumes, and stagnations, and detect the influence of 660-km depth endothermic phase transition and mid-mantle spin transition on the mantle dynamics.

Bioengineering of green-synthesized TAT peptide-functionalized silver nanoparticles for apoptotic cell-death mediated therapy of breast adenocarcinoma

Green synthesized silver-nanomaterial has exhibited significant advantages as cancer therapeutics due to their exclusive characteristics that cause inducing various forms of cell death; particularly, they have attracted much attention in the treatment of breast cancer. More specifically, the exploration of silver nanoparticles (SNPs) in investigation of cancer treatment is of booming interest due to the opportunity to customize the physicochemical properties of NPs, to enhance their biocompatibility and interactive potentials through surface functionalization. In the present study, first SNPs were fabricated from Staphylococcus aureus cell-free extract, and then the surface modification was executed by conjugating trans-activator of transcription (TAT) peptide, which is a cell-penetrating peptide to enhance the induction of apoptosis in the breast adenocarcinoma cells. The physicochemical characteristics of both virgin SNPs and TAT peptide conjugated SNPs (cSNPs) were evaluated using UV–vis spectrophotometer, FTIR, SEM-EDX, TGA, DSC, and TEM. FTIR analysis revealed the involvement of amide and amines in SNPs synthesis. The SEM analysis confirmed the spherical shape of SNPs, while EDX showed the elemental nature of silver. TGA determined the protein loss at second weight loss of nearly 45%, and DSC confirmed the endothermic phase transition of both SNPs and cSNPs. Moreover, TEM revealed the particle size of about 26.94 nm and 21.94 nm for SNPs and cSNPs, respectively. In regard to the cancer therapeutic potentials of NPs, the cSNPs exhibited potential cytotoxic activity of IC50 (30.05 μg/mL) against MDA-MB-231 breast cancer cells compared to SNPs that induced apoptosis by enhancing the upregulation of p53 protein expression. Internment flow cytometry data confirmed the productions of ROS radicals in the treated cells of the MDA-MB-231 cells. Overall, our study shows that the surface functionalization of SNPs by employing potential inhouse human-derived peptides could be a new and promising approach in cancer therapy.

Effects of Solar Drying on the Structural and Thermodynamic Characteristics of Bee Pollen

Background: Bee pollen is a natural product collected and transformed by bees, intended for human consumption, given its nutritional and bioactive richness. The fundamental operation of adequacy is drying, which allows its preservation, avoiding chemical or microbiological degradation, typically using tray dryers with hot air that use electricity or fuel for heat generation. Solar drying is an alternative that uses radiation as an energy source. However, it should be ensured that this type of process guarantees the quality of the product while not degrading its properties and, therefore, maintaining its morphological integrity. Objective: to establish the effect of solar drying on bee pollen structure compared to the conventional cabin dehydration process. Methods: Bee pollen was dehydrated using two types of dryers: a solar dryer and a forced convection oven. The solar dryer operating conditions were an average temperature of 19-35 °C with a maximum of 38 °C and average relative humidity (RH) of 55 %. Cabin dryer operating conditions were a set point temperature of 55 ± 2 °C and 10 % RH average humidity. The morphologic and thermodynamic properties of dried bee pollen, such as phase transition enthalpy through Differential Scanning Calorimetry (DSC), porosity and surface area through surface area analysis, and microscopic surface appearance by Scanning Electron Microscopy (SEM), were measured. Results: The results showed dry bee pollen, both in the cabin dryer and solar dryer, did not suffer morphological changes seen through SEM compared to fresh bee pollen. Moreover, surface area analysis indicated the absence of porosity in the microscopic or macroscopic structure, demonstrating that solar or cabin drying processes did not affect the specific surface area concerning fresh bee pollen. Additionally, Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA) showed that endothermic phase transitions for dried bee pollen by cabin or solar dryer were at 145 °C and 160 °C, respectively. This can be mostly associated with free water loss due to the morphological structure preservation of the material compared to fresh bee pollen. Conclusion: These results demonstrate that solar drying is a reliable alternative to bee pollen dehydration as there were no effects that compromised its structural integrity.

Experimental and computational studies on transition metals interaction with Leucine and Isoleucine

In this study, we reported the leucine and isoleucine based metal complexes with Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II). The complexes were synthesized in an aqueous medium followed by characterization with various experimental techniques. Besides experimental investigation, the density functional theory (DFT) calculation is performed which confirms a square planar structure for the Co, Ni and Cu complexes whereas Zn, Cd and Hg complexes adopt the distorted tetrahedral structure. The stability of the complexes is ensured by some calculated thermodynamic parameters. In addition, the elemental and thermos-gravimetric study are also conducted. Metal chelating affects the frontier molecular orbital energies of the ligand and reduces the HOMO-LUMO gap. The complexes are more reactive than the parent ligand. The FT-IR, UV-Visible and NMR spectral analysis of the complexes are reported. The experimental FT-IR and the electronic absorption properties agree with the calculated values. The presence of the characteristic metal-ligand charge transfer and d-d transitions in the complexes is confirmed through photo-excitation study. The UV-Visible reflectance spectral analysis indicates good conducting behavior of the complexes. The differential scanning calorimetry (DSC) analysis shows that the complexes undergo endothermic phase transition. The magnetic moment value agrees with the paramagnetic behavior of Co, Ni and Cu complexes but diamagnetic behavior of Zn, Cd and Hg complexes.

Facile Synthesis and Catalytic Activity Assessment of Copper Chromite Nanoparticles for Ammonium Perchlorate Decomposition

The universal burning rate modifier used in composite solid propellants is copper chromite. The fabrication of copper chromite nanoparticles (CCNs) is highly appreciated; as superior performance could be accomplished. This research looks at how copper chromite nanoparticles can be made in a sustainable way using hydrothermal processing. Mono-dispersed particles with a medium particle size of 12 nm were seen in TEM micrographs. The XRD diffractogram revealed a crystalline structure. The co-precipitation approach was used to incorporate CCNs into ammonium perchlorate (AP). Differential scanning calorimetry (DSC) and thermal gravimetric analysis were used to analyze the activity of catalysis in CCNs on AP breakdown (TGA). The enthalpy of AP breakdown was enhanced from 742 J/g to 1391 J/g. CCNs caused the Peak of high-temperature decomposition shift toward lower temperatures, resulting in the overlapping of the two peaks into a single peak. At 244 °C, CCNs showed a decrease in AP endothermic phase transition. These characteristics could ensure high-burning-rate catalyzed decomposition processes.

An entropy method for geodynamic modelling of phase transitions: capturing sharp and broad transitions in a multiphase assemblage

SUMMARY Phase transitions play an important role for the style of mantle convection. While observations and theory agree that a substantial fraction of subducted slabs and rising plumes can move through the whole mantle at present day conditions, this behaviour may have been different throughout Earth’s history. Higher temperatures, such as in the early Earth, cause different phase transitions to be dominant, and also reduce mantle viscosity, favouring a more layered style of convection induced by phase transitions. A period of layered mantle convection in Earth’s past would have significant implications for the secular evolution of the mantle temperature and the mixing of mantle heterogeneities. The transition from layered to whole mantle convection could lead to a period of mantle avalanches associated with a dramatic increase in magmatic activity. Consequently, it is important to accurately model the influence of phase transitions on mantle convection. However, existing numerical methods generally preclude modelling phase transitions that are only present in a particular range of pressures, temperatures or compositions, and they impose an artificial lower limit on the thickness of phase transitions. To overcome these limitations, we have developed a new numerical method that solves the energy equation for entropy instead of temperature. This technique allows for robust coupling between thermodynamic and geodynamic models and makes it possible to model realistically sharp phase transitions with a wide range of properties and dynamic effects on mantle processes. We demonstrate the utility of our method by applying it in regional and global convection models, investigating the effect of individual phase transitions in the Earth’s mantle with regard to their potential for layering flow. We find that the thickness of the phase transition has a bigger influence on the style of convection than previously thought: with all other parameters being the same, a thin phase transition can induce fully layered convection where a broad phase transition would lead to whole-mantle convection. Our application of the method to convection in the early Earth illustrates that endothermic phase transitions may have induced layering for higher mantle temperatures in the Earth’s past.

Critical Conditions for the Ignition of a Gel Fuel under Different Heating Schemes

A model was developed to research the critical conditions and time characteristics of the ignition of gel fuels in the course of conductive, convective, radiant and mixed heat transfer. MATLAB was used for numerical modeling. Original MATLAB code was established pursuant to the developed mathematical model. For gel fuel ignition at initial temperatures corresponding to cryogenic storage conditions with different heating schemes, a numerical analysis of interconnected processes of heat and mass transfer in the chemical reaction conditions and exothermic and endothermic phase transitions was conducted. The model was tested by comparing the theoretical results with the experimental data. Dependencies were established between the key process characteristic (i.e., the ignition delay time) and the ambient temperature when the following parameters were varied: emissivity, heat emission coefficient, activation energy and pre-exponential factor of the fuel vapor oxidation reaction. The critical values of the main parameters of the energy source were determined. For these values, gel fuel ignition conditions were consistently realized for each heating scheme. The critical heat fluxes necessary and sufficient for the ignition of typical gel fuels were determined.

Ammonium Percholorate/HMX Co-crystal: Bespoke Energetic Materials with Tailored Decomposition Kinetics via Dual Catalytic Effect

ABSTRACT Ammonium perchlorate (AP)/HMX co-crystal with dual catalytic effect was developed. Proper integration of AP particles into the HMX matrix was verified with the evolution of novel crystalline structure. AP/HMX co-crystal demonstrated an increase in HMX decomposition enthalpy by + 57.5%. HMX demonstrated activation energy of 343.2 and 354.4 kJ/mol using Kissinger and KAS models, respectively. AP/HMX co-crystal demonstrated a decrease in HMX activation energy by −75% and −76%, correspondingly. AP could act as an active point with the release of reactive gases that could boost HMX decomposition. HMX experienced a catalytic effect with the disappearance of AP endothermic phase transition.

Controllable Frontal Polymerization and Spontaneous Patterning Enabled by Phase-Changing Particles.

Frontal polymerization provides a rapid, economic, and environmentally friendly methodology to manufacture thermoset polymers and composites. Despite its efficiency and reduced environmental impact, the manufacturing method is underutilized due to the limited fundamental understanding of its dynamic control. This work reports the control and patterning of the front propagation in a dicyclopentadiene resin by immersion of phase-changing polycaprolactone particles. Predictive and designed patterning is enabled by multiphysical numerical analyses, which reveal that the interplay between endothermic phase transition, exothermic chemical reaction, and heat exchange govern the temperature, velocity, and propagation path of the front via two different interaction regimes. To pattern the front, one can vary the size and spacing between the particles and increase the number of propagating fronts, resulting in tunable physical patterns formed due to front separation and merging near the particles. Both single- and double-frontal polymerization experiments in an open mold are performed. The results confirm the front-particle interaction mechanisms and the shapes of the patterns explored numerically. The present study offers a fundamental understanding of frontal polymerization in the presence of heat-absorbing second-phase materials and proposes a potential one-step manufacturing method for precisely patterned polymeric and composite materials without masks, molds, or printers.

Structures of a Phosphoryl Derivative of 4-Allyl-2,4-dihydro-3H-1,2,4-triazole-3-thione: An Illustrative Example of Conformational Polymorphism

Two polymorphic forms of a conformationally flexible molecule, 5-[(Diphenylphosphoryl)methyl]-4-(prop-2-en-1-yl)-2,4-dihydro-3H-1,2,4-triazole-3-thione, were obtained by crystallization and characterized by X-ray diffraction analysis and differential scanning calorimetry. The relative stability of polymorphic forms was estimated with DFT calculations of crystal structures and isolated molecules. It turns out, that in the first more dense polymorph with higher cohesion energy and crystal lattice energy, the molecule adopts an energetically unfavorable conformation, and forms dimers with lower H-bond strength, as compared to the second polymorph. On the other hand, in the second polymorph, the molecule adopts almost the lowest-energy conformation and forms infinite chains via strong H-bonds. The first form that seems to be more thermodynamically stable at room temperature transforms into the second form via two endothermic phase transitions; the apparent irreversibility of the transition is due to high energy difference between the molecular conformations in crystals.

Preparation and characterization of phase-change energy storage nonwoven fabric

In this work, a phase-change energy storage nonwoven fabric was made of polyurethane phase-change material (PUPCM) by a non-woven melt-blown machine. Polyethylene glycol 2000 was used as the phase transition unit and diphenyl-methane-diisocyanate as the hard segment to prepare PUPCM. Thermal stability of the PUPCM was evaluated through thermal stability analysis. The performance of pristine PUPCM was determined by Fourier transform infrared spectroscopy and differential scanning calorimetry to analyze the spinning technology of spinning temperature and the stretching process. Phase-change energy storage nonwoven fabric (413.22 g/m2) was prepared, and the morphology, solid–solid exothermic phase transition, mechanical properties, and the structures were characterized. The enthalpy of solid–solid exothermic phase transition reached 60.17 mJ/mg (peaked at 23.14°C). The enthalpy of solid–solid endothermic phase transition reached 67.09 mJ/mg (peaked at 34.34°C). The strength and elongation of phase-change energy storage nonwoven fabric were found suitable for garments and tent fabrics.

Теплофизические характеристики теплозащитного материала корпуса ракетного двигателя при температурах до 1000 оС

An experimental determination of the temperature dependences of the specific heat capacity and the thermal conductivity coefficient of the multifunctional coating MFP-92 at temperatures up to 1000 °C has been carried out. At temperatures up to 450 °C, an IT-c-400 device was used to determine the specific heat capacity. IT-l-400 device was used for the determination of thermal conductivity. At higher temperatures, the determination of the thermophysical characteristics (TPC) was carried out by solving the inverse problem of thermal conductivity (IPT) in a flat plate under conditions of one-sided heating in a muffle furnace. Composite material MFP-92 is a multilayer structure with upper layers based on silica fabric and chromophosphate binder and lower layers based on mullite-silica fabric and aluminosilicate binder. The TPC of the layers also differ from each other, and, accordingly, the properties of this material as a whole can be determined only in the form of their effective values, averaged in one way or another over the thickness of the coating. In addition, during heating, the material undergoes significant physicochemical transformations associated with the thermal destruction of its components, manifested in the form of abundant gas release, and a decrease in the density of the material, which significantly changes its TPC and determines its dependence on the heating rate. Therefore, studies of the thermophysical characteristics of the MFP-92 material were carried out with several (2-5) consecutive heating cycles. It was found that in four heating cycles of the MFP-92 material up to 450 °C for 75 minutes when measuring the specific heat on the IT-c-400 device, its temperature dependence significantly changes qualitatively and quantitatively. With furnace heating to 1000 °C, the temperature dependences of the TPC of the material, determined in the first and second heating cycles, have a different form, but change insignificantly in subsequent heating cycles. This makes it possible to ascribe to the MFP-92 material a set of two sets of TPC related to its initial (phase A) and annealed after heating to 1000 °C (phase B) states. Using the obtained TPС of phase A (including the magnitude of the thermal effect of irreversible endothermic phase transition at 100 °C) and phase B, good agreement was obtained between the calculated and experimental temperature fields in the samples under furnace heating conditions.

Microencapsulation of Thermochromic Material by Silicon Oxide Nanoparticles

This study is mainly focused on the fabrication of SiO2 as an inorganic shell material encapsulated an organic thermochromic (TC) core material comprises of either the (i) three-component as-synthesized blue dyes [BDTCM@SiO2] or (ii) off-the-shelf (commercial) black dyes [CDTCM@SiO2]. Both the SiO2 encapsulated thermochromic systems have successfully demonstrated the color transition at around 31 °C. For the three-component thermochromic microcapsules, we have used the crystal violet lactone (CVL) as a leuco dye, bisphenol-A (BPA) as a color developer, and 1-tetradecanol (TD) as a solvent. Different ratios of the thermochromic dye and the metal oxide were prepared to examine the effect of the core@shell ratio on the microstructural and thermal properties of the encapsulated microcapsules. The mean particles sizes of the BDTCM@SiO2 are below 100 nm, whereas, the CDTCM@SiO2 samples exhibited the mean particle sizes varied in a range of 100-1000 nm. The endothermic phase transition due to melting and in general, the thermal stabilities of these SiO2 encapsulated TCMs have been explored for the purpose of deploying these systems for thermal energy savings or storage applications.