Multiple Heating-cooling Cycles Research Articles

Modeling of a Single-Band-Ratiometric Sensor Based on Lattice Positive Thermal Expansion in Eu3+-Activated Halide Perovskite Cs2NaEuCl6.

Recently, single-band ratiometric (SBR) thermometry has emerged as an innovative approach to traditional fluorescence thermometry, overcoming uncertainties associated with emission spectrum overlap or scattering while maintaining high spatial resolution and remote monitoring. This paper presents a novel Cs2NaEuCl6 perovskite prepared through a slow-cooling solution method. Additionally, it proposes a temperature sensor model that relies on the thermal quenching of charge-transfer state absorption. Mechanical studies highlight the role of lattice positive thermal expansion in affecting Eu3+ emission. Conversely, a significant emission enhancement is observed upon excitation corresponding to both the ground state and excited state absorption. The distinct luminescent behavior of this Eu3+-activated halide perovskite model makes it suitable for developing a highly sensitive SBR-type sensor with a relative sensitivity (Sr) exceeding 1.5% K-1 and temperature resolution (𝛿T) below 1 K at room temperature. Furthermore, it demonstrates the thermal stability during multiple heating-cooling cycles. Finally, the practical applicability of the proposed SBR model is demonstrated by employing a self-manufactured film sensor that enables precise real-time temperature detection for electronic components. The work is regarded as a significant stride toward the development of cutting-edge and exquisitely sensitive thermometers based on lanthanide-based halide double perovskites.

Highly stable mesoporous-controlled corncob biochar confined paraffinic material with exceptional latent heat retention performance

Bio-based composites fabricated from bio-sourced waste feedstocks have attracted increasing interest and have shown potential applications in sustainable energy infrastructure development. Thermal management using phase-change materials (PCMs) has appeared as an innovative approach for energy storage and cooling, where pure PCMs that lack thermal stability are encapsulated in solid matrices to ensure the charge/discharge of the latent heat of the composite. However, their energy storage density, thermal stability, and durability are reduced after multiple thermal cycles, besides the complicated and expensive nonrenewable fossil feedstock utilization. Biochar, mostly used for soil remediation, can be redirected and repurposed for the encapsulation of PCMs in renewable energy storage infrastructures. In this study, a “greener” biochar-based composite was fabricated from agricultural corncob-derived biochar (88.9 % mesopore proportion) and a commercially available paraffinic PCM (n-hexadecane) following vacuum impregnation strategies. Corncob biochar combined with hexadecane exhibited an efficient energy per unit mass of 250.6 kJ kg−1 and a latent heat retention of 110.3 % after 500 consecutive thermal cycles. In addition, the corncob biochar/hexadecane composite demonstrated high fractional crystallinity and relative latent heat efficiency (98.9 %). The composite exhibited promising chemical compatibility with composite components, stability, and competitive energy density even compared with a composite made of nonrenewable fossil-based materials, like exfoliated graphene nanoplatelets, which demonstrated reduced latent heat retention after multiple heating-cooling cycles. Intermolecular interactions, such as hydrogen bonding, between the guest molecular chains and host materials played a significant role in the thermal performance of the as-synthesized composite materials. This approach will contribute to overcoming the complexities and costs of composite PCM development in thermal management and thermal energy storage applications and support and advance the UN's sustainable development goal (affordable and clean energy).

Thermo-mechanical characteristics of laterally loaded energy piles under multiple heating-cooling cycles in mountain area

In this paper, model tests of energy piles used in mountain area under asymmetry filed condition with and without an external lateral load under multiple heating-cooling cycles were conducted. The asymmetry of the soil will produce asymmetric temperature field and stress field in mountain area. The variation of pile top displacement, horizontal soil pressure, and pile bending moment due to cyclic temperature load were measured and analyzed. The results showed that the pile top horizontal displacement with an external lateral load decreased when the energy pile was heated and increased when it was cooled. However, the variation trends of pile top horizontal displacement with and without an external lateral load showed a significant difference. When the pile subjected to an external load was heated, the soil pressure at the upper part behind the pile would increase and that at the lower part would decrease, and the change was opposite during cooling. The bending moment would be changed by the thermal load, and it increased during heating with an external lateral load, while the variation of bending moment was not obvious during cooling.

Pullulan Films with PCMs: Recyclable Bio-Based Films with Thermal Management Functionality

The use of phase-changing materials (PCMs) is a practical and powerful way of buffering thermal fluctuations and maintaining the isothermal nature of the storage process. In this study, melamine formaldehyde microcapsules with paraffin cores were used as PCMs; pullulan films with PCMs were prepared by the film-casting method; and the composite films prepared were analysed with regard to their chemical structure, thermal properties, thermal stability, and recyclability. Uniform films displaying thermal management functionality were prepared. The amount of 75 wt.% PCM were added to the pullulan film structure which enabled the preparation of a composite film that displayed 104.85 J g−1 of heat storage during heating and 103.58 J g−1 of heat release during cooling. Multiple heating and cooling cycles showed that the composite films maintained their thermal management functionality after multiple heating-cooling cycles. The PCMs could be recovered with a yield of approximately 95% by the application of a simple dissolution and filtration process. The morphology, chemical structure, and thermal properties of the PCMs were maintained after the recovery process. The bio-based composite films with thermal management functionality and recyclability are proposed as an innovative, practical, and effective system for thermoactive storage and packaging applications.

Synthesis of Thermally Stable and Highly Luminescent Cs5 Cu3 Cl6 I2 Nanocrystals with Nonlinear Optical Response.

Low-dimensional Cu(I)-based metal halide materials are gaining attention due to their low toxicity, high stability and unique luminescence mechanism, which is mediated by self-trapped excitons (STEs). Among them, Cs5 Cu3 Cl6 I2 , which emits blue light, is a promising candidate for applications as a next-generation blue-emitting material. In this article, an optimized colloidal process to synthesize uniform Cs5 Cu3 Cl6 I2 nanocrystals (NCs) with a superior quantum yield (QY) is proposed. In addition, precise control of the synthesis parameters, enabling anisotropic growth and emission wavelength shifting is demonstrated. The synthesized Cs5 Cu3 Cl6 I2 NCs have an excellent photoluminescence (PL) retention rate, even at high temperature, and exhibit high stability over multiple heating-cooling cycles under ambient conditions. Moreover, under 850-nm femtosecond laser irradiation, the NCs exhibit three-photon absorption (3PA)-induced PL, highlighting the possibility of utilizing their nonlinear optical properties. Such thermally stable and highly luminescent Cs5 Cu3 Cl6 I2 NCs with nonlinear optical properties overcome the limitations of conventional blue-emitting nanomaterials. These findings provide insights into the mechanism of the colloidal synthesis of Cs5 Cu3 Cl6 I2 NCs and a foundation for further research.

An innovative phase change composite with high thermal conductivity and sensitive light response rate for thermal energy storage

In recent years paraffin-based organic phase change materials have been widely employed in thermal-energy storage systems due to their relatively high latent thermal capacity. However, the risk of leaks, low thermal conductivity, and low light-to-thermal conversion capacity has, to date, limited their use in the storage of solar thermal energy. To address these issues, we have developed a novel bio-based shape-stable organic phase change composite (SSOPCC) by encapsulating paraffin C22 with the double-supporting component consisting of poly (styrene-b-ethylene-co-butylene-b-styrene) (SEBS) and expanded perlite (EP), and improving the thermal conductivity and increasing the sensitive light response rate by introducing boron nitride (BN) and a lignin biomass-derived carbon material carbonized lignin (CL). Our investigations show that, with the introduction of the BN sheets and biomass CL into the SSOPCCs, the thermal conductivity of the composites is improved (from 0.407 W/mK to 0.596 W/mK), and the light-to-thermal conversion ability is also considerably enhanced. The obtained SSOPCCs possess not only good thermal storage performance, such as high latent heat enthalpy (as large as 185.5 J/g) and high relative enthalpy efficiency (>95%) but also exhibit excellent thermal stability and reliability after multiple heating-cooling cycles. The findings of this study will both provide a promising way for fabricating new bio-based phase change composites for real solar energy storage and conversion applications and broaden the high-value utilization of lignin-based biomass.

Coaxial two-capillary electrosprayed double-layered shells microcapsules used for in-situ thermally induced coatings

Breathability and flexibility losses caused by binder utilization, complex operations, long-term consumption, and toxic emissions always limit the development of functional microcapsule-coated textiles. Herein, an integrated process including the optimization of functional microcapsules and their non-destruction adhesions on textile surface is completed to get rid of the use of binder and realize green and high-efficiency production. The coaxial two-capillary electrospray is used to create double-layered shells consisting of poly(lactic acid) (PLA) inner shell and poly(-caprolactone) (PCL) outer shell for encapsulating n-hexadecane, and then these ternary microcapsules are electro-sprayed directly on the textile surface. PLA as a supporting shell ensures the stability of the microcapsule and the high encapsulation efficiency of active substance, and PCL with a low melting temperature as an adhesive shell completes the in-situ adhesion between microcapsule and textile via its melting-solidification behavior after heat treatment. Experimental results show that spherical ternary microcapsules with a 9–15 μm of mean diameter and a mono-dispersed size distribution can be obtained. When less n-hexadecane is microencapsulated in double-layered shells, n-hexadecane mainly localizes in the center of the PLA shell to form a triple-layered core-shell structure. With the increase of n-hexadecane addition, the core area changes from bulk n-hexadecane to the side-by-side structure of n-hexadecane and PLA layer, finally to a mixture of n-hexadecane and PLA due to the diffusion of excessive n-hexadecane. When PLA content is higher than PCL content in double-layered shells, not only can a near 100 % of n-hexadecane encapsulation efficiency be obtained under 50 wt% n-hexadecane addition in ternary electrosprayed droplets, but also good thermal stability of ternary microcapsules during heat treatment. The phase-transition enthalpy of the n-hexadecane40-PLA40-PCL10 microcapsule can reach about 100 J/g, and the latent heat of coated textile also reaches 55 J/g. Due to the protection as well as the melting adhesion of double-layered shells, the latent heat of coated textiles and the adhesion between microcapsules and textile surfaces do not change after multiple heating-cooling cycles and soap-washing processes, still exhibiting good stability and durability. With the increase of PCL content, not only stronger adhesion performance between microcapsules and textiles is obtained, but also a higher thermal degradation temperature of encapsulated n-hexadecane. Finally, this in-situ thermally induced coating of microcapsules preserves the flexibility, the porous morphology, and the gas permeability of textiles.

Core-shell CsPbBr3@Cs4PbBr6 nanocrystals dispersed in thermoplastic polyurethane as writeable heat-resistant fluorescent inks

The cesium lead halide perovskites CsPbX3 (X = Cl, Br, I) have received extensive attention in the solar cell and light-emitting devices owing to their excellent optical and electronic properties. However, in practical applications, CsPbX3 often suffers from many disturbances caused by changes in the external environment, which will weaken its performance. In order to better solve this issue, a series of encapsulation strategies have been proposed to protect the stability of CsPbX3. In particular, the derivative Cs4PbX6 of CsPbX3 was well received as a shell protective material because it does not introduce new elements. Here, we prepared large-yield stable CsPbBr3@Cs4PbBr6 core-shell nanocrystals (NCs) by adjusting the initial ratio of Cs/Pb using one-pot route. At the same time, the growth process of CsPbBr3@Cs4PbBr6 NCs were analyzed, and their stability was evaluated under atmospheric conditions. The results show that CsPbBr3@Cs4PbBr6 NCs exhibit excellent stability compared to the pure phase CsPbBr3 NCs, and thus the passivation of Cs4PbBr6 to CsPbBr3 was obtained. Subsequently, a writable fluorescent ink by mixing CsPbBr3@Cs4PbBr6 NCs and thermoplastic polyurethane (TPU) was developed, which held excellent heat-resistance stability under multiple heating-cooling cycles. Our research will greatly simplify the preparation process of stabilized CsPbBr3@Cs4PbBr6 core-shell NCs and provide alternative options for the commercial development of perovskite materials.

Reversible Thermosalience in a One-Dimensional Coordination Polymer Preceded by Anisotropic Thermal Expansion and the Shape Memory Effect.

Thermally responsive crystals hold great potential for their use as actuating materials by acting as energy transducers to convert heat energy to mechanical work. Control over defined phase transition temperature with rapid reconfiguration is of great advantage for actuation. The thermosalient (TS) effect is a rarely observed phenomenon in coordination polymers (CPs), let alone the reversibility of thermosalience in CPs. Herein, we report the reversible TS effect in a one-dimensional CP due to the martensitic phase transition during both heating and cooling cycles. The TS effect was preceded by anisotropic thermal expansion showing high expansion coefficients. In addition, the nonmolecular crystals show reversible contraction and recovery during multiple heating-cooling cycles due to the self-restorative shape memory effect. The reversible actuation of the CP could be repeated for 20 heating-cooling cycles in differential scanning calorimetry experiments, suggesting its great potential as a multicyclic actuator. Such thermal responsive behavior is unique in metal-organic materials.

A Review of Composite Phase Change Materials Based on Porous Silica Nanomaterials for Latent Heat Storage Applications.

Phase change materials (PCMs) can store thermal energy as latent heat through phase transitions. PCMs using the solid-liquid phase transition offer high 100–300 J g−1 enthalpy at constant temperature. However, pure compounds suffer from leakage, incongruent melting and crystallization, phase separation, and supercooling, which limit their heat storage capacity and reliability during multiple heating-cooling cycles. An appropriate approach to mitigating these drawbacks is the construction of composites as shape-stabilized phase change materials which retain their macroscopic solid shape even at temperatures above the melting point of the active heat storage compound. Shape-stabilized materials can be obtained by PCMs impregnation into porous matrices. Porous silica nanomaterials are promising matrices due to their high porosity and adsorption capacity, chemical and thermal stability and possibility of changing their structure through chemical synthesis. This review offers a first in-depth look at the various methods for obtaining composite PCMs using porous silica nanomaterials, their properties, and applications. The synthesis and properties of porous silica composites are presented based on the main classes of compounds which can act as heat storage materials (paraffins, fatty acids, polymers, small organic molecules, hydrated salts, molten salts and metals). The physico-chemical phenomena arising from the nanoconfinement of phase change materials into the silica pores are discussed from both theoretical and practical standpoints. The lessons learned so far in designing efficient composite PCMs using porous silica matrices are presented, as well as the future perspectives on improving the heat storage materials.

Construction of polyimide films with excellent dimensional stability and toughness via incorporating point-to-face multi-coordination structure

Flexible polyimide (PI) films with simultaneously excellent dimensional stability and toughness were vital for the application and reliability of flexible display. Thus, in this paper, we designed a novel PI film containing point-to-face multi-coordination structure. The coordination structure was constructed by introducing Cu2+ and benzimidazole ligands into polyimides, and the existence of the point-to-face multi-coordination was proved. Excellent toughness and dimensional stability under high temperature, multiple heating-cooling cycles, and cyclic tension of PI films were realized, resulting from destruction and rapid reconstruction of point-to-face multi-coordination structure with the advantage of large bonded areas. Compared with PI without Cu2+ (PICu0), the thermal expansion coefficient of PI with 20mol% Cu2+ (PICu20) reduced 94%, and the tensile strength, percentage of breaking elongation and fracture energy of PICu20 increased by 40%, 45% and 174%, respectively. Furthermore, the water absorption of PICu films dropped and the dielectric breakdown strength was maintained.

Thermal Expansion Behavior of Poly(amide-imide) Films with Ultrahigh Tensile Strength and Ultralow CTE

A series of novel poly(amide-imide) (PAI) films with different amide contents were prepared from pyromellitic dianhydride and four amide-containing diamines. These PAI films exhibited excellent mechanical and thermal properties with tensile strength of 203.7–297.4 MPa and Tg above 407 °C. The rigid backbone structures combined with strong intermolecular interactions provided PAI films with ultralow in-plane CTE values from −4.17 ppm/°C to −0.39 ppm/°C in the temperature range of 30–300 °C. The correlation between thermal expansion behavior and aggregation structures of PAI film was investigated. The results suggested that hydrogen bonding interactions could be maintained even at high temperature, thus resulting in good dimension reversibility of films in multiple heating-cooling cycles. It is demonstrated that dimensional stabilities of PAI films are determined by the rigidity, orientation, and packing of molecular chains. Heat-resistant PAI films with ultralow CTE can be developed as flexible substrates by regulating backbones and aggregation structures for optoelectronic application.

Effects of multiple heating-cooling cycles on the permeability and microstructure of a mortar

Cement-based materials can be used as a sealing layer in compressed air energy storage (CAES) underground storage caverns to ensure airtightness. This experimental study investigated the effects of multiple heating-cooling cycles with variations in the gas permeability, porosity, and microstructure of a mortar sample. Three different temperature ranges, namely, 20–50 °C, 20–60 °C and 20–70 °C, were selected according to different operation conditions of the CAES plants. The results showed that the gas permeability decreases with an increase in temperature in the heating process within each temperature cycle due to a reduction in the pore volume. After the sample was subjected to multiple heating-cooling cycles, the gas permeability has an overall increasing tendency with an increase in cycle number, and the magnitude of the permeability increase is related to the maximum cycling temperature. The microstructure observed by SEM indicates that the temperature cycles will induce some microcracks, which are mainly distributed on the cement matrix surface and in the interfacial transition zone (ITZ) between the cement matrix and sand aggregate. The expansion of the existing cracks and appearance of new cracks caused by a temperature effect led to an increase in the gas permeability.

Pyroelectric signals in (Ba,Ca)TiO3-xBa(Sn,Ti)O3 ceramics: A viable alternative for lead-based ceramics

(1-x)(Ba0.9Ca0.1)TiO3-xBa(Sn0.2Ti0.8)O3 ceramics x=0, 0.4, 0.5 and 0.6 were synthesized. With Sn addition, orthorhombic to tetragonal transition temperature increased to higher temperature side and tetragonal to cubic transition temperature reduced towards room temperature for x=0.4 and x=0.5 and all phase transitions merged into one for x=0.6. Multiple heating-cooling cycles' measurement of pyroelectric current was carried out over an excursion of temperature relevant to the pyroelectric applications. The pyroelectric coefficient increased from 1×10−4C/m2.K (x=0) to 2.05×10−4C/m2.K (x=0.4) sample at 303K. Such enhancements could prove to be advantageous in deriving pyroelectric figures of merit.

Enhanced Thermal Conductivity of Copper Nanofluids: The Effect of Filler Geometry.

Nanofluids are colloidal dispersions that exhibit enhanced thermal conductivity at low filler loadings and thus have been proposed for heat transfer applications. Here, we systematically investigate how particle shape determines the thermal conductivity of low-cost copper nanofluids using a range of distinct filler particle shapes: nanospheres, nanocubes, short nanowires, and long nanowires. To exclude the potential effects of surface capping ligands, all the filler particles are kept with uniform surface chemistry. We find that copper nanowires enhanced the thermal conductivity up to 40% at 0.25 vol % loadings; while the thermal conductivity was only 9.3% and 4.2% for the nanosphere- and nanocube-based nanofluids, respectively, at the same filler loading. This is consistent with a percolation mechanism in which a higher aspect ratio is beneficial for thermal conductivity enhancement. To overcome the surface oxidation of the copper nanomaterials and maintain the dispersion stability, we employed polyvinylpyrrolidone (PVP) as a dispersant and ascorbic acid as an antioxidant in the nanofluid formulations. The thermal performance of the optimized fluid formulations could be sustained for multiple heating-cooling cycles while retaining stability over 1000 h.

Ferroelectric triglycine sulphate crystals with a profile distribution of chromium impurity

Some features of the ferroelectric behavior of triglycine sulphate crystals with a nonuniform distribution of chromium impurity have been considered. The dielectric hysteresis loop of the samples is characterized by a large shift along both the polarization axis and the electric field direction. The results are explained well within the phenomenological approach with allowance for the gradient term in the expansion of free energy. It is established that the unipolarity coefficient and pyroelectric signal of inhomogeneous crystals barely changes during multiple heating-cooling cycles.

10.1007/s11451-008-1021-4

The specific features of the ferroelectric behavior of triglycine sulfate crystals with a nonuniform distribution of chromium impurities are analyzed. It is demonstrated that the dielectric hysteresis loops of the samples exhibit large shifts both along the polarization and electric field directions. The results obtained are well explained within the phenomenological approach with due regard for the gradient term in the expansion of the free energy. It is established that the unipolarity coefficient and the pyroelectric signal of nonuniform crystals remain virtually unchanged in multiple heating-cooling cycles.

D-80 In-Situ Observation of Dynamic Recrystallization and Related Phenomena in the Bulk of Zirconium Alloy

The nuclear reactor structural material Zircaloy-4 grade R60804 of nominal composition Zr 1.5%Sn 0.2%Fe 0.1%Cr 0.1%O (in weight %) has been tested under thermo-mechanical load on the high energy X-ray beamline 1-ID at the Advanced Photon Source while diffraction patterns were recorded in-situ and continuously on a sub-second time scale. Multiple heating-cooling cycles were run between 690 K and 1280 K under mechanical load increasing stepwise from 0 N to 225 N. The temperature cycles transform the metal from its low temperature α phase below 1083 K through an α+β phase field into its single β-phase of bcc structure stable above 1253 K and back. Initially, the β-phase precipitates in a fine grain breaking also the coexistent α-grains. After α disappears, grain growth is rapid resulting in only a very few sharp spots on the diffraction rings. Upon cooling, the α-phase reappears and grows into the β-grains and the well known Burgers orientation relationship is observed, i.e. the α-{002} orientation aligns with the β-{110} plane orientation, which can be reversed upon subsequent heating. The β-phase being very ductile and soft shows plastic deformation, which escalates at 225 N and a cross section of 30 mm. While temperature is increased, first we observe grain breakage into sub-grains due to the deformation process, which recovers dynamically. Plastic deformation is faster at higher temperature when new grain orientations pop up and disappear continuously and the system recrystallizes dynamically. The details and fingerprints for the different stages during an in-situ observation from the bulk of a metallic material measured for the first time.

Ferroelectric properties of triglycine sulfate crystals with a nonuniform distribution of chromium impurities

The specific features of the ferroelectric behavior of triglycine sulfate crystals with a nonuniform distribution of chromium impurities are analyzed. It is demonstrated that the dielectric hysteresis loops of the samples exhibit large shifts both along the polarization and electric field directions. The results obtained are well explained within the phenomenological approach with due regard for the gradient term in the expansion of the free energy. It is established that the unipolarity coefficient and the pyroelectric signal of nonuniform crystals remain virtually unchanged in multiple heating-cooling cycles.

Thermophysical properties of dental filling materials. Part II: thermal expansivity

The thermal linear expansivity of three light-curable dental filling materials is reported. The materials under test were: the compomer Compoglass® F, and two hybrid composites, Tetric® and Valux Plus. The measurements were performed with the use of an absolute laser-interferometry dilatometer. With it, high thermal resolution of measurements has been achieved. Experiments have been carried out on heating and on cooling. Both the coefficient of linear thermal expansion (CLTE) and the linear expansion (LE) have been determined. Attention has been paid to the effect of multiple heating-cooling cycles and thermal ageing. The investigation revealed the effect of initial heating on reduction in CLTE. For the purpose of numerical calculations the results have been expressed with the use of approximation functions. The present study complements the investigation of strictly thermal properties of the above-mentioned materials.