Solid-state Phase Change Research Articles

NiTiCu shape memory alloys with ultra-low phase transformation range as solid-state phase change materials

Shape memory alloys (SMAs) have been demonstrated as effective phase change materials (PCMs) for thermal energy storage (TES) applications. NiTi and NiTiHf SMAs have shown high TES performance, as quantified by PCM figure of merit (FOM) but their use in applications requiring narrow operation temperature windows is limited by large overall phase transformation ranges (OTR). This work investigates NiTiCu SMAs as PCMs with high FOM and low OTR. A full-factorial design of experiments is used to examine 24 NiTiCu compositions. The compositions were fabricated using vacuum arc melting and their phase transformation and thermophysical properties were characterized using calorimetry, thermal diffusivity, and density measurements. The NiTiCu compositions spanned martensitic transformation temperatures between -22 and 84 °C and exhibited greater FOM (250–1050 106J2K−1s−1m−4), compared to traditional PCMs (typically <100 106J2K−1s−1m−4), with major benefits associated with higher density and higher thermal conductivity values. In addition, the NiTiCu compositions in this study show ultra-low OTR (12–20 °C) compared to NiTi and NiTiHf SMAs (>50 °C), enabling utility in narrow operating temperature windows. Thermal cycling was also performed revealing extreme stability of martensitic transformation with only 0.04 °C shift in transformation temperatures after 80 thermal cycles, which is the lowest reported to date in SMA literature.

Planar, longitudinal, compressive waves in solids: Thermodynamics and uniaxial strain restrictions

A new tri-axial pressure-based constitutive expression has been found using Cauchy's stress tensor. This stress state emphasizes pressure and shear stress. The description is a pressure plus an effective shear stress allowing for a constitutive law based on atomic solid-state phase changes in crystalline cells due to pressure plus shear-based dislocation motion commonly associated with plasticity. Pressure has a new role in the material's constitutive response as it is separated from plasticity. The thermo-mechanical system describes third-order Gibbs’ expressions without specific volume restrictions placed upon the material. Isothermally, the ratio of heat to shear work in elastic copper is shown to approach zero at a very low temperature and become larger than one as temperature approaches melting. Wave compression models investigated are elastic and plastic: in fully elastic materials, the planar wave is restricted by Poisson's effect although plastic shear changes this constraint. Plastic deformation, dominated by dissipative shear stresses in uniaxial strain, heats the material while excluding phase changes from hydrostatic pressures. The material properties per se across Hugoniot shocks are described with entropy concepts. Shock waves are exceedingly complex since the constitutive laws are linked at extreme temperatures, pressures, and shear stresses. Isothermal, isentropic, isochoric, and iso-shear conditions are used throughout with Jacobian algebra.

Correlating Reaction Dynamics and Size Change during the Photomechanical Transformation of 9-Methylanthracene Single Crystals.

Photomechanical molecular crystals that expand under illumination could potentially be used as photon-powered actuators. In this study, we find that the use of high-quality single crystals of 9-methylanthracene (9MA) leads to more homogeneous reaction kinetics than that previously seen for polycrystalline samples, presumably due to a lower concentration of defects. Furthermore, simultaneous observation of absorbance and shape changes in single crystals revealed that the dimensional change mirrors the reaction progress, resulting in a smooth expansion of 7 % along the c-axis that is linearly correlated with reaction progress. The same expansion dynamics are highly reproducible across different single crystal samples. Organic single crystals exhibit well-defined linear expansions during 100 % photoconversion, suggesting that this class of solid-state phase change material could be used for actuation.

LiVO2 as a new solid-state phase change material

Herein, we study the effect of off-stoichiometry on the properties of a phase change material (PCM)—LiVO2—which is a new type of PCM based on the phase change of electron. The PCM properties such as latent heat, transition temperature, and hysteresis of transition temperature varied linearly with respect to the distance of vanadium ions, which was systematically controlled through off-stoichiometry in the composition of LixVO2+δ (0.85 <x < 1.15). The latent heat of the PCM reached a maximum of 300 J/cm3 at the shortest distance where the V3 trimer was stable. These findings reveal the potential of LixVO2 as a solid-state PCM with tunable properties.

Modeling the temperature distribution during laser hardening process

A mathematical model has been developed here to calculate the temperature distribution on the surface and bulk of a steel plate under the laser hardening process. The model starts from the basic heat equation, is then developed to a volumetric form and is connected to the various solid phases existing. The model is based on two strongly influencing parameters of the laser hardening process: velocity of the laser spot and irradiation time. The results are compared to the available experimental data reported in the literature. The volumetric model provides an assessment of temperature distribution in both the vertical and horizontal axis. Laser irradiation at sufficiently high fluence can be used to create a solid state phase change on the surface. Primary calculations show that the temperature profile has a Gaussian distribution in horizontal x-and y-axis and presents an exponentially decreasing distribution in the horizontal and vertical depth directions.

The equilibrium phase diagram of the pentaerythritol-pentaglycerine-2-amino-2methyl-1,3, propanediol (PE-PG-AMPL) system

Polyalcohols and amines have been considered as potential thermal energy storage materials, owing to their energetic solid-solid phase transitions. In this paper, we present equilibrium phase diagram of Pentaerythritol (PE)–Pentaglycerine (PG)– 2-amino-2methyl-1,3, propanediol (AMPL) ternary system that has been thermodynamically assessed using the CALPHAD method. A special class of, so called, “Plastic Crystals” have tetrahederally configured molecules with O–H⋯O or N–H⋯O layered or chained bonds in the low temperature phase, and store latent heat of transformation during solid-solid phase change in orientationally disordered crystals at higher temperatures. For example, in polyalcohols, there are O–H⋯O bond rotations around the C–C bonds that are responsible for storing large amounts of solid state phase change energy. Several binary equilibrium phase diagrams of polyalcohols, amines and combination thereof have been calculated and experimentally validated. We only know of three ternary phase diagram of these plastic crystals reported, to the best of knowledge. In the thermodynamic calculations of thePE-PG-AMPL system, we used the binary phase diagram experimental data for the optimization and calculation of excess energies. The binary systems have been optimized using regular and sub-regular solution models. The binaries as well as the ternary system have been calculated from room temperature to the liquid phase. The solution phases are modeled as substitutional solutions, in which the excess Gibbs energies are expressed by the Redlich–Kister–Muggianu polynomial. There is a very good agreement between previously reported experimental data and the calculated phase diagrams.

Distortion control in a wire-fed electron-beam thin-walled Ti-6Al-4V freeform

The solid-state phase change (SSPC) temperature is important in the accurate thermal-mechanical simulation of a wire-fed electron-beam freeform. The SSPC temperature of the Ti-6Al-4V material was determined to be 850 °C by variable temperature XRD measurements. The forming process of a typical thin-walled TC4 piece was modeled, and the most accurate predictions were achieved with the determined SSPC temperature. The thin-walled piece could be formed if the electron beam operated at a scan current between 100 and 150 mA and a speed below 100 mm/s. The distributions of the residual stress were consistent in the reciprocating and unidirectional scan modes; however, the former produced less distortion. In the reciprocating mode, shrinkage distortion dominated and increased with the scan current. The maximum distortion along the x-axis increased from 0.18 to 0.32 mm when the current increased from 100 to 150 mA. A dynamic current scheme reduced the maximum distortion along the x-axis to 0.12 mm, and a constant temperature constraint at the bottom of the substrate reduced the distortions along the x- and z-axes to approximately zero.

Experimental study on the thermal performance of nano enhanced pentaerythritol in IC engine exhaust heat recovery application

The performance of IC engine can be enhanced by exhaust gas heat recovery using solid state phase change materials, such as pentaerythritol (C5H12O4). Further enhancement was achieved by adding Al2O3 nanoparticle to improve heat transfer performance of C5H12O4, that has rather poor thermal conductivity. In this study the effect of adding Al2O3 nanoparticle on heat transfer performance of pentaerythritol (PE) was studied using a heat recovery heat exchanger integrated with the exhaust pipe of an internal combustion engine. The experimental results showed when 0.1% and 0.5% Al2O3 were added to PE, instead ofusing purePE, the charging efficiency increased by 5.48% and 14.77% and energy savings by 11.46% and 18.3%, respectively. The characterization methods such as TGA-DTA, DSC, FTIR and LFA were used. Thermal degradation kinetics of pentaerythritol added with Al2O3 nanoparticles was studied by Coats-Redfern method. The dispersion stability, thermal/chemical degradation and thermal energy storage performance of PE with Al2O3 nanoparticles are reported in this paper.

Experimental Studies and Modeling of the Drying Kinetics of Multicomponent Polymer Films

The process of drying thin polymer films is an important operation that influences the film structure and solid state, and the stability of the product. The purpose of this work was to study and model the drying kinetics of multicomponent films based on two polymers: hydroxypropyl methylcellulose (HPMC, amorphous) and polyvinyl alcohol (PVA, semicrystalline). The isothermal drying kinetics of the films at different temperatures (40, 60, and 80°C) were studied using thermo-gravimetric analysis (TGA) and convection oven methods. Solid-state characterization tools used in the study included polarization and hot-stage microscopy, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The drying kinetics of HPMC and PVA films in the TGA apparatus and convection oven were comparable. The three-parameter (Wmax, τ, n) Hill equation successfully modeled the experimental drying kinetics. The time factor τ in the Hill equation nicely explained two drying phases in the films. Solid-state phase changes occurring in the films during dehydration had a bearing on the drying kinetics and mechanisms. TGA can be used as a simple tool to determine the end points in drying processes using ovens or tunnels. The three-parameter Hill equation explained the drying kinetics and diffusion mechanisms of the solvent through the polymer films for the first time. This study advances our understanding of film drying, in particular for pharmaceutically relevant thin films.

A one-pot synthesis of 1,6,9,13-tetraoxadispiro(4.2.4.2)tetradecane by hydrodeoxygenation of xylose using a palladium catalyst

In an effort to expand the number of biobased chemicals available from sugars, xylose has been converted to 1,6,9,13-tetraoxadispiro(4.2.4.2)tetradecane in a one-pot reaction using palladium supported on silica-alumina as the catalyst. The title compound is produced in 35–40% yield under 7 MPa H2 pressure at 733 K using 3–10 wt%Pd on silica-alumina catalyst. It is isolated using a combination of liquid-liquid extractions and flash chromatography. This dimer can be converted to its monomer, 2-hydroxy-(2-hydroxymethyl)tetrahydrofuran, which ring opens under acid conditions to 1,5-dihydroxy-2-pentanone. This diol can then be esterified with vinylacetate in phosphate buffer to produce 1,5-bis(acetyloxy)-2-pentanone which is an inhibitor of mammalian 11β-hydroxysteroid dehydrogenase 1. 1H and 13C nmr spectra of each of these species are reported. The single crystal X-ray structure of the title compound is also reported. These data were collected in a temperature range of 100 K–273 K and show a solid state phase change from triclinic to monoclinic between 175 K and 220 K without a conformational change.

Thermodynamic assessment of binary systems Tris(hydroxymethyl)aminomethane-Pentaglycerine (TRIS-PG) and 2-amino-2-methyl-1,3-propanediol-Pentaglycerine (AMPL-PG) phase diagrams

Solid state phase change materials are considered as potential candidates for thermal energy storage. Among the solid–solid heat storage materials, the most promising heat storage materials are organic polyalcohol globular tetrahedral molecular crystals such as (CH3)C(CH2OH)3 for PG, (NH2)C(CH2OH)3 for TRIS, and (CH3)(NH2)C(CH2OH)2 for AMPL, which store a large amount of thermal energy in their solid state high temperature phases with orientationally disorder crystal structure. In this study, we obtained the Gibbs energies of pure PG and pure TRIS derived utilizing the available experimental data including temperature-dependency of heat capacity, enthalpy, and transitions temperatures, as well as obtained optimized binary phase diagrams of TRIS-PG and AMPL-PG by CALPHAD calculations. The phase boundaries are verified by in-situ X-ray diffraction (XRD). Optimized database of these two binaries will allow exploration of ternary and higher order systems using CALPHAD methodology that will provide a wider selection of materials for practical thermal energy storage applications. Regular and sub-regular solution models are used for calculations in which the excess Gibbs energies are expressed by the Redlich–Kister–Muggianu polynomial. A set of self-consistent interaction parameters formulating the Gibbs energies of various phases in binary systems are obtained. The TRIS-PG binary phase diagram was calculated from room temperature to the liquid phase temperature, the modeled phase diagram and the experimental data from our work are in good agreement. We also used experimental data of TRIS-PG from the literature which shows a good agreement between the two data sets. Our optimized TRIS-PG phase diagrams show a wider solid-state two phase region, where there is de-mixing of phases, whereas the calculations from the literature show a very narrow region. We also present optimized AMPL-PG binary phase diagram using PARROT module in Thermal-Calc software. The calculated phase diagrams for the two systems mentioned above are presented along with the experimental data.

Infra-red techniques for thermomechanical characterisation of materials and structures

The application of infra-red (IR) imaging techniques to the mechanics of materials and structures has grown considerably over past decades. The expansion is marked by the increased spatial and temporal resolution of the infra-red detectors, faster processing times and much greater temperature resolution. The improved sensitivity and more reliable temperature calibrations of the devices have meant that more accurate data can be obtained than were previously available. The purpose of the special issue is to bring together novel work on all aspects of thermomechanics with the focus on the application of IR imaging approaches. The main thrust is on the analysis of thermomechanical behavior of materials and using this behavior to elicit information on material characteristics, stress patterns, deformation mechanisms and failure modes. Of particular interest are strong thermomechanical couplings that result in complex, often nonlinear behaviour such as visco(thermos)elasticity, anisotropic heat diffusion mechanisms, strain and damage localisation and solid state phase changes. An objective is to share experience on how datarich experimental mechanics can help scientists and engineers to better understand and simulate the behavior of materials and structures. An important aspect is the use of other imaging techniques in conjunction with IR imaging, demonstrating how imaging is the route to a full thermomechanical characterization of both material behaviour and structural response. The special issue starts with a paper that uses a technique known as thermoelastic stress analysis (TSA), which exploits the thermoelastic coupling that exists in materials under load. The thermoelastic coupling was first observed in the 1830s and the mathematical formulation of the thermoelastic effect was derived in the 1850s by Lord Kelvin. Essentially when a material experiences a strain change in the elastic range a small temperature change occurs that can be related to the trace of the stress tensor. In the 1980s single cell scanning IR detection systems were developed to obtain the ‘thermoelastic response’, essentially the output from system was a digital level. The first commercially available system was called SPATE ‘Stress Pattern Analysis by Thermal Emissions’, which was developed in the UK by and organization called SIRA ‘Scientific Instruments Research Associations. The review by Lin, Saman, Khaja, and Rowlands, covers developments from the early days of SPATE to the present, where array based calibrated detection systems are used. One clear shortcoming of TSA is that can only deliver the sum of the principal stresses. The hybrid TSA approach described provides a route for determining the individual stress components by combining the measured thermal data with Airy stress functions. In developing the formulation for TSA it is assumed that the small temperature change occurs isentropically. This is achieved by cyclically loading the specimen in the elastic range (reversible) and at such a rate that the thermal diffusion length is small (adiabatic). A key component of TSA is the use of a lock-in algorithm, which uses a reference signal (usually from a test machine signal generator), to process the data. The IR detection systems used for TSA are costly as they are cryogenically cooled photon detectors with fast framing rates that enable sufficient data to be captured to reconstruct the cyclic thermal response with great accuracy. The second paper in the issue is by Pitarresi and proposes an off-line lock-in correlation algorithm enabling TSA and lock-in thermography A. Chrysochoos University of Montpellier, Montpellier, France

Atomic scale dynamics of a solid state chemical reaction directly determined by annular dark-field electron microscopy.

Dynamic processes, such as solid-state chemical reactions and phase changes, are ubiquitous in materials science, and developing a capability to observe the mechanisms of such processes on the atomic scale can offer new insights across a wide range of materials systems. Aberration correction in scanning transmission electron microscopy (STEM) has enabled atomic resolution imaging at significantly reduced beam energies and electron doses. It has also made possible the quantitative determination of the composition and occupancy of atomic columns using the atomic number (Z)-contrast annular dark-field (ADF) imaging available in STEM. Here we combine these benefits to record the motions and quantitative changes in the occupancy of individual atomic columns during a solid-state chemical reaction in manganese oxides. These oxides are of great interest for energy-storage applications such as for electrode materials in pseudocapacitors. We employ rapid scanning in STEM to both drive and directly observe the atomic scale dynamics behind the transformation of Mn3O4 into MnO. The results demonstrate we now have the experimental capability to understand the complex atomic mechanisms involved in phase changes and solid state chemical reactions.

Graphite Foam Infused with Pentaglycerine for Solid-State Thermal Energy Storage

The use of a solid-state phase change material, pentaglycerine, in thermal energy storage was investigated. The motivation for exploring a thermal energy storage system that relies on a solid-state phase transition is to eliminate phase change material leakage and sealing issues. Pentaglycerine was effectively injected into graphite foam, and this combination was studied for potential use in a thermal energy storage device. Graphite foam samples that contained pentaglycerine demonstrated a storage capacity that was close to the theoretical capacity. The graphite foam infused with pentaglycerine retained 100% of its storage capacity after 59 separate thermal cycles under various conditions, with many of those cycles contiguous. It was subjected to a 28% duty cycle of applied heat flux under active cooling conditions, and the duty cycle of the sample was not adversely affected by subcooling of the pentaglycerine. The one-dimensional model developed for this study assumed a homogeneous mixture of pentaglycerine and foam which were in local thermal equilibrium with each other. The numerical results reasonably represented the effects of phase change as reflected by the temperature histories for several locations within a graphite foam–pentaglycerine sample. The current study showed that the graphite foam–pentaglycerine combination has potential for use in thermal energy storage devices.

Synthesis and Characterization of Solid-State Phase Change Material Microcapsules for Thermal Management Applications

Polyalcohols such as neopentyl glycol (NPG) undergo solid-state crystal transformations that absorb/release significant latent heat. These solid–solid phase change materials (PCM) can be used in practical thermal management applications without concerns about liquid leakage and thermal expansion during phase transitions. In this paper, microcapsules of NPG encapsulated in silica shells were successfully synthesized with the use of emulsion techniques. The size of the microcapsules range from 0.2 to 4 μm, and the thickness of the silica shell is about 30 nm. It was found that the endothermic phase transition of these NPG-silica microcapsules was initiated at around 39 °C and the latent heat was about 96.0 J/g. A large supercooling of about 43.3 °C was observed in the pure NPG particles without shells, while the supercooling of the NPG microcapsules was reduced to about 14 °C due to the heterogeneous nucleation sites provided by the silica shell. These NPG microcapsules were added to the heat transfer fluid PAO to enhance its heat capacity and the effective heat capacity of the fluid was increased by 56% with the addition of 20 wt. % NPG-silica microcapsules.

Microstructure characterization of NiFe2O4-NiO solid-solid diffusion couple

The solid state interdiffusion between NiFe2O4 and NiO in nitrogen atmosphere was studied by means of diffusion couple technique. NiFe2O4/NiO diffusion couple with plane interfaces was made by clamping method and sintering at 1 300 °C for 10 h. Scanning electronic microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS) were used to analyze the microstructure and phase composition of the diffusion couples. The results indicate that a porous layer of uniform thickness forms along the NiFe2O4/NiO bonding interface and exhibits a deep penetration in the NiFe2O4 due to the Kirkendall effect. Furthermore, SEM observations reveal that the needle-like nickel ferrite precipitates form in NiO near the interface and the formation mechanism of them are inferred to be diffusion type solid-state phase changes.

Investigation of a hyperbranched polyurethane as a solid-state phase change material

As phase change material (PCM), doped hyperbranched polyurethane (D-HBPU) was synthesized by PEG6000 via two steps: at first take tetrafunctional pentaerythritol as soft segment, and then use liquefaction-modified isocyanate, and chain extender as hard segment. This material’s molecular structure, phase change behaviors, thermal-resistant property, and crystalline morphology had been investigated by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analyses, wide-angle X-ray diffraction (WAXD), and polarization optical microscopy (POM). Results showed that D-HBPU was a typical solid-state PCM with better heat storage property and thermal resistance when compared with hyperbranched polyurethane. The transition enthalpy and the main decomposition temperature of D-HBPU were 125.0 J/g and 437 °C, respectively. From WAXD and POM, the results suggested that D-HBPU has good crystallization.

ANALYSIS OF 100-METER RAIL TEMPERATURE FIELD DURING COOLING PROCESS BEFORE STRAIGHTENING BY FEM

The straightness of the 100-meter rail after straightening is directly affected by the bending deformation during cooling before straightening, and the analysis of the temperature field in the cooling process is the basis of studying the bending deformation. By analyzing the heat boundary conditions in the cooling process, the temperature field was calculated and its variable law was analyzed by using the 3-D transient non-liner finite element method. The factors such as the solid-state phase change and the physical parameters with change of the temperature were considered, and the numerical results were coincident with the experimental data. The results show that the velocities of temperature changing at different positions of the rail's cross-section are different in the cooling progress, and the phase change and the irregular cross-section of rail are important influencing factors.

MICROSTRUCTURAL CHARACTERIZATON AND EFFECTS ON MECHANICAL PROPERTIES OF BORON ADDED ARMOR STEELS

ABSTRACTThe performance of steels depends on the properties associated with theirmicrostructures, that is type, volume fraction, form factor, size and the area distributionof the various phases involved. Because all the phases in steels are crystalline, steelmicrostructures are made up of various crystals, sometimes as many as three or fourdifferent types which are physically blended by solidification, solid-state phase changes,hot deformation, cold deformation and heat treatment. Each type of microstructure isdeveloped to characteristic property ranges by specific processing routes that controlthe microstructural changes. Thus processing technologies are used to tailor the finalmicrostructure.In this study boron added armor steel has been rolled to form sheet product.Austenitization treatment, rapidly quenching and then tempering at varioustemperatures and times have been performed on the materials respectively. After all ofthese operations, the phases of the alloy system formed during equilibrium state havebeen examined and also their amounts are calculated with Thermocalc. Microstructuresformed after different heat treatments have been examined by optical microscopy. Theeffect of formed microstructures on mechanical properties are comparatively given bystrength, toughness and elongation values.

Doped sodium aluminium hydrides as hydrogen storage materials-characterizations and mechanistic insights

The dehydriding and rehydriding of sodium aluminium hydride,NaAlH 4, is kinetically enhanced and rendered reversible in the solid state upon doping with a small amount of catalyst species, such as titanium, zirconium or tin. The catalyst doped hydrides appear to be good candidates for development as hydrogen carriers for onboard proton exchange membrane (PEM) fuel cells because of their relatively low operation temperatures (120–150 °C) and high hydrogen carrying capacities (4–5 wt.%). However, the nature of the active catalyst species and the mechanism of catalytic action are not yet known. In particular, using combinations of Ti and Sn compounds as dopants, a cooperative catalyst effect of the metals Ti and Sn in enhancing the hydrogen uptake and release kinetics is hereby reported. In this paper, characterization techniques including XRD, XPS, TEM, EDS and SEM have been applied on this material. The results suggest that the solid state phase changes during the hydriding and dehydriding processes are assisted through the interaction of a surface catalyst. A mechanism is proposed to explain the catalytic effect of the Sn/Ti double dopants on this hydride.