Thermal Expansion Measurements Research Articles

The Thermomechanical, Functional and Biocompatibility Properties of a Au-Pt-Ge Alloy for PFM Dental Restorations.

A high-noble Au-Pt-Ge porcelain-fused-to-metal (PFM) dental alloy without the known adverse metallic elements and with the addition of germanium (Ge) was produced as a more cost-effective alternative to other precious alloying metals, with investigations for determining the functionality and clinical use of this alloy. The thermomechanical, biocompatibility, durability, workability and economic characteristics of the produced dental alloy were investigated. These properties were investigated with in vitro biocompatibility testing on human gingival fibroblasts (HGFs); static immersion testing for metal ion release; DSC analysis; hardness, tensile testing, density and coefficient of thermal expansion (CTE) measurements; metallographic and SEM/EDX microstructure investigations; and finally with the production of a test PFM dental bridge. The results of the thermomechanical testing showed alloy properties suitable for dental restorations and clinical use, with somewhat lower mechanical properties, making the alloy not suitable for extensive multiunit fixed restorations. The microstructure investigations showed segregations of Ge in the homogeneous alloy matrix, which reduce the alloy's mechanical properties. The produced PFM dental bridge showed excellent workability of the alloy in a dental laboratory setting, as well as a high standard of the final dental restoration. The ion release was negligible, well below any harmful quantities, while the cell viability examination showed significantly higher viability ratings on polished alloy samples as compared to as-cast samples. The results showed that a dental substructure in direct contact with oral tissue and fluids should be highly polished. The performed investigations showed that the produced PFM dental alloy is suitable for clinical use in producing high-quality dental restorations with high biocompatibility for patients prone to metal allergies.

High-temperature structure, elasticity, and thermal expansion of ε-ZrH1.8

Zirconium hydride is a promising candidate material for nuclear microreactor applications as a solid-state moderator component, owing to its favorable neutronics properties and good thermal stability over other metal hydrides. In the present work, the crystal structure, thermal expansion, and elastic properties of the hydrogen-rich ε phase hydride were measured at elevated temperatures in the range 300–900 K. Samples were prepared by direct hydriding Zircaloy-4 metal – a nuclear-grade zirconium alloy. Room-temperature lattice parameters agree well with those reported from literature for unalloyed zirconium hydride and fall within an observed quadratic H-content dependence. The coefficients of thermal expansion, determined from lattice expansion and dilatometry, agree well within our work but were about 30 % lower than those reported by others for unalloyed hydrides. Density functional theory-based molecular dynamics simulations were used to compare with thermal expansion and elasticity measurements. Results showed lattice parameter temperature dependence and slope of thermal expansion align with those from measurements. Based on diffraction scans at select temperatures, ε phase remained stable in air up to at least 770 K. Likewise, dilatometry showed smooth thermal expansion up to the thermal decomposition temperature around 950 K. The precise decomposition temperature was not determined via diffraction due to sparse scanning. The complete elastic property measurements were gathered for ε-phase Ziracloy-4 hydride for the first time. Young's modulus was lower compared to the metal and δ hydride phases. High-temperature elasticity measurements were limited to <350 K due to acoustic dissipation effects.

Thermal expansion, quasi-metamagnetism and spin-reorientation in Fe7Se8 substituted with chromium

The properties of the selenide compound Fe7Se8 with a layered crystal structure of the NiAs type are strongly influenced by substitutions and the distribution of vacancies. The Cr-substituted compound Fe6.5Cr0.5Se8 was obtained in single-crystalline form and studied by x-ray diffraction, energy-dispersive x-ray spectroscopy, thermal expansion and magnetization measurements. It was observed that the partial replacement of iron with chromium led to a twofold decrease in spontaneous volume magnetostriction due to changes in competing magnetoelastic contributions to thermal expansion along and perpendicular to the c axis of the crystal. The replacement of iron with chromium slightly decreases the Néel temperature (from 440 to 435 K) and significantly enhances the critical temperature of spin reorientation transition Tsr (from 115 to 160 K), apparently due to a change in the crystal electric field. Below 160 K, the Fe6.5Cr0.5Se crystal is found to exhibit metamagnetic-like behavior of the magnetization when the magnetic field is applied along the c axis. A jump-like change of the magnetization at a critical field up to ∼10 kOe is attributed to the presence of pinning centers of domain walls presumably due the ordering of chromium atoms substituting iron in cationic layers.

Characteristics of 3D Printed Functionally Graded Material for Replacement of Dissimilar Metal Weld in Nuclear Reactor

The dissimilar metal welds in the most of the reactors are connections between low alloy steel parts and stainless steel piping. There is a high possibility of primary water stress corrosion cracking (PWSCC) damage attributed to residual stress caused by the difference in material properties in the dissimilar metal weld joints. A number of accidents such as leakage of radioactive coolant due to PWSCC have been reported around the world, posing a great threat to nuclear safety. The objective of this study is to develop a technology that can fundamentally remove dissimilar metal welds by replacing the existing dissimilar metal parts with the functionally graded material (FGM) manufactured by metal 3D printing consisting of low alloy steel and austenitic stainless steel. A powder production, mixing ratio calculation, and metal 3D printing were performed to fabricate the low alloy steel-stainless steel FGM, and microstructure analysis, mechanical properties, and coefficient of thermal expansion (CTE) measurement of the FGM were performed. As a result, it is observed that CTE tended to increase as the austenite content increased in FGM. The gradual change of coefficient of thermal expansion in a FGM showed that the additive manufacturing using 3D printing was effective for preventing an abrupt change in thermal expansion properties throughout their layers.

Pressure dependence of phase transformation, thermal expansion and barocaloric property in a polycrystalline Ni54Mn23Ga23 alloy

An experimental investigation was conducted to understand the influence of hydrostatic pressure on phase transition, thermal expansion and barocaloric property of a polycrystalline Ni54Mn23Ga23 alloy. Two pressure ranges of 0–1.28 GPa and 0–0.74 GPa were selected for thermal expansion and barocaloric property measurements due to the different test limits of instrumentals. The pressure dependence of fourteen parameters was studied systematically. It was found that the sample experiences a martensitic transformation (MT) near room temperature and the response of MT peak temperature (TM) to pressure is about 15.89 K/GPa. The phase transition strain (λtr), transformation width (ΔTtr) relative volume change (|ΔV/V|) and maximum adiabatic temperature change (ΔTad)max increase linearly with pressure and their shifting rates are about 0.071 %/GPa, 7.5 K/GPa, 0.211 %/GPa and 12.2 K/GPa, respectively. Simultaneously, applying hydrostatic pressure can also enhance the barocaloric property of the sample, leading to a large increase in the absolute value of the maximum entropy change (|ΔS|max), the refrigerating capacity (RC) and their reversible values. On cooling, the sensitivities of the reversible RC and its proportion to pressure are around 185.52 J/kg GPa and 16.7 %/GPa, respectively. Finally, the average linear expansion coefficient (αave) of both martensite and austenite phases keeps unchanged while in the MT region it decreases from -99.84×10–6/K to -86.04×10–6/K with increasing pressure from 0 to 1.28 GPa. These findings indicate that applying hydrostatic pressure can effectively adjust the phase transformation, thermal expansion and barocaloric property of Ni-Mn-Ga alloys, which are meaningful for their application in solid-state refrigeration.

Precise density measurements of refractory metals over 3000 K: Revisiting UV imaging technique at ultrahigh temperatures

Precise density and thermal expansion measurements of refractory materials are extremely challenging due to the chemical reactions and thermal gradients at ultrahigh temperatures. The UV image technique has been successfully applied to the density measurements at high temperatures above 3000 K. However, intense radiation from the sample can blur the edge of the sample image, leading to uncertain measurements. In this study, we investigate the influence of the contrast between the UV background light and sample radiation (B–S) on density measurements. We find that lower B–S contrast can significantly affect the calibration factor that converts image pixels to real size, resulting in underestimated density with scattering and overestimated thermal expansion coefficients at ultrahigh temperatures. This result underscores the necessity of adequate B–S contrast to ensure the precision of density measurements using UV imaging methods for refractory materials beyond 3000 K. By considering the critical minimum value of the B–S contrast, we successfully measure the densities and thermal expansion coefficients of four refractory metal liquids (tungsten, rhenium, osmium, and tantalum) with the improved UV technique, which are crucial for high-temperature industries. This work will be valuable for other imaging methods measuring the thermophysical properties at ultrahigh temperatures.

A comparative study of magnetic behaviours in bulk and ribbon samples of PrMn2Ge2 compound

The magnetic properties of PrMn2Ge2 samples in both the as-cast bulk and melt-spun ribbon forms have been investigated in detail by a comprehensive set of x-ray and neutron powder diffraction, magnetic and heat capacity measurements and corresponding sets of data analyses. Thermal expansion measurements indicate the presence of magnetoelastic coupling effects around all transition temperatures in the bulk sample. The bulk modulus K0 = 42.0 GPa and its first derivative K0’ = 18.7 have been derived from the pressure-volume data. The Curie temperature from the intralayer antiferromagnetism (AFl) of PrMn2Ge2 to a canted spin structure (Fmc) is TCinter = 332 K for the bulk sample, decreasing to TCinter = 320 K for the ribbon sample. The critical components γ, β and δ of this second order magnetic transition as determined from Kouvel-Fisher analyses, indicate long range magnetic interactions around TCinter. Based on these critical exponents the magnetization, field and temperature data around TCinter collapse onto two curves obeying the single scaling equation M(H,ε)=εβf±(Hεβ+γ). The Debye temperatures and the density of states at the Fermi level are θD=306K and N(EF)=3.47state/eVatom for the bulk sample and θD=320K and (EF)=2.18state/eVatom for the ribbon sample with the nuclear specific heat coefficient for bulk PrMn2Ge2 derived from the splitting of the nuclear hyperfine levels as CN = 517 mJ mol−1 K−1. With a field change of ΔB = 5 T, the maximum values of the magnetic entropy changes -ΔSmax in the region around TCinter are -ΔSmax = 3.00 J/kg K and 2.35 J/kg K for the bulk and ribbon samples respectively, while the relative cooling power (RCP) for the ribbon-spun sample, RCP = 135.9 J/kg, is significantly higher than the value of RCP = 116.6 J/kg for the bulk sample. These findings indicate that PrMn2Ge2 could be a promising candidate for magnetic refrigeration applications in the room temperature region.

Anisotropic thermo-mechanical response of layered hexagonal boron nitride and black phosphorus: application as a simultaneous pressure and temperature sensor.

Hexagonal boron nitride (hBN) and black phosphorus (bP) are crystalline materials that can be seen as ordered stackings of two-dimensional layers, which lead to outstanding anisotropic physical properties. Knowledge of the thermal equations of state of hBN and bP is of great interest in the field of 2D materials for a better understanding of their anisotropic thermo-mechanical properties and exfoliation mechanism towards the preparation of important single-layer materials like hexagonal boron nitride nanosheets and phosphorene. Despite several theoretical and experimental studies, important uncertainties remain in the determination of the thermoelastic parameters of hBN and bP. Here, we report accurate thermal expansion and compressibility measurements along the individual crystallographic axes, using in situ high-temperature and high-pressure high-resolution synchrotron X-ray diffraction. In particular, we have quantitatively determined the subtle variations of the in-plane and volumetric thermal expansion coefficients and compressibility parameters by subjecting these materials to hydrostatic conditions and by collecting a large number of data points in small pressure and temperature increments. In addition, based on the anisotropic behavior of bP, we propose the use of this material as a sensor for the simultaneous determination of pressure and temperature in the range of 0-5 GPa and 298-1700 K, respectively.

Thermal expansion of 4H and 6H SiC from 5 K to 340 K

The first thermal expansion measurements of the 4H and 6H polytypes of SiC below room temperature are reported. The measurements were carried out on single-crystal specimens using high-resolution capacitive-based dilatometry. For both polytypes, the thermal expansion coefficient is below 2.4 × 10−6 1/K near room temperature. No phase transitions are observed over the 5 K to 340 K temperature range of the measurements. The thermal expansion coefficient α of 4H SiC is slightly anisotropic for measurements parallel and perpendicular to the crystallographic c axis with α|| about 2.2 × 10−7 1/K larger than α⊥ near room temperature. For 6H SiC no discernible anisotropy is observed. The differences in anisotropy can be understood by considering the ratio of hexagonal to cubic bonds of each polytype. Narrow regions with negative thermal expansion that are within the limits of our resolution (∼1×10−8) are observed in the vicinity of 30 K for both specimens. Tabulated data, polynomial fits, fit parameters, and comparison to data based on lattice-parameter measurements are provided.

Electroactive actuator composites using volume change induced by insulator-to-metal transition in VO2

This report describes the actuator functionality of a ceramic composite that uses the volume change caused by the insulator–metal (I–M) transition of VO2. When an electrical field was applied at 295 K, 50 vol. %-VO2/Al2O3 ceramic composite underwent the I–M transition because the VO2 powder dispersed in the composite became metallic. Simultaneous measurement of I–V characteristics and linear strain demonstrated that this I–M transition was accompanied by a positive strain. This strain increased with increase in the limit current value, which limits excessive current flow after transition. The strain exceeded 1300 ppm at maximum. Its magnitude corresponded to the volume change obtained from thermal expansion measurements on the composite. This composite performs a volume-change-driven actuator function that is distinct from the strain-driven counterpart of piezoelectric materials.

Experimental measurement and modeling of lattice thermal expansion and specific heat capacity of C15-Cr2Nb Laves phase intermetallic compound

In order to determine the lattice thermal expansion and specific heat capacity (Cp) of the C15-Cr2Nb Laves phase, an experimental investigation and modeling were carried out in the present paper by employing high-temperature X-ray diffraction (HTXRD) and differential scanning calorimetry (DSC). A thorough analytical model was utilized to predict the temperature-dependent variations of enthalpy and specific heat, and the predicted findings were compared to the experimentally measured data. Arc melting was employed to synthesize Cr2Nb samples with distinct hexagonal (C14/C36) and cubic (C15) Laves phase structures, which were then subjected to the appropriate heat treatment. Room temperature XRD patterns, SEM, and EDAX experiments on homogenized samples at 1273 K for 72 h validated the homogeneity and C15 (Fd-3 m) crystal structure of Cr2Nb. Rietveld refinement was used to determine the lattice parameters and relative phase fractions of the constituent phases. The average thermal expansion coefficient was determined to be αai = 0.659 × 10−5 and αVi = 1.977 × 10−5 K−1 respectively. The Cp of the C15-Cr2Nb Laves phase intermetallic compound was measured employing heat flux DSC, utilizing conventional “three-step” procedures, and being reported for the first time. The measured Cp and enthalpy increment data (HT – H298.15) with varying temperatures reported in the present investigation are being correlated utilizing the theoretical model applying the quasi-harmonic Debye Grüneisen model in the temperature range 0–860 K and illustrated different contributions to the total heat capacity i.e., vibrational, anharmonic, and electronic.

Thermal diffusivity and thermal expansion investigations of WLV steel

WLV steel (32CrMoV12-28) with a density 7.80 g/cm3 at room temperature (RT) was used to study the temperature characteristics of thermal diffusivity and thermal expansion in the temperature range from RT to 1100°C Two types of NETZSCH flash devices were used, i.e. low-temperature LFA 467 and high-temperature LFA 427. A sample of NETZSCH Inconel 600 with a density of 8.35 g/cm3 at room temperature in the temperature range from RT to 480°C was used as the reference material. The reference material was used to determine the thermal conductivity and specific heat by the comparative method. The results of thermal diffusivity tests of WLV steel made with the LFA 467 and LFA 427 apparatus turned out to be consistent with each other. Measurements of thermal expansion of WLV steel were carried out using a NETZSCH DIL 402 C dilatometer. The results of thermal expansion studies indicated a ferrite-austenite phase transition at 835°C, which causes shrinkage of the material. WLV steel has been tested for military use as barrel steel. The paper presents the thermophysical properties of this steel in a wide range of temperatures so that they can be used as input data for numerical simulations of heat transfer in cannon barrels.

Linear magnetoresistance and structural distortion in layered SrCu4–x P2 single crystals

We report a systematic study on layered metal SrCu4−x P2 single crystals via transport, magnetization, thermodynamic measurements and structural characterization. We find that the crystals show large linear magnetoresistance without any sign of saturation with a magnetic field up to 30 T. We also observe a phase transition with significant anomalies in resistivity and heat capacity at T p ∼ 140 K. Thermal expansion measurement reveals a subtle lattice parameter variation near T p, i.e., ΔLc /Lc ∼ 0.062%. The structural characterization confines that there is no structure transition below and above T p. All these results suggest that the nonmagnetic transition of SrCu4−x P2 could be associated with structural distortion.

Structure–property relations in graphitic pebbles for nuclear applications

This work presents an analytical approach for holistically characterizing graphitic matrix pebbles for nuclear applications whereby the macrostructure, microstructure, and thermophysical properties of pebbles are determined. A systematic sectioning method was applied to several pebbles to describe the regional properties of the samples. Intact matrix-only spheres and sections of spheres fabricated by Kairos Power were characterized via optical imaging, x-ray computed tomography, x-ray diffraction, and ellipsometry to determine 2D and 3D macrostructure and anisotropy. The thermophysical properties of these materials were determined via measurements of density, specific heat, thermal expansion, and thermal diffusivity. The results of this study indicate that the pebble fabrication methods and their resultant effect on microstructure have a nontrivial effect on thermophysical properties, confirming the importance of robust characterization of these components. A discussion of the characterization approach and its applicability to nuclear fuel development activities is also included.

Influence of cation species on thermal expansion of Y2Si2O7–Gd2Si2O7 solid solutions

Mixtures of Y2Si2O7 and Gd2Si2O7 were synthesized by solid-state reaction at 1600°C and characterized via in situ x-ray diffraction (XRD) to determine their coefficients of thermal expansion (CTE). All solid solutions within the system exhibited the orthorhombic δ-RE2Si2O7 (Pna21) structure. Thermal expansion measurements of Y2Si2O7 and Gd2Si2O7 correlated well with reported values in literature, and all synthesized solid solutions exhibited CTEs between Y2Si2O7 and Gd2Si2O7. Generally, there was a slight decrease in CTE exhibited by the materials with increasing Gd2Si2O7 content, with Gd2Si2O7 having the lowest CTEs and Y2Si2O7 the highest CTEs. The decrease in CTE was attributed to stronger bonds of Gd–O over Y–O, as determined by calculated crystal orbital Hamilton populations using density functional theory. However, such differences were very small and crystal structure was the dominating factor in CTE trends.

Effect of Si Content on the Thermal Expansion of Ti15Mo(0-2 Si) Biomaterial Alloys during Different Heating Rates.

Thermal expansion measurements were used to characterize phase transformations in metastable β-Ti alloys (Ti15MoxSi) without and with various Si additions (where x = 0, 0.5, 1.0, 1.5, and 2 in wt.%) during linear heating at two heating rates of 5 and 10 °C/min up to 850 °C. For this study, five alloys were developed and examined in terms of their presence phases, microstructures, and starting and final transformation temperatures. According to the results, all of the as-cast samples primarily include an equiaxed β-Ti phase. The influence of phase transformation on the material dimensions was discussed and compared with the variations in Si contents. The transformation was investigated using a dilatometric technique for the developed alloys during continuous heating and cooling. The dilatometric curve of heating revealed two distinct reflection points as the heating temperature increased. The starting transformation temperature (Ts) to obtain the ω-phase was reported at 359 °C without Si addition; whereas the final transformation temperature (Tf) of the dissolution of α-phase was obtained at 572 °C at a heating rate of 10 °C/min. At 2 wt.% Si, the first derivative curves reported Ts and Tf transforming temperatures of 314-565 °C (at a 5 °C/min heating rate) and 270-540 °C (at a 10 °C/min heating rate), respectively. The Ts and Tf transforming temperatures were significantly decreased with Si additions, which decreased the β-transus temperature. Moreover, the thermal expansion coefficient curves of the investigated alloys without and with 2 wt.% Si were studied. The transformation heating curves have an S-shaped pattern, according to the results.

From magnetic order to valence-change crossover in EuPd$_2$(Si$_{1-x}$Ge$_x$)$_2$ using He-gas pressure

We present results of magnetic susceptibility and thermal expansion measurements performed on high-quality single crystals of EuPd_22(Si_{1-x}1−xGe_xx)_22 for 0 \leq x \leq≤x≤ 0.2 and temperatures 2 K \leq T \leq≤T≤ 300 K. Data were taken at ambient pressure and finite He-gas pressure pp\leq≤ 0.5 GPa. For x = 0x=0 and ambient pressure we observe a pronounced valence-change crossover centred around T'_VT′V\approx≈ 160 K with a non-magnetic ground state. This valence-change crossover is characterized by an extraordinarily strong pressure dependence of dT'_VT′V /dpp = (80 \pm 10)±10) K/GPa. We observe a shift of T'_VT′V to lower temperatures with increasing Ge-concentration, reaching T'_VT′V\approx≈ 90 K for x = 0.1x=0.1, while still showing a non-magnetic ground state. Remarkably, on further increasing xx to 0.2 we find a stable Eu^{(2+\delta)+}(2+δ)+ valence with long-range antiferromagnetic order below T_NTN = (47.5 \pm± 0.1) K, reflecting a close competition between two energy scales in this system. In fact, by the application of hydrostatic pressure as small as 0.1 GPa, the ground state of this system can be changed from long-range antiferromagnetic order for pp&amp;#60;&lt; 0.1 GPa to an intermediate-valence state for pp\geq≥ 0.1 GPa.

Thermal and magnetic properties of Fe7Se8 studied on single crystals

Specific heat, thermal expansion and magnetic measurements on single crystalline samples have been employed to study the interplay between the lattice and the magnetic state in the layered iron selenide compound Fe7Se8, which exhibits a ferrimagnetic order below TN ≈ 440 K and a spin reorientation transition upon cooling below Tsr ∼ 115 K. Thermal expansion measurements performed on single-crystal samples revealed significant anisotropic deformations of the crystal lattice with decreasing temperature below TN, an increase in the c/a ratio, and negative volume spontaneous magnetostriction (ωs ∼ −5.3⋅10−3 at 120 K). The first-order spin reorientation transition in Fe7Se8 is found to be accompanied by a hysteretic behavior of the specific heat and thermal expansion, and an anomaly in the ωs vs T dependence. The results obtained are indicative of a strong influence of the magnetoelastic interactions on the properties of Fe7Se8.

Subtle lattice distortion-driven phase transitions in layered ACu4As2 (A = Eu, Sr)

The compounds composed of transition metal cations and pnictide anions provide a rich platform for studying novel physical phenomena. Here we report on the observation of a phase transition at ∼ 70 K and 145 K in layered compound EuCu4As2 and SrCu4As2, respectively. from both the transport and heat capacity. The thermal expansion measurements show that the variation of the lattice parameters (ΔLb /Lab ) around T P is much less than that for a typical crystalline phase transition. Our experimental results reveal that the transition in EuCu4As2 and SrCu4As2 should be driven by subtle structural-distortion.

Single-Crystal Growth of a Cubic Laves-Phase Ferromagnet HoAl2 by a Laser Floating-Zone Method

The successful growth of single crystals of a cubic Laves-phase material HoAl2 with the space group Fd-3m is reported in this study. The crystals were grown by a floating-zone method with five laser diodes as a heat source. Al-rich feed rods were prepared as compensation for heavy evaporation during the growth. The nominal ratio for the feed rods was optimized as Ho:Al = 1:2.5. Single crystals of HoAl2 with a length of 50 mm were first grown in this technique. Obtaining the large-sized crystal by the floating-zone method enabled us to systematically explore the physical properties using the same batch crystal. The crystal possessed a second-ordered ferromagnetic transition at 29 K and a first-ordered spin-reorientation transition at 20 K. The bulk physical properties, such as specific heat, magnetic susceptibility, isothermal magnetization, and thermal expansion measurements, were measured. Additionally, a magnetocaloric effect was evaluated by the magnetic entropy change. We demonstrate that anisotropic physical properties along the principal axes ([100], [110], and [111]) emerged below the magnetically ordered states, in contrast to the isotropic behavior in the paramagnetic state.