Thermal Expansion Experiments Research Articles

Influence of Solute Drag Effect and Interphase Precipitation of Nb on Ferrite Transformation.

The significant impact of Nb on ferrite transformation, both in terms of solute drag effect (SDE) and interphase precipitation, was investigated quantitatively. Ferrite transformation kinetics were characterized using thermal expansion experiments and theoretical calculations. The microstructures were characterized using high-temperature confocal laser scanning microscopy (CLSM), a field-emission scanning electron microscope (FESEM), and a transmission electron microscope (TEM). Under a higher driving force, interphase precipitations were observed in the sample with a higher Nb content. A three-dimensional (3D) reconstruction method was used to convert the two-dimensional (2D) image of interphase precipitation into a three-dimensional model for a more typical view. The SDE and interphase precipitation had opposite effects on the kinetics of ferrite transformation. A lower Nb content showed a strong contribution to the SDE, which delayed ferrite transformation. A higher concentration of Nb was expected to enhance the SDE, but the inhibition effect was eliminated by the interphase precipitation of NbC during interfacial migration. Both the experimental results and theoretical calculations confirmed this phenomenon.

High intrinsic thermal conductive polymer films by engineered interchain hydrogen bond interactions

AbstractA series of polyvinyl alcohol (PVA) composite films containing different hydrogen bond acceptors 4,4′‐dihydroxydiphenyl (BP), 1,1′‐biphenyl‐4,4′‐diyl dihexanoate (DHB) and benzene‐1,3,5‐triyl tribenzoate (TBB) were prepared by casting method. Due to the existence of strong intermolecular interaction, the highest in‐plane thermal conductivity of the above films is 1.298 Wm−1 K−1, which is about 65% higher than pure PVA films. Fourier Transform infrared spectroscopy (FT‐IR) and wide‐angle X‐ray diffraction (WXAD) demonstrated that the TBB acts as a thermal bridge to enhance the internal interaction force and make the internal structure more regular. Strong molecular contact forces were demonstrated by mechanical tensile testing. The thermal expansion rate of the system was explored through molecular dynamics. Thermal expansion experiments proved that hydrogen bond can effectively reduce the free volume. Molecular dynamics simulations were also performed in this work. The number and density of hydrogen bonds inside different polymers were calculated, and the phonon thermal transport was quantitatively analyzed. The thermal bridge and intermolecular contact force were discovered to effectively restrict the molecular chain's activity and reduce its free volume. The results of the experiments and molecular dynamics reveal that strong intermolecular interactions and thermal bridges can significantly improve polymer intrinsic thermal conductivity.

Effects of Al2O3 doping on the microstructural evolution and densification process of AZO targets

Aluminum-doped zinc oxide (AZO) and zinc oxide (ZnO) slurries with high solid content and low viscosity were prepared by milling, and a new pressure slip casting technology was used to produce green compacts. Based on the shrinkage data obtained from thermal expansion experiments, activation energies for the densification of AZO and ZnO at different heating rates were calculated by the master sintering curve (MSC) method, and activation energies for grain growth were separately calculated. The optimal sintering process of AZO targets was investigated by the two-step sintering method, and AZO targets with a relative density of 99.8% and a grain size of 3.89 μm were obtained.

Microstructure investigation of the Na/Ca aluminosilicate hydrate gels and its thermal compatibility in fly ash–GGBS cementitious binder

The synthesis of geopolymers (Na/Ca alumino silicate hydrate gels) was carried out in different proportions of fly ash and GGBS: 0/100 (A), 50/50 (B) and 100/0 (C). The gel composition at elevated temperature was characterised by studying the microstructure through X-ray diffraction (XRD). In addition, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were also employed for structural characterisation. Thermal expansion and thermal conductivity experiments were conducted through thermal gravimetric analysis/differential thermal analysis (TGA/DTA). The compressive strength gain in the composites after exposure to a temperature of 800 °C was compared and found to be higher in CpT than ApT samples, which is attributed to thermal transformation enabled by dehydration and dehydroxylation of the N-A-S-H gel. The thermal stress–induced microcracks were observed to be higher in ApT and BpT samples but lower in CpT samples as evidenced by SEM. The lines representing binding energy (BE) in XPS showed marked changes in their position, intensity and % composition related to crystal field of the elements and it is reflected in the compressive strength. It was found that the addition of slag in Bp decreases the binding energies of Si, Ca, Al, Na and O by changing the local environment in the network by charge delocalisation and reducing the intensity of Ca peaks to a greater extent at 800 °C. The O1s peak of all heated samples correspond to the non-bridging oxygen atoms. These research findings open up the possibility for the fabrication of thermally insulated ceramic type geopolymers.

Thermomechanical constitutive equations for glass and numerical simulation on automobile glass forming technology

To establish a comprehensive numerical model for automotive glass forming, firstly, this paper conducts material tests of 3·2 SG glass to obtain detailed material properties. Through thermal expansion experiments, the thermal expansion coefficients including glassy and liquid states are obtained; then by using three-point bending stress relaxation and differential scanning calorimetry experiments, the stress relaxation and structural relaxation properties of the glass are obtained. Finally, a comparison analysis of the simulation and the actual spherical deviation for an actual automobile glass product is carried out. The result shows that the product simulation and the actual product spherical deviation correspond. The maximum value of the spherical deviation is within 0·94 mm between simulation and the actual product spherical deviation. The accuracy can meet the design requirements, and the established numerical model is reliable.

Evidence of overpressure at the base of huge landslide

Overpressuring from generation of CO2 gas caused by thermal decomposition of basal carbonates can raise pore-fluid pressure and reduce friction during landsliding. We used thermogravimetry and dilatometry to determine the evidence of raised pore-fluid pressure from carbonate thermal decomposition at the base of the 2009 Jiweishan landslide. Results from thermal expansion experiments showed that the rock undergoes expansion and thermal fracture. At a heating rate of 20°C/min, the coefficient of linear thermal expansion increased sharply at 807.3 °C and reached a maximum of 36.6×10−6 °C −1 at 827.3 °C. DTG data show that the temperature of the maximum thermal decomposition rate of calcite is 852.5°C. The evidence showed that CO2 gas can produce great pressure during the rapid sliding process of Jiweishan landslide, and it is conducive to reduce the effective normal load. In addition, thermal fracture may be a explanation for the ultra-low friction during the rapid sliding by reducing the strength of the rock at the sliding surface and making it more easily entrained.

Phase Transformation of ER70-Ti for Gas Shielded Wire

ER70-Ti is a high strength gas shielded welding wire steel, which is suitable for ships, bridges and other structures, and can be used for thick plate welding with high current. In the welding wire industry, ER70-Ti is a high-tech deep-processing product with high added value. In this study, the thermal expansion experiment of ER70-Ti wire rod was carried out. The critical temperature of ER70-Ti phase transformation was measured and the continuous cooling transformation curve (CCT curve) of undercooled austenite was drawn. The microstructure and hardness of the samples under different cooling rates were observed. The results show that Ac1 temperature of ER70-Ti sample was 690 °C, Ac3 temperature was 877°C, and Bs temperature was 575°C. When the cooling rate was low (0.1°C/s~2.5°C/s), the phase transformation products of ER70-Ti were equiaxed polygonal ferrite and granular bainite. With the increase of cooling rate, the grain size of ER70-Ti sample was refined and the bainite content increased from 53% to 85%. When the cooling rate was higher than 5°C/s, all the phase transformation products were bainite. The Vickers microhardness also increased with the increase of cooling rate, from 185HV to 325HV.

Elastic Modulus, Thermal Expansion, and Pyrolysis Shrinkage of Norway Spruce Under High Temperature

The orthotropic and temperature-dependent nature of the mechanical properties of wood is well recognized. However, past studies of mechanical properties at elevated temperatures are either limited to temperatures below 200 °C or focus only on the direction parallel to grain. The effect of time-dependent pyrolysis during measurement is often neglected. This paper presents a novel method for determining elastic modulus at high temperatures and thermal expansion coefficient in different orthotropic directions via Dynamic Mechanical-Thermal Analyser (DMTA). The method allows for drying, drying verification, and measurement in one chamber, eliminating the possibility of moisture reabsorption from ambient air. The repeatable measurements can be carried out in temperatures up to 325°C, adequate for observing time-dependent pyrolysis during measurement. Results of the measurements of Norway Spruce provide data of its mechanical response at temperature range previously not explored widely, as well as in the orthotropic direction. Time-dependent behaviour was observed in the thermal expansion and shrinkage experiment, where above 250°C the amount of shrinkage depends on heating rate. At such temperature, elastic moduli measurement also shows time dependence, where longer heating at certain temperature slightly increases the measured elastic modulus. Additionally, bilinear regression of the relationship between elastic moduli and temperature shows quantitatively good fit. Numerical simulation of the DMTA temperature history and wood chemical components mass losses show the onset of shrinkage and onset of hemicellulose mass loss occurring at around the same time, while decomposition of cellulose correlate with the sudden loss of elastic moduli.

Experimental Research on Wind-Cooling Quenching of 20Mn2CrSi Steel

Compared to aluminum alloy wheels, steel wheels have been widely used in the automobile industry due to the low cost and high plasticity and toughness. In this report, wind-cooling quenching of the wheels made of 20Mn2CrSi steel is studied. The CCT curves of 20Mn2CrSi are firstly drawn based on the thermal expansion experiment. Then the samples with different thicknesses (4mm, 6mm, 11mm) are tested under air cooling and wind cooling conditions to find out their optimum transfer time of quenching, and the cooling rates of the surfaces and internal of the sample under wind-cooling condition. The Vickers hardness of the samples after wind-cooling quenching are also measured by a Vickers hardness meter. The results show that the cooling rate is slow when the air volume during cooling is 900m3/h, making the hardness of the samples fail to meet the use standard. Therefore, in order to improve the cooling rate and reduce the thermal stress and structural stress during quenching, water atomization quenching method is proposed, which can provide a certain reference value for the quenching process of 20Mn2CrSi steel wheels.

Thermoelastic properties and \u03b3\u2019-solvus temperatures of single-crystal Ni-base superalloys

The present work shows that thermal expansion experiments can be used to measure the γʼ-solvus temperatures of four Ni-base single-crystal superalloys (SX), one with Re and three Re-free variants. In the case of CMSX-4, experimental results are in good agreement with numerical thermodynamic results obtained using ThermoCalc. For three experimental Re-free alloys, the experimental and calculated results are close. Transmission electron microscopy shows that the chemical compositions of the γ- and the γʼ-phases can be reasonably well predicted. We also use resonant ultrasound spectroscopy (RUS) to show how elastic coefficients depend on chemical composition and temperature. The results are discussed in the light of previous results reported in the literature. Areas in need of further work are highlighted.Graphical abstract

Structural and physical properties of trilayer nickelates R4Ni3O10 ( R=La , Pr, and Nd)

We investigate the low temperature structural and physical properties of the trilayer nickelates R4Ni3O10 (R = La, Pr and Nd) using resistivity, thermopower, thermal conductivity, specific heat, high-resolution synchrotron powder X-ray diffraction and thermal expansion experiments. We show that all three compounds crystallize with a monoclinic symmetry, and undergo a metal-to-metal (MMT) transition at 135 K (La), 156 K (Pr) and 160 K (Nd). At MMT, the lattice parameters show distinct anomalies; however, without any lowering of the lattice symmetry. Unambiguous signatures of MMT are also seen in magnetic and thermal measurements, which suggest a strong coupling between the electronic, magnetic and structural degrees of freedom in these nickelates. Analysis of thermal expansion yields hydrostatic pressure dependence of MMT in close agreement with experiments. We show that the 9-fold coordinated Pr ions in the rocksalt (RS) layers have a crystal field (CF) split doublet ground state with possible antiferromagnetic ordering at 5 K. The Pr ions located in the perovskite block (PB) layers with 12-fold coordination, however, exhibit a non-magnetic singlet ground state. The CF ground state of Nd in both RS and PB layers is a Kramers doublet. Heat capacity of R = Nd shows a Schottky-like anomaly near35 K, and an upturn below T = 10 K suggesting the presence of short-range correlations between the Nd moments. However, no signs of long-range ordering could be found down to 2 K despite a sizeable theta_p ~ -40 K. The strongly suppressed magnetic long-range ordering in both R = Pr and Nd suggests the presence of strong magnetic frustration in these compounds. The low-temperature resistivity shows a T^0.5 dependence. No evidence for the heavy fermion behavior could be found in any of the three compounds.

Diffusion transformation model in TA15 titanium alloy: The case of nonlinear cooling

The cooling processes of hot working for TA15 titanium alloy are highly nonlinear, during which non-isothermal and non-isokinetic phase transformations often occur leading to the changes in the microstructures and mechanical properties. The existing phase transformation models, that are established based on isothermal transformations, are either difficult to reflect the real transformation process or complicated for use. Therefore, in this paper a succinct model suitable for the transformations at any cooling path was developed by separating the transformation process into a series of linear cooling steps. First, the transformation behaviors during linear cooling processes were studied by thermal expansion experiments, and then a kinetic model of the transformations at constant cooling rates was developed based on the JMAK law. Second, the additivity of the transformations during linear cooling processes was proved, and therefore the additivity rule was extended to calculate the incubation period of the transformation during non-linear cooling process. Finally, based on the crystallization model built by T. Ozawa, the new transformation model was established, and its reliability was proved by experiments.

Ab Initio Calculations on Elastic Properties of IF Steel Matrix Phase at High Temperature Based on Lattice Expansion Theory

Elucidating the evolution law of the elastic properties of the matrix phase is of great significance for the control of steel properties and quality during continuous casting and subsequent heat treatment. In this paper, thermal expansion experiments and ab initio calculations are used to study the elastic properties of the interstitial free (IF) steel matrix phase in different magnetic states and crystal structures. The results show that the bulk modulus B and the tetragonal shear elastic constant C’ for the entire temperature range decrease with increasing temperature, but C44 is the opposite. While from paramagnetic (PM) to ferromagnetic (FM) state, C’(C44) have changed ~188% (~27%), B increases by ~55% during the crystal structure change (fcc→bcc). With the FM to PM state, the Zener anisotropy parameter increases sharply, and Young’s modulus decreases significantly in the [001] direction; the maximum difference is ~76 GPa. The evolution rate of average Young’s modulus in single bcc-phase FM (fcc-phase PM) range reaches ~5.5(~5.6) × 10−2 GPa K−1. The research provides an effective method for ab initio calculation of the elastic properties of interstitial free and ultra-low carbon steels at high temperature, also furnishing a basis for the application of ab initio calculations to the high temperature performance of steel materials.

Study on the influence mechanism of Mg2+ modification on vermiculite thermal expansion based on molecular dynamics simulation

The thermal insulating performance of expanded vermiculite is closely related to expansibility. A novel method of Mg2+ modification was proposed to improve the vermiculite expansion ratio. The modification process was characterised by energy dispersive X-Ray spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric-differential scanning calorimeter and scanning electron microscopy. Moreover, the thermal expansion experiment was performed to investigate the expansion behaviours of Raw-V and Mg–V samples at various temperatures. The result indicated that the introduction of Mg2+ could increase the vermiculite interlayer water content through hydration interaction, and the expansion ratio increased 13.7% under the heating temperature of 900 °C after modification. To explain the interaction of magnesium ion and water molecules, a molecular dynamics model was developed, and the simulation results were validated using the binding energy calculation. The results of this study can provide a new perspective and theoretical guidance for the commercial process of vermiculite expansion.

Thermal Expansion and Hydrostatic Pressure Experiment Using Common Materials for Supporting Science Education in a Rural Area at Central Sulawesi, Indonesia

Experiments are needed in science learning. However, the instruments used cost high; thus, it is difficult to find, especially in rural areas. The purpose of this study was to develop a low-cost tool for science learning. This science experiment has been successfully developed from inexpensive common materials. Research and Development design employing Gall and Borg Model was used in developing the science instruments. Analysis, design, fabricate, validate, revising, and implementation were the steps in producing the devices. Observation sheet and questionnaire were used for evaluating and validating the instrument. The subject of this study was students of SMPN 1 Sigi, Sigi Sub Province, Central Sulawesi. After designed and fabricated, the devices were validated by two judges to know the practicality and convenience. The tools were set up to demonstrate the expansion concept of gas and liquid; also, to establish the presence of hydrostatic pressure inside the fluid. The N-gain analysis was performed to know the increase of student understanding after employing the instruments in science learning. The results showed that student understanding was increased by about 30.13% after using devices in science learning. In other words, the designed tools were succeeded in introducing the concept of gas and liquid well and in establishing the fact that the higher hydrostatic pressure of the fluid is discovered in a deeper location inside the liquid. Based on the success, the devices were socialized to other science teachers in the area.

Magnetostriction reveals orthorhombic distortion in tetragonal Gd compounds

We report detailed thermal expansion and magnetostriction experiments on GdCoIn$_5$ and GdRhIn$_5$ single crystal samples that show a sudden change in the dilation at a field B$^\ast$ for temperatures below the N\'eel transition temperature TN. We present a first-principles model including crystal-field effects, dipolar and exchange interactions, and the dependence of the exchange couplings with lattice distortions in order to fully account for the magnetostriction and magnetic susceptibility data. The mean-field solution of the model shows that a transition between metastable states occurs at the field B$^\ast$. It also indicates that two degenerate phases coexist in the sample at temperatures below TN. This allows to explain the lack of observation, in high resolution x-ray experiments, of an orthorhombic distortion at the N\'eeel transition even though the magnetic structure breaks the tetragonal symmetry and the magnetoelastic coupling is significant. These conclusions could be extended to other tetragonal Gd-based compounds that present the same phenomenology.

An anomalous thermal expansion phenomenon induced by phase transition of Fe-Co-Ni alloys

The thermal expansion and the phase transition of Fe-15.6 wt. %Co-12 wt. %Ni single-phase solid solution alloy were systematically investigated by thermal analysis experiments and molecular dynamics simulations. The coefficient of thermal expansion (CTE) was accurately measured in the temperature range of 300-1580 K. The eccentric changes of thermal expansion ranging from 900 to 1150 K were verified from the incomplete transformation of α-Fe phase to γ-Fe phase by differential scanning calorimetry (DSC) and in situ X-ray diffraction experiments. The CTE of α-Fe phase increases nonlinearly from 9.29 × 10−6 to 1.278 × 10−5 K−1 in the range of 300-900 K, which is in good agreement with the results obtained by molecular dynamics simulation, whereas the CTE of γ-Fe phase increases linearly from 2.024 × 10−5 to 2.398 × 10−5 K−1 in the range of 1150-1580 K. Meanwhile, the visual atomic positions at different temperatures indicate that thermal expansion is attributed to the anharmonic vibration and short-range diffusion of atoms when the temperature exceeds a certain value. Furthermore, the Curie temperature is determined as 725 K by the thermal expansion and DSC experiments. Additionally, the isothermal sections of the Fe-rich corner [Fe-5x wt. %Co-5y wt. %Ni(2 ≤ x + y ≤ 8)] in Fe-Co-Ni non-equilibrium ternary phase diagram at 300 K are derived by X-ray diffraction. Moreover, the CTE ranging from 300 to 1700 K of the Fe-rich corner in Fe-Co-Ni ternary phase diagram was predicted theoretically on the basis of the molecular dynamics method.

Sub-gap optical response in the Kitaev spin-liquid candidate α-RuCl3

We report detailed optical experiments on the layered compound α-RuCl3 focusing on the THz and sub-gap optical response across the structural phase transition from the monoclinic high-temperature to the rhombohedral low-temperature structure, where the stacking sequence of the molecular layers is changed. This type of phase transition is characteristic for a variety of tri-halides crystallizing in a layered honeycomb-type structure and so far is unique, as the low-temperature phase exhibits the higher symmetry. One motivation is to unravel the microscopic nature of THz and spin-orbital excitations via a study of temperature and symmetry-induced changes. The optical studies are complemented by thermal expansion experiments. We document a number of highly unusual findings: A characteristic two-step hysteresis of the structural phase transition, accompanied by a dramatic change of the reflectivity. A complex dielectric loss spectrum in the THz regime, which could indicate remnants of Kitaev physics. Orbital excitations, which cannot be explained based on recent models, and an electronic excitation, which appears in a narrow temperature range just across the structural phase transition. Despite significant symmetry changes across the monoclinic to rhombohedral phase transition and a change of the stacking sequence, phonon eigenfrequencies and the majority of spin-orbital excitations are not strongly influenced. Obviously, the symmetry of a single molecular layer determines the eigenfrequencies of most of these excitations. Only one mode at THz frequencies, which becomes suppressed in the high-temperature monoclinic phase and one phonon mode experience changes in symmetry and stacking. Finally, from this combined terahertz, far- and mid-infrared study we try to shed some light on the so far unsolved low energy (<1 eV) electronic structure of the ruthenium 4d5 electrons in α-RuCl3.

Improved uniformity of hardness by continuous low temperature bainitic transformation in prehardened mold steel with large section

Expanding automobile industry energized the demand for large section plastic mold steel, large (465mm × 1325mm × length) pre-hardened mold (PHM) steel was trial-produced by quenching the forged slab at temperature between start (Ms) and finish (Mf) temperature of martensite, followed by tempering, according to the thermal expansion experiments and finite element modeling (FEM) of cooling rate from core to surface. Continuous low temperature bainitic transformation in PHM steel created high volume fractions of refined bainitic-ferrite laths, filmy retained austenite and dispersed carbides. Uniformity of microstructure and hardness, and the impact toughness of the PHM steel were remarkably superior to the one produced by conventional quenching & tempering (QT) process.

The FCC to BCC phase transformation kinetics in an Al0.5CoCrFeNi high entropy alloy

In this paper, thermal expansion method is used to characterize the phase transformation process of Al0.5CoCrFeNi high entropy alloy (HEA), and the FCC-BCC phase transformation kinetics, microstructure and mechanical properties are investigated. Results show that during continuous heating process, three stages of phase transformation process for Al0.5CoCrFeNi HEA are characterized by thermal expansion curves, and the third stage is corresponding to FCC-BCC phase transformation. The FCC-BCC phase transformation kinetics is analyzed using the thermal expansion experiments carried out at different heating rates. The FCC-BCC phase transformed fraction, f, as a function of temperature is determined from thermal expansion curve. The activation energies, Q, determined by KAS model show an increasing trend which is from 144.4 kJ/mol at initial stage (f = 0.2) to 209.2 kJ/mol when f = 0.8, indicating the barrier for transformation is increasing. The Avrami exponent, n, determined by modified JMA model, varies with transformed fraction, indicating the FCC-BCC phase transition firstly is interface controlled with decreasing nucleation rate (f < 0.05), and changed to diffusion controlled with an increasing nucleation rate (f < 0.15), then diffusion controlled with decreasing nucleation rate. The microstructure and mechanical properties of the corresponding FCC-BCC phase transformation process are also studied.