Axial Thermal Expansion Coefficients Research Articles

An experimental strategy and investigation of preparing high-strength and low-expansion carbon fiber reinforced Al matrix composite

In the pursuit of advancing the aerospace application of carbon fiber-reinforced aluminum matrix (CF/Al) composites, achieving a balance between strength, toughness, and a reduced coefficient of thermal expansion (CTE) is imperative. This research introduces a novel approach to fabricating a carbon fiber-reinforced titanium/aluminum (Ti-CF/Al-Ti) sandwich composite using a liquid-solid infiltration extrusion method. The microstructure, mechanical properties, thermal deformation, and corrosion resistance were thoroughly analysed. The results show that a 10 μm wide transition layer interface (Al3Ti) generated by Ti/Al interdiffusion is formed in the sandwich composite and forms an inlay structure with carbon fibers. Compared with CF/Al composites, the tensile strength of this sandwich composite was enhanced by 137.04% and 207.55% in the axial and radial directions of the fibers, respectively, while the compressive strength was also significantly increased. Notably, the CTE of the sandwich composite in the radial direction of the fibers was reduced by 51.2% after the introduction of the TC4, while the axial CTE remained unchanged. Additionally, the corrosion current density (icorr) exhibited a remarkable decrease by two orders of magnitude, indicating a substantial improvement in corrosion resistance. These findings provide valuable insights into the preparation of CF/Al composite and their applications in aerospace.

Compressibility, thermal expansion and Raman scattering of synthetic whitlockite Ca9Mg(PO3OH)(PO4)6 at high pressures and high temperatures

Abstract In-situ X-ray diffraction and 16 Raman scattering of synthetic whitlockite, Ca9Mg(PO3OH)(PO4)6, have been systematically measured at high pressures and high temperatures, respectively. The results show that whitlockite is stable up to ~ 15 GPa at ambient temperature and undergoes a temperature-induced dehydrogenation to merrillite above 973 K at ambient pressure. The obtained pressure-volume data were fitted using a third-order Birch-Murnaghan equation of state to yield the isothermal bulk modulus as K0 = 79(4) GPa with pressure derivative K0' = 4.3(6). When K0' was fixed at 4, the refined isothermal bulk modulus was 81(1) GPa. The volumetric thermal expansion coefficient (αV) is equal to 4.05(8) × 10-5 K-1. The axial thermal expansion coefficients (αa and αc) are 1.07(5) × 10-5 K-1 and 1.91(6) × 10-5 K-1. Both compressibility and thermal expansion show an axial anisotropy. The effects of pressure and temperature on the Raman spectra of whitlockite have been quantitatively analyzed. The isothermal and isobaric mode Grüneisen parameters, and the intrinsic anharmonic mode parameters of whitlockite were calculated. Some amounts of OH--bearing whitlockite may be preserved and could be discovered in meteorites if whitlockite undergoes a low temperature process.

Thermal expansion behavior of vanadium pernitride, CuAl2-type VN2, synthesized under high pressures

CuAl2-type VN2, which is synthesized under high pressure, is a recoverable material at ambient conditions and has a high bulk modulus. In this study, we investigated the thermal expansion behavior of CuAl2-type VN2 by low-temperature X-ray diffraction measurements between 109.3(5) K and 298.3(8) K. The axial thermal expansion coefficient of VN2 was determined to be αa = 2.7(9) × 10−6 K−1 and αc = 17.8(12) × 10−6 K−1 at 298.3(8) K, which has large anisotropy similar to that of compression behavior. It is found that the small coefficient of thermal expansion of the a-axis is due to the negative and positive effects on the a-axis length with increasing temperature of the bond angles and bond lengths of VN2, respectively. As a result, VN2 exhibits very large anisotropic thermal expansion behavior.

Synchrotron X-ray diffraction of pyrolusite (MnO2) and rutile (TiO2) during heating to ∼1000 °C

To compare thermal expansion behaviors in isomorphic structures with different redox behaviors, we separately heated pyrolusite (Mn4+O2) and rutile (Ti4+O2) powders from 25 to ∼1000 °C at a rate of 0.05 °C/s at ambient pressure and analyzed them using synchrotron X-ray diffraction and Rietveld refinement. The pyrolusite exhibited two reduction-induced phase decompositions. Between 531 and 583 °C, pyrolusite decomposed to bixbyite (Mn3+2O3), and between 972 and 998 °C, bixbyite decomposed to hausmannite (Mn2+Mn3+2O4). The rutile experienced no phase decompositions or transitions over this same temperature interval.The refined bond lengths and angles for pyrolusite showed that the Mn4+ coordination octahedron became more distorted near the phase decomposition to bixbyite due to the approach of two coordinating oxygen atoms. The 3d electrons of each Mn4+ ion in pyrolusite make π bonds with the 2p electrons of the surrounding O2− ions, whereas the Ti4+ of rutile has no 3d electrons. Thus, π bonding between octahedral Mn4+ and the surrounding O2− anions increases the strength of the Mn–O bonds of pyrolusite relative to the Ti–O bonds of rutile. However, we observed a small decrease in O–O distances in pyrolusite before the decomposition, suggesting that at high temperature, increased π bonding between adjacent O anions precedes the release of O2 and the reduction of Mn4+ to Mn3+. Analogous behavior was observed for bixbyite before its reductive phase decomposition to hausmannite. In contrast, no anomalous changes in the O–O distances occurred for rutile.Our X-ray diffraction analyses provided accurate thermal expansion coefficients for these materials over a broader temperature range than reported in previous studies. The Mn–O bond lengths in pyrolusite were shorter and stronger than the Ti–O bonds of rutile; for example, at 60 °C, <Mn–O> bond distances in pyrolusite refined to 1.8854(6) Å whereas the <Ti–O> bond lengths of rutile were 1.9575(4) Å. Accordingly, the axial and volumetric thermal expansion coefficients refined for rutile were greater than those for pyrolusite. The axial coefficients of thermal expansion (CTE) for pyrolusite were 96% (a-axis) and 69% (c-axis) of the corresponding values for rutile, and the volumetric CTE for pyrolusite was 85% of that for rutile.

Thermal expansion behavior of Li-bearing tourmalines investigated by high-temperature synchrotron-based X-ray diffraction

The high-temperature unit-cell parameters and volumes of three Li-bearing tourmalines (elbaite (CC05), elbaite (CC11) and schorl (D54)) have been determined through in situ synchrotron radiation angle-dispersive X-ray diffraction experiments. No phase transition of these tourmalines has been observed up to the maximum temperature in this study. The volumetric thermal expansion coefficients of the three Li-bearing tourmalines are determined from the measured unit-cell volumes at high temperatures with Berman's equations. And the elbaite (CC05) has the least volumetric thermal expansion coefficients among the three Li-bearing tourmalines in this study. Furthermore, the axial thermal expansion behavior of these Li-bearing tourmalines is also fitted with “linearized” Berman's equation. The results show that Li-bearing tourmalines has an intense anisotropic axial thermal expansivity, where the c-axis has a larger axial thermal expansion coefficient than a-axis. The potential factors influencing on the thermal expansivity and the anisotropic axial thermal expansivities of Li-bearing tourmalines are further discussed.

High temperature structure and vibrational properties of GdVO4

In this manuscript the temperature evolution of crystal structure and vibrational properties of tetragonal GdVO4 as observed from in situ high temperature powder XRD and Raman spectroscopic studies are reported. The material shows anisotropic expansion with a larger coefficient of thermal expansion along c-axis (αc) compared to that along the a-axis (αa). The average axial thermal expansion coefficients in the temperature range of 298–1373 K are: αa = 3.75 × 10−6 K−1 and αc = 11.1 × 10−6 K−1. The degree of anisotropy in thermal expansion decreases with increasing temperature. The thermal expansion behavior of GdVO4 was mainly contributed by the orientation and expansion of Gd–O bonds in the structure. The temperature dependent Raman spectroscopic investigations indicate decreasing trend of all the observed phonon mode frequencies. All the low energy modes show larger anharmonicity compared to the high energy stretching modes and they contribute significantly to the expansion of GdVO4.

The improvement of temperature sensitivity by controlling the thermal expansion coefficient of no-core fiber

In this paper, a liquid sealed temperature sensor is assembled based on single-mode-no-core-single-mode (SNCS) optical fiber structure. Theoretical calculations and experiments verify the sensing characteristics of this structure. The structure improves the temperature sensitivity to −355 pm/°C by encapsulating an organic solvent with large thermal optical coefficient and using packaging material with large thermal expansion coefficient. The theoretical results are in good agreement with the experimental results. Theoretical simulations are completed on MATLAB using far from the cut-off condition. The SNCS structure is encapsulated in a microfluidic chamber by applying microfluidic processing technology. The axial thermal expansion coefficient of the no-core fiber (NCF) is increased and radial thermal expansion coefficient is suppressed by the polydimethylsiloxane (PDMS) mold stretching NCF to improve the temperature sensitivity. The enhancement effect of PDMS stretching NCF on temperature sensitivity is verified by contrast experiment. Due to the wrapping of PDMS, the sensor has strong resistance to mechanical damage and external interference.

Investigating negative thermal expansion property of decahedral Sc2Mo3O12 prepared via hydrothermal method

Orthorhombic Sc2Mo3O12 with decahedral structure have been prepared via hydrothermal method. The phase evolution, morphology and negative thermal expansion (NTE) behavior of the decahedral Sc2Mo3O12 were investigated using XRD, SEM, TMA and high-temperature XRD. XRD and SEM analyses indicate that orthorhombic Sc2Mo3O12 particles with decahedral structure were obtained after annealing at 800 °C. The decahedral Sc2Mo3O12 particles are uniform and regular with a size of about 20 μm × 20 μm × 5 μm. Decahedral Sc2Mo3O12 shows stable NTE. TMA analysis shows the coefficient of thermal expansion (CTE) of decahedral Sc2Mo3O12 is −4.12 × 10−6 K−1 in 25–700 °C. High-temperature XRD analysis reveals that it displays anisotropic NTE at the same temperature range. The axial CTEs of decahedral Sc2Mo3O12 are αa = −4.37 × 10−6 K−1, αb = 3.61 × 10−6 K−1 and αc = −2.96 × 10−6 K−1, respectively. The linear CTE is −1.22 × 10−6 K−1.

Investigation on the free expansive deformation of concrete during the heating process

Concrete experiences expansive deformation at high temperatures. The thermal stress resulted in the development of cracks inside the concrete members. To investigate the free expansive deformation of concrete during the heating process, the concrete specimens were heated from room temperature to different target temperatures with an electric furnace. The temperature in the furnace was maintained at the target temperature to provide a thermostatic condition until the center of the specimen also reached the target temperature. The deformation values of the concrete specimens in both of the temperature rising stage and temperature holding stage were measured and analyzed. The experimental results show that the concrete began to deform at 40–60 °C. The thermal-induced axial strain and thermal expansion coefficient of concrete gradually increased with a rise in temperature. After being heated to 800 °C, thermal-induced axial strain and thermal expansion coefficient of concrete M35 reached 1.018% and 13.135 × 10−6 °C, respectively. The thermal-induced axial strain of concrete continued to increase during the temperature holding stage and gradually stabilized after 60–65 min. After the temperature in the center of the specimen reached 800 °C, the thermal-induced axial strain and thermal expansion coefficient of concrete M35 reached 1.252% and 16.155 × 10−6 °C, respectively. For concrete M45 with higher compressive strength than M35, the thermal-induced axial strain and thermal expansion coefficient of concrete M45 show a variation law similar to concrete M35.

ANN-Based Model for the Prediction of the Bond Strength between FRP and Concrete

In the last decades, the uses of fiber reinforced polymer (FRP) composites in the structural strengthening of reinforced concrete (RC) structures have become the state of the art, providing a valid alternative to the traditional use of steel plates. These relatively new materials present, in fact, great advantages, including high corrosion resistance in aggressive environments, low specific weight, high strength-to-mass-density ratio, magnetic and electric neutrality, low axial coefficient of thermal expansion and sustainable costs of installation. In flexural and shear strengthening of RC members, the effectiveness of the epoxy bonded FRP strongly depends on the adhesion forces exchanged with the concrete substrate. When the flexural moment is present, the FRP strengthening is activated through the stress transfer on the tension side, which is guaranteed by the contact beam region to which the adhesive is bonded to the beam itself. Hence, the determination of the maximum forces that cause debonding of the FRP-plate becomes crucial for a proper design. Over the years, many different analytical models have been provided in the scientific literature. Most of them are based on the calibration of the narrow experimental database. Now, hundreds of experimental results are available. The main goal of the current study is to present and discuss an alternative theoretical formulation for predicting the debonding force in an FRP-plate, epoxy-bonded to the concrete substrate by using an artificial neural networks (ANNs) approach. For this purpose, an extensive study of the state of the art, reporting the results of single lap shear tests, is also reported and discussed. The robustness of the proposed analytical model was validated by performing a parametric analysis and a comparison with other existing models and international design codes, as shown herein.

Thermal Stability Design of Asymmetric Support Structure for an Off-Axis Space Camera

With the development of space optical remote sensing technology, especially off-axis space cameras, the thermal dimensional stability of the support structure has become increasingly demanding. However, the asymmetry of the camera structure has not been fully considered in the past design of the thermal stability of off-axis cameras. In order to solve this problem, a support structure with very low thermal deformation in the asymmetric direction is presented in this paper for an off-axis TMA camera. By means of the negative axial thermal expansion coefficient of carbon-fiber-reinforced plastics (CFRP), a composite laminate with near zero-expansion was obtained by adjusting the direction of fiber laying, and the asymmetric feature of the off-axis remote sensing camera structure was fully considered, thus enabling the support structure to have good thermal dimensional stability. We carried out a thermal load analysis and an optical analysis of the whole camera in the case of a temperature rise of 5 °C. The results show that the zero-expansion support structure has good thermal stability, and the thermal deformation in the asymmetric direction of the camera is obviously smaller than that of the isotropic laminate support structure. Compared with the isotropic support structure, the influence of thermal deformation on MTF is reduced from 10.43% to 2.61%. This study innovatively incorporates the asymmetry of the structure into the thermal sta-bility design of an off-axis TMA camera and provides a reference for the thermal stability design of other off-axis space cameras.

Interaction dependent anisotropic thermal expansion of a hydrogen bonded cocrystal

A binary cocrystal of 2,4,6-triethyl-1,3,5-benzenetricarboxylic acid (TEBH3) and trans-4,4′-bispyridylethylene (BPE), 1, exhibits a volumetric thermal expansion (αV,298K) of 162(19) [10−6 K−1] between 118 ─ 298 K. The axial thermal expansion coefficients are α1(010), 298K = 15(9) [10−6 K−1], α2(100), 298K = 17(5) [10−6 K−1], and α3(001), 298K = 113(3) [10−6 K−1] respectively. The structure of 1 is a typical 2―fold interpenetrated hydrogen bonded corrugated square lattice (sql) net, sustained by strong O–H⋯O (along the b axis) and O–H⋯N (along the a-axis) hydrogen bonds. The 2‒fold interpenetrated sql nets get stacked into layers along the 001 direction sustained by weak C–H⋯O hydrogen bonds. The α1(010), 298K and α2(100), 298K directed along the plane of the sql net, are attributed to the presence of strong O–H⋯O and O–H⋯N hydrogen bonds which restrict expansion along the plane of the sql net. The major principle axis of expansion is directed along the direction of the stacking of the interpenetrated nets linked by weak C–H⋯O hydrogen bonds resulting into α3(001), 298K being ∼ 7 times higher than α1(010), 298K and α2(100), 298K. Between 118 K and 208 K a shortening of the strong O–H⋯N hydrogen bond is observed along with a negligible increase in O–H⋯O which accounts for the biaxial NTE exhibited by 1 between 118 K - 208 K along the a and the b axes respectively.

Role of fiber arrangement in the thermal expanding behavior of unidirectional metal matrix composites

The influence of fiber arrangement on thermal expanding behavior of unidirectional fiber-reinforced metal matrix composites (MMCs) is evaluated using a unit cell micromechanical approach. Both regular and random fiber arrangements are considered in the MMC simulation by extending the number of sub-cells of the representative volume element (RVE). Moreover, the unit cell micromechanical model is used to investigate the role of fiber cross-section on the coefficients of thermal expansion (CTEs) of unidirectional MMCs. The validity of the model is verified by comparing the predictions and those available experimental measurements. The effective axial CTEs are not dependent on the MMC microstructure with different types of fiber arrays and cross-sections. However, the results show that besides the volume fraction, shape and the arrangement type of fibers plays a significant role in the effective transverse CTEs of MMCs. The discrepancy between the transverse predictions of the model with a random fiber arrangement and those of the model with a regular fiber arrangement increases with the rise of difference between the constituent material properties. Also, the effects of different statistical distributions of the random fiber arrangement, the number of RVE sub-cells and fiber orientation on the MMC thermal expanding response are examined.

An analytical approach to determine coefficients of thermal expansion of CNT/polymer nanocomposites

In this study, thermo-mechanical properties of CNT/polymer nanocomposite were investigated. Semi-continuum analytical method was used to simulate thermal behavior of CNT-reinforced polymers. CNT was modeled in an atomistic scale, whereas polymer was modeled as a continuum. Interfacial effects or the Van Der Waals interactions between matrix and CNT were simulated employing cohesive strength. The results indicate that using the cohesive law for CNT/polymer interface could provide very close results to the available experimental data. Also, adding a small quantity of CNTs to polymer leads to a slight decrease in the radial and axial thermal expansion coefficients of polymer matrix depending on temperature, volume fraction, aspect ratio, and also diameter of CNTs.

Investigation of the changes in hydrogen bonding accompanying the structural reorganization at 103 K in ammonium iodate.

Neutron powder diffraction has been used to observe the changes in hydrogen bonding that occur as a function of temperature in ND4IO3 and, thus, determine the structural features that occur during the low-temperature (103 K) phase transition. It is shown that in the deuterated material the change is not a phase change per se but rather a structural reorganization in which the hydrogen bonding becomes firmly locked in at the phase transition temperature, and stays in this configuration upon further cooling to 4.2 K. In addition, both the differences and changes in the axial thermal expansion coefficients in the region 100-290 K can be explained by the changes involving both the hydrogen bonding and the secondary I...O halogen bonds.

Drastic tailorable thermal expansion chiral planar and cylindrical shell structures explored with finite element simulation

Design of materials and structures with quite low coefficient of thermal expansion (CTE), even zero or negative CTE is important for industrial application where drastic temperature changes are encountered. In this paper, making use of the bending of bi-material beam and the unique deformation mechanism of chiral lattice structures, five sets of chiral lattice composite structures with tailorable CTEs are proposed, where synergic effects of rigid node rotation and bi-material ligament bending deformation are responsible for giant range of structural deformation due to temperature change, from positive CTE to negative CTE through adjusting the geometrical parameters of composite bi-material chiral unit cell, and the relationship between unit cell geometric parameters and CTEs of the structure are studied systematically through finite element analysis. Finally, design of bi-material cylindrical shells consisting of anti-tetra chiral unit cells are proposed, and its axial CTEs with different number of the unit cells along the circumferential are studied systematically, demonstrating the robust range of CTEs can be generated through adjusting the geometrical parameters of chiral bi-material unit cells. The proposed chiral structures demonstrated promising application potentials in industrial fields, such as: aerospace and microelectronics, where extremely high structural accuracy is required during harsh working temperature environment.

Crystal Chemical Substitution at Ca and La Sites in CaLa4(SiO4)3O To Design the Composition Ca1- xM xLa4-xRE x(SiO4)3O for Nuclear Waste Immobilization and Its Influence on the Thermal Expansion Behavior.

The oxysilicate apatite host CaLa4(SiO4)3O has been explored for immobilization of radioactive nuclides. Divalent ion, trivalent rare earth ion, and combined ionic substitutions in the silicate oxyapatite were carried out to optimize the simulated wasteform composition. The phases were characterized by powder X-ray diffraction, FT-IR, TGA, SEM-EDS, and HT-XRD techniques. The results revealed the effect of ionic substitutions on the structure and thermal expansion behavior. The investigation resulted in the formulation of simulated wasteforms such as La3.4Ce0.1Pr0.1Nd0.1Sm0.1Gd0.1Y0.1(SiO4)3O (WF-1) and Ca0.8Sr0.1Pb0.1La3.4Ce0.1Pr0.1Nd0.1Sm0.1Gd0.1Y0.1(SiO4)3O (WF-2). In comparison to the average axial thermal expansion coefficients of the hexagonal unit cell of the parent CaLa4(SiO4)3O measured in the temperature range 298-1073 K (α' a = 9.74 × 10-6 K-1 and α' c = 10.10 × 10-6 K-1), rare earth ion substitution decreases the thermal expansion coefficients, as in the case of La3.4Ce0.1Pr0.1Nd0.1Sm0.1Gd0.1Y0.1(SiO4)3O (α' a = 8.67 × 10-6 K-1 and α' c = 7.94 × 10-6 K-1). However, the phase Ca0.8Sr0.1Pb0.1La3.4Ce0.1Pr0.1Nd0.1Sm0.1Gd0.1Y0.1(SiO4)3O shows an increase in the values of thermal expansion coefficients: α' a = 11.74 × 10-6 K-1 and α' c = 11.70 × 10-6 K-1.

Transversely isotropic thermal properties of carbon nanotubes containing vacancies

In this work, the transversely isotropic thermal properties of carbon nanotubes (CNTs) containing vacancies were determined using molecular dynamics simulations with adaptive intermolecular reactive empirical bond-order force fields. The effects of vacancy concentrations, their position, and the diameter of armchair CNTs were taken into consideration. The current results reveal that vacancies affect (i) the axial coefficient of thermal expansion of the larger diameter CNTs and (ii) the thermal conductivities of the smaller diameter CNTs due to the phonon scattering from defect sides leading to a severe degradation in their thermal conductivity. The results also reveal that the position of vacancies along the length of CNTs is the main influencing factor which governs the change in the thermal properties of CNTs, especially for vacancy concentration of 1%.

Numerical study of the electronic structure, elastic and optical properties of defect quaternary semiconductor CuGaSnSe4

Abstract The electronic structure, elastic and optical properties of the defect quaternary semiconductor CuGaSnSe4 in I 4 ¯ structure are systematically investigated using first-principles calculations. We summarize and discuss some of the studies on CuGaSnSe4 in partially ordered chalcopyrite structure and find that there are three atomic arrangements so far, but it is still uncertain which is the most stable. Through detailed simulation and comparison with the corresponding literature, we get three models and predict that M1 model should be the most stable. The band structure and optical properties of compound CuGaSnSe4, including dielectric constant, refractive index and absorption spectrum, are drawn for a more intuitive understanding. The elastic constants are also calculated, which not only prove that CuGaSnSe4 in I 4 ¯ structure is stable naturally but also help solve the problem of no data to accurately predict axial thermal expansion coefficients. The calculated values of the zero frequency dielectric constant and refractive index are comparable to those of the corresponding chalcopyrite structure but slightly larger.

Numerical study of the defect adamantine compound CuGaGeSe4

ABSTRACTThe electronic structure, elastic and optical properties of the defect adamantine compound CuGaGeSe4 in structure are systematically investigated using first-principles calculations. Through detailed calculation and comparison, we obtain three independent atomic arrangements and predict the most stable atomic arrangement according to the lattice constants and enthalpy formation energies. The elastic constants are calculated, which can be used to predict the axial thermal expansion coefficients accurately. The optical properties of compound CuGaGeSe4, including the dielectric function, refractive index and absorption spectrum, are depicted for a more intuitive understanding. Our calculated zero-frequency limits ϵ1(0) and n(0) are very close to the other theoretical values, which proves that our calculations are reliable.