Expansion Properties Research Articles

The Effect of Temperature on Synthetic Nano β-Eucryptite and Alumina Ceramic Materials: Thermal Expansion, Mechanical, and Physical Properties

The capability to fabricate ultra-low and customizable CTE materials with good mechanical properties in a simple method was demonstrated in this work. For this purpose, nano beta-eucryptite and alumina powders were synthesized and used in the composite's fabrication. Four composites of alumina and a second-phase beta-eucryptite were prepared, containing 10, 20, 30, and 40 wt.% beta-eucryptite. The temperature effect on prepared composites is investigated. The results of XRD analysis and the microstructures of prepared composites are discussed with results of mechanical strength and thermal expansion at temperature ranges of 1400, 1500, and 1550 °C. The CTE of alumina-beta-eucryptite composites decrease as the beta-eucryptite content increases, reaching -1.036 × 10–6 °C−1. The findings show that a composite with a very low thermal expansion coefficient and good mechanical properties can be designed and used in different applications.

Theoretical study on the stability mechanism of a high energy system composed of molecules containing C[sbnd]O[sbnd]C or –N3 groups and aluminum hydride

The stability of aluminum hydride(AlH3) based high-energy propellants is important for its large-scale application. In this work, to explore the stability mechanism of systems composed of AlH3 and a binder containing COC or –N3 groups, molecular dynamics simulations were carried out to explore the thermal expansion properties of AlH3, and density functional theory calculations were employed to study the micro-interactions between molecules containing COC or –N3 groups and AlH3. More specifically, CH3OC2H5 and CH3N3 were used to model polyethylene glycol and glycidyl azide polyether, respectively. It is found that AlH3 is more sensitive to temperature changes than its oxide layer. Upon contact between the alumina layer and CH3OC2H5 or CH3N3, these compounds exist stably on the α-Al2O3(0001) and γ-Al2O3(110) surfaces. Upon direct contact with the α-AlH3(010) surface, CH3OC2H5 is relatively stable, while CH3N3 can trigger the surface hydrogen transfer reaction due to the low energy barrier(5.0 kcal/mol). The current work provides a theoretical basis for understanding the sensitivity of AlH3 and binders containing COC or –N3 groups, and is useful in the research and development of superior composite energetic propellants.

Null-thermal expansion coefficient LAS-nSiC composite by slip-casting

In the present work, lithium aluminosilicate (LAS) reinforced with SiC nanoparticles (nSiC) is successfully prepared by slip-casting for the first time. The stability of aqueous suspension is investigated in terms of its rheological properties. The isoelectic point (IEP) of β-Eucryptite particulate system was found to be at pH 6.1. To obtain the best processing conditions, LAS-nSiC suspension with 55 wt% of solids and 0.06 wt% of Tetramethyl ammonium hydroxide (TMAH) as dispersant is recommended. The slurry is slip-casted in plaster of Paris molds and sintered at 1430ºC for different holding times in controlled atmosphere. Microstructure, mechanical and coefficient of thermal expansion (CTE) properties of the sintered samples have been evaluated. LAS-nSiC composite sintered at 1430ºC shows dense and free-cracked microstructure with a CTE close to zero.

Effects of supplementary cementitious materials on the durability of glass aggregate mortars

The durability performance and sustainability of concrete and mortar can be enhanced by incorporating supplementary cementitious materials (SCMs), such as fly ash, slag (SG), silica fume (SF), and metakaolin (MK). In this study, binary and ternary blends of the aforementioned SCMs were investigated to determine an optimal combination that enhances the durability of glass aggregate mortars. Compressive strength, chloride permeability, and sorptivity experiments were conducted for all mixtures at specimen ages of 28 and 90 days. Fourteen day alkali silica reaction tests were also performed to determine the expansion properties. It was determined that ternary blends of fly ash and SF effectively mitigate expansions, with mixtures containing fly ash being most effective due to its high silica (SiO2) content. Ternary blends of SG and SF were also found to be successful in reducing permeability. In addition, it was determined that optimal durability performance can be achieved with 10% MK and SF replacements.

Research progress on sparse array MIMO radar parameter estimation

Making full use of the virtual aperture expansion property with the sparse array multi-input multi-output (MIMO) radar, we can achieve positive contributions for parameter estimation. We focus on the design of the sparse array MIMO radar and the optimization of conventional algorithms. According to the joint subspace-based method and compressive sensing theory, we study the analysis and design of the sparse arrays, direction of arrival estimation, and joint angle estimation for improved performance and low complexity, aiming to establish systematic parameter estimation theory for the sparse array MIMO radar. Combining the aspects of array optimization design, mixed target parameter estimation, nonideal factor suppression, and distributed platform construction, the future development trend of the sparse array MIMO radar is discussed.

Properties and mechanism of amorphous lead aluminosilicate passivation layers used in semiconductor devices through molecular dynamic simulation

With the rapid development of the semiconductor industry, the glass passivation process is being optimized as an important process for the protection of electronic components. Lead aluminosilicate glasses, with a stable network structure, adjustable thermal expansion coefficient and high voltage resistance, are valuable for use in power devices such as diodes. In this work, the effects of PbO content on the expansion and thermal properties of lead aluminosilicate glasses were investigated by combining molecular dynamics simulations and experimental tests. The relationship between structural changes and performance is analyzed in detail, and the passivation mechanism of lead aluminosilicate glass for semiconductor devices is also elucidated. The results show that the thermal expansion coefficients of glass and silica wafers can match the glass composition with PbO contents of 15–25 mol%. The diffusion ability of Pb atoms in the network structure is also the lowest in this concentration range. The glass transition temperature (Tg) and fluidity at high temperature, both decrease with increasing PbO content. In addition, the glass powder was applied to MOS devices for electrical performance testing. It was found that when the PbO content was at 20 mol%, the glass passivation layer and the silicon wafer had tight interfacial contact after sintering. The interfacial defect density reached the minimum value (5.276 × 1010 cm−2eV−1) along with a high fixed charge density (2.124 × 1010 cm−2). In other words, the glass powder composed of 20PbO-4.8Al2O3-75.2SiO2 (mol%) can minimize the interfacial carrier compound, reduce the interfacial contact resistance and increase the current density to achieve a more desirable interfacial passivation effect in semiconductor devices.

The Eremenko–Lyubich constant

Eremenko and Lyubich proved that an entire function whose set of singular values is bounded is expanding at points where its image has large modulus. These expansion properties have been at the centre of the subsequent study of this class of functions, now called the Eremenko-Lyubich class. We improve the estimate of Eremenko and Lyubich, and show that the new estimate is asymptotically optimal. As a corollary, we obtain an elementary proof that functions in the Eremenko-Lyubich class have lower order at least $1/2$.

Mechanical, expansion and rheological properties of circulating fluidized bed fly ash based ecological cement: A critical review

Mechanical, expansion and rheological properties of circulating fluidized bed fly ash based ecological cement: A critical review

Thermodynamic assessment of iron and the expansion behavior of porous ceramsite in pure mineral systems relating to solid waste components

Herein, Factsage software and sintering experiment were conducted to predict and correlate thermodynamic calculations of Fe in a synthetic solid waste and the expansion behavior of ceramsite. With the increase of Fe2O3 content, the liquid phase content and viscosity in the multi-component system gradually decreased and the melting temperature range became wider. This can match with the generation of the liquid phase with proper viscosity in the ceramsite and the full expansion properties. At 400–1000 °C, iron as a network former was tetrahedrally coordinated with oxygen to form Hercynite (Al2FeO4) phase; at 1180–1200 °C, iron as a network modifier dissolved into the silicate mineral structure to form the eutectic composition of Diopside (Ca4Mg3.62Fe0.78Si7.6O24) and Ferrosolite (Si16Mg5.09Fe10.66Ca0.26O48). The formation of iron-bearing silicate facilitated the generation of the viscous layer, so that the outer layer of the ceramsite exhibited sealing performance. Finally, a preferable porous ceramsite with compressive strength of 10.7 MPa and an apparent density of 708 kg/m3 was obtained. This study analyzes the effect of Fe2O3 on the expansion behavior of porous ceramsite and provides new insight into how to analyze different solid wastes to produce ceramsite in a predictable way.

Highly Thermally Conductive Epoxy Composites with AlN/BN Hybrid Filler as Underfill Encapsulation Material for Electronic Packaging.

In this study, the effects of a hybrid filler composed of zero-dimensional spherical AlN particles and two-dimensional BN flakes on the thermal conductivity of epoxy resin were studied. The thermal conductivity (TC) of the pristine epoxy matrix (EP) was 0.22 W/(m K), while the composite showed the TC of 10.18 W/(m K) at the 75 wt% AlN–BN hybrid filler loading, which is approximately a 46-fold increase. Moreover, various essential application properties were examined, such as the viscosity, cooling rate, coefficient of thermal expansion (CTE), morphology, and electrical properties. In particular, the AlN–BN/EP composite showed higher thermal stability and lower CTE (22.56 ppm/°C) than pure epoxy. Overall, the demonstrated outstanding thermal performance is appropriate for the production of electronic packaging materials, including next-generation flip-chip underfills.

Invar Effect of the Fe13 Cluster.

The Invar effect, which refers to magnetic alloys having an anomalously small thermal expansion, has been under extensive investigations over the past century. However, study on the thermal expansion of clusters and their Invar effect is still lacking. In this letter, we calculate the thermal expansion properties of Fe13-nNin (n = 0, 3, 6, 9, 12, 13) clusters and find that the Fe13 cluster has an abnormally small thermal expansion, which is due to its remarkable magneto-volume effect. It is also revealed that the strong magneto-volume effect of the Fe13 cluster is highly related with the two magnetic states, the same as the interpretation for the Invar effect of a bulk alloy. The anomalously small thermal expansion of the Fe13 cluster is the manifestation of the Invar effect at the cluster scale.

High-entropy titanate pyrochlore as newly low-thermal conductivity ceramics

Low-thermal conductivity ceramics play an indispensable role in maximizing the efficiency and durability of hot end components. Pyrochlore, particularly zirconate pyrochlore, is currently a highly promising and widely studied candidate for its extremely low thermal conductivity. However, there are still few pyrochlores that offer both stiffness, insulation, and good thermal expansion properties. In this work, the solidification method was innovatively introduced into the preparation of titanate pyrochlore, and combined it with the compositional design of high-entropy. Through careful composition design and solidification control, the high-density and uniform elements distributed high-entropy titanate pyrochlore ceramics were successfully prepared. These samples possess high hardness (15.88 GPa) and Young’s modulus (295.5 GPa), low thermal conductivity (0.947 W·m−1·K−1), excellent thermal expansion coefficient (11.6 ×10−6/K) and an exquisite balance between stiffness and insulation (E/κ, 312.1 GPa·W−1·m·K), in which the E/κ exhibits the highest value among the current reported works.

Effects of Proportion of Anhydrous CaCl2 on the Expansion Properties of Soundless Cracking Agents

Effects of Proportion of Anhydrous CaCl₂ on the Expansion Properties of Soundless Cracking Agents

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.

Room temperature deposition of freestanding BaTiO3 films: temperature-induced irreversible structural and chemical relaxation

The room temperature aerosol deposition method is especially promising for the rapid deposition of ceramic thick films, making it interesting for functional components in energy, mobility, and telecommunications applications. Despite this, a number of challenges remain, such as an enhanced electrical conductivity and internal residual stresses in as-deposited films. In this work, a novel technique that integrates a sacrificial water-soluble buffer layer was used to fabricate freestanding ceramic thick films, which allows for direct observation of the film without influence of the substrate or prior thermal treatment. Here, the temperature-dependent chemical and structural relaxation phenomena in freestanding BaTiO3 films were directly investigated by characterizing the thermal expansion properties and temperature-dependent crystal structure as a function of oxygen partial pressure, where a clear nonlinear, hysteretic contraction was observed during heating, which is understood to be influenced by lattice defects. As such, aliovalent doping and atmosphere-dependent annealing experiments were used to demonstrate the influence of local chemical redistribution and oxygen vacancies on the thermal expansion, leading to insight into the origin of the high room temperature conductivity of as-deposited films as well as greater insight into the influence of the induced chemical, structural, and microstructural changes in room temperature deposited functional ceramic thick films.Graphical abstract

Low-temperature nanoscale heat transport in a gadolinium iron garnet heterostructure probed by ultrafast x-ray diffraction.

Time-resolved x-ray diffraction has been used to measure the low-temperature thermal transport properties of a Pt/Gd3Fe5O12//Gd3Ga5O12 metal/oxide heterostructure relevant to applications in spin caloritronics. A pulsed femtosecond optical signal produces a rapid temperature rise in the Pt layer, followed by heat transport into the Gd3Fe5O12 (GdIG) thin film and the Gd3Ga5O12 (GGG) substrate. The time dependence of x-ray diffraction from the GdIG layer was tracked using an accelerator-based femtosecond x-ray source. The ultrafast diffraction measurements probed the intensity of the GdIG (1 −1 2) x-ray reflection in a grazing-incidence x-ray diffraction geometry. The comparison of the variation of the diffracted x-ray intensity with a model including heat transport and the temperature dependence of the GdIG lattice parameter allows the thermal conductance of the Pt/GdIG and GdIG//GGG interfaces to be determined. Complementary synchrotron x-ray diffraction studies of the low-temperature thermal expansion properties of the GdIG layer provide a precise calibration of the temperature dependence of the GdIG lattice parameter. The interfacial thermal conductance of the Pt/GdIG and GdIG//GGG interfaces determined from the time-resolved diffraction study is of the same order of magnitude as previous reports for metal/oxide and epitaxial dielectric interfaces. The thermal parameters of the Pt/GdIG//GGG heterostructure will aid in the design and implementation of thermal transport devices and nanostructures.

Phase transition, thermal expansion and hygroscopicity of Fe2-2x(HfMg)xW3O12

Solid solutions Fe2-2x(HfMg)xW3O12 are synthesized to reduce the monoclinic-to-orthorhombic phase transition temperature of Fe2W3O12 and realize near zero thermal expansion over wide temperature range. The solid solutions Fe2-2x(HfMg)xW3O12 (0.3 ​≤ ​x ​≤ ​1.0) are easier to synthesize than Fe2W3O12. The X-ray diffraction and Raman analyses show that Fe2-2x(HfMg)xW3O12 adopt either a monoclinic (0.3 ​≤ ​x ​≤ ​0.5) or an orthorhombic (0.7 ​≤ ​x ​≤ ​1.0) structure at room temperature. Dilatometry measurements demonstrate that they display either low positive (x ​= ​0.3) or negative (x ​≥ ​0.5) thermal expansion above the temperature of monoclinic-to-orthorhombic phase transition or dehydration. The orthorhombic samples (0.7 ​≤ ​x ​≤ ​1.0) have intrinsically negative thermal expansion covering large temperature range involving room temperature, but are hygroscopic. Crystal water formation and releasing modify their thermal expansion property significantly. The influence of crystal water releasing process on the phonon behaviors is also observed by temperature dependent Raman spectroscopy.

Dynamic interferometric measurements of thermally-induced deformations on telescope based on high-strain composite tape-springs

Thin carbon fibre reinforced polymer (CFRP) tape-springs are attractive structures for use in space-based optical instruments because of their compact stowed form, and their high dimensional stability when deployed. In this paper we present, with examples, two inexpensive methods to assess the thermal expansion properties of tape-spring structures: one based on strain gauges to obtain coupon level values, and another based on laser interferometry for structure level measurements. The strain gauge technique is a versatile approach that exploits the thermal output characteristics of the sensors. The thermal expansion characterisation of thin-composite samples measured a longitudinal expansion of 4.44 ppm/∘C and transverse expansion 5.95 of ppm/∘C. The interferometry system is designed with a view to capturing the displacements and tilts that occur when a structure with a low thermal mass, like a tape-spring, experiences a rapid change in flux, as occurs in the space environment. The homodyne interferometer is developed for three degree-of-freedom (DoF) measurements with a resolution of 10−8 m for distances and 10−6 rad for angles. The interferometric setup is based on the classical Michelson architecture and consists of few inexpensive commercial optical components. The source is a 0.8 mW Helium–Neon laser with a wavelength of 632.8 nm. The other elements include two spherical singlets, a right-angle prism, a cubic beamsplitter and a CMOS camera. The recorded interference fringes are analysed by using an algorithm based on Discrete Fourier Transform (DFT). Spectral information on the light intensity signals can be used to determine relative displacements and tilts. The dimensional stability of an optical payload based on high-strain composites was tested. The telescope has a deployable Cassegrain design, which uses six extendable members for the separation of its secondary mirror. Axial deformations between 20–30μm along with angle variations of the order of 0.1 mrad were recorded with good repeatability.

Thermal expansion behaviour of Invar 36 alloy parts fabricated by wire-arc additive manufacturing

Invar 36 alloy is of high interest in various industrial sectors, due to its reduced thermal expansion properties. This study aims to validate Wire-Arc Additive Manufacturing (WAAM) technology as a valid method for manufacturing aerospace tooling in Invar 36. The main novelty and the objective of this work is to study the properties of Invar deposited by WAAM technology and to provide guidelines for the manufacture of parts using this technology. To do so, the thermal expansion behaviour of Invar specimens manufactured using Gas Metal Arc Welding (GMAW)-based WAAM technology and Plasma Arc Welding (PAW)-based WAAM technology is analyzed for subsequent comparison with the values obtained from the laminated Invar sample used as the reference specimen. A wall is manufactured with each technology, for comparative purposes, from which specimens were extracted for the dilatometry test and metallographic analysis. The results of these analyses show the advantages of GMAW technology for the manufacture of Invar alloy parts, as it presents the same thermal expansion behaviour as the laminated reference material with less presence of precipitates and no macrostructural failures such as pores, cracks and lacks of fusion. Furthermore, to conclude, an aeronautical tooling that has been manufactured within this work demonstrated the potential of this technology to manufacture specialized aeronautical parts.

The influence of severe plastic deformation on the thermal expansion of additively manufactured Ti6Al4V alloy

The thermal expansion properties of the Ti6Al4V alloy deposited with direct energy subjected to severe plastic deformation through ECAP were studied in the temperature region 23–700 °C. The deposit samples exhibited two orientations: with the longitudinal axis in the deposition plane and perpendicular to the deposited layers. The microstructure of the deposited alloy and the alloy after thermomechanical treatment was analysed on a scanning electron microscope using the EBSD method. The ECAP process substantially refined the structure of the grains. The temperature dependence of the thermal expansion coefficient estimated for the alloy after ECAP processing exhibited a non-monotonous course. The microstructural changes are the reason for this finding.