Small Thermal Expansion Coefficient Research Articles

Thermal Properties of Wood-Plastic Composites with Different Compositions.

The thermal performance of wood–plastic composites (WPCs) with different fiber, different fiber contents, and different lubricants were investigated in this paper. The results show that the thermal degradation temperature, melting temperature, crystallization temperature, crystallinity, and viscosity of WPCs with wood fiber were slightly higher than those of WPCs with floor sanding powder and rice husk. As the wood fiber content increased, the melting temperature and crystallinity of WPCs decreased while the crystallization temperature, viscosity, and pseudoplasticity increased. When the wood fiber content was increased to 60%, the dimensional stability of WPCs tended to be constant, and a higher wood fiber content was not conducive for processing of WPCs. WPCs had a small coefficient of linear thermal expansion at low temperature and demonstrated a good dimensional stability. The presence of lubricant reduced the viscosity and increased the pseudoplasticity of the WPCs, which is advantageous for the dimensional stability of WPCs at low temperature while making it worse for high temperatures.

Recent progress in Mg-Li matrix composites

Abstract Mg-Li matrix composites are one of the ideal structural materials in the fields of aerospace and military due to their high specific strength and stiffness, good damping and wear resistance, and small thermal expansion coefficient. The preparation technologies of Mg-Li matrix composites including powder metallurgy, pressure infiltration, stir-casting, foil metallurgy, and in-situ synthesis were introduced, and their advantages and disadvantages were compared. The common matrix alloys and reinforcements for Mg-Li matrix composites as well as the structure and performance of typical composites were mainly summarized. Then the interface chemistry between matrix and reinforcement was briefly reviewed. Finally, some problems existing at present and the possible solutions were discussed.

Thermal Expansion and Thermal Stress Behavior of Electroless-Plated Fe–Ni–B Alloy Thin Film for High-Density Packaging

Fe–Ni–B alloy thin films were prepared by using an electroless plating method, and their thermal-expansion behavior, thermal-stress generation, and crystal structure were evaluated. By heating from 30°C to 300°C, the electroless-plated Ni–5 wt%B alloy film showed a marked increase in tensile stress at approximately 270°C, which is caused by a phase separation from the amorphous Ni–B alloy into a highly crystalline Ni and Ni3B compound. The coefficient of thermal expansion (CTE) of electroless-plated Ni–B alloy film from 300°C to 30°C, after heating to 300°C, was 14 ppm/K. In contrast, the electroless-plated Fe–Ni–B alloy film in the Invar composition range had a small CTE (8 ppm/K to 9 ppm/K) and no substantial change in crystal structure during heating to 300°C. As a result, the Fe–Ni–B alloy film on the silicon substrate (CTE = 3 ppm/K) exhibited a low thermal stress compared with the electroless-plated Ni–B alloy film. Thus, it is suggested that the electroless-plated Invar Fe–Ni–B alloy films are suitable as an under-bump metal layer from the viewpoint of the thermal-expansion behavior.

Measuring temperature-dependent thermal diffuse scattering using scanning transmission electron microscopy

Scanning transmission electron microscopy (STEM) thermometry techniques offer the potential for mapping temperature (T) with high spatial resolution. Existing STEM thermometry methods based on thermally induced strains must contend with small thermal expansion coefficients [<10 parts per million (ppm)/K] for some materials of interest, as well as non-local relationships between strain and temperature. In contrast, the well-known mechanism of thermal diffuse scattering (TDS) offers promise for inherently local T measurements with larger temperature coefficients (>1000 ppm/K) for almost all materials at room temperature. This T-dependent TDS has not been leveraged for STEM thermometry, however, due to experimental difficulties in quantifying the relatively small thermal signals. Here, we demonstrate quantitative TDS measurements using STEM by measuring diffuse scattering in energy-filtered scanning electron nanodiffraction patterns. Applying virtual apertures to these diffraction patterns during post-processing allows us to quantify the T-dependent TDS between the Bragg spots. We measure a position-averaged temperature coefficient of 2400±400 ppm/K for a single-crystal gold film averaged between T=100 K and T=300 K and compare this result with the predictions of Debye-Waller theory. This TDS-based STEM thermometry technique demonstration provides a step towards the goal of non-contact nanoscale temperature mapping of thin nanostructures.

Active Thermal Control of 5 nm Gap Terahertz Antennas

AbstractMetallic nanostructures are combined with various active materials for electrical, optical, and thermal modulations of their optical properties. In particular, for the thermal modulation, deformation of metallic nanostructures at high temperatures limits the applications to relatively low temperatures, where thermal expansion of metals is negligible. Here, a unique regime is reported where terahertz (THz) waves transmitting through 5 nm wide slot antennas can be significantly modulated via controlled thermal expansion of metals without active materials. The normalized amplitude is modulated by 20% and the resonant frequency by 22% at an elevated temperature of 150 °C, indicating a decrease in the gap width by 50%. The extreme width‐to‐length ratio of the THz slot antennas compensates the small thermal expansion coefficient of metals, enabling the gap width to be considerably changed. COMSOL simulation and coupled‐mode method (CMM) calculation quantitatively support the experimental data. This works suggests a new possibility of thermally active metallic nanostructures.

Unusually Small Thermal Expansion of Ordered Perovskite Oxide CaCu₃Ru₄O12 with High Conductivity.

We measured the coefficient of thermal expansion (CTE) of conducting composite ceramics 30 vol.% CuO-mixed CaCu3Ru4O12 together with CaCu3Ru4O12 and CuO. Although conducting ceramics tend to show higher CTE values than insulators, and its CTE value does not match with other ceramic materials, the CTE of CaCu3Ru4O12 (7–9 × 10−6/K) was as small as those of insulators such as CuO (9 × 10−6/K), alumina (8 × 10−6/K), and other insulating perovskite oxides. We propose that the thermal expansion of CaCu3Ru4O12 was suppressed by the Cu-O bond at the A-site due to the Jahn–Teller effect. This unusually small CTE of CaCu3Ru4O12 compared to other conducting oxides plays a vital role enabling successful coating of 30 vol.% CuO-mixed CaCu3Ru4O12 thick films on alumina substrates, as demonstrated in our previous study.

Effects of Heat Input Conditions on the Local Thermophysical Properties of Super Duplex Stainless Steels

The thermal properties of the super duplex stainless steels are strongly affected by the thermal history when welding procedure are applied leading to substantial changes on the mechanical properties of the welding region. The controlled dual phase microstructure (ferrite and austenite) guarantee excellent mechanical properties such as mechanical strength and corrosion resistance, in addition to small thermal expansion coefficient and high thermal conductivity. In this research a model able to predict the thermal history of the welding pieces coupled with local mechanical properties developed during welding procedure is developed. The model was verified by measured temperature profile and used to predict local properties such as grain size evolution, hardness and mechanical strength. An inverse method was implemented to obtain the parameters fitting for the grain growth evolution, hardness and yielding strength compatible with the final microstructure and grain size measured using SEM images and stereological techniques.

Influence of a Coil Bobbin on Transient Thermal Stress in a REBCO Pancake Coil

It has been often reported that a superconducting property of a coil wound by a coated conductor is degraded by epoxy impregnation. The degradation is considered that a superconducting layer or a buffer layer is peeled from a metal substrate by thermal stress. The steady thermal stress in the winding at the operating temperature is examined frequently. However, the transient thermal stress in a cooling process becomes larger than the steady thermal stress due to the difference of heat contraction of each material and temperature distribution, since heat contraction is dependent on a temperature. In this study, by using finite-element analysis, we examined the transient temperature distribution and the transient thermal stress distribution inside a coated conductor's coil winding with epoxy impregnation, when the cooling process with liquid nitrogen was considered. The transient one at the edge of the winding with a glass fiber rein-forced plastic bobbin is more than twice as large as the steady thermal tensile stress and is greater than the cleavage stress strength. Moreover, we have found that it is desirable to use a material with a smaller thermal expansion coefficient and larger heat transfer as the coil bobbin in order to reduce the transient thermal stress in the winding. The effectiveness of the stainless steel bobbin to reduce the transient thermal stress in the winding was showed. Furthermore, it was shown that sufficient precooling was required for reduction of transient thermal stress when a bobbin material with smaller thermal conductivity is used.

Effects of Local Heat Input Conditions on the Thermophysical Properties of Super Duplex Stainless Steels (SDSS)

The properties of the super duplex stainless steels (SDSS) are strongly affected by the thermal history imposed by welding procedures. The controlled dual phase microstructure (ferrite and austenite) guarantee excellent mechanical properties such as mechanical strength and corrosion resistance, in addition to small thermal expansion coefficient and high thermal conductivity. In this paper, we newly proposed a model able to predict the thermal history of the welding pieces coupled with local mechanical properties developed during welding procedure that combine the effects of temperature and phase changes during welding. We applied inverse method to fit the thermophysical parameters based on measured data. The model was verified by comparing measured and predicted temperature profiles using thermocouples located within the heat affected zone. Thus, an inverse method was implemented to obtain the parameters fitting for the grain growth evolution compatible with the final microstructure and grain size measured using SEM images and stereological techniques. We demonstrated that very small amount of non-equilibrium deleterious phases and nanosized precipitated are expected during the welding procedures depending upon the local conditions of temperature, compositions and alloying dilution evolutions.

Effect of Wafer Level Underfill on the Microbump Reliability of Ultrathin-Chip Stacking Type 3D-IC Assembly during Thermal Cycling Tests.

The microbump (μ-bump) reliability of 3D integrated circuit (3D-IC) packaging must be enhanced, in consideration of the multi-chip assembly, during temperature cycling tests (TCT). This research proposes vehicle fabrications, experimental implements, and a nonlinear finite element analysis to systematically investigate the assembled packaging architecture that stacks four thin chips through the wafer level underfill (WLUF) process. The assembly of μ-bump interconnects by daisy chain design shows good quality. Results of both TCT data and the simulation indicate that μ-bumps with residual SnAg solders can reach more than 1200 fatigue life cycles. Moreover, several important design factors in the present 3D-IC package influence μ-bump reliability. Analytical results show that the μ-bump’s thermo-mechanical reliability can be improved by setting proper chip thickness, along with a WLUF that has a low elastic modulus and a small coefficient of thermal expansion.

Isotropic Zero Thermal Expansion and Local Vibrational Dynamics in (Sc,Fe)F3.

Scandium fluoride (ScF3) exhibits a pronounced negative thermal expansion (NTE), which can be suppressed and ultimately transformed into an isotropic zero thermal expansion (ZTE) by partially substituting Sc with Fe in (Sc0.8Fe0.2)F3 (Fe20). The latter displays a rather small coefficient of thermal expansion of -0.17 × 10-6/K from 300 to 700 K. Synchrotron X-ray and neutron pair distribution functions confirm that the Sc/Fe-F bond has positive thermal expansion (PTE). Local vibrational dynamics based on extended X-ray absorption fine structure indicates a decreased anisotropy of relative vibration in the Sc/Fe-F bond. Combined analysis proposes a delicate balance between the counteracting effects of the chemical bond PTE and NTE from transverse vibration. The present study extends the scope of isotropic ZTE compounds and, more significantly, provides a complete local vibrational dynamics to shed light on the ZTE mechanism in chemically tailored NTE compounds.

Polymer-derived ceramic tapes with small and negative thermal expansion coefficients

A polysiloxane filled with ß-eucryptite and/or SiC was used for the processing of polymer derived ceramic tapes. The combination of both fillers in varying proportions allowed to tailor the overall bulk thermal expansion and the flexural strength of the resulting composite materials simultaneously. Incorporation of SiC increased noticeably the flexural strength of the samples and influenced the phase changes resulting from the interactions between the β-eucryptite filler and the polymer derived ceramic matrix. Changes in the phase composition and changes of the unit cell parameters of β-eucryptite because of the formation of solid-solutions with silica originating from the SiO2 constituent of the polymer derived ceramic matrix were observed by Rietveld refinement. Tapes resulting from this process possess a sufficient mechanical stability and their coefficient of thermal expansion can be adjusted from slightly positive to moderate negative values.

A study of the current density analysis for two type method on the invar alloy in electrochemical machining

Invar alloy is important material used for the OLED (Organic light emitting diode) shadow-mask in the mobile display industry due to its characteristics of smallest thermal expansion coefficient. Consumers in modern society demand higher display resolution. Electrochemical machining is one of the methods for obtained these high-resolution requirements. Electrochemical machining is a non-contact method that has advantages regarding defects like thermal strain and micro burrs compared to other non-conventional machining methods. For precision electrochemical machining using different shape electrodes, the current density should be controlled precisely. The purpose of this study is to apply the FEM (Finite elements method) analysis in order to investigate the current density in the electrochemical machining. And the current density distribution between invar alloy and electrode are carried out with shape electrode type and micro array film type under the same conditions by simulation methods. FEM analysis results show that using shape electrode type, current density distribution is very concentrated. And also by micro array pattern film, desired current density which is needed for electrochemical machining could be obtained easily. More precise electrochemical machining can be available by controlling the current density between the suitable type and invar alloy.

The passive thermal management system for electronic device using low-melting-point alloy as phase change material

In this paper, the alloy with melting point of 334.15K was prepared and successfully composited with carbon foam (Poco foam). From the systematic test of thermal properties, Low-melting-point alloy (LMPA) shows some considerable advantages, such as high conductivity (up to 50 times of paraffin’s), low thermal expansion and large volume latent heat (2.11 times of paraffin’s). The numerical investigation of the thermal performance of the LMPA-based heat sink is based on enthalpy-porosity method. The numerical results are validated by experimental data. Comparing with paraffin (RT60) that has a similar melting point of 333K, the main finding of the investigation is that the thermal management performance is much better that the LMPA can effectively extend the protection time to nearly 1.5 times longer as well as reduce the heater’s temperature by up to 15K during the heating period. Unlike the organic phase change material (PCM), the natural convection is nearly negligible owing to its much smaller thermal expansion coefficient and larger liquid viscosity, which means that the orientation and position has almost no effect on performance of the LMPA-based heat sink. In spite of the latent heat loss, the heat transfer performance is effectively improved by adding Poco foam that the heater’s temperature could be managed more uniformly with LMPA/Poco foam composite-based heat sink during the melting process. These results indicate that for some passive thermal management system with high heat flux, LMPA and LMPA/Poco foam composite could be preferred to serve as promising PCM candidates, especially for some particular situation where the volume of the device is strictly limited and the weight factor is less important.

Chemical Analysis of Activation Process of LSM Thin Film Electrode

Strontium-doped lanthanum manganite (LSM) is one of the most widely used cathode material for yttria-stabilized zirconia (YSZ)-based solid oxide fuel cells (SOFCs), due to its superior chemical stability and small coefficient of thermal expansion (TEC) mismatch with YSZ. The activation process of the cell, which can be attributed to the cathode and cathode electrode interface, has a significant effect on the long-term electrochemical performance and stability of SOFCs. Therefore, it is essential to understand the origin of this underlying activation process. In this study, thin film LSM on YSZ half cells were fabricated with an LSCF counterelectrode and the effects of cathodic current density and overpotential on the polarization behavior of the LSM thin film electrode were investigated. The surface morphology as well as surface chemistry and bonding environment of LSM before and after polarization was investigated using scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. The formation of SrO was found on the LSM surface after polarization. The cross-section microstructure of LSM, as well as interfacial chemistry of LSM/YSZ, were investigated using transmission electron microscope (TEM) and TEM-based energy dispersive X-ray spectroscopy (EDS). The presence of Mn-rich phases were observed before and after polarization. The pre- and post-activation electrode performances were investigated at various temperatures and oxygen partial pressures, which helps reveal the nature of the activation mechanism in combination with the microstructural and chemical analysis.

Dehydration studies of natrolites: Role of monovalent extra-framework cations and degree of hydration

Rietveld refinements of natrolite analogs [M 16 Al 16 Si 24 O 80 ·nH 2 O, M-NAT, M = Li, Na, Ag, K, NH 4 , Rb, and Cs, 14.0(1) 2 O content and monovalent extra-framework cations (EFC) contained in the channels have on dehydration and thermal expansion. Dehydration temperatures are found to be inverse proportional to the size of the EFC. Isostructural K-, Rb-, and Cs-NAT with disordered EFC-H 2 O distribution exhibit negative thermal expansions before dehydration. The thermal expansion coefficients increase linearly from K-, Rb-, to Cs-NAT, the latter exhibits has the smallest thermal expansion coefficient of all NAT analogs [3.0(1) × 10 −6 K −1 ]. After dehydration, the EFC distribution of K-, Rb-, and Cs-NAT becomes ordered and their thermal expansion coefficients become positive. In the isostructural Li-, Na-, and Ag-NAT with ordered EFC-H 2 O distribution, the thermal expansion coefficients are positive for the Li- and Ag-NAT and negative for Na-NAT. After dehydration, this behavior is reversed, and Li- and Ag-NAT show negative thermal expansion coefficients, whereas Na-NAT exhibits a positive thermal expansion. Upon dehydration, the channels in Li- and Ag-NAT reorient: the rotation angles of the fibrous chain units, ψ, change from 26.4(2)° to −29.6(2)° in Li-NAT and from 22.3(2)° to −23.4(2)° in Ag-NAT. The structure models of the dehydrated Li- and Ag-NAT reveal that the change in the channel orientation is due to the migration of the Li + and Ag + cations from the middle of the channel to the walls where they are then coordinated by four framework oxygen atoms. Further heating of these dehydrated phases results in structural collapse and amorphization. X-ray O1s K -edge absorption spectroscopy reveals that the binding energy between the EFC and the oxygen of the framework (O f ) is larger in Li- and Ag-NAT than in Cs-NAT due to an increase of the basicity of the framework oxygen. The interaction between the H 2 O molecules and EFCs allow a clear separation in structures with disordered H 2 O molecules in the center of the channels (K-, NH 4 -, Rb-, and Cs-NAT) and those in close proximity to the aluminosilicate framework (Li-, Na-, and Ag-NAT), which leads to systematic dehydration and thermal expansion behaviors. Our structure work indicates that the effects of EFCs are more important to stabilize the NAT structure than the degree of hydration.

Tunable air-suspended polymer grating couplers

We present thermal tuning of air-suspended SU-8 polymer waveguide grating couplers for TE-polarized light. Numerical simulations have been performed to estimate the wavelength shift caused by the change of temperature. Due to the small positive thermal expansion and large negative thermo-optic coefficient of SU-8, a shift toward shorter wavelengths is expected. In the experimental evaluation, a negative wavelength shift from 1542 nm at 20°C toward 1527 nm at 56°C is obtained with approximately −0.42 nm K−1 matching the theoretical considerations.

Inhibitory effect of Ni-P coating on thermal expansion of carbon steel

The thermal expansion of carbon steel can be inhibited by electroless deposited Ni-P coating. The diameter of sample increases by only 3% after plated. The linear coefficient of thermal expansion (CTE) of the substrate is decreased from 16ppm/K to as low as 12.68ppm/K with a reduction rate of 20.72%. At 613K, Ni-P coating crystallizes with a volume shrinkage which partly counteracts the thermal expansion of the substrate and then induces a small CTE, which is named crystallization compensation mechanism. After crystallization, a diffusion layer composed mainly of FeNi3, one of the primary phases of NiFe Invar alloys, generates in-situ at the interface of coating and substrate. This diffusion layer plays a key role in inhibiting the thermal expansion of iron substrate, which is named diffusion-layer inhibitory mechanism. These findings are, in principle, applicable to all the ferrous alloys so that a potential easy way can be promoted to decrease the CTEs of ferrous alloys.

Multialloying effect on thermophysical properties of Cr7C3‐type carbides

AbstractThe alloying element effect on the thermophysical properties of Cr7C3‐type ceramics is essential for the applications. The thermal expansion for these compounds is calculated using quasi‐harmonic approximation combined with density functional theory. The linear expansion coefficient along [100] direction is larger than that along [010] and [001] direction. The B‐ and Mo‐codoped Fe4Cr3C3 has the smallest thermal expansion coefficient. We obtained the temperature dependence of bulk modulus, pressure derivative modulus, and the Grüneisen constants. Furthermore, we propose a new method to calculate the anisotropy of minimum thermal conductivity which is suitable to the large complex unit cells. The three‐dimensional (3D) expression of anisotropy of minimum thermal conductivity are presented companied with planar projections on (100), (010), (001), and (110) crystal planes. The minimum thermal conductivity of Fe3Cr3WC2B is lower than other multicomponent compounds. The charge density differences and chemical bonding between Mo/W and B are found to be the key factor on the thermophysical properties of these compounds.

A review on the utilization of natural graphite and graphite-based materials

As a type of inorganic non-metallic resources, the natural graphite has a small thermal expansion coefficient (1×10−6–30×10−6 K), a high coefficient of thermal conductivity (129 W m−1 K−1), high temperature resistances, excellent electrical conductivity (resistivity 8×10−6–13×10−6 Ω m), brilliant lubricity with a friction coefficient of 0.08–0.16, plastic feature, good chemical stability, excellent thermal shock resistance and other properties, which makes it well-known as one of the “universal” mineral materials. Graphite has been widely used in the machinery, metallurgy, petrochemicals, light industry, electronics, electrical appliances, military defenses, aerospace and other economic fields. China is one of the countries that have the largest resources of natural graphite in the world. Based on data of the graphite mineral resources, production/consumption, and the international trade of China during the past several years, this paper gives an overview of the development of graphite mining, technologies in purifying raw ores, comprehensive utilization of graphite, applications and the technological innovations of graphite-base materials. The most important three types of graphite products including the expanded graphite, the fluorinated graphite, and graphene (2D graphite) are particularly reviewed. The production process based imported graphite products, technological innovation and the gap between China and developed countries are analyzed, and the development of the comprehensive utilization of graphite resources is introduced. Finally, the future direction of the graphite science was proposed according to the disciplinary development in the non-metallic mineral materials.