Thermal Expansion Coefficient Research Articles

Poly(ester imide)s with Low Linear Coefficients of Thermal Expansion and Low Water Uptake (VIII): Structure-Flame Retardancy Relationship.

A series of ester-linked tetracarboxylic dianhydrides containing multiple para-phenylene units (TA-pPhs) was synthesized to obtain novel modified polyimides, namely poly(ester imide)s (PEsIs). The flame retardancy and film toughness of PEsIs tended to deteriorate with the structural extension of the repeating units (or monomers) via ester groups. To identify the structural factors necessary for achieving the highest flame retardancy rank (UL-94, V-0), we systematically investigated the structure-property relationships of a series of TA-pPh-based PEsIs. Among them, a PEsI derived from para-quaterphenylene-containing TA-pPh (TA-DPQP) and p-phenylenediamine (p-PDA) exhibited the best property combination, featuring an extremely high glass transition temperature (Tg), very low linear coefficient of thermal expansion (CTE), low water uptake (WA), ultralow linear coefficient of humidity (hygroscopic) expansion (CHE), unexpectedly high film toughness, and excellent flame retardancy (V-0 rank). Moreover, we examined the effects of substituents of TA-pPh and discussed the mode of action for the increased film toughness. This study also investigated the structure-property relationship for a series of PEsIs derived from isomeric naphthalene-containing tetracarboxylic dianhydrides. Some of the PEsIs obtained in this study, such as the TA-DPQP/p-PDA system, hold promise as novel high-temperature dielectric substrates for use in flexible printed circuits.

Serendipitous relationship between discrete distribution models representing random orientations of fillers in composite materials and the golden ratio

The purpose of this study is to establish simple discrete distribution models capable of expressing the two and three-dimensional random orientation states of fillers in composite materials. Initially, a new method is proposed to divide the elastic constants into isotropic and anisotropic parts. Employing this method, for the composite material containing ellipsoidal fillers with various orientations in the material, the macroscopic elastic constants and thermal expansion coefficients of the material are derived based on the Mori–Tanaka method. Subsequently, the analysis of the macroscopic properties is performed for fillers oriented two and three-dimensional discrete distributions. As a result, it is found that when both angular pitches of the azimuth angle and the rotational angle of the fillers in a plane are at most 72°, the macroscopic elastic constants and the thermal expansion coefficients of the material exhibit in-plane isotropy, leading to the realization of a two-dimensional random state. Furthermore, if the angular distribution of the zenith angle and azimuth angle corresponds to the vertices of the regular dodecahedron and icosahedron, and the angular pitch of the rotational angle of the fillers is at most 72°, the macroscopic properties of the material become isotropic, resulting in a three-dimensional random state. Notably, the angle of 72° and the orientation angles of the vertices of the regular dodecahedron and icosahedron are associated with the golden ratio. Therefore, this analysis suggests a serendipitous relationship between the golden ratio and the angular pitch that simplifies the random orientation distribution of fillers.

Preparation and Property Modulation of Multi-Grit Diamond/Aluminum Composites Based on Interfacial Strategy

The development of electronic devices has a tendency to become more complicated in structure, more integrated in function, and smaller in size. The heat flow density of components continues to escalate, which urgently requires the development of heat sink materials with high thermal conductivity and a low coefficient of expansion. Diamond/aluminum composites have become the research hotspot of thermal management materials with excellent thermophysical and mechanical properties, taking into account the advantages of light weight. In this paper, diamond/Al composites are prepared by combining aluminum as matrix and diamond reinforcement through the discharge plasma sintering (SPS) method. The micro-interfacial bonding state of diamond and aluminum is changed by adjusting the particle size of diamond, and the macroscopic morphology performance of the composites is regulated. Through this, the flexible design of diamond/Al performance can be achieved. As a result, when 150 μm diamond powder and A1-12Si powder were used for the composite, the thermal conductivity of the obtained specimens was up to 660.1 W/mK, and the coefficient of thermal expansion was 5.63 × 10−6/K, which was a good match for the semiconductor material. At the same time, the bending strength is 304.6 MPa, which can satisfy the performance requirements of heat-sinking materials in the field of electronic packaging.

High sensitivity optical fiber temperature sensor based upon a polydimethylsiloxane filled Fabry-Perot interferometer

A high-sensitivity temperature sensor based upon an optical fiber Fabry-Perot interferometer (FPI) filled with polydimethylsiloxane (PDMS) is reported that employed a single mode fiber (SMF) and a hollow core fiber (HCF) to enhance the sensitivity. The sensing characteristics were investigated from 20 °C to 40 °C. The experimental results demonstrate that the sensor is sensitive to temperature due to the high thermal optical coefficient (TOC) and high thermal expansion coefficient (TEC) of PDMS, achieving a high sensitivity of 2.155 nm/°C. The designed sensor shows great potential for high-precision temperature sensing applications due to its high sensitivity, compact structure, and simple preparation.

Crystallization and microwave dielectric properties of CaO-B2O3-SiO2 glass-ceramic/Al2O3 for LTCC applications

High-frequency electronic devices with low dielectric loss and electronic components with high integration densities require high-performance electronic packaging materials. In this study, materials primarily composed of CaO-B2O3-SiO2 (CBS) with an elevated boron content were fabricated through solid-phase sintering using Al2O3 as the ceramic phase. The phase compositions, densification process, microstructures, thermal conductivity, thermal expansion, and dielectric properties of the LTCC were investigated. Remarkably, the CBS-1 LTCC composite sintered at 850 °C for 4 h, exhibited a dense and nonporous microstructure. It demonstrated exceptional thermoelectric properties, including a thermal shrinkage of 5.61 %, coefficients of thermal expansion of 4.86 ppm/°C, thermal conductivity of 2.36 W/m·K, dielectric constant (εr) of 4.88, and tan δ of 1.05× 10−3 at 15 GHz. These characteristics are conducive to minimizing the signal propagation time delay and filtering noisy signals. Consequently, the CBS-1 LTCC composite emerged as a promising substrate for LTCC applications.

Analysis of thermal residual deformation using different FVFs for each ply

The thermal stresses and residual deformations in composite materials are caused by differences in the thermal expansion coefficients between the fiber and matrix, chemical shrinkage of the matrix, and temperature distribution during curing. Complex thermal stresses can cause residual thermal deformations, including spring-in, spring-out, and warpage. Consequently, modifying composite molds is time-consuming and labor-intensive.In this study, composite laminate plates were fabricated using the VARTM and VIP processes. For each ply, thermal deformation analysis using different FVFs was performed, and the results were compared with the experimental results. The analysis error of the thermal residual deformations using various FVF for each ply was 9.9–36.1%, which was lower than that using the uniform FVF for all plies. Additionally, the residual thermal deformations caused by the VIP process were smaller than those caused by the VARTM process.

Molecular dynamics study on the thermal properties of DGEBA/DETA/Ag/SWCNT-Ag composite materials.

Traditional conductive adhesives based on epoxy resin system often encounter problems such as high brittleness and low heat resistance. Therefore, it is particularly important to improve the thermal and mechanical properties of the conductive adhesive. In this study, the effects of SWCNT-Ag and SWCNT fillers on the thermal properties of DGEBA/DETA/Ag conductive adhesive system were studied by using molecular dynamics to construct different cross-linking models. The final results show that the addition of SWCNT and SWCNT-Ag can significantly improve the thermal properties of the conductive adhesive. However, the nanosilver particles on the surface of SWCNT-Ag act as a bridge for the connection between SWCNT and Ag in the conductive adhesive. Therefore, SWCNT-Ag has a more positive impact on the thermal properties of DGEBA/DETA/Ag conductive adhesive system. In this paper, the influence of SWCNT-Ag on the thermal properties of traditional DGEBA/DETA/Ag conductive adhesive system was studied by using Materials Studio software. The volume shrinkage, glass transition temperature, thermal expansion coefficient, and thermal conductivity of the material were calculated based on COMPASS force field. The thermal conductivity is calculated by using reverse non-equilibrium molecular dynamics method. Finally, it is found that SWCNT-Ag has a positive effect on the thermal properties of the conductive adhesive system by comparing several groups of calculation data.

Comparison of diffusion coatings resistance on ferritic and austenitic-stainless steels at 650 °C in steam oxidation

Iron-aluminide coatings were deposited on T24, P92 and Incoloy 800HT (IN-800HT) by pack-cementation and by a water-based slurry. According to the differences in heat treatments between the two processes, Al-rich phases, i.e. Fe4Al13 and Fe2Al5 were obtained by pack cementation and only B2-(Fe, Ni)Al by slurry. Vertical or horizontal cracks were present on certain coatings, the former being due to the coefficient of thermal expansion (CTE) mismatch with the substrate while the latter were related to the brittleness of the Al-rich phases. The oxidation behaviour of uncoated and coated substrates was studied at 650 °C up to 1000 h under a low steam flow rate (1.07 × 10−5 m/s). The aluminide coatings were very protective on the low Cr substrates (i.e. T24 and P92) because of the formation of a very thin oxide scale compared to the non-protective thick layers of Fe3O4 and Fe2O3 that grew on both uncoated substrates. In contrast, none of the coatings significantly improved the oxidation resistance of the IN-800HT steel despite the growth of a thin oxide layer made of (Fe, Cr)2O3 and (Fe, Cr)3O4 at 650 °C.

Effect of Solution-to-Binder Ratio and Molarity on Volume Changes in Slag Binder Activated by Sodium Hydroxide at Early Age.

This research investigates the impact of solution concentration and solution-to-binder ratio (S/B) on the volume changes in alkali-activated slags with sodium hydroxide at 20 °C. Autogenous and thermal strains are monitored with a customized testing device in which thermal variations are controlled. Consequently, both the autogenous strain and coefficient of thermal expansion (CTE) are determined. Heat flow and internal relative humidity (IRH) are also monitored in parallel, making this research a multifaceted study. The magnitudes of autogenous strain and CTE are higher than those of ordinary Portland cement paste. Decreasing the solution concentration or S/B generally decreases the autogenous strain (swelling and shrinkage) and the CTE. The shrinkage amounted to 87 to 1981 µm/m, while the swelling reached between 27 and 295 µm/m and was only present in half of the compositions. The amplitude of the CTE, which increases up to 55 µm/m/°C for some compositions while the CTE of OPC remains between 20 and 25 µm/m/°C, can be explained by the high CTE of the solution in comparison with water. The IRH of paste cannot explain the autogenous strain's development alone. Increasing S/B eliminates the self-desiccation-related decrease.

Vacuum sintering of the self-developed Chang’E-5 lunar regolith simulant

The utilization of in-situ lunar resources through the additive manufacturing of lunar regolith (LR) has attracted considerable interest. Sintering of LR is considered a promising method for lunar construction due to its high utilization rate and excellent service stability. However, numerous studies have been carried out on Apollo series LRs with similar chemical compositions in air or inert gas atmospheres. The effects of the lunar ultra-high vacuum conditions and the complex chemical composition of LRs on the sintering process require extensive investigation. In this study, a self-developed Chang’E-5 lunar regolith simulant (LRS) with a high-Fe content was used as the only raw material to investigate its potential applicability for future lunar construction in vacuum environment. The effects of sintering temperature on the microstructure, linear shrinkage, bulk density, weight loss ratio, and mechanical and thermal expansion properties were investigated. The results show that the linear shrinkage and weight loss ratio increase with increasing sintering temperature. However, the bulk density and unconfined compressive strength (USC) initially increase and then decrease, with the sample sintered at 1075℃ giving the highest bulk density of 2.10 ± 0.03 g/cm3 and a USC of 31.19 ± 1.96 MPa. This is attributed to the transformation of the sample sintered at 1090℃ into a semi-porous material with many cracks. Furthermore, the mechanism of pore and crack formation was revealed. The coefficient of thermal expansion (CET) of the sintered samples is approximately 7×10–6°C−1, which maintains a good service stability after cyclic temperature stress from room temperature up to 200°C. Both the USC and CET of the sample sintered at 1075℃ are superior to those of common terrestrial concrete materials. This indicates that the vacuum sintering process appears feasible for the production of building materials with sufficient mechanical strength and thermal durability for lunar base construction.

In-situ study of σ phase evolution in 25Cr-7Ni duplex stainless steel (DSS): Unrevealing critical insight

The current understanding of the formation mechanism and kinetics of the σ phase in DSS remains ambiguous. This study investigates the in-situ evolution of the σ phase in DSS through a multi-faceted approach. Distinct σ phase formation mechanisms were identified at 850 °C and 950 °C, with short-range diffusion of eutectoid decomposition at 850 °C and long-range diffusion of nucleation and growth at 950 °C. In-situ X-ray diffraction (XRD) revealed that the lattice parameter of the γ phase peaks at ∼ 600 °C. The thermal expansion coefficient (CTE) of the γ phase is 1.8 times higher than that of the α phase at low temperatures. Interestingly, the convergence of the CTEs of the α and γ phases above 600 °C triggers σ nucleation. The strain field diagram shows maximum impinging strain at the lattice parameter maxima just before the σ formation range. The adverse effects of the σ phase on DSS heat transport properties were also explored, showing an initial increase in thermal conductivity with an increasing γ volume fraction, followed by an 18 % decrease upon σ evolution. First-principle calculations highlight the correlation between Ni enrichment and lattice parameter maxima, supporting these findings.

A DFT insight of the electronic, thermodynamic, and thermoelectric properties of RuO2

In this study, we explore the structural, electronic, thermodynamic, and thermoelectric properties of RuO2 using density functional theory. The derived equilibrium structural parameters agree with other theoretical and experimental results. The widely used modified Becke–Johnson (mBJ-GGA) potential is adopted for accurate electronic band gap estimation. To incorporate the effect of the extended orbital of the Ru atom, spin-orbit coupling has been used in combination with the mBJ potential. The investigation of electronic properties revealed an indirect semi-conducting nature with a band gap along the W-L symmetry. The calculated band gaps are 1.685 and 1.658 eV from mBJ and mBJ + SOC, respectively. The dynamical stability is tested and verified by calculating the phonon dispersion curve. We have employed the quasiharmonic approximation-based Gibbs2 package to determine the pressure and temperature-dependent thermodynamical parameters, such as cell volume, Debye temperature, heat capacity, entropy, and thermal expansion coefficient. This study uses the BoltzTraP simulation algorithm to determine the thermoelectric parameters such as the Seebeck coefficient, electrical conductivity, and thermal conductivity.

Photo‐Directed Growth of Surface Micro‐Patterns on Photosensitive Semicrystalline Polymers

AbstractPatterning polymeric materials with controllable microstructures can meet diversified requirements and realize promising applications. Exploring micro‐/nano‐pattern methodology offers possibilities for future techniques, however, the self‐organized growth of polymeric materials has some limitations and the development of direct and noncontact patterning processes is still challenging. In this work, the study presents a facile strategy for endowing polymers with spatially regulated microstructures by direct photo‐printing, which incorporates both advantages of typical top‐down and bottom‐up approaches. By employing the photodimerization of anthracene‐containing semi‐crystallized polymers, the gradient crosslinking results in a mismatch of thermal expansion coefficients between the crosslinked surface and the uncrosslinked bottom layer. After heating treatment, constrained by the crosslinked surface, the uncrosslinked bottom polymer of the molten state in the exposed region tends to flow and migrate toward the unexposed region, similar to a volcanic eruption, which accurately determines the height and morphology of pattern. Besides, the well‐defined patterns can controllably grow upon thermal treatment due to phase transformation and migration. The versatility of the proposed strategy not only provides a brand‐new reliable platform to pattern functional materials with photo‐regulated and reversible microstructures, but also promotes the development of smart materials that can find applications in information safety, reversible microfluidics, and electronic devices.

Wide-Temperature Characteristics of Additively PBF-LB/M Processed Material Ti6Al4V

Titanium-based alloys are a widely applicable engineering material with high strength, low weight, non-magnetic, and corrosion resistance. At the same time, resistance to low temperatures is declared, which offers the material’s applicability for, e.g., aircraft or ship technology. Additive technologies are part of the industrial spectrum of material processing, especially the Laser Powder Bed Fusion of Metals method for metal alloys, which creates a layered structure of the resulting body. The topology of the internal structure, in relation to the temperature history of the functional environment, influences thermal expansion and the associated functional characteristics. Knowledge of the thermal expansion of printed strength and non-strength functional components and accessories is essential for future applications, especially in environments with high repeatable temperature changes, such as the aerospace industry. This paper presents the results of testing the expansion, mechanical, microstructural, and mineralogical characteristics of Ti6Al4V over the temperature range of −70 to 60 °C using a combination of instrumental techniques such as X-ray diffraction and nanoindentation. It was found that the topological orientations of the printed samples directly influenced the tested properties, e.g., the coefficient of thermal expansion in the direction perpendicular to the printed layers showed approximately 12% lower value compared to the other directions. Due to the progression of the application of the manufacturing method and its applicability within selected industries, the research provides results in a new area, which is supported by the relevant research.

Metrological assessment of the carbon tubes behavior under thermal variation for the compensation of 3D devices

Abstract Composite materials are increasingly used in 3D metrology, especially for portable measuring devices such as articulated arm coordinate measuring machines (AACMM), 3D scanners, and ball bars. Their use is justified by their interesting mechanical properties including their low density, good rigidity, and especially their light weight, which makes them ideal for portable devices, that are meant to be often transported by the user. However, due to their complex composition, the characterization of the thermal behavior of composite materials remains complicated compared to standard materials and is nowadays an active research subject. In fact, the coefficient of thermal expansion of composite materials is dependent of the very specific composition of the composite material considered. Hence, it is function of several parameters such as the orientation of the fibers, the fiber volume fraction, the ply sequence, the cooling rate, etc. In the other hand, in 3D metrology, and especially in portable 3D metrology, determining the expansion coefficient of the different part of the measurement devices used is necessary. In fact, the portable measurement machines are often integrated and used directly on the shop floor, where the thermal variations can be important and then heavily impact the measurements results. In some cases, the lack of knowledge of the coefficient of thermal expansion of the composite materials that compose the portable measuring machine can significantly increase the measurement uncertainty.

Observation of the liquid metal phase transition in optofluidic microcavities

Gallium (Ga) exhibits remarkable potential in flexible electronics, chemistry, and biomedicine due to its exceptional physical properties. The phase transition and supercooling characteristics of Ga have led to the emergence of numerous valuable applications. In this paper, we capitalize on this foundation by utilizing optofluidic microcavities supporting both high quality factor optical and optomechanical modes to investigate the phase transformation process and supercooling properties of Ga. Our study provides comprehensive insights into the dynamic behavior of Ga during the complete phase transition, such as measuring a hysteresis loop between the solid-to-liquid and liquid-to-solid transitions, revealing nonreciprocal resonance wavelength shift, and identifying a unique metastability state of Ga during melting. The linear thermal expansion coefficients of Ga were precisely measured to be 0.41 × 10−5 K−1 and −0.75 × 10−5 K−1 for solid and liquid Ga, respectively. Our research provides a comprehensive and versatile monitoring platform for newly fabricated liquid metal alloys, offering multidimensional insights into their phase transition behavior.

تأثيرات التكنولوجيا النانوية على الخواص الميكانيكية والفيزيائية للمعادن في أنظمة التبريد

Nanotechnology has revolutionized various scientific and engineering fields, including materials science. In this investigation, the focus is on examining the influence of titanium nanoparticle size on the mechanical and physical properties of metal. Incorporating nanoparticles into metal matrices presents an exciting opportunity to enhance material performance through size-dependent effects. Titanium nanoparticles have been chosen as the primary focus due to their unique properties and extensive applications. To assess the impact of nanoparticle size on mechanical properties, a series of experiments were conducted involving the production of metal composites with varying sizes of titanium nanoparticles. Mechanical properties, including yield strength and hardness, were measured using standard testing methods such as tensile testing and nanoindentation. The results indicate that smaller titanium nanoparticles contributed to improve mechanical properties, increased yield strength and hardness compared to the bulk metal. Additionally, the investigation explored the effects of titanium nanoparticle size on the physical properties of the metal composite. Thermal conductivity and coefficient of thermal expansion were measured to evaluate the thermal behavior of the composites. The findings demonstrate that the incorporation of titanium nanoparticles influences thermal conductivity and coefficient of thermal expansion, with variations that depend on nanoparticle size. Keywords: Nanotechnology, Titanium Nanoparticles, Mechanical Properties, Physical Properties, Metal Composites.

Microstructure and performance of carbon fiber reinforced aluminum matrix composites with molybdenum carbide coating on carbon fibers

In this work, a molybdenum carbide coating on the surface of short carbon fibers prepared using molten salt method was proposed to ameliorate the interfacial bonding and improve the performance of carbon fiber/Al composites. The carbon fiber/Al composites were produced using vacuum hot pressing. The characteristics of molybdenum carbide coating were analyzed. Besides, the microstructures, bending strength and thermal properties of the carbon fiber/Al composites were explored. Furthermore, the interfacial thermal resistance of the composites was investigated in relation to theoretical evaluations derived from the combined Maxwell-Garnett effective medium approach and acoustic mismatch model schemes. The results indicated that a homogeneous Mo2C coating with a thickness of 0.5 μm was obtained by proper molar ratio of carbon fibers, MoO3 and chloride salts mixture and heated at 1000 °C for 60 min. The Mo2C coating greatly enhanced the bond between the aluminum matrix and carbon fiber, leading to improvements in the densification behavior and bending strength of the coated composites. The enhanced thermal properties including improved thermal conductivity and reduced coefficient of thermal expansion (CTE) were also achieved by the Mo2C coating. The in-plane thermal conductivity of 60 vol.% Mo2C-coated carbon fiber/Al composite was 221 W·m−1·K−1 enhanced by 92% compared to that of uncoated composite and the CTE was 6.0 × 10–6 K−1 which was suitable for electronic packaging materials.

Multifunctional design of lattice metamaterial with desired thermal expansion behaviors using topology optimization

Designing metamaterials with unprecedented coefficients of thermal expansion (CTEs) is an urgent demand for the majority engineering structures suffering from ambient temperature variation. Current studies on such artificial materials are mainly focused on achieving CTE tunnability through the purposeful design of material microstructure using an intuition based mechanism. In this study, the mechanical properties including maximum bulk modulus, specific stiffness and high thermal conductivity are combined with desired CTEs for designing multifunctional lattice metamaterials through the application of a non-intuitive topology optimization method. Toward this end, the continuous variable of member cross-sectional area is adopted to optimize lattice topology, section sizes of lattice members and material distributions, simultaneously. To meet the manufacturing requirements, an improved member intersection constraint that can cooperate with the present continuous design variable is introduced. A self-programmed routine that can be coupled with any commercial FEA software is developed to implement the present optimization method for the design of lattice metamaterials. Four typical optimization cases corresponding to different practical engineering issues are completed. Compared with the previously reported representative lattice metamaterials that are devised from the intuition or experience of designers, the optimization results obtained in this work demonstrate an obvious superiority in bulk modulus and specific stiffness. Additionally, a bimetallic specimen, fabricated using mechanical processing technology and composed of the metallic constituents Invar and Aluminum alloy, is presented to demonstrate the manufacturability of the optimized lattice microstructures.

Effect of mullite fiber on the properties of glass composite sealing materials

Glass-based sealing materials exhibit significant potential for utilization in solid oxide fuel cells (SOFCs). We conducted a study on the impact of mullite fibers with varying particle sizes on glass composite sealing materials. We evaluated and discussed properties such as coefficient of thermal expansion (CTE), softening temperature (Ts), gastightness, interfacial compatibility, and flexural strength of the sealing materials with different ranges of fiber particle sizes. Our findings indicate that the three different particle sizes of mullite fiber-glass composite sealing materials met the required coefficients of thermal expansion, displayed good interfacial compatibility, and exhibited gastightness lower than 0.0016 sccm cm−1. Notably, the mullite fiber-reinforced sealing material that underwent ball-milling for 1 h outperformed the other two variants. It demonstrated fewer defects, a 57.1 % increase in flexural strength, and a 117.4 % higher maximum strain value.