High Thermal Properties Research Articles

Development of Mg–Zn–Mn–Y magnesium alloy with high thermal conductivity and compression properties via injection molding

Development of Mg–Zn–Mn–Y magnesium alloy with high thermal conductivity and compression properties via injection molding

Coexistent improvement of thermal and mechanical performance at Si/Cu joint by thickness-controlled Sn-Ag bond layer

In this study, sound Si-Cu joints with high thermal conductivity and mechanical property were achieved at 260 °C with thickness-controlled Sn-Ag bond layer. The microstructure evolution, thermal and mechanical properties were proposed systematically. The bond layer was fabricated by micro electroforming technology to precisely control the thickness and improve the bond ability. The electroformed Ag layer could protect the sputtered Cu film and restrict the diffusion of Cu elements, which could decrease the residual stress and remove the interface defects. At the joints, the electroformed Sn layer was consumed to form Ag3Sn and Cu6Sn5 intermetallic compounds. The thermal conductivity and shear strength both increased firstly and then decreased with the thickness of bond layer increasing. The highest thermal conductivity of 283.21 W/(m·K) and shear strength of 88.74 MPa were achieved synchronous with 15-μm-thickness Sn-Ag bond layers, which were attributed to the reduction of the interface stress and elimination of interfacial defects. This technology had potential to be applied in the microelectronic heat dissipation at the future.

Polyacrylonitrile Fibers with a Gradient Silica Distribution as Precursors of Carbon-Silicon-Carbide Fibers.

This study presents preparing and characterization of polyacrylonitrile (PAN) fibers containing various content of tetraethoxysilane (TEOS) incorporated via mutual spinning solution or emulsion using wet and mechanotropic spinning methods. It was shown that the presence of TEOS in dopes does not affect their rheological properties. The coagulation kinetics of complex PAN solution was investigated by optical methods on the solution drop. It was shown that during the interdiffusion process phase separation occurs and TEOS droplets form and move in the middle of the dope's drop. Mechanotropic spinning induces the TEOS droplets to move to the fiber periphery. The morphology and structure of the fibers obtained were investigated by scanning and transmission electron microscopy, as well as X-ray diffraction methods. It was shown that during fiber spinning stages the transformation of the TEOS drops into solid silica particles takes place as a result of hydrolytic polycondensation. This process can be characterized as the sol-gel synthesis. The formation of nano-sized (3-30 nm) silica particles proceeds without particles aggregation, but in a mode of the distribution gradient along the fiber cross-section leading to the accumulation of the silica particles either in the fiber center (wet spinning) or in the fiber periphery (mechanotropic spinning). The prepared composite fibers were carbonized and according to XRD analysis of carbon fibers, the clear peaks corresponding to SiC were observed. These findings indicate the useful role of TEOS as a precursor agent for both, silica in PAN fibers and silicon carbide in carbon fibers that has potential applications in some advanced materials with high thermal properties.

Glasses and Glass–Ceramics from Li2O-KF-TiO2-SiO2 System Doped with SiC

Unfamiliar invert host silicate glass from the system SiO2-TiO2-KF-Li2O was prepared together with SiC doped samples by traditional melt-quenching technique. Collective characterization of the prepared glasses through FTIR, optical, thermal and microhardness properties were measured to justify the effect of silicon carbide (SiC) on the resultant data. Silicon carbide is selected because its known high mechanical and thermal properties and extended applications of SiC- containing candidates in several domains. Structural FTIR characterization of the prepared glasses reveals familiar silicate network in spite of their invert percent together with the suggested sharing of Si-Ti or Ti-Ti or fluoride units. Optical spectra show only distinct UV absorption with additional small peaks at 380–420 nm in high percent of SiC. Such UV spectra are assumed to originate from unavoidable traces of ferric ions contaminated within the raw materials used for the preparation of glasses. The known high thermal and mechanical properties of silicon carbide are identified to be reflected on the measured thermal expansion and Vickers microhardness data. Samples from the parent glasses were thermally heated to produce their corresponding glass-ceramic derivatives. X-ray diffraction analysis indicate the formation of the peculiar orlovite crystalline phase as a major one due to the presence of all the constituents within the chemical composition of the invert glass. Also, some minor crystalline phases of lithium silicate or lithium titanium silicate are identified. It is assumed that the presence of self-nucleation Li2O and high negatively charged fluoride anions beside the conditional oxide of TiO2 facilitate the ease of nucleation and crystallization of the formed crystalline phase. SEM results confirm the x-ray data showing different crystalline features with the addition of SiC.

Ambient pressure dried silica aerogel – Melamine foam composite with superhydrophobic, self-cleaning and water remediation properties

With their low density, high surface area and thermal insulation properties, silica aerogels are proper candidates for water remediation or thermal insulation applications. However, their fragility, lengthy and costly fabrication process restricts their application. The inclusion of a flexible melamine foam (MF) along with a co-precursor system consisting of monomeric methyltrimethoxysilane (MTMS) and polymeric polyvinyltrimethoxysilane (PVTMS) can make the fabrication process feasible and improve the durability of aerogels. Also, PVTMS with a doubly-crosslinked network brings mesoporous structure and high surface area to MF. MTMS alters the hydrophilic nature of MF to superhydrophobic, without surface modification steps.Varying concentration of PVTMS and MTMS were used to fabricate the MF- aerogel composite. Acid and base catalysts were used for the hydrolysis and condensation. The MF-aerogel composite was obtained using ambient pressure drying, and the overall fabrication process took around 48 hrs.The inclusion of MF enabled the ambient pressure drying and brought flexibility for silica aerogels. On the other hand, the presence of mesoporous aerogels improved the thermal insulation properties of MF (λ ∼ 0.027 W·m−1·K−1), making it superhydrophobic (θ ∼ 160°), self-cleaning, and moisture resistant. Excellent oil adsorption (up to 36 g·g−1) and oil–water separation performance (oil flux of 120,000 L·m−2·hr−1) of MF-aerogel composite were also confirmed.

Graphene-based thermally conductive material cross-linked by poly(ethylenimine) with high thermal and mechanical properties

Graphene-based thermally conductive material cross-linked by poly(ethylenimine) with high thermal and mechanical properties

Upcycling Waste Polycarbonate to Poly(carbonate imine) Vitrimers with High Thermal Properties and Unprecedented Hydrolytic Stability

The global market for polycarbonate (PC) increases steadily because of its heat resistance, toughness, and optical transparency. To achieve sustainability, the waste polycarbonate (WPC) should be recycled. This work reports a 100% atom-efficiency upcycling of WPC to a WPC-derived aldehyde (WPC-CHO). Then, poly(carbonate imine) vitrimers (PCIs) based on the WPC-CHO and two aromatic diamines were prepared. Generally, polyimines can cleave in mild acidic conditions such as 0.1 M HCl(aq) and seldom show good thermal and tensile properties. The PCIs in this work showed good thermal and tensile properties and an unprecedented resistance toward acid hydrolysis. They can survive even immersing in a 5 M H2SO4 THF/H2O solution for 6 months. This unusual resistance toward acid hydrolysis expands the application of PCIs in an acidic environment. Small pieces of PCIs can be compression-molded into a newly formed polymer film at 240 °C. This thermal reprocessability demonstrates the vitrimer characteristic of the PCIs. The PCIs can be degraded through simultaneous aminolysis of carbonate and transimination of imine by hexylamine (HA) in a catalyst-free mild condition. Based on the aminolysis and transimination, we degraded the cross-linking network in the PCI-based carbon fiber-reinforced polymer (CFRP) and recovered undamaged carbon fiber. This environmentally friendly work will attract the attention of researchers who are interested in sustainability and circularity.

Preparation and properties of zirconium-doped copper calcium titanate ceramics for broadband electromagnetic spectrum conversion

In this paper, zirconium-doped CaCu3Ti4-xZrxO12 (0 ≤ x ≤ 0.3, CCTZO) ceramics were prepared by traditional solid-state reaction. The prepared CaCu3Ti4-xZrxO12 display cubic phase structure, as shown by the XRD analysis, and interplanar spacing increase, as obtained by TEM. The surface morphologies, electrical conductivity, optical properties, solar and microwave thermal conversion characteristics of the synthesized samples were investigated in detail. The experimental results indicate that both the solar absorbance and thermal emittance of the samples could be tailored by Zr ions doping. In general, the CaCu3Ti4-xZrxO12 system displays relatively high thermal radiation properties, with an optimal composition of CaCu3Ti3.9Zr0.1O12 exhibiting a solar absorbance of 0.85 and a thermal emittance of 0.75. The incorporated Zr ions enhanced the solar–thermal conversion while weakened the microwave–thermal conversion. Under simulated solar irradiation (3 W/cm2), the equilibrium temperature of CaCu3Ti3.9Zr0.1O12 could reach above 260 °C. The equilibrium temperature of CaCu3Ti4O12 could reach up to 493 °C at a frequency of 2.45 GHz over 140 s. The results demonstrate that the CCTZO ceramics have the potential to emerge as the broadband electromagnetic wave–thermal conversion materials.

The Effect of Different Stabilisers on Stability and Photothermal Profiling of Gold Nanorods

AbstractThe photothermal application of gold nanorods (AuNRs) as a photothermal agent has gained popularity due to their optical, photothermal and biological properties. However, AuNRs are synthesised using a biotoxic surfactant (cetyl trimethyl ammonium bromide) which limits their biological applications. Though different techniques have been established to address this challenge using different stabilizers or passivating agents, the effect of these stabilizers on AuNRs' colloidal stability, thermal stability, and photothermal conversion efficiency still need to be investigated. In this study, we evaluated the effect of different polymers or stabilisers; two synthetic polymers [methoxy polyethylene glycol thiol (mPEG-SH) and polyvinylpyrrolidone (PVP)] and one biopolymer (gelatin) on the stability and photothermal properties of AuNRs. AuNRs absorbing around 800 nm were synthesised and coated with these three stabilisers. The colloidal stability of the as-synthesised material was evaluated in Dulbecco's phosphate-buffered saline (PBS) and Roswell Park Memorial Institute (RPMI-1640) using Ultraviolet–Visible–Near-Infrared (UV–Vis–NIR). The results show that PEG@AuNRs was more stable in both media due to fewer functional groups on its structure to bond with ions and protein. PVP@AuNRs showed good thermal stability under heat incubation (at 37, 50 and 70 °C) for 24 h because of its high thermal decomposition properties, while PEG@AuNRs proved superior in improving the AuNRs heat generation. In addition, coating with different polymers did not affect the photothermal ability of AuNRs. This study demonstrated that it is crucial to choose polymers with less functional groups when coating nanoparticles for biological application.

Particle creation and entanglement in a dispersive model with step velocity profile

We investigate particle creation and entanglement structure in a dispersive model with subliminal dispersion relation. Assuming the step function spatial velocity profile of the background flow, mode functions for a massless scalar field is exactly obtained by the matching method. Power spectrums of created particles are calculated for the subsonic and the transsonic flow cases. For the transsonic case, the sonic horizon exists and created particles show the Planckian distribution for low frequency region but the thermal property disappears for high frequency region near the cutoff frequency introduced by the non-linear dispersion. For the subsonic case, although the sonic horizon does not exist, the effective group velocity horizon appears due to the non-linear dispersion for high frequency region and approximate thermal property of the power spectrum arises. Relation between particle creation and entanglement between each mode is also discussed.

Thermal properties of tungsten/tungsten carbide-coated double-size diamond/copper composite

Diamond‑copper composites with high thermal properties and low density show huge potential applications in thermal management. Solving the interface between diamond and copper and increasing the volume fraction of diamond in the composite are crucial for its thermal conductivity. In this work, tungsten/tungsten carbide (W/WC) was used as an interface and fabricated on diamond surface by the molten salt method. Well-coating with higher than 95 % of coverage was obtained at the mass ratio of diamond and W of 3:3, which owns a 200 nm ± 10 nm thickness of W/WC layer. Meanwhile, double-size diamonds with 200 μm and 40 μm were compounded with the copper matrix to increase the volume fraction of the diamond. Theoretical calculation displays only 14.5 % of porosity in the bimodal diamond composite when 74.2 vol% of the large-size diamond is in the total volume fraction of the diamond. Microstructure characterization displays that the interfacial bonding was enhanced by the W/WC interface and morphology was improved by using the double-size diamonds even at 70 % of the volume fraction. Compared with single-size diamond/copper composite, the thermal conductivity was also increased and obtained the highest value of 640 Wm−1 K−1 for the double-size diamonds/copper composites. Finite element analysis and testing of actual scenarios further confirm the excellent thermal performance of double-size diamonds/copper composite, which meets the requirements of thermal management in high-power devices.

Mechanically strong and multifunctional nano-nickel aerogels based epoxy composites for ultra-high electromagnetic interference shielding and thermal management

With the development of highly integrated electronic equipment, electromagnetic pollution and heat congregation have become serious problems. Electromagnetic interference (EMI) shielding materials with high thermal conductivity and mechanical properties are highly desirable. Herein, the reduced graphene oxide/Ni nanowire aerogels (GNiA) were firstly prepared via hydrothermal reducing process and freeze-drying. Subsequently, using epoxy (EP) as a polymer matrix, the GNiA/EP composites with high compression strength of 147 MPa were fabricated by vacuum filtration and curing. The GNiA endows the composites with great electromagnetic wave loss, as well as improved phonon propagation efficiency, resulting in the super high EMI SE. With the GNiA content of 12.14 wt%, the EMI SE and thermal conductivity of GNiA/EP composites can reach as high as 85 dB and 1.69 W/(m·K) respectively. The obtained GNiA/EP composites provide a strategy to meet the demand for electronic equipment for new-generation EMI shielding materials.

Recyclable thermally conductive poly(butylene adipate‐co‐terephthalate) composites prepared via forced infiltration

AbstractWith the rapid development of electronic equipment and communication technology, the demand for polymer composites with high thermal conductivity and mechanical properties has increased significantly. However, its nondegradable polymer matrix will inevitably bring more and more serious environmental pollution. Therefore, it is urgent to develop biodegradable thermally conductive polymer composites. In this work, biodegradable poly(butylene adipate‐co‐terephthalate) (PBAT) is used as the matrix material, and vacuum‐assisted filtration technology is employed to prepare carbon nanotube (CNT) and cellulose nanocrystal (CNC) networks with high thermal conductivity. Then CNT–CNC/PBAT composites with high thermal conductivity and excellent mechanical properties are prepared by the ultrasonic‐assisted forced infiltration method. Both experiment and simulation methods are used to systematically investigate the thermally conductive and dissipation performances of the CNT–CNC/PBAT composites. Above all, a simple alcoholysis reaction is applied to realize the separation of the PBAT matrix and functional fillers without destroying the conductive network skeleton, which makes it possible for the recycling of thermally conductive polymer composites.

High Tg, Bio-Based Isosorbide Methacrylate Resin Systems for Vat Photopolymerization.

The use of isosorbide-derived polymers has garnered significant attention in recent decades as a high-performance, renewable material sourced from biomass. Of particular interest is isosorbide methacrylate, which possesses low viscosity (<500 cps), high thermal properties (Tg ≈ 220 °C), and high modulus (>4 GPa). These characteristics present a promising opportunity to replace BPA-derived methacrylate compounds in various applications. This investigation aims to synthesize and characterize isosorbide-based low-viscosity resin systems for 3D printing. The resin blends are composed of isosorbide methacrylate and two bio-renewable methacrylates, furfuryl methacrylate (FM) and bis-hydroxymethyl-furan methacrylate (BHMF-M), polymerized through a digital light processing (DLP) technique. The addition of the bio-based co-monomers serves to enhance the fracture toughness of the brittle isosorbide methacrylate crosslinked homopolymer (GIc = 37 J/m2). The resulting polymers exhibit Tg values greater than 200 °C and GIc around 100 J/m2. These resin systems hold potential for imparting high bio-based content to polymers used in additive manufacturing for high-performance applications.

Versatile spider-web-like cross-linked polyimide aerogel with tunable dielectric permittivity for highly sensitive flexible sensors

With the development of intelligent electronic power systems, the performance of flexible electronic sensors with portability and miniaturization is increasingly in demand. It is extremely challenging to achieve high modulus and high elasticity of polymer matrix simultaneously due to the inherent strength-elasticity conflict of elastic polymer. Here, a series of “spider-web-like” cross-linked polyimide aerogels (CPAs) had been successfully prepared. Benefiting from the robust dynamic network structure, the CPAs exhibited excellent compressive resilience, tunable dielectric permittivity, high thermal insulation property (λ = 0.040 W/m∙K) and modulus (E = 1073 KPa). Additionally, due to the excellent resilience of the CPAs and tunable permittivity, a CNTs/CPA-3 composite aerogel-based strain sensor obtained by assembling the CPA-3 with carbon nanotubes (CTNs) possessed synergistically enhanced sensitivity, high selectivity and “multi-touch” stress detection, without deterioration even after 2000 cycles. Furthermore, the established mathematical model revealed the internal mechanism of the synergistic enhancement of sensing performance of sensor with strain-controllable permittivity. Thus, the fabricated CPAs might be an ideal substrate material for flexible electronic sensors in electronic power systems, and the mathematical model established could also provide a reliable reference for improving the sensitivity and detection limits of sensors.

Development and characteristics of multifunctional ultra-lightweight engineered cementitious composites incorporating cenospheres and PE fibre

Ultra-lightweight, high ductility, high strength, and multi-functionality are recent development trends in concrete. This study proposed a design concept of multifunctional ultra-lightweight engineered cementitious composites (ULW-ECCs) without functional fillers using fly ash cenosphere (FAC) and polyethylene (PE) fibre, which has heat insulation, self-sensing, and self-healing functions. The mechanical (tension, compression, flexure) and corresponding self-sensing properties under monotonic and cyclic loading, self-healing, thermal conductivity, and thermal effusivity properties were examined. The ULW-ECCs were developed based on the maximum packing density of the matrix, which showed high pseudo-strain-hardening indices and had an apparent density of 1055–1333 (Oven-dry density: 946–1261) kg/m3, compressive strength of 36–58 MPa, and a tensile strain capacity of 4%–8% under standard curing condition. With the use of FAC with a highly stiff shell, the ULW-ECCs show high strength and high thermal insulation properties. ULW-ECCs incorporating FAC show excellent self-sensing properties without any conductive fillers under compression, bending and tension. The electromechanical behaviour was consistent and repeatable during cyclic and monotonic loading processes, and a microstructure model was used to explain the self-sensing mechanism. The cement paste in the matrix can form a 3D-like honeycomb structure because a large number of FACs evenly divide the cement paste, which shows sensitive self-sensing ability. Additionally, the multiple micro-cracks of ULW-ECCs show excellent self-healing properties. Optical microscope and SEM analyses of ULW-ECC were used to explain the results. The developed multifunctional ULW-ECCs without functional fillers would be a promising material for sustainable development.

Thermodynamic properties of aluminum titanate‐mullite composite ceramics containing heat stabilizer

AbstractUsing Al2O3 and TiO2 as raw materials, adding MgO as heat stabilizer and mullite as enhancer, aluminum titanate‐mullite multiphase ceramics were successfully prepared by solid phase synthesis. The effects of MgO and mullite were systematically studied on the phase composition, microstructure, thermal stability, sintering properties, and mechanical properties of aluminum titanate ceramics. The results showed that the introduction of Mg2+ can partially replace Al3+ to form MgxAl2(1‐x)Ti(1+x)O5 solid solution, improved the thermal stability of aluminum titanate ceramics, and promoted the formation and growth of grains, which reduced the sintering temperature. The crack deflections caused by mullite particles improved the mechanical properties. The filling effect of mullite particles and the formation of silica in mullite raw materials were conducive to ceramic densification. The statistics of Mg4M10 sample were as follows: the porosity was only 2.9%, the flexural strength was as high as 64.15 MPa, and the thermal expansion coefficient was 1.35 × 10−6 K−1 (RT‐700°C), encouraging the application of ceramics with high thermal mechanical properties.

Paper-based building envelopes – Thermal and environmental properties of original envelope designs

Paper-based materials, due to their availability, environmental benefits and high thermal properties, have already been implemented in several building envelope designs. However, most of them either did not optimise the use of the material or did not provide sufficient thermal insulation for use in permanent buildings. The presented research analyses six original paper-based building envelope core proposals, suitable for use in permanent buildings in temperate climate of Europe, in terms of thermal and environmental efficiency. Proposals include cores with embedded paper tubes structural elements, timber-cardboard studs and sandwich designs. The heat transfer coefficient of the envelopes was obtained for repeatable modules via 2D computer simulations (ThermCAD software), and the environmental impact was assessed for a representative square metre of the envelope via LCA analysis, based in ecoinvent 3.8 database. All analysed designs showed high thermal insulation properties and met the requirements for Umax = 0.20 W/m2K, did not cause the risk of surface condensation, nor have excessive thermal bridges. The analysed building envelope designs based on embedded frame wall structure showed environmental superiority over conventional envelopes (timber frame and SIP panels). The research may serve as a proof of concept, for using paper-based building envelopes in sustainable architecture.

Microstructure and properties of graphene oxide reinforced copper-matrix composite foils fabricated by ultrasonic assisted electrodeposition

In this paper, graphene oxide (GO)/Cu composite (GO/Cu) foils with high thermal and mechanical properties were prepared by ultrasonic-assisted direct current electrodeposition. The effect of ultrasonic power and graphene concentration on the microstructure and properties of the composite foils was systematically investigated. It was found that the average grain size can be refined by both the addition of GO reinforcement and ultrasonic treatment. Under the optimized preparation condition with 120 W ultrasonic power and GO concentration of 0.8 g/L GO in plating solution, the average grain size was about 0.26 μm and illustrated strong crystallographic orientation of (220). In addition, the GO content in the composites was increased from 0.67 wt% without ultrasonic treatment to 1.72 wt%, and it was uniformly dispersed in the composite foil with ultrasonic effect. Compared with pure copper foil, the hardness value of the GO/Cu composite foil nearly doubled to 74.6 HV0.1, the average friction coefficient was decreased from 0.87 to 0.72 and the tensile strength of the composite foil was improved to 239 MPa with an elongation of 17%. Meanwhile, the thermal conductivity with optimized condition increased 39.8% to 556.57 W m−1 K−1. The improved mechanical and thermal properties of the GO/Cu composite foil were mainly ascribed to the grain refinement, change of preferred orientation and the presence of reduced GO reinforcement as a network in the composite foil.

Dopamine-Mediated Graphene Bridging Hexagonal Boron Nitride for Large-Scale Composite Films with Enhanced Thermal Conductivity and Electrical Insulation.

Heat accumulation generated from confined space poses a threat to the service reliability and lifetime of electronic devices. To quickly remove the excess heat from the hot spot, it is highly desirable to enhance the heat dissipation in a specific direction. Herein, we report a facile route to fabricate the large-scale composite film with enhanced thermal conductivity and electrical insulation. The well-stacked composite films were constructed by the assembly of polydopamine (PDA)-modified graphene nanosheets (GNSPDA) and hexagonal boron nitride (BNPDA), as well as bacterial cellulose (BC). The introduction of the PDA layer greatly improves the interface compatibility between hybrid fillers and BC matrix, and the presence of GNSPDA-bridging significantly increases the probability of effective contact with BNPDA fillers, which is beneficial to form a denser and complete "BN-GNS-BN" heat conduction pathway and tight filler-matrix network, as supported by the Foygel model fitting and numerical simulation. The resulting BC/BNPDA/GNSPDA film shows the thermal conductivity and tensile strength of 34.9 W·m-1·K-1 and 30.9 MPa, which separately increases to 161% and 155% relative to the BC/BNPDA film. It was found that the low electrically conductive and high thermal conductive properties can be well balanced by tuning the mass ratio of GNSPDA at 5 wt%, and the electrical conductivity caused by GNSPDA can be effectively blocked by the BNPDA filler network, giving the low electrical conductivity of 1.8 × 10-10 S·cm-1. Meanwhile, the BC/BNPDA/GNSPDA composite films effectively transfer the heat and diminish the hot-spot temperature in cooling LED chip module application. Thus, the present study may pave the way to promoting the industrialization of scalable thermal management devices.