Low Coefficient Of Thermal Expansion Research Articles

Properties of polyphenylene sulphide/glass fibre composites with negative thermal expansion ceramic fillers

The high coefficient of thermal expansion (CTE) of polymeric composites can cause large deformation under temperature changes, affecting coupling with devices made of other materials in radio frequency (RF) communication systems and limiting their application in RF systems. In order to obtain polyphenylene sulphide (PPS)-based composites with low CTE, a series of PPS-based composites containing different loadings of ceramic powders (including Zr2WP2O12, BN, AlN, Al2O3) were fabricated by melt extrusion method using PPS with 40 wt% glass fibre (GF) as matrix material. The experimental results showed that the PPS composites with Zr2WP2O12 (ZWP) as a filler had a lower CTE compared to the samples with other fillers at the same filler loading. The CTE of PPS/GF/ZWP steadily decreased with increasing ZWP addition. At 20 vol% ZWP loading, a 67% (about 18 ppm/°C) reduction of CTE compared to the PPS/GF was achieved. The addition of ZWP powder to PPS/GF also led to an improvement in the dielectric loss of the composite. When the ZWP content is 20 vol%, the dielectric loss of the composites is about 0.0035, which is 24.4% lower than PPS/GF. Hence, the PPS/GF/ZWP composites have great potential for applications in RF communication systems.

Preparation and characterization of low CTE thermoplastic copolyimide resins based on the structural design of block sequence

In order to solve the challenge of balancing the thermoplastic processing properties and thermal dimensional stability of polyimide (PI) resin, in this research, 3,3′,4,4′-biphenyl tetracarboxylic diandhydride (BPDA) and 2,2′-bis(trifluoromethyl)benzidine (TFMB) were used as rigid components, 4,4′-oxydiphthalic anhydride (ODPA) and 4,4′-diaminodiphenyl sulfone (DDS) as flexible components. A series of random copolyimide resins was prepared by adjusting the molar ratio of rigid and flexible monomers. Determining the molar ratio which could balance the thermoplastic processing properties and thermal dimensional stability, block copolyimide resins with different rigid and flexible block lengths were then prepared in this ratio. The research showed that the molar ratio of monomers and the sequence structure of molecular chains had a strong influence on the performance of PI resins. When the content or block length of rigid component increased, the coefficient of thermal expansion (CTE) decreased but the glass transition temperatures (Tg) and melt viscosity increased. The PI-B343 resin had a CTE value of 40.63 ppm/K and the lowest melt viscosity reached 675 Pa·s, achieved the simultaneous regulation of the thermoplastic processing properties and thermal dimensional stability for PI resin.

Exploring the effects of substrate and substrate temperature on the properties of radio frequency magnetron sputtered ZnO thin films

The physical and optical properties of zinc oxide thin films strongly depend on the film deposition techniques. In this work, RF magnetron sputtering was used to deposit ZnO thin films on various substrates (glass, quartz, ITO-coated glass, FTO-coated glass, Si(100), Si(100)/ SiO2) to study the role of substrate and substrate temperature on the morphological, structural and optical properties of the film grown. A detailed discussion on various aspects like surface morphology, strain, photoluminescence, bandgap, surface roughness, and material composition has been done. Compressive stress was present in the films created at room temperature and differed for various substrates based on the lattice mismatch. The nature and temperature of the substrate are found to affect the surface topography of films. Substrate and substrate temperature influenced the emission characteristics of ZnO thin films. In oxygen-rich substrates, defect emissions differed. We found that quartz is a better substrate to fabricate ZnO at room temperature and both Si and Si/SiO2 are preferable at high temperatures due to the lower lattice mismatch and thermal expansion coefficient. Comparing the electrical characteristics of ZnO thin films grown on glass and quartz substrates, ZnO on glass exhibited lower resistivity and higher carrier concentration. The Triboelectric nanogenerator (TENG) combining ZnO and PDMS, was developed to operate in vertical contact-separation mode. The obtained open circuit voltage was 30 V and 33 V for ZnO grown over ITO and FTO respectively, and the slight increase is due to the rougher film's surface on FTO than ITO. The selection of substrate is crucial in many applications and our findings provide an overview of the suitability of substrate and substrate temperature for the fabrication of ZnO thin film-based optoelectronic devices.

Construction of novel Cu-α-diimide interactions for enhancing thermal resistance and dimensional stability of polyimide films

The new-generation polyimide films with simultaneously outstanding thermal stability and low coefficient of linear thermal expansion (CTE) are urgently needed. Herein, coordination bonds were employed to improve polyimide films' heat resistance and dimensional stability. Polyimide-Cu complex films were fabricated by incorporating α-diimide units (bidentate ligands) into the BPDA-ODA (the structure of commercially available Upilex-R® polyimide films) backbones. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Energy dispersive X-ray mapping results showed that the coordination interactions occur between α-diimide and copper ions. Wide-angle X-ray diffraction (WAXD) and two-dimensional small-angle X-ray scattering (SAXS) spectra demonstrated that Cu-α-diimide coordination structures introduced in intermolecular chains leading polyimide films transformed from a semi-crystalline state to amorphous state, and inhibited the long-period formation structures. The plateau modulus and longer characteristic relaxation time (τ∗ = 1996.5 s) revealed by dynamic thermomechanical analysis indicated that crosslink networks were successfully formed by constructing coordination bonds. As a result, polyimide films' thermal resistance and dimensional stability were simultaneously enhanced. The typical PI-Cu50 films exhibited elevated glass transition temperatures of 353 °C (pristine PI-Cu0 ∼ 302 °C) and a lower CTE of 47.4 ppm/K (pristine PI-Cu0 films ∼ 64.4 ppm/K) in ranges of 300–400 °C, showing a promising application in the field of high-temperature environments.

A novel stress-relaxing approach based on forming Fe–Ni invar effect interlayer for joining C/C composites

Taking advantage of the invar effect of Fe–Ni alloy at low temperatures, a novel stress-relaxing approach based on forming Fe–Ni invar interlayer was proposed for joining carbon fiber reinforced carbon (C/C) composites in this paper. Mixed Fe + Ni62Ti38 (at %) powders were used as the filler materials. Microstructure, mechanical property, and formation mechanism of the bonded joints were investigated. The results indicate that, based on the eutectic reaction of (Fe,Ni)–C at the C/C/interlayer interface and the in-situ reaction of Ti–C in the interlayer, a (Fe,Ni)–C eutectic reaction layer was formed at the C/C side interface and the Fe–Ni invar effect interlayer reinforced by TiC particles was obtained. Owing to the low thermal expansion coefficient and good plasticity of the Fe–Ni alloy matrix at low temperatures, the high residual thermal stress of the joint was effectively reduced and the shear strength of the joint was improved. With the increase of Ni content in the Fe–Ni alloy matrix of the interlayer, the shear strength of the joint decreases gradually. When the composition of the Fe–Ni matrix was designed to be Fe–36Ni, i.e., the invar alloy with the lowest thermal expansion coefficient at 100 °C, the average shear strength of the bonded joint reached the highest value of 36 MPa. The fracture of the joint occurred in the (Fe,Ni)–C eutectic reaction layer close to the C/C composite.

Microstructures and mechanical properties of reactively sintered CaAl12O19/CaAl4O7 porous composites

Porous CaAl12O19 ceramics attract much attention as a light-weight structural material. In this study, CaAl12O19/CaAl4O7 porous ceramic composites have been prepared by the reactive sintering, and their thermo-mechanical properties were evaluated by the three-point bending test, micro-Vickers hardness test to investigate the effect of the presence of CaAl4O7 second phase. The rod-shaped samples with 4 different compositions were heated at 5 °C/min and sintered at 1600 °C for 3 h to obtain sintered bodies. Microstructural observation confirmed that the composite materials with CaAl4O7 had larger particles than the CaAl12O19 single phase. Compositing with CaAl4O7, which has a low coefficient of thermal expansion, made it possible to reduce the coefficient of thermal expansion. The sample with a CaAl12O19/CaAl4O7 volume fraction of 65.2/34.8 exhibited the highest micro-Vickers hardness.

Thermo-mechanical vibration and buckling analysis of porous FG sandwich plates with geometric discontinuity based on physical neutral surface

The effect of thermo-mechanical load coupling and porosity distributions on vibration and buckling characteristics of Functionally Graded Sandwich Plates (FGSPs) with cutouts is investigated by Finite Element (FE) formulation. Two sandwich configurations are considered and physical neutral surface is incorporated due to material asymmetry. Novel dynamic approach is proposed to evaluate buckling loads. Results obtained are compared with experimental, numerical solutions in literature and revealed that the FGSP buckling capacity under thermomechanical loads improves on using ceramic with lower thermal expansion coefficient. Also, at higher temperature rises, buckling capacity increases due to increasing porosity content, whereas capacity reduces at lower temperature rises.

Experimental study on pre-hydrogenation of catalytic slurry oil and co-carbonization of middle distillate and high boiling point distillate

A catalytic slurry oil (SO) was treated by moderate pre-hydrotreating, and the structural compositions, the thermal stability, the distillate oil yield, and the coking behavior of SO before and after hydrotreating were analyzed. The carbonization performance as well as the co-carbonization performance of the middle distillate (350–500 °C) and the high boiling point distillate (500–550 °C) derived from the hydrogenated SO (HSO) were investigated. The results show that the content of naphthenes and hydrogenated aromatics of HSO increases, while the olefin content decreases, and the olefinic hydrogen content of HSO decreases from 2.71% to 0.97%. Thus, the thermal stability of HSO is fundamentally improved. Additionally, compared with SO, the yields of the middle distillate and the high boiling point distillate of HSO increased by 25.8% and 23.1%, respectively. More importantly, there is no significant coke formation during distillation of HSO. The carbonization experimental results show that the anisotropic textural structure of the coke obtained from the middle distillate derived from HSO is the large flow domain structure, and the coke has the lowest coefficient of thermal expansion (CTE) value of 2.25×10−6 °C−1. The carbonization performance of the high boiling point distillate derived from HSO is poor, while the co-carbonization with the middle distillate significantly improves the carbonization performance of the high boiling point distillate. The anisotropic textural structure of the coke derived from carbonization of combined fraction is the large flow domain structure and the CTE value is less than 2.30×10−6 °C−1, when the mass ratio of aromatic fraction to middle fraction is not higher than 2:1.

Mechanical behavior and slag corrosion resistance of ZrSiO4/SiC reinforced MgO-C refractories

This investigation proposes a novel solution to enhance the thermal shock and slag corrosion resistance of low-carbon MgO-C refractories by integrating yttria-stabilized zirconium silicate (YSZS) and silicon carbide (SiC) powders in them. The results of this study revealed that incorporating YSZS and SiC particles in low-carbon MgO-C refractories improved the overall qualities of the refractories synergistically and increased the thermal shock resistance (TSR) from 11 cycles (for MgO) to 18 and 15 cycles, respectively, owing to their lower coefficients of thermal expansion (CTE) compared to magnesite. The addition of YSZS caused the cold compressive strength (CCR) of the MgO-C refractories to increase from 450 to 480 kg/cm2. The mechanical properties of the refractories were elevated as a result of fracture toughness enhancement and crack propagation within and between grains on the fracture surface. CaZrO3, Mg2SiO4, and MgSiO3 phases developed in the grain boundaries and served as corrosion-resistant materials, thereby resulting in reduced porosity and pore closure. Additionally, the TSR of the reinforced bricks was significantly improved due to their low CTE as compared to MgO, while slag resistance enhancement was caused by the formation of the CaZrO3, Mg2SiO4, and MgSiO3 phases.

Microwave dielectric characterization and thermal analysis of B2O3-La2O3-ZnO glass-ceramic/Al2O3 composites for LTCC applications

High frequency performance and the content of glass are the direct factors affecting the performance of LTCC. In order to reduce the content of glass and improve the performance, we conducted a systematic study on the composition regulation of B2O3-La2O3-ZnO (BLZ) glass. Glass with low softening point is helpful for LTCC to achieve compact structure. DSC shows that the softening point of BLZ glass can be reduced from 580 ℃ to 537 ℃ by adjusting the composition. XRD analysis indicate that the glass and Al2O3 formed ZnAl2O4 interfacial phases. Combined with the thermal shrinkage curve, it can be proved that the softening of glass and the formation of interfacial phases are the reasons for the shrinkage and densification of LTCC. The lowest coefficient of thermal expansion of 2.878 ppm/℃ was obtained, and the minimum loss of LTCC is 0.00277 at 15 Ghz. These properties are making LTCC more suitable for high-frequency applications.

Investigations on Phthalonitrile – Cyanate ester blends and their light weight composites; Synthesis, thermal, mechanical and ablative characteristics

Newer high performing polymer matrix resins are highly demanded given the rapid development trend in aero-space exploration sector. The present work focuses on synthesis and performance evaluation of Phthalonitrile- Cyanate ester blend as matrix resin for ablative composite applications. Incorporation of Cyanate ester facilitated early cure initiation (by about 35 °C) of Phthalonitriles without comprising thermal stability, a novel strategy that improves the sluggish cure profile of phthalonitriles. Low density (0.5g/cc) syntactic foam composites prepared from the blend exhibited low Coefficient of Thermal Expansion (CTE) (1.3 × 10−5 – 1.7 × 10−5/°C), high specific heat (0.32–0.38 J/g/°C at 80 °C) and low thermal conductivity (0.11–0.13 W/mK at 80 °C). Exposure of the composites to moderate re-entry heat flux conditions using radiant heating facility (∼55W/cm2, 1200s) and Plasma Arc jet (70&125 W/cm2, 50s) resulted in excellent surface uniformity with minimal of mass loss (4.77–5.77%) and excellent heat of ablation (8000–12000 cal/g) with reduced back-wall temperature (230–260 °C). The composites possessed very good mechanical properties such as Flexural strength of 5–6.5 MPa and compressive strength of 5–9 MPa. 1:1 combination of pyrolyzed system possessed high degree of graphitization. The promising results confirm that the new matrix blend can be a potential replacement for conventionally used phenolics as ablative Thermal Protection System (TPS) matrix.

Structure and microwave dielectric properties of novel walstromite-type MCa2Si3O9 (M = Ba, Sr) ceramics

Novel walstromite-type MCa2Si3O9 (M = Ba, Sr) ceramics, with triclinic space group P-1, were prepared through a solid-state reaction method. The P–V-L theory proves that the lattice energy and bond energy of the Si–O bond play a leading role in the quality factor and the dielectric constant is mainly determined by the ionic polarization. Excellent microwave dielectric properties of BaCa2Si3O9 and SrCa2Si3O9 ceramics could be obtained: εr = 8.99 ± 0.23, Q × f = 44,542 ± 500 GHz, and τf = −25.9 ± 3.0 ppm/°C and εr = 7.39 ± 0.23, Q × f = 48,772 ± 500 GHz, and τf = −27.5 ± 3.0 ppm/°C, when sintered at 1240/1280 °C for 4 h. Then SrCa2Si3O9 ceramic is applied to a new microstrip bandpass filter, because of its high microwave dielectric properties and low thermal expansion coefficient. With reduced dimension, the filtering performance of the circuit is also highly improved, including reduced capacitor parasitic effect and the optimized stopband insertion loss. Accordingly, the SrCa2Si3O9 ceramic is a promising candidate for sub-6 GHz a filter of microstrip bandpass applications.

Study of temperature and frequency dependences of quartz glass in the microwave range

The use of glass in microwave devices requires study of the dielectric properties of the material. We present the results of studying temperature and frequency dependences of the dielectric properties of quartz glass in the microwave region. The frequency dependence of the dielectric permittivity and dielectric loss tangent were determined using high-precision devices based on resonant cavity at a fixed frequency within a range of 8 – 26 GHz under a normal temperature. The temperature dependence was obtained using resonant cavity made of platinum coated quartz glass with a low thermal-expansion coefficient and insignificant change of intrinsic parameters under heating up to 1200°C. Experimental temperature and frequency dependences of the dielectric permittivity and dielectric loss tangent were obtained using classical conduction mechanisms taking into account the structural peculiarities of quartz glass. The effect of ionic conductivity was also evaluated in quartz glass in the microwave region. The revealed changes in the temperature dependence of the permittivity do not exceed the measurement error. The results obtained can be used for practical application of quartz glass in radio-engineering devices.

Synergistic Improvement of Flame Retardancy and Mechanical Properties of Epoxy/Benzoxazine/Aluminum Trihydrate Adhesive Composites.

Epoxy resin was mixed with benzoxazine resin and an aluminum trihydrate (ATH) additive to provide flame retardancy and good mechanical properties. The ATH was modified using three different silane coupling agents and then incorporated into a 60/40 epoxy/benzoxazine mixture. The effect of blending compositions and surface modification on the flame-retardant and mechanical properties of the composites was investigated by performing UL94, tensile, and single-lap shear tests. Additional measurements were conducted including thermal stability, storage modulus, and coefficient of thermal expansion (CTE) assessments. The mixtures containing more than 40 wt% benzoxazine revealed a UL94 V-1 rating with high thermal stability and low CTE. Mechanical properties including storage modulus, and tensile and shear strength, also increased in proportion to the benzoxazine content. Upon the addition of ATH to the 60/40 epoxy/benzoxazine mixture, a V-0 rating was achieved at 20 wt% ATH. The pure epoxy passed a V-0 rating by the addition of 50 wt% ATH. The lower mechanical properties at high ATH loading could have been improved by introducing a silane coupling agent to the ATH surface. The composites containing surface-modified ATH with epoxy silane revealed about three times higher tensile strength and one and a half times higher shear strength compared to the untreated ATH. The enhanced compatibility between the surface-modified ATH and the resin was confirmed by observing the fracture surface of the composites.

A binder-free ice template method for vertically aligned 3D boron nitride polymer composites towards thermal management

Hexagonal boron nitride (BN) is an attractive filler candidate for thermal interface materials, but the thermal conductivity enhancement is limited by the anisotropic thermal conductivity of BN and disordered thermal pathways in the polymer matrix. Herein, a facile and economic ice template method is proposed, wherein BN modified by tannic acid (BN-TA) directly self-assemble to form vertically aligned nacre-mimetic scaffold without additional binders and post-treatment. The effects of the BN slurry concentration and the ratio of BN/TA on three-dimensional (3D) skeleton morphology are fully investigated. The corresponding polydimethylsiloxane (PDMS) composite via vacuum-impregnation achieves a high through-plane thermal conductivity of 3.8 W/mK at a low filler loading of 18.7 vol%, which is 2433% and 100% higher than that of pristine PDMS and the PDMS composite with randomly distributed BN-TA, respectively. The finite element analysis results theoretically demonstrate the superiority of the highly longitudinally ordered 3D BN-TA skeleton in axial heat transfer. Additionally, 3D BN-TA/PDMS exhibits excellent practical heat dissipation capability, lower thermal expansion coefficient, and enhanced mechanical properties. This strategy offers an anticipated perspective for developing high-performance thermal interface materials to address the thermal challenges of modern electronics.

Experimental and Investigation of Heat Transfer for Radiator by Changing Composite (Bronze And Copper Oxide) Using Pin-Fin Apparatus

This paper discussed composite of bronze, copper oxide alloy and beryllium material and to evaluate the heat transfer properties through PIN FIN apparatus. Within the last few years there has been a rapid increase in the utilisation of Composite, particularly in the automobile industries, due to their high strength to weight ratio, high wear resistance, low density and low coefficient of thermal expansion. The advancements in the field of application make the study of their mechanical behaviour of utmost importance. In this present investigation, bronze and copper, beryllium composite were using Stir casting method. Finally investigate of bronze and copper, beryllium material and to evaluate the Mechanical properties of the model composite plate. Key Word: Copper; Radiator; Heat Transfer; Convection; Composition.

Fabrication of low defect multi-layer graphene using electrochemical intercalation of graphite electrode and its application for graphene/Al nanocomposites

Low defect multi-layer graphene has been synthesized by electrochemical intercalation of graphite electrode in ammonium sulfate aqueous solution, followed by microwave heating and subsequent ultrasonication. Combination of addition of ethanol as antifoaming agent, alternating current and end-face electrolysis was very effective for high yield production (>75%) of low defect graphene. We applied as-synthesized graphene for graphene/Al composites using stir casting method. Graphene/Al composites with a graphene loading of 0.3% have approximately 40% higher tensile strength (142.2 MPa) and much lower coefficient of thermal expansion (19.8 × 10-6/K) as compared with pure Al (104.0 MPa, 22.7 × 10-6/K).

Lightweight diamond/Cu interface tuning for outstanding heat conduction

AbstractWith rapid developments in the field of very large‐scale integrated circuits, heat dissipation has emerged as a significant factor that restricts the high‐density integration of chips. Due to their high thermal conductivity and low thermal expansion coefficient, diamond/Cu composites have attracted considerable attention as a promising thermal management material. In this study, a surface tungsten carbide gradient layer coating of diamond particles has been realized using comprehensive magnetron sputtering technology and a heat treatment process. Diamond/Cu composites were prepared using high‐temperature and high‐pressure technology. The results show that, by adjusting the heat treatment process, tungsten carbide and di‐tungsten carbide are generated by an in situ reaction at the tungsten–diamond interface, and W–WC–W2C gradient layer‐coated diamond particles were obtained. The diamond/Cu composites were sintered by high‐temperature and high‐pressure technology, and the density of surface‐modified diamond/Cu composites was less than 4 g cm−3. The W–WC–W2C@diamond/Cu composites have a thermal diffusivity as high as 331 mm2 s−1, and their thermal expansion coefficient is as low as 1.76 × 10−6 K−1. The interface coherent structure of the gradient layer‐coated diamond/copper composite can effectively improve the interface heat transport efficiency.

Low-dielectric polyimide constructed by integrated strategy containing main-chain and crosslinking network engineering

Polyimide (PI) is widely used as a mainstream antenna material for fourth-generation communication technology (4G) due to its excellent dielectric properties and mechanical properties. However, the relatively high dielectric constant and dielectric loss make traditional polyimide unable to meet the requirement of the fifth-generation communication technology. The molecular engineering strategy is an effective method to improve the dielectric properties and control the comprehensive performance of the polyimide. In this work, an m-phenylenediamine containing tetrafluorostyrol pendant group [(4-(2,3,5,6-tetrafluoro-4-vinylphenoxy) benzene-1,3-diamine (TFVPDM)] has been designed. On the one hand, the rigid m-phenylene and biphenyl structure in TFVPDM is beneficial for balancing the solubility and thermal properties of the TFVPDM-based polyimides. On the other hand, the tetrafluorostyrol pendant group can provide cross-linkable sites and help construct the hydrophobic network in the TFVPDM-based cross-linked fluorinated polyimides (CL-FPIs: CL-FPI-10; CL-FPI-20; CL-FPI-30), which can improve their dielectric properties and water resistance. The CL-FPIs films were obtained through polymerization of TFVPDM, 2,2′-bis(trifluoromethyl) benzidine (TFDB), and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), and subsequent cross-linking reaction. Among CL-FPIs, the CL-FPI-30 shows the best comprehensive performance including low dielectric constant (2.29 at room temperature and 2.03 at 200 °C), low dielectric loss (0.0051 at 1 MHz), high glass transition temperature (Tg) (346.9 °C), low coefficient of thermal expansion (CTE) (44.1 ppm °C−1), low water absorption (0.128%) and good stability of dielectric constant in a humid environment.

MXenes (Ti3C2Tx) incorporated polyimide nanohybrid composite films

In this study, polyimide (PI)/MXene hybrid composite films as electromagnetic interference (EMI) shielding materials were fabricated using MXene (Ti3C2Tx) as a filler. The PI/MXene nanohybrid composite films were fabricated by casting an aqueous solution containing water-soluble poly (amic acid) ammonium salt (PAS) and MXene colloid, followed by thermal imidization. PI/MXene hybrid composite films with different contents (1.36 wt. % ∼ 20 wt. %) were prepared. The PI/MXene hybrid composite films showed high EMI shielding effectiveness up to 159 dB/mm as well as low moisture contents, controlled dielectric constants, improved thermal stability, and low coefficients of thermal expansion.