Near-zero Coefficient Of Thermal Expansion Research Articles

High-Energy Laser Protection Performance of Fibrous Felt-Reinforced Aerogels with Hierarchical Porous Architectures.

Continuous-wave lasers can cause irreversible damage to structured materials in a very short time. Modern high-energy laser protection materials are mainly constructed from ceramic, polymer, and metal constitutions. However, these materials are protected by sacrificing their structural integrity under the irradiation of high-energy lasers. In this contribution, we reported multilayer fibrous felt-reinforced aerogels that can sustain the continuous irradiation of a laser at a power density of 120 MW·m-2 without structural damage. It is found that the exceptional high-energy laser protection performance and the comparable mechanical properties of aerogel nanocomposites are attributed to the unique characteristics of hierarchical porous architectures. In comparison with various preparation methods and other aerogel materials, multilayer fibrous felt-reinforced aerogels exhibit the best performance in high-energy laser protection, arising from the gradual interception and the Raman-Rayleigh scattering cycles of a high-energy laser in the porous aerogels. Furthermore, a near-zero thermal expansion coefficient and extremely low thermal conductivity at high temperature allow the lightweight felt-reinforced aerogels to be applied in extreme conditions. The felt-reinforced aerogels reported herein offer an attractive material that can withstand complex thermomechanical stress and retain excellent insulation properties at extremely high temperature.

Fluorine atom substituted aromatic polyimides: Unlocking extraordinary dielectric performance and comprehensive advantages

Low-dielectric polymers face prominent development challenges at high frequency. Particularly, the relationship between the high-frequency dielectric loss and polymer structures remains not clear enough. Besides, the strategies for achieving low dielectric loss usually have to scarify other important materials properties, e.g., heat resistance or dimensional stability. Herein, fluorine-containing aromatic polyimides were systematically investigated. Among them, simple fluorine atom (-F) substituted polyimides exhibit remarkable low dielectric loss at high frequency (10 GHz) as well as comprehensive advantages, including near-zero thermal expansion coefficient, extremely high thermal decomposition stability, high optical transmittance and excellent mechanical properties. The fundamental mechanisms of low dielectric loss are fully discussed. Benefiting from the unique electric effect and compact size of -F group, -F substituted polyimides display low dipolar density and strongly restricted dipolar motion, contributing to a reduced permanent dipolar polarization loss. Moreover, the concept of induced dipolar polarization was introduced to illustrate the nontrivial impact of F-substituted effect on conjugated electron cloud polarization loss in aromatic polymer system. This work not only provides valuable insights for understanding the mechanism of dielectric loss at high frequency for aromatic polymers, but also opens up broader application possibilities of polyimides in microelectronic and wireless communications industries.

Near-Zero Thermal Expansion and High Heat-Resistance Polyimide Films Based on a Symmetric and Rigid Pyrazine Structure

Regarding the applications of polyimide (PI) films in emerging flexible devices and precision apparatus, their low coefficient of thermal expansion (CTE), especially near-zero expansion, is an urgent requirement for weakening the internal stress between the organic/inorganic layers. Other properties of PI films including the high heat-resistance and superior toughness are also demanded in actual scenarios. Herein, a set of PI films was developed by copolymerization of 2,5-bis(4-aminophenyl)pyrazine (PRZ) into a pyromellitic dianhydride (PMDA)/4,4′-oxydianiline (ODA) system. The monocrystal analysis of the PRZ monomer reveals its rigid, symmetric, and nearly coplanar steric structure. Thanks to the synergy and balance of flexible ODA and rigid PRZ units in PI chains, the near-zero expansion, high heat-resistance, and optimal mechanical properties of the PI films are simultaneously achieved. Particularly, the PI film with ODA/PRZ = 4.5/5.5 presents a near-zero CTE of −0.41 ppm/K, high glass transition temperature (Tg) of around 417 °C, superior fracture strength of 191 MPa, and initial modulus of 3.83 GPa. Interestingly, via adjusting the ODA/PRZ ratios, the precise control of CTE values can be realized, enabling the thermal expansion matching of PI films on broad types of device substrates, e.g., Cu (15–17 ppm/K) and Si (3–5 ppm/K).

Hypocrystalline ceramic aerogels for thermal insulation at extreme conditions

Thermal insulation under extreme conditions requires materials that can withstand complex thermomechanical stress and retain excellent thermal insulation properties at temperatures exceeding 1,000 degrees Celsius1–3. Ceramic aerogels are attractive thermal insulating materials; however, at very high temperatures, they often show considerably increased thermal conductivity and limited thermomechanical stability that can lead to catastrophic failure4–6. Here we report a multiscale design of hypocrystalline zircon nanofibrous aerogels with a zig-zag architecture that leads to exceptional thermomechanical stability and ultralow thermal conductivity at high temperatures. The aerogels show a near-zero Poisson’s ratio (3.3 × 10−4) and a near-zero thermal expansion coefficient (1.2 × 10−7 per degree Celsius), which ensures excellent structural flexibility and thermomechanical properties. They show high thermal stability with ultralow strength degradation (less than 1 per cent) after sharp thermal shocks, and a high working temperature (up to 1,300 degrees Celsius). By deliberately entrapping residue carbon species in the constituent hypocrystalline zircon fibres, we substantially reduce the thermal radiation heat transfer and achieve one of the lowest high-temperature thermal conductivities among ceramic aerogels so far—104 milliwatts per metre per kelvin at 1,000 degrees Celsius. The combined thermomechanical and thermal insulating properties offer an attractive material system for robust thermal insulation under extreme conditions.

Quasi-isotropic fiber metal laminate with high specific modulus and near-zero coefficient of thermal expansion

On the basis of lamination theory, a quasi-isotropic fiber metal laminate (FML) with a near-zero coefficient of thermal expansion (CTE) and high specific modulus was designed, using pitch-based carbon fiber reinforced plastic (CFRP) prepreg and stainless steel (SST). The SST to CFRP thickness ratio was determined so that the laminates had an exact-zero CTE at room temperature (25 °C). The CTE of a fabricated FML was accurately measured using embedded fiber Bragg grating (FBG) sensors, to verify that the CTE had a near-zero value around room temperature. The temperature dependence of the FML CTE from 20 to 120 °C was investigated via finite element analysis (FEA) taking the temperature-dependent material properties into account. It was demonstrated from the experiment and FEA that the present FML had a near-zero CTE around room temperature (20–45 °C) and a higher Young's modulus and specific modulus compared with other relevant materials.

Study of Microwave Heating Effect in the Behaviour of Graphene as Second Phase in Ceramic Composites.

The choice of the right material is essential in microwave processing. The carbon materials are good microwave absorbers, which allows them to be transformed by microwave heating into new carbon materials with adapted properties, capable of heating other materials indirectly. In this paper, the microwave heating of graphene as reinforcement of the lithium aluminosilicate (LAS) ceramics has been explored. LAS ceramics have a near-zero coefficient of thermal expansion and exhibit an effective and efficient heating by microwave. Nevertheless, we have found that the graphene did not show any significant response to the microwave radiation and, hence, the interaction as mechanical reinforcement with the LAS material is harmful. The possible benefits of graphene materials to microwave technology are widely known; however, the mechanism involved in the interaction of microwave radiation with ceramic-graphene composites with high dielectric loss factors has not been addressed earlier.

Dimensionally and environmentally ultra-stable polymer composites reinforced with carbon fibres.

The quest to develop materials that enable the manufacture of dimensionally ultra-stable structures for critical-dimension components in spacecraft has led to much research over many decades and the evolution of carbon fibre reinforced polymer materials. This has resulted in structural designs that feature a near-zero coefficient of thermal expansion. However, the dimensional instabilities that result from moisture ingression and release remain the fundamental vulnerability of the matrix, which restricts many applications. Here, we address this challenge by developing a space-qualifiable physical surface barrier that blends within the mechanical properties of the composite, thus becoming part of the composite itself. The resulting enhanced composite features mechanical integrity and a strength that is superior to the underlying composite, while remaining impervious to moisture and outgassing. We demonstrate production capability for a model-sized component for the Sentinel-5 mission and demonstrate such capability for future European Space Agency (ESA) and National Aeronautics and Space Administration (NASA) programmes such as Copernicus Extension, Earth Explorer and Science Cosmic Visions.

Thermal deformation isolation for satellite platforms via flexible connections

Thermal deformation is a serious issue for many space structures when travelling around Earth. This paper presents a method to achieve extremely low thermal deformation in satellite platforms with prototype applications. In addition to using the traditional nearzero coefficient of thermal expansion (CTE) material, the platform succeeded in comparison to the traditional energy-consuming methods mainly due to the unique isolation of the residual thermal expansion by flexible connections. First, the design of the composite with near-zero CTE is briefly introduced and used to develop the precision satellite platform. Next, the isolation mechanism to minimize the thermal deformation is presented. Then, the deformation isolation is detailed through the “flexible connecting” method. The effectiveness of this method is demonstrated by finite element (FE) analyses and further verified with a prototype. The experimental results from the prototype recorded a 90% reduction in comparison to the traditional platforms in the wrapping deformation of the payload panel, which was measured by projection moire methods. The thermal wrapping deformation decreased from 1.013 mm using the rigid connection to 0.104 mm using the flexible connection. This result proves that the proposed method is effective for a high-precision satellite structure and has considerable potential in engineering applications.

Trapping of Micro Particles in Nanoplasmonic Optical Lattice.

The plasmonic optical tweezer has been developed to overcome the diffraction limits of the conventional far field optical tweezer. Plasmonic optical lattice consists of an array of nanostructures, which exhibit a variety of trapping and transport behaviors. We report the experimental procedures to trap micro-particles in a simple square nanoplasmonic optical lattice. We also describe the optical setup and the nanofabrication of a nanoplasmonic array. The optical potential is created by illuminating an array of gold nanodiscs with a Gaussian beam of 980 nm wavelength, and exciting plasmon resonance. The motion of particles is monitored by fluorescence imaging. A scheme to suppress photothermal convection is also described to increase usable optical power for optimal trapping. Suppression of convection is achieved by cooling the sample to a low temperature, and utilizing the near-zero thermal expansion coefficient of a water medium. Both single particle transport and multiple particle trapping are reported here.

Trapping of Micro Particles in Nanoplasmonic Optical Lattice

The plasmonic optical tweezer has been developed to overcome the diffraction limits of the conventional far field optical tweezer. Plasmonic optical lattice consists of an array of nanostructures, which exhibit a variety of trapping and transport behaviors. We report the experimental procedures to trap micro-particles in a simple square nanoplasmonic optical lattice. We also describe the optical setup and the nanofabrication of a nanoplasmonic array. The optical potential is created by illuminating an array of gold nanodiscs with a Gaussian beam of 980 nm wavelength, and exciting plasmon resonance. The motion of particles is monitored by fluorescence imaging. A scheme to suppress photothermal convection is also described to increase usable optical power for optimal trapping. Suppression of convection is achieved by cooling the sample to a low temperature, and utilizing the near-zero thermal expansion coefficient of a water medium. Both single particle transport and multiple particle trapping are reported here.

Effects of doping Fe cations on crystal structure and thermal expansion property of Yb2Mo3O12

Crystal structures and thermal expansion properties of Yb2−xFexMo3O12 (x=0.0, 0.6, 1.0, 1.1, 1.4) solid solutions have been studied by X-ray powder diffraction (XRPD) at different temperatures. Rietveld analysis of the XRPD data shows that Yb2−xFexMo3O12 solid solutions adopt orthorhombic structure and have variable thermal expansion coefficients controlled by the ratio of Yb3+ to Fe3+. Yb2Mo3O12 shows anisotropic negative thermal expansion property, induced by the reductions in average Yb–O–Mo angle and average apparent Mo2–O bond length with increasing temperatures. As more Yb3+ substituted by Fe3+, the linear thermal expansion coefficients of Yb2−xFexMo3O12 increase from negative to positive. A near-zero thermal expansion coefficient of 0.55×10−6K−1 for Yb0.6Fe1.4Mo3O12 is observed in the temperature range of 573–873K

Design and application of composite platform with extreme low thermal deformation for satellite

Thermal dimensional stability is an important issue for many space structures. An extremely low thermal deformation composite platform is designed with the prototype application in the satellite payload-mounting platform. The platform was achieved through using composite material to provide near-zero coefficient of thermal expansion (CTE) and isolating the residual thermal expansion by flexible structure connection to obtain the entire stability rather than the traditional thermal control technology, which is energy-consuming. Firstly, the design of systematical scheme with near-zero CTE is investigated, by which the extremely low CTE components of satellite structure were developed. Then, a flexible connecting method is proposed to further minimize the thermally induced deformation through “deformation isolation”. The effectiveness of this method is demonstrated by finite element analyses and further verified by physical Composite Fiber Reinforced Plastics (CFRP) prototype. The experiment results of the prototype recorded a 90% reduction measured by theodolites and projection moiré methods. The thermally induced pointing accuracy is dramatically decreased from 72.6″ down to 3.6″ in the flexible connection compared with the rigid connection, while the panel wrapping displacement reduced from 1.013mm to 0.104mm. The result proves that this method is effective to the thermal deformation isolation so that it has an extraordinary potential to engineering practical application.

Effect of sintering technology in β-eucryptite ceramics: Influence on fatigue life and effect of microcracks

β-eucryptite ceramics with low negative or near-zero coefficient of thermal expansion (CTE) with excellent mechanical properties, such as Young's modulus ≥100GPa, have attracted attention for many important industrial applications. The extremely anisotropic thermal expansion behavior of this material leads to thermal residual stresses, and causes spontaneous microcracking. These microcracks cause large negative CTE with mechanical weaknesses. The appearance of microcracks is due to different factors. The most important are prolonged sintering time and heating source used.The present work shows experimentally the evolution of grain microcracks and residual stresses of the sintered β-eucryptite material going through many thermal fatigue cycles (∼3600). The effect of stresses applied on β-eucryptite crystals due to the thermal cycling could be considered for explaining the small change observed of β-eucryptite to β-spodumene phase, which is higher in the samples obtained by microwave sintering. Therefore, the study of residual stresses has suggested that the heating source employed, such as conventional or microwave, has a great influence on thermal fatigue life and the final mechanical and thermal properties. The microwave heating has a significant impact on β-eucryptite materials lifetime.

A Study on Accelerated Thermal Aging of High Modulus Carbon/Epoxy Composite Material

Composite materials have been used increasingly for various space applications due to the favorable characteristic of high modulus to density ratio and potential for near-zero coefficient of thermal expansion. In composite system, depending on the orientation of fibers, strength and stiffness can be changed so that the optimum structure can be accomplished. This is because the coefficient of thermal expansion (CTE) of carbon fibers is negative. For spacecraft and orbiting space structure, which are thermally cycled by moving through the earth' shadow for at least 5 years, it is necessary to investigate the change of properties of the material over time. In this study, thermal aging of epoxy matrix/high modulus carbon fiber composite materials are accelerated to predict the long term creep property. Specimens are tested at various temperatures of 100~140�� with dynamic mechanical analysis to obtain creep compliances that are functions of time and temperature. Using Time Temperature Superposition method, creep compliance curves at each temperature are shifted to the reference temperature by shift factor and a master curve is generated at the reference temperature. This information is useful to predict the long term thermal aging of high modulus composite material for spacecraft application.

Tuning the monoclinic-to-orthorhombic phase transition temperature of Fe2Mo3O12by substitutional co-incorporation of Zr4+and Mg2+

Abstract

A near zero coefficient of thermal expansion ceramic: Tantalum oxyfluoride

Cubic tantalum oxyfluoride (TaO2F) powders were synthesized and consolidated by hot pressing. The effects of sodium fluoride (NaF) and lithium fluoride (LiF) sintering aids on the densification and microstructure of TaO2F were investigated. Hot pressing conditions employed in this study appeared to change the stoichiometry of TaO2F, and most likely created an oxygen deficient TaO2−δF. It was shown that TaO2F decomposes in air at temperatures ≥500°C but that the kinetics of its decomposition is very slow up to 750–800°C. Hot-pressed TaO2F had a near-zero coefficient of thermal expansion over 25–600°C that did not change after exposure to air for extended periods of time (24h) at 600°C. TaO2F has no inherent absorption bands in the mid-infrared (mid-IR) region up to about 5μm suggesting that polycrystalline TaO2F ceramic can be IR transparent provided that it can be densified without altering its chemistry.

ZrW 2O 8-containing composites with near-zero coefficient of thermal expansion fabricated by various methods: Comparison and optimization

Various fabrication methods for producing ZrW 2O 8-containing composites were developed and evaluated. By adjusting the ratio among the components, those composites attained nearly zero thermal expansion. The resulting samples were measured for the coefficient of thermal expansion (CTE) and Young’s modulus using a Thermomechanical Analyzer (TMA). The microstructure, final density, mechanical strength, and ability to maintain their shape in the sintering process were investigated and compared among the sintered samples fabricated by various methods. One of the fabrication methods, the in-situ reaction of ZrO 2, Al 2O 3 and WO 3 with mass ratio 2.61:0.03:1, offers the best attainable final density without any geometric distortion from sintering. The zero CTE of these composites allows them to be utilized as the ceramic substrate of optical fiber Bragg gratings and some components in microelectronics to eliminate thermal stresses due to the thermal gradient or transient temperature change.

Thermal Expansion of NaZr2(PO4)3 Family Ceramics in a Low-Temperature Range

NZP family ceramics – NaZr2(PO4)3 (NZP), KZr2(PO4)3, RbZr2(PO4)3, Cs Zr2(PO4)3, CaZr4(PO4)6, SrZr4(PO4)6 (SrZP), and BaZr4(PO4)6 – were synthesized by a solid-state reaction, and their thermal expansion properties were investigated by X-ray diffraction measurement in a temperature range of -150 to 250 °C. The increases in the average thermal expansion coefficients of all the NZP family ceramics in this low temperature range (-150 to 250 °C) were smaller than those in a high temperature range (room temperature to 1000 °C). The thermal expansion coefficient of the SrZP ceramic was 0.2×10-6/°C between -150 to 250 °C, which is very small. This proved that SrZP has a near-zero thermal expansion coefficient in a low-temperature range.

Thermo-optic properties of B2O3 doped Li2O–Al2O3–SiO2 glass–ceramics

Reduction in the temperature coefficient of the optical path length, dS/dT of Li2O–Al2O3–SiO2 glass–ceramics with near-zero thermal expansion coefficient was attempted using control of the temperature coefficient of electronic polarizability, ϕ, and the thermal expansion coefficient, α. The dS/dT value of 2.6mol% B2O3-doped glass–ceramic was 12.5 ×10−6/°C, which was 0.9× 10−6/°C smaller than that of B2O3-free glass–ceramic. On the other hand, reduction in dS/dT through B2O3 doping was not confirmed in precursor glasses. Results showed that reduction in dS/dT of the glass–ceramic through B2O3 doping is caused by the reduction in ϕ. The reduction in ϕ from B2O3 doping was probably attributable to numerical reduction in non-bridging oxide ions with larger ϕ value by the concentration of boron ions in the residual glass phase. In addition, application of hydrostatic pressure during crystallization was effective to inhibit precipitation of β-spodumene solid solution, which thereby decreases dS/dT. The dS/dT value of B2O3-doped glass–ceramic crystallized under 196MPa was 11.7× 10−6/°C. That value was slightly larger than that of silica glass. The α value of this glass–ceramic was smaller than that of silica glass.

Optical Property of Li2O-Al2O3-SiO2 Glass-Ceramic Crystallized under High Pressure

The optical property of Li2O-Al2O3-SiO2 glass-ceramic, with a near-zero thermal expansion coefficient, crystallized under high pressure has been studied. A hydrostatic pressure of 196 MPa was applied by a hot isostatic pressing (HIP) technique during the nucleation process and the crystal growth process. The temperature coefficient of the optical path length, 1/l•dS/dT, decreased by 0.6×10-6 K-1, because the temperature coefficient of the refractive index, dn/dT, was decreased by the HIP treatment. The decrease in dn/dT was ascribed to the suppression of the temperature coefficient of the molar polarizability, φ, of the glass-ceramic crystallized by the HIP treatment. It was concluded that the suppression of φ occurs in the crystalline phase during the HIP treatment, based on the fact that the reduced 1/l•dS/dT was maintained even after the relaxation of the densified structure in the glass phase upon thermal annealing. The decrease in the number of lattice defects in the crystalline phase was hypothesized to be a cause of the reduced φ.