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The Al 2 W 3 O 12 ceramic with near-zero thermal expansion is a promising candidate for thermal shock resistance applications. However, the often-reported microcracks in the microstructure hinder the practical use of Al 2 W 3 O 12. This work focuses on optimising the material processing—powder synthesis, calcination, milling, and sintering—to prepare dense polycrystalline Al 2 W 3 O 12 with fine microcrack-free microstructure. The amorphous powder produced by the co-precipitation method had the highest specific surface area reported for this material, resulting in improved sinterability. Two rapid sintering methods were employed—Rapid Pressure-less Sintering and Spark Plasma Sintering. Both methods led to shorter processing times and lower sintering temperatures. However, Al 2 W 3 O 12 samples produced by Spark Plasma Sintering were nearly fully dense with a density of ∼98% of theoretical density, the best value reported to date for this phase. The obtained fine crack-free microstructure of the samples led to a superior mechanical response compared to that achieved by Rapid Pressure-less Sintering. [ABSTRACT FROM AUTHOR]

Near-zero thermal expansion (NZTE) materials have important scientific significance and several potential applications. In this work, a NZTE GeNb 18 O 47 ceramic has been successfully synthesized by the solid-state method, and its phase, structure, expansion properties, and NZTE mechanism were investigated. Results show that the pure phase GeNb 18 O 47 ceramic is successfully obtained, and the crystal structure is composed of NbO 6 octahedron and Nb/GeO 4 tetrahedron. GeNb 18 O 47 shows a near-zero linear coefficient of thermal expansion (CTE) of 1.23 × 10−6 °C−1 (−100–400 °C), which is caused by negative thermal expansion (NTE) originating from the rotational coupling of NbO 6 octahedron and Nb/GeO 4 tetrahedron. In addition, GeNb 18 O 47 is a NZTE semiconductor with a band gap of 3.05 eV, which has great application value in integrated circuits, and chip manufacturing. [ABSTRACT FROM AUTHOR]

Novel BaMg 2 Al 6 Si 9 O 30 -based ceramics were prepared using the traditional solid-phase reaction method, and this paper presents the fabrication procedure, crystal structure, microstructure, microwave dielectric properties and temperature coefficient of thermal expansion of BaMg 2 Al 6 Si 9 O 30 -based ceramics. BaMg 2 Al 6 Si 9 O 30 -based ceramics were found to possess a hexagonal crystal structure with the P 6/ mcc space group. The BaAl 2 Si 2 O 8 and BaMg 2 Al 6 Si 9 O 30 phases coexisted in BaMg 2 Al 6 Si 9 O 30 ceramic given that raw MgO material reacted easily with water vapour in the air, and the BaMg 2 Al 6 Si 9 O 30 single-phase ceramic could be synthesized with calcined raw MgO material. The BaMg 2 Al 6 Si 9 O 30 single-phase ceramic exhibited ultralow ε r (5.68 at 14.05 GHz), moderate Q × f value (28534 GHz at 14.05 GHz), a self near-zero τ f value (7.35 ppm/°C), a near-zero average temperature coefficient of thermal expansion (+1.89 ppm/°C) at 30 °C 1000 °C and a rare negative temperature coefficient of thermal expansion (9.43 ppm/°C) at 655 °C 710 °C. The rare near-zero and negative thermal expansions of the BaMg 2 Al 6 Si 9 O 30 single-phase ceramic were mainly related to the strong Si/Al-O bonds with high relative covalency and 2 coordinate O(1) allowing longitudinal vibrations. [ABSTRACT FROM AUTHOR]

Materials that exhibit very small dimensional changes with temperature, i.e., near-zero thermal expansion (NZTE) properties, find attractive prospects in fields such as precision instrumentation and aerospace. However, how to manually design and synthesize NZTE materials with high performance instead of laboriously exploring composition has been a long-standing challenge. In this study, based on the excellent bonding and forming abilities of metallic glass (MG), a composite with continuous regulation of thermal expansion was obtained by combining different volume ratios of MG with beta-LiAlSiO4 (beta-LAS) possessing negative thermal expansion (NTE). Interestingly, excellent NZTE performance of 0.693 and 1.587 ppm/K was achieved over the 150–700 K temperature range when the volume ratio of MG was 40% and 50%, respectively. In addition, the compressive strength of the NZTE composite reached 320 and 436 MPa for the above two ratios, respectively. The thermal shock resistance results show that the composite can withstand thermal cycling tests of not less than 80 times. The proposed strategy not only provides new NZTE materials with high performance but also facilitates a shift in the preparation of high-performance NZTE composites from laborious search to customizable design.

Lightweight materials with near-zero thermal expansion (NZTE) and high thermal conductivity have potential applications in precision instruments, aerospace industry and electronic packaging due to their high thermal stability. In this study, multiphase Mn 3 Zn 1-x Sn x N (MnZnSnN) with abnormal negative thermal expansion (NTE) were used to inhibit the positive thermal expansion of AlSi. The resulting composites multiphase-MnZnSnN/AlSi (mMnZnSnN/AlSi) achieved NZTE (0.40 × 10-6 °C-1) in a wide temperature range (-5–60 °C, ΔT = 65 °C). Compared with other NZTE materials, mMnZnSnN/AlSi exhibits high thermal conductivity of 60 W·m-1·K-1 and high bending strength of 211 MPa. The density of the composite is only 4.46 g/cm3, 45% lower than invar alloy. This work provides guidance for designing and fabrication of aluminum matrix materials with combined advantages of wide temperature range zero thermal expansion behavior, high thermal conductivity and high mechanical properties. [ABSTRACT FROM AUTHOR]

Thermal expansion is inevitable for space structures under the alternating temperature of outer space around the earth. This may lead to the thermal stress and deformation due to the mismatch of the coefficient of thermal expansion. Near-zero thermal expansion (Near-ZTE) is a vitally essential demand for large-scale space telescopes or antennas to preserve their spatial precision and resolution. Recently, mechanical metamaterials with superior and tailorable properties have attracted significant interest with regard to developing negative materials or ultra-property materials. In this paper, the near-ZTE space structure architected by a dual-hourglass bi-material lattice is achieved by the structural optimization method with the gradient-based algorithm. First, an hourglass lattice with adjustable structural parameters is optimized to seek the design of effective negative thermal expansion (NTE) in the thickness direction. Then, two building blocks with both NTE and legacy positive thermal expansion (PTE) are combined as a dual-layered lattice to obtain the near-ZTE. Finally, a structure with near-ZTE of about ~10−9 m/(m·K) is obtained. Furthermore, the various lattice configurations, such as the hexagonal pyramid and triangle pyramid, are investigated in detail. Finally, the natural frequencies of two near-ZTE lattices are calculated by the modal analysis method, and the stiffness is discussed for the optimal solution of space applications. This work demonstrates that the near-ZTE structure can be achieved by utilizing the negative metamaterial and structural optimization method. It provides a novel solution to design the large-scale space structures with the near-zero thermal induced deformation, and may be constructed and assembled by the on-orbit fabrication technology. [ABSTRACT FROM AUTHOR]

The quest for the materials that boast efficient electromagnetic interference (EMI) shielding, strong strength and superb thermal dimensional stability is a burgeoning research area, particularly due to their critical applications in safeguarding sensitive circuits against microwave radiation, especially in the space environments. Graphene-based composites, leveraging the remarkable attributes of individual graphene nanosheets, emerge as prime contenders for fulfilling these sophisticated application requirements. In this study, we prepared boron-graphene composites via spark sintering, combining graphene sheets and boron nanoparticles. This method not only ensures high-performance outcomes but also remains cost-effective and suitable for large-scale production. Boron serves as a binder, facilitating the connection between adjacent graphene sheets and enhancing the graphitization process. The resulting composites demonstrated exceptional electrical conductivity (4.53 × 105 S m−1) and superior EMI shielding effectiveness (average SE T 83 dB, with the thickness of 0.25 mm), markedly surpassing previous graphene-based materials in terms of compressive strength (171.3 MPa), and exhibiting low thermal expansion and an ultra-low friction coefficient (0.04). Additionally, to unravel the evolution of boron in the graphene composite and the impact of boron on electrical conductivity, first principles calculations and density functional theory (DFT) were utilized. This investigation underscores the significant promise of boron-graphene composites as high-performance, multifunctional materials across various domains. [Display omitted] • Boron-graphene composite was high-efficiently fabricated by SPS. • Boron plays a role as binders and promotes the graphitization of graphene. • The resultant composite demonstrates excellent EMI shielding effectiveness. • The resultant composite also shows outstanding multifunctional properties. • Density functional theory elucidates the evolution mechanism of boron in graphene. [ABSTRACT FROM AUTHOR]

Thermal expansion is inevitable for space structures under the alternating temperature of outer space around the earth. This may lead to the thermal stress and deformation due to the mismatch of the coefficient of thermal expansion. Near-zero thermal expansion (Near-ZTE) is a vitally essential demand for large-scale space telescopes or antennas to preserve their spatial precision and resolution. Recently, mechanical metamaterials with superior and tailorable properties have attracted significant interest with regard to developing negative materials or ultra-property materials. In this paper, the near-ZTE space structure architected by a dual-hourglass bi-material lattice is achieved by the structural optimization method with the gradient-based algorithm. First, an hourglass lattice with adjustable structural parameters is optimized to seek the design of effective negative thermal expansion (NTE) in the thickness direction. Then, two building blocks with both NTE and legacy positive thermal expansion (PTE) are combined as a dual-layered lattice to obtain the near-ZTE. Finally, a structure with near-ZTE of about ~10−9 m/(m·K) is obtained. Furthermore, the various lattice configurations, such as the hexagonal pyramid and triangle pyramid, are investigated in detail. Finally, the natural frequencies of two near-ZTE lattices are calculated by the modal analysis method, and the stiffness is discussed for the optimal solution of space applications. This work demonstrates that the near-ZTE structure can be achieved by utilizing the negative metamaterial and structural optimization method. It provides a novel solution to design the large-scale space structures with the near-zero thermal induced deformation, and may be constructed and assembled by the on-orbit fabrication technology.