ZrW₂O₈/ZrO₂ Composites with Low/Near-Zero Coefficients of Thermal Expansion Fabricated at Ultralow Temperature: An Integration of Hydrothermal Assembly and a Cold Sintering Process

Abstract

ZrW 2 O 8 /ZrO 2 composites with tunable low/nearzero coefficients of thermal expansion (CTE) are promising candidates in several fields including aerospace, precision manufacturing and measurement, electronic circuit, etc., for counteracting the thermal expansion effect. However, bottleneck issues (such as the unstable decomposition of ZrW 2 O 8 phase, manufacturing size limitation, etc.) caused by conventional hightemperature sintering impede the development and application of ZrW 2 O 8 /ZrO 2 . To solve these scientific issues, a methodology integrating hydrothermal assembly with a cold sintering process (CSP) is exploited. The ZrW 2 O 8 /ZrO 2 composite powders with a mace-like structure, in which the spherical ZrO 2 nanoparticles peripherally embed on the rod-like ZrW 2 O 8 matrix particles, are hydrothermally assembled. Then, the relatively dense ZrW 2 O 8 /ZrO 2 composites with excellent low or even near-zero CTE are successfully achieved by CSP (as low as 190 °C) with a postannealing treatment (550 °C). The evolution of sintering densification, phase composition, and microstructure followed by the fundamental mechanism regarding the hydrothermal assembly of the macelike structure and densification of CSP are investigated in detail. This research not only effectively overcomes the bottleneck issues of ZrW 2 O 8 /ZrO 2 via integrating the hydrothermal assembly with the sintering technology at ultralow temperature but also develops a promising prospect for the fabrication of a broader range of metastable functional materials. KEYWORDS: ZrW 2 O 8 /ZrO 2 composites, ceramics, low/near-zero coefficients of thermal expansion, hydrothermal assembly, cold sintering process

Water and SnF2 Assisted Ultralow-Temperature Sintering of Mechanically Tough Y3Fe5O12 Composites for Magneto-Dielectric Antennas

“…So, the main mechanism behind the densification in the SnF 2 -based system may be the liquid phase formation followed by pressure solution creep and plastic deformation. Such a type of mechanism was reported for the ionic salts mechanically stressed at wet conditions. ,− The microstructures of all of the composites also show a similar kind of melting nature. Thus the microstructure and density confirm that liquid phase sintering accompanied by plastic deformation is the densification mechanism in SnF 2 -added composites.…”

The effects of cold sintering parameters on the densification of Na2WO4 ceramics using Na2WO4·2H2O dry powders

“…Up to now, several cold sintering mechanisms have been reported, and the most accepted mechanisms include the “dissolution–precipitation” process and plastic deformation process 1,18,19 . The “dissolution–precipitation” process is driven by the mediate liquid phase and has been confirmed in many ceramics such as ZnO, Li 2 MoO 4 and BaTiO 3 1,20–23 . The plastic deformation is mainly affected by the external pressure that is proved by the material system of CaCO 3 and NaCl 18,19 .…”

“…1,18,19 The "dissolution-precipitation" process is driven by the mediate liquid phase and has been confirmed in many ceramics such as ZnO, Li 2 MoO 4 and BaTiO 3 . 1,[20][21][22][23] The plastic deformation is mainly affected by the external pressure that is proved by the material system of CaCO 3 and NaCl. 18,19 In the "dissolution-precipitation" process, the mediate liquid phase is selected based on the material system, which needs a certain solubility, and there are two types of dissolution: congruent dissolution where the composition of the precipitated solid has the same stoichiometry to the parent phase, and incongruent dissolution where the composition of the precipitated solid has a different stoichiometry with the parent phase.…”

Sodium molybdate‐hexagonal boron nitride composites enabled by cold sintering for microwave dielectric substrates

“…Provided there is one phase that is the major volume fraction in the composite (the matrix) that can undergo sintering, other phases (the filler) can be integrated into the body and from the composite. [9][10][11][12][13][14] A range of works have demonstrated that novel phases and materials, such as polymers (thermoplastics and thermosets), [15][16][17][18][19][20] 2D materials, 21,22 and buckminsterfullerene, 23 can all be readily incorporated into the grain boundaries of a sintered ceramic material. Previously, a number of examples have been made of the cold sintering of low-loss dielectrics with other fillers.…”