Control of Reaction Pathways for Rapid Synthesis of Negative Thermal Expansion Ceramic Zr₂P₂WO₁₂ with Uniform Microstructure

Abstract

The reaction pathways to synthesize Zr 2 P 2 WO 12 (ZPW) from ZrO 2 , WO 3 , and P 2 O 5 are studied. It is found that there exist two different reaction pathways: One is direct reaction, while another is through an intermediate phase ZrP 2 O 7 . The reaction pathways are determined by drying and sintering temperatures. By controlling the reaction pathways, namely avoiding the intermediate phase, negative thermal expansion ceramic ZPW can be synthesized within several minutes. Besides, as-synthesized specimens possess much smaller and uniform grain size distribution than those synthesized by conventional methods. The investigation paves a way toward rapid and environmental friendly synthesis of ZPW and related compounds.

First-Principles Structural, Mechanical, and Thermodynamic Calculations of the Negative Thermal Expansion Compound Zr2(WO4)(PO4)2

“…The mean linear CTE calculated here for orthorhombic single-crystal Zr 2 (WO 4 )(PO 4 ) 2 is −3.1 × 10 –6 K −1 in the temperature range ∼0–70 K. This value is in good agreement with the mean linear CTE of −3 × 10 –6 K −1 measured by Evans et al 32 using XRD measurements in the temperature range ∼50–450 K, although only half of the value of −6 × 10 –6 K −1 reported by these authors using dilatometer data was over the same temperature range and smaller than the estimate of −5 × 10 –6 K −1 as reported by Cetinkol and Wilkinson 34 from neutron diffraction data between 60 and 300 K. Other recent experimental mean linear CTE estimates above room temperature are consistent with the value calculated in this study at low temperature. For example, Isobe and coworkers 33 measured a value of −3.4 × 10 –6 K −1 in the range ∼300–875 K, and Liu et al 36 reported values of −2.36 × 10 –6 and −2.61 × 10 –6 K −1 in the temperature range ∼300–1000 K for Zr 2 (WO 4 )(PO 4 ) 2 samples sintered at 1573 and 1673 K, respectively. It is important to note that, as mentioned in the Introduction section, differences in the CTE for Zr 2 (WO 4 )(PO 4 ) 2 can be attributed to different porosities or average grain sizes resulting from sintering conditions and/or synthesis reactions and to possible pressure-induced phase transformations during sample fabrication.…”

Elucidating Structure–Spectral Property Relationships of Negative Thermal Expansion Zr2(WO4)(PO4)2: A First-Principles Study with Experimental Validation

“…However, a major hindrance for the wider application of Zr 2 (WO 4 )­(PO 4 ) 2 has remained the synthesis of this material with consistent NTE properties. Indeed, previous experimental studies showed that the different porosities and average grain sizes resulting from sintering conditions and/or synthesis reactions − or pressure-induced phase transformations during Zr 2 (WO 4 )­(PO 4 ) 2 fabrication can lead to significant variations in its coefficient of thermal expansion (CTE). For example, mean linear CTE values of −6 × 10 –6 and −3 × 10 –6 K were measured in the temperature range of 50–450 K by Evans and co-workers using dilatometer and XRD measurements, while values of −5 × 10 –6 and −3.4 × 10 –6 K were obtained by Cetinkol and Wilkinson from neutron diffraction data between 60 and 300 K and by Isobe et al in the range of 300–875 K, respectively.…”

Relationship between sintering methods and physical properties of the low positive thermal expansion material Al2W3O12

“…Sintering and mechanical properties of thermomiotic (ie, showing negative thermal expansion) and related phases are still scarcely studied, although near‐zero thermal expansion phases (coefficient of thermal expansion at the order of 10 −7 K −1 ) from these families are good candidates for thermal shock resistance applications . Prisco et al, reached 91% of theoretical density (TD) for Al 2 W 3 O 12 bodies with a coarse‐grained and inhomogeneous microstructure, starting from an initially agglomerated nanopowder synthesized by total evaporation, via conventional pressureless constant‐ramp‐and‐hold sintering.…”

“…Its microstructure consisted of micron‐size grains. Liu et al, reported nanometric grains (~200 nm) for Zr 2 WP 2 O 12 sintered at 1400°C for a few minutes with ~91% TD. Therefore, the preparation of A 2 M 3 O 12 materials with nanometric grain sizes and low porosity represents an ongoing challenge for researchers.…”