Thermal expansion properties and hygroscopicity of Y2−x Sm x W3O12 (x = 0.0–0.4) compounds

Abstract

A novel class of solid solutions of Y 2−x Sm x W 3 O 12 (x = 0.0-0.4) were synthesized and studied by means of powder X-ray diffraction. All samples crystallize in an orthorhombic space group Pnca. The lattice parameters a, b and c of Y 2−x Sm x W 3 O 12 increase with increasing Sm content. Since the compounds of this series hydrate at room temperature, thermogravimetric (TG) analysis was carried out. The result shows that the compound stores less water with increasing Sm content. The thermal expansion properties of Y 2−x Sm x W 3 O 12 (x = 0.1, 0.3 and 0.4) were investigated with high temperature X-ray diffraction. Negative thermal expansion coefficient α l becomes less negative from −6.644×10 −6 to −6.211×10 −6 ℃ −1 when x changes from 0.1 to 0.4. rare earth tungstates, negative thermal expansion, hygroscopic, XRD

Negative and Near-Zero Thermal Expansion in A2M3O12 and Related Ceramic Families: A Review

“…Furthermore, some phases within the Al 2-x Fe x Mo 3 O 12 solid solution (x 1 and 1.4) presented linear CTEs higher than for pure Al 2 Mo 3 O 12 and Fe 2 Mo 3 O 12 (Ari et al, 2008), a feature which would not be expected based on the A 3+ radius model. Similarly, reports for Y 2-x Nd x W 3 O 12 (Peng et al, 2008), Y 2-x Sm x W 3 O 12 (Yu et al, 2008) and Sc 2-x Al x W 3 O 12 showed that partial substitution with rare earths with higher ionic radius, such as Nd and Sm for Y and Al for Sc did not cause a continuous change of CTE between the limits of CTEs of the end-member phases; instead the linear CTE seemed to change in a random fashion.…”

“…However, with more information it became evident that the A 3+ radius was not the only factor that influences the CTE (Ari et al, 2008;Peng et al, 2008;Yu et al, 2008;Xiao et al, 2008a). It was shown that some phases and solid solutions did not follow the A 3+ radius model (Ari et al, 2008) (Wu et al, 2009b).…”

“…Water molecules likely interact with the framework through hydrogen bonding and it has been proposed that the oxygen atoms from water molecules intact with A 3+ or M 6+ , while hydrogen atoms from water molecules interact with the framework 2-fold oxygens (Wu et al, 2016). These interactions between water molecules and the framework can cause amorphization in molybdates and tungstates (Marinkovic et al, 2005;Yu et al, 2008;Li et al, 2012) or even change the crystal symmetry in some tungstates (Kol'tsova, 2001;Sleight, 2003;Cao et al, 2016;Pontón et al, 2017;Machado et al, 2021). Symmetry lowering by transformation to the monoclinic phase, or the presence of water molecules in channels, will inhibit, or attenuate, the asymmetrical framework librations of the quasi-rigid polyhedra, due to freezing of polyhedra rocking motions or due to steric effects, respectively.…”

“…Molybdates become amorphous when hygroscopic and lose water at temperatures higher than 403 K (Sumithra and Umarji, 2004;Sumithra and Umarji, 2006). Tungstates, on the other hand, lose water more easily, at temperatures not higher than 373 K and do not necessary become amorphous (Yu et al, 2008;Muller et al, 2019;Machado et al, 2021). It has been proposed that differences in hygroscopicity between tungstates and molybdates are due to lower absorption energies of water molecules into the crystal framework in tungstates (Wu et al, 2016).…”

Initial-stage Sintering Kinetics of Nanocrystalline Tungsten

“…[5] Nanocrystalline tungsten powder of submicron sizes was also used to produce near fully dense (above 99.7 pct theoretical density) tungsten heavy alloy. [6] Tungsten is the most used high-temperature refractory metal in various applications, retention of the nanocrystalline/ultrafine grain (UFG) structure after sintering is a concern, and several processing strategies using newly developed consolidation techniques (e.g., SPS) have been reported earlier. [7][8][9] Nano-grained tungsten (~50 nm) with 91 pct theoretical density was produced by Zhou et al [10] using resistance sintering under ultra-high pressure.…”