ZrW2O8 Research Articles

Synthesis, characterization, and functionalization of zirconium tungstate (ZrW2O8) nano‐rods for advanced polymer nanocomposites

Nanomaterials based on zirconium tungstate (ZrW2O8) exhibit numerous outstanding properties that make them ideal candidates for the development of high‐performance composites. Low coefficient of thermal expansion for advanced materials is a promising direction in the field of insulating nanocomposites. However, the agglomeration of zirconium tungstate (ZrW2O8)‐based nanomaterials in the polymer matrix is a limiting factor in their successful applications, and studies on surface functionalization ZrW2O8 for advanced nanocomposites are very limited. In this work, ZrW2O8 nano‐rods were synthesized using a hydrothermal method and subsequently functionalized in a solvent‐free aqueous medium using dopamine. Both pristine and functionalized nano‐rods were thoroughly characterized using Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, X‐ray diffraction, Scanning Electron Microscopy (SEM), and transmission electron microscopy techniques, which confirmed the successful functionalization of the nanomaterials. Polymer nanocomposites were also prepared using epoxy resin as a model matrix. Polymer nanocomposites with functionalized ZrW2O8 nano‐rods exhibited low coefficient of thermal expansion and enhanced tensile properties. The improved properties of the nanocomposites render them suitable for electronic applications. Copyright © 2017 John Wiley & Sons, Ltd.

Influence of Sintering Time on the Structure Formation of Al-ZrW2O8 Pseudo Alloys

Al – ZrW2O8 pseudo alloys were synthesized by free sintering of Al – ZrW2O8 powder mixture. Influence of sintering time on the structure formation of the pseudo alloys obtained was investigated. It has been shown that during sintering process zirconium tungstate decomposes into constituent oxides and re-synthesis of zirconium tungstate proceeds through intermediate stage – formation of WAl12 and ZrAl3 intermetallic compounds.

Synthesis, characterization and isotherm studies of new composite sorbents

With different methods, different molar ratios and different surfactants have been investigated to reach the optimum conditions for synthesized zirconium tungstate (Zr(IV)W). Zr(IV)W with different molar ratios of o-toluidine was synthesized to reach the optimum conditions for poly-o-toluidine zirconium tungstate (POTZr(IV)W). POTZr(IV)W with different molar ratios of tungstate was used to achieve the optimum conditions for poly-o-toluidine Zr(IV) tungstophosphate (POTZr(IV)WP). The Na+ capacity for all the prepared materials was investigated in order to determine the best ion exchanger towards the absorbed ions. The chemical and physical properties of materials were determined. Sorption isotherm studies of La3+, Ce3+, Nd3+ and Sm3+ ions were performed at different reaction temperatures and analysed by Langmuir, Freundlich, Dubinin–Raduchkivich and Temkin isotherm models. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were determined and found to be endothermic and spontaneous in nature.

Thermomechanical properties of zirconium tungstate/hydrogenated nitrile butadiene rubber (HNBR) composites for low-temperature applications

Rubber compounds for pressure sealing application typically have inferior dimensional stability with temperature fluctuations compared with their steel counterparts. This effect may result in seal leakage failures when subjected to decreases in temperature. Composites of hydrogenated nitrile butadiene rubber (HNBR) and zirconium tungstate as a negative thermal expansion filler were prepared in order to control the thermal expansivity of the material. The amount of zirconium tungstate (ZrW2O8) was varied in the range of 0 to about 40 vol%. The coefficient of thermal expansion (CTE), bulk modulus, uniaxial extension and compression set properties were measured. The CTE of the ZrW2O8-filled HNBR decreases with the filler content and it is reduced by a factor of 2 at the highest filler concentration used. The filler effect on CTE is found to be stronger when HNBR is below the glass transition temperature. The experimental thermal expansion data of the composites are compared with the theoretical estimates and predictions given by FEA. The effect of ZrW2O8 on the mechanical characteristics and compression set of these materials is also discussed.

Characterization of zirconium tungstate filler and performance investigation on asphalt mastic made with zirconium tungstate filler

Thermal cracking is a widespread distress for asphalt pavement in cold regions. The main reason causing thermal cracking is due to the contraction of asphalt concrete. Once thermally induced contraction stress exceeds the fracture resistance of the asphalt concrete, cracks start to develop. Comparing to aggregate, asphalt mastic is believed to have much larger thermal coefficient of contraction, therefore play a more significant role in determining the thermal cracking resistance of asphalt pavement. To modify the inherent thermal property of asphalt mastic, a new-developed material, zirconium tungstate (ZT), was utilized in this study. Different from normal material’s heated expansion and cooled contraction properties, ZT has a negative thermal expansion property of heated contraction and cooled expansion. Being as a substitute for mineral filler, the physical properties of ZT fillers and performances of asphalt mastics made with ZT fillers were investigated. Results show that ZT can better absorb and adhere asphalt binder when comparing with mineral filler. The addition of ZT is able to decrease the thermal coefficients of volume contraction and creep stiffness, improve the adhesive bond between filler and asphalt binder and reduce the complex modulus of asphalt mastic.

Structure and thermal behavior of zirconium tungstate under heating

The morphology and properties of powders ZrW2O7(OH)2·2H2O and ZrW2O8, obtained under the conditions of hydrothermal synthesis was studied. Using the high-temperature X-ray analysis, the mechanism of formation of zirconium tungstate was established. The influence of temperature on the structure and properties of materials was studied using shadow-casting method.

Study of Phase Decomposition in ZrW2O8

This paper describes the decomposition behavior of zirconium tungstate (ZrW2O8) materials above 1 050 K. The materials are synthesized according to a sol–gel‐route and a solid‐state route, and have been characterized with respect to their crystallographic properties. Apart from the initial phase and decomposition products ZrO2 and WO3, the additional phase γ‐ZrW2O8 is found, which results from a phase transition initiated by local pressures higher than 200 MPa. Residual stresses induced by the thermal mismatch between different phases within the composite material are found to be 1.15 GPa(ZrO2/ZrW2O8) and 1.26 GPa (WO3/ZrW2O8). Obtained stress values are high enough to induce this transition.

Synthesis and application of Poly(acrylamide-itaconic Acid)/Zirconium tungstate composite material for cesium removal from different solutions

ABSTRACTThis study is conducted to find the conditions required to synthesize composite material for cesium (134Cs+) removal from the generated liquid waste associated with nuclear, medical, industrial, and/or research activities. The study shows that the optimum conditions required for synthesizing “Poly [acrylamide (AM)-itaconic acid (IA)]/N,N′-methylenediacrylamide (DAM)/Zirconium tungstate (ZrW)” or “Poly(AM-IA)/DAM/ZrW” are 0.01 g DAM dose as a cross-linker, a co-monomer concentration of 20%, a co-monomer composition (AM-IA) (12:88), and 0.03 g (melted at 450 °C–500 °C) ZrW with gamma irradiation dose of 30 kGy. The composite material was characterized by Fourier infrared (FTIR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscope (SEM), and Brunauer-Emmett-Teller (BET) surface area measurements. The adsorption performance of the composite was investigated. The maximum removal efficiency of 134Cs+ ions was found to be 93% in moderate alkaline solutions at pH 8 ± 0.2 after 90 min. Kinetic studies indicated that the adsorption process is controlled by the pseudo-second-order kinetic model as a chemisorption process. Fitting of the adsorption data has pointed out that the adsorption process follows the Freundlich isotherm model as heterogeneous process. The maximum adsorption capacity (qmax) is 5.298 mmol Cs+ g−1 adsorbent. Applicability of the synthesized composite material was also examined to remove 134Cs+ ions in different aqueous solutions.

An Investigation of the Thermal Expansion Coefficient for Resin Concrete with ZrW2O8

This paper presents a novel resin concrete obtained by adding cubic zirconium tungstate (ZrW2O8) as filler. A prediction algorithm on the thermal expansion coefficient (CTE) of resin concrete (including filler) was established on the basis of the meso-mechanics method and a three-phase model for concrete. The concept of twice mixing was also proposed for prediction accuracy. Then, a 2D and 3D irregular polygon aggregate particles packing model was set up by Matlab and the properties of the packing model were simulated by finite element analysis. Finally, resin concrete samples were made and their CTE were measured. Mix proportion and addition of ZrW2O8 as influencing factors were considered in this experiment. The CTE of resin concrete was verified by comparing results of the prediction model, simulation model and experiment. The optimum CTE obtained from the experiment was 1.504 × 10−6/K. Compared with 6.817 × 10−6/K without ZrW2O8, it was found that the addition of ZrW2O8 to resin concrete can make it perform significantly better in thermal expansion.

Thermal Expansion Reduction in Alumina‐Toughened Zirconia by Incorporation of Zirconium Tungstate and Aluminum Tungstate

A series of composites containing yttria‐stabilized zirconia, Al2O3, and the thermomiotic (negative thermal expansion) materials ZrW2O8 and Al2W3O12 were prepared by an in situ solid‐state reaction during sintering. Microstructural analysis of the composites indicated several sub‐micron sized components. 27Al MAS NMR was used to characterize the aluminum‐containing phase distribution. Measurement of the coefficients of thermal expansion showed that the addition of thermomiotic components reduced the thermal expansivity of the alumina‐toughened zirconia matrix, but the reduction was considerably smaller than what would be predicted by the rule of mixtures. The Turner model was much more accurate in predicting the coefficients of thermal expansion of the composites due to the large differences in stiffness between the components.

Some peculiarities of zirconium tungstate synthesis by thermal decomposition of hydrothermal precursors

This article discusses some peculiarities of the synthesis of ZrW2O8 (1) using thermal decomposition of the precursor ZrW2O7((OH)1.5,Cl0.5)·2H2O (2) prepared by hydrothermal method. On hydrothermal synthesis of 2 the optimal concentration of hydrochloric acid in the reaction mixture is about 2.3М. TG approach to determine the chemical composition of the precursor was suggested. It has been found that the precursor for the synthesis of zirconium tungstate has chemical formula 2. Thermal decomposition of the precursor 2 begins at 200°С and affords an amorphous intermediate, which crystallizes as a cubic phase 1 above 550°С with an exoeffect. The temperature of the beginning of the transition from amorphous to the crystalline state is 350±25°С.

The preparation and structural features of zirconium tungstate possessing abnormal thermal properties

Single-phase ZrW2O8 was prepared by hydrothermal synthesis via the decomposition of ZrW2O7(OH1.5, Cl0.5) · 2H2O at 570°C. Transmission electron microscopy, in situ high-temperature X-ray diffraction, and thermogravimetric-differential thermal analyses of synthesized ZrW2O8 were performed. The morphology of the material was represented as rod-shaped particles having a block structure. The stability fields of ZrW2O8 were determined. ZrW2O8 demonstrated a negative thermal expansion behavior from 25 to 750°C.

Effect of annealing on the elastic moduli of amorphous zirconium tungstate

Amorphous zirconium tungstate (a-ZrW2O8), prepared at 7.7GPa, was subjected to successive heat treatments at increasingly higher temperatures, up to 640°C. Evidence of recrystallization into α-ZrW2O8 was found in the room temperature X-ray powder diffraction pattern of samples previously heated above 600°C. Changes in elastic moduli and linear thermal expansion coefficient upon annealing of a-ZrW2O8 up to 600°C cannot be accounted for by assuming a composite sample consisting of α-ZrW2O8 domains dispersed into an amorphous zirconium tungstate matrix. The irreversible relaxation of a-ZrW2O8 and recrystallization into α-ZrW2O8 is accompanied by an increase of bulk modulus (from 61.8(8)GPa to 74.4(9)GPa) and Poisson's ratio (from 0.267(3) to 0.302(3)) and diminution of density (from 6.54(1)g/cm3 for a-ZrW2O8 to 5.18(1)g/cm3 for α-ZrW2O8). Despite the greater density, a-ZrW2O8 (as well as γ-ZrW2O8, a high pressure polymorph) is more compressible than α-ZrW2O8, possibly owing to the new degrees of freedom provided by lowering symmetry, which allow external stresses to be accommodated by polyhedral tilting. Furthermore, the observed increase of Poisson's ratio upon thermal treatments at increasingly higher temperatures indicates that annealing of a-ZrW2O8 is accompanied by the irreversible reduction in the average number of bridging oxygen atoms.

Toward an Understanding of the Local Origin of Negative Thermal Expansion in ZrW2O8: Limits and Inconsistencies of the Tent and Rigid Unit Mode Models

Although zirconium tungstate (ZrW2O8) is the most popular negative thermal expansion (NTE) material, the exact mechanism responsible for its NTE still remains controversial. Specifically, the “Tent” model [Cao et al. Phys. Rev. Lett. 2002, 89, 215902; Bridges et al. Phys. Rev. Lett. 2014, 112, 045505] and the “rigid unit mode” (RUM) model [Tucker et al. Phys. Rev. Lett. 2005, 95, 255501] were subjects of debate during recent years. This work aims to shed light on this issue by means of molecular dynamics simulations which allow us to separate, for each bond distance, the “true” thermal expansion from the “apparent” thermal expansion, as well as to study the effective bond strength and the anisotropy of relative thermal motion. In spite of the good agreement with the experimental data of Cao, Bridges, and co-workers, a decrease of the “true” W–Zr distances has been observed accompanied by large transverse vibrations of the O atoms in the middle of the W–O–Zr linkage, in sharp contrast to the “tent” model. Moreover, in contrast to the RUM model, it has been found that the WO4 and ZrO6 polyhedra are strongly distorted by thermal motion, and, more importantly, that intra-polyhedra contributions to NTE are present. Accordingly, we can conclude that both the tent and RUM models are inadequate to explain NTE in ZrW2O8, and a more flexible model, simply based on rigid nearest W–O and Zr–O bonds and tension effect, should be adopted.

A Facile and Efficient Synthesis of Quinoxalines from Phenacyl Bromides and Ortho Phenylenediamine Promoted by Zirconium Tungstate

Quinoxaline derivatives have been synthesized by a simple, efficient, one-pot, two-component condensation of α,β-unsaturated ketones, o-phenylenediamine in the presence of a catalytic amount of 5% WO3/ZrO2 in excellent yields. The effect of electron releasing and electron with drawing substituent on the aromatic ring of phenacyl bromides on the reaction was investigated. Electron releasing groups and electron withdrawing groups did not affect significantly on the yields and the reaction times. Using 1,2-diamines possessing electron-withdrawing substituent needed longer reaction times and the yields were lower. Environmental acceptability, low cost, high yields and recyclability of the 5%WO 3 /ZrO 2 are the important features of this protocol.

Zirconium Tungstate/Epoxy Nanocomposites: Effect of Nanoparticle Morphology and Negative Thermal Expansivity

The ability to tailor the coefficient of thermal expansion (CTE) of a polymer is essential for mitigating thermal residual stress and reducing microcracks caused by CTE mismatch of different components in electronic applications. This work studies the effect of morphology and thermal expansivity of zirconium tungstate nanoparticles on the rheological, thermo-mechanical, dynamic-mechanical, and dielectric properties of ZrW2O8/epoxy nanocomposites. Three types of ZrW2O8 nanoparticles were synthesized under different hydrothermal conditions and their distinct properties were characterized, including morphology, particle size, aspect ratio, surface area, and CTE. Nanoparticles with a smaller particle size and larger surface area led to a more significant reduction in gel-time and glass transition temperature of the epoxy nanocomposites, while a higher initial viscosity and significant shear thinning behavior was found in prepolymer suspensions containing ZrW2O8 with larger particle sizes and aspect ratios. The thermo- and dynamic-mechanical properties of epoxy-based nanocomposites improved with increasing loadings of the three types of ZrW2O8 nanoparticles. In addition, the introduced ZrW2O8 nanoparticles did not negatively affect the dielectric constant or the breakdown strength of the epoxy resin, suggesting potential applications of ZrW2O8/epoxy nanocomposites in the microelectronic insulation industry.

Zirconium(IV) tungstate nanoparticles prepared through chemical co-precipitation method and its function as solid acid catalyst

In this paper, we report the synthesis of zirconium(IV) tungstate nanoparticles, a new and efficient catalyst for the oxidation of benzyl alcohol and esterification of acetic acid with various alcohols. The nanoparticle catalyst was prepared using the room temperature chemical co-precipitation method. The catalyst was characterized with thermogravimetric and differential thermal analysis, elemental analysis, X-ray diffraction analysis (XRD), fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM) and the Brunauer–Emmett–Teller (BET) surface area. The crystallite size was found to be ~20 nm as revealed by XRD, HRTEM and AFM. The Na+ exchange capacity was found to be 2.76 meq g−1 and the surface area of the compound measured using BET method was found to be 250–265 m2 g−1. The high value of ion exchange capacity indicates the presence of surface hydroxyl groups. The prepared nanoparticles have proven to be excellent catalysts for both oxidation and ester synthesis under mild reaction conditions. The mechanism of the catalytic reaction was studied as well.

Development of Hybrid Mixed Zirconium-Tungsten Oxide Supports for Activation of Dispersed Pt and PtRu Nanoparticles towards Oxidation of Alcohols

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Preparation and properties of polyimide nanocomposites with negative thermal expansion nanoparticle filler

Nanocomposites with tunable coefficient of thermal expansion (CTE) were prepared by incorporating cubic zirconium tungstate (ZrW2O8) nanoparticles at various volume percentages in a polyimide (PI). Rod-shaped nanoparticles of cubic ZrW2O8, which has isotropic negative thermal expansion, were synthesized using a hydrothermal method. The interfacial interaction between the PI and ZrW2O8 was enhanced by covalently bonding different organic moieties, including a short aliphatic silane and PI oligomer, to the surface of ZrW2O8. Structure–property relationships for the PI–ZrW2O8 nanocomposites were investigated for thermal degradation, glass transition, tensile and thermal expansion properties. Addition of ZrW2O8 nanoparticles did not alter the thermal degradation and glass transition temperature of the base PI. The addition of ZrW2O8 nanoparticles increased the Young's modulus of the polymer, indicating stiffening of the polyimide matrix. The increase was higher for nanocomposites with engineered interfaces due to the efficient load transfer achieved through the presence of linker groups. The addition of ZrW2O8 reduced the in-plane CTE of the base PI at all loadings studied. The CTE of the base PI was reduced by around 22% with the addition of ZrW2O8 at 15 volume% loading.

Effect of Hydrothermal Synthesis Conditions on the Morphology and Negative Thermal Expansivity of Zirconium Tungstate Nanoparticles

Zirconium tungstate (ZrW2O8) is a unique ceramic material that exhibits isotropic negative thermal expansion behavior, which can be produced at relatively low temperatures using hydrothermal synthesis and subsequent heat treatment. In this work, the effect of reaction conditions on morphology and crystallite size of ZrW2O8 nanoparticles is characterized through careful selection of initial reactants, acid types and concentration, reaction time, and temperature. Three types of ZrW2O8 nanoparticles with distinct morphologies and crystallite size scales were chosen to characterize and compare thermal and physical properties. Nano‐sized ZrW2O8 particles for two of the morphologies exhibit a negative coefficient of thermal expansion (CTE) that is about 30% larger than the CTE of bulk ZrW2O8 in the α‐phase (ca. −11.4 vs.−8.8 ppm/°C). A dependence of CTE on crystallite size and crystalline structure is demonstrated. It is also found that the morphology of the zirconium tungstate has a significant effect on the pore structure and level of hydration in the nanoparticles.