ZrW2O8 Powders Research Articles

Effects of ZrW2O8 Content on the Microstructures and Properties of Composite Coatings Produced by Laser Cladding

Addressing the issue of cracking in laser-cladding Ni-based composite coatings with WC particles, this study explored an approach to fabricating a crack-free coating by incorporating ZrW2O8 powder. The influence of varying ZrW2O8 contents on the crack susceptibility, microstructure, microhardness, wear resistance, and corrosion resistance of Ni60/WC composite coatings was systematically examined. The findings indicate that the ZrW2O8 content significantly impacts the microstructure and functional properties of the coating. Furthermore, it is suggested that the main contributors to preventing crack formation and diffusion are believed to be the pressure interaction caused by the negative expansion effect of ZrW2O8, as well as the in situ phase transition and diffusion toughening of ZrO2 during its decomposition process. The feasibility of achieving crack selfhealing through the addition of specific amounts of ZrW2O8 powder has been conclusively demonstrated.

In-Situ Al-Mg Alloy Base Composite Reinforced by Oxides and Intermetallic Compounds Resulted from Decomposition of ZrW2O8 during Multipass Friction Stir Processing.

In the presented work, the effect of friction stir processing admixing the zirconium tungstate ZrW2O8 powder on the microstructure, mechanical and tribological properties of the AA5056 Al-Mg alloy stir zone has been studied. The FSP resulted in obtaining dense composite stir zones where α-ZrW2O8 underwent the following changes: (i) high-temperature transformation into metastable β'-ZrW2O8 and (ii) decomposition into WO3 and ZrO2 oxides followed by the formation of intermetallic compounds WAl12 and ZrAl3. These precipitates served as reinforcing phases to improve mechanical and tribological characteristics of the obtained fine-grained composites. The reduced values of wear rate and friction coefficient are due to the combined action the Hall-Petch mechanism and reinforcement by the decomposition products, including Al2O3, ZrO2, β'-ZrW2O8 and intermetallic compounds such as WAl12 and ZrAl3. Potential applications of the above-discussed composites maybe related to their improved tribological characteristics, for example in aerospace and vehicle-building industries.

Particle size and purity control study on ZrW2O8 powders using coprecipitation method

ZrW2O8 powders with different particles size are synthesized by coprecipitation method. The effects of pH, PEG and calcination temperature on the phase, morphology and particle size of ZrW2O8 powders were investigated. The purity of the ZrW2O8 powder is also detected by XRF, and the optimal parameters of the coprecipitation method are obtained. The coprecipitation precursor is prepared by adding PEG400 into W6+ solution with a preferred pH of 2, and then calcined at 600 °C for 2 h and 1160 °C for 2 h to obtain the small particles size ZrW2O8 powder with narrow particle size distribution. The average particle size of ZrW2O8 powder is about 0.51 μm. The purity of ZrW2O8 powder is 97.95% with 2.05% ZrO2 as impurity due to the thermodynamic instability of ZrW2O8 and the volatilization of WO3 at high temperature.

Structure and Properties of Al – ZrW2O8 Pseudo Alloys

Al – ZrW2O8 powder mixture was sintered to obtain alloys were Al – ZrW2O8 pseudo alloys. The structure formation process of the pseudo alloys obtained was investigated. During sintering process zirconium tungstate was found to decompose into constituent oxides with consequent formation of WAl12 and ZrAl3 intermetallic compounds. Increasing the sintering time up to 5 hours leads to re-synthesis of the zirconium tungstate represented with elongated particles - microfibers. The formation of internal stresses in the material was shown using XRD and Williamson-Hall analyses. The value of internal compression stresses was estimated to be 90 MPa. Vickers hardness of the pseudo alloys obtained increases by two times with increasing sintering time from 1h to 5h.

Preparation and Characteristics of ZrO<sub>2</sub>/ZrW<sub>2</sub>O<sub>8</sub> Composites with Low Thermal Expansion

The ZrO2/ZrW2O8 ceramic matrix composites have been prepared by the two different processes: (1) ZrO2 and ZrW2O8 powders were mixed directly as raw material, then compacted by cold isostatic pressing under 200MPa, and finally, the ceramic matrix composites with low thermal expansion can be prepared by use of heat-pressing sintering or atmospheric sintering at temperature 1215oC. (2) ZrO2 (with excess mass) and WO3 powers were mixed as raw material, then compacted by cold isostatic pressing under 200MPa, and finally, the ZrO2/ZrW2O8 ceramic matrix composites can be made by use of heat-pressing sintering or atmospheric sintering at temperature 1215 oC after ZrW2O8 were synthesized by in-situ reaction of ZrO2 and WO3 powders at the same temperature. The microstructure, density, ZrW2O8 decomposition degree and the thermal expansion coefficient were compared among the sintered samples fabricated by the above two different methods, and affected by the different process parameters. The results show that the ceramic matrix composites with low thermal expansion are really composed of ZrO2, ZrW2O8 and WO3, and their relative densities are all more than 95%. Compared with the composites prepared by in-situ reaction, the densities, ZrW2O8 decomposition degree and the thermal expansion coefficient of the composites made by direct mixing are higher, less and smaller, respectively.

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.

Effect of the Cooling Ways on the Properties and Microstructure of ZrO<sub>2</sub>/ZrW<sub>2</sub>O<sub>8</sub> Ceramic Composites

ZrO2 has been widely used due to its good physical and chemical properties and the ZrO2/ZrW2O8 ceramic composites with adjustable thermal expansion coefficient can be prepared by mixing and sintering the ZrO2 and ZrW2O8 powders. In this paper, the ZrO2/ZrW2O8 ceramic composites have been prepared by mixing, cold isostatic pressing and atmospheric sintering, and then being cooled in air or in water. We focus on the effect of the cooling ways on the properties and microstructure of the ZrO2/ZrW2O8 ceramic composites. The results show that the relative density of all samples is more than 98%. For the in-situ method, the density and flexural strength of the samples cooled in air and in water are 98.1% and 98.4%, 112.96MPa and 45.23MPa, respectively. The ZrW2O8 content and thermal expansion coefficient of the samples cooled in the air are less and higher than those in the water, respectively. For the direct mixture method, the density and flexural strength of the samples cooled in air and in water are 98.9% and 99.3%, 195.99MPa and 58.71MPa, respectively. For the four groups of the composite samples, they behave better mechanical properties after cooled in air, and lower thermal expansion coefficients after cooled in water.

Zirconia – based nanopowders synthesized by the chemical precipitation method

The influence of annealing on the structure and properties of ZO2 – Y2O3 and ZrW2O8 powders obtained by the chemical precipitation method is studied. It is shown that the increase in annealing temperature leads to the decrease in the average size of particles, which initially represent porous agglomerates with high specific surface, to the size of monolithic polydomain particles, the sizes of which are comparable with the sizes of crystallites. The grain growth in the ZO2 – Y2O3 system during annealing is defined by surface diffusion. ZrW2O8 has a negative thermal expansion and it was equal to −12*10−6 C−1.

Hydrothermal synthesis of ZrW2O8 nanorods and its application in ZrW2O8/Cu composites with controllable thermal expansion coefficients

High purity ZrW2O8 powders with negative thermal expansion were hydrothermally synthesized in HCl solution. Unreacted ZrW2O8/Cu was fabricated by hot-pressing. Sn addition enhanced the densification of composite compact. Low hot-pressing pressure and relative loose microstructure of the composites can effectively prohibit the formation of high pressure γ-ZrW2O8. The thermal expansion curves were stable and uniform without anomalously large expansion. The coefficients of thermal expansion decreased with the ZrW2O8 volume fraction and a value of 1.6×10−6/°C was obtained for 68vol.% ZrW2O8/Cu. Microstructural anisotropy led to obvious thermal expansion coefficient anisotropy.

Rheological Behaviors of the Glass Paste for Hermetic Sealing the Edge of the Vacuum Glazing

AbstractVacuum glazing is a new building material with excellent energy conservation and sound insulation properties. Usually, the edge sealing layer between two sheets of glass substrates is prepared by spraying the seal glass paste and then sintering. In the present research, a more effective preparation method is reported. The edge sealing layer is prepared with a glass paste by screen printing and then sintering. The glass paste for the preparation of edge sealing layer of vacuum glazing was composed of low melting glass powder, ZrW2O8 powder with negative coefficient of thermal expansion and ethyl cellulose terpineol solution. The rheological, thixotropy and the screen printing behaviors of the typical paste were characterized and discussed. To get a thicker as-printed layer, the paste has high solid content and little thixotropy. The typical paste behaves a typical rheological behavior of pseudoplastic fluid. The test result of the shear strength of the sealing layer indicated that the sealing is reliable.

A Novel Method to Seal the Edge of the Vacuum Glazing

Vacuum glazing is a new building material with excellent energy conservation and sound insulation properties. Usually, the edge sealing layer between two sheets of glass substrates are prepared by spraying the seal glass paste and then sintering. In the present research, a more effective preparation method is reported. The edge sealing layer is prepared with a glass paste by screen printing, and then sintering. The glass paste for the preparation of edge sealing layer of vacuum glazing was prepared by using low melting glass powder, ZrW2O8 powder with negative coefficient of thermal expansion and ethyl cellulose terpineol solution. The test result of the shear strength of the sealing layer indicated that the sealing is reliable.

Effect of acids on the morphology and negative thermal expansion analysis of ZrW2O8 powders prepared by the hydrothermal method

Different acids were used to prepare ZrW2O8 powders at 570°C by the hydrothermal method. The products were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, thermogravimetric and differential scanning calorimetry and Fourier transform infrared absorption spectra. The results indicate that among the chosen acids, only HCl and HNO3 can be used to prepare pure ZrW2O8 powders with high crystallinity and rod-like shape. When the hydrothermal temperature reduces to 160°C, nano-sphere particles with an average diameter of 30nm is obtained, if prepared by HNO3 addition. The results of in situ X-ray diffraction measurement indicate that ZrW2O8 powders prepared by pure HCl or HNO3 have strong negative thermal expansion.

ZrW2O8-doped epoxy as low thermal expansion insulating materials for superconducting feeder system

Epoxy resin insulating materials used in superconducting feeder system of fusion device are required to be low thermal expansion coefficient (TEC). In this paper, negative thermal expansion (NTE) material ZrW2O8 filled epoxy resins were fabricated. To improve the dispersion of fillers in epoxy matrix, plasma polymerization was performed on the surface of ZrW2O8 powders. Transmission electron microscope (TEM) and surface wettability analysis were performed before and after the surface modification of ZrW2O8 powders. The TEC of ZrW2O8/epoxy composites were measured from 77K to room temperature. The results show the doping of ZrW2O8 can significantly reduce the TEC of epoxy resins. The sedimentation rate of ZrW2O8 before and after modified in epoxy was compared by density measurement. It can be seen that the ZrW2O8 surface modified by plasma polymerization can enhance its dispersion properties in epoxy matrix.

Synthesis and thermal expansion of 4J36/ZrW2O8 composites

Gas atomized 4J36 alloy powder was milled for 72 h then mixed with ZrW2O8 powder and sintered at 600°C for 4 h under argon atmosphere. 4J36/ZrW2O8 composites containing 10 vol.%, 20 vol.%, 30 vol.%, and 40 vol.% ZrW2O8 were fabricated, the relative density of which ranged from 70% to 80%. Thermal expansion coefficients of the composites decreased as the amount of ZrW2O8 increased, in agreement with the rule of the mixture. The coefficient of thermal expansion of the 4J36/40 vol.%ZrW2O8 composite in 25–100°C is 0.55 × 10−6/°C.

Low-temperature sintering of ZrW2O8–SiO2 by spark plasma sintering

Amorphous ZrW2O8 powder and amorphous SiO2 powder were prepared by a sol–gel process as raw materials, and high-density ZrW2O8–SiO2 were successfully prepared at a much lower temperature of 923 K for a much shorter holding time of 10 min by spark plasma sintering (SPS) method rather than by conventional melt-quenching method. The relative densities of 0.85ZrW2O8–0.15SiO2 and 0.70ZrW2O8–0.30SiO2 were 99.4% and 96.6%, respectively. The combined technique of a sol–gel process and SPS should enable us to prepare the varied types of high-density composites of ZrW2O8 without severe thermal cracking caused by melt-quenching. The thermal expansion properties and dielectric properties of ZrW2O8–SiO2 were also investigated.

Preparation and thermal properties of zirconium tungstate/copper composites

AbstractZrW2O8/Cu composites were prepared by the powder metallurgy method. Electroless plating was used to deposit copper on ZrW2O8 powder before sintering. The thermal expansion and thermal conductivity of composites were measured in the temperature range from 25 oC to 200 oC and compared with those predicted from various theoretical models. The results show that the coefficient of thermal expansion of ZrW2O8/ Cu composites with a different volume fraction of ZrW2O8 is greater than the theoretically calculated value. The thermal conductivities of ZrW2O8/ Cu composites increase with a higher copper content and decrease upon elevated temperature. The thermal conductivity of composites with a different volume fraction of ZrW2O8 is lower than the theoretically calculated value.

Preparation of Cu Coated ZrW<sub>2</sub>O<sub>8</sub> Composite Powders via Heterogeneous Precipitation Process

ZrW2O8 powder was prepared by the solid-state method. A heterogeneous precipitation process was developed to fabricate Cu coated ZrW2O8 composite powders based on a cementation process under 100oC. SEM and XRD were applied to assess the coating quality as well as the phase composition. The result shows that the mean size of ZrW2O8 powders is less than 2 microns. The nanometer compounds are easier formed on the surface of the spheric agglomerated ZrW2O8 powders. The Cu coated ZrW2O8 composite powders can be obtained with flowing hydrogen at 300oC.

Zirconium Tungstate (ZrW2O8)/Polyimide Nanocomposites Exhibiting Reduced Coefficient of Thermal Expansion

ZrW2O8 is obtained as microparticulate powder following traditional methods or as nanoparticulate powder using an inverse micelle sol−gel synthesis strategy. As-prepared ZrW2O8 powders, surface-derivatized with (3-aminopropyl)siloxy linker molecules, disperse well in BTDA-ODA polyamic acid resins to give thermally cured ZrW2O8/polyimide hybrid films showing good wetting of embedded ceramic particles. Measured CTE values of ZrW2O8/BTDA-ODA hybrid films containing 0−50 wt % (0−22 vol %) ceramic loading show a controlled reduction in thermal expansion with increasing ceramic content. Reduction in CTE is modeled best assuming mixed-law behavior with incorporation of an interfacial phase region. A 22 vol % ceramic loading gives a 30% (10 ppm/K) reduction of CTE. ZrW2O8/BTDA-ODA films containing 0.8 vol % (3 wt %) ceramic loading exhibit unusually low thermal expansion, although the significance of this observation remains to be confirmed.