Synthesis of zirconium tungstate–zirconia core–shell composite particles (original) (raw)
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International Journal of Refractory Metals & Hard Materials, 2011
In this study the W-ZrC composites fabricated by in situ reaction sintering of two precursors were compared, 1-The conventional WC and ZrO 2 which are ball milled with established molar ratio of 3-1 for 12 hours, gelcasted to form a green body and then undergo a pressure less sintering cycle, 2-A new and innovative way in which for the first time ZrSiO 4 was used instead of ZrO 2 , and by testing different molar ratio between WC and ZrSiO 4 it was understood that the optimum ratio is 3-1 once again. Furthermore the starting ZrO 2 and ZrSiO 4 powder were selected in nano size and it was understood that by using nano powders the amount of unreacted and unwanted phase reduce, the reaction progress and the mechanical proprieties improve. Although the reaction sintered WC/ZrO 2 possess better properties, regarding the cost considerations, reaction sintering of WC/ZrSiO 4 is a much cheaper process.
Development of ZrO 2–WC composites by pulsed electric current sintering
Journal of The European Ceramic Society, 2007
ZrO 2 -WC ceramic composites with 40 vol% WC were consolidated by pulsed electric current sintering (PECS) for 4 min at 1450 • C under a pressure of 60 MPa. The effect of ZrO 2 stabilizers and the source of WC powder on the densification, phase constitution, microstructure and mechanical properties of the ZrO 2 -WC composites were investigated and analyzed. The experimental results revealed that the amount and type of ZrO 2 stabilizers played a primary role on the phase constitution and mechanical properties of the composites in comparison to the morphology and size of the WC powder. The 2 mol% Y 2 O 3 -stabilized composites exhibited much better mechanical properties than that of 1.75 mol% Y 2 O 3 -stabilized or 1 mol% Y 2 O 3 + 6 or 8 mol% CeO 2 co-stabilized composites. A Vickers hardness of 16.2 GPa, fracture toughness of 6.9 MPa m 1/2 , and flexural strength of 1982 MPa were obtained for the composites PECS from a mixture of nanometer sized WC and 2 mol% Y 2 O 3 -stabilized ZrO 2 powder.
Frontiers of Materials Science, 2011
ZrO 2 -WC composites exhibit comparable mechanical properties as traditional WC-Co materials, which provides an opportunity to partially replace WC-Co for some applications. In this study, 2 mol.% Y 2 O 3 stabilized ZrO 2 composites with 40 vol.% WC were consolidated in the 1150°C-1850°C range under a pressure of 60 MPa by pulsed electric current sintering (PECS). The densification behavior, microstructure and phase constitution of the composites were investigated to clarify the role of the sintering temperature on the grain growth, mechanical properties and thermal stability of ZrO 2 and WC components. Analysis results indicated that the composites sintered at 1350°C and 1450°C exhibited the highest tetragonal ZrO 2 phase transformability, maximum toughness, and hardness and an optimal flexural strength. Chemical reaction of ZrO 2 and C, originating from the graphite die, was detected in the composite PECS for 20 min at 1850°C in vacuum.
Processing of ultrafine ZrO2 toughened WC composites
Journal of the European Ceramic Society, 2009
The interrelationships between the dispersion of the secondary ZrO 2 phase and the material properties of WC-based composites with up to 10 vol% of ZrO 2 are investigated. The homogeneity of the ultrafine WC-nanometric ZrO 2 powder mixtures was optimized by means of multidirectional milling and bead milling. In an alternative route, zirconium butoxide was used as a ZrO 2 source. The composites were fully densified by means of pulsed electric current sintering (PECS), also known as spark plasma sintering, within a few minutes at 1700 • C allowing to maintain an ultrafine grained microstructure combining a hardness of 2600 kg/mm 2 with an indentation toughness of 6 MPa m 1/2 . The ZrO 2 content and Y 2 O 3 stabilization were found to strongly influence the mechanical properties and especially strength of the WC-ZrO 2 composites.
Journal of Alloys and Compounds, 2011
In this investigation, 3 mol% Y 2 O 3 stabilized ZrO 2-based composites reinforced with 10 vol.%, 20 vol.% and 40 vol.% WC (named as 3Y-TZP/10WC, 3Y-TZP/20WC and 3Y-TZP/40WC) were fabricated by using injection molding and sintering. Mechanical properties of these composites varied due to WC addition and dwelling time. Density, strength and toughness decreased with shorter dwelling time and increasing WC content however a significant enhancement in fracture toughness was obtained by 3Y-TZP/20WC composite which had 9.2 MPa m 1/2 toughness. Severe unlubricated wear tests which were performed under 55 N normal load and 45 km sliding distance showed that 3Y-TZP/20WC composite had the lowest wear rate and wear volume values which are 2 × 10 −8 mm 3 /(N m −1) and 0.05 mm 3 , respectively.
High purity nanocrystalline α-alumina powder was mixed with 20 wt% ZrO 2 by slurry method sintered at temperature (T s) 1450°C, 1500°C, 1550°C and 1600°C for 2 hour. The density, porosity, structural properties and mechanical properties of Al 2 O 3 -ZrO 2 composites with respect to sintering temperature have been explored in the present work. The XRD spectra indicate that α-Al 2 O 3 , t and m-ZrO 2 are the crystalline phases present in 20 wt% ZTA composites for all sintering temperature. It is observed that with higher sintering temperature the intensity of m-ZrO 2 phases increases and the t-ZrO 2 phases decreases. However, t-ZrO 2 retention becomes much easier to trigger the transformation to monoclinic. Higher density of 20 wt% ZTA has been achieved at 1600ºC, whereas the highest porosity was obtained for sintering temperature 1450°C.The microstructures of the samples was studied by using SEM which represents highly homogeneous and finer structure at 1600ºC. The effect of sinterin...
THE INFLUENCE OF SINTERING TECHNIQUE ON MICROSTRUCTURE AND PROPERTIES OF ZrO2/Al2O3 COMPOSITE
2020
The following paper presents the results of investigations on the microstructure and mechanical properties of sintered composites in the zirconia-alumina system, fabricated by various sintering techniques. The investigations were performed for a particulate composite consisting of two continuous ceramic phases – zirconia (TZP) and alumina (α-Al2O3), 50 vol.% each. Two different methods were used to produce the samples: pressureless sintering and the U-FAST technique. The microstructure of the obtained sintered composite samples was evaluated using a scanning electron microscope. In addition, the density of the sintered bodies, their hardness and fracture toughness were investigated to evaluate the mechanical properties. Based on the obtained results of the investigations, the influence of the sintering technique on the microstructure and mechanical properties of the sintered composites was determined.
Densification and microstructure development in spark plasma sintered WC–6 wt% ZrO2 nanocomposites
Journal of Materials Research, 2007
In this paper, we report the results of a transmission electron microscopy investigation on WC–6 wt% ZrO2nanocomposite, spark plasma sintered at 1300 °C, for varying times of up to 20 min. The primary aim of this work was to understand the evolution of microstructure during such a sintering process. The investigation revealed the presence of nanocrystalline ZrO2particles (30–50 nm) entrapped within submicron WC grains. In addition, relatively coarser ZrO2(60–100 nm) particles were observed to be either attached to WC grain boundaries or located at WC triple grain junctions. The evidence of the presence of a small amount of W2C, supposed to have been formed due to sintering reaction between WC and ZrO2, is presented here. Detailed structural investigation indicated that ZrO2in the spark plasma sintered nanocomposite adopted an orthorhombic crystal structure, and the possible reasons for o-ZrO2formation are explained. The increase in kinetics of densification due to the addition of Zr...
ZrO2–WC nanocomposites with superior properties
Journal of the European Ceramic Society, 2007
Fully dense ZrO 2 -based nanocomposites with 5-40 vol.% WC were produced by hot pressing at 1450 • C for 1 h. The hardness and bending strength of the composites increases with increasing WC content, whereas the toughness hardly changes. An exceptionally high strength of 2 GPa combined with a hardness of 14.80 GPa and an excellent fracture toughness of 9.4 MPa m 1/2 was obtained for the 2 mol% Y 2 O 3 stabilised ZrO 2based composite with 40 vol.% WC. Such an attractive combination of properties is quite unique for a ceramic composite and is only matched by WC-Co cermets. The composites are substantially harder and stronger than the fine-grained Y-TZP, whereas the excellent toughness of Y-TZP is maintained. The strength improvement was accompanied with a change in fracture mode of the ZrO 2 grains from intergranular to transgranular. The ZrO 2 -WC nanocomposites were found to slightly plastically deform before fracturing during bending.
Sintering kinetics of ZrO2 nanopowders modified by group IV elements
International Journal of Applied Ceramic Technology, 2019
The sintering behavior of tetragonal zirconia nanopowders modified by the IV group elements at the initial sintering stage has been investigated. It was found that different additives SiO 2, SnO 2, GeO 2 have a significant influence on the densification kinetics of 3Y-TZP nanopowders obtained by co-precipitation during the sintering in depends on the amount (0-5 wt%). The shrinkage of zirconia based specimens during the non-isothermal sintering has been analyzed using the dilatometric data. The constant rate of heating technique was applied in order to determine the dominant mass transfer mechanism at the initial stage of Accepted Article This article is protected by copyright. All rights reserved. sintering in modified zirconia nanopowders. It was found that mass transfer mechanism and activation energy of diffusion in 3Y-TZP have changed as a result of the additives effect. The dominant sintering mechanism in 3Y-TZP was changed from volume diffusion to the grain boundary diffusion due to the SiO 2 and SnO 2 addition and the activation energy of sintering increased in this cases. However, GeO 2 additive caused participation of viscous flow mechanism in sintering process of 3Y-TZP nanopowders which led to acceleration of the densification due to the decrease in the activation energy of diffusion.