Synthesis of zirconium tungstate and its use in composites with tunable thermal expansion coefficient

Download
2011
Vural, İrem
Thermal mismatch between different components of a system could be sources of problems like residual stress induced cracking, thermal fatigue or even optical misalignment in certain high technology applications. Use of materials with tailored thermal expansion coefficient is a counter-measure to overcome such problems. With its negative thermal expansion coefficient zirconium tungstate (ZrW2O8) is a candidate component to be used in synthesis of composites with controlled thermal expansion coefficient (CTE). ZrW2O8 is typically produced by solid-state reaction between zirconium oxide and tungsten oxide at 1200oC. However, it has been demonstrated that ZrW2O8 can also be synthesized using wet chemical techniques, which provide a superior chemical homogeneity that often extents down to the atomic scale, and the convenient means of controlling nucleation and growth of the primary crystallites. With the commonly adopted wet chemical approaches, it is possible to crystallize particles with sizes in the submicrometer range at temperatures as low as 600 oC or even lower. In these studies, precursors are aged either below 100 oC (7 days – 3 weeks), or at 160-180 oC under hydrothermal conditions (1–2 days). Besides the obvious disadvantage in the ageing steps, use of tungsten sources with high cost in all approaches, constitutes the other disadvantage. Production of composites with tunable controlled thermal expansion (CTE) has been achieved by blending negatively and positively expanding materials in different proportions. In majority of these studies composites have been produced by conventional sintering methods. Spark Plasma Sintering (SPS) is a recent technique; in which sintering can be achieved at relatively low temperatures in short durations. There is only one study made by Kanamori and coworkers on the use of SPS in sintering of a composite, in which ZrW2O8 is one of the constituents [1]. This study aims the synthesis of ZrW2O8 particles and composites that possess tunable or zero CTE. A novel precursor recipe for ZrW2O8 synthesis was developed. In preparation of the precursor a total of 2 days of ageing and a temperature less than 100 oC was used. It was developed using a cost-effective tungsten source, namely tungstic acid and its final pH was lower than 1. The particles obtained from ‘unwashed’ procedure had sizes in micrometer range, while those obtained from ‘washed’ case had sizes in the range of 400-600 nm. These precursors could readily be crystallized at 600 oC, which in turn provided the desired particle sizes for composite applications. Experimental details on the precursor development are hereby presented with a discussion on the effects of solution parameters (i.e. solubility of tungstic acid, adjustment of the stoichiometry, ageing time) on the phase purity of the fired product. Zirconium oxide (ZrO2) has positive vi thermal expansion, therefore ZrW2O8/ZrO2 was selected as the composite system, and for their synthesis both conventional and spark plasma sintering methods were experimented. Composition ranges that provide composites with almost zero CTE’s were determined. The composite having a composition of containing 35% ZrW2O8, 65% ZrO2, and 35 w/o Al2O3 and sintered at 1200 oC for 24 hours had an expansion coefficient of 0.20 x 10-6/K for conventional method, while the one having a composition of 55% ZrW2O8, 45% ZrO2 and sintered at 1000 oC for 5 minutes had an expansion coefficient of 0.94 x 10-6/K for spark plasma sintering method. For characterization of the products X-ray diffraction (XRD), scanning electron microscopy (SEM), photon correlation spectroscopy (PCS), and thermal and dilatometer analyses (DTA/TGA/DMA) were used.

Suggestions

Synthesis and characterization of zirconium tungstate-zirconia core-shell composite particles
Khazeni, Nasser; Gündüz, Güngör; Maviş, Bora; Department of Chemical Engineering (2013)
Thermal mismatch between different components of a system could cause of problems like residual stress induced cracking, thermal fatigue or even optical misalignment in certain high technology applications. Use of materials with customized thermal expansion coefficient is a counter-measure to resolve such problems. Zirconium tungstate (ZrW2O8) with negative thermal expansion coefficient is capable of being used in synthesis of composites with tailored coefficient of thermal expansion (CTE). In this work, th...
Analysis of the thermoviscoplastic behavior of [0/90] SCS-6/timetal®21S composites
Çöker, Demirkan; Nicholas, Theodore (1996-01-01)
Micromechanical modeling is used to determine the stresses and strains due to both mechanical and thermal loads in [0/90] titanium matrix composites (TMCs) subjected to cooldown from the processing temperature and subsequent thermomechanical fatigue (TMF) loading conditions. The [0/90] composite is treated as a material system composed of three constituents: fiber and matrix in the [0] ply, and a [90] ply. The [0/90]s layup is modeled by a uniaxial stress rule of mixtures model for the [0] ply and adding a ...
An Experimental and numerical investigation of warpage behavior of silicon substrates at cryogenic temperatures
Baloğlu, Eyüp Can; Okutucu Özyurt, Hanife Tuba; Dursunkaya, Zafer; Department of Mechanical Engineering (2016)
Surface deformations and thermal stress behavior of microelectronic devices that operate at cryogenic temperatures (less than 120 K) and under vacuum conditions are important phenomena that aff ect the reliability requirements of such components. Excessive deformation and thermal stress on these devices may result in interconnect failure, performance degradation or other direct mechanical failure of one or more components. To obtain reliable products, surface deformations, named as warpage most widely, and ...
Nonlinear static aeroelastic behavior of composite missile fin with interlaminar and intralaminar damage
Özkaya, Özge; Kayran, Altan; Department of Aerospace Engineering (2017)
Accurate prediction of the static aeroelastic behavior of the lifting surfaces is crucial since aeroelasticity triggers instabilities, changes the load distribution and affects the control effectiveness and thereby the overall performance of the aerospace structures. Composite structures are prone to failure either because of the defects which may occur inside the structure during the manufacturing or in service. Damages are both inherent and unavoidable in composite materials and some of them are hard to d...
Investigation of warpage behavior of single crystal silicon on a silicon Adhesive ceramic integrated structure at cryogenic temperatures
Baloğlu, Can; Okutucu Özyurt, Hanife Tuba; Dursunkaya, Zafer (2016-03-17)
Understanding thermal stress and warpage behavior of heterogeneous component assemblies is vital in infrared sensor applications of silicon semiconductor material. The silicon semiconductor warpage behavior of the integrated structure composed of silicon material itself, an adhesive layer and a ceramic layer is analyzed by both FEM and experimental studies. The studies are performed between room temperature and 80 K. Thickness of each layer has an effect on the warpage. The silicon warpage of the initial ba...
Citation Formats
İ. Vural, “Synthesis of zirconium tungstate and its use in composites with tunable thermal expansion coefficient,” M.S. - Master of Science, Middle East Technical University, 2011.