Search

Abstract: 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. [Copyright &y& Elsevier]

Abstracts: ZrMo2O8 film with cubic β-ZrW2O8 structure was prepared on glass substrates via the sol–gel dip coating method. The structural, compositional, morphological and thermal expansion properties of the ZrMo2O8 film were studied using X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The bonding strength of the as-prepared films was measured by scratch testing. The results indicated that crystalline ZrMo2O7(OH)2(H2O)2 precursor powders changed into amorphous gel as the coordination reaction of citric acid and polyvinylpyrrolidone (PVP) with metal ions. Cubic β-ZrMo2O8 film consisting of ball-like particles could be obtained after annealing the gel film, and the bonding strength decreased from 27.8N (gel film) to 8.7N (β-ZrMo2O8 film). The room temperature lattice parameters of resulting cubic β-ZrMo2O8 film are a = b = c =8.976Å, and this film exhibited excellent negative thermal expansion (CTE=−8.66×10−6 K−1) property from room temperature to 430°C. [Copyright &y& Elsevier]

ZrWMoO8 powders with different morphologies were obtained using ammonium tungstate, molybdate tungstate and zirconium tungstate as the starting materials by dehydrating the precursor ZrWMoO7(OH)2(H2O)2. The precursor was studied by thermo-gravimetric and differential scanning calorimetry (TG-DSC). The influence of the gelling agents (HCl, HClO4, HNO3, H2SO4 and H3PO4) on the crystallization process and crystal morphology of the products prepared was investigated by X-ray powder diffraction (XRD), scanning electron micrograph (SEM) and X-ray fluorescence spectrometer (XRF). Results showed that the morphology of the ZrWMoO8 particles can be simply adjusted by changing the gelling agents, and the thermal expansion coefficients of cubic ZrWMoO8 prepared in HCl solution are −3.84 × 10−6 K−1 from 100°C to 700°C. [ABSTRACT FROM AUTHOR]

Abstract: A series of solid solutions of Al2−δScδW3O12 (δ = 0–2) were successfully synthesized by the solid-state reaction with aluminum oxide, scandium oxide and tungsten trioxide as raw materials. The phase composition and structure of the products were analyzed by X-ray powder diffraction and scanning electron microscopy, while the linear thermal expansion coefficients were measured by thermo dilatometer. The results indicate that Al2−δScδW3O12 with high purity can be successfully prepared by the solid-state method. All samples of different δ values crystallize in the same orthorhombic structure with space group of Pnca. The lattice constants and cell volume increase linearly with increasing Sc content. The average linear thermal expansion coefficients of Al2−δScδW3O12 measured by thermo dilatometer indicate that the thermal expansion coefficients of the solid solutions could be adjusted to the desired values, such as positive, near zero or negative by simply changing the δ value. [Copyright &y& Elsevier]

Abstract: A composite of Sc2W3O12/Cu where Sc2W3O12, the core, is coated by the Cu shell was synthesized using simple electroless plating method. As-prepared Sc2W3O12/Cu composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and thermomechanical analyzer (TMA) techniques. The study results show that the Pd–Sn activator was successfully formed on the surface of Sc2W3O12 after the sensitization and activation. In the electroless plating process, Cu nanocrystals formed firstly, and then grew together to form a continuous coating. Sc2W3O12/Cu core–shell composites exhibit a negative linear coefficient of thermal expansion CTE=−4.47×10−6 °C−1 from room temperature to 200°C. [Copyright &y& Elsevier]

Reducing thermal expansion and improving thermal conductivity of copper based materials are particularly important for improving thermal stability of electronic packaging materials. Herein, Cu/Sc 2 W 3 O 12 /SiC composite with a moderate coefficient of thermal expansion (CTE) of 8.28 ppm/K and a high thermal conductivity of 287.2 W/m⋅K was successfully prepared by partial replacement of Sc 2 W 3 O 12 by the nano SiC particles to compensate sacrificial thermal conductivity of the reported Cu/Sc 2 W 3 O 12 composites using a hot-pressing method. Theoretical calculation and Ashby plot map suggests that this Cu/Sc 2 W 3 O 12 /SiC composite facilitate the best combination between tunable thermal expansion and high thermal conductivity, which may due to that SiC nanoparticles can strengthen the driving force of vacuum hot-pressing sintering and thus lead to more homogeneous microstructure accounting for improved thermal reliability. This work can provide useful insights into the design and synthesis of composites used as packaging material for various semiconductors. [ABSTRACT FROM AUTHOR]

Abstract Owing to that, efficient cooling the chip demands a heat sink material possess high thermal conductivity and low CTE equivalent to the gallium arsenide (GaAs) or silicon (Si). Addressing this target, we have synthesized Sc 2 W 3 O 12 /Cu composites by hot-pressing sintering at 700 °C, which was based on the uniform submicron Sc 2 W 3 O 12 powder prepared for the first time. The resulting product not only possessed a low CTE (8.31 ppm/K, which was identical to GaAs of 6.2 ppm/K) and high thermal conductivity (243.99 W/m K), but also exhibited extremely stable CTE within a temperature range of 25 °C–300 °C and high Vickers hardness (234.32 HV) due to its uniform and nearly full dense microstructure. A 'thermoelastic-micro-mechanics'model was used to predict the CTE quantitatively and the estimated values were in good agreement with the experimental CTE values. Moreover, the excellent compatibility of thermal properties between Sc 2 W 3 O 12 and Cu possesses an isolated spot in Ashby map based on CTE and thermal conductivity, and the as-synthesized composite exhibits nearly greatest thermal stability indicated via its low thermal distortion parameter (TDP). Highlights • The uniform submicron Sc 2 W 3 O 12 particles were prepared by via high energy ball mill for the first time. • The Sc 2 W 3 O 12 /Cu composites with homogeneous microstructure were synthesized via hot-pressing method. • The Sc 2 W 3 O 12 /Cu composites exhibited extremely stable CTE within a temperature range of 25 °C–300 °C. • The Sc 2 W 3 O 12 /Cu composite obtained at 700 °C possesses high Vickers hardness of 234.32 HV. • The Sc 2 W 3 O 12 /Cu composite realize a good compatibility between high thermal conductivity of Cu and stable NTE property. [ABSTRACT FROM AUTHOR]

Antiperovskite manganese nitrides Mn 3 Cu 1− x Sn x N and carbon nanotubes/Mn 3 Cu 1− x Sn x N composites were prepared by mechanical ball milling and solid state sintering. The crystal structure, microscopic morphology, thermal expansion properties and electrical conductivities of Mn 3 Cu 1− x Sn x N and CNTs/Mn 3 Cu 1− x Sn x N were studied. The results show that the dominating phase of the samples has a Mn 3 CuN-type structure. The Mn 3 Cu 1− x Sn x N has fine and dense grains. The CNTs are distributed among the Mn 3 Cu 1− x Sn x N grains in the composites. The transition temperature of negative thermal expansion (NTE) tends to increase with increasing the content of Sn. The NTE coefficient of Mn 3 Cu 1− x Sn x N is between −27.7 × 10 −6 K −1 ( x = 0.2) and −87.5 × 10 −6 K −1 ( x = 0.3). The operation temperature window is narrower and the absolute value of NTE coefficient is smaller in CNTs/Mn 3 Cu 1− x Sn x N compared to Mn 3 Cu 1− x Sn x N. The electrical conductivities of Mn 3 Cu 1− x Sn x N and CNTs/Mn 3 Cu 1− x Sn x N composites are in the ranges of 0.90–2.62 × 10 3 S/cm and 1.38–3.34 × 10 3 S/cm, respectively. The electrical conductivities decrease with increasing Sn contents for both Mn 3 Cu 1− x Sn x N and CNTs/Mn 3 Cu 1− x Sn x N. [ABSTRACT FROM AUTHOR]

Novel ZrV 2 O 7 microfibers with diameters about 1–3 μm were synthesized using a sol–gel technique. For comparison, ZrV 2 O 7 powders were prepared by the same method. The resultant structures were studied by X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy. The results indicated that both the pure ZrV 2 O 7 microfibers and powders could be synthesized by the sol–gel technique. The thermal expansion property of the as-prepared ZrV 2 O 7 microfibers and powders was characterized by a thermal mechanical analyzer, both the fibers with cylindrical morphology and irregular powders with average size between 100 and 200 nm showed negative thermal expansion between 150 °C and 600 °C. The photocatalytic activity of the microfibers was compared to that of powders under UV radiations. The band gap of ZrV 2 O 7 microfibers decreased and its absorption edge exhibited red shift. The microfibers also had a higher surface area compared with the powders, resulting in considerably higher photocatalytic characteristics. The large surface area and the enhanced photocatalytic activity of the ZrV 2 O 7 microfibers also offer potential applications in sensors and inorganic ion exchangers. [ABSTRACT FROM AUTHOR]

Abstract: A novel photocatalytic ZrWMoO8/Ag composite with core–shell structure was prepared. The composites were composed of ZrWMoO8 rods with negative thermal expansion (NTE) property as cores and Ag nanoparticles as shell. The resulting products were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–visible spectrophotometer (UV–vis DRS). The results showed that ZrWMoO8 rods displayed not only negative thermal expansion but also photocatalytic efficiency toward Rhodamine B (RB) degradation under UV-irradiation. The as-prepared ZrWMoO8/Ag composites exhibited a higher photocatalytic activity than that of pure ZrWMoO8, thereby implying that the ZrWMoO8/Ag interfaces promote the separation of photogenerated electron–hole pairs and enhance the photocatalytic activity. [Copyright &y& Elsevier]

Abstract: Negative thermal expansion ZrW2O8 thin films has been grown on quartz substrates by pulsed laser deposition (PLD) method followed by annealing at various temperatures. The influences of annealing temperature on the morphology and phase composition of the ZrW2O8 thin films were investigated. The X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS) analyses revealed that the as-deposited ZrW2O8 thin film showed an amorphous phase, the stoichiometry of the as-deposited thin film was close to that of the ZrW2O8 ceramic target, the crystallized cubic ZrW2O8 thin films were prepared after annealing at 1200°C. The scanning electron microscope (SEM) confirmed that the ZrW2O8 thin film deposited on the substrate heated at 650°C was smooth and compact, the crystallized cubic ZrW2O8 thin film was a polycrystalline film and its grain size grew to be larger. The high temperature X-ray diffraction analyses showed that all the peaks ascribe to the ZrW2O8 thin film shifted to higher angle with the increasing temperatures, which demonstrated that the cubic ZrW2O8 thin film exhibited negative thermal expansion and its thermal expansion coefficient was calculated to be −11.378×10−6 K−1 from 20°C to 600°C. [Copyright &y& Elsevier]