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In this paper, 50 ... 680 nm thick AlN-Al2O3 coatings are deposited by magnetron sputtering on the surface of a steel substrate and a piece of copper is melted on top of the ceramic. Upon heating the ceramic layer is cracked, and the phase inversion of the two top phases from steel/ceramic/copper configuration to the steel/copper/ceramic configuration takes place within 30 s of liquid time of copper. This phase inversion process is accompanied by a Gibbs energy change of about − 1.78 J/m2, due to good wettability of solid deoxidized steel by liquid copper in contrary to poor wettability of the ceramic by the copper. When copper is melted on AlN-Al2O3 coating with its thicknesses smaller than a critical value of about 170 ± 60 nm, liquid copper droplets hanging down into the cracks within the ceramic reach the solid steel surface at the bottom of the cracks, thus the flow of Cu down along the cracks is enabled. However, when copper is melted on AlN-Al2O3 with its thickness larger than the critical value of 170 ± 60 nm, Cu first forms a non-wetting droplet on top of the ceramics, and only after a certain incubation time it starts flowing down the cracks. This incubation time was found to depend linearly on the thickness of the ceramic, as cracks are filled from the bottom upwards by liquid copper via the evaporation–condensation mechanism. By the end of the process, the steel/copper/ceramic configuration is further stabilized by gravity. [ABSTRACT FROM AUTHOR]

Gd3+ was chosen as a substitute for Bi3+ in BiNbO4 ceramics, and the substitution effects on the sintering performance and microwave dielectric properties were studied in this paper. The high temperature triclinic phase was observed only in the Bi0.98Gd0.02NbO4 ceramics when sintered at 920 °C. Both bulk densities and dielectric constant (εr) increased with the sintering temperature, while decreased with the Gd content. The quality factor ( Q) exhibited a correlation to the Gd content and the microstructures of Bi1− x Gd x NbO4 ceramics. At the sintering temperature of 900 °C, Bi0.992Gd0.008NbO4 ceramics exhibited microwave dielectric properties of εr ∼ 43.87, Q × f ∼ 16,852 GHz (at 4.3 GHz), and its temperature coefficient of resonant frequency (τf) was found to be near-to-zero. [ABSTRACT FROM AUTHOR]

The formation of the gold layer in mercury gilding occurs through the heating a gold amalgam. As a result, the formation mechanism and technical characteristics of gilded products are closely related to the temperature at which they are heated. In this study, XRD and XPS analysis of a copper-gilded coronet from the Sui or Tang dynasties revealed that Au3Cu was one of the main phases of the gold layer. Therefore, base on the thermodynamic stability of ordered phases like Au3Cu, the estimated heating temperature for this copper-gilded coronet ranged from 240 to 285 ℃. Furthermore, SEM–EDS analysis of the cross-sectional concentration distribution of Cu indicated that the diffusion distance of Cu during heating did not exceed 2 μm. At 240–285 ℃, Cu diffused along the defects of the gold layer, and the diffusion process followed Fick's second law. Previous research has indicated that the defect path diffusion coefficient of Cu is on the order of 10–12 cm2/s, and the heating time of the gilding process is typically considered to be 15 min. Using the diffusion equation, the calculated diffusion distance of Cu aligned with the diffusion behavior of Cu at 240–285 ℃, confirming the inferred heating temperature range. Additionally, at these temperatures, the gold layer was formed through the solid-state reaction of the gold amalgam and was bonded to the substrate through the diffusion of Cu. [ABSTRACT FROM AUTHOR]

Ceramic powders of Cu doped lead Titanate (Pb0.5Cu0.5TiO3) are synthesized through a solid-state reaction method at high-temperature. Different percentage of ceramic filler into the polymer matrix was prepared by solution casting techniques. The structural studies of this polymeric composite were characterized by the X-ray diffraction technique and a tetragonal phase was found. Moreover, the surface morphology of this material was done by scanning electron microscopy. The impedance studies of this polymeric composite were characterized by an LCR meter between the frequencies range 102 and106 Hz. The modulus study of the material was done between the frequency ranges 102 and106 Hz. The variation of ac conductivity with frequency at different temperatures satisfied Jonscher's universal power law. [ABSTRACT FROM AUTHOR]

A novel processing was developed to fabricate Cu/AlN composite ceramic substrates derived from copper paste containing TeO2–V2O5–CuO (TVC) glass frit. The copper pastes containing proper compositions of TVC glasses and Cu powder were screen printed on AlN ceramic substrates, followed by a heat treatment under temperatures ranging from 550 to 750 °C. The effect of heat-treatment temperatures on morphology of obtained thick copper layers and the interface bonding properties of Cu/AlN composite substrates have been explored by scanning electron microscopy and mechanical testing. After being experienced heat treatment under 700 °C for 20 min, the copper layer exhibited the lowest resistivity of 14.04 μΩ cm and a maximum bonding strength of 24.6 MPa to AlN substrate. It is deduced that heat treatment under 700 °C bring about the close packing of Cu particle and the structure that copper embedded in the glass network, which resulted in the best tensile strength and lowest resistivity. [ABSTRACT FROM AUTHOR]

The high-temperature reliability of active metal brazed copper (AMC) on SiN ceramic substrates used for fabricating SiC high-temperature power modules was investigated under harsh environments. The AMC substrate underwent isothermal storage at 300°C for up to 3000 h and a thermal cycling test at −40°C to 300°C for up to 3000 cycles. During isothermal storage at 300°C, the AMC substrate exhibited high reliability, characterized by very little deformation of the copper (Cu) layer, low crack growth, and low oxidation rate of the Cu layer. Under thermal cycling conditions at −40°C to 300°C, no detachment of the Cu layer was observed even after the maximum 3000 cycles of the experiment. However, serious deformation of the Cu layer occurred and progressed as the number of thermal cycles increased, thus significantly roughening the surface of the Cu metallized layer. The cyclic thermal stress led to a significant increase in the crack growth and oxidation of the Cu layer. The maximum depth of the copper oxides reached up to 5/6 of the Cu thickness. The deformation of the Cu layer was the main cause of the decrease of the bond strength under thermal cycling conditions. The shear strength of the SiC chips bonded on the AMC substrate with a Au-12 wt.%Ge solder decreased from the original 83 MPa to 14 MPa after 3000 cycles. Therefore, the cyclic thermal stress destroyed the Cu oxides and enhanced the oxidation of the Cu layer. [ABSTRACT FROM AUTHOR]

In this work, pure-CaCuTiO was successfully prepared by a simple thermal decomposition method. This can easily be achieved by direct firing of starting raw materials dissolved in an aqueous citric acid solution at 800 °C for 6 h. The results show that sintering conditions have a remarkable influence on the microstructure of the CaCuTiO ceramics. Interestingly, dense CaCuTiO ceramic sintered at 1,050 °C for 2 h exhibits a high dielectric constant of ~5.1 × 10 with low loss tangent of ~0.048 at 30 °C and 1 kHz. The dielectric properties, electrical response of grain boundaries, and related nonlinear current-voltage behavior are found to be associated with the microstructure of CaCuTiO ceramics. [ABSTRACT FROM AUTHOR]

The influence of BaCu(B2O5) (BCB) addition on the sintering temperature and microwave dielectric properties of ZnO-2TiO2-Nb2O5 (ZTN) ceramic has been investigated using dilatometry, x-ray diffraction, scanning electron microscopy, and microwave dielectric measurements. A small amount of BCB addition to ZTN can lower the sintering temperature from 1100°C to 900°C. The reduced sintering temperature was attributed to the formation of the BCB liquid phase. The ZTN ceramics containing 3.0 wt.% BCB sintered at 900°C for 2 h have good microwave dielectric properties of Q × f = 19,002 GHz (at 6.48 GHz), εr = 45.8 and τ f = 23.2 ppm/°C, which suggests that the ceramics can be applied in multilayer microwave devices, provided that Ag compatibility exists. [ABSTRACT FROM AUTHOR]

Sintering of aluminum alloys is usually performed by the formation of a liquid phase. A liquid phase in 2xxx series alloys is formed from α+Al2Cu eutectic. In this work, the influences of trace elements like Sn or Pb, and the addition of a ceramic reinforcement, such as TiCN, on 2014 alloys are studied. Mechanical properties as well as a microstructural study show improved results. [ABSTRACT FROM AUTHOR]

Transient liquid-phase (TLP) bonding of aluminium-based metal matrix composite (MMC) and Al2O3 ceramic materials has been investigated, particularly the relationship between particle segregation, copper interlayer thickness, holding time and joint shear strength properties. The long completion time and the slow rate of movement of the solid–liquid interface during MMC/Al2O3 bonding markedly increased the likelihood of forming a particle-segregated layer at the dissimilar joint interface. Preferential failure occurred through the particle-segregated layer in dissimilar joints produced using 20 and 30 μm thick copper foils and long holding times (≥20 min). When the particle-segregated layer was very thin (<10 μm), joint failure was determined by the residual stress distribution in the Al2O3/MMC joints, not by preferential fracture through the particle-segregated layer located at the bondline. Satisfactory shear strength properties were obtained when a thin (5 μm thick) copper foil was used during TLP bonding at 853 K. [ABSTRACT FROM AUTHOR]