Song Zhe Jin

SPS Sintering of NaNbO3-KNbO3 Piezoelectric Ceramics

Lead-free piezoelectric ceramics have received more attention due to the environmental protection of the earth. Niobate ceramics such as NaNbO3 and KNbO3 have been studied as promising Pb-free piezoelectric ceramics, but their sintering densification is fairly difficult. In the present study, Spark Plasma Sintering (SPS) was applied to the sintering of Na0.5K0.5NbO3 ceramics, whose powder was synthesized by the conventional oxide mixing method. No loss of sodium and potassium were found in the SPS sintering process, by which the density of the K0.5Na0.5NbO3 solid solution ceramics was raised to 4.21g/cm3 (>93% of the theoretical density) at temperatures as low as 920°C. The crystal phase of the Na0.5K0.5NbO3 is an orthorhombic structure. The piezoelectric parameter (d33) of the K0.5Na0.5NbO3 ceramics reached 49 pC/N.

TiB2/AlN/Cu Functionally Graded Materials (FGMs) Fabricated by Spark Plasma Sintering (SPS) Method

The TiB2/(TiB2+AlN)/AlN/(AlN+Cu)/Cu functionally graded materials were successfully fabricated via spark plasma sintering (SPS) method, in which a temperature gradient was achieved by using a specially designed mold and different sintering sequences were carried out. XRD analysis and SEM observations were respectively performed upon the TiB2/AlN/Cu composites. The results show that no new phases were introduced into the composites after mechanically milling or SPS process. The layered composites were found to have a dense microstructure, which changes gradually along a composition gradient. The present FGMs are developed as electrode materials of a solar thermoelectric module.

TiB2/Cu Electrode Material Fabricated via SPS

TiB2 and copper are difficult to be sintered together by conventional sintering process. In this article, the TiB2/Cu functionally graded materials (FGMs) were successfully fabricated via spark plasma sintering (SPS) method, in which a temperature gradient was achieved by using a specially designed mold and a two-step sintering was performed. The SEM observations show that the TiB2/Cu FGMs have dense microstructures. The XRD analysis suggests that no new phases were introduced into the TiB2/Cu composites after mechanical milling or SPS process. The TiB2/(TiB2+Cu)/Cu FGMs are promising electrode materials of solar thermoelectric modules.

Joining CoSb3 to Metal Surface of FGM Electrode for Thermoelectric Modules by SPS

The fabrication of electrodes is one of the key techniques in constructing thermoelectric elements for the practical applications. In this work, the commercial active brazing alloy “Incusil-ABA” was used for the joining of CoSb3 to the Cu surface of the graded electrode materials (Cu/AlN/Cu) by using spark plasma sintering (SPS). The bonding was performed in vacuum at temperatures 500°C for 10min. The brazing and diffusion bonding process were investigated by analyzing the crystal structure and microstructure of the bonding interface using X-ray diffraction and scanning electron microscopy, and its composition distribution was also analyzed by energy dispersive X-ray.

Fabrication of High-Content Ti3AlC2 Powders by Mechanical Alloying

In the present study, high-content Ti3AlC2 ceramic powders were fabricated by mechanical alloying (MA) using the Ti, Al and C as the starting materials. And the effect of Al content on the formation of Ti3AlC2 was investigated. The results showed that the large-sized granules were obtained to coexist with the powders after ball milling of 3Ti/Al/2C powder mixtures for 3 h. Ti3AlC2 in the synthesized powders is the main phase based on the XRD analysis. For the composition of 3Ti/1.1Al/2C, high-content Ti3AlC2 powders (87.6 wt.%) have been obtained after milling for 3h. Excessive Al, however, would reduce the content of Ti3AlC2 in the products.

Effect of Aluminum on Fabrication of Ti3SiC2 by Mechanical Alloying and Spark Plasma Sintering

In the present study, we fabricated high purity and electrically machinable Ti3SiC2 ceramics by mechanical alloying and subsequent spark plasma sintering. The effect of a trace amount of Al on these synthesis processes was examined. Our results showed that Ti3SiC2 could be synthesized by high energy milling. Spark plasma sintering of mechanically alloyed powder at the temperatures of 1000-1200°C produced nearly single-phased Ti3SiC2 materials. The purity of the sintered Ti3SiC2 bulk was remarkably increased by addition of a small amount of Al. Ti3SiC2 with a purity of 99.3 wt% and a relative density of 98.9% was obtained by mechanical alloying and subsequent spark plasma sintering from a starting mixture composed of n(Ti) : n(Si) : n(Al) : n(c) = 3 : 1 : 0.2 : 2 at 1100°C.

Fabrication of Si3N4 Micro-Components by a Combined Microfabrication Process

Si-based high-temperature ceramics are attractive materials for power microelectromechanical systems (power MEMS), such as microscale gas turbines, micro-combustors and micro-reactors. This presentation introduces a novel process for the microfabrication of Si3N4 ceramics, which mainly consists of pre-sintering of Si powder compacts, micromachining of pre-sintered Si preforms and reaction sintering of the micromachined Si preforms. The present process has its high potential for Si3N4 3-dimensional microfabrication because it combines the machinablity of pre-sintered Si powder compacts and near-net shaping characteristic of S3N4 reaction sintering. Si3N4 micro-components such as micro nozzle arrays and micro-rotor were fabricated by using the present process.