Xiong Weihao

Spark plasma sintering properties of ultrafine Ti(C,N)-based cermet

Ultrafine Ti(C,N)-based cermet was sintered by SPS from 1050°C to 1450°C and its sintering properties, such as porosity, mechanical properties and phase transformation, were investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimeter (DSC). It is found that the spark plasma sintering properties of Ti(C,N)-based cermet differ from those of conventional vacuum sintering. The liquid phase appearance is at least lower by 150°C than that in vacuum sintering. The porosity decreases sharply below 1 200°C and reaches minimum at 1 200°C, and afterwards it almost keeps invariable and no longer increases. SPS remarkably accelerates the phase transformation of Ti(C,N)-based cermet and it has a powerful ability to remove oxides in Ti(C,N)-based cermets. Above 1 350°C, denitrification occurred. Fresh graphite phase formed above 1 430°C. Both the porosity and graphite are responsible for the poor TRS.

Structure and properties of BaFe12O19 coated fly ash cenospheres by sol-gel process

Thin films of barium hexaferrite were prepared on fly ash cenosphere particles by the sol-gel method using Fe(NO3)3·9H2O, Ba(NO3)2 and citric acid as raw materials. The prepared films were characterized by differential thermal and thermogravimetric analysis (DTA-TG), X-ray diffractions analysis (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry. The magnetic and structural properties of barium hexaferrite coated cenosphere particles were also studied. The experimental results show that even and continual barium hexaferrite coatings were prepared on fly ash cenospheres, and the magnetic conductivity was imparted to these non-conducting oxide ceramic particles. The low density barium hexaferrite coated cenosphere particles may be utilized for manufacturing microwave absorbing materials.

Corrosion and Tarnish Behaviour of 925Ag75Cu and 925Ag40Cu35Zn Alloys in Synthetic Sweat and H2S Atmosphere

Abstract The purpose of this paper is to investigate the corrosion and the tarnish behaviour of 925Ag75Cu and 925Ag40Cu35Zn alloys in synthetic sweat at 37 °C and H 2 S atmosphere at room temperature. The alloys were in two hardening states, viz ., aging at 250 °C for 4 h and 70 % cold rolling + aging at 200 °C for 4 h, and tested by means of static corrosion, examined by XRD, SEM, EDS and XPS. The results show the corrosion and the tarnish in synthetic sweat at 37 °C of these two 925Ag alloys are induced by Cl − and OH − anions. The tarnish of 925Ag40Cu35Zn alloy is much slower than that of 925Ag75Cu alloy, and the white AgCl and the grayish black Ag 2 O produced by corrosion are difficult to deposit on the surface of 925Ag40Cu35Zn alloy resulting in grayish black corrosion film. The corrosion and the tarnish in H 2 S atmosphere at room temperature of these two 925Ag alloys are induced by S 2− anion. The corrosion and the tarnish of 925Ag40Cu35Zn alloy are much slower than 925Ag75Cu alloy. This is because Zn in 925Ag40Cu35Zn alloy reacts earliest with H 2 S to form white ZnS, which significantly retards the reaction between Ag or/and Cu and H 2 S to form grayish black Ag 2 S and black Cu 2 S.

Effects of Zn Content on Microstructures and Hardness of Ag925CuZn Alloys

Abstract The effects of Zn content on the microstructures and hardness of Ag925CuZn alloys were systematically investigated. The experimental results show that alloying element Zn significantly reduced the porosity of the as-cast microstructure of Ag925CuZn alloys and induced their grains coarsening during intermediate annealing and led convex microstructure forming during aging, which possesses face center cubic solid solution α-Ag. Moreover, high Zn content led to the decrease of solution-annealed hardness and aged hardness of Ag925CuZn alloys. For Ag925CuZn alloys with low Zn content, their proper aging temperatures are between 200 °C and 250 °C after solution-annealing, and their proper aging temperatures are between 150 °C and 200 °C after cold rolling.

In-situ TEM study on microstructural evolution of nanostructured TiO2

The effect of electron beam on the microstructures and phase transformation of nanostructured TiO2 heat treated at various temperatures for different time was studied by in-situ TEM and SAED. Anatase ex-situ heated at 250 °C and 360 °C transformed to rutile while irradiated by the electron beam. With the increasing sizes and distribution of the powders on the amorphous carbon, the process of phase transformation by the electron beam was encumbered. These evolutions may be due to the changes of vacuum atmosphere and the properties of powders.