Guojian Cao

Effect of annealing treatment on morphologies and gas sensing properties of ZnO nanorods

Abstract The high-temperature stabilization of ZnO nanorods synthesized by hydrothermal treatment was investigated. The structure and morphologies of ZnO nanorods were characterized by XRD and SEM, respectively. The thermal stability of ZnO nanorods was also detected by thermal gravity analyzing. Thermal annealing treatment results indicate that ZnO nanorods are fundamentally stable when annealing temperature is lower than 600 °C. When annealing temperature is beyond 600 °C, the diameters of ZnO nanorods obviously decrease and the aggravating tendency of nanorods between each other also increase. Annealing treatment can greatly influence the gas sensing properties of ZnO nanorods. Comparing with ZnO nanorods without annealing treatment, the gas sensing property of ZnO nanorods to H 2 with concentration of 2.5×10 −6 can increase from 2.22 to 3.56. ZnO nanorods annealed at 400 °C exhibit optimum gas sesing property to H 2 gas.

Fabrication and photodegradation properties of TiO2 nanotubes on porous Ti by anodization

Abstract Both Ti foil and porous Ti were anodized in 0.5%HF and in ethylene glycol electrolyte containing 0.5%NH 4 F (mass fraction) separately. The results show that TiO 2 nanotubes can be formed on Ti foil by both processes, whereas TiO 2 nanotubes can be formed on porous Ti only in the second process. The overhigh current density led to the failure of the formation nanotubes on porous Ti in 0.5%HF electrolyte. TiO 2 nanotubes were characterized by SEM and XRD. TiO 2 nanotubes on porous Ti were thinner than those on Ti foil. Anatase was formed when TiO 2 nanotubes were annealed at 400 °C and fully turned into rutile at 700 °C. To obtain good photodegradation, the optimal heat treatment temperature of TiO 2 nanotubes was 450 °C. The porosity of the substrates influenced photodegradation properties. TiO 2 nanotubes on porous Ti with 60% porosity had the best photodegradation.

Microstructure and mechanical properties of AM60B magnesium alloy prepared by cyclic extrusion compression

The cyclic extrusion compression (CEC) process was introduced into the AM60B magnesium alloy. The use of the CEC process was favorable for producing finer microstructures. The results show that the microstructure can be effectively refined with increasing the number of CEC passes. Once a critical minimum grain size was achieved, subsequent passes did not have any noticeable refining effect. As expected, the fine-grained alloy has excellent mechanical properties. The micro-hardness, yield strength, ultimate tensile strength and elongation to failure of two-pass CEC formed alloy are 72.2, 183.7 MPa, 286.3 MPa and 14.0%, but those of as-cast alloy are 62.3, 64 MPa, 201 MPa and 11%, respectively. However, there is not a clear improvement of mechanical properties with further increase in number of CEC passes in AM60B alloy. The micro-hardness, yield strength, ultimate tensile strength and elongation to failure of four-pass CEC formed alloy are 73.5, 196 MPa, 297 MPa and 16%, respectively.

Effect of combined RE–Ba–Sb addition on microstructure and mechanical properties of 4004 aluminum alloy

Abstract As a brazing foil, 4004 Al alloy has good welding performance. However, the high Si content decreases the plasticity of the alloy. In order to improve the plasticity of 4004 Al alloy and subsequently improve the productivity of 4004 Al foil, 4004 Al alloy was modified by RE–Ba–Sb. As a comparison, the 4004 Al alloy was also modified by RE with different addition. The tensile properties of the alloy reach the best when the addition of RE was 0.2%, in which the tensile strength and elongation were 194 MPa and 5%, respectively. For RE–Ba–Sb modification, the addition of three elements was optimized by orthogonal analysis. The results showed that the greatest impact parameter of RE–Ba–Sb modification was RE addition, followed by addition of Ba and Sb. The optimum addition amounts of RE, Ba and Sb obtained by orthogonal analyses were 0.01%, 0.3%, and 0.05%, respectively. The tensile strength and the elongation of 4004 Al alloy modified by the optimal modification process were 224 MPa and 6%, respectively. The amount of RE addition in RE–Ba–Sb modification is lower than that in RE modification.

Study on rotary impeller refinement of 4004 Al alloy

The effects of gas flow, rotational speed, refining time and still time on rotary impeller refinement of 4004 Al alloy have been studied. The results show that the rotational speed effect of rotary impeller refinement is superior to that of gas flow, refining time and still time. The optimum purification parameters are obtained by orthogonal analysis: rotor speed of 500 r/min, inert gas flow of 0.4 m3/h, refining time of 15 min, and still time of 6 min, and degassing rate can be 68%. Tensile results show that tensile strength and elongation of the alloy are slightly improved with increasing gas flow, rotational speed, and refining time. But the tensile strength and elongation will first increase and then decrease when the tensile strength and elongation are improved to a maximum value.

Effect of Cerium addition on microstructure and mechanical properties of 4004 aluminum alloy

The effects of Cerium addition on the microstructure and mechanical properties of 4004 aluminum alloy were investigated. The results showed that Cerium(Ce) addition can improve mechanical properties and microstructure of 4004 aluminum alloy when the percentage of Ce is below 2.0%. The best tensile properties, in which ultimate tensile strength was 220MPa and elongation was 5.6%, were obtained when the addition of Cerium were 2.0%. Meanwhile, tensile fracture slightly reveals ductile fracture. However, tensile strength and elongation decreases when Cerium content was above 2.0%.