Jian Feng Zhu

Microwave Hydrothermal Synthesis of GaN Nanorods

The GaOOH Nanocrystal rods were successfully synthesized by microwavehydrothermal method using Ga2O3 ,HNO3 and NH3·H2O as raw materials. Simple heat treatment of GaOOH in the flow of NH3 gas leads to the formation of submicron GaN rods even at 800°C through GaOOH. The resultant GaOOH and GaN nanomaterials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The growth mechanism of GaOOH and GaN was proposed. The results indicate that the as synthesized GaN were hexagonal nanorods with average aspects ratio of 5:1(diameter 800 nm and length about 4μm). Photoluminescence spectrum shows that a blue emission peak originates at 473.5 nm, indicating that the GaN nanorods displayed luminescence emission in the blue-violet region, which was related to crystal defects, and may be helpful for electro-optical applications of GaN material.

Synthesis of Layered-Ternary Ti2AlC/Al2O3 Composites by an In Situ Reaction and Hot Pressing Sintering

Mo modified Ti2A1C /Al2O3 composites were successfully fabricated from an elemental power mixture of Ti, Al, TiC and MoO3 by an in situ reaction/hot pressing method. The reaction path and effect of the molar ratio of the initial materials on the phase composition were investigated in detail. The as-prepared materials are mainly composed of (Ti1-xMox)2AlC solid solutions, Al2O3, and a small amounts of the Mo rich compounds. It is found that the in situ formed fine Al2O3 particles tend to disperse on the matrix grain boundaries. Compared with the monolithic Ti2A1C, (Ti,Mo)2AlC/10 wt% Al2O3 composite possesses a fine grain sized structure. The Vickers hardness, flexural strength, fracture toughness, and compressive strength of the as composite are 4.75 GPa, 458 MPa, 6.03 MPa·m1/2, 971 MPa, respectively.

Effect of Sintering Temperature on Al2O3/TiAl Composite from Ti-Al-TiO2-Eu2O3 System

In this work, the composites were fabricated by in-situ synthesis reaction and hot-pressing using Ti, Al, TiO2 and Eu2O3 as starting materials. Effects of the sintering temperature on the microstructures and properties of the Al2O3/TiAl composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and universal properties tests. The result shows that the sintering temperature had effect on improving the mechanical properties of TiAl composites. The phase of the composites composed of γ-TiAl/α2-Ti3Al matrix and reinforcing phases of Al2O3 and EuAlO3. The grain size of composite was smaller than 0.5 µm at 1200 °C. And the mechanical properties reached to the maximum value (477.96 MPa and 9.73 MPa•m1/2). The properties decreased with grain growth at 1300 °C.

High Purity Ti2AlC Powder Prepared by a Novel Method

Ti2AlC powders with high purity were successfully synthesized via high energy milling and heat treatment of Ti, C and Al powders. The effects of composition and thermal treatment on the formation and purity of Ti2AlC were examined in detail. The results shown a mechanically induced self-propagating reaction (MSR) was triggered to form Ti3AlC2, TiC and TiAlx during the high energy milling. When the as-milled powders were heat treated, Ti2AlC was initially formed by the reaction between TiAl and TiC. With continuously increasing temperature, Ti2AlC was also produced by the reaction between TiAl and Ti3AlC2.

Synthesis of Ti3AlC2 Powder by High Energy Ball Milling and High Temperature Heat Treatment

Highly pure Ti3AlC2 powder was fabricated by combination of high energy milling and heat treatment with Ti, C and Al as starting materials. The details of reactions and phase evolution in fabrication process were investigated. The results shown that the Ti-Al intermetallics, Ti3AlC2 and TiC were formed in high energy milling. The as-milled powders were heat treated subsequently, and the Ti3AlC2 powder with high purity was produced from the reaction among Ti-Al intermetallics, Ti3AlC2 and TiC at relative low temperature (1100 °C).

Reaction Synthesis of TiAl/Ti2AlC In Situ Composites

Full dense and highly pure TiAl/Ti2AlC in situ composites were successfully synthesized by reactive synthesis from the powder mixtures of Ti, Al and carbon black by hot-press-assisted reaction process. The reaction process, microstructure and bending strength of the TiAl/Ti2AlC in situ composites were investigated in detail. The results show that the as fabricated composites posses three phases, namely, TiAl, Ti3Al and Ti2AlC. The matrix phases are mainly equiaxed TiAl with a minor lamellar Ti3Al phase. Ti2AlC particles with size less than 1 μm are distributed uniformly in matrix grains as a reinforcing phase. When C content is 0.44 wt %, the flexural strength reaches 426.21 MPa, which is increased by 35 %.

Effect of Carbon Addition on the Microstructure and Mechanical Properties of the In Situ Formed TiAl/Ti2AlC Composites

TiAl/Ti2AlC composites were successfully fabricated by hot-press-assisted reactive synthesis method from elemental powder mixtures of Ti, Al and C. The effect of C addition on the microstructures and mechanical properties of TiAl/Ti2AlC composites was investigated in detail. The results show that the Rockwell hardness, flexural strength and fracture toughness of the composites are modified by incorporation of in situ formed Ti2AlC. When the C content was 0.44 wt %, the flexural strength and the fracture toughness reach the maximum values of 658.7 MPa and 10.03 MPa•m1/2, respectively. The reinforcing mechanism was also discussed.

The Effects of Calcium Fluoride Addition on Crystallization Characteristics of Hydroxyapatite-Zirconia Composite

Hydroxyapatite (HA) doped with 3% Yttria-stabilized 20vol%m-ZrO2 composite were synthesized by solid state reaction between tricalcium phosphate (TCP) and Ca(OH)2 at various temperature(1000 to 1200°C) for 3h with adding 5~20wt% calcium fluoride (CaF2), respectively. The effects of various amount of CaF2 on crystallization characteristics of HA-20vol%ZrO2 composite were investigated in details. The results show that when small amount of CaF2 was added, the reactions of HA with CaF2 occurs, which leads to the formation of fluorapatite (FA). With the increasing of the amount of CaF2, the decomposition of HA to β-TCP decreases gradually and the CaZrO3 peaks disappear, while t-ZrO2 increases because of the formation of thermally stable FHA solid solutions. When the sintered temperature is above 1100°C and the addition of CaF2 is about 10wt%, the main phases are FHA and t-ZrO2 with a negligible amount of Ca5P8, which suppress the reaction between HA and ZrO2. From SEM, it can be seen that with 10wt% of CaF2 addition, the morphology of the composite powder is a mixture of spherical ZrO2 particles embedded within agglomerated HA shaped like a small rod.

Microwave Hydrothermal Synthesis of ZrSiO4 Nano-Powders

High purity ZrSiO4 powders were prepared using zirconium oxychloride and tetraethoxysilane as raw materials by the microwave hydrothermal (M-H) method, in which NaF was added as mineralizer to promote the crystallization of zircon. The results show that the microwave-hydrothermal method greatly reduces the starting crystallization temperature of ZrSiO4 powders to 160~200 °C in 30 minutes, the characteristics of the microwave hydrothermally synthesized powders are superior to that synthesized by conventional hydrothermal in stability, purity and morphologies. And the XRD analysis shows that all peaks of the former powders are abnormal broadness except the (200) and (220) peaks, and the crystallization of powders can be improved by adding seed crystals of ZrSiO4. The ZrSiO4 particles are disk-like platelets which are monocrystal and have a trend of Single crystal to polycrystalline transition. The synthesis mechanism of ZrSiO4 by microwave hydrothermal (M-H) process is discussed.

Crystallization Characteristics and Microstructure of Yttria-Stabilized Zirconia / Hydroxyapatite Composite

Good crystallized Hydroxyapatite was synthesized using H3PO4 and Ca(OH)2 as raw materials by wet chemical method and sintered at 800°C for 3h. The as-prepared HA powders were mixed with 15%, 20%, 25% yttria-stabilized m-ZrO2, respectively, and sintered at 900°C- 1200°C for 1h, respectively. The main phases and rules of phases changing with the content of yttria-stabilized m-ZrO2 and sintered temperature was investigated by XRD and the microstructure features of the composite powders were analysed by scanning electron microscopy. The results show that when the temperature is at 1000°C, HA starts to decompose to β-TCP and CaO, the m-ZrO2 is then partly converted into t-ZrO2 by partial consumption of CaO, which in turn results in a mixture of β-TCP and HA further. The CaO produced reacts further with m-ZrO2 generating a mixture of t-ZrO2 and CaZrO3 in different proportions. The microstructure of the HA-ZrO2 composite further indicates that when sintered at 1000°C for 1h, gray slice area represent a mixture of HA and a small amount of β-TCP. While in the white area, some spheric ZrO2 mixed with a negligible amount of CaO. When sintered at 1200°C, distinguished reduced spherical ZrO2 particles embed within mixed HA and β-TCP, which change from slice to agglomeration. As a result, when the sintered temperature is about 1000°C and the addition of m-ZrO2 reaches 20wt%, superior main phases are HA and t-ZrO2, which improves the combination of mechanical and biological properties.