Papers by Author: Yong Huang

Abstract: A synthesis method of high-pure Ti3AlC2 powder with a large scale was presented as pressureless synthesis using TiC, Ti and Al powders as starting materials at 1300~1450°C in flow Ar. The different raw material scales were tested from 2 g to 1.0 kg, and the results showed that the purities of Ti3AlC2 powders could be kept around 97 wt% at different scales of raw materials. SEM observation and particle size analysis revealed that the synthesized Ti3AlC2 powders were uniform and around 5 μm in particle size. This method can be used for mass production of Ti3AlC2 powders with high-purity.

Abstract: A new method to synthesize high-purity Ti3AlC2 bulk material by hot-pressing was presented through adding a little amount of B2O3 as a low-temperature aid. The elemental Ti, Al, and active carbon powders were used as raw materials with a molar ratio of 3:1.2:2.The effect of sintering temperature on the purity of Ti3AlC2 was investigated at the range of 1200°C to 1500°C. XRD and SEM were used to characterize the product synthesized. High-purity Ti3AlC2 bulk materials, in which almost no TiC phase could be found, were synthesized by hot-pressing at 1400°C and 1500°C for 1h in flow Ar atmosphere. The roles of B2O3 addition were considered as weakening the thermal explosive reaction in the mixture of elemental Ti, Al, and active carbon and increasing the purity of Ti3AlC2 in addition.

Abstract: A two-step method was presented to fabricate Ti3AlC2-based ceramics. The first step was to synthesize a reactive powder, which mainly contains Ti2AlC, by pressureless sintering (PLS) in argon at 1500°C for 10 mins with a heating rate of 20°C×min-1. The second step was to hot press the powder to a bulk material at 1300°C for 60 mins. The second step not only densified the powder, but also promoted the phase transformation from Ti2AlC to Ti3AlC2. The ceramic sample prepared by this method consists of Ti3AlC2, Ti2AlC and a little amount of TiC. It has excellent mechanical properties: density is 4.26 ± 0.02 g×cm-3, flexural strength is 664.4 ± 90 MPa, Vickers hardness is 6.4 ± 0.5 GPa, and fracture toughness (KIC) is 9.9 ± 0.5 MPa m1/2. The so high values of strength and fracture toughness are never reported in any literature about this material, as far as we aware.

Abstract: Ti3SiC2 bulk materials by hot-pressing sintering were presented through adding a little amount of B2O3 as a low-temperature additive in different raw-material systems. In one system, elemental titanium, silicon and active carbon were used as reactants with a molar ratio of 3: 1: 2. In another one, titanium carbide, titanium and silicon reacted together with a molar ratio of 2:1:1. At different temperatures, samples were synthesized by hot-pressing with a heating rate of 30°C min-1 before 1200°C and then 10°C min-1 to peak temperatures, holding for 2h. The effect of sintering temperature on the purity of Ti3SiC2 was investigated at the range of 1200°C to 1500°C. The products mainly contained Ti3SiC2 with TiC as the second phase. In some cases, Ti5Si3 appeared as well. When sintered at 1300°C, above 98vol% Ti3SiC2 was obtained in the elemental system. The roles of B2O3 additive were considered as weakening the thermal explosion reaction in the elemental mixture and affecting the diffusion procedure at low temperature in both systems.

Abstract: The high-temperature mechanical properties were very important to structural materials, especially structural ceramics. Hence, the strength, elastic modulus, stress relaxation and creep behavior of the multilayer materials at elevated temperature were studied in this paper. According to the curves of mechanical properties varieties with temperature risen from room-temperature to 1300°C, the multilayer materials could remain relatively high mechanical properties until 1150°C. Otherwise, the creep function of the multilayer composites was also determined, in which the stress exponent was 1.4 and activation energy was 204kJ/mol. By contrasting to the monolithic ceramics of Al2O3 and Ti3SiC2, the main creep mechanisms include: interface diffusion creep (in Al2O3 layers), dislocation movement creep, grain delamination and sliding (in Ti3SiC2 layers).

Abstract: Laminated ceramics with high mechanical properties were fabricated in the Si3N4/BN system. The mechanical properties at elevated temperatures were tested, and the oxidation behavior during tested procedure was studied at the same time. The flexure strength of the Si3N4/BN laminated ceramics changed a little below 1000°C. The displacement-load curves appeared non-linear characteristic even at high temperature. During testing procedure at high temperature, oxidation behavior of silicon nitride and silicon carbide happened, and no oxidation product of boron nitride was found. The silicon nitride layers were oxidized to form a protective silicate scale, which prevented oxidation of the boron nitride interlayers. The stability of boron nitride was beneficial to the boron nitride interlayer to partition the silicon nitride matrix layers at high temperature.

Abstract: Pores in ceramics have their peculiarity different from common porous materials, so the existing characterization methods should be re-recognized. In the present work, thermal shrinkage curves adequately characterize the dynamic process of porosity evolution in ceramics, and the results are checked by Archimedes method. In order to detect pore-size distribution quantitatively, gas adsorption (BET method), mercury penetration and a new Scanning Acoustic Microscope (SAM) technique are used on Alumina ceramics with large and median pores. The results acquired by these three methods are discussed in detail and unified by the introduction of effective pore-size coefficient t. It shows that a complete characterization system adapt to pores in ceramics should be established.

Abstract: Colloidal injection moulding of ceramics (CIMC), an innovative technique combining the advantages of conventional injection moulding and colloidal forming process, is applied to prepare thin-wall rutile tube for high capacity ozone generator. The forming process is studied detailed and the processing parameter of forming, drying and sintering schedule is determined in this research. The wall thickness of the sintered tube is 1.5~2mm and its inner diameter is about 26 mm, length is about 300 mm. The electric properties of the tube are also measured under different conditions. The above-mentioned tube is applied in ozone generator and the yield of ozone is about 55mg·L-1.

Abstract: Polycrystalline silicon layers were grown on AlN ceramic substrates in a rapid thermal chemical vapor deposition system at high temperature (~1150°C). Larger columnar grains, > 5µm in size, were obtained by the zone melting recrystallization (ZMR) technique. The p-n junction is formed by a phosphorous diffusion process to make a solar cell. Solar cell devices based on this Si layer result possess an open-circuit voltage of about 0.17V and a short-circuit current of about 6.6mA/cm2.

Abstract: The thin-film of silicon deposited by RTCVD on pressureless sintered SiC substrate with the size of 30mm×20mm, which is cleaned by ultrasonic method and chemical treatment. The crystal size of silicon columnar grain can reach 190 µm and its preferred orientation is [111] after ZMR process.