Shi Bin Li

Effect of Adding Phase on the Properties of ZrB2 Based Ultra-High-Temperature Ceramics

ZrB2 belongs to a class of ceramics defined ultra-high-temperature ceramics with extremely high melting temperatures, but ZrB2 ceramics is difficultly sintered and easily oxidized. To make ZrB2 ceramics possess the high relative density and the better oxidation resistance. The effects of adding phase on the sintering and oxidation resistance mechanism of ZrB2 based high-temperature multi-phase ceramics were investigated. YAG and Al2O3 help for the densification of ZrB2 based ceramics. The oxidation layer thickness of sintered ceramics adding YAG or YAG-Al2O3 phase is thinner than that of sintered pure ZrB2 ceramics under the same oxidation condition, the oxidation layer thickness of sintered ceramics adding YAG-Al2O3 phase is thinner than that of sintered ceramics adding YAG phase, the oxidation layer thickness of sintered ceramics is decreased with an increased Al2O3 content.

Effect of Sintering Aids on the Properties of Porous YAG Ceramics

Yttrium aluminum garnet (YAG) with a chemical composition of Y3Al5O12 is an important advanced structural and functional material due to some excellent properties. The porous YAG ceramics were prepared via vacuum sintering technology, the effect of sintering aids on the properties of porous YAG ceramics were investigated in this paper. Through an analysis and discussion, the conclusions are that the porosity increases with the increasing sintering temperature from 1300°C to 1500°C, the pore is moved to the surface of sample, which forms the open pore to make the porosity increase, the more and bigger sintering neck is increased. Porous YAG ceramics are sintered at 1500°C, the regular outside shapes of porous YAG ceramic are kept using CaO and MgO as sintering aids, the outside shape of porous YAG ceramic is wrecked using Al2O3 as sintering aids, which shows the over fired phenomenon.

Synthesis Parameters of Ultrafine YAG Powder Materials via Hydrothermal Precipitation Method

YAG materials has a number of unique properties, the application is very extensive. In this paper, the superfine YAG powder materials were prepared by hydrothermal precipitation method. The influence of synthesis process on the morphology of the powder was investigated. The results showed that when the molar ratio of salt to alkali that Y3+: OH- is 1:8, the more uniform morphology of the particles can be prepared, when the molar ratio of salt to alkali is increased, the morphology of the particles will not change. The reaction time is longer, the particle size will be thicker. The smaller the concentration of Y3+ ions is, the larger the particle size will be small. The experimental results show that the rod-like particles have a poly-crystal structure at the reaction temperature of 200°C, reaction time of 2 days and the molar ratio of salt to alkali of 1:8. The diameter of the rod-like particles is most of the powders have a particle size of 1000 nm and a small amount of powder has a particle size of about 5000 nm. The purity of powder is higher through the test of XRD.

Preparation of YAM Coating on the ZrB2 Composites and their Ablation Resistance

The YAM coatings on the ZrB2 composites surface were prepared by co-precipitation technique and with Al (NO3)3 and Y(NO3)3 solutions acting as precursor. The effect of matrix surface treating conditions, dipping times and calcination temperature was investigated. Phase compostion, coating morphology and interface between matrix and coating were analyzed by XRD and SEM. The results indicated that the YAM coating was formed after calcined at 1250°C in vaccum. The thickness of coating was increased with the dipping times, the smoothest coating was obtained by two dipping times, and matrix surface coarsing was beneficial for improving the adhension between matrix and coating. The ablative teste was evaluated at 2000°C by oxy-acetylene flame, the ablative properties was obviously improved by coating compared with uncoated composites.

Oxidation Kinetics of ZrB2 Ceramic Matrix Composite Materials

Zirconium diboride is widely applied because of some excellent performances. The oxidation kinetics of ZrB2-YAG-Al2O3 composite materials were researched, which helps to improve the performance of ultra-high-temperature composite materials. The results show the oxidation weight gain is decreased with increasing the content of YAG-Al2O3 and the molar ratio of Al2O3. The oxidation weight gain is increased with prolonging the oxidation time under 1300°Cæ, the oxidation weight gain ratio is decreased with prolonging the oxidation time. The effecting tendency of oxidation weight gain is not abvious with varying the contend of YAG-Al2O3 upon 1300°Cæ, however, the effecting tendency of oxidation weight gain is very abvious with varying the molar ratio of Al2O3.

Effect of Auxiliary on the Dispersibility of ZrB 2 Powder in the Liquid

The composite ZrB2 powder coated A12O3-Y2O3 prepared by co-precipitation method were densified via the spark plasma sintering (SPS) and then researched the oxidation resistance at high temperature. ZrB2 powder must have the better dispersibility during the coating processing for obtaining the better coating effect. Effect of dispersant on the dispersibility of ZrB2 powder in the liquid is researched in this paper, the results show ZrB2 powder have the better dispersibility as the dispersant for PMAA and the content for 2vol%, which lay foundation for synthsising the better coating effect coated A12O3-Y2O3-ZrB2 composite powder.

Effect of Molding Pressure on Densification of Al 2 O 3 /Al Cermet Materials

Cermet materials is a important new engineering materials with the advantages of ceramics and metal materials. The Al2O3/Al cermet materials is prepared via the powder metallurgy method, the effect of sintering technology on properties of Al2O3/Al cermet materials is researched in this paper, which lay the base for preparing the high performance cermet materials. The results are shown through the study, the denstity of cermet is increased with an increasing moliding pressure, the sample density is 2.084g/cm3 as the pressure for 40MPa and the sintering temperature at 600¡æ, the density is higher, that is to say it is highest performance, the distribution of aluminum and alumina is most uniform. When the sintering temperature is higher, howerver, the molding pressure is lower, the lower density of the sample is shown, the aluminum is easier to overflow the surface of the sample.

Influence of Synthesis Process on Coated Properties of Al(OH)3-Y(OH)3/ZrB2 Composite Powders

Zirconium diboride (ZrB2) ceramics with high melting point, high hardness, good electrical and thermal conductivity, good neutron control and other characteristics, can be widely used in high-temperature structural ceramics, composite materials, electrode materials. In order to improve ZrB2 difficult densification and high-temperature oxidation, the properties of coated Al (OH)3-Y(OH)3/ZrB2 composite powders prepared by co-precipitation method were investigated in this paper, The conclusions are shown that the effect of coated composite powders is getting worse with the accelerated titration rates. the coating effect will be worse with the increasing reaction time. When the concentration of mixed solution is lower, the coated effect is better. When the synthesis condition is that the titration rate of 10ml/min, and the reaction time was 1h, mixed solution ion concentration of Y3+=0.119mol/L and Al3+=0.231mol/L, the coated effect of composite powders is better.

Mechanism of Controlled Pore Structure of Quartz Pore Gradient Materials

Pore gradient material has obvious uneven, making the material porosity, pore size and strength changes with the thickness of the material exhibits a special distribution, pore gradient material is therefore in the chemical industry, environmental protection, metallurgy, food, biotechnology and other industries widely used, it is a very promising new material. In this paper, low-grade quartz sand as the main raw material, by adding auxiliary ingredients, using foam deposition method, the pore graded material were prepared. Through experimental results and analysis, the conclusions can be obtained, quartz pore gradient material body after sintering at 1300¡æ posing obvious gradient structure. When the ratio of water to 1.4 and 1.5, the sample can be observed that there is a clear gradient structure. Considering the combination of price, quality quartz pore gradient material should be water feed ratio of 1.4, the sintering temperature is 1300 ¡æ more appropriate, the porosity of prepared quartz graded materials was 32.45%.

Densification Mechanism of Al2O3/Al Metallic Ceramics Prepared via Powder Metallurgy Method

Alumina ceramics with good mechanical and corrosion resistance, is one of the most widely used engineering ceramics. The aluminum has a high strength, high conductivity, high plasticity, etc. than aluminum ceramics used in more and more industries. In this paper, aluminum and alumina powder as raw material, mixing, forming, sintering and a series of processes for preparing the alumina/aluminum metallic ceramic materials, through performance testing and analysis can be found in the ratio of raw materials 50wt% Al, 50wt % Al2O3 relatively good moldability. After sintering, after measuring the density contrast is found better density in the pressing process pressure of 20MPa and holding pressure time for 20min. By comparing the sintering process, after the interface structure by scanning electron microscopy and found help improve density through the secondary sintering metallic ceramic materials.