Effect of Surface Oxidation at 1500 °C on Flexural Strength and Thermal Shock Resistance of the ZrB2-SiC-ZrC Ceramic

2013 ◽  
Vol 712-715 ◽  
pp. 115-118
Author(s):  
Min Wang ◽  
Zhi Wang ◽  
Shi Chao Li ◽  
Jian Zhang ◽  
Bao Shuai Zhang
Keyword(s):  
Flexural Strength ◽  
Thermal Shock ◽  
Oxide Layer ◽  
Thermal Shock Resistance ◽  
Surface Oxidation ◽  
Isothermal Oxidation ◽  
Before And After ◽  
Shock Resistance ◽  
Original Strength ◽  
Effect Of Surface

The isothermal oxidation of the ZrB2-SiC-ZrC ceramic was carried out in static air at a constant temperature of 1500±15 oC for 20 min. Compared with the original strength of 580 MPa, the strength of the oxidized specimen increased to 655±45 MPa, because the flaws in the surface of the specimen were sealed by the oxide layer. The thermal shock resistance of the specimens before and after the oxidation was measured by the water quenching. The measured ΔTcritfor the oxidized specimen was 641 oC that was obviously greater than 348 °C for the unoxidized specimen. The improvement in the thermal shock resistance was attributed to the formation the oxide layer on the surface of the specimen. The results here pointed to a promising method for improving strength and thermal shock resistance of ZrB2-based ceramics.

Evaluation of Thermal Shock Resistance of Alumina Ceramics

2011 ◽  
Vol 492 ◽  
pp. 333-336
Author(s):  
Kai Li ◽  
Lu Cun Guo
Keyword(s):  
Flexural Strength ◽  
Thermal Shock ◽  
Temperature Difference ◽  
Thermal Shock Resistance ◽  
Alumina Ceramics ◽  
Sharp Drop ◽  
Quenching Temperature ◽  
Before And After ◽  
Shock Resistance ◽  
Thermal Shock Behavior

The thermal shock behavior of alumina ceramics tested by two different approaches, water and air quenching, using an automatic experimental set was investigated. The changes of the flexural strength before and after the thermal shock was measured and used as an indicator of thermal shock resistance. The study reveals that air quenching test has limited impact on the changes of flexural strength, whereas the water quenching yields considerable decreases of the strength. The alumina ceramics was quenched in water at various temperature differences for five cycles. It is shown that the retained strength of the quenched specimens decreases abruptly at the temperature difference of 300°C, which indicates a great severity of thermal shock in this point. The thermal shock behavior of the specimens is evaluated by quenching in water as three different temperature differences, ΔT, setting at 300°C, 600°C and 800°C, respectively. The results show, for three different ΔT quenches, the strength reductions caused by the quenching exhibit similar trends: After a sharp drop, the residual strength remains almost unchanged at a certain level for each given quenching temperature difference, and the turning points all fall in the very first five to ten thermal cycles range. And the rank of the damage severity of alumina ceramics among the three different temperature differences is: ΔT800°C > ΔT600°C > ΔT300°C

Properties of Ceramic Coatings on the Wall of Coke Oven

2011 ◽  
Vol 189-193 ◽  
pp. 1105-1108
Author(s):  
Shu Xian Liu ◽  
Li Li Shen ◽  
Qian Ping Wang
Keyword(s):  
Thermal Shock ◽  
Thermal Shock Resistance ◽  
High Hardness ◽  
Coke Oven ◽  
Ceramic Coatings ◽  
Good Adhesion ◽  
Before And After ◽  
Shock Resistance ◽  
Uncoated Specimen ◽  
Better Than

Flame sprayed ceramic coatings on the wall of coke oven are characterized before and after melting. The attempt has been made to investigate thermal shock resistant, carbon deposit resistant, wear resistant of the coated and melted samples. The techniques used are SEM and XRD. The results show that: 1) Presence of quartz, corundum and mullite are identified in the surface of the coated specimen. Good adhesion between the coating and the substrate is caused by presence of quartz which is the same content as the substrate.2) The thermal shock resistance cycles of the coating samples are 15 ~ 30 times, but uncoated samples are only 1~2 times. The main reason is that he coating–substrate interface shows no gaps or cracks, and it has a characteristic feature of good adhesion between the coating and the substrate. 3) The wear resistance of the coated samples are better than that of the uncoated samples because glass-coating is more smooth than the uncoated specimen and the mullite and corundum in the coating have the high hardness value that makes the hardness of the coating increased.

Effect of AlF3 Content on Microstructure and Properties of Mullite/Al2O3 Composite Ceramics

2018 ◽  
Vol 922 ◽  
pp. 62-67
Author(s):  
Ke Zheng Sang ◽  
Fan Wang ◽  
De Jun Zeng ◽  
Hong Wei Li
Keyword(s):  
Fracture Toughness ◽  
Flexural Strength ◽  
Thermal Shock ◽  
Thermal Shock Resistance ◽  
Diameter Ratio ◽  
Pressureless Sintering ◽  
Composite Ceramics ◽  
Microstructure And Properties ◽  
Shock Resistance ◽  
Mullite Whiskers

To reinforce the mullite/Al2O3 composite ceramics through formation of mullite whiskers, the composite ceramics were prepared by pressureless sintering using different AlF3 content. The microstructure, porosity, fracture toughness and thermal shock resistance of the composite ceramics were investigated. The results show that the addition of AlF3 can promote the mullite whisker formations, and the whiskers with the size of 3～10μm in diameter and a length-diameter ratio of 10～15 are obtained by sintering at 1600°C with the AlF3 content of 5wt%. Fracture toughness and thermal shock resistance of the composite ceramics are improved by the formation of mullite whisker. The fracture toughness of 4.79MPa•m1/2 can be obtained, and the 95.18% flexural strength remained after thermal shock.

Preparation and Performance of β-Sialon Bonded ZrO2 Composites

2011 ◽  
Vol 415-417 ◽  
pp. 138-141
Author(s):  
Rui Sheng Wang ◽  
Jun Hong Zhao ◽  
Ying Na Wei ◽  
Fu Hua Peng ◽  
Heng Yong Wei
Keyword(s):  
Thermal Expansion ◽  
Flexural Strength ◽  
Thermal Shock ◽  
Thermal Shock Resistance ◽  
Reaction Sintering ◽  
Sintering Process ◽  
Carbon Addition ◽  
Shock Resistance ◽  
And Performance ◽  
Sialon Powder

β-Sialon bonded ZrO2 composites were prepared by reaction sintering process using β-Sialon and CaO stabilized ZrO2 powders as raw materials.The effect of β-Sialon powder additions on the properties of the composites was investigated. The results show that the samples with 10 wt% of β-Sialon addition had the lowest apparent porosity (29.80%) and the highest of flexural strength (68.70MPa). The thermal shock resistance in carbon addition of the composites could be improved by addtion of 5wt% β-Sialon. It may be relative with that the sample had the lowest thermal expansion coefficient in vacuum.

Fabrication, Microstructure, and Properties of Zirconium Diboride Matrix Ceramic

2013 ◽  
pp. 354-412 ◽  
Author(s):  
Zhi Wang ◽  
Zhanjun Wu
Keyword(s):  
Thermal Stress ◽  
Thermal Shock ◽  
Thermal Shock Resistance ◽  
Zirconium Diboride ◽  
Isothermal Oxidation ◽  
Rate Of Change ◽  
Oxide Layers ◽  
Sic Ceramic ◽  
Shock Resistance ◽  
Quenching Method

The crystal structure, synthesis, and densification of zirconium diboride (ZrB2) are summarized in detail. In this chapter, ZrB2-ZrC-SiC ceramic was synthesized by reactive hot pressing a mixture of Zr, B4C, and Si powders. The thermal shock resistance of the ZrB2-SiC-ZrC ceramic was estimated by the water-quenching method and was significantly greater than that of a ZrB2-15vol.% SiC ceramic. The isothermal oxidation of the ZrB2-SiC-ZrC ceramic was carried out in static air at constant temperatures of 1000±15, 1200±15, and 1400±15 ºC for different amounts of time at each temperature. The mechanism of strength increase for the oxidized specimen indicated that the strength increased with the reaction rate, which was related to the rate of change in volume induced by reaction, initial crack geometry, elastic modulus, and surface free energy. The formation of oxide layers resulted in (I) repair of surface flaws, (II) increase in flexural strength, (III) appearance of a compressive stress zone beneath the surface oxide layers, (IV) decrease in thermal stress, and (V) consumption of thermal stress. These five aspects were favorable to the improvement of the thermal shock resistance of the ZrB2-SiC-ZrC ceramic. The isothermal oxidation of the ZrB2-SiC-ZrC ceramic was carried out in static air at 1600±15 ºC. In the different oxidation stages, quantitative models were proposed for predicting oxidation kinetics.

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