Thermal Shock Times Research Articles

Study on Thermal-Shock-Resistance of the Composite Coating of 20 Steel Substrate by Hot Dip Aluminum and Micro-Arc Oxidation

By combined process of hot dip aluminum and micro–arc oxidation, a multilayer composite coating was obtained on the surface of 20 steel plates. The micro-hardness, morphology, residual stress and thermal-shocking performance of the coating were investigated by HVS-1000 micro-hardness instrument, SEM, X-350 stress instrument and etc. The results showed that the micro-hardness of the coating appeared hard-soft-hard from surface to inner, the effective thermal-shock times of the coating was 130, its residual stress of the coating was 181.7 MPa after hot shock 80 times.

Effect of molar ratios of MgO/Al2O3 on the sintering behavior and thermal shock resistance of MgOAl2O3SiO2 composite ceramics

In order to determine the relationship between the property of MgOAl2O3SiO2 composite ceramics and molar ratios of MgO/Al2O3, especially the sintering behavior and thermal shock resistance, the MgOAl2O3SiO2 composite ceramics were fabricated with micro-size MgO, Al2O3 powder and nano-size SiO2 as main raw materials. The sample was characterized by phase analysis, densification and thermal shock times. Moreover, field emission scanning electron microscope was also conducted to study microstructure of the samples before and after thermal shock. Effect of different molar ratios of MgO/Al2O3 on the sintering behavior and thermal shock resistance of composite ceramics were investigated. The results showed that the sample possess better sintering behavior and thermal shock resistance with the molar ratio of MgO/Al2O3 equal to 2/1. Grains of periclase and spinel were directly bonded together, resulting in a dense and compact microstructure, and the bulk density of obtained sample reached 3.4 g/cm3. The microstructure of sample after thermal shock revealed that the crack propagation path was deflected and bifurcated, the main-crack propagation was restricted and more fracture energy was consumed, the thermal shock resistance of composite ceramics was greatly improved.

Study on preparation of thermal storage ceramic by using clay shale

Shale was used as main raw material for developing thermal storage ceramics. The samples were fabricated via semi-dry pressing followed by pressureless sintering. The result showed that the sample (75% shale, 10% kaolin, 10% potash feldspar and 5% soda feldspar) fired at 1080°C exhibited the best comprehensive performance. Ocular examination reveals that no cracks were observed after 30 cycle times thermal shock tests (wind cooling from 600°C to room temperature). The results presented that the high bending strength remained after 20 cycle times thermal shock tests but plummeted at the thirtieth time. Other properties were given as follows: bulk density: 2.60g/cm3; thermal conductivity: 2.33W/(m°C); and heat storage density: 578.50mJ/m3. XRD analysis indicated that the quartz and hematite were the main solid phases in the sample. Some isolated pores, quartz crystals, granular hematite crystals and needle-like mullite crystals were observed in the matrix according to the SEM (Scanning Electron Microscope) analysis. More pores were found with temperature rizing according to SEM analysis. The relatively high content of Fe2O3 contributed to the formation of the vitreous phase and favored the densification. Overall, the introduction of shale effectively reduced the firing temperature and performed the better thermal storage properties.

Effects of doping Al2O3/2SiO2 on the structure and properties of magnesium matrix ceramic

To improve the sintering properties and the thermal shock resistance of magnesium matrix ceramic, this work used micron-sized MgO as the main raw material and nano-Al2O3 and SiO2 as additives. Magnesium matrix ceramic was doped with different amounts of Al2O3 and SiO2 (Al2O3 and SiO2 at a molar ratio of 1:2) and sintered under standard atmospheric conditions. The effect of Al2O3/2SiO2 doping amounts on sintering properties, thermal shock resistance, phase composition, and microstructure of composite ceramic materials were investivigated. The results suggested that introducing Al2O3/2SiO2 could improve the sintering properties of magnesium matrix ceramic. The grain boundary migration of its periclase phase could be hindered by the magnesium aluminate spinel and forsterite formed by solid reaction including Al2O3, SiO2 addition, and the MgO itself. Furthermore, according to the mechanism of thermal expansion mismatching, with increasing Al2O3/2SiO2 addition, thermal shock times increased significantly, the number of ceramic internal micro-cracks increased after the thermal shock and the material fracture surface energy was improved. It is found that the way of transgranular combining intergranular fractures can decrease the stress concentration at the crack tips and hinder crack propagation. The secondary phase particles deflected matrix internal micro-cracks and the crack propagation path length thus increased, residual stress field were subjected to interference and energy dissipation mechanisms improved. Meanwhile, thermal shock times for the material were enhanced and the degree of densification increased with increasing sintering temperature.

Thermal shock behavior and infrared radiation property of integrative insulations consisting of MoSi2/borosilicate glass coating and fibrous ZrO2 ceramic substrate

An integrative insulation consisting of a MoSi2/borosilicate glass coating and a fibrous ZrO2 ceramic substrate was explored for applications up to 1673K. The MoSi2/borosilicate glass coating was prepared using the slurry dipping and subsequent firing method. The thermal shock behavior of the integrative insulation and the evolution of the surface morphology of the coatings for various thermal shock times were evaluated using confocal laser scanning microscopy (CLSM). The results revealed that the as-prepared coatings could maintain the dense structure and infiltrate into the substrate, forming a gradient structure and exhibiting good compatibility and adherence. After thermal cycling between 1673K and room temperature 15 times, the integrative insulation is also without micro cracks and spalling, and the weight loss is only 2.84%, revealing outstanding thermal shock performance. Additionally, the emissivity of the coatings reached 0.8 at room temperature, which was attributed to the synergistic effect of inter band absorption, crystal lattice vibration and the roughness of the coating. The gradual increase in the roughness resulted in the increase of the emissivity in 200–2500nm at room temperature, which was explained with a “circular grooves” model. These results imply that the integrative insulation can be a promising candidate material in high temperature application.

Preparation and properties of Fibre–Metal Laminates based on carbon fibre reinforced PMR polyimide

A novel Fibre–Metal Laminates (FMLs) based on carbon fibre reinforced PMR polyimide were prepared using a hot press process in this paper. Pre-treatment on the titanium surface were conducted prior to laminating. Scanning Electron Microscope (SEM) were used to observe the morphologies of the titanium and the cross-sections of the FMLs. SEM results showed that micro-roughness structures were formed on the titanium surface after anodization. This structure enhanced the interlaminar bond strength between titanium and polyimide. Flexural and Interlaminar shear (ILSS) tests showed that the FMLs possess excellent flexural and interlaminar properties at both room temperature and elevated temperature. Thermostability tests proved that the FMLs based on carbon fibre reinforced PMR polyimide offered excellent thermal properties. It is shown that no delamination appears between titanium layer and the fibre-reinforced polyimide layer after 1000 times thermal shock.

Determining the Thermal Shock Elastic Behavior of Mullite Ceramic Regenerator Material by Ultrasonic Testing

Mullite material is a material commonly used in honeycomb regenerator, because in the process of using material under big temperature difference effect, so have a great demand for its thermal shock resistance. The used mullite ceramics were made by the direct solid phase sintering method, and the modulus of elasticity of the mullite ceramics measured by ultrasonic pulse-echo method in a thermal shock and thermal fatigue experiment, respectively. In the air-cooling condition, the study found the mullite ceramic without thermal shock that the longitudinal wave velocity and shear wave velocity respectively 3970(m/s) and 2492(m/s). After 45 times thermal shock of temperature difference of 800°C, longitudinal wave velocity and shear wave velocity decreased to 3910(m/s) and 2457(m/s), and the value of the modulus of elasticity changed 1020MPa. By observing the change of the elastic modulus value rule, can know the elastic deformation of thermal shock on the material performance of thermal shock damage. Moreover, the results can provide the data basis for the calculation of the residual strength and the numerical simulation of thermal stress.

Microstructure and Thermal Shock Behaviour of Alumina Composite Ceramic for Heat Transmission Pipeline

Al2O3 composite ceramics materials used for heat transmission pipeline were prepared by pressureless sintering in air. Calcined bauxite, talc and commercial alumina powder were used as the main raw materials, partially stabilized zirconia was also added to improve the thermal shock resistance of the samples. The effects of composition and sintering temperature on density, phase composition, microstructure and thermal shock behavior of samples were evaluated. It shows that the B2 sample which was sintered at 1400 °C for 2 h has optimal properties with porosity 0.4%, bulk density 3.2 g•cm-3.The bending strength increases 19.46 MPa after 30 times thermal shock cycles from 1100 °C to room temperature. The main phases of B2 are corundum and spinel, meanwhile, a small amount of monoclinic zirconia and α-quartz are also detected according to XRD pattern. Microstructure analysis reveals that spinel crystals are interlocked by prismatic corundum crystals, bright white beaded monoclinic zirconia particles are distributed uniformly, and it is beneficial to improve the thermal shock resistance of sample.

Effect of Repeated Thermal Shock on Mechanical Properties of ZrB2-SiC-BN Ceramic Composites

ZrB2-20 vol.% SiC-10 vol.% h-BN (particles) ceramic composites (ZSB) were fabricated by hot pressing under inert gas protected. ZSB samples with mean size 75 × 55 × 40 mm3 were heated using current heating method and then cooled down to low temperature by circulating water. ZSB samples repeatedly went through thermal shock with 10–50 times under various conditions, respectively. Diverse effects on residual strength of ZSB at different experiment conditions (temperatures, thermal shock times, and heating rates) were investigated. The test results indicated that the residual strength of specimen materials all reached the maximum while the temperature was 1600°C and thermal shock number was less than 50 times. Because ZSB samples could not stand the extremely serious hyperoxidation at very high temperature (1800°C), the residual strength of samples decreased sharply. At 1600°C, when the thermal shock times was 20, ZSB samples' residual strength reached the maximum, but it decreased to the lowest point while the thermal shock times was 30. So we argued that the sensitive thermal shock number was 30. Finally, we analyzed the influences on samples residual strength generated by different heating rates at the same temperature and thermal shock number; the results showed that when heating rate was equal to cooling rate, the residual strength of specimen materials reached the maximum.

In-Situ Preparation and thermal shock resistance of mullite-cordierite heat tube material for solar thermal power

In order to improve the thermal shock resistance of solar thermal heat transfer tube material, the mullite-cordierite composite ceramic as solar thermal heat transfer tube material were fabricated by pressureless sintering using α-Al2O3, Suzhou kaolin, talc, and feldspar as starting materials. The important parameter for solar thermal transfer tube such as water absorption (Wa), bulk density (Db), and the mechanical properties were investigated. The phase composition and microstructure of the composite ceramics were analyzed by XRD and SEM. The experimental results show that the B3 sintered at 1 300 °C and holding for 3 h has an optimum thermal shock resistance. The bending strength loss rate of B3 is only 2% at 1 100°C by air quenching-strength test and the sample can endure 30 times thermal shock cycling, and the water absorption the bulk density and bending strength are 0.32%, 2.58 g·cm−3, and 125.59 MPa respectively. The XRD analysis indicated that the phase compositions of the sample were mullite, cordierite, corundum, and spinel. The SEM images illustrate that the cordierite is prismatic grain and the mullite is nano rod, showing a good thermal shock resistance for composite ceramics as potential solar thermal power material.

Preparation and Performance of Andalusite Bonded SiC Solar Heat-Absorbing Ceramics

Using andalusite, SiC, Su Zhou Kaolin and Guang Xi quartz as materials, andalusite bonded SiC heat absorbing ceramic was prepared by pressureless firing in the ceramic preparation process. The influence of gradient SiC on microstructure and properties of the samples were studied. Using the testing technology of XRD, SEM, and etc., physical and chemical properties, phase composition and microstructure were tested and analysised.The results indicate that andalusite bonded SiC heat absorbing ceramic, which prepared to have a low firing shrinkage rate, high refractoriness and a good microstructure. The best firing temperature of the best formula C4 is 1460°C, firing expansion rate is 0.98%, bending strength is 32.52MPa,porosity is 30.74%, bulk density is 2.05g·cm-3, refractoriness is 1650°C,growth rate of oxidation weight is 2.769mg·cm-2and have no crack after 30 times thermal shock. The bending strength has increased 11.15% after thermal shock. XRD analysis indicated that the main phase compositions are α-SiC, mullite and cristobalite.SEM studies show that there are many connected pores in the samples, the diameters of the pores are 10~20μm. Andalusite bonded SiC heat absorbing ceramic have a low firing expansion rate, high bending strength and good microstructure, which is suit for tower type solar thermal power generation.

Preparation of ASZ Thermal Storage Ceramics for Solar Thermal Power Generation

This paper aims to investigate the properties and microstructure of Al2O3-SiC-ZrO2(ASZ) composite ceramics for solar thermal power generation. The composite ceramics were prepared from α-Al2O3, partially stabilized zirconia (Y2O35.2 wt%) and silicon carbide fired at 1280 °C for 2 h through pressureless sintering. Influence of the contents of SiC and ZrO2on the performance of ASZ composite ceramics have been observed and extensively investigated via XRD, SEM, etc. The results revealed that the thermal shock resistance and high-temperature thermal properties would increase with the increase of the SiC content. No cracking occurred after 30 times thermal shock (from room temperature to 800°C with air cooling) while the bending strength after thermal shock test, the thermal expansion coefficient, the heat capacity, the thermal conductivity coefficient and the thermal conductivity were 76.99MPa (with a growth rate of 27.89% after thermal shock), 5.85×10-6°C-1, 1.05 kJ(kgK)-1, 0.01 cm2s-1, 2.26 W(mK)-1, respectively. The XRD patterns indicated that the main crystal phases included corundum, silicon carbide and zirconium silicate while the SEM images illustrated the well-grown crystal grains had the sizes distributed among 5-120 μm.Key words: Al2O3-SiC-ZrO2composite ceramics, Silicon carbide, Thermal properties,Microstructure, Solar thermal power generation

Research on Electrode Propertie of Heater for Planar Oxygen Sensor

Through screen-printing technology, we prepared heater which is used for planar oxygen sensor with YSZ solid electrolyte, alumina insulating layer and platinum(Pt) paste, then sintered at different temperatures.Analysis the properties of Pt electrode through aging time test and thermal shock test. The results show that 1100°C is the best sintering temperature for Pt electrode.Resistance and surface morphology of Pt electrode changed obviously with aging time increasing and 100 times thermal shock is not enough to affect the morphology of electrode and the change of resistance has no regularity.

Thermal shock behavior of nano-sized ZrN particulate reinforced AlON composites

Aluminum oxynitride (AlON) has been considered as a potential ceramic material for high-performance structural and advanced refractory applications owing to its excellent stability and mechanical properties such as high rigidity and good chemical stability. Thermal shock resistance is a major concern and an important performance index of refractories and high-temperature ceramics. While zirconium nitride (ZrN) particles have been proven to improve mechanical properties of AlON ceramic, the thermal shock behavior has not been evaluated yet. The aim of this investigation was to identify the thermal shock resistance and underlying mechanisms of hot-pressed 2.7% ZrN–AlON composites by a water-quenching technique over a temperature range between 225°C and 275°C. The residual strength and Young's modulus after thermal shock decreased with increasing temperature range and thermal shock times due to large temperature gradients and thermal stresses caused by abrupt water-quenching. The presence of nano-sized ZrN particles exhibited a positive effect on the improvement of both residual strength and critical temperature difference of AlON ceramic due to the toughening effects, the higher thermal conductivity of ZrN, the refined grain size and the reduction of porosity. Different toughening mechanisms including crack deflection, crack bridging and crack branching were observed during thermal shock experiments, thus effectively enhancing the crack initiation and propagation resistance and leading to a considerable improvement in thermal shock resistance in the ZrN–AlON composites.

Effect of Multiple-Binders on Properties of Al<sub>2</sub>O<sub>3</sub>-Based Ceramic Foam Filter

In this paper，Al2O3ceramic foam filters prepared by polyurethane sponge impregnation.The effect of multiple binders on properties of ceramic foam was studied . The results show that using 90g dihydrogen phosphate and 30g under the CMC 1350°C sintered alumina matrix ceramic foam filters are the best performance. The compressive strength of the Al2O3-based foam ceramics prepared with optimal multiple-binder and sintered at 1350°C could reach up to 1.697MPa. At the same time,it is obtained through test that the thermal shock times of sintered samples reached 5 by staying at 1100°C for 10 min.

Thermal shock behavior of nano-sized SiC particulate reinforced AlON composites

Aluminum oxynitride (AlON) has been considered as a potential ceramic material for high-performance structural and advanced refractory applications. Thermal shock resistance is a major concern and an important performance index of high-temperature ceramics. While silicon carbide (SiC) particles have been proven to improve mechanical properties of AlON ceramic, the high-temperature thermal shock behavior was unknown. The aim of this investigation was to identify the thermal shock resistance and underlying mechanisms of AlON ceramic and 8 wt% SiC–AlON composites over a temperature range between 175 °C and 275 °C. The residual strength and Young's modulus after thermal shock decreased with increasing quenching temperature and thermal shock times due to large temperature gradients and thermal stresses caused by abrupt water-quenching. A linear relationship between the residual strength and thermal shock times was observed in both pure AlON and SiC–AlON composites. The addition of nano-sized SiC particles increased both residual strength and critical temperature from 200 °C in the monolithic AlON to 225 °C in the SiC–AlON composites due to the toughening effect, the lower coefficient of thermal expansion and higher thermal conductivity of SiC. The enhancement of the thermal shock resistance in the SiC–AlON composites was directly related to the change of fracture mode from intergranular cracking along with cleavage-type fracture in the AlON to a rougher fracture surface with ridge-like characteristics, crack deflection, and crack branching in the SiC–AlON composites.

Preparation of ZrO<sub>2</sub> Composite Ceramics with High Thermal Shock Resistance

The physical and mechanical properties of nanometer ZrO2-ZrO2fiber composite ceramics were studied by introduction of ZrO2fiber. ZrO2composite ceramics at different sintering temperature was investigated by porosity and water absorption measurements, flexual strength and thermal shock resistance analysis. Results showed that ZrO2composite ceramics containing 15 wt% ZrO2fiber with sintering temperature of 1650°C exhibited good mechanical properties and thermal shock resistance. The porosity and the water absorption were 8.84% and 1.62%, respectively. The flexual strength was 975 MPa and the thermal shock times reached 31 times. Scanning electron microscope (SEM) was used to analyze the microstructure of ZrO2composite ceramics.

Fabrication and Properties of APS- and RTS-Sprayed TiB<sub>2</sub>/Mo<sub>2</sub>FeB<sub>2 </sub>Multiphase Ceramic Coating on Q235 Steel

A kind of TiB2/Mo2FeB2 composite powders for reactive thermal spraying (RTS) and atmospheric plasma spraying (APS) were prepared using Mo powder, Fe-B alloy powder, Fe powder and TiB2 powder. The TiB2/Mo2FeB2 composite ceramic coatings were synthesized and deposited by APS and RTS on Q235 steel. Microstructure and phases were investigated by X-ray diffraction (XRD) and scanning electrical microscopy (SEM). The thermal shock resistance, wear resistance and corrosion resistance were characterized with the relevant lab testing equipment. The result indicates that the coatings are composed of the major phases Mo2FeB2, TiB2 and α-Fe, a little of Fe2O3, FeO, and B2O3.The thermal shock times of RTS-sprayed coatings is 44, the corrosion resistance is 6.07 times than those of the substrate, respectively, while those of APS-sprayed coatings are 55 and 15.5, respectively. The mass loss of Q235 steel is 138.6g/m2, while the mass loss of the coatings with 30% TiB2 which were prepared by RTS is 28.0952g/m2, the mass loss of the coatings with 30% which were prepared by APS is 15.4028g/m2, when the testing load was 400N. Therefore, the coatings with 30%TiB2 prepared by APS possess better wear resistance than the Q235 steel substrate.

Thermal Shock Resistance of ZrO<sub>2</sub> Fiber/Al<sub>2</sub>O<sub>3</sub> Ceramics

The physical and mechanical properties of alumina (Al2O3) ceramics by introduction of zirconia (ZrO2) fiber were studied. ZrO2/Al2O3ceramics at different sintering temperature was investigated by porosity and water absorption measurements, flexual strength and thermal shock resistance analysis. Results showed that Al2O3 ceramics containing 15 wt% ZrO2fiber with sintering temperature of 1650°C exhibited good mechanical properties and thermal shock resistance. The porosity and water absorption were 7.4% and 0.69%, respectively. The flexual strength was 613 MPa and the thermal shock times reached 29 times. Scanning electron microscope (SEM) was used to analyze the microstructure of Al2O3 ceramics.

Preparation and properties of flame-sprayed Mo-FeB-Fe cermet coatings

The powders of Mo 2FeB 2 cermet were prepared with Mo powders, Fe-B alloy powders and Fe powders as raw materials. Mo 2FeB 2 cermet coatings were prepared on Q235 steel by reactive thermal spraying (RTS) method and heated at 1 000 °C in vacuum oven of 1 kPa for 5 h. The properties of coatings were investigated. The results indicate that Fe 2B appears after milling for 15 h in the powder at room temperature, a part of ternary borides (Mo 2FeB 2) are generated in powder sintered at 900 °C. The coatings are composed of the major phases Mo 2FeB 2 and a-Fe, a little of Fe 2O 3, FeO and some pores. The bonding strength between the substrate and the ceramic coating is 32.73 MPa, the thermal-shock times is about 43 and the wear resistance is enhanced by approximately 5.28 times compared with that of the substrate, respectively. The comprehensive properties of Mo 2FeB 2 cermet coatings can be improved further after vacuum heat-treatment at 1 000 °C for 5 h.