Development of Thermal Shock Resistant and Low Creep Bricks for Hot Blast Stove

The paper describes the ries with high thermal shock development of brick seresistance and low creep rate for hot blast stove, including research target and research plan on the basis of analysis on how to enhance the thermal shock resistance and to lower creep rate of the bricks. Efforts have been made on the selection of starting materials such as corundum, mullite, andalusite and sillimanite etc., together with some measures taken on multi-grade formulation, homogenizing of the matrix of bricks and addition of some special additives. The results indicated that the bricks were with characteristics such as higher thermal shock resistance of 〉 30 cycles under quenching in water from 1000℃, and creep rate of 0. 2 under 1400℃ for 20 -50hrs with load of 0.2 MPa. Now a series of products of this kind have been developed and produced. The application of the products in Wuhan Iron and Steel Co. showed very prospective results. Now most of domestic large sized blast furnaces say ≥- 1000m^3, including those of Baoshan Iron and Steel Co. , have selected the series products made by Gongyi No. 5 Refractories Head Factory（GYWN） for their hot blast stoves.

Thermal shock resistant 3D printed ceramics reinforced with MgAl_(2)O_(4) shell structure

The demand for the swirl nozzle with enhanced temperature resistance and lightweight properties is in-creasing as the thrust-to-weight ratio of aero-engines rises.The Al_(2)O_(3) ceramic swirl nozzle can maintain high strength in a hostile environment of high temperature and severe corrosion,while also meeting the requirements of aircraft to enhance efficiency and decrease weight.However,Al_(2)O_(3) ceramics are limited in their application for aerospace components due to their poor thermal shock resistance(TSR)stemming from their inherent brittleness.This work reported an innovative design and fabrication strategy based on photopolymerization 3D printing technology to realize the three-dimensional shell structure through element interdiffusion and nanoscale stacking of the reinforced phase.With this strategy,a novel type of the new dual-structure Al_(2)O_(3) ceramic composed of MgAl_(2)O_(4) shell structure and matrix could be con-structed in situ.The nano-sized MgAl_(2)O_(4) caused a crack passivation effect after the thermal shock,which could improve the strength and TSR of 3D-printed Al_(2)O_(3) ceramic.In addition,the effects of MgO content and sintering temperature on sintering behavior,flexural strength,porosity,and TSR of Al_(2)O_(3) ceram-ics manufactured by digital light processing(DLP)processing were systematically studied.The optimum overall performance of Al_(2)O_(3) ceramics was obtained at the sintering temperature of 1550℃and the MgO content of 1.0 wt.%,with a maximum flexural strength of 111.929 MPa and a critical temperature difference of 374.24℃for TSR.Based on the above research,an aero-engine swirl nozzle with high ther-mal shock resistance has been successfully prepared by ceramic 3D printing technology,which enhances high-temperature resistance and promotes lightweight design in aero-engine.

Preparation of micro-arc oxidation coatings on magnesium alloy and its thermal shock resistance property

In the NaAlO2-Na2SiO3 compound system, the ceramic coatings were prepared on magnesium alloy by micro-arc oxidation. The morphology, phase composition, and thermal shock resistance of the ceramic coatings were studied by scanning electron microscope, X-ray diffraction and thermal shock tests, respectively. The results showed that the ceramic coating contains MgO, MgAl2O4, as well as a little amount of MgESiO4. The thickness of the ceramic coatings increases with the current density increasing, when the current density is 12 A·dm^-2, the thermal shock resistance of the produced ceramic coating is the best. The hardness of the ceramic coating is up to 10 GPa or so.

Relationship Between Thermal Shock Behavior and Cutting Performance of a Functionally Gradient Ceramic Tool

Based on the deep understanding of the requirements of cutting conditions on ceramic tools, a design model for functionally gradient ceramic tool materials with symmetrical composition distribution was presented in this paper, according to which an Al 2O 3-TiC functionally gradient ceramic tool material FG-1 was synthesized by powder-laminating and uniaxially hot-pressing technique. The thermal shock resistance of the Al 2O 3-TiC functionally gradient ceramics FG-1 was evaluated by water quenching and subsequent three-point bending tests of flexural strength diminution. Comparisons were made with results from parallel experiments conducted using a homogeneous Al 2O 3-TiC ceramics. Functionally gradient ceramics exhibited higher retained strength under all thermal shock temperature differences compared to homogeneous ceramics, indicating the higher thermal shock resistance. The experimental results were supported by the calculation of transient thermal stress field. The cutting performance of the Al 2O 3-TiC functionally gradient ceramic tool FG-1 was also investigated in rough turning the cylindrical surface of exhaust valve of diesel engine in comparison with that of a common Al 2O 3-TiC ceramic tool LT55. The results indicated that the tool life of FG-1 increased by 50 percent over that of LT55. Tool life of LT55 was mainly controlled by thermal shock cracking which was accompanied by mechanical shock. While tool life of FG-1 was mainly controlled by mechanical fatigue crack extension rather than thermal shock cracking, revealing the less thermal shock susceptibility of functionally gradient ceramics than that of common ceramics.

Effect of Rare Earth on Thermal Shock Resistance of Steel 9Cr2Mo

The effect of rare earth elements on thermal shock resistance of cold roller steel 9Cr2Mo was investigated by means of X-ray diffractometry and optical microscopy. Experimental results show that the process of carbide precipitation of heat effect zone is restrained by adding RE elements in steel 9Cr2Mo. Therefore, thermal shock resistance of this steel can be improved.

Effect of Nano-ZrO_2 on Microstructure and Thermal Shock Behaviour of Al_2O_3/SiC Composite Ceramics Used in Solar Thermal Power

The Al2O3-ZrO2（3Y）-SiC composite ceramics used in solar thermal power were prepared by micrometric Al2O3,nano-ZrO2 and SiC powders under the condition of pressureless sintering.The bulk density and bending strength of samples with 10vol% nano-ZrO2 sintered at 1480℃ were 3.222 g/cm3 and 160.4MPa,respectively.The bending strength of samples after 7 times thermal shock tests （quenching from 1000℃ to 25℃ in air medium） is 132.0MPa,loss rate of bending strength is only 17%.The effect of nano-ZrO2 content on the microstructure and performance of Al2O3-ZrO2（3Y）-SiC composite ceramic was investigated.The experimental results show that the bending strength of samples with above 10vol% nano-ZrO2 content has decreased,because the volume expansion resulting from t-ZrO2 to m-ZrO2 phase transformation is excessive;Adding proper nano-ZrO2 would be contributed to improve the thermal shock resistance of the composite ceramics.The Al2O3-ZrO2（3Y）-SiC composite ceramic has promising potential application in solar thermal power.

Thermal Shock Resistance of Nano SiC-BN Composites

Nano SiC - BN composite powders were prepared by dissolving analytically pure H3BO3 and CO（ NH2 ）2 with the mole ratio of 1：2.5 in the absolute alcohol, adding 80% E-SiC with 0. 2 μm average grain size while stirring, firing at 850 ℃ in nitrogen （purity： 99. 99%, pressure： O. 92 -0. 93 MPa） for 15 h. Nano SiC -BN composite specimens were prepared by hot-pressed sintering the nano SiC - BN composite powder in N2 atmosphere with 0. 92 - 0. 93 MPa and at 30 MPa axial pressure for 0. 5 - 1 h at 1 750 - 1 800 ℃. The thermal shock resistance of nano SiC -BN composites was studied by three-point bending, TEM and SEM. The results show that, adding BN can decrease the modulus of elasticity of SiC materials, which improves thermal shock resistance;furthermore, because of the large difference of thermal expansion coefficient between matrix SiC and second phase hexa-BN, thermal mismatch effect results in intercrystalline delamination of h-BN grains and forming many micropores in composite ceramic, which can relax the thermal expansion caused by high tempera- ture effectively, and improve the thermal shock resistance significantly.

Preparation and Thermal Shock Resistance of Mullite Ceramics for High Temperature Solar Thermal Storage

Mullite thermal storage ceramics were prepared by low-cost calcined bauxite and kaolin.The phase composition,microstructure,high temperature resistance and thermophysical properties were characterized by modern testing techniques.The experimental results indicate that sample A3(bauxite/kaolin ratio of 5:5)sintered at 1620℃has the optimum comprehensive properties,with bulk density of 2.83 g·cm^(-3)and bending strength of 155.44 MPa.After 30 thermal shocks(1000℃-room temperature,air cooling),the bending strength of sample A3 increases to 166.15 MPa with an enhancement rate of 6.89%,the corresponding thermal conductivity and specific heat capacity are 3.54 W·(m·K)^(-1)and 1.39 kJ·(kg·K)^(-1)at 800℃,and the thermal storage density is 1096 kJ·kg^(-1)(25-800 mullite ceramics;sintering properties;high-temperature thermal storage;thermal shock resistance).Mullite forms a dense and continuous interlaced network microstructure,which endows the samples high thermal storage density and high bending strength,but the decrease of bauxite/kaolin ratio leads to the decrease of mullite content,which reduces the properties of the samples.

Effect of CaO doping on mechanical properties and thermal shock resistance of 10NiO-NiFe_2O_4 composite ceramics

The CaO doped 10NiO-NiFe2O4 composite ceramics were prepared by the cold isostatic pressing-sintering process, and the effects of CaO content on the phase composition, mechanical property and thermal shock resistance of 10NiO-NiFe2O4 composite ceramics were studied. The results show that the samples mainly consist of NiO and NiFe2O4 when content of CaO is less than 4%(mass fraction), bending strength increases obviously by CaO doping. Bending strength of the samples doped with 2% CaO is above 185 MPa, but that of the samples without CaO is only 60 MPa. Fracture toughness is improved obviously by CaO doping, the samples doped with 2% CaO have the maximum fracture toughness of 2.12 MPa ·m1/2 , which is about two times of that of the undoped ceramics. CaO doping is bad to thermal shock resistance of 10NiO-NiFe2O4 composite ceramics.

Relation Between Sintering Reactivity of Matrix and Thermal Shock Resistance of Ultra-low Cement Bonded Corundum-spinel Castables for Fired Purging Plugs

Purging plugs installed in the bottom of steel ladles are widely used for the secondary refining of high quality steel grades.The dynamic service conditions and temperature gradients caused by the cold inert gas blown through the plug during stirring create a strong thermal shock impact on the materials.This can affect its service life and restrict the safety and efficiency of steel making if the plug fails during use.In this work,the influence of the particle size distribution (PSD) and amount of reactive alumina on the sintering behavior of ultra-low cement bonded corundum-spinel based castables was investigated on lab scale.The relationship between sintering reactivity of matrix and thermal shock resistance of castables was evaluated in detail.Results show that the sintering of castables can be intensified by using finer reactive alumina.However,excessive sintering of the castable through finer reactive alumina is negative for thermal shock resistance.The microstructure characterization reveals that castables with more intense sintering show denser matrix structure,which is less effective in hampering crack propagation and therefore results in decline of their thermal shock resistance.

Effect of Fused MgO-ZrO_2 Clinker Addition on Thermal Shock Resistance of MgO-ZrO_2 Unfired Bricks

MgO -ZrO2 unfired bricks with ZrO2 content up to 8% at the interval of 2% were prepared, using fused magnesia （ MgO ： 97% ） and fused MgO - ZrO2 clinker （ ZrO2 ： 14. 33% ） as starting materials and phenolic resin as binder. The effects of ZrO2 content on thermal shock resistance （TSR） and other properties such as cold and hot modulus of rupture have been investigated. Re- sidual cold modulus of rupture ratio after heating at 1 000 ℃ and quenching by air blowing was adopted to characterize TSR. Addition of the MgO -ZrO2 clinker improves TSR, attributing to the microcrack toughening effect by thermal expansion mismatch between different phases. When ZrO2 content goes above 4%. the impro- ving effect tends to be moderate. The introduction of MgO- ZrO2 clinker can also improve the HMOR at 1 500 ℃, while the increased ZrO2 content reduces CMOR of the bricks prefired at 1 600 ℃, due to the thermal expansion mismatch effect. Compromising the overall properties, the optimal ZrO2 content for such magnesia based unfired brick is suggested to be 4%.

Thermal Shock Resistances of FeMnCr/Cr_3C_2 Coatings Deposited by Arc Spraying

Arc spraying with the cored wires was applied to deposit FeMnCr/Cr3C2 coatings on low carbon steel substrates, namely FM1, FM2 and FM3. Thermal shock resistances of the coatings were investigated to assess the influence of Cr3C2 content on thermal shock resistance. Characteristics of the coatings under thermal cycling test were studied by optical microscopy, field emission scanning electron microscope （FE-SEM） and energy dispersion spectrum （EDS）, X-ray diffraction （XRD）. The experimental results show that hardness of the coatings increases, bonding strength decreases slightly with increase of the Cr3C2 content of the coatings. As a result, FM2 coating possesses the best thermal shock resistance, attributing to its better thermal expansion matches and wettability than those of FM3 coating, less oxide rate than that of FM1 coating restraining from cracks formation and propagation in coatings.

Effects of Additive CeO_2 on Thermal Shock Resistance of Plasma-Sprayed Cr_2O_3 Coating

The influence of CeO2 with different content on the thermal shock resistance of plasmasprayed Cr2O3 coating was investigated. The thermal shock failure mechanism of coating was also studied. It is found that the thermal shock failure mechanism of coating is thermal stress fatigue destruction, and the destruction takes place at interface of ceramic and bond coating. The experimental results show that the lifetime of coating fracture and failure increase considerably when 3% CeO2 is added into the plasma-sprayed Cr2O3 coating. The suitable content of CeO2 makes the microcracks exist in network form. The microcrack net can release internal stress in coating, delay the crack forming and expanding and decrease holes in coating. Thus the thermal shock resistance increase largely.

Thermal Shock Resistance and Erosion Resistance of TiB_2 Multiphase Ceramic Composites

The thermal shock resistance and anti- aluminum erosion of TiB2 - BN multiphase ceramics composites were studied. The experimental results show that the TiB2-BN multiphase ceramic possesses a good thermal shock resistance at high temperatures （ 1000, 1200, 1400, 1500 ℃ ）, with the increasing in thermal shocking temperature, the electro-conductivity of TiB2-BN ceramics increases. The metal aluminum has a great influence on the properties of TiB2 - BN ceramics and the main reason is that the aluminum reacts seriously with BN. It is suggested that the content of BN should be reduced to the greatest extent.

Effects of mechanical boundary conditions on thermal shock resistance of ultra-high temperature ceramics

The effects of mechanical boundary conditions, often encountered in thermalstructural engineering, on the thermal shock resistance（TSR） of ultra-high temperature ceramics（UHTCs） are studied by investigating the TSR of a UHTC plate with various types of constraints under the first, second, and third type of thermal boundary conditions. The TSR of UHTCs is strongly dependent on the heat transfer modes and severity of the thermal environments. Constraining the displacement of the lower surface in the thickness direction can significantly decrease the TSR of the UHTC plate, which is subject to the thermal shock at the upper surface. In contrast, the TSR of the UHTC plate with simply supported edges or clamped edges around the lower surface is much better.

Crack Characteristic Measurement in Beryllium after Thermal Shock

he numbers and distribution of cracks in bulk beryllium which was loaded by intense electron beam were observed by optical image analysis, where the crack characteristic measurement and analysis were performed. The results show that: 1) The crack numbers in TR30 of beryllium with fine grain size and relatively high BeO content (no more than 3%) are about 2～4 times more than that in DShG200 of beryllium, whose grain size is larger but BeO content is less than 0.8%, under the same electron beam loading conditions, the ceramic phase of BeO in beryllium makes beryllium more brittle. 2) The successive electron pulse irradiation results in the wider cracks since the cracks formed by the former shot might be enlarged by following shots. The reason might be that there was a stress concentration at original cracks when the second shot came and so that thermal stress raised. DShG200 exhibit the better thermal shock resistance than that of TR30.

Properties and appropriate conditions of stress reduction factor and thermal shock resistance parameters for ceramics

Through introducing the analytical problem of the plate with convection into the solution of the transient heat conduction thermal stress field model of the elastic plate, the stress reduction factor is presented explicitly in its dimensionless form. A new stress reduction factor is introduced for the purpose of comparison. The proper- ties and appropriate conditions of the stress reduction factor, the first and second ther- mal shock resistance （TSR） parameters for the high and low Biot numbers, respectively, and the approximation formulas for the intermediate Blot number-interval are discussed. To investigate the TSR of ceramics more accurately, it is recommended to combine the heat transfer theory with the theory of thermoelasticity or fracture mechanics or use a numerical method. The critical rupture temperature difference and the critical rup- ture dimensionless time can be used to characterize the TSR of ceramics intuitively and legibly.

Fabrication and plasma arc thermal shock resistance of HfB_2-based ultra high temperature ceramics

Two hafnium diboride based ceramic matrix composites containing 20% （volume fraction） SiC particle and with or without AIN as sintering additives were fabri,aated by hot-pressed sintering. The mechanical properties and microstructures of these two composites were tested and the thermal shock resistances were evaluated by plasma arc heater. The results indicate that the composite with A1N as sintering additive has a denser and finer microstructure than composite without sintering additive, and the mechanical properties, thermal shock resistance of the composite with A1N as sintering additive are also higher than those of the composite without A1N. Microstructure analysis on the cross-section of two composites after thermal shock tests indicates that a compact oxidation scale contains HfO2 and Al2O3 liquid phase is found on the surface of composite with A1N, which could fill the voids and cracks of surface and improve the thermal shock resistance of composite.

Thermal Shock Resistance of Bauxite-based β-Sialon Bonded Corundum Materials

Thermal shock resistant properties of reaction sintered bauxite-based β-Sialon bonded corundum have been investigated, and the results are compared with those of Al_ 2O_ 3 based counterpart. It is found they all have very good thermal shock resistance. Their residual strength ratios after one thermal shock cycle at ΔT=1200℃ and ΔT=1350℃ are 61%~73% and 53%~65% respectively. Their critical temperature difference (TSR) is 600℃~800℃. TSR parameters are calculated based on thermal expansion, modulus of elasticity, and fracture toughness determined. The reasons for improving TSR of these composite materials are discussed.

Refractories with Improved Thermal Shock Performance Serving Low Carbon Economy

Nanoengineered carbon bonded refractories as well as fine grained carbon free refractories with improved thermal shock performance are presented in terms of this contribution.