Effect of phase composition on the thermal shock resistance of zirconia

Conclusions Products made on the basis of granular bodies from zirconium dioxide that has been completely stabilized in the cubic form or containing the monoclinic phase in a very limited quantity (about 8–10%), are unstable and unacceptable for operations in conditions where sharp periodic temperature changes or a high temperature gradient are possible.The presence of 20–40% monoclinic phase in the products guarantees a microcracked structure in the material, capable of resisting thermal impact. It also prevents growth in these microcracks during repeat heating and cooling of the material, as a result of volume changes connected with polymorphism of ZrO₂.The choice of the conditions for determining thermal shock resistance should be made bearing in mind the proposed service conditions for the material. Together with a determination of the thermal shock resistance using the heat-cycle method up to a weight loss of 20%, it is desirable to determine the residual strength of the material (tensile), and also to use the calculated coefficient of thermal expansion of the material obtained from its physicomechanical characteristics.Translated from Ogneupory, No. 1, pp. 42–49, January, 1968.     

添加剂对锆质定径水口烧结性能和抗热震性的影响

采用粉末成型工艺,以粒度为0.045mm的斜锆石粉和粒度均为0.154mm和0.074mm的MgO部分稳定电熔氧化锆和CaO部分稳定电熔氧化锆为原料,分别加入不同添加剂Y2O3、CeO2和Y2O3 CeO2,在300MPa的压力下成型,并于1720℃烧后制成锆质定径水口试样。结果表明通过合理控制颗粒级配和优化工艺参数,当添加剂中Y2O3和CeO2的含量(w)分别为0.6%和0.4%时,氧化锆的稳定率约为70%,同时可得到显气孔率低,体积密度高,抗热震次数≥5次的锆质定径水口。     

Study of thermal shock resistance of fired and unfired zirconia refractories

Conclusions Comparative studies were made of fired and unfired refractories based on zirconium dioxide. The fired refractories are more resistant to cracking. However, the unfired materials possess a higher resistance to the development of cracking which is noted during the registration of surface deformations in the process of destruction of the specimen; and this is confirmed by analytical criterial evaluation.The determination of the destructive drop in temperatures before the development of the first crack in specimens based on granular bodies should not be considered as a reliable evaluation of the thermal shock resistance of the refractories.A new method was developed for observing the nature of the failure in specimens during thermal loading.Translated from Ogneupory No. 1, pp. 52–56, January, 1973.     

Influence of mullite additions on thermal shock resistance of dense alumina materials. Part 2: Thermal properties and thermal shock behaviour

Abstract

The thermal properties and thermal shock behaviour of homogeneous, fine grained (≈ 0·5–2 µm), dense (≥ 98% of theoretical density) alumina–mullite (5–15 vol.-%) composites have been studied and compared with those of a reference alumina ceramic with similar microstructure. Thermal expansion (25–600°C) thermal diffusivity, and thermal conductivity (25–400°C) were determined and a correlation between these results and microstructural characteristics was established. On the basis of the predicted theoretical relative performance under thermal shock, one of the composites (10 vol.-% mullite) was chosen and the thermal shock behaviour on quenching was compared with that of the reference alumina. A test that accounts for the detrimental effect of mullite on the heat transfer properties of alumina has been proposed. The results obtained agree with the theoretical predictions. In particular, the composite material had a critical temperature increment for failure larger (～ 12%) than that of alumina.     

Nondestructive acoustic emission control of thermal shock resistance of mullite-corundum products

Translated from Steklo i Keramika, No. 1, pp. 25–27, January, 1988.     

Microstructure, mechanical properties and thermal shock resistance of plasma sprayed nanostructured zirconia coatings

Nanostructured yttria stabilized zirconia (YSZ) coatings were deposited by Atmospheric Plasma Spraying (APS). X-ray diffraction (XRD) was used to investigate their phase composition, while scanning electron microscopy (SEM) was employed to examine their microstructure. The coatings showed a unique and complex microstructure composed of well-melted splats with columnar crystal structure, partially melted areas, which resembled the morphology of the powder feedstock, and equiaxed grains. Vickers microhardness of nanostructured zirconia coatings was similar to that of the conventional ones and strongly depended on the indentation load. Otherwise, a higher thermal shock resistance was found. This effect was addressed to the retention of nanostructured areas in coating microstructure and to the corresponding high porosity.     

氧化锆对刚玉-尖晶石浇注料热震稳定性的影响

以刚玉、尖晶石、纯铝酸钙水泥和氧化铝微粉为主原料 ,研究了氧化锆对刚玉 -尖晶石浇注料热震稳定性的影响 ,并采用X射线衍射和扫描电镜分析了试样的相组成和显微结构。结果表明 :加入约 3%的氧化锆可以大幅度提高刚玉 -尖晶石浇注料的热震稳定性 ,但过多的氧化锆对刚玉 -尖晶石浇注料的热震稳定性不利 ;含锆刚玉 -尖晶石浇注料热震稳定性提高的机理为微裂纹增韧。     

Improvement in thermal shock resistance of gadolinium zirconate coating by addition of nanostructured yttria partially-stabilized zirconia

Gadolinium zirconate (Gd₂Zr₂O₇, GZ) as one of the promising thermal barrier coating materials for high-temperature application in gas turbine was toughened by nanostructured 3 mol% yttria partially-stabilized zirconia (YSZ) incorporation. The fracture toughness of the composite of 90 mol% GZ-10 mol% YSZ (GZ–YSZ) was increased by about 60% relative to the monolithic GZ. Both the GZ and GZ–YSZ composite coatings were deposited by atmospheric plasma spraying on Ni-base superalloys and then thermal-shock tested under the same conditions. The thermal-shock lifetime of GZ–YSZ composite coating was improved, which is believed to be mainly attributed to the enhancement of fracture toughness by the addition of YSZ. In addition, the failure mechanisms of the thermal-shock tested GZ–YSZ composite coatings were discussed.     

Effect of grain size and orientation degree on thermal shock resistance of BN-matrix textured ceramics under cyclic thermal shock

Hexagonal boron nitride (h-BN) has a typical two-dimensional flake structure, so the anisotropy of h-BN grains caused by directional arrangement cannot be ignored when studying the thermal vibration resistance of materials under thermal cycling. In this paper, h-BN-matrix textured ceramics prepared with different holding time were selected, and the effects of thermal vibration temperature difference and thermal cycles on the phase and thermal vibration resistance of h-BN-matrix textured ceramics were studied. The results show that under the condition of high-frequency thermal cycling, the residual strength ratio (RSR) of BN-based textured ceramics is closely related to the holding time and showing obvious anisotropy. At the same time, there is a thermal vibration temperature range in which the internal stress will change from relief to re-accumulation.     

添加剂对刚玉-莫来石质承烧板抗热震性的影响

以电熔莫来石为粗颗粒,α-Al2O3粉、硅线石粉和少量结合粘土等为基质,羧甲基纤维素为结合剂,分别添加钛白粉、锆英石粉及同时添加这两种粉体,经混合,液压成型,在1530℃保温2 h烧成制备了承烧板试样;研究了电熔白刚玉或莫来石中颗粒、钛白粉添加量(4%、6%、8%)、锆英石粉添加量(4%、6%、8%)及同时添加两种粉体(锆英石粉均为6%,钛白粉添加量分别为4%、6%、8%)对承烧板抗热震性能的影响.试验结果表明:以刚玉为中颗粒的试样的抗热震性能优于以莫来石为中颗粒的试样;在此基础上加入锆英石粉或钛白粉制成的试样的抗热震性会明显改善;当两者同时加入时,试样的抗热震性能改善更为显著.SEM分析显示:加入锆英石粉的试样析出锆石相,加入钛白粉的试样有钛酸铝生成,锆英石粉和钛白粉都添加的试样既存在锆石相,又生成钛酸铝晶体,这些相的存在使材料引入微裂纹和沿晶裂纹,有助于抗热震性能的提高.     

Evaluation of the thermal shock resistance of the coke oven dinas products according to the panel method

Conclusions It was established that the thermal shock resistance of the dinas products subjected to water quenching is lower than those undergoing air cooling.A decrease of the absolute value of the calculated index of thermal shock resistance C indicates an improvement of the thermal shock resistance of the dinas products. This is confirmed by the experimental data concerning the thermal shock resistance of dinas that were generated according to the panel method using a laboratory test stand.The dinas products having an open porosity of 19–21% and a density not exceeding 2.37 g/cm³ exhibit a high thermal shock resistance. Using the products possessing the aforementioned properties makes it possible to improve the service life of the lining in the zone of verticals (partitions) of the high-capacity coke ovens. The indicated property indices were incorporated in the standard concerning the coke oven dinas.Translated from Ogneupory, No. 3, pp. 10–13, March, 1992.     

沥青涂覆镁砂对MgO-C质底吹供气元件抗热震性的影响

为了提高顶底复吹转炉用MgO -C质底吹供气元件的使用寿命 ,研究了沥青涂覆量和沥青涂覆镁砂颗粒添加量对MgO -C砖性能的影响。结果表明 ,添加沥青涂覆镁砂颗粒能明显改善MgO -C砖的抗热震性能 ,同时在保证合理的体积密度、显气孔率和强度的基础上 ,得出了能够提高供气元件抗热震性能的合理配比方案为 :沥青涂覆量为 3% ,沥青涂覆镁砂和电熔镁砂的质量比为 1 1。MgO -C砖抗热震性能提高的原因是由于高温下沥青涂覆镁砂中的沥青炭化而在镁砂颗粒周围形成缝隙 ,这些缝隙能吸收和消除较多的变形能量     

抗热震抗侵蚀承烧座的研制

选用优质合成莫来石和电熔刚玉为骨料，加入复合添加剂，对骨料颗粒级配、中颗粒的加入形式、添加剂加入量、骨料与细粉比例等进行了研究，选出合理的配方，制得的承烧座符合磁性材料窑炉的使用条件，即抗热震抗侵蚀性能好，强度高。产品经用户试用，其寿命达到使用要求。     

Effect of humidity on the thermal conductivity of porous zirconia ceramics

This study focuses on the role of the water content on the effective thermal conductivity of porous ceramics placed in different conditions of relative humidity. Fully stabilized zirconia samples with variation in the capacity to take up water were prepared by varying the temperature of the thermal treatment. The pore volume fraction of the dried samples decreases from 56% down to 30%. Thermal conductivity measurements were made on samples placed in a chamber where the relative humidity was fixed between 3% and 99%. For all samples, the experimental values of the effective thermal conductivity increase significantly with the water content. Experimental results agree closely to analytical predictions based on the upper limit of the Hashin and Shtrikman expressions for calculating the thermal conductivity of the pores (constituted by air and water) and Landauer's effective medium expression for calculating the effective thermal conductivity of the material.     

Effect of particle grading on fracture behavior and thermal shock resistance of MgO-C refractories

Two types of MgO-C refractories with tight particle grading and non-tight particle grading were prepared according to Andreasen's continuous packing theory. Fracture behaviors were investigated using wedge splitting tests combined with digital image correlation method and acoustic emission techniques. The results indicated that MgO-C refractory with non-tight particle grading treated at 1400 ℃ had more in situ phases (e.g., AlN and MgAl₂O₄) and exhibited less brittleness than specimens with tight particle grading even though they had similar nominal tensile strengths. In contrast, specimens with non-tight particle grading had greater horizontal strain under various loading stages, reflecting their better ability to resist rupture deformation. In addition, more microcracks were initiated earlier in the pre-peak region, and more energy was consumed. The decrease in coarse particles and corresponding increase in fine powder content increased the interface between particles, benefiting for reducing the local stress concentration and improving the thermal shock resistance of refractories.     

Effect of MgO on thermal shock resistance of CaZrO3 ceramic

In order to improve the thermal shock resistance of CaZrO_3, CaZrO₃ was synthesized by a solid-state reaction method with analytical ZrO₂ and CaCO₃ as raw materials, and MgO as additive. The effects of MgO on Flexural strength at room temperature, thermal shock resistance, XRD and microstructure of CaZrO₃ were characterized. The results show that the grain growth of CaZrO₃ is inhibited and the thermal shock resistance of CaZrO₃ is improved by adding MgO. With the increasing of MgO, the flexural strength at room temperature of samples are improved due to the grain refinement. When the addition of MgO is 8%, the flexural strength at room temperature increases to 270.15?MPa. The thermal shock resistance of samples are improved by MgO deflecting and bridging cracks. When the addition of MgO is 4%, the residual flexural strength of samples is the maximum (26.94?MPa).