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Preparation of ZnAl2O4 and its effect on fatigue resistance of alumina castables Preparation of ZnAl2O4 and its effect on fatigue resistance of alumina castables
Lv, Lihua; Wang, Zhanmin; Cao, Xiying; Han, Shuang; Ju, Chaochao; Han, Jun
2023-04-03 00:00:00
JOURNAL OF ASIAN CERAMIC SOCIETIES https://doi.org/10.1080/21870764.2023.2186006 RESEARCH ARTICLE Preparation of ZnAl O and its effect on fatigue resistance of alumina castables 2 4 a,b b b a a c Lihua Lv , Zhanmin Wang , Xiying Cao , Shuang Han , Chaochao Ju and Jun Han The Cultivation Base of Shanxi Key Laboratory of Mining Area Ecological Restoration and Solid Wastes Utilization, Shanxi Institute of Technology, Yang Quan, Shanxi, China; State Key Laboratory of Advanced Refractories, Sinosteel Luoyang Institute of Refractories Research Co., Ltd, Luoyang, Henan, China; Institute of Refractories, Comprehensive Inspection and Testing Center, Yang Quan, Shanxi, China ABSTRACT ARTICLE HISTORY Received 2 December 2022 Refractories subject to loading and unloading repeatedly because of physical effects and Accepted 25 February 2023 thermal stress attack in the service process, which is an important issue shortening the service life of the thermal equipment. Therefore, researches of predicting the service life of refractories KEYWORDS under cyclic loading have the guiding significance. The present work investigated the synthesis ZnAl O ; alumina castables; 2 4 of ZnAl O and discussed its effects on the alumina castables. The results show that the 2 4 cyclic loading; hysteresis optimized generation temperature of ZnAl O phase is 1400°C and the hysteresis loop in the loop 2 4 curves of cyclic loading reveals a general trend of first sparse and then dense. The cycle times of the specimen with 3 wt.% ZnAl O is 50 times, and the time from starting to loop to fracture is 2 4 about 4300 s. The fatigue resistance of the specimen with 3 wt.% ZnAl O is superior to ZA-0 2 4 and ZA-1.5. The new method of cyclic loading was innovatively adopted in refractories, which provide data and theoretical support for the thermal shock evaluation methods. 1. Introduction excellent physical and chemical characteristics that benefit special by the structure including high hard- Carbon peaking and carbon neutrality is an important ness, high melting points (1950°C), low thermal expan- measure to break the serious problems of resource and sion coefficient (25–900°C, 7.0 × 10–6/℃), good environmental constraints faced by the world. chemical attack resistance and strong slag resis- Castables with properties approaching those of tance [7,8]. shaped refractories, have quicker and cheaper installa- Refractories subject to loading and unloading tion, and need not sinter. As people increased regard repeatedly because of physical effects and thermal on environment protection, the development of stress shock in the service process, which is coin- castables has become an inevitable trend in the refrac- cided with the fluctuation of the process para- tories field. The performance of castables is usually meters or the production cycles of the furnace stable [1,2]. Also, it is much quicker and easier to [9–11]. Fatigue damage and even breaking are build compared with shaped refractories. Castables prone to occur in refractories under the repeated are widely used for thermotechnical equipment in loading, which will affect the service life of the iron and steel making industry, such as steel ladle thermal equipment. Therefore, researches of pre- linings, tundish linings, iron runner, and torpedo car dicting the service life of refractories under cyclic linings, et al. Recently, the development of castables loading definitely have the guiding significance. has contributed to a rapid increase in the field of iron The above questions have been analyzed by and steel making, especially in Japan, where the con- many researchers. K. Andreev et al. [12] discussed sumption of castables has increased to more than alternative methods to assess thermal shock in 75% [3]. refractories. Methods involve repetitive thermal There have been numerous researches [4–6] inves- shock tests, cyclic strain controlled fatigue experi- tigating the influence of MgAl O spinel on castable 2 4 ments and fracture mechanical experiments of properties, including the effect on grain size, density, monotonic loading. The results showed that strain chemical composition, hot strength and spalling resis- tolerance is a property correlating the results of tance and et al. However, research on the effects of the alternative test methods and those from the ZnAl O gahnite on the alumina castable properties is 2 4 service loads. The mechanical behavior of cement rather little. ZnAl O , same spinel compounds as MgAl 2 4 2 concrete refractory, a quasi-brittle material, was O , belongs to the cubic lattice system. The general 4 studied by F. Thummen et al. [13] under the tensile structural formula of spinel is AB O . Spinels have 2 4 cyclic and static loading at room temperature. The CONTACT Zhanmin Wang wangzm@lirrc.com State Key Laboratory of Advanced Refractories, Sinosteel Luoyang Institute of Refractories Research Co., Ltd, Luoyang, 471039, Henan, China © 2023 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of The Korean Ceramic Society and The Ceramic Society of Japan. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The terms on which this article has been published allow the posting of the Accepted Manuscript in a repository by the author(s) or with their consent. 2 L. LV ET AL. results suggest that maximum stresses are the pre- reducer (p108, Wuhan Shanda Co., LTD) were used dominant influencing factors. In addition, T. Xu as the raw materials. The constituents of high alu- et al. [14] performed the damage and fracture mina castable samples are shown in Table 1. Calcium tests on sandstone at different upper and lower aluminate cement was used as the binder. All the stress ratios. The results indicated that the hyster- raw materials in certain proportion were mixed and esis loop in the damage failure curve of the model cast in metal molds. The dimensions of all the speci- presents the characteristics of “sparse-dense- mens were 40 mm × 40 mm × 160 mm. The green sparse”, and the upper limit stress is one of the samples were cured at room temperature for 24 h important factors affecting the fatigue life of the in airtight containers, then dried at 110°C in drying sandstone. However, the above mentioned works oven for another 24 h before firing. The samples mainly investigated the compressive fatigue beha- were fired for 3 h at 1500°C in a laboratory electric vior of refractories. In the actual application, the furnace in air atmosphere. working conditions of refractories are poor, which acted pull and pressure forces. It is believed that 2.3. Characterization and testing the bending force in the cyclic loading should be feasible to research the fatigue impairment. And, X-ray diffraction (XRD, Aeris, Panaco Co., Netherlands) mechanical cycle tests can simulate several thou- was used to determine the phase compositions of the sand cycles, while, the traditional damage tests for specimens. Scanning electronic microscope (SEM, JSM- refractories only recycle several times. Therefore, 1T200, Japan Electronics Corporation) was used to the bending cyclic tests are more functional for observe the microstructures of the specimens. The studying fatigue degradation. distribution of powder clusters of ZnAl O was mea- 2 4 In the present research, ZnAl O gahnite powders sured by of laser granularity analyzer (Rise-2018, Jinan 2 4 were fabricated from ZnO and Al O , using solid state Rise Science & Technology Co., Ltd.). The three-point 2 3 sintering technology. Furthermore, the effect of ZnAl bending test and mechanical cyclic test were con- O graphite content on the mechanical properties and ducted at ambient temperature with a universal tester fatigue characteristics of the alumina castables was (WD-P4105, Jinan Puye Electromechanical Technology investigated by cyclic loading method. Co. Ltd). The loading rate of the three-point bending test is 0.2kN/S. Mechanical Cyclic test was conducted with triangle loading waveform, as shown in Figure 1. 2. Materials and experiments σ is the maximum stress of cyclic load, taking 0.94σ max (σ is the rupture strength of the specimen). σ is the min 2.1. Preparation of ZnAl O powders 2 4 minimum stress of cyclic load, taking 0.2σ. Firstly, the The raw materials, alumina (Al O , Purity≥99.0%, 2 3 specimens were loaded to the lower limit stress with <74um) and Zinc oxide (ZnO, purity ≥ 99.0%), were the constant loading speed of 0.5 mm/min. Then, the purchased from Sinopharm Chemical Reagent Co. Ltd mechanical cyclic tests were carried out in triangle (Shanghai). The molar ratio of Al O to ZnO is 1:1 2 3 loading waveform until the specimens breaking. The according to the chemical formula of ZnAl O . The 2 4 present work focuses on the fatigue characteristics of raw materials ZnO and Al O were mixed thoroughly 2 3 high alumina castables with different contents of ZnAl in a ball mill, then sintered at 1400°C for 4 h. O powders. Additionally, to better investigate the formation pro- cess of ZnAl O powders, ZnO and Al O , were sintered 2 4 2 3 at 900°C, 1000°C, and 1200°C. 2.2. Preparation of high alumina castables Fused alumina (98% wt% Al O , 8–5, 5–3, 3–1, 1-0 2 3 mm, 320 mesh; Henan, China), the prepared ZnAl O 2 4 powders, activated Al O (99%wt%, CL370), water 2 3 Table 1. Constituents of high alumina castable samples. Ingredient(wt.%) ZA-0 ZA-1.5 ZA-3 Fused alumina 75 75 75 Alumina powder 10 8.5 7.0 ZnAl O gahnitel powder - 1.5 3.0 2 4 Active alumina powder 10 10 10 P108 +0.1 +0.1 +0.1 Figure 1. Schematic diagram of triangle loading waveform. CA80 5 5 5 Water +4.6 +4.6 +4.6 JOURNAL OF ASIAN CERAMIC SOCIETIES 3 ZnAl O powder products have agglomerate struc- 2 4 tures as well as the raw material Al O . While ZnO has 2 3 short rod-like structure. This results conform with that obtained from previous research [15], further demon- strating the diffusion ability of the various atoms as 2+ 3+ 2- follows: Zn ＞Al ＞O . It means that the diffusion rate of Al O is lower than that of ZnO during the 2 3 reaction. Hence, ZnO diffuses onto the surface of Al O and reacts in situ to generate ZnAl O phase. This 3 2 4 explains that the formed ZnAl O has similar morphol- 2 4 ogy and particle size to the original Al O powders. The 2 3 particle size distribution curve is shown in Figure 4. It can be seen that the average particle size of the synthesized ZnAl O powders is about 80 um. 2 4 Figure 2. Full XRD patterns of the synthesized powders. 3.2. Mechanical and physical characteristics 3. Results and discussion The results of physical properties (apparent porosity 3.1. Microstructural characterizations of and bulk density) and mechanical properties (cold synthesized powders modulus of rupture and cold crushing strength) of the high alumina castables containing different con- The mixture of ZnO and Al O with the molar ratio of 1:1 2 3 tent (0, 1.5 wt%, 3 wt%) of ZnAl O , were shown in 2 4 was placed at 900°C, 1200°C, and 1400°C in the electric Figures 5 and 6. It can be seen that the values of furnace for 4 h to identify the reaction at high tempera- apparent porosity decrease firstly, and then increases, ture. As shown in Figure 2, the XRD patterns indicate that while the values of bulk density exhibit an opposite the raw materials consist of ZnO and γ-Al O . At 900°C, 2 3 trend with the increasing of the content of ZnAl O . 2 4 the characteristic peaks of γ-Al O almost disappear, and 2 3 Also, the specimen ZA-1.5 exhibits the highest the characteristic peaks of ZnAl O phases appear, reveal- 2 4 strength. It may be related to its higher density and ing that ZnAl O was generated at about 900°C. In the 2 4 lower porosity. stage from 900°C to 1200°C, the possible reactions are as follows: (i) ZnO reacted with γ-Al O ; (ii) γ-Al O trans- 2 3 2 3 formed into α-Al O , which is more stable; (iii) ZnO further 2 3 3.3. Mechanical cyclic test reacted with the formed α-Al O . The possible reactions 2 3 described above include the following: Figure 7 shows the stress–strain curves by monotonic loading (Figure 7(a)) and the results of the specimens γ Al O þZnO ! ZnAl O (1) 2 3 2 4 under cyclic loading (Figure 7(b,d)). As can be seen from the figure, the hysteresis loop in the curves of γ Al O ! α Al O (2) 2 3 2 3 cyclic loading revealed a general trend of first sparse and then dense. In the early stage of cyclic loading, the α Al O þZnO ! ZnAl O (3) 2 3 2 4 specimen will deform elastically, and the spacings of At 1400°C, the formation of the ZnAl O phase was hysteresis loop are relatively large. Due to compacted 2 4 completed. No impurity phase was detected and no microfractures the deformation of specimen devel- phase transition occurred in the specimen, indicating oped quickly, which indicates that more energies that the product was of high purity. were consumed at each circulation, and the damage The SEM images of ZnO, Al O and ZnAl O pow- quantity within the specimen is large. After a few 2 3 2 4 ders are displayed in Figure 3. It can be observed the cycles, the development rate of specimen deformation Figure 3. (a) SEM images of ZnO; (b) SEM images of γ-Al O ; (c) SEM images of ZnAl O . 2 3 2 4 4 L. LV ET AL. the same. ⅰ. the stage of crack arises: While the stress increasing, micro-cracks are originated quickly within the specimen. The main reason is that the stress has made some weak area almost unbearable inside the specimen. In this stage, the specimens have obvious deformation, and the hysteresis loop is sparse in the cyclic loading curves. ⅱ. expand stage: The contact strength of particles varies evenly under the continu- ous cyclic load. In this stage, the number of micro- cracks increased slowly, and the tip of micro-crack extended gradually. ⅲ. break stage: The initiation and propagation of micro-cracks lead to the through cracks, which result in the breakage of the specimens [16,17]. Figure 4. Particle size distribution of ZnAl O powders. 2 4 Bucking failure of the specimen ZA-1.5 was observed after only seven mechanical cyclic tests in the range of 0.2σ to 0.94σ. The area of hysteresis loop of the specimen ZA-1.5 is significantly smaller than others in the stable cycle stage, because the density of specimen ZA-1.5 is the highest, and the cracks pro- pagate under every cycle. The cycle times of specimen ZA-0 and ZA-3 are both 50 times, but the time from starting to loop to fracture of specimen ZA-0 is about 2750 seconds, while 4300 seconds for specimen ZA-3, as shown in Figure 7. The results clearly indicated that specimen ZA-3 has more extreme resistance to damage than specimen ZA-0. So, the specimen ZA-3 is expected to have longer service life under the same Figure 5. Apparent porosity and bulk density of high alumina condition. In addition to filling the inter-particle voids, castables. some ZnAl O powders added to ZA-3 may remain 2 4 free, which cannot maintain the closest packing of particles. This will result in more micro-cracks formed interior of the fired specimen. And these micro-cracks decreased gradually, and the hysteresis loop is getting closed and opened under cyclic loading, which can much denser. The specimen deformation step into absorb some shock and improve the toughness. Thus, a new stage of steady growth. The damage quantity the cycle times increased. at every circulation reduced sharply. Finally, the speci- SEM images of the specimens are shown in Figure 8, men appeared brittle fracture, when it reached the which reveals the micro-structure of the castables prior to fatigue limit. mechanical testing. It can be seen that the densest speci- It can be seen that the distribution configuration of men is ZA-1.5, the micro-cracks of ZA-0 specimen mainly the fatigue cumulative damages of high-alumina exist in the grain matrix boundary, while the pores of ZA- castables with different ZnAl O content are basically 2 4 3 specimen are mainly from matrix. When the micro- Figure 6. Cold modulus of rupture and cold crushing strength of high alumina castables. JOURNAL OF ASIAN CERAMIC SOCIETIES 5 Figure 7. (a) Stress–strain curves by monotonic loading; (b-d) Hysteresis loop curves under cyclic loading: (b) ZA-0; (c) ZA-1.5; (d) ZA-3. Figure 8. SEM images of the specimens prior to mechanical testing. (a) ZA-0; (b) ZA-1.5; (c) ZA-3. Figure 9. Pictures of fractured specimens after cyclic loading test. 6 L. LV ET AL. cracks develop into macro-cracks, catastrophic fracture [2017YFB0310305]; State Key Laboratory of Advanced Refractory Materials Open Subject Fund Project will happen. The typical fractured specimens after cyclic [SKLAR202209]; Scientific Research Program Funded by loading test are shown in Figure 9. The low interface Shaanxi Provincial Education Department [2021L589]. strength of ZA-0 results in the cracks propagation along the boundary of Al O grains and matrix. Therefore, there 2 3 are many whole Al O grains in the fractured surfaces, as 2 3 References red area shown in Figure 9. The specimens of ZA-1.5 and ZA-3 exhibit transgranular fracture. The fatigue resistance [1] Yang S, Xiao G, Ding D, et al. Effect of in-situ carbon containing calcium aluminate cement on properties of of ZA-3 is superior to ZA-1.5, due to the matrix has some Al O -SiC-C based trough castables. 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