Implementation of image analysis on thermal shock and cavitation resistance testing of refractory concrete

This paper presents monitoring of changes during thermal shock and cavitation testing for low cement concrete that was synthesized and sintered at 1600 °C for 3 h. Water quench test was applied as an experimental method for thermal stability testing. Image analysis of the samples showed some level of deterioration at the surface and inside the samples before water quench test. During the testing, the level of samples destruction was increasing. Damages inside the samples and at the surface during the water quench test were correlated to the number of quench experiments. Models based on the damage level of both the surface and inside the bulk were proposed for calculation of the strength degradation. Cavitation damages of the samples were induced by the modified vibratory cavitation set-up. Mass loss and surface erosion were determined during the experiment. The results indicated excellent thermal shock behavior and resistance to cavitation erosion.     

Effect of the quality of microsilica on the flow properties of cement slurry and characteristics of low-cement refractory concrete on a chamotte filler

The effect of impurity content in different grades of microsilica (MS) on the physicomechanical characteristics of a low-cement refractory concrete based on a chamotte filler is considered. The high content of impurities in MS degrades the flow properties of cement slurry and the respective concrete slurry. It is shown that as ambient temperature grows to 30°C, the impurities in MS increase the cement slurry thickness and impede the placement of refractory concrete in summer period. If low-quality MS is used in concrete, an increased crack formation is observed under the cyclic high-temperature effect. __________ Translated from Novye Ogneupory, No. 5, pp. 41–46, May, 2007.     

提高刚玉质耐火材料热震稳定性的研究

利用微气孔和弥散的ＺｒＯ２能改善耐火材料热震稳定性的特点，在含有一定数量微气孔的刚玉质耐火材料中，加入弥散的ＺｒＯ２，将ＺｒＯ２的增韧作用应用于刚玉质耐火材料热震稳定性的设计中。实验结果表明，当气孔的数量控制在１４％左右，ＺｒＯ２的外加量达６～９ｗｔ％时，能有效地改善刚玉质耐火材料的热震稳定性。在１１００℃，水冷的条件下，经１０次热震试验后，耐压强度保持不变，残余抗折强度为４５％。     

Thermal shock resistance of thermal barrier coating with different bondcoat types and diffusion pre-coating

This paper investigates the resistance of two types of thermal barrier coatings and compares their behavior with common coatings. Coatings’ layers in the first and second target sample were fabricated as HVOF/APS/APS (two bondcoats and one topcoat) and APS/APS (one bondcoat and topcoat) with diffusion pre-coating, respectively. Also, to accurately compare the behavior of these two types of coatings with conventional coatings used in gas turbines, this paper explored the resistance of three types of coatings applied as APS/APS, HVOF/APS, and HVOF coatings against thermal shock. In order to create shock loading, five types of laboratory samples were heated under regular cycles and cooled down with water. During the experiment, the sample changes caused by thermal shock loading were investigated through visual inspections. Then, after the experiment, the SEM images were leveraged to inspect the changes. In addition, changes in the structure of coating layers and their degradation process were studied. The results show that using two bond layers increases the resistance and life of the coating against heat shock by up to 1.40 times. Among the samples with one band coat, the sample with a diffusion coating applied under the BC showed the best performance. The sample life increased by 1.25 times compared to the common APS/PAS coating.     

改善耐火制品热震稳定性的方法

提出了改进耐火制品热震稳定性的方法：1制品的气孔率适当;2控制原料的颗粒配比;3增加微细裂纹并形成网络结构;4形成界面结合;5添加膨胀性材料。     

湿化学法制备锆铝质耐火材料的抗热震性研究

采用湿化学方法制备了不同团聚度的氧化锆粉体,并将其复合到氧化铝基体中,旨在引入弥散氧化锆所伴随产生的微裂纹来代替传统刚玉耐火材料中的结构微气孔,以提高材料的抗热震性能。研究表明,以水清洗工艺所获材料的抗热震性能明显优于酒精清洗工艺,其原因在于前者对团聚氧化锆形成有利。同时,还对该类复合材料的抗热震机理、热震性能表征作了深入分析。     

A new generation of deflocculants and microsilica used to modify the properties of a conventional refractory castable based on a chamotte filler

An efficient deflocculant for a conventional refractory castable based on a chamotte filler is proposed. Aparticle distribution analysis is given for a dry castable mix containing microsilica, and the physicomechanical properties of the conventional refractory castable modified with microsilica and Castament FS40 polycarboxylate deflocculant are studied. __________ Translated from Novye Ogneupory, No. 5, pp. 44–48, May, 2006.     

Heat treatment effect on coating shock resistance of thermal barrier coating system with different types of bond coat

The effect of heat treatment, growth of the TGO layer, oxidation of bond coat, and the impact of the presence of two bond coats on the TBC's thermal shock resistance has been investigated experimentally. TGO oxide layers were created with two-time heat treatment of 12 and 24 h at 1000. Then the thermal shock test was performed on the APS/APS and HVOF/APS/APS samples. The results show that the use of two BCs and the presence of a thin TGO layer has a good effect on TBC performance. The presence of two BC layers increased the shock resistance by an average of 37.2%. 12 h heat treatment caused a 14.0% and 17.4% shock resistance increase in samples with the HVOF/APS/APS layer and APS/APS layer, respectively. 24 h heat treatment decreased the samples' performance by 6.7% and 10.2% for samples with two BC and one BC, respectively.     

Effects of different filler types on decay resistance and thermal,physical, and mechanical properties of recycled high-density polyethylene composites

In this study, flexural properties, impact strength, thermal performance, water absorption, biological durability, and morphology of wood-plastic composites (WPCs) filled with different filler types were investigated. Six different formulations of WPCs were fabricated from mixtures of carpenter waste and recycled high-density polyethylene (R-HDPE). The carpenter waste was derived from wood and particle board wastes, and R-HDPE was used as the polymer matrix, with and without addition of maleic anhydrite grafted polyethylene (MAPE). All formulations were compression moulded in a hot press for 3 min at 170 °C. Investigations on the compression moulded specimens revealed that water absorption values in the particleboard waste flour specimens were lower than in the wood-waste flour WPCs. However, the wood-waste flour-filled composites exhibited higher mechanical property values than the particleboard waste flour WPCs. Statistically, only the wood-waste flour-filled composites with MAPE were significantly different. The use of MAPE (3 wt%) had a positive effect on the water absorption, crystallinity degree, and flexural properties of the WPCs. In addition, the peak temperatures of the composites did not show any variation, while thermal decomposition of the composites showed minor variations under the thermogravimetric analysis. Furthermore, the decay resistance of the composites improved with the use of particleboard waste flour. The obtained results demonstrate that particleboard waste flour, such as wood-waste flour, is potentially suitable as a raw material in WPCs.     

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     

Influence of firing temperature on correlation between thermal shock and mechanical impact resistance of refractory castables

Abstract

Three refractory castables used in the aluminium industry were investigated to establish correlations, which can be applied in practice, among the relevant properties important for performance in service. To determine the influence of firing temperature on the correlations, samples were fired at 1200 and 1450°C followed by mechanical impact (at 900°C) and thermal shock tests (quenched from 950°C into water). The relevant properties were evaluated including modulus of rupture, elastic modulus, work of fracture, and thermal expansion coefficient. The results show that there is a positive correlation between thermal shock and the mechanical impact resistance as well as with the σ_o R_st parameter at 1200°C. Two other positive correlations were established at 1450°C, the first involving mechanical impact resistance, modulus of rupture, and σ_o R_st , and the second between thermal shock resistance and the R′′′′ and R_st parameters.     

Effect of microsilicon on the properties of heat-resistant castable with chamotte scrap filler

Chamotte scrap with an elevated water absorption is used as a filler in low-cement heat-resistant concretes (castables) of the new generation. The studied castable compositions contain from S to 16% microsilicon. The effect of heat treatment of the castable to up to 1300°C on the change in its density, the ultimate compressive strength, deformation, and the speed of an ultrasonic pulse is determined. It is shown how microsilicon affects the setting of mortar and a hypothesis is made on the mechanism of the interaction of thin-phase components in the studied composition.     

The theory of thermal shock in heterogeneous refractory materials

Conclusions Increases in the thermal shock resistance with the addition of high-molecular organic liquids to the grog, proven experimentally, is confirmed by calculations of the factors for thermal-shock resistance of fireclay articles according to the theory of maximum stresses.The established reduction of thermal resistance with the addition of organic liquids in the bond is not reflected by the calculations. Hence, the theory of maximum stresses, although it can in certain cases be applied to bodies which are heterogeneous, it is not universal.On account of the growth in microcracks, the experimentally determined thermal-shock resistance for firebrick increases with chaotic orientation of the microcracks, and with their distribution over the grog grains, but diminishes when the microcracks are located in the bond parallel to each other.In this and other cases, the coefficient of homogeneity of the material diminishes, and the associated probability of destruction (calculated by Weibull) increases. Thus, the statistical theory of strength evolved by Weibull cannot be used to account for the effect of the orientation of microcracks in the structure on the distribution of cracks developed in the material during thermal shock.Calculation of the developed thermal stresses, as a function of the Biot and Fourier criteria, established that with the addition to the grog grains in the fireclay mass of organic liquids, these stresses diminish by a factor of 3–4; there is an increase in the time period and difference in temperature at which the cracks develop, and also the depth of the development of the latter. However, the distribution of the developing thermal cracks is limited when the microcracks are arranged chaotically and around the grog grains. This also increases the thermal resistance of the fireclay refractories when the high-molecular organic liquids are added to the grog grains.     

Influence of structural and phase conversions on the thermomechanical properties of chamotte concrete based on high-alumina cement

Conclusions The dehydration of the calcium hydroaluminates and aluminum hydrates when the concrete is heated causes the binder to lose strength and results in the formation of a porous structure.The structure of the cement block depends on the fineness of the cement. During heating at 1100°C, two processes develop in the binder, viz., solid-phase diffusion sintering accompanied by shrinkage, and coalescence of the pores.The reaction of the cement with the chamotte results in the formation of low-temperature minerals in the form of calcium aluminosilicates, the consequence being that liquid-phase sintering continues accompanied by considerable shrinkage.Above 1200°C and especially above 1300°C a large amount of liquid phase is formed in the concrete and dissolves the crystalline minerals (calcium aluminosilicates, mullite, cristobalite, and corundum).The peak temperature at which the chamotte concrete based on high-alumina cement can be used is 1350°C.Translated from Ogneupory, No. 1, pp. 52–57, January, 1977.     

不同结合方式碳化硅质窑具材料的抗热震性研究

概述了不同结合方式的碳化硅（SiC）质窑具材料的抗热震性能．表明Si2N2O结合SiC窑具材料的抗热震性优于其它结合方式的SiC窑具材料。并对Si2N2O结合SiC窑具材料抗热震性的影响因素进行了较系统的研究。结果表明：当Si2N2O含量≤20％时，增加Si2N2O含量．可提高Si2N2o结合SiC试样的抗热震性；当Si2N2O含量超过20％时，试样的抗热震性能反而变差，Si2N2O结合SiC试样的抗热震性优于Si3N4结合SiC试样。固定试样中Si2N2O的含量为25％，当Si／SiO2（摩尔分数）在2．7％～3．3％范围内时，增加Si／SiO2（摩尔分数）可提高试样的抗热震性，而当Si／SiO2（摩尔分数）在3．3％～4％范围内时．增加Si／SiO2（摩尔分数）对试样抗热震性的影响规律不明显。     

Study of medium-cement concrete based on mixed Chamotte-periclase chromite filler

The possibility is demonstrated of using an addition of periclase-chromite filler (PCF) prepared from PCF grade broken material articles in medium-cement concrete with chamotte filler. The effect of this addition on cement hardening duration, strength and heat resistance is considered. Translated from Novye Ogneupory, No. 8, pp. 42–46, August 2008.