Corundum Castables Research Articles

The Effect of Alumina-Rich Spinel Exsolution on the Mechanical Property of Calcium Aluminate Cement-Bonded Corundum Castables.

This study investigates the effect of the exsolution behavior of alumina-rich spinel on the formation and distribution of CA6 (CaAl12O19) in corundum castables bonded with calcium aluminate cement. In this study, alumina-rich spinel is substituted for tabular corundum in the same proportions and grain size. The matrices after curing were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The phase composition and microstructure of the matrices containing alumina-rich spinel were analyzed after firing at 1600 °C. These results showed that the addition of alumina-rich spinel significantly improved the mechanical strength of the castables. This improvement was attributed to the alumina produced by spinel exsolution during firing at 1600 °C, which reacted in situ with CA2 (CaAl4O7) to form CA6. CA6 connects the different particles and forms an interspersed interlocking structure within the spinel. The CA6-MA interspersed interlocking structure replaces part of the CA6-Al2O3 structure and significantly improves the mechanical strength of the castables.

Effect of solid solution of magnesia-alumina spinel on the microstructure and mechanical properties of CAC-bonded corundum castables

Effect of solid solution of magnesia-alumina spinel on the microstructure and mechanical properties of CAC-bonded corundum castables

Improving the green mechanical strength and thermal shock resistance of colloidal silica‐bonded castables using La2O3

AbstractImproving the green mechanical strength of colloidal silica‐bonded corundum castables is essential to their widespread utility. The effects of varying contents (0–2 wt%) of La2O3 on the green mechanical strength of colloidal silica‐bonded corundum castables were investigated. The findings demonstrate that La2O3 has a positive impact on the green mechanical strength of colloidal silica‐bonded castables. The colloidal silica‐bonded corundum castable containing 2 wt% La2O3 exhibits higher green mechanical strength than the cement‐bonded corundum castable. Additionally, the castable shows excellent construction performance. The basic properties of La2O3 and La(OH)3 facilitate the absorption of H+ from the surface of colloidal silica to form more siloxane bonds and speed up gelation. Fourier transform infrared spectroscopy and X‐ray fluorescence spectroscopy analyses indicate that La3+ ions participate in the condensation of –Si–OH and bond the broken Si–O bonds to create Si–O–La chemical bonds. La3+ ions bridge the colloidal silica particles, leading to stable three‐dimensional network structures that result in an increased green mechanical strength of the castables. The water consumption during the hydration reaction expedites gelation, further contributing to the enhancement of the green mechanical strength of the corundum castables. Given its wide sources and stable performance, La2O3 can be considered an efficient setting agent with the potential for extensive industrial application.

Image-processing-based automatic crack detection and classification for refractory evaluation

Crack generation and propagation in refractories is inevitable during their service life, which ultimately contributes to their failure. Accordingly, this study proposes a method that includes a watershed algorithm and classification criterion to quantitatively evaluate the fracture behavior in refractories. Additionally, to demonstrate the stability and reliability of the algorithm, its crack analysis results were compared with those of manual methods for alumina-magnesia ramming materials and corundum castables. The results indicated that the algorithm was capable of automatically identifying, extracting, and classifying cracks. Additionally, the type of crack propagation and its length and width were analyzed to determine the performance and properties of refractories. The proposed method was highly effective and accurate for the automated evaluation of material fracture behavior.

Pore evolution and slag resistance of corundum castables with nano zirconia addition

The effect of nano-zirconia addition on the microstructure and properties of corundum castables was studied using corundum, kyanite, alumina powder, gel powder, and nano-ZrO2 as raw materials. The results showed that adding 1.2(wt)% nano-ZrO2 could reduce the median pore diameter of the castables from 480 to 200 nm at 110 °C. After the castables were heated at 1100 °C, the cold modulus of rupture increased by 29.95%, to 24.71 MPa, and the cold compressive strength increased by 50.32%, to 116.37 MPa. The hot modulus of rupture increased by 114.95%, to 3.59 MPa after being treatment at 1500 °C, the high surface energy of nano-ZrO2 can increase the interface energy and bonding strength between adjacent particles.

Effect of in-situ formation of columnar mullite and pore structure refinement on high temperature properties of corundum casatbles

The effects of in-situ synthesis columnar mullite and pore structure on the hot modulus of rupture (HMOR), thermal shock resistance and corrosion resistance of corundum castables have been investigated in this paper. When 2% nano silica was added, the pore diameters of castables could be decreased to 15 nm (at 110 °C), 1 μm (1100 °C) and 6 μm (1500 °C), respectively. The corresponding reducing magnitude of pore size is 98.5%, 83.3% and 33.3%. The HMOR of castables fired at 1500 °C increased by 110% to 3.64 MPa. Furthermore, after three thermal shock cycles, the residual strength ratio of castables increased from 5.2% to 15.3%. A large amount of cross-distributed columnar mullite was formed between nano silica and α-Al2O3 by the two-dimensional nucleation mechanism, which remarkably enhanced the high temperature properties. The penetration index reduced from 30.86% to 19.88%, suggesting that smaller pore size and higher viscosity had a great influence to the penetration process.

Influence of Setting Accelerating Agents on Properties of Colloidal Alumina Bonded Corundum Castables

Influence of Setting Accelerating Agents on Properties of Colloidal Alumina Bonded Corundum Castables

Investigation of fracture behavior of cement-bonded corundum castables using wedge splitting test and digital image correlation method

To investigate the fracture behavior of cement-bonded corundum castables, various cement contents and pre-treating temperatures have been comparatively studied using the wedge splitting method and the digital image correlation technique. The results show that the microstructure enhances the mechanical properties, so the fracture energy and the maximum load as well as the fracture modes are affected correspondingly. The castables demonstrate the highest fracture energy and maximum load at 1600 °C with cement content of 10 wt% due to an appropriate amount of CA6. At the temperatures of 110 and 1100 °C, the crack propagation within the matrix and along the interface are dominated whereas within the aggregates significantly increased at 1600 °C, leading to the brittleness of materials. However, increasing the cement content can reduce their brittleness, caused by the maximum strain in thex-direction, largest length of the main crack, and high ratio of crack propagation in the matrix.

Effects of cement content on the microstructural evolution and mechanical properties of cement-bonded corundum castables

The cement-bonded corundum castables are often subjected to great temperature gradient in the service process of purging plugs for refining ladle. The mechanical properties of such castables are of particular interest in the serviceability and the safety of purging plug, which are significantly influenced by the microstructures including the amount, size and morphology of materials. The reported cement contents in compounds of purging plugs are generally low or ultralow, which inevitably limits the adjustable range of the mechanical properties enhancement by regulating their microstructures. In the present research, a serial of comprehensive experiments have been carried out, including the high cement contents (10–15 wt%), so as to further understand the role of cement content on the microstructural evolution and mechanical properties of castables. It is found that the phase compositions and microstructure can be optimized through adjusting the cement content in corundum castables. When the cement content is below 10 wt%, the hexagonal flake CA6 grains are platelet-shaped both in the matrix and at the border of the aggregates, their amount and size increase and distributions are more uniformly with cement content. When the cement content is above 10 wt%, small amount of granular crystals CA2 are detected in matrix, and CA6 crystals transform to equiaxial morphologies after cement content of 10 wt%. This research also provides quantitative relationship between the mechanical properties of the castables and the cement content. Castables with cement content of 10 wt% contain most hexagonal flake CA6 crystals, so that they have the highest CMOR and HMOR after heating at 1600 °C. However, CMOR decreases after cement content of 10 wt% due to the porosity and volumetric expansion from the formation of in-situ CA6 and CA2.

Optimization of matrix pore structure and its effects on physicochemical properties of corundum castables

In this paper, the effects of the matrix pore structure on the strength and corrosion resistance of corundum castables are reported. Pore diameters of castables fired at 110 °C could be decreased from 550 nm to 72 nm when 4% Al2O3-SiO2 gel powder was added. The pore diameter of the castables decreased from 850 nm to 500 nm after firing at 1100 °C, but increased from approximately 2 μm–8 μm after firing at 1500 °C. The strength of castables fired at 1500 °C increased remarkably with the addition of Al2O3-SiO2 gel powder. A maximum cold modulus of rupture (CMOR) of 62.34 MPa was obtained when 4% Al2O3-SiO2 gel powder was added. After slag corrosion, the penetration index fell from 16.6% to 4%, suggesting that a homogeneous pore size distribution and a smaller pore size played an important role in improving the penetration resistance.

Improvement of the alkali corrosion resistance and mechanical properties of corundum castables by coating of Li2O-Al2O3-SiO2 glaze

In terms of improving the alkali corrosion resistance of corundum castables, coating technology is applied to preparing the excellent properties of corundum castables with a glaze layer. The work focuses on the effect of the ratio of Al2O3/SiO2 on the properties of Li2O-Al2O3-SiO2 glazes. Furthermore, the influence of Li2O-Al2O3-SiO2 glazes on the alkali corrosion resistance of corundum castables is investigated. The results show that at a high temperature with increasing of the ratio of SiO2/Al2O3 in Li2O-Al2O3-SiO2 glazes, the viscosity and amount of liquid phase in the glaze increase gradually, which has a great influence on the quality of the glaze at a high temperature. And as the ratio of Al2O3/SiO2 in the glaze is between 6 and 8, the apparent porosity of corundum castables with the glaze layer decreases significantly resulting in preventing the permeation of alkali vapor into the castables, which can improve the alkali corrosion resistance and mechanical properties of corundum castables dramatically. Moreover, as the thermal expansion coefficient of the matrix is higher than the glaze layer, the compressive residual stress (tangential direction) will exist in the glaze layer, resulting in enhancing crack bifurcation, which is beneficial to improving the properties of corundum castables.

Improvement in fatigue resistance performance of corundum castables with addition of different size calcium hexaluminate particles

Cyclic loading of catalytic gasifier lining refractories is one of the most important factors causing fatigue failure. A three-point bending fatigue experiment was carried out to explore the influence of calcium hexaluminate (CA6) particle size distribution on the fatigue resistance of corundum castables. Five different castables were damaged by fatigue, the curve of the fatigue strain against the number of cycles has a classical sigmoid shape with three phases: firstly, the strain rate decreases; secondly, it remains unchanged; thirdly, it increases significantly. The maximum strain during fatigue failure is generally greater than in monotonic loading. It has been found that the combination of the grain-matrix plays a critical role in fatigue failure. The fatigue resistance of pure corundum castable decreased significantly at 1100 °C. The surface roughness of CA6 can be effectively combined with the matrix. The fatigue resistance of the corundum based castable where 3-1 mm tabular alumina particles were replaced by he same size of CA6 particles is best after treatment at either 110 °C or 1100 °C.

Effect of Cr2O3 addition on corrosion mechanism of refractory castables for waste melting furnaces and concurrent formation of hexavalent chromium

Cr2O3 containing refractories are used as the linings of various waste melting furnaces. Formation of hexavalent chromium (Cr(VI)) has been a major concern despite its admirable corrosion resistance properties. Al2O3-CaO-Cr2O3 refractory castables (0, 4%, 8%, and 12wt% Cr2O3) were fabricated in reducing condition to inhibit Cr(VI) formation while subsequent corrosion tests using waste slag was performed in air atmosphere to simulate the operating conditions. The corrosion mechanism between Cr2O3-containing corundum castables and synthetic waste slag were investigated by XRD and SEM-EDS, whereas concurrent formations of Cr(VI) were assessed effectively by leaching tests. Corrosion of castables (0wt% Cr2O3) occurs via dissolution of Al2O3 and CA6 phases, and formation of Ca2(Al,Mg)(Al,Si)2O7 and (Ca,Na)(Al,Si)2Si2O8, which were significantly restricted by the formation of Al2O3-Cr2O3 (III) solid solution (4%, 8%, and 12wt% Cr2O3). Most of the specimens exhibited less than 5mg/L (EPA limit) of Cr(VI). Only specimen M3 (12wt% Cr2O3) from slag-refractory interface (stage C) leached out 5.41mg/L of Cr(VI) which is above the EPA limit. Specimen M2 (8wt% Cr2O3) exhibits optimum properties in terms of corrosion and Cr(VI) formation.

Size-dependent hydration mechanism and kinetics for reactive MgO and Al2O3 powders with respect to the calcia-free hydraulic binder systems designed for refractory castables

This work investigates the time-dependent hydration behavior of 1:1 molar ratio mixture of reactive α-Al2O3 nano- or micro-powder and reactive MgO in relation to the development of new hydraulic binder systems for in situ spinel refractory corundum castables. Mg–Al–CO3 hydrotalcite-like phases formed in the cementitious matrices cured in the corresponding curing condition up to 280 days of age at 50 °C were subjected to morphological, chemical and structural characterization using XRD, FT-IR, NMR, SEM and TEM techniques. The observations indicate that both the short-term cured MgO–nano-Al2O3 cementitious matrix and the long-term cured one containing micro-Al2O3 contain mainly OH–(Mg3) hydroxyl group, whereas the long-term cured MgO–nano-Al2O3 cementitious matrix is dominated by OH–(Mg2Al) hydroxyl group. The thermal stability of hydrotalcite-like compounds (Mg0.667Al0.333(OH)2(CO3)0.167(H2O)0.5, Mg6Al2CO3(OH)16·4H2O) (HTlcs) through combined DTA–TGA–EGA–MS analyses shows that HTlcs undergo dehydration first and then dehydroxylation overlapping with decarbonization processes. According to EGA–MS and FT-IR measurements, the Mg–Al cementitious matrices were progressively carbonated over curing time and then interlayer water molecules were preferably coordinated by interlayer CO32− ions that exist in a complex network of hydrogen bonds between octahedral layers. In the near-fully-hydrated binder paste, dehydration of crystalline water molecules occurs at 262 °C and the thermal stability of hydroxyl groups in HTlcs is OH–(Mg2Al) (422 °C) > OH–(Mg3) (337 °C) at a ramping rate of 10 °C/min. The basic information provided by the microcalorimetric measurement is such that the starting grain size significantly affects the heat flow curve. From the SEM and TEM images, the hydrates are found to be hexagonal in shape.

Properties Analysis of Corundum Castables and Corundum MA Spinel Castables

Due to its excellent properties and good workability, castables is widely used in metallurgical field especially in steel and nonferrous metallurgical industry. In this article, we mainly had a comparative analysis of corundum castables and corundum MA spinel castables with 15% and 30% MA spinel addition . The physical and mechanical properties such as the bulk density, apparent porosity, cold modulus of rupture, cold crushing strength and thermal shock resistance of samples were studied after different temperature heating treated at 110°C×24h, 1100°C×3h and 1400°C×3h, respectively. The thermal conductivity of different samples at 750°C were tested by plate heat conduction method, phase composition and microstructure of samples with 15% MA spinel addition after different temperature heating treated were tested by XRD and SEM respectively. The results showed that: the properties of corundum MA spinel castables with 15% MA spinel addition is relatively good, the corundum castables take second place, samples with 30% MA spinel addition showed the worst performance among the three. After the heating treatment at 1400°C×3h, the CCS and CMOR of the samples is higher than that of 110°C×24h and 1100°C×3h due to the CA6 formation. Coefficient of thermal conductivity of the corundum-based castables at 750°C is relatively higher compared with that of 15% and 30% MA addition, reaches at 1.260w/ (m.k).

The Characteristics of Silica-Sol Combining Refractories

Traditionally, calcium aluminate cement is always used as the binding agent for refractory castable applied in steel and iron, but cement contains many impurities, it is easy to generate low-melting additives and excessive liquid phase may be formed in material calcination, so the thermal shock resistance and moderate temperature intensity of corundum castables bonded with cement is worse; in addition, the flowability of cement-bonded castables also is poorer and it is difficult to construction. In the recent years, China and other countries have started to study properties of colloidal sol bonded castables to improve physical/chemical properties and workability of cement castables. This paper summarizes some characteristics of silica sol bonded materials via test and analysis.

Materials based on highly concentrated ceramic binding suspensions (HCBS). Corundum and corundum-mullite ceramic castables based on plasticized hcbs of bauxite

HCBS of roasted Chinese bauxite, plasticized with additives of refractory clay, and corundum or bauxite filler are used for the production of pressed ceramic castables of corundum and mullite-corundum compositions with 93–95% and 80–85% A12,O3, respectively. The optimum clay additive does not exceed 1–2%. The ceramic castables have a porosity of 15–18% and an ultimate compressive strength of 100–200 MPa after treatment at 1200–1300°C. As compared to traditional corundum refractories they are characterized by a finer capillary structure and a higher mechanical strength attained at a diminished (by a factor of 2–3) pressing pressure and a lower (by 400- 500°C) firing temperature.