Tabular Alumina Research Articles

Effects of Alumina Bubble Addition on the Properties of Corundum-Spinel Castables Containing Cr2O3.

Purging plugs made of corundum-spinel castables containing Cr2O3 have been widely utilized in secondary refining process. However, their poor thermal shock resistance has greatly limited the improvement of their service life. Aiming to enhance their properties, we introduced alumina bubbles (ABs) to corundum-spinel castables, and the effects of the AB addition on the properties of the castables are studied in this manuscript. The results indicate that the apparent porosity, permanent linear change, cold strength, and hot strength all increased with an increasing AB amount. The thermal shock resistance of the samples with the AB addition was improved; the residual strength and residual strength ratio of the sample with 4 wt% ABs was the best. The effects of ABs on the tabular alumina aggregate distribution and relationship between the cold strength of the samples and the AB content was evaluated via the box dimension method. With the increments of AB content, the box dimension value of the tabular alumina within the samples significantly decreased, indicating that the tabular alumina aggregate distribution was related to the amount of ABs. In addition, the relationship between the box dimension and the strength was also established.

Effect of nano-oxides on corrosion resistance of Al2O3–ZrO2–C material

The Al2O3–ZrO2–C material was prepared using tabular alumina aggregates and fines, zirconia-corundum, zirconia-mullite, flake graphite, B4C powder, Si powder and different nano-oxides (nano-ZrO2, nano-TiO2, and nano-Al2O3) as raw materials, the effects of different nano-oxides on the corrosion resistance and microstructure evolution of Al2O3–ZrO2–C material were investigated. The results showed that the high reactivity nano-ZrO2, nano-TiO2, and nano-Al2O3 particles reacted with CaO to generate high melting point phases of CaZrO3, CaTiO3, CaO·6Al2O3 (CA6) at high temperature, which forms a protective layer at the interface between corroded media and samples, inhibiting CaO penetration into the material. Additionally, nano-oxides can fill the pores and increase the density of material, thereby contributing to improving the penetration resistance and corrosion resistance of material.

Lightweight corundum–spinel ladle wear lining castable with low thermal conductivity

AbstractDesigning a lightweight wear‐lining refractory is of great significance for energy savings and consumption reduction. In this study, an in‐house manufactured porous alumina aggregate was selected to replace the commercial tabular alumina aggregate to prepare lightweight corundum–spinel castable (LCSC) for ladle linings. The effect of the porous alumina aggregate on the properties of the corundum–spinel castable was investigated. Compared to tabular alumina, porous alumina possesses higher closed porosity (12.1%) and a small pore size (4.25 µm). The thermal conductivity of LCSC is 21.5% lower than that of dense castable at 1000°C. Owing to the existence of micropores in the porous alumina, the fabricated corundum–spinel castable showed an improved degree of bonding between the aggregate and matrix. Therefore, the lightweight castable showed higher flexural strength and considerable slag corrosion resistance than the dense castable.

Preparation of AlN–SiC bonded Al2O3–C refractory and its properties evolution after oxidation

The low carbon Al2O3–C refractory was prepared using tabular alumina aggregates and fines, Al2O3 micro-powder, Al powder, and Si powder as starting materials. The physical properties, hot modulus of rupture (HMOR), and thermal shock resistance (TSR) as well as oxidation behavior of samples before and after oxidation at 1500 °C for 3–9 h were investigated. Furthermore, the relationship between properties degradation due to oxidation and microstructure evolution was discussed. The results showed that the in-situ AlN and SiC whiskers forming network structure in Al2O3–C materials conferred good thermo-mechanical properties of the obtained composites. However, the materials were seriously oxidized at 1500 °C for 3–9 h, which resulted in a significant decrease in both physical properties and HMOR. The oxidation percent reached 86% after oxidation for 9 h, and HMOR decreased from 25.8 MPa to 10.5 MPa with increasing oxidation time from 0 to 9 h. However, the oxidized samples have excellent TSR and the residual strength ratio exceeds 90%, which is attributed to the formation of microcracks, mullite, and glass phase in the oxidized layer, and the residual non-oxide whiskers in the unoxidized layer.

Effect of additives on densification of tabular alumina: A case of single additive doping and co-doping

The effect of doping and co-doping of oxide additives on sintering properties and microstructural features of tabular alumina is investigated. To examine the effects of single doping, 2 wt % of each of CaO, Fe2O3, SiO2 and TiO2 were added to tabular alumina fines and the samples were sintered at 1550 °C, 1600 °C and 1650 °C. Single oxide doped batches showed improved density except the samples doped with CaO. The phase analysis and microstructural results of CaO doped samples revealed the formation of calcium hexa-aluminate phases which resulted in poor density. The abnormality in grain-growth on addition of TiO2 was found to have a deteriorating effect on the strength of samples at 1650 °C despite of maximum densification. To observe the effects of co-doping of oxides, 1 wt % of each of CaO, Fe2O3, SiO2 and TiO2 were added to tabular alumina in unique combinations under same sintering conditions. Co-doping of oxides was found to be effective in property development of samples at higher sintering temperatures. The characteristics of secondary phases so formed influenced the properties of tabular alumina through liquid phase sintering, abnormal grain growth or decreasing the bulk density of samples. The strength value increases with temperature, more prominently for samples with liquid phase formation, but decreases for samples with abnormal grain growth and hexagonal shaped secondary phase formation.

Investigation on a postmortem Al-Al2O3-fused mullite-containing Ti2O3 sliding gate

A resin-bonded Al-Al2O3-fused mullite containing Ti2O3 sliding gate was prepared from metallic Al, tabular alumina and fused mullite containingTi2O3, and was used at the steel-making works. XRD, SEM and EDS analyses were used to investigate the damage mechanism of the postmortem sliding gate. The results show that non-oxide-reinforced phases such as Al4C3, SiC, Al4O4C, Al2OC-AlNss and Ti(C,N)ss are formed which effectively improve the thermal shock and erosion resistance. And the service life of the sliding gate with a fused mullite content of 30 wt% reaches 4 cycles. The phase evolution of the postmortem sliding gate can be described as follows: the oxygen partial pressure is at a very low level due to the active oxidation reaction of the Al. At this time, the Ti2O3 in the fused mullite is unstable and transforms towards the more stable Ti(C,N)ss, while releasing O2. O2 further reacts with the Al to form the highly reactive Al2O(g). The highly reactive Al2O(g), AlN reacts with phenolic resin residual carbon or graphite to form Al2OC-AlNss. As the content of high titanium fused mullite increases, Al4O4C and Al4C3 gradually transform into the more stable Al2OC-AlNss and Ti(C,N)ss. The introduction of Al and high titanium fused mullite enables the synergistic formation of high performance Ti(C,N)ss and Al2OC-AlNss.

Improved comprehensive properties of Al2O3-MgO-C refractories containing lightweight tabular alumina aggregates

The lightweight of ladle lining refractories is of great significance to energy saving and consumption reduction. In this work, the lightweight alumina aggregates were selected to partially replace traditional tabular alumina aggregates to prepare lightweight Al2O3-MgO-C refractories used for steel ladle linings. And, the influence of lightweight alumina aggregates on the comprehensive properties of Al2O3-MgO-C refractories was investigated in detail. The results illustrated that the introduction of lightweight alumina aggregates can improve the strength of Al2O3-MgO-C refractories, due to the optimized interface bonding between aggregates and matrix. In addition, the thermal shock resistance of Al2O3-MgO-C refractories was also enhanced after adding lightweight alumina aggregates, which should be attributed to that the addition of lightweight alumina aggregates reduced the thermal expansion coefficient of such refractories, and micron-sized pores of lightweight alumina aggregates absorbed partial thermal stresses during thermal shock test. Furthermore, the addition of lightweight alumina aggregates improved the slag corrosion resistance of Al2O3-MgO-C refractories remarkably, which can be ascribed to the formation of continuous CA6 protective layer and densified matrix.

Influence of calcium hexaluminate gradation on interfacial microstructure and fracture behavior of cement-bonded alumina castables

To reduce the brittleness of cement-bonded alumina castables for purging plug, different gradations (5-3, 3-1 and 1-0 mm) of calcium hexaluminate aggregates are introduced to replace the tabular alumina aggregates. The interfacial microstructure and fracture behavior with or without calcium hexaluminate aggregates are systematically analyzed. The results show that the large (5-3/3-1 mm) and small (1-0 mm) particle sizes of calcium hexaluminate contributed to the interfacial bonding and prolonged crack propagation path of cement-bonded alumina castables, respectively. Accordingly, the strength is promoted and the fracture mode is significantly affected under tensile stress. Specifically, the proportion of cracks propagating along the interface can be reduced by introducing 5-3-or 3-1 mm calcium hexaluminate particles. Besides, the introduction of 1-0 mm particles reduces the proportion of cracks propagating within the aggregate. Cement-bonded alumina castables containing three particle sizes (5-3/3-1/1-0 mm) of calcium hexaluminate have simultaneously better strength and toughness than castables containing a single particle size.

Preparation of resin coated alumina aggregate and its effect on the properties of alumina-spinel castables for purging plugs

Secondary refining processes were indispensable for high-quality steel in the modern steelmaking process, and refining processes in ladles were necessarily performed by argon bubbling through purging plugs, therefore properties and service life of purging plugs were directly impacted on the production efficiency and cleanliness of steel products. To date, purging plugs with slots have been widely used in steel ladles because of their higher strength, stable permeability and higher service lifes. However, poor thermal shock resistance limited their application and enhancement of service life, it is of great significance to improve their thermal shock resistance. In this manuscript, coated aggregates were prepared by coating with phenolic resin on tabular alumina aggregates, and effect of coated aggregates on the properties of alumina-spinel castable was studied. The results show that apparent porosity and permanent linear change rate increase, cold strength and hot strength decrease, and residual strength ratio markedly increase with rising of coating layer thickness of the aggregates, indicating that thermal shock resistance of the sample is significantly improved. The improvement mechanism in the thermal shock resistance of the castables was also discussed in details. The alumina-spinel castables containing microspaces with enhanced thermal shock resistance can be utilized to fabricate longeval purging plug materials for steel ladles.

Role of nano-ZrO2 powder in in-situ formation of ceramic whiskers in Al2O3-C slide plate materials

The effects of nano-ZrO2 powder on the evolution of phase composition and microstructure of Al2O3–C materials during firing have been investigated using tabular alumina, Si powder, Al powder, graphite and nano-ZrO2 powder as starting materials. The residual content of Al and Si gradually decreased with increasing temperature, and the added nano-ZrO2 facilitates the reactions involving Si and Al. The quantity of in-situ synthesized AlN and SiC whiskers exhibiting continuous interlocking networks increased gradually with temperature. Nano-ZrO2 facilitates more ceramic whiskers generated in samples, which play a strengthening and toughening role in the materials, thus improving the thermal shock resistance and high temperature strength of Al2O3–C materials. In addition, physical properties are improved due to the nano-ZrO2 filling the pores and increasing the density of materials.

Microstructure, Thermal and Mechanical Properties of Refractory Linings Modified with Polymer Fibers

The reduction in the inherent brittleness of coatings applied on parts of ceramic shielding used for continuous steel casting (CSC) processes is highly desired, since it can significantly diminish losses occurring during post-application handling and mounting. One of such coatings, prepared mostly from fused silica, ludox, tabular alumina, chamotte, cenospheres, dextrine and aluminum powder, is known commercially as Thermacoat™. The present experiment is focused on the effect of the modification of its composition by rising the content of the cenospheres (max. 2.5 wt.%) or by introducing up to 1.5 wt.% of polymer Belmix™ fibers (~34 μm diameter/12 mm length) on the microstructure and mechanical properties. The maximum amount of introduced additions was limited by the accompanying loss of mass viscosity, which must allow for deposition through immersion. Next, the differential scanning calorimetry and differential thermogravimetric analysis techniques were employed to evaluate the extent of the weight change and heat response of the mass during the drying and annealing stages. The dried materials’ microstructure was investigated with light and scanning electron microscopy, while the chemical composition was studied by energy dispersive spectroscopy. Finally, a three-point flexural bending method was used to determine changes in the material mechanical properties. The performed experiments proved that the small addition (~1 wt.%) of polymer fibers is sufficient for the significant improvement of the Thermacoat™ green mechanical strength at ambient temperature, presenting a reproducible ultimate flexural strength of ~0.2 MPa.

Erosion mechanism of tabular alumina of various microstructures under different basicity of blast furnace slag

In this study, three types of commercial tabular alumina aggregates with different microstructural characteristics were selected for corrosion tests on blast furnace slags with varying basicities. A corrosion mechanism with different microstructural characteristics is proposed, and the dominant microstructures in high- and low-basicity environments are evaluated. The pore structure was found to have a crucial influence on the dissolution of tabular alumina aggregates in the blast furnace slag. Under low-basicity (0.5–0.7) conditions, a small amount of clustered pore structure was beneficial for obtaining the maximum thickness (40–60 μm) of the isolation layer between the tabular alumina aggregate and slag. Under high-basicity (0.9–1.1) conditions, the circular pore structure tended to form a uniform and stable double-layer isolation structure of calcium hexaaluminate and MgAl2O4 spinel.

Research on high‐temperature creep properties of Al2O3‐MgAl2O4 refractory

AbstractIn this study, the Al2O3‐MgAl2O4 refractory samples were prepared with tabular alumina and fused magnesia‐alumina spinel as the raw materials. A creep resistance test was performed at 1400°C and studied. The tested samples after the creep resistance test were characterized and analyzed by X‐ray diffraction, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy to investigate the effect of adding the amount and particle size of MgAl2O4 on high‐temperature creep resistance of Al2O3‐MgAl2O4 refractory, as well as its mechanism. As indicated by the results, under the same amount of spinel added, the sample with 3‐1 mm spinel had higher creep resistance than the sample with 1‐0 mm spinel. In the creep test, spinel aggregates would react with the alumina matrix to form a secondary spinel layer around the spinel particles, thereby connecting the matrix and the aggregates and improving the creep resistance of the specimens. As clearly indicated by the observed result of the microstructure, in the formation of the secondary spinel layer, Mg2+ had a higher migration rate and showed the secondary spinel layer's higher thickness ratio on both sides of the reaction interface, which would induce the Kirkendall effect. Accordingly, considerable pores generated and accumulating at the interface tended to reduce the creep resistance of the material, and this effect was highly dependent on the size of the spinel and the activation solid solution reaction intensity.

Restructuring-diffusion mechanism of calcium alumino-titanate in CaAl12O19–MgAl2O4–Al2O3 castables

Calcium alumino-titanate (CAT), a secondary material obtained from ferrotitanium slag, was used as a hibonite source to prepare CaAl 12 O 19 –MgAl 2 O 4 –Al 2 O 3 castables. The restructuring effect of CAT aggregate was compared by replacing tabular alumina aggregates with CAT aggregates of different particle sizes. The effects of CAT particle size on cold mechanical strength and thermal shock resistance of CaAl 12 O 19 –MgAl 2 O 4 –Al 2 O 3 castables were studied. The results showed that CAT aggregates with particle size of 5–3 or 3–1 mm led to more internal cracks or pores and reduced the cold mechanical strength of the castable samples fired at 1600 °C for 3 h. The use of CAT aggregates with particle size of 1–0 mm led to the formation of a well-bonded CAT aggregate and matrix, improving the cold mechanical strength and thermal shock resistance of the castable samples fired at 1600 °C for 3 h. The enhancement mechanism of fine CAT aggregates in this process was proposed based on the sintering of the matrix–aggregate interface with the formation of Ca(Al, Mg, Ti) 12 O 19 .

Effect of carbon black on corrosion resistance of Al2O3–SiC–C castables to SiO2–MgO slag

Metallurgical solid waste recycling is the shape of things to come in green development of Chinese iron and steel industry. Utilization of ironworks slag for producing mineral wool at high temperature is an important approach. However, refractory lining is seriously corroded by the SiO2–MgO based slag at 1600 °C during the production process. Different production steps need different atmospheres, the changeable service atmospheres (air and reducing atmosphere) put forward high requirements for slag resistance. The Al2O3–SiC–C castables containing carbon black are usually used in iron runner, which faces high-temperature service condition of 1450 °C–1500 °C. Nevertheless, the function of carbon black in the Al2O3–SiC–C castables at 1600 °C is till essentially unknown. In the current study, the carbon black was introduced to tabular alumina based Al2O3–SiC–C castables to improve corrosion resistance to SiO2–MgO based slag at 1600 °C. The result showed that 0.4 wt% carbon black was suitable for the castables, which the slag resistance of castables was significantly improved. The carbon black had contributed to block slag by wettability resistance. By comparison with the castables without carbon black, the corrosion index and penetration index had been reduced by 20.2% and 28.0%, respectively, under air atmosphere. And there were little corrosion or penetration under reducing atmosphere for castables with 0.4 wt% carbon black. For the mechanical properties, the Al2O3–SiC–C castables with 0.4 wt% carbon black could serve production process although the carbon black impaired the physical properties.

Effect of silicon powder-modified tabular alumina aggregates on the mechanical properties and microstructures of carbon-bonded alumina refractories

Effect of silicon powder-modified tabular alumina aggregates on the mechanical properties and microstructures of carbon-bonded alumina refractories

Influence of the granular component type and the ratio of batch components on the properties of pressed alumina-chromia-zirconia-silica refractories with a mass fraction of 60 % Cr2O3

Investigations on the influence of granular component type and ratio of batch components on the properties of pressed alumina-chromia-zirconiasilica refractories with a content of 60 % Cr2O3 have been carried out.
 The optimal composition of batch, which includes scrap bakor products, scrap chromia products, alumina and metallurgical chromium oxide, was established.
 This composition provides, after firing in an oxidizing atmosphere, obtaining refractory samples with an open porosity of 23.1 %, an apparent density of 3.52 g/cm3, cold crushing strength 120 N/mm2, thermal shockresistance 950 °C — water 5 thermal cycles.It was shown that, the introduction of granular tabular alumina intothe batch composition (instead of granular fused white alumina) leads to adecrease in the open porosity of samples, although to a lesser extent thanwith the introduction of scrap bakor products.It was established that, for samples containing 60 % metallurgicalchromium oxide, the introduction of scrap bakor products instead of fusedwhite alumina does not lead to a significant decrease in their open porosity.
 It was shown that, firing in a reducing atmosphere and titanium oxide addition do not significantly affect the increase in apparent density and cold crushing strength of the studied samples.
 Comparative studies of the corrosion resistance of alumina-chromiazirconia-silica refractories containing 60 % Cr2O3 of different composition to melts of E glass and basalt have found that, E glass and basalt impregnate refractories, and under the influence of glass, some samples were slightly corroded. The samples of developed optimal composition were less impregnated than samples of other compositions and were not corroded by E glass and basalt, which makes it possible to predict an increase in the stability of these refractories in service in glass furnaces for the production of glass fiber from E glass and basalt.
 As a result of the carried out research, the technology of aluminachromia-zirconia-silica refractories with a content of 60 % Cr2O3 has been improved.

Graphene-Reinforced Carbon-Bonded Coarse-Grained Refractories.

Carbon-bonded alumina refractories offer excellent thermal shock performance but are lacking in terms of mechanical strength. In the present contribution, the influence of the particle packing and the addition of graphene oxide (GO) to carbon-bonded alumina refractories on the physical and mechanical properties before and after thermal shock was investigated. Coarse tabular alumina grains were coated by a GO suspension and used to prepare dry-pressed compacts. The included graphite fraction (15 wt%) was either regarded as a lubricating matrix component or as a quasi-spherical component of a calculated density-optimized aggregate size distribution. During coking, the GO was reduced to thermally reduced graphene. The porosity, true density and thermal shock behavior in terms of the cold modulus of rupture (CMOR) and Young’s modulus were compared. Samples with a higher density were obtained when the irregularly shaped graphite was considered as the matrix component (lubricant). The results showed that the use of GO had a positive impact on the mechanical properties of the graphene-reinforced Al2O3–C refractories, especially in the case of a less optimized packing, due to the bridging of delamination gaps. In addition, the thermal shock only had a minor impact on the Young’s modulus and CMOR values of the samples. SEM investigation revealed very similar microstructures in coked as well as thermally shocked samples.

Preparation, microstructure and properties of Al2O3–ZrO2–C slide plate material in presence of nanoscale oxides

Low carbon Al2O3–ZrO2–C refractories with nano-oxides are prepared at 1500 °C in graphite embedded condition using tabular alumina, reactive alumina powder, zirconia-mullite, zirconia-corundum and flake graphite as well as nano-ZrO2, nano-TiO2 and nano-Al2O3 powders as additives. The effects of nano-ZrO2, nano-TiO2 and nano-Al2O3 powders as single additive on the properties and microstructure of Al2O3–ZrO2–C material are investigated. The results show that nano-oxides take the catalytic effect in SiC nanowires (NWs) formation and growth, leading to increasing in length-diameter (L/D) ratio of SiC NWs. Samples with nano-oxides addition possess improved sinterability, thermal shock resistance and oxidation resistance.

Enhancing mechanism of improved slag resistance of Al2O3-spinel castables added with pre-synthesized (Al,Cr)2O3 micro-powder

In order to enhance the slag resistance of Al2O3-spinel castables, (Al,Cr)2O3 is added into Al2O3-spinel system as a pre-synthesized micro-powder. Firstly, (Al,Cr)2O3 micro-powder is synthesized by sintering under reduction conditions to prevent the formation of hexavalent chromium. The Al2O3-spinel castables are prepared using tabular alumina, fused spinel, α-Al2O3 micro-powder, calcium aluminate cement and (Al,Cr)2O3 micro-powder as the raw materials. The bulk density, porosity, mechanical properties, and slag resistance of the samples are tested. Afterward, the effects of (Al,Cr)2O3 micro-powder (0–3 wt%) on the slag resistance and microstructures of the Al2O3-spinel castables are assessed by X-ray diffraction (XRD) and energy-dispersive (SEM-EDS) analysis. The results show that the addition of (Al,Cr)2O3 micro-powder can could inhibit the deteriorating effects of Cr3+ on the mechanical properties of the samples. The microstructure results also shows that with the addition of the (Al,Cr)2O3 micro-powder, a secondary solid solution of Ca(Al,Cr)12O19 formed, causing the unit cell to become larger. In the slag erosion area, CA6 crystals formed with network-like interwoven structures, high density, and greater thickness. These characteristics significantly reduce the erosion and permeability indices of the castables, and improve the slag erosion resistance of the material.