Low Cement Castables Research Articles

Benefits of Enhanced Mullitization upon Addition of Micronised Andalusite to Low Cement Castables

In the formulation of low cement castables, microfine additives are so selected that predominating phase will be mullite in the matrix of the alumina based castable refractories. Andalusite behaves like a reactive mullite as during mullitization the expelled glass from the grains can be easily combined with required amount of micronised alumina, giving rise to a secondary mullite acting as a binder and converting the total castable matrix into a well distributed mullite. Mullitization process in andalusite depends on its grain size; attrition milled micronised andalusite grains undergo Mullitization even at 1200°C with release of glassy phase through a topochemical and topotactic process resulting in volume stability and high thermal shock resistance. The effect of micronised andalusite and coarse grained andalusite on the properties like bulk density, apparent porosity, volume change, strength before and after spalling cycles of the low cement castables have been compared. XRD studies have been made to identify the phases and SEM studies have been performed to get an idea about the microstructure.

Improvement of properties of self-flowing low-cement castables based on brownfused alumina

Improvement of properties of self-flowing low-cement castables based on brownfused alumina

Properties of alumina based low-cement self flowing castable refractories

The main aspects that determine flowing properties of self flowing alumina based low-cement castables are determined. From the point of view of particle size distribution, different particle size distributions are compared by using Andreassen model according to n-value. The n-values are varied as 0.20, 0.21, 0.22, 0.23, 0.24 and 0.25 to define which one corresponds to the best flowing properties. The prepared castables are fired at different temperatures. Rheological and physical properties of prepared castable refractories were examined. It is found that the self flowing refractory which is prepared by using 0.23 n-value has the best self flowing properties. In addition to these studies, different alumina types which affect the aggregate system, and the roles of additives (calcined alumina, microsilica) are also examined by using n = 0.23 value. Finally SEM studies are performed to investigate the microstructure of these self flowing castables.

Control of Strength Enhancement Conditions of Low Cement Castable on The Construction Cite

Control of Strength Enhancement Conditions of Low Cement Castable on The Construction Cite

Influence of gel-derived nanocrystalline spinel in a high alumina castable: Part 2

An in situ spinel–alumina castable was prepared by incorporating 8.0 wt.% chemical grade pure magnesia fine in a high alumina-based low cement castable. Its porosity, density, spalling resistance and crushing strength were compared elaborately with the similar kind of refractory prepared with 8.0 wt.% of nano-dimensional spinel synthesized via sol–gel route. The microstructural aspects of both of them were carefully analysed, with special emphasis on the respective fired matrices by scanning electron microscopy (SEM) and the energy dispersive spectral (EDS) analysis. The co-precipitated spinel bonded specimen (CN) used in the previous work was also considered, particularly to estimate the rank of its slag corrosion resistance relative to the other two types. Infra red (IR) spectra and transmission electron microscope (TEM) micrographs of the selective additives with X-ray diffraction (XRD), hot modulus of rupture (HMOR), thermal shock behaviour of the selected castables were taken into consideration to evaluate the prospect of the gel-routed nanocrystalline additive.

The effect of deflocculants on the self-flow characteristics of ultra low-cement castables in Al 2O 3–SiC–C system

The influence of several deflocculants on the self-flow characteristics of an ultra low-cement high-alumina castable in the Al 2O 3–SiC–C system has been studied. The behavior of various deflocculants in high-alumina castables was evaluated in terms of apparent viscosity and pH of the matrix and self-flow value of the castable. Our study shows that the best self-flow characteristics in the Al 2O 3–SiC–C system is obtained using sodium polyacrylate and the optimum content is considered to be 0.06 wt.%.

Improving the structure and properties of a refractory castable containing porous chamotte fillers

The potential use of a porous (∼20%) chamotte filler in a low-cement castable with an integrated matrix is considered. Results of a study of the properties of conventional, medium-cement, and low-cement castables are presented.

Synthesis of mullite aggregates from fly ash: effect on thermomechanical behaviour of low cement castables

Refractory aggregates were synthesised from beneficiated fly ash by reaction sintering with calcined alumina at 1600°C, and 83% mullite yield was achieved. The aggregates had low porosity, low thermal expansion and good refractoriness. To study compatibility in castable refractories, the aggregates were used in high alumina cement based low cement castables and their thermomechanical behaviour was studied. Microstructural characterisation revealed that the emergence of new bond phases such as mullite and calcium hexa-aluminate had a beneficial effect on the hot modulus of rupture and creep resistance of castables. An attempt was made to establish a structure-property relationship.

Kinetics of Sintering of a Low-Cement Corundum Castable Modified by an Eutectoid Phase

The effect of an eutectoid additive on the kinetics of sintering of a low-cement corundum castable is studied. An eutectic in the CaO – Al2O3 system produced at 1395°C is shown to accelerate the sintering.

Comment on “Thermo-mechanical behaviour of low cement castables derived from mullite aggregates synthesised from beach sand sillimanite”

Comment on “Thermo-mechanical behaviour of low cement castables derived from mullite aggregates synthesised from beach sand sillimanite”

Design of bauxite-based low-cement pumpable castables: a rheological approach

The growing demand for pumping of refractory castables, as a high efficient placing technique, has stimulated the development of compositions with specific rheological properties. In this work, a new type of rheometer has been used to measure the rheological behaviour and to predict the pumpability of bauxite-based low-cement castables. This overcomes the shortages of traditional techniques based on either flow measurements or working with the matrix portion of castable. The parameters which strongly influence the rheological properties and pumpability of bauxite-based low-cement castable such as particle size distribution, ratios of coarse to matrix and water to matrix, water addition and time have been studied. It has been found that the optimal flow resistance and torque viscosity are two important properties to be taken into consideration while designing a castable.

Effects of Andalusite Grain Size on Microstructure and Mechanical Properties of Low Cement Alumina-Based Castables

Three high alumina-based, low cement castables each containing a 15% addition of andalusite of different grain size were compared to a similar castable containing micro-silica (3.7%) and no andalusite. All castables were fired at 1450 °C for 12 hours. High temperature mechanical properties of the castables were measured employing a wedge splitting test (WST). While the castable with the micro-silica addition exhibited superior strength properties, both strength and work-of-fracture values at high temperature improved in castables containing ultra fine andalusite powder. Microstructural factors leading to the observed differences in properties are discussed.

Effect of silica sol of different routes on the properties of low cement castables

Silica sols synthesized through different routes viz. inorganic, organic and ion-exchange routes, have been incorporated in the low cement alumina castable composition in various proportions and cast samples in the form of 2 inch cube briquettes were prepared. The cast briquettes after curing were subjected to heat treatment at various temperatures. The effect of different sources of such sols on the important physico-mechanical properties of the castables such as bulk density, apparent porosity, compressive strength, volume shrinkage and residual strength after spalling have been studied. Some of the selected samples were also subjected to microstructural evaluation. It is observed that silica sol synthesized through cation exchange routes has significant beneficial role on the properties of castable with 3% addition.

Ceramic Castables — Final Stage in the Evolution of Low-Cement Refractory Castables. Part 3

Technological and service characteristics of ceramic castables and low-cement refractory castables (LCRCs) are compared. Unlike LCRCs prepared from dry-ground powders, the ceramic castables contain a nanoparticle phase (5 – 100 nm), which to a significant extent determines their operational properties. The initial mechanical strength of ceramic binders can be increased substantially by adding water-soluble resins to their composition. A way toward developing oxide-carbon ceramic castables is outlined. Compositions for binding agents with enhanced high-temperature strength are developed.

Thermo-mechanical behaviour of low cement castables derived from mullite aggregates synthesised from beach sand sillimanite

Mullite aggregates were synthesised from beach sand sillimanite, a by-product generated during rare earth extraction, by reaction sintering with calcined alumina. The aggregates were characterised in terms of chemical composition, mineral phases, microstructure and important thermo-mechanical properties critical for refractory applications. To evaluate its suitability in castable refractories, low cement castables were prepared using the aggregates with commercial high alumina cement. The physical and thermo-mechanical properties such as bulk density, apparent porosity, cold crushing strength, hot modulus of rupture and compressive creep was studied in relation to temperature. The castables exhibited good modulus of rupture and excellent creep resistance at 1400 °C. Attempts were made to correlate these properties with corresponding microstructure and phases.

Bauxite based low and ultralow cement castables

Five batches consisting of 90 wt-% graded bauxite aggregate with 10 wt-% of different cement matrices were investigated for the processing of low (LCC) and ultralow (ULCC) cement castables. The influence of variation in high alumina cement (HAC) content and fine alumina/fumed silica ratio on the physical and thermomechanical properties of the hydrated castables before and after firing at 1400°C was studied. The results were interpreted in the light of solid phase composition and microstructure, on the basis of XRD and SEM characterisation. As high alumina cement content decreases from 5·0 to 3·3 wt-% and fine alumina/fumed silica ratio increases from 1·5-2·3 to 2·3-9·1, in the matrices of LCC and ULCC respectively, a gradual decrease in green bulk density and cold crushing strength occurs. The inverse of this behaviour occurs after firing the hydrated samples for 2 h at 1400°C. All processed LCC and ULCC samples show high thermal shock resistance on successive quenching from 1000°C to ambient temperature, high volume stability on refiring for 2 h at 1500°C, and high loadbearing capacity on firing under load up to 1600°C. The temperatures corresponding to maximum expansion T0 and the beginning of subsidence T0 0·5 gradually increase from 1400 to 1500°C and from 1560 to > 1600°C respectively on increasing the fine alumina/fumed silica ratio from 1·5-2·3 in LCC to 2·3-9·1 in ULCC samples, owing to the formation of acicular mullite.

Development of Low Cement Castables of the Al2O3 – SiC – C System

The use of refractory castables as a material for the lining of runners of blast furnaces is considered. LC- and ULC-type castables are developed in conformance with modern technological requirements and environmental standards. Coal-tar resin as an environmentally friendly alternative to coal-tar pitch is proposed. SiC-containing regenerates (SiC-containing fireclay sagger scrap) are proposed as an ingredient for LC-type castables without detriment to their service properties.

Easy-to-use mullite and spinel sols as bonding agents in a high-alumina based ultra low cement castable

This paper deals with the preparation of colloidal suspensions of mullite and magnesium-aluminate spinel via a cheaper precursor of alumina sol. Viscosity, pH, solid content, DTA, TGA and XRD studies at different temperatures were performed to characterize those two sols. These mullite and spinel sols were used separately as bonding agents in a high-alumina based ultra low cement castable composition prepared by simple tapping technique and their performances have been compared in terms of bulk density, apparent porosity, cold crushing strength, flexural strength, slag corrosion, thermal shock, XRD and SEM reports. The results confirm that the mullite sol excels while the spinel sol degrades the refractory castable quality.

Influence of in situ phase formation on microstructural evolution and properties of castable refractories

The microstructural evolution on firing and quenching two commercial composition castable refractories, a vibratable ultralow cement castable and an in situ spinel low cement castable, was fully characterized and related to high-temperature properties. The emergence of refractory phases such as calcium hexaluminate, magnesium aluminate spinel and mullite was observed to have beneficial effects on hot bend strength and refractoriness under load due to the development of morphologies which interlocked other phases and to pore filling from expansile reactions.

Furnaces: Improving low cement castables by non-wetting additives

Aluminosilicate castables, which are widely used in aluminum transformation furnaces, are susceptible to chemical reactions between molten aluminum and the furnace refractory lining. To prevent those reactions, commercial additives such as BaSO4, CaF2, and AlF3 are generally added in castables. This article presents and analyzes the effect of various amounts of the above additives as well as the influence of pre-firing temperatures on the corrosion behavior of an aluminosilicate low cement castable matrix in contact with liquid Al-5%Mg alloy.