Ceramic Castables Research Articles

Cementless refractory castable. Part 9. HCBS and ceramic concretes in the Al<sub>2</sub>O<sub>3</sub>‒SiO<sub>2</sub>‒SiC system

The priority-chronological aspect of research and technological development in the field of SiC-containing HCBS and ceramic castables in the systems Al2O3‒SiO2‒SiC and Al2O3‒SiO2‒SiC‒C is characterized. The results of studies on the effect of the firing temperature and prolonged (up to 100 h) high-temperature heat treatment on the oxidation kinetics of SiC of different dispersion and content are considered. A noticeable oxidation, accompanied by an increase in the mass and growth of samples, is noted after 1200 °C and significant at 1300‒1400 °C. The effect of the firing temperature in the range of 1000‒1400 °C and long holding in a tunnel furnace (60 h at 1300‒1400 °C) on the dynamics of phase transformations and the structure of samples of the matrix system based on HCBS of composite composition (bauxite + 11 % VFQG), as well as with an additional content of 15% SiC. In contrast to firing in air, during the service of monolithic gutter masses in the Al2O3‒SiO2‒SiC‒C system, the working surface of concrete is largely isolated from the air due to cast iron and slag. This drastically reduces the rate of both SiC oxidation and carbon burnout. The zonal structure of the lining is characterized. The data on the effect of heating and cooling on the modulus of elasticity of ceramic castable are presented.

Design of Experiments (DOE) applied to high-alumina calcium aluminate cement-bonded castables

Using statistical methods (such as Design of Experiments – DOE) is an important issue due to the increasing demand to reduce costs and optimize properties of different processes and products. In order to assess the feasibility of these techniques in the refractory field, the Response Surface Method (RSM) and Tukey test were applied to optimize the modulus of rupture of high-alumina calcium aluminate cement (CAC)-bonded castables after curing and drying, considering three continuous factors (the amount of water, cement and dispersant) and a categorical one (the drying process). In addition to the cold mechanical strength, the flowability and apparent porosity of all the castable samples were also measured. The Tukey test pointed out the composition with the highest strength after curing and after drying. Based on the attained RSM models, the first one (considering all four factors) indicated the composition with the highest modulus of rupture after curing, but it could not properly predict the castables' properties after drying. The other two RSM models analysed different processing conditions (post curing and post drying, separately) highlighting that the complexity of the drying stage related to the hydration of the cement phases invalidated the models used for the post drying condition. The major difficulty in using statistical techniques comes from the transient and non-equilibrium conditions experienced by refractory ceramic castables during their processing and working conditions.

Pressure-molded high-alumina ceramic castables. 3. Effect of processing additives on pressure-induced compaction and properties of bauxite-quartz glass matrix systems

The effect of lignosulfonate (LST) and surface-active substances (SAS) on compaction and properties of bauxite-quartz glass matrix systems is studied. LST added at an optimum concentration to bauxite-based highly concentrated ceramic binding suspensions (HCBS) causes a 2–3% decrease in preform porosity. In materials sintered at high temperature the effect of decreased porosity is more pronounced. In preforms molded at 500–700 MPa no defect due to overpress is observed. The SAS, judged from their efficiency for decreasing porosity, are arranged in ascending order: sodium silicate water glass, sodium tripolyphosphate, complex organomineral thinner, and FS-20 castament.

A new generation of unshaped refractories

The world trends in the development and consumption of refractory materials are considered. A brief overview of the advance in the foreign production of zero-cement refractory castables (ceramic castables) is given. The importance of controlled gelation techniques for accelerated structure formation in refractories is emphasized.

Pressure-molded high-alumina ceramic castables. 2. Compaction and properties of materials based on plasticized bauxite HCBS, reactive alumina, and their binary mixtures

The effect of compacting pressure (20–100 MPa) on the densification of refractory clay plasticized molding mixes based on bauxite HCBS containing 10% highly dispersed quartz glass, reactive STS-30 alumina, and their binary compositions has been studied. The properties of these materials subjected to heat treatment are discussed. Optimum compositions for binary systems are formulated that show promise as matrices for refractory materials and for preparation of engineering ceramics.

Press-Molding of High-Alumina Ceramic Castables. 1. Compaction and Properties of Matrix Systems Based on Mixed HCBS of Composition: Bauxite, Quartz Glass, and Commercial Alumina

Preparation of powders based on bauxite HCBS (Highly Concentrated Ceramic Binding Suspensions) containing high-disperse quartz glass and plasticized with refractory clay is described. The powders, molded at moderate pressure (50 – 100 MPa), give a high-density material with an initial porosity of 20 – 25%. Mixes containing 10 to 43% commercial alumina are tested. The materials can be used as matrices for press-molded high-alumina ceramic castables which, when sintered, show a high mechanical strength and volume constancy.

Effect of Thinning Agents on Properties of High-Alumina Ceramic Castables

The effect of thinning agents on molding mixtures for the production of high-alumina ceramic castables composed of bauxite HCBS (highly concentrated ceramic binding suspensions) and a refractory filler based on fused corundum and SiC is studied. The thinners used were sodium tripolyphosphate (STPP), SB-5-grade organic plasticizer, mixtures thereof, and liquid glass. The maximum thinning effect is observed for complex organomineral additives (10 – 33% SB-5 + 67 – 90% STPP). The optimum thinner concentration is 0.08 – 0.1 wt.%. The use of thinners makes it possible to reduce significantly the water demand of concrete mixes and leads to a decrease in porosity and an increase in strength of ceramic castables. The composition and concentration of alkali-containing thinners produce little (if any) effect on the deformation behavior of ceramic castables at high temperatures.

Nanoparticles and Their Effective Use in the Technology of Highly Concentrated Binding Suspensions (HCBS) and Refractory Castables. Part 2

Properties of sintered preforms based on bauxite HCBS with and without finely dispersed quartz glass are compared. The sintering of preforms based on nanoparticles separated from these suspensions are studied. The incipient sintering process in nanoparticles is 300 – 400°C lower in comparison to HCBS-based materials. The porous structure of ceramic castables of different composition is analyzed and shown to be controlled to a significant extent by nanoparticles contained in them.

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.

Structurization of unshaped refractories

The pore structure and properties of vibration-cast high-alumina ceramic castables of three compositions based on highly concentrated binding suspensions of bauxite (HCBS) and different refractory fillers are studied. The matrix (binding) system of ceramic castables is characterized by a structural porosity with a median pore diameter of 0.55 μm. HCBS particles with a size less than 1 – 2 μm are mainly responsible for the structural porosity of both the matrix system and ceramic castable.

HIGHLY CONCENTRATED CERAMIC BINDING SUSPENSIONS (HCBS) AND CERAMIC CASTABLES. STAGES IN RESEARCH AND DEVELOPMENT

Precisely 25 years ago, in the journal Ogneupory (February, 1978), our paper “Fundamentals of ceramic castable technology” was published [1]. Earlier, the principles outlined in that paper were reported and discussed at All-Union conferences held in 1976 in Sverdlovsk and Leningrad. Dating back to 1968, the first data on highly concentrated binding suspensions based on quartz glass were reported in [2, 3]. The technology of ceramic castables is precisely based on the use of ceramic binding suspensions. In 1969 [4], a method for preparation of refractory castables of granular structure using ceramic binding suspensions was reported. A survey of world trends in the development, production, and application of new refractory materials [5 – 8] shows that, viewed in this light, the papers [1 – 4] were pioneering in the field. In particular, these papers provided data, previously unreported, on the preparation of ultra-low-cement and zero-cement refractory castables, that is, refractory materials that at present have a potential for wide applications [6, 7]. In this paper, we discuss, in a historical aspect, priorities and achievements in the field of materials based on highly concentrated ceramic binding suspensions (HCBS).

Cast (self-flow) ceramic castables. 4. Spreadability of molding systems and some properties of mullite - silicon carbide ceramic castables

The rheological properties of molding systems are shown to depend on the spreadability of the mixture under the action of its own mass; some of the factors influencing the self-flow are determined, namely, the moisture content, the content of the filler, and the temperature of the mixture. The described self-flow castables based on a mullite HCBS and a SiC filler have a porosity of 18% after drying and 16 – 16.5% after heat treatment. Their ultimate bending strength is 45 MPa and the ultimate compressive strength is 110 MPa, which is higher than those of the known refractories of similar compositions. The temperature of 4% deformation of mullite – silicon carbide refractory heat treated at 1350°C and having CVf = 0.4 is 1710 – 1720°C, which is 70 – 80°C higher than that of a similar material molded by pressing and heat treated at 1500°C.

Production and service of high-alumina ceramic castables. 1. Ramming mixtures based on modified bauxite HCBS

The prospects of using bauxite-base HCBS in the production of high-quality ramming mixtures for lining blast furnace spouts are considered. A system of Chinese bauxite (filler) and bauxite HCBS (binder) is shown to give a ramming mixture with a porosity of 18 – 22% and σc of 120 MPa. The effect of some process factors on the properties of the new refractory material is considered. The life of the mixture in the main hearth spout is shown to be 70 – 90 thousand tons cast iron before the first repair at a consumption of 0.53 – 0.63 kg mixture per one ton cast iron. The processes that occur in the interaction between the material and blast furnace slags of various chemical compositions is considered. The characteristics of the developed mixture are compared with those of the standard ones.

Ceramic castables: Concluding stage in the evolution of low-cement refractory concretes (part I)

Ceramic castables: Concluding stage in the evolution of low-cement refractory concretes (part I)

Cast (Self-Flow) Ceramic Castables. 3. Rheotechnological Properties of Molding Systems for Fabrication of Silicon Carbide Ceramic Castables

Results of a study of the rheotechnological properties of high-alumina suspensions with a granular silicon carbide filler are presented. It is shown that the rheological behavior of the suspensions changes with the introduction of the filler. The dependence of the effective and relative viscosities on the volume fraction of the filler is considered, and ηmin is calculated for systems with nonuniform chemical composition. The minimum viscosity of filled suspensions is shown to obey the Pivinskii equation for chemically uniform and nonuniform systems. The minimum distance between the filler grains is determined depending on the amount of the filler and its mean grain size.

Cast (self-flow) ceramic castables. 2. Effect of structurizing additives of high-alumina cement on the properties of silica ceramic castables

HCBS of quartz sand modified by additives of high-alumina cement (HAC) and polydisperse silica fillers are used to obtain self-flow cast ceramic castables with a porosity of 16–18% and an ultimate compressive strength of 20–50 MPa after a heat treatment at 1000‡C and 60–110 MPa after a heat treatment at 1300°C. A low additive of HAC (0.35–0.45%) accelerates the process of hardening and causes a certain (by 1–2%) increase in the porosity as compared with ceramic castables without such an additive. An increase in the HAC content to 1–3% causes a marked increase in the porosity and a decrease in the strength of the castable.

A study of components of the binding (matrix) system of new refractory concretes. Part I. components and general characteristics of binding systems

New refractory concretes (such as ceramic castables and super-low-cement concretes) are considered and analyzed as composite materials consisting of a highly disperse binding system (matrix) and a polydisperse refractory filler. The mineral and grain compositions of binding systems used in fabricating ceramic castables and low-cement concretes are characterized. HCBS are characterized by the presence of ultradisperse particles in their composition (a colloidal component < 0.1 (μm) which determine the binding properties. A pioneering definition of a binding system for new refractory concretes is suggested.

Cast (self-flow) ceramic castables. 1. Fabrication and some properties of cast silica ceramic castables

A classification of methods for manufacturing cast (without the use of vibration) ceramic castables is suggested and the mechanism of their structure formation is formulated. Cast (self-flow) castable mixtures with a moisture content of 4.8–5.5% are developed based on HCBS of quartz sand and a polydisperse silica filler (dmax = 1–7 mm). The mixtures are used to cast ceramic castables with an open porosity of 11–16%. After drying and heat treatment at 1200 and 1300°C their ultimate compressive strength is 6–14, 20–35, and 60–120 MPa, respectively. As compared with similar pressed and rammed ceramic castables; cast ones are characterized by a lower porosity and a substantially higher strength.

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.

Materials based on highly concentrated ceramic binding suspensions (HCBS). The effect of heat treatment temperature on the strength properties of siliceous ceramic castables

Mechanical properties of siliceous ceramic castables shaped by vibration and static pressing with binders of quartz sand HCBS (pure and with a 5% additive of refractory clay) are studied. Other conditions being equal the porosity and the strength of the materials is affected by the content of the binder (varied from 10 to 33%). Ceramic castables heat treated at 1200 — 300°C exhibit a compressive strength of 50 –60 MPa at a porosity of 12–16%. The effect of the porosity on the strength of the materials is analyzed.