Low Cement Castables Research Articles

Non-destructive Evaluation of Cavitation Erosion Behavior of Alumina-based Ceramic Samples

Numerous industrial parts, devices, and processes are designed to withstand the conditions that lead to cavitation erosion. Metallic, ceramic, and composite materials used for these conditions must achieve specific mechanical characteristics required to resist cavitation erosion. When molten metal or alloy flows and comes into contact with refractory material or coated furnace linings, cavitation erosion can occur. This phenomenon is particularly expected in metallurgy, especially in casting operations. Alumina-based refractories, specifically low cement castable (ALCC), are often used in furnace lining applications due to their superior properties, such as high refractoriness, thermal stability, and mechanical characteristics. Mullite is another refractory material frequently used in foundry lining applications. It can be utilized as a coating in casting processes, such as the Lost Foam process, which is a novel method for producing high-quality, cost-effective castings. These two refractory materials were chosen to study their behavior under cavitation conditions. An ultrasonic vibratory test with a stationary specimen (ASTM G-32) was used for experimental cavitation determination. The results of mass loss and surface morphological parameters of degradation revealed that ALCC samples eroded predominantly at the surface, while the mullite samples exhibited more significant degradation by depth.

Recent progress in microsilica-gel bonded no-cement castables

This paper focuses on the recent advance in no-cement technology, mainly focusing on their properties, benefits, and prospects when calcium aluminate cement is replaced by a “dry-version” silica binder, using microsilica powder to replace silica-sol. A microsilica-gel bond system has been designed using microsilica powder and a tailor-made dispersant package to give excellent flow and to control the setting behaviour of the NCCs. The flow, set-behaviour and mechanical properties have been studied in comparison with silica-sol bonded NCCs and cement-bonded low cement castables (LCC). The microsilica-gel bonded NCCs not only exhibit higher flow, better workability and adequate green strength compared to the silica-sol bond system, but also entail easier handling, storage, and transportation thanks to the all-in-the-bag solution. The microsilica-gel bond system contains only a minor amount of cement as gelling agent; hence, the hot properties are much better than that of LCCs. Phase transformations and bond mechanism were investigated by SEM and XRD techniques after pre-firing at 1400 and 1500°C. Furthermore, the effect of drying agents on both lab- and industrial-scale explosion resistance was studied. The drying behaviour and explosion resistance of microsilica-gel bonded NCCs was further significantly improved by using a speciality drying agent (EMSIL-DRY™); a perfect 400 kgs block was produced with no problems using a fast-firing program (20°C to 850°C at a heating rate of 50°C).

Industrial waste-derived alumina-zirconia-silica low cement castable

High-strength low cement castables have been produced for the first time from the demolished waste of glass furnaces (AZS). Rheology studies indicate the high prominence of longchain ionizable sodium tripolyphosphate STPP (0,2 wt. %) as a dispersant for electrostatic stabilization and rheological characteristics improvement of the entire alumina-zirconiasilica refractory castable. In this work, four castable mixes of various Andreasen packing modulus (n 0,22, 0,23, 0,24, and 0,25) have been formulated using the Andreasen equation. The castable of Andreasen packing modulus n = 0,25 demonstrates an outstanding compressive strength (1118,15 kg/cm2 ) and a moderate bulk density (2,65 g/cm3 ) when fired at 1375 o C. It has showed the highest dimensional stability and its permanent linear change hasn’t exceeded 0,6 % at 1300 o C. This castable displays high thermal shock resistance (30 cycles) and high abrasion resistance (abrasion loss ~ 2,05 % after 280 abrasion test cycles) when fired at 1300 o C. Its superb abrasion resistance recommends its usage in high wear rate sections of cement kiln and its great thermal shock resistance makes it an excellent choice in the case of kiln instability. The outcomes indicated that the tailored castable of n = 0,25 is highly recommended for lining the inlet of rotary cement kiln at temperatures 1000‒1300 o C. In this context, this work opens the door wide for the use of glass kiln demolished waste for the installation of high-strength lowcement refractory castable for lining the inlet cement kiln. Ill. 11. Ref. 50. Tab. 3.

Properties dependence of castable samples from low-cement silicon carbide castable on the firing temperature and the gas atmosphere

The influence of firing temperature of 1000, 1100, 1200, 1300, 1400, 1580 °C and atmosphere (air and reducing) on the main properties of castable samples from low-cement silicon carbide castable grade of “NKBS” with a combined additive has been investigated.
 It was shown that, in air with an increase in the firing temperature in the range 1000—1580 °C, the content of silicon carbide in the castable samples decreases. Up to temperatures of 1200—1300 °C, the content of silicon carbide in the castable samples practically does not change, and oxidation slows down due to the formation of a viscous melt of a glassy phase of an alumina silicate composition on the surface of silicon carbide grains. An increase in the firing temperature above 1300 °C leads to a more intense oxidation of silicon carbide grains to SiO2, which causes a change in the porosity, density and strength of the samples. As a result of the carried out studies, it was found that, the using temperature in the air of the above mentioned low-cement silicon carbide castable should not exceed 1300 °C.
 It was found that, after firing in a reducing atmosphere in the temperature range of 1000—1580 °C in the samples of silicon carbide castable, the content of silicon carbide remains almost the same, and the density and strength increase, which ensures the efficiency of its use for lining thermal units operating in a reducing atmosphere up to temperatures of 1580 °C.

Dependence of the structural and rheological properties of a refractory vibrocasting low-cement alumina-chromia castable and the properties of samples from it on the type of dispersant additives

The effect of a new dispersant additive (on a polycarbonate basis) in comparison with a known additive based on polyethylene glycol on the structural and rheological properties of low-cement alumina-chromia castables with a moisture content of 4.5 % (flowability during vibration of freshly prepared castables and the kinetics of changes in the strength of their structure depending on holding time) and on the main properties of castables has been studied.
 Studies of the freshly prepared castables flowability during vibration have established that the additive based on polyethylene glycol has a 1.3 times greater thinning ability compared to the additive on a polycarbonate basis, but the latter is also suitable for the manufacture of vibrocasting aluminachromia castable. It has been shown that the shelf life of the mass with the addition based on polyethylene glycol is 5.5—6.0 hours, and the mass with the addition on the polycarbonate base is 3.0—3.5 hours. During the indicated time, these masses are still mobile and suitable for vibration casting.
 The formation mechanism of a coagulation-condensation-crystallization structure in the mass with the dispersant additive based on polyethylene glycol has been established. The final mechanism of structure formation in the mass with the dispersant additive on a polycarbonate basis is to be studied.
 It was shown that with the introduction of additives studied in this work into the low-cement alumina-chromia castable, castable samples with the additive based on polyethylene glycol were characterized by significantly higher property indices than castable samples with the additive on a polycarbonate base, however, the latter samples also have property indices that meet the specified requirements of the technical specifications. The properties of prepared dried unfired samples with the additive based on polyethylene glycol and on a polycarbonate base, respectively: apparent density — 3.12 and 2.93 g/cm3; cold crushing strength after hydration hardening for 7 days — 64 and 56 N/mm2.
 The properties of samples after firing at a temperature of 1580 °C: apparent density — 3.06 and 2.91 g/cm3; open porosity — 19.8 and 21.9 %; cold crushing strength — 196 and 70 N/mm2, respectively, with the additive based on polyethylene glycol and on a polycarbonate basis. But the properties of samples with the additive on a polycarbonate base are quite high, and it can be used, if necessary, as an alternative additive.
 As a result of the carried out research, the raw material base for the production of coarse-grained alumina-chromia castable and castable products from it has been expanded.

High-Temperature Chemical Stability of Cr(III) Oxide Refractories in the Presence of Calcium Aluminate Cement.

Al2O3-CaO-Cr2O3 castables are used in various furnaces due to excellent corrosion resistance and sufficient early strength, but toxic Cr(VI) generation during service remains a concern. Here, we investigated the relative reactivity of analogous Cr(III) phases such as Cr2O3, (Al1−xCrx)2O3 and in situ Cr(III) solid solution with the calcium aluminate cement under an oxidizing atmosphere at various temperatures. The aim is to comprehend the relative Cr(VI) generation in the low-cement castables (Al2O3-CaO-Cr2O3-O2 system) and achieve an environment-friendly application. The solid-state reactions and Cr(VI) formation were investigated using powder XRD, SEM, and leaching tests. Compared to Cr2O3, the stability of (Al1−xCrx)2O3 against CAC was much higher, which improved gradually with the concentration of Al2O3 in (Al1−xCrx)2O3. The substitution of Cr2O3 with (Al1−xCrx)2O3 in the Al2O3-CaO-Cr2O3 castables could completely inhibit the formation of Cr(VI) compound CaCrO4 at 500–1100 °C and could drastically suppress Ca4Al6CrO16 generation at 900 to 1300 °C. The Cr(VI) reduction amounting up to 98.1% could be achieved by replacing Cr2O3 with (Al1−xCrx)2O3 solid solution. However, in situ stabilized Cr(III) phases as a mixture of (Al1−xCrx)2O3 and Ca(Al12−xCrx)O19 solid solution hardly reveal any reoxidation. Moreover, the CA6 was much more stable than CA and CA2, and it did not participate in any chemical reaction with (Al1−xCrx)2O3 solid solution.

Effect of zircon surface coating on alumina grog and its influences on the properties of low‐cement castables

AbstractIn this investigation, four types of low‐cement castables (LCC) were prepared with sintered mullite, high alumina grog, unfired, and fired zircon coated on alumina grog. These castables were evaluated in terms of their physical, thermal, and thermomechanical properties. The castables prepared using sintered mullite showed good physical and thermal properties with higher TSR than castables with fired zircon coated on alumina grog due to higher mullite with lower anorthite phases. Fired zircon coated on alumina grog castables were superior with lower corrosion and higher TSR of castables to those of castables with unfired zircon coated on alumina grog and high alumina grog due to formation of zircon and zirconia phases and surface coated on alumina grog gave better corrosion resistance. Castables prepared using unfired zircon coated on alumina grog and high alumina grog showed poorer properties than the other castables due to formation of higher porosity of alumina grog.

Production of Fine-Ground NK-Alumina 11 and NK-Alumina 14 for Low-Cement Refractory Castables

Production of Fine-Ground NK-Alumina 11 and NK-Alumina 14 for Low-Cement Refractory Castables

Influence of lithium carbonate and superplasticizer as admixtures on low calcium dialuminate cement castable submitted to thermal shock

ABSTRACT The purpose of this study was to investigate the hot properties of low calcium dialuminate cement castable as binder with varying amount of Li2CO3 and castament FS20 superplasticizer as admixtures. Thermal damage test was carried out through quenching in air for five cycles ΔT = 1175°C. The samples were preheated at 1500°C for 2 h. The results gave a retained Young’s modulus of low-cement castable with 0.3 wt.% Li2CO3 and 0.5 wt.% castament down to 10.36% while 0.1 wt.% Li2CO3 and 0.5 wt.% castament showed a retained modulus down to 13.47%. For the samples without admixture, the loss of Young modulus was 92.4% and 93.7% with 0.3 wt.% of Li2CO3 admixture. The superplasticizer has a great effect on thermal shock resistance of low calcium dialuminate cement castable. The results confirmed that 0.1 wt%Li2CO3 and 0.5 wt% castament have better thermal shock resistance and longer service life for applications in refractories. The increase of mass of the refractory materials during five thermal shock cycles in air is the main factor affecting the degradation of this refractory material due to the oxidation of SiC to SiO2.

Effect of heat treatment and zircon addition on the properties of low-cement castables based on recycled alumina grog

In this investigation, low-cement castables were prepared using 70% alumina grog aggregates obtained from crushed alumina brick waste. The aggregates were thermally treated at 1550 °C for 3 h. Four types of low-cement castables were prepared with various types of aggregates (alumina grog with or without thermal treatment) and fillers (with or without zircon addition), and they were evaluated in terms of their physical, thermal, and chemical properties. Microstructural analysis via scanning electron microscopy (SEM) was performed on the castables before and after slag attack. Compared to the other fabricated castables, the thermally treated alumina grog castables with zircon showed better physical properties, such as a higher bulk density, cold crushing strength, and modulus of rupture and a lower apparent porosity and water absorption. In addition, they had a higher positive linear thermal expansion, refractoriness under load, permanent linear change, and hot modulus of rupture. The results of the SEM with energy dispersive X-ray analysis of the prepared castables confirmed that the mullite and anorthite phases were predominant when zircon was not added and the zircon–mullite phase additionally appeared upon the incorporation of zircon. A quantitative elemental analysis via X-ray fluorescence spectroscopy was employed to determine the composition of the castables. X-ray diffraction analysis showed that the alumina grog castables had a high mullite and low anorthite content, and the thermally treated alumina grog had a high anorthite, low mullite, and high zircon content. The improvement in the mechanical and thermo-mechanical properties of the castables with thermally treated alumina grog and added zircon can be attributed to the formation of the zircon–mullite phase with a low mullite phase content.

Cement free castable. Part 5. CFC on alumina hydraulic binder

Cement free castables (CFC) based on alumina hydraulic binders by the hardening mechanism are similar to low-cement castables (LCC) and ultra-low-cement castables (ULCC). They are characterized by significant strengthening in the heat treatment temperature range of 200‒300 °C and sharp softening in the 600‒1000 °C range. By introducing silica sols or microsilica into their composition, it is possible not only to reduce or eliminate the softening effect, but also to increase their strength after firing due to the process of mullite formation. Compared to LCC, CFC based on alumina binders are characterized by improved thermomechanical properties. A comparative assessment of CFC based on hydraulic binders with other types of refractory concretes is given.

Effects of Heating Rate on the Thermal and Mechanical Properties of the Bauxite-Based Low-Cement Refractory Castables

This study was conducted to investigate the effects of sintering conditions on the phase composition, microstructure, and physico-mechanical properties of the bauxite-based low-cement refractory castables. For this purpose, the specimens were sintered at various temperatures (1350-1450 °C) and heating rates (3-10 °C/min). Results showed that the sintering conditions have a remarkable effect on the physico-mechanical properties of the refractory castables. The mechanical strength was considerably increased by increasing the heating rate from 3 to 10 °C/min which was attributed to lower amounts of porosity and higher amount of the platy crystals of CA6 phase. The lower porosity of the specimens sintered at lower temperature with 10 °C/min of heating rate also resulted in the higher mechanical strength. The results obtained in this study showed a negative linear relationship between the cold crushing strength and porosity of the specimens with a high degree of measurement conformity.

Correlation of Thermo-Elastic Material and Corrosion Behavior of Refractory Castables by In-Situ Measurements

Corrosion is one of the most common wear mechanisms of refractories. Corrosive attacks lead to chemical and microstructural changes. Hot corrosion compromises chemical and/or physical interactions. Thus, the process is complex and not yet fully understood. Currently, corrosion is investigated post mortem by means of X-ray diffraction or scanning electron microscopy. These methods have the drawback that some information is lost on cooling. In-situ measurements, however, take measurements within the process. In resonant frequency and damping analysis (RFDA), a sample is excited to vibrate by a mechanical impulse. The vibrating sample emits an acoustic signal. This is recorded with a microphone and evaluated by means of Fast Fourier Transformation (FFT). We measured the change of the frequency of a low cement castable during the corrosion process. Further simplified experiments with less complex materials were done to confirm the results. Distinctive points of the curves could be correlated to specific corrosion phenomena, like melting or infiltration. The applied methods include a first characterization of the material with open porosity, density and in-situ high-temperature (HT)-RFDA measurements as well as a study of the slag behavior.

Improvement in Slag Resistance of No-Cement Refractory Castables by Matrix Design

The corrosion resistance of spinel containing cement bonded castables has been extensively investigated in the past. However, corrosion of no-cement refractory castables (NCC) has not been widely studied since the use of NCC has been relatively limited up till now. This paper focuses on the slag resistance of NCCs, and the often-used spinel containing low cement castable (LCC) is used as the reference. Three different NCC binders were designed: (i) Al2O3 + MgO (alumina bond), in situ spinel formation; (ii) Al2O3 + SiO2 (microsilica-gel bond), mullite formation; and (iii) Al2O3 + MgO + SiO2 (MgO-SiO2 bond). Slag resistance tests were conducted using the static crucible method with ladle slag. The corrosion mechanisms were studied by means of Scanning Electron Microscopy (SEM/EDS), X-ray Diffraction (XRD), and thermodynamic simulations. The results confirmed that the mineral phases, microstructure, and liquid formation at a high temperature of the refractory materials had a strong impact on the corrosion resistance. The slag resistance was significantly improved when the cement was replaced by the cement-free binders.

Customized Additives Solutions for Low-Cement Castables Technology

Customized Additives Solutions for Low-Cement Castables Technology

Effect investigation of the dispersion and type of fine-ground component, as well as the type of dispersing additives on the properties of low-cement periclase castable and samples from it

Researches have been carried out, as well as technological parameters have been developed for obtaining of low-cement periclase castable and products from it based on sintered periclase, periclase scrap, high alumina cement and dispersing additives. The possibility of using as cement brand of “VGTS-73” of own production of JSC “URIR named after A. S. Berezhnoy”, as well as cement Gorkal-70 (Poland) is established. The dispersion of fine-ground component of charge (mainly periclase and in a small amount of high alumina cement) and the possibility of using Castament FS-10 + Castament FW-10 (Germany), SioxX-Mag (Norway) and Lithopix P 5 (Germany) are established. Castament FS-10 + FW-10 and SioxX-Mag are more effective in terms of obtaining periclase castable products with better service properties. The temperature of thermal treatment of unburned products (350 оC), the firing temperature of products (~ 1450 оC) and the possible application temperature of fired products (1580 оC and above) are established.
 The developed low-cement periclase castables and samples from them are characterized, depending on the used dispersing additives, by the following indicators of physicochemical properties: content, wt. %: MgO — 85—86, SiO2 — 2.0—6.0, CaO — 1.5—2.5, Fe2O3 — not more than 2.0; grain composition, mm — 6—0; open porosity of the samples after thermal treatment at temperatures of 350 and 1450 оC is 20.3—23.0 and 18.8—22.8 %, respectively; apparent density of the samples after thermal treatment at temperatures of 350 and 1450 оC is 2.63—2.69 and 2.74—2.86 g/cm3, respectively; cold crushing strength of the samples after thermal treatment at 350, 1450 and 1580 оC — 19—38, 31—65 and 29—72 N/mm2, respectively; refractoriness under a load of 0.2 N/mm2 of the samples after thermal treatment at 1450 оC is 1450—1470 оC.
 The developed low-cement periclase castables and products from them are recommended for service in the conditions, above all, the impact of basis slags. The manufacture of castables and products from them is mastered at the pilot production of JSC “URIR named after A. S. Berezhnoy”.

Microwave and conventional treatment of low-cement high-alumina castables with different water-to-cement ratio; Part II. Dehydration

Modern refractory castables contain between 3.5 and 5 wt.-% water that is necessary for sufficient flow during emplacement and for the formation of hydrate phases, necessary for the green strength of the material. Prior to the high temperature use of this material, it must be dried very carefully to avoid explosive spalling.This paper will demonstrate that beside conventional drying of pre-shaped materials in resistance furnaces microwave radiation is an energy saving and rapid method to remove pore water as well as hydrate bond water from the castable. In comparison to resistance furnaces, the use of microwave radiation does not affect the castable properties as there are mechanical strength (MOR, CCS), open porosity and pore size distribution. This study proved microwave radiation as valuable alternative with a series of tabular alumina based low cement castables (LLC) in which the water-to-cement-ratio (wcr = 0.64, 0.75, 0.82 and 1.13) was systematically altered by changing the cement concentration at constant mixing water concentration of 4.5%.

Reduction of POME final discharge residual using activated bioadsorbent from oil palm kernel shell

Abstract A double insulated carbonisation-activation reactor was developed in order to produce activated carbon with high yield and surface area. This reactor was double insulated using low cement castable and covered around the internal space of the reactor with stainless steel plated and fibre glass jacketed heat insulation layer, which allow efficient heat transfer into the bed of material in the reactor. The carbonisation of oil palm kernel shell (OPKS) at 400 °C, followed by steam activation at 500–1000 °C continuously in the same reactor, with steam flow rate of 12.80–18.17 L/min had improved the activated carbon surface area from 305 ± 10.2 m2/g to 935 ± 36.7 m2/g and gave a high yield of 30% within 7 h retention time with a low gaseous emission. The activated carbon produced was successfully applied as bioadsorbent for the treatment of POME final discharge with the reduction of TSS, COD, colour and BOD up to 90%, 68%, 97% and 83%, respectively which met the standard set by Department of Environment Malaysia (DOE).

The influence of Al 2 O 3 nanoparticles addition on the microstructure and properties of bauxite self–flowing low-cement castables

In this research, the impact of Al2O3 nanoparticles addition on microstructure, mechanical, and physical properties of bauxite self–flowing low-cement castables were investigated. Also, the optimum amount of Al2O3 nanoparticles is determined. For this propose, up to 3 wt% Al2O3 nanoparticles were added to the bauxite castable compositions. The physical and mechanical properties of castable compositions such as bulk density (BD), apparent porosity (AP), self-flow values (SFV), and cold crushing strength (CCS) were examined. Also, the X-ray diffraction (XRD) and scanning electron microscopy (SEM/EDX) techniques were used for detection the ceramic phase's formation and microstructural analysis of the castables compositions, respectively. Results show that addition of Al2O3 nanoparticles up to 1 wt% improved the properties of bauxite self–flowing low-cement castables. As well as, the use of Al2O3 nanoparticles led to the formation of the platy and needle crystalline phases such as hibonite (CaO·6Al2O3), calcium dialuminate (CaO·2Al2O3), and mullite (3Al2O3·2SiO2), between the grain boundaries of the bauxite particles. Also, Al2O3 nanoparticles addition led to aforementioned phase formation occur at the lower temperatures.

High Temperature Erosion of Dense Refractory Castables for CFBC Boilers

The erosion resistance of dense refractory bricks or castables used in CFBC boilers is tested as per ASTM C 704. This method of testing determines the relative erosion of a refractory at room temperature only. Hence, solid particle erosion at elevated temperatures is desired in selecting the suitable refractory quality for boiler applications. The dense refractory materials for CFBC boilers are usually eroded at operating temperature (∼900°C) by hot circulating solids at high temperatures. In this work, low cement castable−45, low cement castable−80 and an 80% alumina-based plastic refractory castable, three varieties of dense refractory castables used in CFBC boilers, were selected for testing of erosion properties. The erosion tests were conducted at room temperature and boiler operating temperature of 900°C at three different angles of impingement (30°, 45° and 90°) using specially developed high temperature erosion test equipment following the ISO 16349 (2015) standard. The erosion loss result values (in cm3) were compared, and this comparison is useful in selection of suitable material for various erosion prone zones of the boiler.