Search

Polymeric fibers are often used as a drying additive for refractory castables because they can increase their permeability, reducing the risk of pressurization that is believed to trigger explosive spalling. Despite the potential of synthetic polymers to be engineered and obtain desired properties, the required parameters for inducing permeability enhancement remain unclear. This inhibits the development of novel designed drying additives and improvement of the numerical models. This work investigates the effect of polypropylene (PP), polyethylene (PE) and cellulose fibers on the water transport in refractory castables through rapid neutron tomography, enabling the in situ visualization of the water distribution, the drying front advance and the size, intensity and duration of moisture accumulation. PE and cellulose fibers accelerate drying fronts earlier than PP, in which PE exhibits larger moisture accumulation, residual moisture behind its drying front and a slower drying rate at higher temperatures despite the early water removal initiation. In contrast, cellulose emerged as a better candidate, due to a swelling–shrinkage based mechanism. The neutron tomography observations unveil the dynamic and intricate effect of fibers in the permeability, emphasizing that safer industrial processes require a deeper understanding of the underlying mechanisms to develop better fibers and accurate numerical models. [ABSTRACT FROM AUTHOR]

During tapping of liquid hot‐metal from the blast‐furnace, the blast‐furnace main trough gets exposed to air and the blast‐furnace‐trough refractory becomes prone to oxidation. In this work, isothermal oxidation kinetics of an Al2O3–SiC–C‐based BFT (Blast‐Furnace‐Trough) refractory castable using a high‐temperature vertical tubular furnace equipped with a microbalance is investigated. Herein, it is observed that up to about 800 °C, carbon only oxidizes, resulting in weight loss in the refractory. Around 900 °C, SiC also starts to oxidize via the passive‐oxidation mechanism, leading to the formation of a mullite phase as a result of the reaction between SiO2 generated via passive oxidation and Al2O3 already present in the refractory. This causes a volume expansion and weight gain, both having a beneficial effect on the refractory performance, which is further validated from apparent porosity measurements. Thus, above 900 °C, simultaneous oxidation of C and passive oxidation of SiC occurs, which eventually stabilizes the weight of the refractory. Around 1100 °C, the oxidation process of the refractory is practically complete, with no further increase in the oxidation rate beyond 1100 °C. The activation energy for the oxidation process is obtained as 37.2 ± 5 kJ mol−1 in the temperature range 600–1150 °C. [ABSTRACT FROM AUTHOR]

The anisotropic characteristics of thermal deformation of ultrapure 2,4-dinitroanisole (2,4-DNAN) crystals were determined by the methods of powder thermorentgenography of the internal standard. The points of structural changes are registered in increments of 10 K, and in the melting region of 2 and 1 K. Calculations of powder X-ray diffraction data are performed by methods of full-profile analysis with a cycle of quantum modeling of the structure of molecules integrated into the algorithm. The Pauli, Le Bail (WPPD), Rietveld (WPPF) and WPPM methods were used as reference methods for full-profile analysis. The main crystallographic axes and characteristic surfaces of the thermal deformation tensor α and β-2,4-DNAN are determined. At atmospheric pressure, the main coefficients of linear (α) and volumetric (β) thermal deformation (expansion) were at 293 K for α-2,4-DNAN with α1(293) = 11,516 x 10-5 K-1, α2(293) = - 0,120 x 10-5 K-1, α3(293) = 5,098 x 10-5 K-1, β(293) = 16,333 x 10-5 K-1; at 293 K for β-2,4-DNAN with α1(293) = 13,217 x 10-5 K-1, α2(293) = 0,494 x 10-5 K-1, α3(293) = -8,6504 x 10-5 K-1, β(293) = 6,8191 x 10-5 K-1; at 260 K for β'-2,4-DNAN with α1(260) = 25,214 x 10-5 K-1, α2(260) = -5,823 x 10-5 K-1, α3(260) = 7,741 x 10-5 K-1, β(260) = 27,112 x 10-5 K-1. [ABSTRACT FROM AUTHOR]

In this research, the microstructural and mechanical characteristics of metakaolin-based geopolymer reinforced with chamotte particles was investigated at room temperature and after exposure to high temperatures (600–1200 °C). The flexural strength and the appearance of the samples indicated the effective presence of chamotte particles as a reinforcement within the matrix of geopolymer. This was due to crack control in the composite and enhanced volume stability. The connection between chamotte particles and geopolymer binder boosted the flexural strength to 22.15 ± 1.37 MPa at room temperature. Heated composite samples at 800 °C showed improved mechanical performance of the thermally stable chamotte aggregates. However, leucite crystallization at 1000 °C caused volume instability and upon elevating temperature to 1200 °C, leucite peak intensity was more pronounced, which was responsible for the reduction of the strength in the composite. As a result, leucite phase formation in the matrix changed the connection behavior to the fragile state and the particles departed the matrix at high temperatures. The results of this research revealed good compatibility between the geopolymer matrix and chamotte particles for producing low-cost castable refractories up to 800 °C. [ABSTRACT FROM AUTHOR]

Refractories play an important role in societies' progress as they enable extensively consumed materials to be processed such as steel and cement. Because of the high demand of these supplies, refractory-lined equipment comprises massive structures that have large dimensions and weighs several tons. Conversely, laboratory samples, used to study the behavior of these materials, are orders of magnitude smaller and often found weighing less than 1 kg. Within the context of refractory castable drying, this work aims to investigate the impact of size effects on water removal dynamics during thermogravimetry tests. The analysis of mass loss and its derivative with respect to temperature indicates that increasing the heating rate applied in the small samples can lead to a better reproduction of the evaporation and ebullition stages of the drying of large ones, due to the compensation effect of the faster temperature increase on the smaller sample sizes leading to similar thermal gradients. Furthermore, the presence of polymeric fibers and their influence on the size effect are also examined, showing that the increased permeability induced by such additives reduces the intensity of the scale effect. Additionally, it was found that for cubic samples with sizes equal to or larger than 10 cm, a kink in the temperature evolution measured at the center of the samples took place. A hypothesis based on the results and on observations of recent studies is proposed to explain this phenomenon, attributing it to the rapid evaporation of accumulated liquid water at those positions. This study also highlights the importance of considering the size-dependent nature of drying dynamics in refractory castables, as conventional thermogravimetry on laboratory scale samples may overlook important phenomena. Understanding the mechanisms occurring at real structural scales during water removal is crucial for predicting their behavior upon heating and enabling faster and safer drying processes for refractories. [ABSTRACT FROM AUTHOR]

Magnesia (MgO) based brick type refractories are widely used in basic high temperature processes, especially in steel production, with their positive properties such as good refractoriness, resistance to high temperatures and high chemical stability in basic environments. Although the "brick" types of MgO are widely used, the "castable" applications have not developed at the same pace. This is because MgO is hydrated in an aqueous medium. In this study, the effect of chemical composition on the physical, mechanical and corrosion properties of magnesia-based castable refractories containing tabular alumina in different proportions was investigated. MgO-based pourable mixtures with 0, -3, -6 and -10 wt% Tabular Alumina were prepared and their free flow suitability was determined by self-flow test. According to the results; 6 wt% and -10 Tabular Alumina doped castables, passed the test and its suitability for self-flowing was determined. However, in order to be compared with each other, all mixtures were shaped in vibrating molds. The shaped samples were sintered by firing at 1600℃ after a slow curing regime for effective dehydration and drying of MgO. Physical tests such as bulk density, apparent porosity and water absorption determination, mechanical tests such as cold compressive strength test, and chemical corrosion tests such as slag-refractory corrosion test were applied to the fired samples. The findings obtained as a result of characterization analyzes such as XRD and SEM/EDX were presented and analyzed comparatively. As a result of these studies; By revealing the effects of tabular alumina additive on MgO based castable refractory materials, the limits of self-flowing property were tried to be determined. [ABSTRACT FROM AUTHOR]

Colloidal bonds are realized by sol–gel technology. The binder system of the refractory castable belongs to the Al2O3–SiO2 binary diagram. Mullite is the most thermally stable mineral in this system. This work was motivated by an attempt to maximize the mullite content in the NCC binder system, because a high content of mullite is a guarantee of the long service life of refractories. Initially, the mineralogical composition of the pure gel was tested after drying and firing at temperatures between 1000 °C and 1600 °C. The behavior of the gel during drying was described. Subsequently, a method of minimizing gel shrinkage during drying was sought. To this aim, fine fillers (microfillers) of alumina and silica were tested. In particular, the reactivity of the microfillers, the ability of the microfillers to react with the sol to form mullite, and the drying shrinkage of the microfiller-doped gel were evaluated. The study showed that the least suitable source of Al2O3 in terms of its reactivity is tabular corundum, which produces the lowest amount of mullite. The internal structure of the prepared binder system when using different microfillers was described. Based on the results from the second stage of the work, several complete matrixes of the binder system were designed and the degree of their mullitization at different firing temperatures was studied. During this stage, it was shown that the degree of mullitization of the binder system depends mainly on the microsilica content. In the binder system, the maximum mullite content recorded was 76%. The effect of amorphous SiO2 on the bulk density and internal structure of the binder system was also described. [ABSTRACT FROM AUTHOR]

Creep strain recovery after unloading has been well studied for metals and certain ceramic composites; however, it has not yet been investigated for ordinary ceramic refractories applied in industrial furnaces. The present study explores the question whether creep strain recovery can be observed in ordinary ceramic refractories to justify its consideration in the design of such refractories and refractory linings. To this end, the dependence of creep strain recovery on different loading conditions was investigated for a high-alumina in situ spinel-forming castable, commonly used as refractory lining of steel ladles in secondary steel metallurgy. Several loading/unloading compressive creep tests were performed at 1300 °C for different loading histories. Creep strain recovery was observed to occur and it was significantly affected by the holding time and degree of unloading. A longer holding time for the loading period was found to increase the internal stress, which is the driving force for creep strain recovery. In addition, the findings indicate that a higher excess of internal stress over external stress after unloading induces higher strain recovery. [ABSTRACT FROM AUTHOR]

Refractory castables present special features that render them unique and the most appropriate solution for lining specific high-temperature industrial equipment. Hydraulic bonded monolithics develop mechanical strength at room temperatures due to the hydration of some of its constituents, such as calcium aluminate cement. Their most significant drawback is the drying step, which takes place before firing and requires several hours of slow heating rates and plateaus to reduce the likelihood of facing explosive spalling. This phenomenon is a result of water vapor pressurization, as well as thermomechanical stresses. As an alternative to reduce the time and CO 2 generation, microwave heating can be a promising solution as the volumetric nature of the temperature increase can make this process safer. Besides this benefit, the likelihood of using green energy and the higher efficiency of this method add to the potential benefits. The present work analyses the mass loss of refractory castables by proposing a microwave thermogravimetry equipment. The results suggest that water removal occurs at earlier temperatures and, in total, nine-fold less energy consumption estimation Numerical model results showed the distinct thermal gradients and the resulting drying profiles, highlighting the importance of properly controlling the microwave power during drying. Thus, these findings indicate that the microwave process might be a valid strategy for a safer, greener and faster drying of castable refractories. [ABSTRACT FROM AUTHOR]

In order to improve the performance of Al2O3-SiC-C castables for iron trough, samples were prepared using brown corundum, dense corundum, activated alumina micropowder, ball pitch, and silicon as main raw materials, calcium aluminate cement as the binder. Several kinds of silica fumes (93SiO2, 96SiO2, and 99SiO2) with different particle size distributions and chemical composition were added to research the effects on the properties of castables. The results show that the sample with 99SiO2 fume has high water requirement for molding, but the bulk density is the lowest, the apparent porosity is the highest, the oxidation resistance is the worst, and the permanent linear change on heating is low after firing at 1 450 °C for 3 h. The bulk density and the apparent porosity of the sample with 93SiO2 fume or 96SiO2 fume are equivalent, the hot modulus of rupture of the sample with 93SiO2 fume is the lowest, and the slag resistance of the sample with 96SiO2 fume is the best. The comprehensive performance of the sample with 96SiO2 fume is the best. [ABSTRACT FROM AUTHOR]

Crack propagation in an alumina castable refractory with mullite-zirconia aggregates was investigated in-situ using a wedge splitting test performed inside a laboratory tomograph. Four-dimensional (i.e., 3D space and time) data from digital volume correlation were used to investigate the influence of a realistic crack path on the simulation of the fracture process. A cohesive law was chosen, since toughening mechanisms were present, and calibrated via finite element model updating. When a straight crack path was assumed instead of the experimental crack path, a 10% higher fracture energy and a 35% higher cohesive strength were calibrated. Although the force alone could be used in the minimized cost function, the kinematic information gives valuable insight into the trustworthiness of the geometrical hypotheses assumed in the finite element model. Such framework can be applied to study nonlinear fracture processes for different materials with complex toughening mechanisms such as crack deflection or branching. • A CZM is calibrated via FEMU using force and DVC data from an in-situ wedge splitting test. • The calibration results in differences between experimental and simulated data less than ten times the uncertainty level. • 10% higher fracture energy and 35% higher cohesive strength if a straight crack path is assumed instead of the experimental surface. [ABSTRACT FROM AUTHOR]

When refractory castables are dried, hydrothermal conditions may result inside the bodies if the H 2 O cannot escape from the material. Under such high-pressure conditions, problems such as explosive spalling can arise. As different curing temperatures during the hydration of calcium aluminate cement (CAC)-bound castables lead to the formation of different hydrate phases, different microstructures can develop in the hardened material. This study presents the changes in porosity and in the mineralogical composition of a refractory castable model system under hydrothermal conditions depending on the curing temperature (5, 23 and 40 °C). Quantitative X-ray diffraction (QXRD) measurements show that different hydrate phases are formed during curing, while C 3 AH 6 and boehmite are formed in the same quantities after hydrothermal treatment in an autoclave at ∼11 bar/180 °C. Although the mineralogical composition after autoclaving is not different, the three samples differ in their microstructure. Mercury intrusion porosimetry measurements reveal that although the total porosity after autoclaving is the same, the 40 °C samples have a higher proportion of large pores. SEM images also show that the appearance of C 3 AH 6 in the 40 °C autoclaved samples varies, which originates from the starting phase composition and microstructure after curing. [ABSTRACT FROM AUTHOR]

High-strength low-cement castables have been produced for the first time from waste of demolished glass furnaces. Adispersant of long-chain ionizable sodium tripolyphosphate (STPP, 0.2 wt.%) had a positive effect on electrostatic stabilization and improvement of the rheological characteristics of alumina-zirconia-silica (AZS) castable. Four castable mixes of various packing moduli (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 demonstrated an outstanding compressive strength (1118.15 kg/cm2) and a moderate bulk density (2.65 g/cm3) when fired at 1375°C. It showed the highest dimensional stability and a permanent linear change of less than 0.6% at 1300°C. It displayed high thermal shock resistance (30 cycles) and high abrasion resistance (abrasion loss ~2.05% after 280 abrasion test cycles) when fired at 1300°C. Therefore, this castable can be used in high wear-rate sections of cement kilns and is an excellent choice in case of kiln instability. The results indicated that the castable with n = 0.25 is highly recommended for lining the inlet of rotary cement kilns at 1000 – 1300°C. The results open the door for the use of waste from demolished glass kilns to produce high-strength low-cement refractory castable for lining cement kiln inlets. [ABSTRACT FROM AUTHOR]

In order to improve the anti-explosion performance of p-Al2O3 bonded corundum castables, H2O2 was added (0, 0.025%, 0.050%, 0.075%, 0.100% and 0.125%, by mass) as the anti-explosion agent. After mixing and casting, specimens were prepared. Some specimens were cured at room temperature for 12 h and demoulded for the anti-explosion performance test at different temperatures (450, 500, 550, 600, 650, 700, 750 and 800 °); the other specimens were cured, dried and fired, and tested in terms of the apparent porosity, the density, the cold mechanical properties, the air permeability and the pore size distribution. The results show that: (1) with the increase of the H2O2 addition, the anti-explosion performance of castables increases gradually, the average pore size increases gradually, and the density and the strength decrease gradually; (2) by comprehensive consideration, the appropriate addition of H2O2 shall be within 0.075%. [ABSTRACT FROM AUTHOR]

Reactive MgO was used in the first time as alternative hydraulic binder of calcium aluminate cement (CAC) to prepare Cr 2 O 3 -bearing refractory castable. The formation of Cr(VI), and physical and mechanical properties of MgO-bonded refractory castables after heat-treating were investigated. Microstructural characterization and phase composition analyses on the heat-treated MgO-bonded refractory castable matrices resulted in a comprehensive understanding of the mechanism for the inhibition of Cr(VI), and of the strength development during firing. The results indicate that compared with CAC, Cr(VI) levels were 6.7–28.1 times lower using reactive MgO after firing at 700–1300 °C. The in situ Mg(Cr,Al) 2 O 4 spinel formed from the preferential interactions among MgO and Cr 2 O 3 and Al 2 O 3 would be the main reason leading to the inhibited Cr(VI) formation and strength development during firing. [ABSTRACT FROM AUTHOR]

This article analyzes the mechanism of the protective layer formation under the action of alkali in a refractory castable when ground quartz sand (GQS) is used as an admixture to produce refractory conventional castables (CC) and medium cement castables (MCC). It was found that, independently of the castable composition, the addition of GQS (2.5%) reduces the degree of K2CO3 dissolution at high temperature, and the released potassium reacts with the silica and forms a viscous potassium silicate glass, which reduces the mobility of alkali. The liquid phase formed filled some of the open pores and hindered the penetration of potassium into the deeper layers of the refractory castable. The thickness of the formed protective layer, after three cycles of the alkaline corrosion test, varies from 700 µm up to 1300 µm, depending on the castable composition. [ABSTRACT FROM AUTHOR]

• First report of MOC cement bonding system for cordierite-mullite castables. • Revealed the microstructural evolution from MOC crystals to cordierite and mullite. • Developed castables suitable for use as kiln furniture in ceramic firing processes. Cordierite-mullite ceramics are well-suited for use as kiln furniture due to their superior mechanical strength and thermal shock resistance. This study explores the development of cordierite-mullite refractory castables bonded with magnesium oxychloride (MOC) cement. These castables were created using calcined kaolin aggregates and a matrix comprised light-burned magnesia, calcined alumina, milled sand, and magnesium chloride hexahydrate. Interaction between light-burned magnesia and magnesium chloride hexahydrate produced a needle-like MOC cement phase, significantly enhancing the green strength of the castables. After firing at 1350 °C for 4 h, the MOC crystals decomposed, forming robust cordierite and mullite phases. The resulting sintered castables demonstrated a modulus of rupture of 14.55 MPa, a bulk density of 1.95 g/cm3, a porosity of 24.84 %, and a thermal expansion coefficient of 2.89x10−6°C−1. These findings indicate the effectiveness of MOC cement bonding for manufacturing high-strength cordierite-mullite refractory castables, making them ideal for kiln furniture applications. [ABSTRACT FROM AUTHOR]

• The design of a device for dynamic testing of the corrosion properties of refractory materials (RM). • Selected types of biomass ash are used to evaluate the corrosion resistance of refractory materials. • The device offers more realistic test conditions compared to traditional methods. • EM-EDS Evaluation: Corrosion is evaluated using electron microscopy-energy dispersive spectroscopy (EM-EDS) for detailed analysis The corrosive effects of biomass ash on refractory materials in combustion chambers pose challenges. Development of new castable refractory materials which are more resistant to corrosion requires tests that accurately reflect the conditions occurring in real devices. This article describes the Computational Fluid Dynamics (CFD) design and construction of a device for evaluating the corrosion of refractory materials in dynamic regime. The device allows to simulate combustion chamber conditions accurately, to regulate an injection of corrosive medium on the tested material surface under the specified conditions (temperature, time, and flow). In the present investigation the conventional refractory material was exposed to attack of biomass ash at the temperature of 1300 °C for 3 h to test the functionality of the device. A burner with technology oxygen–enriched combustion was used to heat the device. The corrosion tests were conducted in accordance with the standard P CEN/TS 15,418 and the standard STN EN ISO 21404. The operational state required for corrosion tests at 1300 °C was achieved within 1.12 h. The extent of refractory material degradation in the dynamic corrosion regime was evaluated using electron microscopy-energy dispersive spectroscopy (EM-EDS) and compared with the results of a static crucible test (3 h at 1300 °C). The dynamic test provided sufficient information on the interactions of corrosion medium with the refractories. Its main advantages are the maintenance of non-equilibrium conditions by controlled deposition of the corrosion medium in quantity from 1 to −100 g/h, fast heating rate to operating temperature (20 °C/min), and the possibility of conditions variability during tests (temperature, ox-red. atmosphere, fuel gas flow etc.). [ABSTRACT FROM AUTHOR]

This paper aims to evaluate cohesive properties for an alumina refractory with mullite-zirconia aggregates from wedge splitting tests (WST), and to assess their sensitivity to sintering and testing temperature. Five experiments were analyzed of which four were performed at 600∘C. The sought parameters were determined via weighted finite element model updating. The cohesive strength and the fracture energy were successfully calibrated and resulted in simulated data close to their experimental counterparts (i.e., between 4 and 11 times the measurement uncertainty). Increasing the sintering temperature from 1400∘C to 1450∘C enhanced the cohesion between the mullite-zirconia aggregates and the alumina matrix (20 % increase of the fracture energy and of the fracture process zone length). When the WSTs were performed at 600∘C, the cohesive strength was 10 % smaller while the fracture energy was 70 % higher than that at room temperature. [ABSTRACT FROM AUTHOR]

AI203-SiC-C castables were prepared using C@SiC composite powder modified by molten salts to replace ball pitch gradually. The effects of the C@SiC composite powder addition (0,1%, 1.5%, and 2%, by mass) on the water requirement, the flow value, the physical properties, the thermal shock resistance, the oxidation resistance, and the corrosion resistance of castables were studied. The results show that with the C@SiC addition increasing, the amount of water added to the castable increases, but the apparent porosity of the samples after heat treatment first increases and then decreases, and the cold modulus of rupture increases significantly. After completely replacing the ball pitch, the cold modulus of rupture of the sample increases by 51.2%, and the residual strength ratio increases by 28.7%. In addition, the sample with 2% C@SiC has the best oxidation resistance, and the sample with 1.5% C@SiC composite powder has the smallest corrosion depth. [ABSTRACT FROM AUTHOR]

Ceramic macro-needles incorporation as reinforcement in commercial refractory castable was studied. Ceramic macro-needles (Ø2x20 mm) were made from kaolinite clay and gibbsite to obtain mullite as the main crystalline phase. Specimens with the ceramic reinforcement were evaluated by compression after being treated at two temperatures (815 and 1400 °C). The results were compared with those obtained using the same commercial concrete but reinforced with steel fibers and without reinforcement. Compression values presented by specimens with ceramic macro-needles were 74% and 50% higher than specimens with steel fibers after exposition to 815 and 1400 °C, respectively. Based on these results, it was established that ceramic macro-needles are a feasible solution to improve the mechanical resistance of castables exposed to high temperatures. [ABSTRACT FROM AUTHOR]

Colloidal silica is used in many kinds of industry. It is an aqueous dispersion of SiO2 nanoparticles. SiO2 colloidal solutions are commercially available in different concentrations, with different particle sizes and are stabilized with different ions. Colloidal SiO2 was used in this study as a cement replacement in refractory castable. The present study, in its first stage, offers an assessment of five different SiO2 colloidal solutions. The particle size of the solutions was 15 nm, the particle concentration was 30% and 40% and the colloidal solutions were stabilized with Na+, OH− and Cl− ions. The effect of the colloidal solutions on selected characteristics of the refractory pastes and on their mineralogical composition after firing at 1000 °C and 1500 °C was described. The most suitable SiO2 colloidal solution from the first stage was subsequently used for the refractory castable test samples' preparation in the second stage. Refractory castables, unlike paste, contain a coarse aggregate (grog) up to a grain size of 6 mm. Four types of coarse refractory grog were evaluated. Their effect on selected characteristics of the refractory castable and on its mineralogical composition after firing at 1000 °C and 1500 °C was described. The selected characteristics, within the scope of this study, include bulk density, apparent porosity, cold modulus of rupture and linear changes after firing. Finally, the study describes the effect of the sol particle concentration and the effect of pore size distribution on corrosion resistance and on the internal structure of the material. Mineral and chemical compositions and microstructures of both the raw materials and designed aggregates were thoroughly investigated by the means of X-ray fluorescence spectroscopy, powder X-ray diffraction and scanning electron microscopy. An analysis of the transition zone between corrosive media (K2CO3) and tested castables showed better corrosion resistance for a sol-gel castable than an ultra-low cement castable. [ABSTRACT FROM AUTHOR]

Low melting temperatures of the biomass ash at the intensive combustion can generate the slag with a portion of unburned fuel. The portion of imperfectly burned fuel reduces the efficiency of its use. An alternative route to solve the problem without changing the combustion condition is a modification of the chemical composition of the ash with the addition of an agent increasing the melting temperature of the ash/slag. In this paper, we report on the impact of adding the magnesite waste sludge to ash on their melting. Three types of ashes with different SiO 2 and K 2 O content were selected for the tests. The melting temperatures of ash and ash mixtures with magnesite sludge (mass ratio 0.5–2:1) have been determined. The addition of magnesite sludge to ash increased the temperature of fusibility index of the mixtures by 50–100 °C. The ash fusibility temperature rose with a decrease of the SiO 2 content in the ash. Subsequently, the interaction of the ash/ash mixtures with the refractory corundum castable was monitored at a temperature of 1450 °C using a static crucible corrosion test. The addition of magnesite sludge to ash reduced the aggression of the slags to the refractory corundum materials. The Al 2 O 3 concentration in the post mortem slags of the ash mixtures with the magnesite sludge (2:1) was about 20–23 wt% lower in comparison to the slag without magnesite. The evaluation of the effect of magnesite sludge addition to ash and the elements (K, Ca, Mg, Fe, Si) penetration on the extent of corrosion is the subject of further work aimed at analyses of the corrosion interface of the slag – corundum refractory material. [ABSTRACT FROM AUTHOR]

In the present work, chemical attacks and corrosion behaviors of a used Al 2 O 3 -MgAl 2 O 4 refractory castable in the non-tapping slag side of a refining ladle were investigated and also compared with that of the counterpart (in the tapping slag side). Corrosion microstructures revealed the stress cracks occurred on the corroded interface and just along the boundary between the infiltration layer and original layer, indicating the thermo-mechanical properties' mismatch above those two layers was the main reason for the formation of cracks on the corroded interface. Furthermore, the corrosion process of Al 2 O 3 aggregates on the interface was studied in detail, and an intergranular mechanism was proposed based on observed microscopic characteristics. [ABSTRACT FROM AUTHOR]

Structural failure of concrete buildings on fire and complete destruction of the monolithic refractory lining during their drying stage are dangerous examples of the effect of explosive spalling on partially saturated porous media. Several observations in both cases indicated the presence of moisture accumulation ahead of the drying front, which are in tune with the most common theories on the explosive spalling of concrete. Previous studies have shown evidence of the existence of this phenomenon, however, they were biased by artifacts and experimental limitations (such as the beam hardening effect and changes in the microstructure of the material due to the presence of pressure and temperature sensors). In the current work, rapid neutron tomography was used to investigate the in‐operando drying behavior of a high‐alumina refractory castable, proposing a novel experimental layout aimed at a truly one‐dimensional drying front. This setup provided more realistic boundary conditions, such as the behavior of a larger wall heated from one of its sides, while also preventing some nonphysical artifacts (notably beam hardening). By eliminating these aspects, a direct proof that moisture accumulates ahead of the drying front was obtained. This work also lays the basis for further studies focusing on the response sensitivity analysis to boundary conditions and other parameters (e.g., heating rates and properties of the sample related to the moisture clog formation), as well as useful data for the validation and characterization stages of numerical models of partially saturated porous media. [ABSTRACT FROM AUTHOR]

Al2O3-SiC castables, for the relining of BF hearths in mid-campaign repair, were sampled and investigated after two years' service. The chemical and mineralogical characteristics of the residual castables were analyzed by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectrometry to study the erosion mechanism. The results show that as gaseous K diffuses in the castables, leucite (KAISi2O8) and multiple cracks are formed. Molten iron and slag penetrate through the cracks to form anorthite ([Ca, Na][Al, Si]4O8) and iron, which will not form an embrittlement layer similar to carbon bricks. The entire repair of the hearth with Al2O3-SiC castables combined with the design of thin-wall lining hearth eliminates "elephant foot shaped " erosion, greatly prolonging the service life of the hearth lining. [ABSTRACT FROM AUTHOR]

The use of a combined additive consisting of silica-containing additives "F" (thinning) and "S" (accelerating castable hardening) instead of the previously used silica-containing additive "A" and a mixture of dispersing additives based on polyethylene glycol in low-cement silicon carbide castable allows to improve the castable workability by increasing (in 5.4 times) the flowability of a freshly prepared castable, and increase by 1.2 and 1.1 times the cold crushing strength of heat-treated at temperatures of 110 and 1 580 °C, respectively, castable samples from low-cement silicon carbide castable with practically equal values of open porosity (15.8% and 16.0%). The petrographic studies of the castable sample microstructure after firing at a temperature of 1 580 °C showed that the investigated silica-containing additives "F" and "S" contribute to the denser and more uniform structure formation. As a result of the carried out research, the manufacturing technology of a low-cement silicon carbide castable was improved, of which the production was mastered at JSC "URIR named after A. S. Berezhnoy". [ABSTRACT FROM AUTHOR]

To satisfy the requirements of alumina castables in specific environment and enhance their properties, alumina castables were prepared using tabular alumina, various alumina powders (07RAL, 15RA, 22RABL, 40CA, 99-20um, and 99-325mesh), and calcium aluminate cement as main raw materials, and heat treating at 110, 1 000, 1 600 °C, respectively. Their flowability and physical properties were tested, and the morphology was researched. The results show that compared with calcined alumina and tabular alumina powders, reactive alumina has higher specific surface area and better filling performance leading to lower water demand and higher viscosity, and the castables prepared with reactive alumina have higher CCS and CMOR after heat treating at 110, 1 000 and 1 600 °C as well as lower PLC than those with calcined alumina and tabular alumina powders. [ABSTRACT FROM AUTHOR]

Tight installation schedules and economic pressures are potential drawbacks for castable installation and performance. Many factors influence the setting behavior and the properties of no‐cement castable refractories, including temperature and chemical composition. In this study, the setting behavior and the mechanical properties of a no‐cement castable were analyzed varying the amount of a chemical additive mix and curing temperature. The chemical additive mix concentration was varied from 0 wt% to 1 wt%. The curing temperature was varied from low (4°C/40°F) to high (40°C/104°F). The mechanical properties were characterized by cold crushing strength (CCS). A variance in the pH level drastically increased the setting time of the castable. Mechanical properties on green samples showed lower strength for castables with a higher concentration of the additive mix. This difference in performance is the result of the lower pH preventing the formation of a chain mechanism in the no‐cement castable bonded with colloidal silica. [ABSTRACT FROM AUTHOR]

A spinel forming castable with an initial MgO content of 8%, commonly applied in refractory linings in the steel industry, was characterised with regard to the creep behaviour. Three creep stages were observed for 1300, 1400, and 1500 °C for application relevant loads between 3 and 8 MPa for sintered samples. The parameters of the Norton–Bailey creep model were determined for all three creep stages. The added microsilica increased the creep strain rate in the temperature range above 1300 °C. The fitting of the results for only one temperature carries the risk of over-fitting. This was observed for the first creep stage at 1400 and 1500 °C. Nevertheless, for the investigated material, it was not possible to achieve a common fit for a larger temperature range. The evaluation of the creep parameters by different combinations of measurements allowed to obtain statistical information about the creep parameters. [ABSTRACT FROM AUTHOR]

Hollow Al2O3 microspheres were synthesized by spray pyrolysis and investigated by x-ray phase analysis, scanning and transmission electron microscopy, and low-temperature nitrogen adsorption. The analytical results demonstrate that the aluminum oxide microspheres are hollow. The size of the microspheres varies from 5 to 10 μm. The dependence of the specific surface area and the size of the microspheres on the synthesis temperature was determined. The wall thickness of the microspheres depends on their diameter and varies from 50 to 200 nm. The paper shows the possibility of using microspheres as an additive for refractory castable and products based on them. [ABSTRACT FROM AUTHOR]

The current trend to replace shaped refractories for monolithics is related to various technical aspects, i.e., lack of joints, easier installation and free format. However, the main drawback of these non-shaped products is their longer first heat-up demand, otherwise mechanical failures or even explosive spalling may take place due to steam pressurization within the well packed consolidated structure. As a consequence, over-conservative drying schedules are commonly used in industrial equipment lined with such ceramics, which increase the energy consumption and the production down-time. Based on this scenario and considering the recent advances in numerical simulations, this article discusses the implications of applying different heating rates during the drying of a refractory castable lining of a steel ladle. Additionally, a novel methodology based on the correlation of the maximum vapor pressure and the mechanical strength of the ceramic material was also proposed. Using some of the castable properties measured as a function of temperature, simulation results pointed out that higher vapor pressures and a displacement of the maximum pressure peak are attained by applying high heating rates and thicker linings. This behavior is associated with the water migration to the inner regions of the refractory structure. It was observed that these conditions displace the maximum resistance ratio position towards the hot face, where most common spallings are observed. The work also emphasizes the importance of carrying out accurate measurements of physical properties as a function of the temperature, otherwise the outcome can be far from the reality of the working conditions. [ABSTRACT FROM AUTHOR]

For the transformation to a CO2 neutral industry, fuel of traditionally fossil‐fired furnaces is substituted by the subsequently addition of hydrogen. In these studies, refractory components are identified for the corrosion of refractories in (highly) reducing atmospheres. A bauxite‐based refractory castable is set up in diluted, 9Ar 1H2, hydrogen atmosphere. Additionally, a focus is set on the behavior of a common matrix phase, anorthite. Corrosion experiments up to 1500°C using a tube furnace with the mentioned atmosphere have been scheduled. Amount and phase stability due to different time and temperature coordinates have been examined by XRD. Furthermore, the microstructure and in particular the bonding phase was observed by means of SEM and EDS. Microstructural components undergoing reaction or loss are identified and explained in regards of complete and incomplete hydrogen combustion. Reduction of impurities such as iron oxides, phosphorus oxides, and titanium oxides are considered in detail. [ABSTRACT FROM AUTHOR]

Calcium aluminate cement (CAC) bonded corundum based castables were prepared using tabular corundum and activated alumina as the starting materials, CAC as the binder, zinc hydroxide (Zn(OH)2) and basic zinc carbonate (BZC) as the ZnO precursors. The effects of the two ZnO precursors on the phase composition and the microstructure of the CAC bonded corundum based castable matrix specimens were analyzed, and the reasons affecting the hot performance of the castables were studied. The results show that Zn(OH)2 with a smaller particle size (d 50=1.26 μm) is prone to agglomerate during sample preparation and generates ZnAl2O4 spinel grains after firing, hindering the growth of CA6, thus decreasing the mechanical strength of the castables. BZC with a larger particle size (d 50=2.91 μm), which shows a sound dispersity, in-situ generates nano-sized ZnO after firing, and ZnO or Zn2+ diffuses into calcium aluminates, promoting the sintering of CA2 and CA6, thereby enhancing the hot properties of the CAC-bonded corundum based castables. [ABSTRACT FROM AUTHOR]

Lightweight insulation refractories are essential for high‐temperature performance to reduce energy consumption. This study investigates a new insulation material, that is, solid waste rice husk ash (RHA) derived lightweight refractory castable, replacing traditional insulation refractory brick. The RHA is generated after the burning of rice husk as biomass fuel. The RHA is used as an aggregate and alkali‐extracted silica sol from RHA as a binder to fabricate the insulation castable. The nanosilica containing (~30 wt%) sol is employed to synthesize the refractory castable by varying the sol amount (2.5‐12.5 wt% silica from sol). The castable specimens are cast by a vibro‐caster and fired at 900‐1200°C in a muffle furnace. The physic‐mechanical and thermal conductivity (κ) of the castable is investigated. At 1100°C with 10 wt% dry sol retaining sample shows an excellent apparent porosity (~65%), low bulk density (~ 0.8 g/cm3), and κ (0.136 W/m k) with sustainable compressive strength (6 MPa). The acquired results are a good match with the literature (other wastes‐derived insulation materials) and industrial (silica insulation brick) obtained data. These promising outcomes may inspire the refractory industries for using RHA as an aggregate and RHA extracted sol as a binder for making insulation castable. [ABSTRACT FROM AUTHOR]

Abstract: This paper compares the thermal shock damage resistance and the slag corrosion resistance of a high-alumina and an alumina-containing andalusite refractory castable. Thermal shock damage resistance was analyzed through thermal cycling and thermal shock damage resistance parameters. Thermal shock cycling damage was analyzed using the dynamic modulus of elasticity (E) and the modulus of rupture (MOR) before and after the thermal shock cycles. The alumina-containing andalusite castable showed superior thermal shock damage resistance in both parameters. The high-alumina castable showed a higher resistance to slag corrosion. These results were linked to material selection for specific industry applications. [ABSTRACT FROM AUTHOR]

• CMOD vs. NOD relationship investigated for two faces of two WSTs. • Brittle and cohesive numerical simulations were also studied. • A quadratic function fits very well the non-linear crack initiation regime. • An affine trend is found to be suitable for the crack propagation regime. • Propagation energy can be estimated from NOD data. The work of fracture of refractories is commonly calculated from crack mouth opening displacements (CMODs) in wedge splitting tests (WSTs). This paper proposes a methodology for estimating the fracture energy from notch opening displacement (NOD) measurements, which is useful for setups where CMOD is not accessible. NODs and CMODs are calculated for both faces of two WSTs experiments on a castable refractory via digital image correlation (DIC) and finite element simulations. A quadratic function fits well the non-linear CMOD vs. NOD behavior in the crack initiation regime, while an affine trend describes the propagation regime. Although the nonlinearity associated with crack initiation is more complex, the crack propagation energy can easily be estimated from NOD data when CMODs cannot be measured. [ABSTRACT FROM AUTHOR]

The contradictory properties required of castable refractories makes selecting castable refractories for industrial applications challenging. This paper seeks to describe the material selection for a blast furnace blowpipe application that is subjected to sudden temperature changes and must prevent heat loss. Three commercial high alumina castables containing andalusite or mullite from different manufacturers were characterized. Thermal shock damage resistance was evaluated using thermal shock damage resistance theory and experiments. The castables' coefficient of thermal expansion was estimated using quantitative X-ray diffraction. Crack propagation resistance was measured using the work-of-fracture technique. Thermal shock damage was experimentally evaluated by measuring the modulus of elasticity and rupture prior to and after thermal cycles. Ultimately, the microstructure of the castables was related to the thermal shock damage behavior by estimating the aggregate size and the fracture toughening mechanisms using light optical and scanning electron microscopes. Heat loss was evaluated by calculating the blowpipe shell temperature using a one-dimensional steady-state heat conduction model. The best commercial castable refractory for blowpipe showed high thermal shock damage resistance and low thermal conductivity. The results in this study agreed with thermal shock damage resistance parameters and showed a correlation between coarse microstructure with large aggregate and higher thermal shock damage resistance. [ABSTRACT FROM AUTHOR]

To achieve better performance of bauxite-corundum refractory castables in the steelmaking industry, we developed two reinforcement approaches (i.e. by removing microsilica or replacing cement with microsilica) for this refractory in this work. Besides, a comparison of their microstructures, thermo-mechanical properties and corrosion resistance was carried out. The abundant generation of liquids and big pores in the matrix is the leading cause of the lower thermo-mechanical and corrosion resistance of the conventional bauxite-corundum castable. The microsilica-free castable showed no liquids but a strong corundum-CA 6 network structure in the matrix, which greatly enhanced the hot strength. Unfortunately, this refractory exhibited poor green strength because of a lower volume fraction of flowable components during preparation. Moreover, some coarse cracks were produced due to violent slag-matrix interaction. In contrast, the ultralow cement (1 wt%) castable with high microsilica content (7 wt%) not only created a stronger and more uniform corundum-mullite network but also showed excellent stability and infiltration resistance during corrosion because of its smaller pore sizes and the formation of a dense protective layer. [ABSTRACT FROM AUTHOR]

The present study aims to clarify the influence of BaSO 4 on composition, microstructural evolution and properties of magnesia refractory castables. Castables with different BaSO 4 contents were prepared using calcined magnesia, microsilica, and BaSO 4 as raw materials. The results show that introducing BaSO 4 can significantly enhance slag resistance of magnesia refractory castables. Castables presented high compactness and mechanical properties with 0–3 wt% BaSO 4 for the liquid sintering process and formation of BaMgSiO 4 at high temperature. Then compactness of castables decreased when BaSO 4 content increased from 5 wt% to 10 wt% for its decomposition and a subsequent increase in the pore content. BaSO 4 presented minor effects on the low temperature (1100 °C) structure of castables and played an important role in enhancing high temperature slag resistance, owing to its high structural stability till 1550 °C. The slag resistance mechanism of castables with BaSO 4 is that Al3+ in slag was incorporated into periclase intergranular to form BaAl 2 O 4 phases during corrosion process, resulting in the increased slag viscosity and suppressed continuing penetration. The research of this work provides a new insight into microstructure and properties enhancement of magnesia refractory castables used in metallurgical field. [ABSTRACT FROM AUTHOR]

Geopolymers are porous, amorphous, alkali‐aluminosilicate hydrate materials formed at room temperature via a solution process. Geopolymer based on metakaolin had a relatively homogeneous microstructure that offered consistent behavior but suffered from dehydration cracking and large densification shrinkages when heated. It was found that by reinforcing a metakaolin geopolymer of composition (K2O·Al2O3·4SiO2·11H2O) with 50 µm diameter alumina platelets, dehydration cracking could be prevented, and shrinkage could be reduced by an order of magnitude. Samples were reinforced with 30, 50, and 70 wt% of alumina platelets. Although the properties of the 30 and 50 wt% conditions were better than those of unreinforced geopolymer, those samples still showed warping, cracking, and strength losses on heating. The 70 wt% samples did not warp or crack when heated to temperatures of up to 1500°C. The room‐temperature 4‐point flexural strength of these samples remained at around 20 MPa regardless of heat treatments. The in situ measured flexural strength increased to almost 40 MPa at 600°C, and remained higher than 20 MPa until 1200°C. Samples subjected to propane‐torch thermal shock heating and subsequent quenching did not crack or fragment. Dilatometry, X‐ray diffraction, and scanning electron microscopy were used for additional characterization. Given these properties, this material showed promise as a castable refractory. [ABSTRACT FROM AUTHOR]

Abstract: Colloidal silica (CS) is a promising raw material for refractory castable ceramics. It consists of stable suspensions of synthetic amorphous silica nanoparticles that behave simultaneously as liquid medium and binder for ceramic particles and as a porogenic agent and highly reactive source of silica to promote in-situ reactions. The setting mechanism of CS balances two opposite effects. Adding more CS to a suspension increases the bonding potential for gelling reactions and strengthening; on the other hand, it also introduces more water into the system, enhancing pore content. Such effects can be advantageously employed in the preparation of porous structures from aqueous suspensions and applied as high-temperature thermal insulators. The present study addresses the production of porous structures of in-situ mullite attained from aqueous suspensions of highly porous transition alumina particles bonded with colloidal silica. Different grades of CS and transition aluminas were combined to present suitable workability (flowability and gelling time) and to generate stoichiometric mullite or mullite-alumina porous structures after sintering. [ABSTRACT FROM AUTHOR]

The effect of the particle size (50–325 mesh) and content (0–0.1 wt%) of metallic aluminum powder on the explosive spalling resistance of corundum-based refractory castables were investigated in this study based on air permeability, pore size distribution, heat release, fracture energy and microstructural analyses. The experimental results show that the addition of Al powder significantly improves their explosive spalling resistance. As observed, the explosive spalling resistance of the castables was mainly influenced by the permeability mechanism and the fracture energy. Permeable paths were generated in the microstructure of the sample during the overlapping period between the curing process and the H 2 gas forming one, derived from the Al–H 2 O reaction. The highest permeability level was obtained when 0.075 wt % of Al powder with size of 100 mesh was incorporated into the corundum-based refractory castables. At the same time, the fracture energy of the castable samples was increased accordingly. [ABSTRACT FROM AUTHOR]

This investigation deals with refractory monolithic materials that are broadly used in thermal treatment facilities as they are necessary e.g. for iron and steel, glass and cement production, thereby withstanding temperatures between 600 and 2000 °C. In the special case of hydraulic bond refractory castables, the components must be mixed with water for two reasons: firstly, to obtain a mouldable suspension; and secondly, to achieve a green strength via the hydraulic reaction of calcium aluminate cement that is high enough to enable a secure refractoriness of the concrete formwork. Prior to their first use in production, castables must have their pore water and hydraulic bond water carefully removed in order to avoid explosive spalling that can cause severe damages inside the furnaces. In this study, we investigate the one-dimensional drying behavior of two specific refractory castable compositions, a microsilica-containing low- and a no-cement castable (LCC/NCC) during first heat-up in the temperature regime between 20 and 300 °C. First results were already presented in a prior publication that demonstrate a specialized high-temperature Nuclear Magnetic Resonance (NMR) setup capable of continuously measuring moisture and temperature profiles on 74 mm-long cylindrical samples, without touching or moving the sample [1]. In this paper we explore how the use of permeability-enhancing agents (fibers and MIPORE 20) beneficially affects the drying behavior and consequently allows higher heating rates. We also demonstrate that the NMR technique as applied here is sensitive enough to resolve differences in the dry-out behavior if said additives are used in the castable formulations. Our results demonstrate that incorporation of fiber and MIPORE 20 significantly alters the dry-out behavior. In particular, it can be resolved that as the fibers begin to melt, there is a noticeable increase in permeability that results in faster drying, as well as a decrease of the drying front temperature and therefore the generated maximum pressure. [ABSTRACT FROM AUTHOR]

This article characterizes fine-ground NK-Alumina 11 and NK-Alumina 14 developed in PKF "NK" for low-cement refractory castables. The quality indicators of the developed aluminas are not inferior to international analogs. [ABSTRACT FROM AUTHOR]

The present contribution focused mainly on the fundamental understanding of the influence of surface-modified graphite on rheology of the matrix of a castable slurry in comparison to the same containing the uncoated one. A special observation on the rheology of a graphite-free matrix of similar high alumina castable has been described. The change in rheological behavior due to the presence of other microfine constituents has also been noticed with a particular attention to the refractory cement bond. The variation in viscosity and shear stresses with shear rate of castable matrices containing as-received and surface-modified graphites has been compared. The 'ball-in-hand' consistency test of respective castables had also been differentiated. The effect of coated and uncoated graphites on the loss and storage moduli of the respective suspensions has been explored. Zeta potential values of individual constituents as well as the slurries have also been measured and correlated with the flow characteristics of castable matrices. The X-ray diffraction (XRD), SEM (scanning electron microscope) and EDS (energy dispersive spectroscopy) studies of the coated graphite have been observed to substantiate the flow pattern of the slurry. The physical properties of refractory castables at different temperatures have been estimated to supplement the rheological pattern. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering & Sustainable Development is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)