Refractory Compositions Research Articles

Novel Porous Refractory Synthesized from Diatomaceous Earth and Rice Husk Ash

Refractory materials are products used in thermal equipment to protect the fire and prevent heat loss to the outside environment. Thermal equipment such as driers, ceramic kilns, glass or metal furnaces and others always consume high heat in the combustion of the fuel. If the thermal equipments have high heat loss which cause wastes of fuel and increases production costs. Therefore, researchers are always looking for a solution to minimize heat loss for the kiln. In which, refractory materials significantly influence to the heat loss of the kiln and they have been studied a lot in recent years.This study focused on utilization of locally available raw materials to product the novel porous refractory composites. The products have high porosity based on chosing the suitable raw materials and forming process. The refractory has high porosity and low thermal conductivity reponded to requirements of saving energy for the thermal equipments. More important, the novel porous refractory products have high shape stability when observed by heating microscope in a range of room temperature to over 1400 o C.

Preparation and slag erosion resistance mechanism of MgAlON based composite refractories synthesized from solid waste

Refractory waste is a typical industrial solid waste. Owing to technical reasons, most of the refractory waste is not efficiently utilized and causes environmental pollution. In this study, we explored a novel technology for the preparation of MgAlON based composite refractories using waste MgO-C and Al2O3-MgO-C refractory materials. The experimental results showed that higher sintering temperatures, enhanced the mechanics of the synthesized MgAlON based composite refractories. Its flexural strength and compressive strength reached 7.7 MPa and 15.87 MPa, respectively, as the sintering temperature increased to 1823 K. Additionally, the slag erosion resistance of the MgAlON based composite refractories was studied and was found to be significantly influenced by the temperature and duration of erosion. The erosion of MgAlON based composite refractories by metallurgical slag was controlled by a combination of chemical reaction and diffusion. The apparent activation energy of slag erosion was approximately 274.6 kJ/mol. During the erosion of MgAlON based composite refractories, the metallurgical slag mainly penetrated the material through its pores. The Si, Ca, and Ti elements in the slag diffused into MgAlON based composite refractories, whereas Mg and Al, diffused into the slag from the MgAlON based composite refractories.

The use of materials based on Si3N4 in the composition of composites for the design of high-temperature thermoelectric generators

The possibility of reducing the thermal conductivity of silicon nitride as a basis of high-temperature electrical converters was investigated in the thesis. Also, the values of thermoelectric figure of merit and efficiency of thermoelectric current generator for the case of refractory oxygen-free composites were simulated. During the study, the dependence between the m coefficient, which determines the maximum possible efficiency of the thermoelectric generator and the ZT thermoelectric figure of merit, was determined. It was shown that the coefficient of thermal conductivity of the studied materials ranges from 1,2 to 4·106 m2/s and is characterized by a negative temperature coefficient over the entire temperature range. It was found that the thermal conductivity of Si3N4-based materials varies from 2,1 to 5,1 W/(m·K) depending on the type of sintering activator. The use of Al2O3 as an activator makes it possible to obtain a 25% lower thermal conductivity value comparing to materials with the addition of MgO. For the first time, it was proved that currently it is not possible to achieve an efficiency of 0,5hT in Si3N4-based materials used as a composite basis for high-temperature thermoelectric generators development.

Highly siderophile elements and Os isotope constraints on the genesis of peridotites from the Kızıldağ ophiolite, southern Turkey

In this contribution, we present whole-rock major and trace element chemistry, including rare earth elements (REE), highly siderophile elements (HSE), and Re-Os isotope data, together with mineral chemistry for the harzburgites and dunites from the Kızıldağ ophiolite of SE Turkey, in an attempt to better constrain its petrogenesis. Both the harzburgites and dunites have refractory compositions with CaO contents <0.90 wt%, Al2O3 contents <0.90 wt% and TiO2 contents <0.01 wt%, indicating that they experienced high degrees of partial melting in the supra-subduction zone (SSZ) setting. Besides, the concave-shaped REE patterns and positive anomalies in some incompatible elements (e.g., Cs, Rb and Pb) suggest that the harzburgites and dunites have also experienced interactions with percolating melts after partial melting. Based on the quantitative melt-rock interaction model, the addition of sulfides derived from the percolating magmas could be responsible for the variable HSE contents and suprachondritic Pd/Ir and Pt/Ir ratios observed in some of the harzburgite samples. The extremely low HSE contents in the dunites can be explained by interaction with S-undersaturated melts. Enrichments of Os and Ru in two dunites could be attributed to the precipitation of a higher amount of spinel grains along with the possible Os-Ru microparticles. The significantly wide range of Os isotopic ratios in the harzburgites (187Os/188Os(90 Ma) = 0.12152–0.13584; γOs(90 Ma) = −4.31 to 6.96) and dunites (187Os/188Os(90 Ma) = 0.12690–0.13267; γOs(90 Ma) = −0.08 to 4.47) seems to be consistent with the multi-stage evolution of the oceanic upper mantle. The low Os isotopic ratios (sub-primitive mantle) in some harzburgite samples suggest the lithospheric mantle has experienced ancient melting processes (>1.0 Ga).

Changes in the Structural Phase of Dinas in Calcining Furnaces of Coke Production

This article presents the results of studies that determine the changes in the phase composition and structure of dinas refractories under the operating conditions of coking coal. Their changes are attributed to differences in the temperatures and rates of dinas cooling/heating during the cyclic loading/unloading of coked materials, the conditions of refractory contact with an operating environment, and the degree and nature of mechanical loads in different masonry zones of coke ovens. The regularities and features of macro- and microstructural organizations in combination with the formation phase composition of dinas refractory in various zones of coke oven masonry have been noted. No critical changes in the integrity of dinas product materials relative to microstructure and phase composition have been revealed. Data have confirmed the further operational suitability of such products under testing conditions on the stand unit of pilot production.

Macroporous high-temperature insulators physical properties by in situ CA6 formation: Does the calcium source matter?

Aiming the in situ formation of CA6 (CaO·6Al2O3) at alumina-based macroporous insulators, distinct Ca2+ sources and contents were used and their effect on some of the refractories properties were investigated. Adding CaCO3, Ca(OH)2 or CaO resulted in the decrease of the onset strengthening temperature (TS) and also of the linear shrinkage. However, a higher amount of Ca(OH)2 and CaO could not be used because of their effect on reducing the insulator total porosity. The composition prepared with 12.9 wt% of CaCO3 was the most promising one, leading to an expansion of 0.81 % after firing at 1600 °C for 5 h, TS of 680 °C and low thermal conductivity. These results point out the potential reduction of sintering temperatures and to the possibility of in situ firing the ceramic insulator. These features enable the development of a macroporous refractory composition with a higher thermal insulating effectiveness, which can help industries to decrease their energy demand.

Ultrahigh-Temperature Ta4ZrC5–xZrB2 Composites by Electrothermal Explosion under Pressure

Ultrahigh-temperature Ta4ZrC5–xZrB2 composites were prepared from mechanically activated Ta–Zr–C–B mixtures by electrothermal explosion under pressure and characterized by XRD, SEM, and metallographic analysis. Special attention was given to the impact of mechanical treatment duration. Synthesized composites represented finely (<2 μm) dispersed Ta4ZrC5 in a ZrB2 binder with a residual porosity of 8–10% and HV around 21 GPa. Our results may turn interesting to those engaged in R & D of refractory fine-grained ceramic composites.

Oxidation mechanism of Al-TiO2-MgO-Al2O3 composites after the treatment at 1500 °C in N2-blowing

In this paper, metal (Al, Al3Ti), oxides (Spinel, corundum) and non-oxides ((Al2OC)x (AlN)1-x, Ti(C,N)) composite refractories with excellent oxidation resistance were prepared by heat treating the Al-TiO2-MgO-Al2O3 composites at 1500 °C in N2-blowing, and the antioxidant mechanism of the composites was studied at 1500 °C in air. Results showed that a dense layer capable of hindering the diffusion of gases was formed in the outer part of the prepared metal, oxides and non-oxides composites. Under high temperature and air conditions, the presence of the dense layer and the metal components made the PO2 inside the composite be controlled by the diffusion and mass transfer of Al2O(g) and TiO(g), which provided a protective atmosphere for the non-oxides. After heat-treated at 1500 °C in air for 2 h, (Al2OC)x (AlN)1-x and Ti(C,N) inside the composite were well preserved, and the composition of the dense layer was transformed into MgAl2O4, TiO2 and Mg0·3Al1·4Ti1·3O5.

Petrology of a Neoproterozoic mantle peridotite–chromitite association from Abu Dahr area, Eastern Desert, Egypt: Infiltration of a boninitic melt in highly depleted harzburgite

Peridotites of Abu Dahr represent the main litho–unit of a Neoproterozoic dismembered ophiolite sequence and are among the best–preserved and well–exposed mantle rocks in South Eastern Desert of Egypt. Here, we present new geochemical and mineral chemical data for peridotites and associated pyroxenites and for chromitites and their platinum–group minerals to constrain their petrogenesis and geotectonic setting. The Abu Dahr ophiolite mantle section consists mainly of harzburgites, cut by pyroxenite dykes and containing dunite–chromitite lenses. The harzburgites are composed of olivine, orthopyroxene, spinel and minor clinopyroxene (˂1.0 vol %) and amphibole. Olivine from harzburgites is highly magnesian (Fo 91–93) and Cr–spinel shows a wide–range of Cr2O3 and Al2O3 contents. The enstatite component of orthopyroxene decreases from harzburgite (En = 90–91) to orthopyroxenite (En = 84–87). Amphiboles are represented by magnesiohornblende and tschermakite. The chromitites are massive to disseminated and composed of magnesiochromite with high Cr# (83–93) and Mg# (66–79), and low TiO2 (<0.1 wt%) content. Solid inclusions in chromite include olivine, orthopyroxene and hornblende. Laurite (RuS2) is the most common PGM detected in the investigated chromitite samples and forms micrometer–size inclusions in fresh chromite. Various Ni–sulfides are found both in fresh chromite and along serpentine veinlets. Harzburgites have a refractory composition with a very low Al2O3 (0.4–0.8 wt%) and CaO (0.2–1.6 wt%) contents and high bulk–rock Mg# (89–92). Geochemical data suggest that the Abu Dahr peridotites are highly depleted SSZ peridotites formed in a forearc mantle wedge setting by high degrees of hydrous partial melting and emplaced as a result of the collision of the intra–oceanic arc with the Beitan gneisses. The podiform chromitites and orthopyroxenites were formed due to impregnation of mantle wedge harzburgites by boninitic melt. The highly depleted nature of the harzburgite is responsible for the small reserves of chromite ore at Abu Dahr and in the South Eastern Desert in general.

Recovery of Copper from Leached Tailing Solutions by Biosorption

Due to the progressive fall of the ore grades and the increasingly refractory composition of minerals, concentrating plants have increased which has led to an increase in the generation of tailings. Tailings, especially those obtained in the past, have remaining copper and other valuable species in quantities that can potentially be recovered, such as gold, silver, vanadium, and rare earth elements which transforms this abundant waste into a potential source of precious or strategic metals for secondary mining. One of the techniques of solid–liquid separation that processes solutions with low concentrations of metals corresponds to adsorption, and more recently biosorption, which is based on the use of biological matrices that do not constitute an environmental liability after application. Biosorption occurs as a consequence of the wide variety of active functional groups present in different types of biomass. Bacterial, fungal, plant, and algal biomasses have been described as biosorbents, mainly for the treatment of diluted and simple solutions. This work aims to recover copper from leached tailings using biomass of the red algae Gracilaria chilensis as a biosorbent. The tailing samples were taken from an abandoned deposit, in the north of Chile, and after an acid leaching copper was biosorbed, kinetics of adsorption and the equilibrium isotherms were studied, applying the Freundlich and Langmuir models. Operational parameters such as adsorbent dose, pH, and initial metal concentration were studied.

Structural-phase changes of dinas in calcining furnaces of coke production

The article presents the results of research in the field of changes determining of the phase composition and structure of dinas refractories in operating conditions during coal coking. The reasons for the observed changes are differences in temperatures and rates of cooling / heating of dinas at cyclic loading / unloading the coked material, as well as the conditions of refractory contact with the operating environment, the degree and nature of mechanical loads in different masonry zones of coke ovens. As a result of the studies, regularities and features of the macro- and microstructure organization in combination with the forming phase composition of dinas refractory in various zones of the coke oven masonry are noted. It has been determined that critical changes for the integrity of the dinas products material relative to microstructure and phase composition have been not revealed given fact confirms the further operational suitability of such products under the testing conditions of experimental production. Ill. 1. Ref. 10. Tab. 1.

Wetting behavior and reactivity of liquid Si-10Zr alloy in contact with glassy carbon

In designing advanced refractory composites for highly demanding applications, reactive infiltration of liquid Si-enriched Si-Zr alloys into C-or SiC-based preforms may be a viable cost-less manufacturing process.In such cases, in view to optimize liquid assisted processes such as reactive infiltration, fundamental investigations of the interfacial phenomena occurring when the liquid Si-Zr alloys are in contact with C and SiC substrates, are key steps.For this reason, aiming to ‘‘mimic’’ the conventional operating conditions imposed within a reactive infiltration process, the contact heating sessile drop method was applied to perform a basic study concerning the interaction phenomena taking place at the interface of Si-10% at Zr alloy/Glassy Carbon substrate under an Ar atmosphere. Specifically, the contact angle values as a function of time were measured in the temperature range of 1354–1500 °C.The final contact angle values decreased slightly with an increase in temperature.Moreover, at T = 1450 °C, the contact angle increased over a larger time interval before reaching its final value. The kinetics of SiC crystal growth at the interface and the related processing parameters such as temperature and time were carefully analysed. The growth of SiC crystals and their packaging phenomenon are time and temperature-dependent phenomena.

Synthesis of Value Added Refractories from Aluminium Dross and Zirconia Composites

Abstract Results of a developmental study on the potential to synthesize industrial grade refractories from aluminum dross with un-stabilized zirconia are reported. The merit of the developed product to perform as refractories suitable for use at or above 1000°C was assessed by studying the thermo - physical behavior as per guidelines of ASTM and IS. Aluminum dross, an industrial waste (slag) is generated in several millions of tons in the production of Aluminum and is dumped into landfills, which releases poisonous gases like methane and ammonia upon contact with moisture present in the land and the heat generated by the earth, warranting stringent mitigation efforts. Rich in aluminum metal (∼15%), α-Al2O3 (7-15%), MgAl2O4 (10-15%) and AlN (20-30%), the general prime dross composition draws interest due to its abundance and presence of α-Al2O3 and MgAl2O4, for the production of refractories with insulating, shock resistance and stability at high temperature (∼1000°C and above) characteristics. Nevertheless, presence of AlN, a good thermal conductor acts as a deterrent in the production of refractories. Aluminium dross (after leaching out AlN) was processed with un-stabilized zirconia (monoclinic ZrO2) to synthesize the refractory composites. Conventional process (calcination, ball milling, compaction and sintering (1550°C/6 hrs)) was employed. Characterization involved thermal shock cycling (air quench at furnace ambient of 1000°C and room temperature) to determine the number of shock cycles endured before failure. Structural phase analyses at various stages of processing were carried out by via XRD. Magnesia present in dross did not appear to stabilize either the tetragonal or cubic ZrO2. Microstructural and chemical composition studies were carried out via SEM and EDS. The favourable results confirm the viability of the process methodology.

Thermo-mechanical behavior of stainless steel fiber reinforced refractory concrete: Experimental and numerical analysis

Stainless steel fibers are widely used as reinforcement in the refractories due to advantages such as high thermal compatibility, cost-effective on account of long life and effective resistance to corrosion at high temperatures. The purpose of this research is to investigate the thermomechanical behavior of alumina based refractory concrete reinforced with different shapes of stainless steel fibers. Straight, wavy and knurled shaped stainless-steel fibers were selected for the study. These refractory composites are extensively procured for the industrial applications. A research program of experimental test and numerical simulations was carried out. Three-point bending, fiber pull-out, direct tensile and compression tests were performed at temperatures ranging from 25 to 1200 °C to obtain the mechanical residual values. The experimental test results allowed the development of the material’s constitutive model that was implemented in the finite element program ABAQUS. The constitutive model was validated through thermomechanical simulations of the round panel test. The flexural results showed the behavior of the reinforcement with knurled fibers was superior for all temperatures due to its higher bond with the matrix. The experimental tests and the numerical simulations showed that the reinforcement benefits the pre-peak and post-peak behavior of the refractory concretes. The influence of the fibers on the shape of the softening curve allows the prediction of the fracture behavior of the composites.

Design of refractory SiC/ZrSi2 composites: Wettability and spreading behavior of liquid Si-10Zr alloy in contact with SiC at high temperatures

Reactive infiltration of liquid Si-enriched alloys into C- or SiC-based preforms is a viable cost-less alternative to manufacture dense and highly performant SiC-based and MMC composites.In view to design and optimize liquid-assisted processes such as reactive infiltration, fundamental investigations on the interfacial phenomena occurring when the liquid Si-based alloys are in contact with C and SiC substrates, are crucial steps. In this context, targeted wettability studies may provide indications for predicting the key factors strongly influencing the reactive infiltration mechanisms, such as, unexpected interaction phenomena, etc. In particular, such preliminary experience may be helpful in finding the suitable set of operating conditions for fabricating tailored composites via reactive infiltration process.Aiming to “mimic’’ the conventional industrial processes for manufacturing SiC/ZrSi2 refractory composites, the sessile drop method was applied to study the interfacial phenomena occurring at Si-10 % atZr/SiC interfaces over the temperature range of T =1360 °C-1450 °C.

Preparation of ZrC/SiC composites by using polymer-derived ceramics and spark plasma sintering

ZrC/SiC composites were fabricated using Spark Plasma Sintering (SPS) combined with the Polymer-Derived Ceramics (PDC) route. The originality of this work, consisted in the direct ceramization/sintering of a ZrC/polymer mixture without any previous crosslinking steps. The presence of a polymer in our mixtures required an optimization of the thermomechanical parameters of SPS in order to promote the polymer-to-ceramic conversion prior to the densification. The optimized SPS conditions were composed of a dwell temperature of 700 °C for 10 min followed by a soaking temperature of 1700 °C for 5 min under an applied load of 75 MPa. A fine and homogenous phase distribution was achieved at relatively low temperature (1700 °C) compared to the high temperatures required for the sintering of the refractory composite. The influence of the addition of SiC (up to 10 wt%) was also studied and related to the final relative densities and mechanical properties of the composites.

Mechanical High-Temperature Properties and Damage Behavior of Coarse-Grained Alumina Refractory Metal Composites.

The present study provides the mechanical properties of a new generation of refractory composites based on coarse-grained Al2O3 ceramic and the refractory metals Nb and Ta. The materials were manufactured by refractory castable technology and subsequently sintered at 1600 °C for 4 h. The mechanical properties and the damage behavior of the coarse-grained refractory composites were investigated at high temperatures between 1300 and 1500 °C. The compressive strength is given as a function of temperature for materials with two different volume fractions of the refractory metals Ta and Nb. It is demonstrated that these refractory composites do not fail in a completely brittle manner in the studied temperature range. The compressive strength for all materials significantly decreases with increasing temperature. Failure occurred due to the formation of cracks along the ceramic/metal interfaces of the coarse-grained Al2O3 particles. In microstructural observations of sintered specimens, the formation of tantalates, as well as niobium oxides, were observed. The lower compressive strength of coarse-grained Nb-Al2O3 refractory composites compared to Ta-Al2O3 is probably attributed to the formation of niobium oxides. The formation of tantalates, however, seems to have no detrimental effect on compressive strength.

High-alumina slurry waste metallurgy aluminium alloys - complex modifier of heat-resistant and refractory composites

The effect of aluminate slimes on the thermomechanical properties of heat-resistant and refractory composites has been investigated. The optimal content of nanotechnogenic raw materials in the studied compositions was revealed. It has been established that the replacement of expensive refractory powders (alumina, chamotte) with high-alumina industrial waste in general has a positive effect on the durability of refractories. The chemical components of aluminate sludges and the principles of their action on refractory compositions in the area of critical operating temperatures are given. The decrease in the water-cement ratio allowed in mineral compositions based on hydraulic binders to form plastic structures with enhanced rheological characteristics. The mechanism of the proceeding processes in refractory materials on phosphate binder is clarified.

Formation mechanism of β-Sialon with different morphologies based on DFT calculation and its effect on the performance of refractory composites

β-Sialon with whisker-like, columnar, and plate-shaped structures was successfully synthesized with Al2O3–C refractory compositions. In the presence of a catalyst, the preferential growth face of columnar β-Sialon was (100), whereas plate-like β-Sialon preferred (101) and (111). DFT calculations demonstrated that the SiO adsorption energy on the (100), (101), and (111) faces of β-Sialon crystal were –34.95, –52.88, and –45.08 eV, respectively. Therefore, the (101) and (111) faces were more stable in Al-rich β-Sialon. With the increase in catalyst content, the Si-rich Si–Al–O–N liquid phases, which contributed to the generation of columnar β-Sialon, were converted into the Al-rich Al–Si–O–N system that was conducive to the formation of plate-like β-Sialon. Compared to the sample without the catalyst, the CMOR and HMOR of the specimen were increased by 45.07% and 60.47%, respectively, with the addition of Fe2O3. This was attributed to the formation of β-Sialon with a one- or two- dimensional shape.

Corrosion mechanism of spray refractory in COREX slag with varying basicity

Bauxite-based spray refractories typically exhibit excellent mechanical strength and wear resistance, and have been widely used as lining materials in various industrial furnaces for many years. However, smelting reduction ironmaking in the COREX-produced slag carried out under a gas flowing at a high speed causes refractory corrosion at high temperature. Herein, Al2O3–SiO2–CaO spray refractories were fabricated, and corrosion tests were conducted in an air atmosphere using the formulated COREX slag by varying the slag basicity from 0.5 to 1.0. The mechanism underlying the corrosion between the fabricated spray refractories and formulated COREX slag was investigated via X-ray diffraction, scanning electron microscopy (backscattered electron image and energy-dispersive X-ray spectroscopy), and thermodynamic simulations to establish a new corrosion model. The results showed that after sintering at 1300 °C, the prepared specimens contained corundum, mullite, and anorthite as the major crystalline phases. The reaction and penetration layers were observed from the surface to the interior of the specimens after corrosion. A high-melting-point phase, Mg(Al,Fe)2O4 spinel layer, was generated at the slag–refractory interface, which effectively protected the specimens from further interaction with the molten slag, and afforded better corrosion resistance. The reaction layer corroded due to the phase conversion into the Ca2Al2SiO7 in the matrix. The thermodynamic simulation results of the interaction between the slag and refractory were consistent with those of the corrosion test. The total corrosion depth of the specimen was optimum when the slag basicity was 0.9. This study investigates the optimal performance environment of the spray refractory inside the COREX and provides an effective guide for designing the phase composition of related refractories.