Calcined Alumina Research Articles

Effect of various additives in activating early age properties of phosphorus furnace slag blended cement

Phosphorus furnace slag (PFS) is an industrial by-product of yellow phosphorus production which causes environmental and landfill problems. Researchers have recently shown increased interest in the environmental benefits of incorporating PFS into mortar and concrete mixes. However, the low early strength and extended setting time of PFS restrict its use as a supplementary cementitious material (SCM). Considering this, the effect of different additives, namely sodium sulfate (Na2SO4), calcium sulfate anhydrite, calcined alumina (CA), and calcium aluminate cement (CAC) at up to 5 %, on the setting time, soundness, and early strength (2d) of 25 % and 50 % phosphorus furnace slag blended cement (PFSC) paste and mortar have been investigated. It is observed that chemical activation of PFSC paste is more critical in reducing the setting time. The addition of 3 % Na2SO4 to PFSC mortar resulted in the most significant improvement in early strength, with a 20 % increase in 25 % PFSC and a 27 % increase in 50 % PFSC compared to the reference PFSC mortar. Additionally, the microstructure analysis revealed the additional formation of calcium silicate hydrate (CSH) and ettringite in the 3 % Na2SO4 added PFSC paste compared to the reference PFSC paste. It is established that the relationship between microstructural changes and the enhancement of early strength in PFSC mortar is due to the chemical activation of PFSC paste.

Evaluation of hybrid sol-gel alumina coating for electrical resistance applications

In an electric motor, bearing plays a vital role in the performance and reliability which fails frequently due to electrical pitting. To avoid this issue, the bearing can be coated with insulation material. In this present investigation, hybrid sol-gel coating was carried out on bearing steel by dip-coating method. The hybrid sol-gel was prepared using aluminium isopropoxide and calcined alumina powder. The ratio of Sol-Gel to calcined alumina and thickness of the coating was optimized to attain a crack-free surface coating. The crack behaviour was studied. The characterization of Hybrid Sol-Gel was carried out using Fourier-transform infrared spectroscopy and the surface morphology was observed using an optical microscope. The electrical resistance of the coating was measured using an insulation resistance tester. The crack-free surface coating of 40 microns was achieved at a low sol-gel to calcined alumina ratio. The electrical resistance of the coating is found suitable for bearing application. The thermodynamically stable hybrid sol-gel i.e., α alumina -ϒ alumina coating surface is proposed for electrical insulation coating.

Sintering, physicomechanical, thermal expansion and microstructure properties of cordierite ceramics based on utilizing silica fume waste

In the present work, cordierite ceramics are prepared through the solid reaction method using calcined alumina, silica fume, and talc as starting materials. Pressed samples and powders are sintered and calcined at various temperatures; 1300, 1350 and 1400 °C. The particle size, phase composition and morphology of the raw materials, and the calcined and sintered cordierite samples are analyzed. The physical properties, surface area, DSC, TG, thermal expansion and electrical and mechanical properties of the cordierite samples are also studied. In addition, the physical, thermal, mechanical, and electrical properties are investigated under the effect of heat treatment. The results indicated that 1350 °C is the optimum sintering temperature with 10.323% apparent porosity and 2.112 g/cm 3 bulk density and the crystallization of the cordierite ceramic was crack-free and has low thermal expansion. It also, showed good dielectrical constant of 5.5 and good mechanical properties such as 2.71 MPa m0.5 fracture toughness and 5.38 GPa micro hardness. • Pure cordierite can be prepared using calcined alumina, fine amorphous silica fume and talc powder mixtures. • The formation of cordierite started at 1300 °C, it was enhanced by increasing the sintering temperature up to 1400 °C. • The optimum physical properties were obtained at 1350 °C with 10.323% apparent porosity and 2.112 g/cm 3 bulk density. • Thermal expansion of cordierite sintered at 1350 °C decreased, producing CTE from −8.18 × 10 −7 at 200 °C to -3x10 −7 at 900 °C. • At 1350 °C, cordierite showed good dielectrical constant of 5.5, fracture toughness of 2.71 MPa m 0.5 & 5.38 GPa micro hardness.

THE EFFECT OF ADDING CALCINED ALUMINA ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ALUMINUM FOAM

In the last decades, Aluminum foam has attracted many researchers and manufacturers due to its unique properties which find a lot of applications, especially in a lightweight structure. The current work aims to study the effect of adding calcined alumina to the melting aluminum on the final mechanical and microstructure of produced aluminum foam. Calcium carbonate was used as a foaming agent. The study reveals that calcination times/temperature have a significant effect on the final foam porosity. with increasing calcination time from 30 min to 90 min the foam density improved from 2.27 to 1.27 g/cm3, which consequently result in increase of samples porosity from 15.9 to 52.7%. also, the results from the compression test show that the variation of calcination time can be used to alter the energy absorption capacity of samples. Tested samples achieved the highest energy absorption of 128 MPa at a calcination time of 90 min. Also, the study reveals that calcination temperature has a significant effect on the final foam porosity. with increasing calcination temperature from 400 to 800°C, the foam density improved from 2.18 to 1.09 g/cm3, which consequently result in increase of samples porosity from 18.94 to 52.79%. Tested samples achieved the highest energy absorption of 325 MPa at a calcination temperature of 800°C. The increase in porosity is measured by ImageJ software, and the energy absorption test was carried out by a quasi-static compression test. These improvements produced material can be used in applications needs high energy absorption like automotive industry.

Combined effects of SiO2 ratio and purity on physical properties and microstructure of in situ alumina‐mullite ceramic

AbstractThe in situ formation of mullite (Al6Si4O13) is a complex process based on solid‐state reactions strongly affected by the characteristics of Al2O3 and SiO2 sources. This study investigated the combined effects of variable SiO2/Al2O3 ratios and the presence of low‐melting‐point impurities on the physical properties and microstructure of in situ alumina‐mullite ceramics. Two grades of synthetic amorphous silica, known as microsilica, of similar physical properties and significant differences in the content of alkali‐based impurities (0.8 and 3.6 wt%), were combined with thin calcined alumina particles in different proportions (from silica‐free up to stoichiometric mullite), pressed and sintered. The samples were tested for total porosity, flexural strength, and pore size distribution, and their crystalline phases and microstructures formed were investigated. Small amounts of both microsilica grades (up to 8.9 wt%) hindered the densification of the alumina‐mullite matrix and favored grain growth events, increasing porosity and reducing strength. For samples containing higher microsilica loads (16.4–28.2 wt%), the impurities content significantly affected the amount of liquid phases formed. Such impurities altered the ratio and shape of the pores and the total amount of mullite after sintering. Therefore, different microstructures and levels of flexural strength and total porosity were observed.

Synthesis of alumina by microwave-assisted combustion method using low fuel content and its use as catalytic support for dry reforming of methane

Alumina powders with high specific surface area (>200 m2g-1) were obtained quickly, easily and using only aluminum nitrate and urea (as fuel) through the microwave-assisted combustion method applying low power (450 W) and low fuel content. The powders obtained were calcined at temperatures of 550, 750 and 950 °C. The X-ray diffraction and Fourrier Transform Infrared (FTIR) results indicate that γ-Al2O3 was formed at temperatures of 550 and 750 °C, while the α and γ phases were identified in calcined alumina at 950 °C. The increase in calcination temperature strongly influenced the specific surface area and the pore size distribution, however no effect on the pore diameter was observed. The Al2O3 powder calcined at 550 °C was evaluated as catalytic support due to its most appropriate textural properties. The catalyst Ni/Al2O3 (Ni-A550) was prepared by wet impregnation method and calcined at 550 °C/3 h. The physical-chemistry properties were evaluated by X-ray diffraction, temperature programmed reduction and scan electron microscopy techniques. The results show that the Ni-A550 have high conversion of CH4 and CO2 and good H2 yield using a gas hourly space velocity (GHSV) of 72 L g−1 h−1. Therefore, the synthesized Al2O3 presents as a potential catalytic support material.

Differences in phase, microstructural, and electrical characteristics of quartz-substituted alumina porcelain insulator

In the present study, total quartz content (30 wt%) of a standard porcelain body was progressively substituted with two different kinds of aluminas (active alumina and calcined alumina) keeping active alumina constant at 5 wt% and varying calcined alumina content to the extent of 5–25 wt%. The alumina incorporated compositions (AP1 to AP7), along with the standard quartz containing porcelain body (SP0), were processed following common ceramic processing techniques. Two types of forming techniques were used to make samples, namely extrusion of plastic mass to get cylinder of desired dimensions and the other one was hydraulic compaction to produce rectangular bars. The extruded and compacted samples were properly dried and then heated in an electrically operated furnace in the temperature range of 1170–1260 °C. The fully densified samples heated at 1260 °C were subjected to various tests, namely phase identification by X-ray diffraction (XRD) pattern studies; scanning electron microscopic (SEM) analysis; and measurement for electrical properties such as dielectric strength (kV/mm), dielectric loss (tanδ), electrical resistivity (ohm-cm), and dielectric constant to confirm suitability of the samples for application in high-tension power transmission system. The results revealed that the body AP6, wherein 25 wt% quartz was substituted by 5 wt% active alumina and 20 wt% calcined alumina and heated at 1260 °C, may be considered the most suitable sample for porcelain insulator.

Effects of alumina and white fused alumina addition on technological properties of transparent floor tile glazes

In ceramic tile manufacturing, α-Al2O3 is the main type of alumina used in ceramic body and glaze formulations. It acts as an opacifier in porcelain tile bodies and as a matting agent in glazes. White fused alumina (WFA) is produced by fusing calcined alumina in an electric arc furnace under carefully controlled conditions. It is generally preferred in ceramic floor tile glazes in order to increase abrasion resistance. The aim of this study was to establish a better understanding of how alumina and WFA addition affects the thermal behavior, microstructural evolution and aesthetic properties of transparent floor tile glazes. The results showed that both alumina and WFA increased the sintering and melting temperatures of the standard commercial glaze. Corund was detected in the main phase with WFA addition in tile glazes. There were no other crystalline phases formed since WFA did not react with glassy phase. This behavior can be attributed to higher refractoriness of fused alumina. Smoother surface and homogenous structure were observed in the glazes with WFA addition. However, anorthite and corund phases were detected in the glazes with alumina addition. High crystallization glazes with rough surfaces were observed in these glazes. Alumina was found to be more effective to increase opacity and reducing glossiness compared WFA addition.

Preparation and Properties of Lightweight Refractories Based on Microporous Calcined Alumina

Characteristics of domestic corundum insulation objects are given. The properties of corundum lightweight objects obtained from microporous calcined alumina are studied. It is shown that product physicochemical properties are no worse than traditional lightweight objects of corundum composition.

Production and properties of lightweight refractories based on microporous calcined alumina

The characteristic of domestic corundum insulation products is given. The properties of corundum lightweight products derived from microporous calcined alumina are studied. It is shown that such products are not inferior in their physicochemical properties to traditional lightweight products of corundum composition. Ill. 5. Ref. 11. Tab. 1.

Preparation and Characterization of Transitional Alumina Obtained through Ammonia Treatment

In this study, different aluminas were obtained by precipitating Al(NO3 )3·9H2O with different concentration of aqueous solution of ammonium carbonate. The obtained aluminas were treated by 50 (vol/vol) % ammonia via low temperature immersing and high temperature hydrothermal treatment, respectively, then, the treated aluminas were calcined again. The crystal types, morphology, textural properties, and pore distribution of the original alumina, ammonia‐treated alumina, and the second calcined alumina were studied by characterizations of X‐ray diffraction, thermogravimetric analyses, nuclear magnetic resonance, Brunauer‐Emmett‐Teller (BET), transmission electron microscopy, and so on. Several modified aluminas with specific morphology, desired pore structure, and pure crystal types were obtained, which can be used in some specific industrial application.

Production and Quantification of High-Purity Mullite at 1600°C from Kaolinitic Clay and Calcined Alumina

A study is performed to determine the reaction time which is required at 1600°C to obtain mullite from clay with a high content of kaolinite (clay from the La Rioja Province of Argentina) and from a stoichiometric mixture of the clay and calcined alumina of grade Almatis-A2G. The chemical composition of the raw materials was determined and they were studied by x-ray diffraction (XRD) and examined on a scanning electron microscope (SEM). The materials were then mixed in the stoichiometric proportions 3Al2O3·2SiO2 and pressed at 100 MPa. The pressed specimens were fired at 1600°C in electric furnaces for different lengths of time: 0.25, 0.5, 1, 2, 3, and 5 h. Their density and porosity were determined after they were fired. In the studies performed on the scanning electron microscope and by x-ray diffraction; the crystalline phases were identified by the Rietveld method and the amorphous phases were determined by means of the Le Bail model. The objective was to determine the amounts of primary and secondary mullite that were present and the total mullite content.

Production of porous ceramic materialusing different sources of alumina and calcia

Numerous papers and publications report the use of microporous calcium hexaluminate (CaO.6Al2O3; CA6) as a key raw material for high temperature insulating materials. This material has unique properties with respect to chemical purity and mineral composition. Another important property of CA6 is its structure, which consists of platelet-shaped crystals that interlock. The free distance between the crystals defines the microporous structure. The low density in combination with the micropores hampers heat transfer by radiation at temperatures exceeding 1000 oC and results in a low thermal conductivity. Given the advantages presented by this material, it is necessary to understand the formation mechanism of CA6 grains in order to better develop the potential applications of this material. CA6 can be fabricated using organic binders to consolidate the Al2O3-CaCO3 powder mixture and to provide green strength so that a green body can be formed and retains the desired shape before heating. However, these organic binders must be completely thermally decomposed so that they do not remain in the sintered body as carbon or ash. Moreover, the use of organic binders releases large volumes of gases such as carbon dioxide from the green body during heating. Therefore, an eco-friendly ceramic fabrication process has been developed that employs an inorganic binder (hydraulic alumina). The aim of the present work was to study the synthesis of porous calcium-hexaluminate ceramics using calcined alumina or hydraulic alumina combined with different sources of calcia (CaCO3 and Ca(OH)2) at different temperatures. The materials produced were characterized by X-ray diffraction, scanning electron microscopy, apparent porosity and mercury intrusion porosimetry. The materials produced by hydraulic alumina presented higher porosity and larger pores compared to those produced from calcined alumina

Effect of Alumina Source and Soaking Time on Properties of Refractory Mortar Using as Slumping Mold

Slumping molds or sagging molds are utilized for shaping glassware containers and many kinds of slumped glass products from glass plates. In Thailand, a large number of slumped glass factories use such molds in their production because slumping process is easy and cheap; however, the major cost of this process is slumping molds. They are imported from other countries and are expensive. In this research, slumping molds are created from local raw materials using the basic method to reduce the cost of the production. One of proper materials for making slumping mold is refractory mortar which can be easily formed into various shapes and sizes. Consequently, it is interesting to prepare slumping molds from refractory mortar. In this study, the effect of different sources of alumina (calcined alumina and aluminum sludge) and soaking time on the properties of the refractory mortar were investigated. Dolomite clay, milled sand and white portland cement were mixed with sources of alumina in distilled water to form pastes. Super plasticizer was added to the pastes to adjust flow ability. Plastic containers were used as molds for specimen forming. Specimens were cured at room temperature for 24 hours and dried in air for 24 hours. After that specimens were dried in an oven at 110 °C for 24 hours and then fired at 1100 °C. The result showed that the suitable condition for making slumping mold is to use calcined alumina as a source of alumina with soaking temperature of 1100 °C for 4 hours. The physical properties, chemical properties and thermal properties were discussed.

Low Concentration Fe-Doped Alumina Catalysts Using Sol-Gel and Impregnation Methods: The Synthesis, Characterization and Catalytic Performance during the Combustion of Trichloroethylene

The role of iron in two modes of integration into alumina catalysts was studied at 0.39 wt% Fe and tested in trichloroethylene combustion. One modified alumina was synthesized using the sol-gel method with Fe added in situ during hydrolysis; another modification was performed using calcined alumina, prepared using the sol-gel method and impregnated with Fe. Several characterization techniques were used to study the level of Fe modification in the γ-Al2O3 phase formed and to correlate the catalytic properties during trichloroethylene (TCE) combustion. The introduction of Fe in situ during the sol-gel process influenced the crystallite size, and three iron species were generated, namely, magnetite, maghemite and hematite. The impregnated Fe-alumina formed hematite and maghemite, which were highly dispersed on the γ-Al2O3 surface. The X-ray photoelectron spectra (XPS), FT-IR and Mössbauer spectroscopy analyses revealed how Fe interacted with the γ-Al2O3 lattice in both catalysts. The impregnated Fe-catalyst showed the best catalytic performance compared to the catalyst that was Fe-doped in situ by the sol-gel method; both had better catalytic activity than pure alumina. This difference in activity was correlated with the accessibility of the reactants to the hematite iron species on the surface. The chlorine poisoning for all three catalysts was less than 1.8%.

Particle Size Characterization of Commercial Raw Materials and Graphite nanoparticles of a Refractory Bricks Mix of the System Al2O3-SiC-C

ABSTRACTIn this work was studied the partial substitution in the design of a refractory mix of the fine crystalline graphite for prefabricate nanoparticles of the seam source of graphite, improving the refractory properties of the material, getting a better resistant to the chemical attack by the slag and steel liquid metal. The raw materials and nanoparticles of crystalline graphite were characterized by X-ray diffraction (XRD), Sherrer equation, and scanning electron microscopy (SEM). The nanoparticles size determines the crystalline of the graphite used in the mixes obtained after different steps of mechanic milling. The nanoparticles of materials were added to the mixes in different proportions. The commercial raw materials used for this investigation were: commercial silicon carbide high purity (97% SiC), calcined bauxite (85% Al2O3), alpha calcined alumina, and crystalline graphite (94% C). Additionally, six different sizes of graphite nanoparticles were selected. The particle size of the initial commercial graphite was 0.044mm and the final nanoparticles obtained in this investigation by mechanic milling was 18 nm. The measurement of the particle size of the nanoparticles was made by the Scherrer equation, XRD and SEM.

THE EFFECT OF FINE ALUMINA TYPE ON COMPOSITION OF IN SITU SPINEL FORMATION IN ALUMINA-MAGNESIA CASTABLES

Three types of low cement castables (LCC) were prepared from 5% reactive alumina ( R 5), 5% calcined alumina ( A 5) and equal proportions of 2.5% (AR). The nest of the composition was fine bauxite (0–1 mm, 57%), coarse bauxite (1–3 mm, 20%), calcined magnesia (5%), secar 71 refractory cemet (7%) and microsilica (1%). By the addition of 5% water, castables were moulded, aged, dried and fired to 1400°C for 2 h. XRD studies showed higher amount of in situ spinel formation in A 5. The lattice constants of spinels in A 5, AR and R 5 were, respectively, 8.0348, 8.0688 and 8.0847 Å. This accounted for respectively alumina rich, stochiometry and magnesia rich spinels. Since calcined alumina is cheaper, produce higher amounts of spinel with the aid of alumina from the aggregate of bauxite and the binder of cement, and alumina rich spinel has better corrosion resistance properties, use of calcined alumina is recommended in LCC.

Evaluation of aluminum dross waste as raw material for refractories

An aluminum dross waste from plasma processing for Al metal reclamation was tested as a replacement raw material in refractories. The main phases of the starting Al dross waste material were MgAl 2O 4 and AlN. The waste was tested to replace calcined alumina in castables and refractory clay in a molded refractory at levels below 6.5%. The results of physical and mechanical tests indicated that the waste may be applied directly, without prior calcination, as a substitute for fine structural components in refractories. The waste and water contents used in processing, however, must be optimized to avoid the formation of crack-like defects in the microstructure. The origin of these defects is related to the generation of gas from the waste at high temperatures. It is not known if these crack defects impact physical properties. The waste was also tested as a replacement for anti-oxidant elements (Al and Si powders) in a resin-bonded refractory. Oxidation tests, however, indicated a negative effect on oxidation resistance.

Effect of Reinforcement Size on the Scratch Resistance and Crystallinity of HVOF Sprayed Nylon-11/Ceramic Composite Coatings

The high-velocity oxyfuel (HVOF) combustion spraying of dry ball-milled nylon-11/ceramic composite powders is an effective, economical, and environmentally sound method for producing semicrystalline micron and nanoscale reinforced polymer coatings. Composite coatings reinforced with multiple scales of ceramic particulate material are expected to exhibit improved load transfer between the reinforcing phase and the matrix due to interactions between large and small ceramic particles. An important step in developing multiscale composite coatings and load transfer theory is determining the effect of reinforcement size on the distribution of the reinforcement and the properties of the composite coating. Composite feedstock powders were produced by dry ball-milling nylon-11 together with 7, 20, and 40 nm fumed silica particles, 50 and 150 nm fumed alumina particles, and 350 nm, 1, 2, 5,10, 20, 25, and 50 μm white calcined alumina at 10 vol.% overall ceramic phase loadings. The effectiveness of the ball-milling process as a function of reinforcement size was qualitatively evaluated by scanning electron microscopy + energy dispersive x-ray spectroscopy (SEM + EDS) microanalysis and by characterizing the behavior of the powder during HVOF spraying. The microstructures of the sprayed coatings were characterized by optical microscopy, SEM, EDS, and x-ray diffraction (XRD). The reinforcement particles were found to be concentrated at the splat boundaries in the coatings, forming a series of interconnected lamellar sheets with good three-dimensional distribution. The scratch resistance of the coatings improved consistently and logarithmically as a function of decreasing reinforcement size and compared with those of HVOF sprayed pure nylon-11.

Utilisation of Egyptian industrial waste material in manufacture of refractory cement

AbstractEgyptian calcium hydroxide byproduct, produced as a waste material during preparation of acetylene gas, causes various ecological problems. The present work had the aim of utilising this waste material as a source of calcium oxide in the production of refractory calcium aluminate cement. Two types of calcium aluminate cement (pure and commercial grade) were prepared, by mixing calcium hydrox ide waste material with pure calcined alumina and calcined bauxite respectively. T he cements were prepared by sintering at 1500-1550 °C for 3 h. The mineralogical compositions of anhydrous and hydrated cements were investigated by X RD. Also, thermal analysis and microstructure were used to identify the hydrated phases. The study revealed good cementing, sintering, mechanical, and refractory properties of the manufactured cements, enabling their use in high temperature applications (> 1500 °C) in the case of pure cement, and in moderate temperature applications (< 1500 °C) in the case of commercial cement.