Dear Label_Name,

Greetings! I hope you are well.

I am writing on behalf of an international publishing house, Science and Education Publishing, USA (http://www.sciepub.com).

Science and Education Publishing (SciEP) is a multidisciplinary open access publisher of Journals covering the fields of Science, Technology and Medicine. All SciEP publications are subject to high-quality peer review, editorial and production processes and are freely available online.

Welcome to the April, 2013 edition of SciEP newsletter, providing monthly summaries of articles on science & education related topics of interest to scientist and professionals. The mission of our journals is to provide an open access forum for publishing new findings on issues pertinent to scientific and academic field. We also invite you to submit original research papers, review articles, short reports, or case studies are considered for publication in our Multidisciplinary Journals.

American Journal of Public Health Research
DOI: 10.12691/ajphr-1-1-3

The Implementation of a Tele-Homecare System with Service Oriented Architecture and HL7 Message Transmission Standard
Ching-Sung Wang

American Journal of Medical and Biological Research
DOI: 10.12691/ajmbr-1-1-2

The Influence of Ethanol on Pyruvate Kinases Activity in Vivo, in Vitro, in Silico
Lelevich Sergey Vladimirovich, Khrustalev Vladislav Victorovich, Barkovsky Eugene Victorovich, Shedogubova Tatyana Aleksandrovna

American Journal of Medical Sciences and Medicine
DOI: 10.12691/ajmsm-1-1-1

Clinical and Histological Features in Wegener Granulomatosis
Li Cavoli Gioacchino, Passantino Rita, Bono Luisa, Tortorici Calogera, Ferrantelli Angelo, Giammarresi Carlo, Rotolo Ugo

American Journal of Infectious Diseases and Microbiology
DOI: 10.12691/ajidm-1-1-2

The Curse of Lymphatic Filariasis: Would the Continual Use of Diethylcarbamazine Eliminate this Scourge in Papua New Guinea?
Anne Lanham, Lillian Mwanri

We have released issues of some journals on February 2013.
American Journal of Public Health Research
American Journal of Medical Sciences and Medicine
American Journal of Medical and Biological Research
American Journal of Pharmacological Sciences
American Journal of Clinical Medicine Research
American Journal of Nursing Research
American Journal of Cancer Prevention
American Journal of Medicine Studies
American Journal of Infectious Diseases and Microbiology
American Journal of Cardiovascular Disease Research
American Journal of Biomedical Research
American Journal of Mechanical Engineering
American Journal of Microbiological Research
Journal of Preventive Medicine
American Journal of Food and Nutrition
American Journal of Hypertension Research
American Journal of Sports Science and Medicine
Journal of Cancer Research and Treatment
American Journal of Zoological Research
Journal of Biomedical Engineering and Technology
American Journal of Microbiological Research
Biomedical Science and Engineering

We are pleased to announce that submissions are now being accepted for peer review for all the journals across all our subject areas in SciEP.

Please submit your manuscript via our online submission system:
http://www.sciepub.com/author/signin

To unsubscribe from our mailing list, please click on the following link: unsubscribe

I am looking forward to hearing from you.

Kind regards,

David Rain
Email:join@sciepub.com
Science and Education Publishing (http://www.sciepub.com)

Preparation of Alumina-Iron Oxide Compounds by Coprecipitation Method and Its Characterization

Fahmida Gulshan*, Kiyoshi Okada

Materials and Metallurgical Engineering Department, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh

Abstract: Fe₂O₃-Al₂O₃ compounds with different Fe/Al compositions were synthesized by coprecipitation (CP) method and calcined at 300°-1000°C. The formation of crystalline phases (e.g., maghemite, hematite), transformation temperature, specific surface area, lattice parameter, crystallite size, magnetic properties of iron oxide were all affected by the component ratio and thermal treatment.

Keywords: Fe₂O₃-Al₂O₃ compounds, coprecipitation, maghemite, hematite, lattice parameter, crystallite size

Received January 10, 2013; Revised February 21, 2013; Accepted March 15, 2013

Citation: Fahmida Gulshan, Kiyoshi Okada, Preparation of Alumina-Iron Oxide Compounds by Coprecipitation Method and Its Characterization. American Journal of Materials Science and Engineering, 1 (1). 6-11. January 2013. doi:10.12691/ajmse-1-1-2

1. Introduction

Mixed oxides, especially binary systems, have been employed successfully in many industrial catalytic processes. The combination of two transitional metal oxides may affect their stoichiometry and their surface, electrical, catalytic, texture and thermal properties. Both Al₂O₃ and Fe₂O₃ individually catalyse many reactions. Binary catalysts with the composition Al₂O₃-Fe₂O₃ are also used for many purposes [1,2].

At present, there are some uncertainties concerning the formation of solid solution in the Fe₂O₃-Al₂O₃ system. The lattice constants at 25°C, in terms of trigonal axes for α-Al₂O₃ are: a = 0.4758 and c = 1.2991nm, and those for α-Fe₂O₃ are a = 0.5034 and c = 1.3752nm. The differences in the a and c constants, 5.80 and 5.86%, respectively, are a consequence of different ionic radii of the metals (for coordination six): 0.054nm for Al³⁺ and 0.065nm for Fe³⁺. Brown et al [3] measured the lattice constants and recorded the Mossbauer spectra for α-Al₂O₃ samples containing Fe³⁺ ions. A linear increase of the constant a with increase of Fe₂O₃ up to 10.5 mol% was observed. A series of aluminium substituted hematites, α-(AlxFe1-x)₂O₃ with x up to 0.32, was prepared by Grave et al [4] by thermal treatment of aluminium substituted goethites, α-FeOOH, at 500°C for 6h. The samples contained particles varying in size from 20 to 100nm, as determined from X-ray diffraction line broadening. Heating of the samples up to 900°C improved the crystallinity, but reduced the maximum obtainable x to ~0.15. Mossbauer spectroscopy was applied for quantitative determination of aluminium substituted goethite-hematite mixtures by Amarasiriwardena et al [5]. The effects of crystallinity and aluminium substitution on the magnetic behaviour and Morin transition of these substituted oxides were also investigated [6,7] and found that aluminium substituted hematite, prepared under hydrothermal conditions from coprecipitated Al(III)/Fe(III)-hydroxides at temperatures not high enough to remove OH⁻ structural groups, exhibited a substantial deviation from the Vegard rule. The anhydrous aluminium substituted hematites, treated at 900°C, fulfilled the Vegard rule in the solid solution range (x≤ 0.15). The ball milling of equimolar mixtures of goethite and hydrated aluminas, γ-Al(OH)₃ (gibbsite), α-Al(OH)₃ (bayerite) or γ-AlOOH (boehmite) significantly affected the temperature of formation of solid solution of the calcined products [8].

The aim of the present study was to obtain more detailed knowledge about the formation of solid solutions in an analogous system Fe₂O₃-Al₂O₃. The effect of component ratio and thermal treatment conditions on the phase composition and structure were investigated. The samples synthesized were used to test their effectiveness for adsorption of toxic ions in waste-water followed by the magnetic separation by applying a simple magnetic field. The study of this system is of particular interest in connection with the polymorphs of its components and possible phase conversions, which can be followed by X-ray diffraction methods for both components and magnetochemistry of phases containing iron.

2. Experimental

2.1. Synthesis Procedures of Fe₂O₃-Al₂O₃ Compound by Coprecipitation Method

The coprecipitation process involves dissolving a salt precursor, usually a chloride, oxychloride or nitrate. The corresponding metal hydroxides precipitate in water upon addition of a base solution such as sodium hydroxide or ammonium hydroxide solution. The resulting salts are then washed and calcined to obtain the final oxide powder. This method is useful in preparing ceramic composites of different oxides by coprecipitation of the corresponding hydroxides in the same solution. One disadvantage of this method resides in the difficulty in controlling the particle size and size distribution.

In this study, ferric nitrate Fe(NO₃)₃.9H₂0 and aluminium nitrate Al(NO₃)₃.9H₂0 were used as precursors of Fe₂O₃ and Al₂O₃ to prepare Fe₂O₃-Al₂O₃ compound. Coprecipitated gels were prepared with various ratios of 0.2M Fe(NO₃)₃•9H₂O and Al(NO₃)₃•9H₂O solutions using conc. NH₄OH (25 mass%) as the precipitant. Samples containing 0, 20, 40, 60, 80 and 100 mol% Fe₂O₃ were prepared. For example, to prepare 20 mol% Fe₂O₃ sample, 4.04g Fe(NO₃)₃•9H₂O was dissolved in 50 ml of distilled water and 15.01g Al(NO₃)₃•9H₂O was dissolved in 200ml of distilled water. Then, these two solutions were mixed with mechanical stirring and 200ml of NH₄OH solution was added with continuous stirring. They were dried in an evaporator at 60°C for 4h and in an oven at 110°C for 2 days.

2.2. High Energy Ball Milling

After drying, the powders were dry-ground in a planetary ball mill (LAPO-1, Ito Seisakusho Ltd., Japan) using a Si₃N₄ pot with 30 Si₃N₄ balls (5 mm) at 300rpm for 3 hours with a ball: sample mass ratio of 30:1. In this process, known as ‘break down’ or ‘top-down’ approach, high mechanical grinding energy is applied to produce nanoparticles.

2.3. Calcination

After grinding, the samples were calcined at 300°-1000°C in air for 5 hours at a heating rate of 10°C /min. The flowchart for the preparation of the sample is shown in Figure 1.

2.4. Characterization of Samples

The crystalline phases in the samples were determined by x-ray diffraction analysis (XRD-6100, Shimadzu) using monochromated CuKα radiation. The lattice parameters of the resulting crystalline phases were calculated by least-squares method using Si powder as the internal standard. The crystallite sizes of the crystalline phases were calculated using the Scherrer equation for the (104) reflection of α-Fe₂O₃ and α-Al₂O₃, and the (400) of γ-Al₂O₃. The instrumental broadening was corrected using the peak widths measured for 100 mol% Fe₂O₃ sample heated at 1300°C. The specific surface area (SBET) was obtained by the method using N₂ as the adsorbate (Autosorb-1, Quantachrome). The magnetic properties were examined using vibrating sample magnetization (VSM) equipment (BHV-50H, Riken Electronics).

Figure 1. Flowchart for the preparation of Al₂O₃-Fe₂O3 compounds by coprecipitation method

3. Results and Discussion

3.1. Characterization of Samples

The x-ray diffraction patterns of the samples calcined at various temperatures are shown in Figure 2 (a-e). From these figures it is clear that the as-synthesized samples were amorphous, but crystallized at 500-700°C in all samples. The crystallization temperature increased with increasing Al₂O₃ content in the Fe-rich compositions, being highest at about 60 mol% Fe₂O₃ composition. In the Fe-rich compositions, the crystalline phase was α-Fe₂O₃ and was thought to incorporate Al₂O₃. The increase of iron content in the CP samples is associated with an increase of intensities of the α-Fe₂O3 reflections, therefore with higher crystallinity of the phase. In the Al-rich compositions, the crystalline phases changed from γ-Al₂O₃ to θ-Al₂O₃ and then to α-Al₂O₃ at higher temperatures

In the 20 mol% Fe₂O₃ sample (Figure 3), the only detectable phase at temperature 600°C is γ-Al₂O₃, located at 2θ= 36.95, 45.46, 66.36o. At temperature 800°C, the XRD pattern shows the appearance of new XRD reflections at 2θ = 24.15, 33.25, 35.72, 49.65, 54.30, 62.68 and 64.28⁰ are attributed to α-Fe₂O₃. The intensity of the latter XRD reflections strongly increased with the increase of calcination temperature indicating the enhancement of crystallinity of α-Fe₂O₃. A phase transition of γ-Al₂O₃ to α-Al₂O3 is clearly observed upon elevating the calcination temperatures to 1000°C.

A field map of the product phases as functions of composition and heating temperature is shown in Figure 4. From this field map, it can be seen that the formation of α-Fe₂O₃ takes place at 600°C in 80 mol% Fe₂O3 samples and 700°C in 60 mol% Fe₂O3 whereas α-Fe₂O₃ is formed at 500°C in 90 mol% Fe₂O₃ sample. The crystallization of α-Fe₂O3 shifted gradually to higher temperature by increasing the alumina content, indicating the effect of alumina.

Figure 2(a). The XRD pattern of the samples heated at 500°C for different Fe/(Fe+Al) ratio. Key: G = γ-Al₂O₃, H = α-Fe₂O₃

Figure 2(b). The XRD pattern of the samples heated at 600°C for different Fe/(Fe+Al) ratio. Key: G = γ-Al₂O₃, H = α-Fe₂O₃

Figure 2(c). The XRD pattern of the samples heated at 700°C for different Fe/(Fe+Al) ratio. Key: G = γ-Al₂O₃, H = α-Fe₂O₃

Figure 2(d). The XRD pattern of the samples heated at 800°C for different Fe/(Fe+Al) ratio. Key: G = γ-Al₂O₃, H = α-Fe₂O₃

Figure 2(e). The XRD pattern of the samples heated at 1000°C for different Fe/(Fe+Al) ratio. Key: C = α-Al₂O₃, H = α-Fe₂O₃,T=θ-Al₂O₃

Figure 3. The XRD patterns of the 20 mol% Fe₂O3 CP samples heated at different calcination temperatures. Key: C = α-Al₂O₃, G = γ-Al₂O₃, H = α-Fe₂O₃

Figure 4. A field map of the phases formed in the samples as functions of composition and calcined temperature

Table 1. Lattice constants (nm) of α-Fe₂O₃ in the various samples

The lattice parameters of the Fe-rich samples (Table 1) decreased with decreasing Fe₂O₃ content up to 40 mol% Fe₂O₃ in samples heated at ≤800°C. The amount of Al₂O₃ estimated from the resulting lattice parameters was about 20 mol% in these samples. By contrast, the lattice parameters of the samples heated at 1000°C decreased in samples containing up to 90 mol% but became constant in the samples containing ≤90 mol% Fe₂O₃. The limit of Al₂O₃ incorporation in these samples is found to be ≤10 mol%, in fair agreement with Pownceby et al. [9]. Thus, the resulting data observed at ≤800°C appear to correspond to a transient state that attains equilibrium on heating at ≥1000°C.

The lattice parameters determined for Al-rich samples suggest that 10-20 mol% of Fe₂O₃ is incorporated in the γ-Al₂O₃ and α-Al₂O₃ phases.

Thus, the crystalline phases in the samples of intermediate compositions are solid solutions of Fe₂O₃ and Al₂O₃. The incorporation of Al or Fe ions in these phases causes broadening of their XRD reflections, suggesting smaller crystallite sizes. The crystallite sizes of the samples [showed in Figure 5] were estimated using the Scherrer’s equation, D= Kλ/βcosθ, where D is the crystallite size, λ is the X-ray wavelength (0.15418nm), K is a numerical constant (0.9), β is the full width at half maximum for the reflection and θ is the Bragg angle [10].The crystallite sizes of the α-Fe₂O₃ in 100 mol% Fe₂O₃ samples varied from 73nm at 500°C to 460nm at 1000°C while those of the 40 mol% Fe₂O₃ samples ranged from 9.1nm at 500°C to 140nm at 1000°C. Thus, the crystallite sizes of the pure Fe₂O₃ samples are several times larger than those of the Al₂O₃-containing samples. The crystallite sizes of the α-Al₂O₃ samples decreased from 150nm in the 20 mol% Fe₂O₃ sample to 71nm in the 40 mol% Fe₂O₃ sample. The crystallite sizes of γ-Al₂O₃ also decreased with higher Fe₂O₃ content, from 5.8nm at 500°C to 6.1nm at 800°C in the 0 mol% Fe₂O₃ and from 3.4nm at 500°C to 5.3nm at 800°C in the 40 mol% Fe₂O₃ sample.

3.2. Magnetic Properties

The magnetic properties of the samples were measured to determine their potential usefulness for magnetic separation after adsorption. The magnetization was determined as a function of magnetic field at room temperature by VSM. It employs an electromagnet which provides the magnetizing field (DC), a vibrator mechanism to vibrate the sample in the magnetic field, and detection coils which generate the signal voltage due to the changing flux emanating from the vibrating sample. The output measurement displays the magnetic moment (M) as a function of the magnetic field (H). This applied magnetic field was varied from -15000 Oe to 15000 Oe. All the samples showed very weak saturation magnetization, <1emu/g.

Figure 5. Crystallite size vs. temperature as a function of Fe/(Fe+Al)

The samples containing α-Fe₂O₃ solid solutions showed very weak hysteresis loops in the magnetization curves [Figure 6] corresponding to the antiferromagnetic property of α-Fe₂O₃ and the magnetization was insufficient to attract these powders to a domestic magnet.

Figure 6. Magnetization curves of 80 mol% Fe₂O₃ CP sample calcined at 800°C [blue line] and that at 1000°C [pink line]

3.3. Specific Surface Area

Changes in the SBET values of the samples of various compositions [values listed in Table 2] are shown in Figure 7 as a function of heating temperature and Fe₂O₃ content, together with the values reported by Li et al. [11]. The SBET values differed greatly, ranging from 330m²/g in the sample with 0 mol% Fe₂O₃ heated at 500°C to 3m²/g in the sample containing 100 mol% Fe₂O₃ heated at 800°C. The SBET values decreased slightly with higher heating temperature to 1000°C. On the other hand, the effect of the Fe₂O₃ content on SBET was different in the samples with Fe₂O₃≤80 mol% and Fe₂O₃=100 mol%. The SBET values were almost constant or slightly less, up to Fe₂O₃≤80 mol% contents, but decreased very steeply from 80 to 100 mol%. Figure 6 suggests that mixtures of crystalline phases are effective in maintaining high SBET values. The SBET values of the present samples (solid lines) are higher than those reported by Li et al. [11] (dashed lines).

Table 2. Specific surface area values [m²/g]

Figure 7. Changes in the SBET values of the samples of various compositions as a function of heating temperature and Fe₂O₃ content, together with the values reported by Li et al

4. Conclusion

The as-synthesized samples were amorphous but crystallized on heating at 500-700°C. The crystalline phases formed were only α-Fe₂O₃ in the Fe-rich compositions, while they ranged from γ-Al₂O3 to θ-Al₂O₃ to α-Al₂O₃ with increasing heating temperature in the Al-rich compositions. About 10-20mol% of Al₂O₃ was incorporated in α-Fe₂O₃ and a similar amount of Fe₂O₃ was incorporated in γ-Al₂O₃ and α-Al₂O₃. The crystallite sizes decreased significantly by incorporation of these ions. The SBET values differed greatly from 330m²/g to 3m²/g . The samples showed very weak magnetization.

References

[1]   | Lee, E. H. “Iron Oxide Catalysts for Dehydrogenation of Ethylbenzene in the Presence of Steam”, Catalysis Reviews, 8(1). 285.1974.
[2]   | Lee, E. H. and Oliver, G. D., “Calculating Homogeneous Reaction Rates and Orders in a Flowing Gas Reactor. Thermal Decomposition of Ethylbenzene”, Ind. Eng. Chem., 1959, 51 (11). 1351-1352. November .1959.
[3]   | Brown,I. W. M., Mackenzie, K. J. D. and Cardile,C. M., “Lattice parameters and Mössbauer spectra of iron-containing corundum (α-Al2O3)”, Journal of Materials Science Letters, 6(5).535-540. May .1987.
[4]   | Grave,E.De., Bowen, L.H. and Weed, S.B., “Mossbauer Study Of Aluminum-Substituted Hematites”, Journal of Magnetism and Magnetic Materials, 27(1). 98-108. 1982.
[5]   | Amarasiriwardena,D.D., Grave, E.De. and Bowen L.H., “Quantitative Determination of Aluminum-Substituted Goethite-Hematite Mixtures by Mössbauer Spectroscopy”, Clays and Clay Minerals, 34( 3). 250-256. June .1986.
[6]   | Grave, E.De., Bowen, L.H., Vochten, R. and Vandenberghe,R.E., “The effect of crystallinity and Al substitution on the magnetic structure and morin transition in hematite”, Journal of Magnetism and Magnetic Materials, 72(2), 141-151. April. 1988.
[7]   | Wolska, E. and Szajda, W., “The effect of cationic and anionic substitution on the α-(Al, Fe)₂O₃ lattice parameters”, Solid State Ionics, 28 (2). 1320-1323. September. 1988.
[8]   | Tsuchida, T. and Sugimoto,K., “Effect of grinding of mixtures of goethite and hydrated alumina on the formation of Fe₂O₃-Al₂O₃ solid solutions”, Thermochim. Acta, 170. 41-50.1990.
[9]   | Pownceby,M.I., Constanti-Carey, K.K. and Fisher-White, M.J., “Subsolidus Phase Relationships in the System Fe2O3-Al2O3-TiO2 between 1000° and 1300°C”, Journal of the American Ceramic Society, 86(6). 975-980. June. 2003.
[10]   | Nedelec, J.M,. Avignant, D. and Mahiou, R., “Soft chemistry routes to YPO4-based phosphors: dependence of textural and optical properties on synthesis pathways”, Chemistry of materials, 14 (2). 651-655. 2002.
[11]   | Li, F.B., Li, X.Z., Liu, C.S. and Liu, T.X., “Effect of alumina on the photocatalytic activity of iron oxides for bisphenolA degradation”, J. Hazard. Mater. 149. 199-207. 2007.