- Nano Review
- Open Access
The Effect of Novel Synthetic Methods and Parameters Control on Morphology of Nano-alumina Particles
© Xie et al. 2016
- Received: 3 February 2016
- Accepted: 9 May 2016
- Published: 21 May 2016
Alumina is an inorganic material, which is widely used in ceramics, catalysts, catalyst supports, ion exchange and other fields. The micromorphology of alumina determines its application in high tech and value-added industry and its development prospects. This paper gives an overview of the liquid phase synthetic method of alumina preparation, combined with the mechanism of its action. The present work focuses on the effects of various factors such as concentration, temperature, pH, additives, reaction system and methods of calcination on the morphology of alumina during its preparation.
- Particle morphology
- Reaction mechanism
- Calcination method
Among the numerous crystal forms of alumina, α-Al2O3 and γ-Al2O3 are the two most common kinds. α-Al2O3 has some excellent physical and chemical properties such as good acid, alkali and heat resistances and high hardness and strength. It is widely used in different fields such as ceramics, surface protective layer materials, refractory materials, catalysts and catalyst supports and optical materials [2–5]. γ-Al2O3, which is also called activated alumina, has a large surface area, strong adsorption capacity, good catalytic activity and wear resistance. It is also widely applied in various fields such as adsorbents , ceramics , catalysts and catalyst supports .
The application performance of alumina depends on not only the size of ultra-fine particles but also the particle shape [9–11]. Alumina has a variety of shapes such as rod , fibrous structure , flake  and sphere . Different shapes of alumina have different physical and chemical properties and applications. For example, the fibrous nano-alumina has a very strong anti-sintering property , which is often used as an additive for epoxy resin to improve its tensile strength and rigidity. The flake-like alumina is generally used as a seed crystal added to ceramics, which significantly enhances the toughness of ceramics .
Alumina is a common catalyst support, whose pore structure is closely related to the activity, selectivity and lifetime of the catalyst. Alumina is divided into different categories such as microporous alumina, mesoporous alumina and macroporous alumina according to its pore size. The pore size of mesoporous alumina is between 2 and 50 nm. It is a rigid porous material with a mutually interconnected or isolated network structure. It has not only the characteristics of a crystalline phase of alumina but also the characteristics of a porous material. Mesoporous alumina is widely used in the catalysis , adsorption  and other fields due to its adjustable pore structure, relatively large internal and external surface area and pore volume.
The morphology, purity, surface acidity and hydrothermal stability, the pore structure and other properties restrict the application of alumina. The research is ongoing on the pore structure, surface acidity and hydrothermal stability . Morphology, as one of the important parameters of particle characterization, has a substantial effect on the properties and applications of the products. The morphology of particles is influenced and controlled by its crystallization habit during the preparation using liquid-phase method [21, 22], which is restricted by the environment and the growth conditions. This article reviews the research carried out on the preparation of alumina starting from the liquid-phase method for its synthesis including its mechanism and discusses the effect of different factors such as reactant concentration, temperature, pH, additives, system environment and calcination methods on the micromorphology of particles.
Liquid-Phase Method for Synthesis of Alumina
There are some common liquid-phase methods for synthesis of alumina, such as sol-gel method, hydrothermal method, template method, precipitation method, emulsion method or microemulsion method and electrolysis method. Alumina with different morphologies can be obtained by using different synthesis methods and optimizing the reaction conditions.
Hydrothermal method is an approach where the mixed solution is poured into a sealed reactor. Utilization of the relatively high temperature in the reactor and the high-pressure growth environment promotes the dissolution and recrystallization of poorly soluble or insoluble material. Hydrothermal methods include hydrothermal synthesis, hydrothermal treatment and hydrothermal reactions. During the hydrothermal process, the crystal grows to its largest possible size under the non-restricted conditions and its characteristics (various shapes, high degree of crystallinity, small size, uniform distribution, lighter particle agglomeration, etc.) form [23, 24]. The development of crystal face and the morphology of the crystal formed by hydrothermal synthesis are closely related to the hydrothermal conditions such as water temperature, pressure and the permittivity and viscosity and diffusion coefficient of the solution. The same type of crystal can be produced with different morphology under different hydrothermal conditions .
The sol-gel method refers to inorganic or organic alkoxide dispersed in solution. Using the transparent sol formed by hydrolysis and condensation of the precursor, a gel with certain structure is formed during the aging process by the aggregation between the gel particles. During the sol-gel process, the microstructure of the material is controlled and cut at the mesoscopic level by means of low-temperature chemical method, which changes the morphology and structure of the particles [35, 36].
Template method is a cutting-edge technology developed in the 1990s. It is widely applied in recent years, and it is an effective synthetic method for controlling the structure, particle size and morphology of materials through a utilization of template. Depending on the differences in template structure, template method can be divided into two groups called hard and soft template methods.
In hard template method, precursor is uniformly dispersed in the pore of the hard template or absorbed onto its surface, thereby converting it into a complex product. Then, by choosing an appropriate method (dissolution, sintering, etching, etc.), the target product can be obtained. The special structure of hard template restricts the crystallization or polymerization of the precursor during the process of synthesis, which leads to formation of a mesoscopic phase with an opposite-phase structure of the template.
The hard template is often used as a microreactor during the synthesis. The type of hard template and the reaction conditions such as concentration of reactants, time of immersion, temperature of immersion and the temperature of heat treatment affect the structure and morphology of the product. Especially, the temperature of heat treatment has a great impact on product. The excessively high temperature causes microscopic particles to gather together which in turn affects the order of the micromorphology and its structure .
Soft Template Method
Soft template utilizes the intermolecular or intramolecular interaction forces, such as hydrogen bonds and bond and static electricity, to form aggregates with certain structural characteristics (liquid crystal, vesicles, micelle, microemulsion, self-assembled film, etc.) during the reaction. The reactants use these aggregates as template to generate a particle with certain morphology and structural features.
In the synthesis by soft template method, it is usually thought that the interaction between liquid crystalline phase and organic/inorganic interface plays a decisive role in the morphology of mesoporous materials [42, 43]. The liquid crystalline phase formed by the surfactant in solution has a rich structure such as lamellar phase, cubic phase and hexagonal phase and is easy to construct and adjust . The interaction of the organic/inorganic interface is a weak hydrogen bond force in the strong acid environment while it is a strong electrostatic attraction force in the strong alkaline environment .
Groenewolt et al.  synthesized the ordered mesoporous γ-Al2O3 by using the soft template method. They have systematically studied the effects of various factors such as the type of aluminum source, the type of surfactant, the type of the acidity regulator and the reaction temperature on the structure and morphology of the products.
Precipitation method produces the target products by adding the precipitant agent to the metal solution and heat treating the precipitate. The particles with different morphology can be obtained by adjusting the reaction temperature, the concentration of the reaction, pH, etc.
The Effect of Calcination System on the Morphology of Alumina
The alumina calcination system is very important for obtaining nanoparticle powder with monodispersity and uniform morphology. Nano-Al2O3 powder, which is composed of widely used α-Al2O3, γ-Al2O3 and amorphous Al2O3, is generally obtained by alumina precursor calcined at different temperatures. Therefore, the compaction among alumina particles of high activity is inevitable at high temperature, which results in severe particle agglomeration and resintering of individual particles with surrounding ones after melting with a formation of dendritic structure called “neckformation” of particle . The result of the experiments showed that the calcination temperature, holding time and heating rate have a significant effect on the morphology of alumina. While the temperature is less than 800 °C, alumina particles can continue to maintain their original morphology. If the temperature becomes higher than 800 °C, the activity of alumina particles is enhanced, and agglomeration begins to occur . Ceresa et al.  first presented the relationship between temperature and phase transformation of alumina during the calcination process.
A significant amount of research is carried out in this area, and effective methods are proposed to control the morphology of alumina particles such as using DI water, alcohol and organic solvent mixtures to wash precursor before calcination in order to prevent agglomeration, enhance the dispersion, and increase the specific surface area of alumina . In addition, the sintering properties of the powder can be improved with ultrasonic pretreatment, so that the neckformation created by agglomeration of the particles will not occur until 1400 °C . The phase transformation temperature of γ-Al2O3 to α-Al2O3 can be decreased if sintering is carried out under the CO2 or ethanol atmosphere; consequently, the well-crystalline spherical α-Al2O3 is eventually obtained .
Dispersants and surfactants also play an effective role in dispersion of particles and control of agglomeration. For example, using poly(methacrylic acid), organic acid, glucose, sucrose, inorganic salts, trimethylsilane and other additives , which results in a strong electrostatic repulsion among particles, eventually change the polarity of the particle surface from hydrophilic to hydrophobic (water-repellent). Polyacrylamide, silica gel and lignin and other polymer dispersants can form a protective layer with certain strength and thickness on the particle surface and prevents the agglomeration of the particles . Surfactants can form a coating layer of several nanometers on the surface of the particles, which can reduce the surface energy and effectively hinder the interactions among the particles .
Effect of calcination temperature on the size of alumina in the presence of additives
Calcination temperature (°C)
Al2O3 crystal type
Grain size (nm)
Color of Al2O3
As shown in Table 1, the amorphous Al2O3 particles obtained at 600 °C are light yellow while the additive is still present on the surface of the particles. This coating gradually disappears while 800 °C is reached. In addition, some additives can decrease the phase transition temperature of α-Al2O3 to 1000 °C. As the temperature increases, the grain size of Al2O3 will inevitably increase, meanwhile the agglomeration will start to occur. This is due to the fact that when Al2O3 completely transformed to α phase, the spatial arrangement of the O2 in α-Al2O3 occurs, which is the reconstruction of phase transition from face-centered cubic to hexagonal close-packed lattice .
The morphology of Al2O3 can be influenced by various factors such as raw materials, concentrations, different synthesis methods, additives and heat treatment system. During the preparation of Al2O3, the morphology of the precursors and the protection of the particles during heat treatment play a decisive role in the final morphology of alumina. The morphology will not change during the low-temperature heat treatment. However, when high temperature is reached, the diffusion of the powder particles accelerates. Thus, the particles diffuse from the inside to the surface of the crystal lattice and spread to the surrounding resulting in the neckformation as well as the agglomeration of surrounded particles. Accordingly, the morphology of the particles changes. The use of various additives effectively reduces the calcination temperature; consequently, the problem of particle agglomeration can be solved. The utilization of template is a new research hotspot with the objective of improving the dispersibility of Al2O3 powder and controlling the shape of the sample particles.
In the research field of the morphology of Al2O3 and its application performance, more work is needed to obtain nano-Al2O3 powder with different shapes, single morphology and good dispersion. There is also a need to expand the application range of this type of nano-Al2O3 powder and improve its application prospect in high tech and value-added product development fields.
This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC). Technical support of the University Research Centre on Aluminum (CURAL) of the University of Quebec at Chicoutimi, Canada, and Civil, Architectural & Environmental Engineering (CAEE) of Drexel University, Philadelphia, PA, the United States of America.
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- Digne M, Sautet P, Raybaud P, Toulhoat H, Artacho E (2002) Structure and stability of aluminum hydroxides: a theoretical study. J Phys Chem B 106(20):5155–5162View ArticleGoogle Scholar
- Xu PK, Dong YB (1999) Corundum refractories. Metallurgical Industry Press, Beijing, pp 56–61Google Scholar
- Wang LS (1994) Special ceramics. Central South University Press, Changsha, pp 133–138Google Scholar
- Lu XJ, Cui XQ, Song MN (2003) Study on the alteration of chemical composition and structure parameters of modified montmorillonite. Miner Eng 16:1303–1306View ArticleGoogle Scholar
- Khatib K, Pons CH, Bottero JY, François M, Baudin I (1995) Study of the structure of dimet hyldioctadecylammonium-montmorillonite by small angle X-ray scattering. J Colloid Interface Sci 172(2):317–323View ArticleGoogle Scholar
- Zhang HY, Shan GB, Xing JM, Zhang HY (2007) Preparation of (Ni/W)-γ-A12O3 microspheres and their application in adsorption desulfurization for model gasoline. Chem Eng Commun 194(7):938–945View ArticleGoogle Scholar
- Bartsch M, Saruhan B, Schmuecker M, Schneider H (2004) Novel low-temperature processing route of dense mullite ceramics by reaction sintering of amorphous SiO2-coated γ-Al2O3 particle nanocomposites. J Am Ceram Soc 82(6):1388–1392View ArticleGoogle Scholar
- Lietti L, Forzatti P, Nova I, Tronconi E (2001) NOx storage reduction over Pt-Ba/γ-Al2O3 catalyst. J Catal 204:175–191View ArticleGoogle Scholar
- Meijere AD, Meyer LU (2000) Shape control of CdSe nanocrystals. Nature 404(6773):59–61View ArticleGoogle Scholar
- Kolosnjaj J, Szwarc H, Moussa F (2007) Toxicity studies of fullerenes and derivatives. Bio-applications of nanoparticles. Springer, New York, pp 168–180View ArticleGoogle Scholar
- Ahmadi TS, Wang ZL, Green TC, Henglein A, El-Sayed MA (1996) Shape-controlled synthesis of colloidal platinum nanoparticles. Science 272(5270):1924–1925View ArticleGoogle Scholar
- Kim SM, Lee YJ, Bae JW, Potdar HS, Jun KW (2008) Synthesis and characterization of a highly active alumina catalyst for methanol dehydration to dimethyl ether. Appl Catal A Gen 348(1):113–120View ArticleGoogle Scholar
- Glemza R. High pore volume and pore diameter aluminum phosphate: US, US RE34911 E[P]. 1995.Google Scholar
- Seri O, Kamazawa R (2012) Preparation of flake alumina by corrosion of aluminum in methanol. J Jpn Soc Matellurgy 59(6):307–310Google Scholar
- Kim KT, Dao TD, Han MJ, Anjanapura RV, Aminabhavi TM (2015) Graphene coated with alumina and its utilization as a thermal conductivity enhancer for alumina sphere/thermoplastic polyurethane composite. Mater Chem Phys 153:291–300View ArticleGoogle Scholar
- Zhu HY, Riches JD, Barry JC (2002) γ-alumina nanofibers prepared from aluminum hydrate with poly(ethylene oxide) surfactant. Chem Mater 14(5):2086–2093View ArticleGoogle Scholar
- Yu JW, Liao QL (2011) Effect of plate-like alumina seed on the fracture toughness of alumina ceramics. J Funct Mater 42(10):1833–1835Google Scholar
- Kim P, Kim Y, Kim H, Song IK, Yi JH (2004) Synthesis and characterization of mesoporous alumina for use as a catalyst support in the hydrodechlorination of 1,2-dichloropropane: effect of preparation condition of mesoporous alumina. J Mol Catal A Chem 219(1):87–95View ArticleGoogle Scholar
- Thomas F, Schouller E, Bottero JY (1995) Adsorption of salicylate and polyacrylate on mesoporous aluminas. Colloids Surf A Physicochem Eng Asp 95(2):271–279View ArticleGoogle Scholar
- Tang GQ, Zhang CF, Sun CS, Yan B, Yang GX, Dai W et al (2011) Research progress of γ-Al2O3 support. Chem Ind Eng Prog 8:1756–1765Google Scholar
- Li WJ, Shi EW, Yin ZW (1999) Growth habit of crystal and the shape of coordination polyhedron. J Synth Cryst 28(4):368–372Google Scholar
- Zheng YQ, Shi EW, Li WJ, Wang BG, Hu XF (1998) Research and development of the theories of crystal growth. J Inorg Mater 14(3):321–332Google Scholar
- Zhang Y, Wang YF, Yan YH (2002) Development and application of hydrothermal method in growing low-dimensional artificial crystal. Bull Chin Ceram Soc 21(3):22–26Google Scholar
- Tian MY, Shi EW, Zhong WZ, Pang WQ, Guo JK (1998) Nano ceramics and nano ceramic powder. J Inorg Mater 2:129–137Google Scholar
- Hu C C, Wu Y T, Chang K H. Low-Temperature Hydrothermal Synthesis of Mn3O4 and MnOOH Single Crystals: Determinant Influence of Oxidants[J]. Chemistry of Materials. 2008; 20(9):2890-894.Google Scholar
- Li YH, Peng C, Zhao W, Bai MM, Rao PG (2014) Morphology evolution in hydrothermal synthesis of mesoporous alumina. J Inorg Mater 29(10):1115–1120View ArticleGoogle Scholar
- Ray JC, You KS, Ahn JW, Ahn WS (2007) Synthesis of mesoporous alumina using anionic, nonionic and cationic surfactants. Stud Surf Sci Catal 165(07):275–278View ArticleGoogle Scholar
- Zhang ZX, Shen ZQ, Ling FX, Xia CH (2013) Impacts of sodium nitrate additive on alumina morphology. Pet Process Petrochem 44(9):47–50Google Scholar
- Pramod KS, Jilavi MH, Burgard D, Nass R (2005) Hydrothermal synthesis of nanosize alpha-al2o3 from seeded aluminum hydroxide. J Am Ceram Soc 81(10):2732–2734View ArticleGoogle Scholar
- Shi EW, Xia CT, Wang BG, Zhong WZ (1996) Application and development of hydrothermal method. J Inorg Mater 2:193–206Google Scholar
- Mikhailov VI, Maslennikova TP, Krivoshapkin PV (2014) Materials based on aluminum and iron oxides obtained by the hydrothermal method. Glass Phys Chem 40(6):650–656View ArticleGoogle Scholar
- Hou HW, Xie Y, Yang Q, Guo QX, Tan CR (2005) Preparation and characterization of γ-AlOOH nanotubes and nanorods. Nanotechnology 16(6):741View ArticleGoogle Scholar
- Buining PA, Pathmamanoharan C, Jansen JBH, Lekkerkerker HNW (1991) Preparation of colloidal boehmite needles by hydrothermal treatment of aluminum alkoxide precursors. J Am Ceram Soc 74(6):1303–1307View ArticleGoogle Scholar
- Wang J, Zhang B, Xu XL (2007) Influence of hydrothermal temperature on structural and microstructural properties of boehmite. Nonferrous Metals Extractive Metallurgy 5:23–26Google Scholar
- Varma HK, Mani TV, Damodaran AD, Warrier KGK, Balachandran U (1994) Sol–spray preparation, particulate characteristics, and sintering of alumina powders. Advanced materials I., pp 11–14Google Scholar
- Li J, Pan YB, Xiang CS, Ge QM, Guo JK (2006) Low temperature synthesis of ultrafine α-Al2O3 powder by a simple aqueous sol–gel process. Ceram Int 32(5):587–591View ArticleGoogle Scholar
- Ning GL, Chang YF (2004) Shape-controlled synthesis of alumina nanoparticles by carboxy-containing organic molecules. Chem Res Chin Univ 23(3):345–348Google Scholar
- Masouleh NSG, Taghizadeh M, Yaripour F (2014) Optimization of effective sol-gel parameters for the synthesis of mesoporous γ-Al2O3, using experimental design. Chem Eng Technol 37(9):1475–1482View ArticleGoogle Scholar
- Ji XW, Tang SK, Gu L, Liu TC, Zhang XW (2015) Synthesis of rod-like mesoporous γ-Al2O3 by an ionic liquid-assisted sol–gel method. Mater Lett 151:20–23View ArticleGoogle Scholar
- Roggenbuck J, Koch G, Tiemann M (2006) Synthesis of mesoporous magnesium oxide by CMK-3 carbon structure replication. Chem Mater 18(17):4151–4156View ArticleGoogle Scholar
- Pang LP, Zhao RH, Guo F, Chen JF, Cui WG (2008) Preparation and characterization of novel alumina hollow spheres. Acta Phys -Chim Sin 24(6):1115–1119Google Scholar
- Zhao DY, Yang PD, Huo QS, Chmelka BF, Stucky GD (1998) Topological construction of mesoporous materials. Curr Opin Solid State Mater Sci 3(1):111–121View ArticleGoogle Scholar
- Brinker CJ, Dunphy DR (2006) Morphological control of surfactant-templated metal oxide films. Curr Opin Colloid Interface Sci 11(2–3):126–132View ArticleGoogle Scholar
- Anderson MT, Martin JE, Odinek JG, Newcomer PP (1998) Surfactant-templated silica mesophases formed in water: cosolvent mixtures. Chem Mater 10(1):311–321View ArticleGoogle Scholar
- Materna KL, Grant SM, Jaroniec M (2012) Poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide)-templated synthesis of mesoporous alumina: effect of triblock copolymer and acid concentration. ACS Appl Mater Interfaces 4(7):3738–3744View ArticleGoogle Scholar
- Gu L, Cui XL, Tang SK, Zhang XW (2015) Morphology-controlled synthesis of mesoporous alumina dependent on triblock copolymer. J Chem Ind Eng 66(9):3782–3787Google Scholar
- Groenewolt M, Brezesinski T, Schlaad H, Antonietti M, Groh P, Iván B (2005) Polyisobutylene-block-poly(ethylene oxide) for robust templating of highly ordered mesoporous materials. Adv Mater 17(17):1158–1162View ArticleGoogle Scholar
- Zhou KG, Li YP, Li JC, He WW, Yang XJ (2009) Preparation of fibrous nano-alumina by direct precipitation. J Hunan Univ 36(8):59–63Google Scholar
- Kao HC, Wei WC (2000) Kinetics and microstructural evolution of heterogeneous transformation of θ-alumina to α-alumina. J Am Ceram Soc 83(2):362–368View ArticleGoogle Scholar
- Sarikaya Y, Sevinç İ, Akinç M (2001) The effect of calcinations temperature on some of the adsorptive properties of fine alumina powders obtained by emulsion evaporation technique. Powder Technol 116(1):109–114View ArticleGoogle Scholar
- Ceresa EM, Gennaro A, Cortesi P (1987) α-alumina in the form of spherical non-aggregation particles having a narrow size distribution and size below 2 μm and process for preparing same. US Pat: 4818515Google Scholar
- Kass MD, Cecala DM (1997) Enhanced sinter ability of alumina particles by pretreating in liquid ammonia. Mater Lett 32(s2-3):55–58View ArticleGoogle Scholar
- Bousquet C, Elissalde C, Aymonier C, Maglione M, Cansell F, Heintz JM (2008) Tuning Al2O3 crystallinity under supercritical fluid conditions: effect on sintering. J Eur Ceram Soc 28(1):223–228View ArticleGoogle Scholar
- Shek CH, Lai JKL, Gu TS, Lin GM (1997) Transformation evolution and infrared absorption spectra of amorphous and crystalline nano-Al2O3 powders. Nanostruct Mater 8(5):605–610View ArticleGoogle Scholar
- Xie ZP, Lu JW, Gao LC, Li WC, Xu LH, Wang XD (2003) Influence of different seeds on transformation of aluminum hydroxides and morphology of alumina grains by hot pressing. Mater Des 24(3):209–214View ArticleGoogle Scholar
- Li JG, Sun X (2000) Synthesis and sintering behavior of a nanocrystalline α-Al2O3 powder. Acta Mater 48:3103–3112View ArticleGoogle Scholar
- Karagedov GR, Lyakhov NZ (1999) Preparation and sintering of nano-sized α-Al2O3 powder. Nanostruct Mater 11(99):559–572View ArticleGoogle Scholar
- Strekopytov S, Exley C (2006) Thermal analyses of aluminum hydroxide and hydroxyaluminosilieates. Polyhedron 25(8):1707–1713View ArticleGoogle Scholar
- Liu HY, Ning GL, Gan ZH, Lin Y (2008) Emulsion-based synthesis of unaggregated, spherical α-alumina. Mater Lett 62(10):1685–1688View ArticleGoogle Scholar
- Bagwell RB, Messing GL, Howell PR (2001) The formation of α-Al2O3 from θ-Al2O3: the relevance of a “critical size” and: diffusional nucleation of “synchro-shear”. J Mater Sci 36(7):1833–1841View ArticleGoogle Scholar