Synthesis of Alumina Nanofibers and Composites

Abstract

IntroductionAlumina, Al 2 O 3 , is a ceramic metal oxide of great importance as building material, refractory material, electrical and heat insulator, attributed to its high strength, corrosion resistance, chemical stability, low thermal conductivity, and good electrical insulation. One phase of alumina, the -phase is widely used as catalyst, catalyst support and adsorbent because its high porosity and surface area. It is conventionally prepared by heating the hydrated trihydroxides, gibbsite and bayerite, to temperature of > 1000 o C to obtain the -alumina, corundum, a material with great hardness and low surface area. The trihydroxides, gibbsite, bayerite, both are Al(OH) 3. nH 2 O and the monohydroxyl oxide, boehmite, AlO(OH)·αH 2 O, have the monoclinic crystal structure with similar lattice parameters (a=0.866 nm, b=0.506 nm, c=0.983 nm, =94°34′ in boehmite, a=0.868 nm, b=0.507 nm, c=0.972 nm, =94°34′ in gibbsite, and a=0.867 nm, b=0.506 nm, c=0.942 nm, =90°26′ in bayerite [1,2]. In the process of heat treatment, the trihydroxide undergoes a series of transformations. It loses the water of hydration, then dehydroxalate at < 300 o C to form the monohydroxyl oxide boehmite, AlO(OH), which on further heating to increasingly higher temperatures, changes to the transition aluminas, including the -, -, -, and -phases, which then transform finally to the -form. These transition aluminas are crystalline solids with high porosity and surface areas as well as acidic and basic properties, which make them suitable as adsorbents, catalyst, catalyst support and fabricated into filtration membranes as well as used as fillers or components in polymer/ inorganic composite materials with enhanced mechanical properties. The conventional alumina as obtained are usually powder of particulates. These could be fabricated into alumina fibers by various method, through melt growth techniques including the internal crystallization method and extrusion, electrospraying [3] and electrospinning [4][5][6][7][8] have been developed for producing Al 2 O 3 fibers. The high surface areas of transition aluminas are due to the presence of pores. These pores are irregular in sizes and size distributions, and are mainly micropores of diameter less than 2 nm. Since the synthesis of mesoporous materials was first reported in the late 1980s , a number of methods for the synthesis of mesoporous alumina have been reported [8,9]. More recently, interest in nano-materials and nanotechnology has spurred a fury of investigations

Mechanical Properties of Epoxy Nanocomposites Using Alumina as Reinforcement - A Review

“…The synthesis strategy of nanoparticles accommodate precursors from liquid, solid or gas phase and the methods can be divided into three main groups: synthesis of particles from the solution of the corresponding salts by controlled addition of ions, hydrolysis, thermal decomposition, or synthesis in aerosols. Among these methods, several procedures exists to produce nanometric alumina powders, such as sol-gel, chemical precipitation from aqueous solutions of aluminium, coprecipitation, hydrothermal synthesis, thermal spraying, aerosol synthesis method or spray pyrolysis [29,[35][36][37][38][39][40][41]. Al 2 O 3 particles with the targeted morphologies are obtained by controlling synthesis variables, such as reaction time, stirring speed, amount of additives (such as methanol), and solids loading [42].…”

“…Alumina, Al 2 O 3 , is a ceramic metal oxide of great importance as building material, refractory material, electrical and heat insulator, attributed to its high strength, corrosion resistance, chemical stability, low thermal conductivity, and good electrical insulation. These characteristics make this oxide an excellent material for structural, microelectronic and technological applications [29].…”

Synthesis of MAl2O4(M = Mg, Co, Ni, Zn, Ba) Nanopowders by Liquid Impregnation of Nanofibrous Alumina

“…Bulk solid materials with an extended open structure have attracted much interest over the last two decades. 1 Between a large variety of related compounds, alumina aerogels discovered over a century ago 2 and extensively studied afterward 3 occupy a particular place because of their interesting electronic and dielectric properties. As well, the properties of alumina-based nanostructured materials can be tailored, leading to functional nanocomposite materials for different fields of application in the environmental and catalytic process, photonics, etc.…”

“…5 Structural studies of the synthesis of these materials have been reported since the early 2000s. 5−9 The UPA monoliths consist of nanofibrils of aluminum oxyhydroxides (Al 2 O 3 •nH 2 O), wherein the water content decreased with the temperature increasing from 20 to 1700 °C accompanied by a mass density increase from ∼0.02 up to ∼3 g/cm 3 and porosity decrease from 99.3 to 25%; the elementary structural element of the raw UPA is fibril, with an average diameter of ∼5 nm and length ∼150 nm progressively shortened and thickened according to mass density variations due to the interface and bulk mass transport. 10 The UPA materials possess a very large open porosity and free internal volume available for the vapor and/or liquid impregnation of molecules and colloids.…”

A global optimisation study of the low-lying isomers of the alumina octomer (Al2O3)8

“…Owing to their large refractories, high hardness, high stabilities, high insulation capabilities, and optical transparency [12] alumina clusters serve as components for diverse purposes and applications. Over the past few decades, nano-sized alumina fibers have been synthesized by diverse techniques (hydrothermal or solvothermal, sol-gel techniques, electrospinning, extrusion, chemical vapor deposition) [13] and have attracted a lot of attention. The fibers are used in electronics, informatics, and communications [14].…”