Showing papers on "Nanocomposite published in 1989"
TL;DR: In this paper, the optical absorption spectra of glass-metal nanocomposite films have been measured over the wavelength range 200 to 2000 nm, and effective medium theories of Maxwell-Garnett and Bruggeman, respectively, have been used to calculate theoretically the absorption of these materials.
Abstract: Glass-metal nanocomposites incorporating ultrafine particles of iron, nickel, cobalt and manganese, respectively, in a silica glass matrix have been prepared by heat treatment of a gel derived from a sol containing silicon tetraethoxide and a suitable metal organic compound. Metal particles in all the nanocomposites are isolated and spherical-shaped with diameters ranging from 3 to 10 nm. Films of these nanocomposites with thickness of the order of a few micrometres have been prepared on glass slides by a simple dip-and-pull technique. Optical absorption spectra of the nanocomposite films have been measured over the wavelength range 200 to 2000 nm. Effective medium theories of Maxwell-Garnett and Bruggeman, respectively, have been used to calculate theoretically the optical absorption of these materials. The Maxwell-Garnett theory gives results which are in better agreement with experimental data than those obtained from Bruggeman formalism. The filling factor f as estimated from the least-squares fit of the experimental results with the Maxwell-Garnett theory has a value in the range 1 to 4%.
92 citations
Patent•
26 Oct 1989
TL;DR: In this paper, a triphasic nanocomposite gel is made by mixing two or more sols of ceramic precursor oxides, which is then dried and ground to a fine powder which is pressed into compact bodies.
Abstract: Compositionally triphasic nanocomposite gel is made by mixing two or more sols of ceramic precursor oxides. Such gel is then dried and ground to a fine powder which is pressed into compact bodies. The compact bodies are thereafter fired in a sintering oven at from 1100° C. to 1400° C. and, aided by the heat of reaction of the two or more nono gel powders, the (heterogeneous) mixture of such powders crystallizes into a homogeneous crystalline ceramic of α-cordierite at up to 100% of theoretical density. Thus, novel method of manufacture and novel ceramic end-product are provided.
25 citations
TL;DR: In this paper, the thermal and dielectric properties of polydimethyl siloxane and Cab-O-Sil composites have been studied and it is suggested that the key to model these nanocomposites with ceramic and polymer phases is to understand the interfaces and their chemical bonding.
Abstract: This paper reviews some of the research efforts in microelectronic packaging to develop composites with dimensions of the fillers ranging down to nanometer dimensions. Some initial experiments have been conducted with nanocomposites, where the thermal and dielectric properties of polymer/fumed silica composites have been studied. The bulk samples were prepared in different ratios of polymer to silica using polydimethyl siloxane and Cab-O-Sil. Differential thermal analyses carried out on these samples showed no changes in the samples till 330°C. The dielectric constant of the 70:30 (Cab-O-Sil- Polymer by Wt.%) composite is 3.8, similar to that of the pure silica. For the same composite the value of the thermal expansion coefficient is 350 ppm, closer to the value of pure polymer (439 ppm). It is suggested that the key to model these nanocomposites with ceramic and polymer phases is to understand the interfaces and their chemical bonding.
2 citations
TL;DR: In this article, the optical absorption properties of a glass-metal nanocomposite system involving bismuth metal were analyzed using effective medium theories with a model incorporating single strand chains and fcc clusters of metallic Bismuth particles.
Abstract: Optical absorption characteristics in a glass-metal nanocomposite system involving bismuth metal have been analysed using effective medium theories with a model incorporating single strand chains andfcc clusters of metallic bismuth particles. The computed values show fair agreement with experimental data.
2 citations
01 Jan 1989
TL;DR: In this paper, the preparation and the microtexture of three classes of precursors for the synthesis of ceramic powders or films of the SiMON family (M=Al, Mg, Y) were described.
Abstract: We describe the preparation and the microtexture of three classes of precursors for the synthesis of ceramic powders or films of the SiMON family (M=Al, Mg, Y). (i) simple mechanical mixtures of a non-swelling clay of the kaolinite family with charcoal, in which the two phases are separated at micronic or slightly submicronic level. The interface area, S, is of the order of a few m2/g. (ii) colloidal microcomposites obtained by a sol-gel method from mixed colloidal suspensions of a swelling clay (montmorillonite or hectorite) and graphitic oxide. This method, which permits the casting of films a few microns thick, leads to a material in which the two phases are dispersed as lamellar stacks a few nanometers thick. S is of the order of 100 m2/g. (iii) layered clay-carbon nanocomposites. The method involves the intercalation of acrylonitrile vapor in a swelling clay, followed by polymerisation and carbonisation of the organic molecules in the interlayer space. It leads to a material in which the carbon and silicate phases are organized as alternate layers of subnanometric thickness. S is larger than 800 m2/g.
1 citations
18 Oct 1989
TL;DR: The role of solid state epitaxy in the crystallization of a very much wider range of glass compositions to make glass ceramics was explored in this article. But this work is limited to the case of glass-ceramic.
Abstract: : The first goal of the current research is to explore the role of solid state epitaxy in the crystallization of a very much wider range of glass compositions to make glass ceramics. The nanocomposite xerogel route is being used to attempt to make a universal glass-ceramic with controllable crystallization. Isostructural seeding of cordierite glass led to a lowering in crystallization temperature due to epitaxy just as in the nucleated crystallization of ceramics. Experiments with other systems such as LiAlSiO4 and LiAlSi2O6 are in progress and preliminary results show that solid state epitaxy is lowering the crystallization temperatures. The second area of current research is to extend the validity of solid state epitaxy proven by the growth of alumina films on alpha Al2O3 single crystals is being extended to other oxides, metals and semiconductors. Epitaxial crystallization of silicon (oxy) carbide glasses such as Nicalon compositions is being investigated in addition to the oxide glasses and gels. Solution Sol Gel. (edc)