Infrared study of the effects of thermal treatment on montmorillonite-benzidine complexes

Transition metal montmorillonites were saturated with benzidine (BEN) and heated gradually to 200°C, in a vacuum cell supported by KBr windows. IR spectra were recorded before and after the thermal treatment and at various temperatures during this treatment. X-ray diffractions were recorded before and after the thermal treatment. Hg clay shows properties similar to those of Mg and Ca clays. In the interlayer BEN is bound to Hg through a water molecule bridge, either by proton accepting (typeA) or by proton donation (typeB). Some BEN is also protonated (typeD). Initially typeA predominates, but after the thermal treatment, when the film is rehydrated, the amounts of typesB andD increase. With Mn-, Co-, Ni-, Zn- and Cd-montmorillonite a direct coordination of the benzidine by the dehydrated metallic cation is obtained (typeC), in addition to small amounts of typesA,B andD. During the thermal treatment water is evolved and associationsA andB are completely transformed toC. At elevated temperatures the following associations were identified in trace amounts, ammonium-amine, BEN bound to non-structured water, hydrophobic adsorbed BEN and BEN bound to the oxygen plane (typesE, F, H andJ, respectively). During the thermal treatment of Co and Cd clays some of the benzidine was oxidized, probably to semiquinone and quinoidal cation.     

Montmorillonite treated with Rhodamine-6G mechanochemically and in aqueous suspensions

The mechanochemical solid-state adsorption of the cationic dye rhodamine-6G (R6G) by montmorillonite was investigated by XRD and simultaneous DTA-TG. Five different mixtures of R6G and montmorillonite were investigated. They contained 10, 20, 35, 50 and 100 mmol R6G per 100 g clay. The solid R6G was ground with the clay for five minutes. Mixtures were ground both in the absence of water (dry grinding) and with the adding of drops of water periodically, (wet grinding). There were no differences between samples obtained by wet or dry grinding. X-ray and DTA data were compared with those of R6G-montmorillonite obtained from aqueous suspensions. The mechanochemical products were different from those obtained from aqueous suspensions. The X-ray and DTA studies suggest that the mechanochemical adsorption of organic cations takes place on the external surfaces of the clay whereas in suspensions the adsorption takes place into the interlayer space. In the latter case the final stages of oxidation occur in temperatures higher than those of the neat dye whereas in the former they occur at lower temperatures. This revised version was published online in July 2006 with corrections to the Cover Date.     

All-fiber zero-insertion-loss add-drop filter for wavelength-division multiplexing

We developed and fabricated an all-fiber add-drop filter by recording a Bragg grating in the waist of an asymmetric mode converter-coupler formed by adiabatic tapering and fusing of two locally dissimilar, single-mode optical fibers. The insertion loss of the device was ~0.1 dB .A narrow spectral bandwidth (<1 nm) and a large add-drop efficiency (>90%) were also demonstrated. In addition, the filter was polarization independent.     

Formation of carnallite type double salts by grinding mixtures of magnesium and alkali halides with the same anions

The formation of carnallite type double salts by grinding mixtures of hydrated magnesium halide and alkali halides with the same anions was investigated by X-ray diffraction, infrared spectroscopy and thermal analysis. Carnallite (KMgCl₃·6H₂O), cesium-carnallite (CsMgCl₃·6H₂O), bromo-carnallite (KMgBr₃·6H₂O) and cesium-bromo-carnallite (CsMgBr₃·6H₂O) were formed by grinding mixtures of MgCl₂·6H₂O with KCl or CsCl and MgBr₂·6H₂O with KBr or CsBr, respectively. Hydrated solid solutions of magnesium in potassium or cesium halides were obtained from that portion of potassium and cesium halides which did not take part in the formation of the double salt.     

The study of the dehydration and dehydroxylation of smectites by emanation thermal analysis

The dehydration and dehydroxylation of the smectites, beidellite and montmorillonite (dioctahedral) and saponite and laponite (trioctahedral), were investigated by ETA, DTA, TG and X-ray diffractions. There are differences between the behaviors of di- and trioctahedral clays which are due to the differences in the ability of the exchangeable cations to migrate into hexagonal holes of the SiO₄ network and due to the fact that the dehydroxylation and recrystallization of dehydroxylated trioctahedral smectites occur simultaneously, whereas there is a temperature gap of about 300°C between the dehydroxylation and the recrystallization of dioctahedral smectites.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthdayThe authors wish to thank Laporte Industries, Inc. UK for the laponite sample.This research was supported under Project No. C12-219, Grant No. HRN5544 G002069, U.S.-IsraelCooperative Development Research Program, Office of the Science Advisor, U.S. Agency for International Development.     

Thermo-XRD-analysis and peptization study of the adsorption of alizarinate by Co-, Ni-, and Cu-montmorillonite

The adsorption of the monovalent anionic dye alizarinate onto Co-, Ni- and Cu-montmorillonite was carried out by adding the dye into aqueous clay suspensions. During the loading of the clay suspension by alizarinate, only some of the added organic anion is adsorbed by the clay forming d-coordination chelate complexes on the clay surface. Maximum adsorption of Co-, Ni- and Cu-clay were 13, 13 and 25 mmol dye per 100 g clay. Since the capacity of the clay for these transition metal cations is 38 mmol per 100 g clay, these saturations indicate that only part of the transition metal cations form positively charged d-coordination chelate complexes with metal:ligand ratio of 1. The complex cations can be located inside the interlayer spaces or on the broken bonds surfaces. Thermo-XRD-analysis and peptization studies of the solids and the clay water systems respectively were used here to identify the sorption sites. The Co and Ni complexes were obtained on the broken bonds surfaces whereas the Cu complexes were obtained in the interlayer space. Co²⁺, Ni²⁺ and Cu²⁺ were extracted from the clay into suspensions containing excess alizarinate.     

Solid‐state lasers based on inorganic–organic hybrid materials obtained by combined sol–gel polymer technology

Sol–gel glass matrices in which organic laser dyes are embedded can be used as the gain medium in solid‐state, continuously tunable lasers. Such lasers are very simple to construct, and potentially very compact and efficient. Unlike the commonly used liquid dye laser systems, solid‐state dye lasers can be made mechanically robust and portable. In this article, the development of sol–gel/dye lasers, including the sol–gel technology, dye properties, and laser operation, is reviewed. In addition, new solid‐state hosts (such as polyurethane/silica ORMOSILs), additional organic dyes (cyanines), and new studies on the stability of the dyes are presented. Copyright © 2004 John Wiley & Sons, Ltd.     

Modal analysis of Bragg onion resonators

From analysis of the high Q modes in a Bragg onion resonator with an omnidirectional reflector cladding, we establish a close analogy between such a resonator and a spherical hollow cavity in perfect metal. We demonstrate that onion resonators are ideal for applications that require a large spontaneous-emission factor beta, such as thresholdless lasers and single-photon devices.     

Dynamic analysis of the semiconductor laser as a current-controlled oscillator in the optical phased-lock loop: applications

A methodology for treating the semiconductor laser as a current-controlled oscillator in an optical phase-lock loop is presented. The formalism is applied to phase demodulation of optical beams, reduction of phase noise by self-homodyning, and phase locking of a semiconductor laser array.     

Asymptotic analysis of Bragg fibers

Using an asymptotic analysis, we obtain an eigenvalue equation for the general mode dispersion in Bragg fibers. The asymptotic analysis is applied to calculate the dispersion relation and the field distribution of TE modes in a Bragg fiber. We compare the asymptotic results with exact solutions and find excellent agreement between them. This asymptotic approach greatly simplifies the analysis and design of Bragg fibers.