David N. Waters

Structural studies of gel phases—IV. An infrared reflectance and Fourier transform Raman study of silica and silica/titania gel glasses

Abstract Infrared reflectance and Fourier transform Raman spectroscopy have been used to study silica and silica/titania monoliths produced by the sol—gel route which had been subjected to a series of heat treatments. With increasing thermal treatment temperature, the gel—glass matrix is strengthed by bond shortening and a reduction in mean SiOSi bond angle and angular distribution for this feature. Results obtained at a range of temperatures were in good agreement to those obtained for vitreous silica. The incorporation of low levels (3% by weight) of titanium led to more disordered glasses which contain titanium in tetrahedral sites only. Evidence was obtained for the formation of SiOTi bonds, principally during the latter stages of densification at temperatures between 615 and 1000°C.

In situ cure monitoring of epoxy resins using optical fibre sensors

This paper describes a comparative study of in situ cure monitoring by three methods: (i) evanescent wave spectroscopy; (ii) refractive index change; and (iii) near-infrared spectroscopy. The cure characteristics of an epoxy/amine reaction were followed in real-time during the crosslinking reaction via the above-mentioned techniques. The evanescent wave spectroscopy technique was based on monitoring the characteristic infrared absorption bands of the resin system to compute the concentration of the amine hardener as a function of cure time. Good correlation was obtained between the evanescent wave spectroscopy data and a conventional method of studying cure reactions, i.e. infrared spectroscopy. During the cure reaction, the refractive index of the resin system increases as a function of the crosslink density. This increase in the refractive index was monitored using two optical fibre techniques. In the first case, a declad region of the optical fibre was immersed in the resin system and in the second method an optical fibre reflectometer was used to track the changes in the refractive index. Once again, good correlation was obtained between the optical fibre techniques and infrared spectroscopy cure data. The results obtained from the optical fibre sensor experiments were used to model the cure kinetics of the resin system. The cure kinetic models were found to predict the cure reaction up to approximately 60% of the reaction.

In-situ cure monitoring using optical fibre sensors - a comparative study

This paper reports a comparative study undertaken for different types of optical fibre sensor developed to monitor the cure of an epoxy resin system. The optical fibre sensors used to monitor the cure process were based on transmission spectroscopy, evanescent wave spectroscopy and refractive index monitoring. The transmission sensor was prepared by aligning two optical fibres within a specially prepared sleeve with a gap between the optical fibre end faces. During cure, resin from the specimen flowed into the gap between the optical fibres allowing transmission spectra of the resin to be obtained. The evanescent wave sensor was prepared by stripping the cladding from a high refractive index core optical fibre. The prepared sensor was embedded in the sample and attenuated total reflectance spectra recorded from the resin/core boundary. Refractive index monitoring was undertaken using a high refractive index core optical fibre which had a small portion of its cladding removed. The prepared sensor was embedded in the resin specimen and light from a single wavelength source was launched into the fibre. Changes in the guiding characteristics of the sensor due to refractive index changes at the resin/core boundary were used to monitor the progress of the cure reaction. The transmission and evanescent wave spectroscopy sensors were used to follow changes in characteristic near-infrared absorption bands of the resin during the cure reaction over the range 1450-1700 nm for the evanescent sensor and 2100-2250 nm for the transmission sensor. Consequently, these techniques required tuneable wavelength sources covering specific wavelength ranges. However, the refractive index based sensor used a single wavelength source. Therefore the equipment costs for this type of sensor were considerably less. Additionally, the refractive index sensor did not require a single wavelength source at any particular wavelength and could be applied to any spectral region in which the optical fibre would transmit light. The advantages and disadvantages of these three methods are discussed.

Application of solvent extraction to the refining of precious metals IV. Practical and structural aspects of the separation of rhodium, palladium, iridium and platinum with organic sulphoxides

Abstract Distribution isotherms have been determined radiometrically for the extraction of Pd II , Pt IV , Rh III and Ir III,IV from aqueous HCl solutions by organic sulphoxides in 1,1,2-trichloroethane (TCE). Partition measurements were also made using two different dialkyl sulphides in TCE. A practical scheme for the separation of the precious metals involving di- n -heptyl sulphoxide (DHSO) is proposed. The nature of the metal-ion species participating in the extraction systems and the chemical bonding in such species have been investigated using physical, spectroscopic, and theoretical methods.

Raman spectroscopy of powders: Effects of light absorption and scattering

Abstract New expressions are derived from Kubelka—Munk theory to describe the Raman intensities observed by back-scattering from powder samples. The equations relate the Raman intensity to the diffuse reflectance R ∞ of the sample for two cases: (i) for a series of samples having constant values of the scattering coefficient, s , but which vary in their values of the absorption coefficient, k ; and (ii) for a series of samples having constant values of k , but differing in their values of s . The predicted intensity dependences are compared with the results of experiment.

The Friedel–Crafts acetylation of naphthalene in 1,2-dichloroethane solution. Kinetics and mechanism

The Friedel–Crafts acetylation of naphthalene, using acetyl chloride and aluminium chloride in 1,2-dichloroethane solution, has been studied kinetically. The α/β isomer ratio changes as a function of concentration of reactants, and time, e.g. from an initial 4–5 to a final 0.7. The results point to a different dependence for the two positions on the concentration of acylating reagent, AcCl, AlCl3, being second-order in this reagent for the α-reaction and first-order for the β-reaction. The rate of the α-reaction is impeded by the presence of free acetyl chloride, whilst the β-reaction is unaffected. The latter reaction exhibits activation parameters in the expected range, ΔH‡=ca. 48 kJ mol–1 and ΔS‡=ca.–99 J K–1 mol–1, whereas for the α-reaction ΔH‡=ca. 21 kJ mol–1 and ΔS‡=ca.–160 J K–1 mol–1 are both very low. Competitive and non-competitive kinetic hydrogen isotope experiments were carried out using [2H8]naphthalene. The mechanism for β-naphthyl acetylation is believed to involve a two-stage process, the second (loss of proton) being rate-limiting. The α-acetylation is believed to proceed through a σ-complex, from which elimination of HCl to give products is prevented for steric reasons; the reaction instead proceeds through a second σ-complex, decomposition of which is usually at least partly rate-limiting.

Rotational isomerism of O,O′-dialkyl esters of phosphorodithioic acid

Abstract Compounds (RO) 2 P(:S)SH, RPr i , Bu n , and Oct n , exhibit rotational isomerism about PO and PS bonds. Temperature-dependence studies of band intensities indicate values of Δ H for the equilibria between isomers to be 2.5 kJ mol −1 , RPr i ; 3.0 kJ mol −1 , RBu n ; and ∼4.5 kJ mol −1 , ROct n .

Comparative study of optical fiber cure-monitoring methods

This paper reports on a comparative study undertaken for different types of optical fiber sensor developed to monitor the cure of an epoxy resin system. The optical fiber sensors used to monitor the cure process were based on transmission spectroscopy, evanescent wave spectroscopy and refractive index monitoring. The transmission sensor was prepared by aligning two optical fibers within a specially prepared sleeve with a gap between the optical fiber end-faces. During cure, resin from the specimen flowed into the gap between the optical fibers allowing transmission spectra of the resin to be obtained. The evanescent wave sensor was prepared by stripping the cladding from a high refractive index core optical fiber. The prepared sensor was embedded in the sample and attenuated total reflectance spectra recorded from the resin/core boundary. Refractive index monitoring was undertaken using a high refractive index core optical fiber which had a small portion of its cladding removed. The prepared sensor was embedded in the resin specimen and light from a single wavelength source was launched into the fiber. Changes in the guiding characteristics of the sensor due to refractive index changes at the resin/core boundary were used to monitor the progress of the cure reaction. The transmission and evanescent wave spectroscopy sensors were used to follow changes in characteristic near-infrared absorption bands of the resin over the range 1450 - 1700 nm during the cure reaction. Consequently these techniques required tunable wavelength sources covering specific wavelength ranges. However, the refractive index based sensor used a single wavelength source. Therefore the equipment costs for this type of sensor were considerably less. Additionally, the refractive index sensor did not require a single wavelength source at any particular wavelength and could be applied to any spectral region in which the optical fiber would transmit light. The advantages and disadvantages of these three methods are discussed.

Surface-enhanced Raman scattering at a flake silver surface

Abstract Supports coated with a flake silver paint show strong surface-enhanced Raman spectra for many molecules, using excitation at 1064 nm. SERS spectra thus obtained for several pyridine derivatives are illustrated, and are discussed in terms of the Bronsted and Lewis acidic properties of surface sites. The technique offers exceptional simplicity, and shows promise for analytical applications.

Vibrational spectra and structure of cyclopropane-d1 and dicyclopropyl ketone

Abstract Infrared spectra have been obtained for cyclopropane- d 1 , C 3 H 5 D(CP- d 1 ), in the vapor phase and for dicyclopropyl ketone (C 3 H 5 ) 2 CO (DCPK) in the liquid state. Raman spectra of the latter compound in the liquid and solid phases have also been recorded. By comparing the experimental with the theoretical spectra of CP- d 1 it has been possible to assign most of the fundamental frequencies of the molecule. Additionably, empirical spectra—structure correlations from the literature for cyclopropyl derivatives containing the COX moiety (X=halogen) have been used to investigate the conformational preference of DCPK. The experimental results confirm that the molecular configuration with the carbonyl group cis to the planes of the two rings is the predominant species in the liquid state, though evidence for a second conformer, which we tentatively identify as the cis—trans conformer, is presented.