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The need for a safe, reliable and cheap method for hydrogen transportation has prompted an intense effort in the synthesis of novel hydrides. To direct the search for better materials, it is essential to understand the bonding present in these systems. A newly synthesized material is LaMg2PdH7 which is best formulated as {La3+}{Mg2+}2{[PdH4]4−}{H−}3. Thus hydrogen is formally present both as a free hydride ion and also as a covalently bound ligand. The combination of inelastic neutron scattering (INS), infrared and Raman spectroscopies and periodic density functional theory (DFT) has been used to characterise the material. We find that the material is less ionic than Ba2[PdH4], which also contains [PdH4]4−. The charges carried by both the coordinating and free hydrides are similar which hints at a degree of covalency in the interactions between the interstitial hydrides and the lanthanum and magnesium ions.

Non-destructive diagnosis of power transformer condition is an increasingly important area of research. Power transformer coils are typically insulated with Kraft paper and immersed in mineral oil. There is a clear need to be able to estimate the aged condition of the coil insulation non-destructively. A portable fibre-optic spectroscopic probe system has been developed which can achieve this quickly by determining the degree of polymerization (DP), an indicator of degradation, to an accuracy of 30 DP units. The system can also determine water content to an accuracy of 0.1% w/w, and oil content and condition, very rapidly from the same measurements. The system uses a broadband spectroscopic diffuse reflectance probe operating in the visible and near infrared (NIR) range and interfaced to dedicated multivariate analysis software. Following calibration and measurement trials in the laboratory, the instrument has recently been adapted for use in the field, in which DP predictions have been made from in-situ measurements on the exposed windings of de-tanked transformers. These values have been validated when checked against DP measurements of the same paper taken in parallel using conventional viscometric methods. The system is now being further optimized and is being developed for other applications in the power industry and other industrial areas such as the paper industry and the plastics recycling industry. The system is modular and different probe types can be attached allowing the measurement of a wide variety of solid material surfaces and liquid media.

To obtain good dispersion of nanofillers in nanodielectrics, the surface of nanopowders or colloidal particles can be chemically treated to make them more compatible with the matrix. Epoxy nanocomposites that contain surface functionalized nanosilica, either colloidal or powdered, show higher breakdown strengths than the reference epoxy material. For nanodielectric composites containing 2 wt % of nanosilica, a breakdown strength some 25% higher than that of the unfilled epoxy was obtained. Spectroscopic measurements were obtained from all samples and multi variate statistical analysis was applied to enable selected material properties to be regressed allowing molecular associations of these properties to be identified. Electrical breakdown strength was found to be related to the presence of silica and the degree of curing whereas space charge accumulation was found to be related to a reduction in polar ester formation. In contrast we find clear evidence of space charge accumulation being related to more shallow charge trapping centers.

A portable fiber-optic spectroscopic system (TRANSPEC) has been developed for nondestructive measurement of aged transformer insulating paper. Following successful measurement of degree of polymerization (DP) of a range of transformer-aged paper samples, the system has now been shown to separate the oil and paper information for measurement of DP in oil-wetted paper samples. In addition, the system has been shown to be capable of the prediction of both oil and water content of paper to a high accuracy, and is also capable of identifying and quantifying different water species. Spectroscopic measurements have been used together with gravimetric water adsorption measurements to investigate the kinetics of uptake of water vapour into paper from air in the case of nominally dry and oil-impregnated samples. Relationships between water adsorption parameters and properties of the paper insulation have also been investigated using measurements under controlled conditions.

Knowledge of the condition of power transformer winding insulation paper is fundamental to making optimum asset replacement decisions in the power industry. The ability to assess the aged condition of Kraft paper quickly and non-destructively using portable instrumentation would significantly increase the opportunities for gaining this knowledge. Insulation paper degrades over time in-service and its degree of polymerization (DP) reduces, eventually affecting its mechanical strength. At low DP levels the insulation may start to disintegrate and the risk of electrical breakdown increases. Currently-used methods of estimating DP are either approximate or destructive. The use of spectroscopy together with multivariate statistical analysis (MVSA) provides a powerful non-destructive evaluation of the condition of paper. From initial feasibility studies, we have developed a simple, portable system (TRANSPEC) using fiber-optics and broad-band spectroscopy that can measure the degree of polymerization of various aged transformer papers to a precision of approximately 30 DP units with a spatial resolution of 14 mm. The system can also measure the chemical composition and condition of the insulating mineral oil. MVSA regression models were constructed from library spectral data, and these models are used to predict the DP of other papers with parameters that fall within the range spanned by the set of calibration samples. Separating oil and moisture information from wetted paper is possible and will be reported in a separate publication. With a single TRANSPEC system, non-destructive in-situ analysis of the DP of insulating paper is possible, providing a rapid cost-effective method for transformer insulation condition assessment and monitoring, which correlates well with current destructive methods.

A detailed study is presented of the high-temperature cure of the difunctional monomer N-(2-biphenylenyl)-4-[2′-phenylethynyl]phthalimide (BPP) and the thermal properties of the resulting homopolymer. Although the phenylethynyl groups are consumed within 1 h at 370 °C, other reactions continue well after this, leading to a cured polymer whose glass transition temperature (Tg) is highly dependent on cure time and temperature. A Tg of 450 °C is achieved after a 16 h cure at 400 °C. Use of chemometrics to analyse the infrared spectra of curing BPP provides evidence for changes in the aromatic moieties during cure, perhaps indicative of co-reaction between the biphenylene and phenylethynyl groups; however, other processes also contribute to the overall complex cure mechanism. Despite the high Tg values, BPP homopolymer exhibits unacceptably poor thermo-oxidative stability at 370 °C, showing a weight loss of about 50 % after 100 h ageing. This is perhaps a result of formation of degradatively unstable crosslink structures during elevated-temperature cure. Copyright © 2004 Society of Chemical Industry

The vibrational spectra of norbornene (bicyclo[2,2,1]hept-2-ene) and nadic anhydride (cis-endo-5-norbornene-2,3-dicarboxylic anhydride) have been investigated by infrared, Raman and inelastic neutron scattering spectroscopies and density functional theory (DFT). For norbornene, the five missing fundamentals have been located. In the C–H stretch region, the infrared and Raman spectra synthesised from the DFT calculations are shown to be in poor agreement with the experimental spectra. Visualisation of the C–H stretch modes shows that assignments made on the basis of group frequency correlations are incorrect. Nadic anhydride has not been previously investigated by vibrational spectroscopy. This paper demonstrates that with state-of-the-art inelastic neutron scattering spectra it is possible to successfully analyse complex systems that have not been studied before.

A multivariate approach to the analysis of cured resin blends comprising cyanate ester and bismaleimides is reported. An analysis of samples subjected to accelerated ageing tests by immersion in water at temperatures up to 70 °C shows that simple near infrared spectroscopic measurements on virgin materials can predict dynamic mechanical thermal analysis results, and provide correlations with thermogravimetric analysis. This suggests a rapid screening method for a range of materials, perhaps in conjunction with a combinatorial approach to advanced composites manufacture.

A series of complexes incorporating diamine (o-phenylene diamine and 2-aminobenzylamine) ligands and containing the acetato and chloro salts of Ni(II) and Cu(II) was incorporated into two commercial epoxy resins recognized as industry standards (MY721 and MY750). The cure properties of the complexes are assessed alongside commercial curative systems. Thermal analysis (principally differential scanning calorimetry) shows that the nature of the cure mechanism can be dramatically affected by the nature of the transition metal and counterion (and the level of curing agent incorporation). For example, by using a nickel(II) acetato complex rather than its chloro analog, the onset of the cure reaction of MY721 may be reduced by 40 K. Thermogravimetric analysis, and visible, infrared, and electron spin resonance spectroscopy are employed to determine the point at which the complexes undergo dissociation. The data show that Cu(2-ABA)2(ac)2 appear to dissociate at temperatures between 70 and 80°C in octan-1-ol. A multivariate approach is applied to the analysis of infrared data obtained for solvated complex samples subjected to a heating program and the results are consistent with the dissociation temperature obtained from the other spectral data. The data suggest that the aromatic amino function in the complex undergoes dissociation from the metal at a lower temperature than the aliphatic amine. The 2-ABA-based complexes containing chloride counterions undergo gelation at higher temperatures than their acetato analogs (for both commercial epoxy systems). The newly prepared complexes generally display ηmin values comparable with the commercial curative systems [the exceptions being Cu(2-ABA)2Cl2 and Ni(OPD)3Cl2, which produce markedly higher values of 14 and 10 P, respectively], but it is believed that this is due to agglomeration and settling of the complex as the resin viscosity decreases during the heating cycle. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2411–2424, 2002

The analysis of cured resin blends comprising a commercial dicyanate, bismaleimide and a range of novel alkenyl-substituted cyanates, to determine the chemical effects of long-term exposure to water, is reported. The cured resin blends underwent accelerated water uptake by immersion at temperatures of 50 °C and 70 °C, for a period of 14–17 months. The presence of about 10–15% (by weight) of alkenyl-substituted cyanate in the blend leads to a marked reduction in moisture absorption in comparison with the unmodified bismaleimide/cyanate blend containing a comparable amount of bismaleimide. All samples display non-Fickian diffusion behaviour at both immersion temperatures, although this is most marked at the higher temperature. Thermogravimetric analysis was performed on alkenyl-modified neat resin samples before and after the immersion period. The modified samples display thermal stabilities that are indistinguishable from cured resins that have not undergone immersion. Spectroscopy (near infrared Raman and mid-infrared attenuated total reflectance) was performed on cured resin plaques to determine the sample composition as a function of modifier content. The elemental composition of the samples was also determined before and after the immersion period, and no significant variation in elemental composition was recorded for the modified samples. © British Crown Copyright 2001/DERA. Reproduced with the permission of Her Majesty's Stationery Office. Published for the SCI by John Wiley & Sons, Ltd.

The use of inelastic neutron scattering (INS) spectroscopy has allowed the determination of the infrared and Raman inactive out-of-plane bending mode ν 5 in the [PdCl 4 ] 2− ion at 136 cm −1 . To our knowledge, this is the first time this mode has been observed in any homoleptic square planar complex. An initial highly anomalous INS spectrum was shown by the use of Raman microscopy to be due to an impurity phase that is most probably a hydrate.

The inelastic neutron scattering and high-resolution FT-Raman spectra of methyltrioxorhenium are reported. Literature assignments of the modes below 1600 cm −1 are largely confirmed with the exceptions of the methyl torsion and the ReO 3 bending modes. The methyl torsion is observed for the first time at 200 cm −1 , while the band at 230 cm −1 assigned previously to the torsion is shown to be a component of the factor group splitting of the solid. In the FT-Raman spectrum, the bands that derive from the E modes in the isolated molecule are split by the C s site symmetry of the crystal. This allows an unambiguous assignment of these modes to be made. On this basis, the assignment of the ReO 3 bending modes is reversed with the asymmetric mode at 325 cm −1 and the symmetric mode at 276 cm −1 .

The ability to determine the molar mass of a polymer is of fundamental importance to describe polymer molecular characteristics. Conventional methods for measuring molar mass include viscometry, osmometry, light scattering and analytical gel permeation chromatography (GPC). Although high quality data can be obtained by these methods, the results can be significantly affected by sample preparation, and they are often time consuming and unsuitable for real-time on-line processing. In this paper, we demonstrate the potential of determining polymer molar mass using optical spectroscopy combined with chemometric analysis. This is technically attractive because optical spectroscopy is routinely used to collect process data on-line and some refineries routinely monitor and control blending using near-infrared (NIR) spectroscopy. A comparable development to monitor polymer molar masses on-line from systems already being used to measure density and melt index, would be of potential value to many sectors of the polymer production and processing industry. Chemometrics is a multivariate methodology that allows the information from entire spectra to be used; it can be considered as a maximal compression technique. Extracted 'factors' can then be regressed against property data by using a well-characterized set of 'training' samples to produce predictive regression models. We will show that simple spectroscopic methods, such as the Raman technique discussed in this paper, when coupled with chemometrics, are capable of providing molar mass and distribution information. We will illustrate this with reference to poly(dimethylsiloxane)s (PDMSs) in the liquid phase.

We have studied the Raman spectrum of β-carotene using excitation wavelengths from visible (514.5 nm) to near-infrared (1064 nm). Qualitatively, the spectrum appears independent of the choice of excitation wavelength, although this is not true in detail; in particular, the ratio of the intensities of the νC-C and νC=C fundamentals to their overtones and combinations varies with the excitation wavelength. The inelastic neutron scattering spectrum shows no evidence for unusual dynamics in this system, and the UV/vis/NIR spectrum shows that there are no allowed electronic transitions from the ground state beyond ∼700 nm. These observations provide strong evidence for the existence of a different mechanism for the enhancement of the bands. Indirect evidence suggests that, with these longer excitation wavelengths, the intensities of the νC-C and νC=C peaks are at least two orders of magnitude smaller than those from resonance enhancement with the use of excitation into the visible absorption bands. The implications for the characterization of polyenes in polymers are discussed.

High resolution, high signal-to-noise ratio Fourier transform Raman (1 cm−1) and infrared spectra of perdeutero-polyethylene have been measured Observation of the residual isolated CH stretch modes has been used to derive a CH bond distance in reasonable agreement with experimental data. Some combination and overtone modes are observed and assigned for the first time. The high resolution has allowed upper limits for the correlation splitting of the Raman bands to be set. Curve resolution of the broadest band, 1251 cm−1 has allowed observation of the correlation split components and a third band that is assigned to the amorphous region of the polymer.

The residual lifetime of primary and secondary insulation materials is a critical parameter for many electrical machines, especially when in service. The analysis of epoxy impregnated materials with conventional techniques is a particularly difficult one, as this often requires removal and repair of at least part of the insulation. We have investigated methods based on reflectance spectroscopy that demonstrate the ability to predict the temperature to which carefully air-aged epoxy-impregnated glass mats have been subjected. The resulting calibrations also provide excellent predictions of the exposure time at a known temperature. Using a time-temperature superposition function based on first-order kinetics to rationalize the widely different temperatures and exposure times examined in our samples, we found that the correlation of this combined function with the reflectance spectra was much better than with temperature or exposure time on their own. The calibrations are constructed using multivariate statistical methods, and one of the outputs is a spectral regression coefficient that shows which chemical components are correlated with the cumulative ageing metrics, and so give insight into the strengths and weaknesses of the resin composition under conditions of use. As the analysis methods can be in-situ and non-destructive, this provides a means to determine the degree of thermally accumulated damage in the insulator.

Condition assessment is an imperative for effective power system asset management and there is a pressing need to rapidly acquire data on the operational performance of high voltage solid and liquid electrical insulation systems, both during the manufacturing process as well as in the field. These systems are governed by a number of manufacturing, operational and environmental variables which affect the time to failure in complex ways. Although forensic examination of solid insulation failures are commonly conducted and there are many electrical tests to assess the condition of the insulation system, there has been limited effort to relate remote, non-destructive analysis methods to rapidly assess chemical characteristics and physical properties, and to directly correlate these to factors that can affect failure. We demonstrate that an extension of engineers' visual inspection methods can provide correlations to conventional test methods - the results then not only provide a predictive capability for insulation condition assessment which can support improved approaches to manufacturing, insulation life prediction and asset management but also show insights into the chemical and physical parameters that effect the desired properties. In addition, we suggest that these approaches can be “wired into” the components through embedded fiber optics and sensors, providing a continuous diagnostic check on the insulation systems.

We have investigated the cure kinetics of the popularly used electrical insulating epoxy system for high voltage rotating machines, consisting of diglycidyl ether of bisphenol A (DGEBA) and methyl hexahydro-phthalic anhydride (MHHPA), when used with a zinc naphthenate (ZnN) accelerator. By using a range of analytical tools, especially the complimentarity afforded by combining thermal and spectroscopic methods, we have obtained the major kinetic parameters of the cure that encompass the behavior from an uncured to an almost fully-cured state. All our experiments show that ZnN accelerated systems do not go to full cure, and the exotherm is considerably lower than that seen with tertiary ethyl ammonium bromide (TEAB). This suggests that the cured state must have fewer cross-links, and hence be somewhat more flexible than in the TEAB case.

We have applied infrared, Raman and UV-VIS spectroscopy to measure spatially resolved chemical composition and structure of cross-linked polyethylene insulated cables used in the EC-funded Artemis project, both before and after electrical and thermal stressing. The work shows that diffusion of the primary products of chemical crosslinking changes the quasi-parabolic concentration radial profile present in new cables to an almost flat distribution in stressed cables. There is also evidence for loss of these products and some level of incorporation with the polymer due to thermal conditioning. The UV data suggest that these compounds are attached to the polyethylene, providing quite large chromophores consisting of aromatic rings, carbonyl groups and unsaturation that can act as trapping centers.

A one-dimensional coupled diffusion and chemical reaction steady-state problem in spherical geometry has been considered. This type of problem is often encountered in atmospheric chemistry when dealing with uptaking of gaseous pollutants in cloud or fog drops. A closed form fundamental solution of the governing equation has been obtained. Making use of this solution and following the standard BEM approach, the boundary value problem under consideration has been transformed into a nonlinear integral equation. The discretization of this equation resulted in a set of nonlinear algebraic equations solved by the Newton-Raphson solver. For specific, linear cases the results obtained have been compared with analytical solutions available in the literature. Good accuracy has been observed. Numerical examples dealing with two coupled nonlinear equations describing diffusion with chemical reaction of two species have been included.

The need for a safe, reliable and cheap method for hydrogen transportation has prompted an intense effort in the synthesis of novel hydrides. To direct the search for better materials, it is essential to understand the bonding present in these systems. A newly synthesized material is LaMg2PdH7 which is best formulated as {La3+}{Mg2+}2{[PdH4]4−}{H−}3. Thus hydrogen is formally present both as a free hydride ion and also as a covalently bound ligand. The combination of inelastic neutron scattering (INS), infrared and Raman spectroscopies and periodic density functional theory (DFT) has been used to characterise the material. We find that the material is less ionic than Ba2[PdH4], which also contains [PdH4]4−. The charges carried by both the coordinating and free hydrides are similar which hints at a degree of covalency in the interactions between the interstitial hydrides and the lanthanum and magnesium ions.

Electrical insulating polymers usually incorporate inorganic fillers to achieve specific electrical, mechanical, thermal properties and reduce cost. In this exploratory work, we have studied the thermal properties, at 40degC, of epoxy resin composites with different filler such as: boron nitride, alumina, diamond, silicon carbide, and silicon nitride, with particle size ranges from micro to nano. The results show that BN is the best material in enhancing the thermal conductivity of the epoxy composites despite the various fillers having comparable or higher thermal conductivities than BN. Our current model shows that large disparities in mechanical modulus - a metric for interfacial compatibility - can cause thermal contact resistance due to increased phonon scattering resulting from the large mismatch between filler particle and resin matrix.

The condition of high voltage electrical insulation systems used in power cables, power transformers and generators is influenced by a number of manufacturing and operating variables which affect performance and failure. Although forensic examinations of solid insulation failures are commonly conducted and there are many electrical tests to assess the condition of insulation systems, there has been only a limited effort to investigate and spatially map the condition of solid insulating materials in regard to their chemical characteristics, physical properties and structure, all of which can affect failure. Non-destructive and portable methods of condition assessment based upon various spectroscopies are now being developed. This includes infrared and Raman based approaches, including so-called wide wavelength methods, and microprobe methods, all of which are capable of rapidly measuring spatially resolved chemical composition and structure of polymeric insulated power cables, power transformer winding insulation and generator stator insulation. By combining multivariate statistical analysis (MVSA) and spectroscopic methods, we have been able to explore and extract relationships between chemical change in the material and "intrinsic variables" such as stressing time, temperature and voltage as well as explore the relationships with physical properties and performance such as electrical breakdown strength, mechanical strength and charge mobility. Recent work illustrates the power of such methods in exploring key property and performance relationships and the ability to map these spatially with new remote and rapid spectroscopic optical probe methods. We conclude that well-populated MVSA models can relate chemical and physical change in solid insulation systems to electrical measurements, to potential indicators of insulation ageing and provide a predictive capability for insulation condition assessment which could assist in insulation life prediction and improved asset management.

The condition of high voltage cable, power transformer and generator insulation is affected by a number of manufacturing and operating variables. Although forensic examinations of solid insulation failures are commonly conducted and there are many electrical tests to assess the condition of the insulation system, there has been only a limited effort to investigate and spatially map the changes in chemical characteristics and properties that can also affect failure. We have applied a range of non-destructive spectroscopic methods such as infrared, Raman, including their respective microprobe methods, and UV-VIS-NIR spectroscopy to measure spatially resolved chemical composition and structure of polymeric insulated cables, power transformers and generator stator insulation both before and after electrical and thermal stressing. By applying multivariate statistical analysis (MVSA), we have been able to explore and extract relationships between chemical change in the material and "intrinsic variables" such as stressing time, temperature and voltage as well as explore the relationships with physical properties and performance such as electrical breakdown strength, mechanical strength and charge mobility. Recent work illustrates the power of such methods in exploring key property and performance relationships and the ability to map these spatially with new remote and rapid spectroscopic optical probe methods. We propose that well-populated MVSA models can relate chemical and physical change in solid insulation systems to electrical measurements, to potential indicators of insulation ageing and provide a predictive capability for insulation condition assessment which could assist in insulation life prediction.

The Raman spectrum of crystalline dodecahedrane, C20H20, a species of nominal I(h) symmetry, exhibits splitting of the H(g) Raman active modes. The Raman inactive gerade vibrations of G(g), T(1g), and T(2g) symmetry are found to have weak Raman activity. The IR forbidden vibrations of T(2u), G(u), and H(u) type have moderate IR activity. All of this is consistent with the T(h) site symmetry. A treatment of the structure and vibrations of dodecahedrane using a periodic lattice DFT method results in a slightly distorted T(h) structure with six C-C bonds that are 0.001 A longer than the other 24. The vibrational spectrum computed for this structure exhibits splittings of the H(g) modes that are consistent with the observed spectra, but the computed splittings are larger than observed in room-temperature data. A complex pattern observed in the C-H stretching region is assigned. The inelastic neutron scattering spectrum calculated from the computed normal modes for the T(h) molecule in the lattice agrees quantitatively with experiment when overtone and combination transitions are included and allowance is made for anharmonicity of the C-H stretch motion. Finally, it is argued that the existing crystallographic determination of the average C-C bond length of 1.544 A is shortened by disorder and should be revised upward to agree with the computed value of 1.558 A.

Bis(acetanilido)-tris(acetato)dicuprate(II), [Cu2(C7H8N2O)2(CH3CO2−)3], is incorporated into MY721, a commercial epoxy resin recognised as an ‘industry standard’. Infrared spectroscopy and thermogravimetry are employed to examine the structure and thermal dissociation behaviour of the newly prepared complex. Multivariate analysis techniques (e.g. principal components analysis) are used to examine the spectral data to corroborate the dissociation temperature. The shelf life and cure characteristics of the commercial epoxy/curing agent formulation are determined using differential scanning calorimetry and vibrational spectroscopy.

Molecular vibrational spectroscopies, including infrared, near-infrared and Raman, and optical UV-VIS spectroscopies providing electronic (colour) and molecular information, have been used to investigate several polymeric materials and extract the relationships between chemical composition, structure and physical characteristics by multivariate statistical analysis. With the appropriate use of spectroscopic microprobe methods it is possible to map these relationships spatially down to a resolution of less than one micron. In particular, these multivariate methods have been applied to studies of cross-linked polyethylene cable insulation materials with a view to exploring possible relationships between bulk and local chemical structure, and electrical properties. This paper will discuss some of these findings and demonstrate that it is possible to construct relational models between key characteristics that give us insight into the behaviour of complex dielectrics.

Rapid in-situ analysis of the condition of power transformer winding insulation to provide information on its aged condition and water content is important for both transformer manufacturers and also asset managers in power utilities. The ability to achieve this with portable instrumentation would be very beneficial. The insulation paper degrades over time, and the degree of polymerisation of the paper affects its structural integrity and its capacity for water absorption. The use of spectroscopy together with multivariate statistical analysis provides a powerful non-destructive tool for the condition assessment of these materials both in the laboratory and in the field. We have developed a simple, portable system (TRANSPEC) using fibre-optics and broad-band spectroscopy that can measure the degree of polymerisation in the range from 100 to 1200, water content from 0.4% to almost full saturation to an accuracy of 0.1%, and oil content of new and aged transformer paper also to high precision. Multivariate statistical analysis regression models have been constructed from spectral library data and these models are used to predict the parameters above and also other physical properties e.g. tensile strength. We have also confirmed that both the water absorption kinetics and water capacity of the paper are strongly affected by the degree of degradation. With a single TRANSPEC system, in-situ analysis of the degree of polymerisation of insulating paper, the water content and, if required, a chemical analysis of the insulating oil and its water content.

Predicting the complex cure and gelation behaviour of epoxy resins used in generator stator ground wall insulation systems is necessary if the manufacturing conditions and final properties of the insulation system are to be optimized. While it is possible to obtain a variety of measurements of cure behaviour using bulk probing of the insulation system it is also important to follow the chemistry of the cure process up to and beyond the gel point and to relate the evolution of physical properties to the chemical conversion process during crosslinking and network formation. Here we describe a variety of molecular spectroscopic and calorimetric investigations into the isothermal and non-isothermal reaction kinetics of a bisphenol-A epoxy-anhydride system accelerated with a carboxylic acid salt. It is shown that the detailed cure process and reaction kinetics can be modelled to produce a predictive tool to describe the complete reaction process for any time-temperature cycle as a function of the accelerator concentration. Generalisation of these findings to the reaction behaviour of mica tape systems utilizing the same resin system is also discussed.

Infrared, Raman and UV-VIS spectroscopies have been used to investigate the chemical composition and structure of cross-linked polyethylene used in a set of high-voltage polyolefin-insulated cables, both before and after electrical stressing and thermal ageing. Acrylate oligomers present in the semi-conducting screen materials, and the breakdown products of cross-linking are observed to diffuse into the insulation with a diffusion profile that is ageing time and temperature dependent - it appears that temperature, not voltage, has by far the biggest effect on migration in these materials. Multivariate statistical analysis has been used to examine the relationships between both the chemical changes in the material and the "intrinsic variables" such as radial distance, ageing time, temperature and voltage stress condition as well as the "physical properties" including AC electrical breakdown strength, charge mobility and oxidation potential. In all cases, the increase or decrease of certain chemical groups can be associated with the changes observed in these properties. Well-populated chemometrics models, based on spectroscopy, can provide sound structure-property relationships and a predictive capability for cable condition assessment that could be extended to cable performance and other insulating materials.

Rapid in-situ analysis of the condition of power transformer winding insulation kraft paper, to provide information on its aged condition, is an imperative in the power industry. The ability to achieve this with portable instrumentation would be very beneficial. The insulation paper degrades over time, and the degree of polymerisation (DP) of the paper affects its structural integrity. At low DP levels the risk of electrical breakdown increases. Currently used methods of estimating DP are only approximate or destructive. The use of spectroscopy together with multivariate statistical analysis (MVSA) provides a powerful non-destructive evaluation of the condition of paper. From initial feasibility studies, we have developed a simple, portable system (TRANSPEC) using fibre-optics and broad-band spectroscopy that can measure the degree of polymerisation of various aged transformer papers to a precision of approximately 50 DP units with a spatial resolution of 25 mm/sup 2/, and also measure the chemical composition and condition of the insulating mineral oil. MVSA regression models were constructed from library spectral data, and these models are used to predict the DP of other papers with parameters that fall within the range spanned by the set of calibration samples. Separating oil and moisture information from wetted paper is possible and water content can be determined to an accuracy of approximately 0.1%. Very low to high concentrations of water have been determined using this method. We have also confirmed that both the absorption rate and water capacity of the paper are strongly affected by the degree of degradation. With a single TRANSPEC system, in-situ analysis of the degree of polymerisation of insulating paper, the water content and, if required, a chemical analysis of the insulating oil and its water content is possible providing a rapid cost-effective method for transformer insulation condition assessment and monitoring, which correlates well with current established methods.

Changes in protein secondary structure and conformation of ovalbumin and beta-lactoglobulin (15% protein w/w) were investigated by Fourier transform Raman spectroscopy and self-deconvolution. The amounts of alpha-helix, beta-sheets, random coil, and beta-turns in native beta-lactoglobulin were 15, 54, 6, and 25%, respectively, and those for ovalbumin (41, 34, 13, and 12%) compared well with published values obtained by X-ray crystallography. The proteins were heated at 90 degrees C for 30 min and high-pressure-treated at 600 MPa for 20 min. Heating increased beta-sheet structures in both proteins at the expense of alpha-helix; for beta-lactoglobulin beta-sheet structures increased from 54 to 70% and for ovalbumin, from 34 to 54%. Random coil increased from 6% in the native protein to 30% in high-pressure-treated beta-lactoglobulin. However, for ovalbumin, the contribution from beta-turns doubled in high-pressure-treated samples, with little change in random coil. Further examination of the deconvoluted amide I band in heated samples revealed several component bands. Bands at 1626 and 1682 cm(-1) for ovalbumin and at 1625 and 1680 cm(-1) for beta-lactoglobulin were observed and are associated with aggregated, intermolecular beta-sheet (beta-aggregation), indicative of heat denaturation. The band seen at 1632-1640 cm(-1) corresponded to intramolecular beta-sheet structures, whereas the band at 1625 cm(-1) is associated with exposed beta-sheets (for example, beta-strands with strong hydrogen bonding that are not part of the core of beta-sheets). In high-pressure-treated samples bands were also observed at 1628 and 1680 cm(-1) for ovalbumin and at 1626 and 1684 cm(-1) for beta-lactoglobulin, suggesting involvement of beta-sheet structures in protein aggregation. Raman bands were observed at 1665-1670 cm(-1) for ovalbumin and at 1663-1675 cm(-1) for beta-lactoglobulin due to random coil structures. The bands at 1650-1660 cm(-1) due to alpha-helices were observed in both heated and high-pressure-treated samples. In addition, in heated samples of both ovalbumin and beta-lactoglobulin, peak intensity increased for beta-sheet in the amide III region, 980-990 cm(-1), and decreased for helix structures (900-960 cm(-1)). In contrast, there was no peak at 1240 cm(-1) (amide III beta-sheet structures) in either high-pressure-treated ovalbumin or beta-lactoglobulin, suggesting that high-pressure denaturation at 600 MPa for 20 min is less extensive than heat denaturation at 90 degrees C for 30 min.

The present work has provided a complete set of assignments for the vibrational spectrum of Rb2PtH6 and Rb2PtD6. To confirm the assignments, a periodic density functional theory (DFT) code has been applied to the analysis of the inelastic neutron scattering (INS) spectrum of an ionic material for the first time. The work has also provided an explanation for the unusual infrared spectrum of the potassium salt. The most significant aspect of the work is the use of the momentum transfer information provided by an INS chopper spectrometer. The straightforward method employed for the analysis of the data is applicable to any molecular system (organic or inorganic) and demonstrates the potential of these instruments for chemistry. Periodic DFT was also used to study the other A2PtH6 (A = alkali metal) including, the at present, unknown Li salt, which is found to be stable. The DFT studies have also highlighted the crucial role of the cation in removing charge from the transition metal and “hydride” ligand. It i...

Poly(hexafluoropropylene-co-tetrafluoroethylene) (FEP) was successfully radiation-grafted with vinylbenzyl chloride (VBC). Subsequent amination with trimethylamine followed by ion exchange with aqueous hydroxide yielded alkaline anion-exchange membranes (AAEMs). Experimental parameters were established for maximising the degree of grafting (d.o.g.); the optimum treatment duration for maximum amination was also established. The graft penetration at different degrees of grafting was investigated and related to the grafting conditions. The stabilities of the grafted membranes and the final AAEMs were thoroughly investigated using thermogravimetry and differential thermal analysis (TG/DTA). The ion-exchange capacities (IECs), water uptake levels, and thicknesses of the AAEMs were measured. These AAEMs have potential for application in low-temperature fuel cell systems.

Kraft paper (cellulose) immersed in mineral oil is used as the insulation system for copper windings in large power transformers. As the system ages under load, the paper and oil can degrade potentially leading to catastrophic failure. Reliable condition monitoring, condition assessment and failure prediction of the insulation system is central to effective transformer asset management and non-destructive/non-invasive approaches are preferred. In this paper we will show that near infrared (NIR) spectroscopy combined with chernometrics is capable of providing rapid non-destructive condition assessment of the paper and the oil components individually.

Lysozyme (25% in D2O, corn oil, and their emulsions (10% w/w oil/D2O solution) were examined by Fourier transform Raman spectroscopy. Emulsions showed three layers, namely, top oil, middle cream, and bottom aqueous layers. Raman spectral analysis revealed hydrophobic interactions involving both protein and lipid components. Compared to lysozyme in D2O, the difference spectrum obtained after subtraction of oil from the cream layer spectrum showed reduced intensity of tryptophan bands at 760, 1013, 1340, and 1360 cm(-)(1), reduced intensity ratio of the tyrosine doublet at 850 and 830 cm(-)(1), and increased intensity of the C-H bending band at 1455 cm(-)(1). Compared to corn oil, the difference spectrum after subtraction of lysozyme from the cream layer spectrum indicated decreased intensity at 2855 cm(-)(1) (lipid CH(2) symmetric stretch) and 3011 cm(-)(1) (unsaturated fatty acid hydrocarbon chain =C-H stretch) and a higher intensity ratio of the C-H stretching band at 2900 cm(-)(1) to bands at 2885 and 2933 cm(-)(1). Spectra of the top and bottom layers resembled corn oil and lysozyme, respectively, except for changes in the D2O band. Raman spectroscopy can be used to detect structural changes in proteins, lipids, and D2O due to protein-lipid interactions.

The correlation of polymer structure with properties has been greatly assisted by the application of statistical methods — chemometrics — to spectroscopic and physical multi-variate data. Chemometrics is a multivariate methodology that allows the information from entire spectra to be used and can be considered as a maximal data compression technique. The extracted “factors” can then be regressed against property data and, given a characterised set of “training” samples, can then be used in a predictive mode. For example, the relationship between the near infrared (MR) spectra of polyolefins and their density and melt flow index (MFI) is already being used for on-line process analysis and control of powder and pellet grades.

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Radiation-grafted alkaline anion-exchange membranes (AAEM) containing pendent groups with either benzyltrimethylammonium (BTM) or benzylmethylimidazolium (BMI) functionality were successfully synthesised from the same base membrane and with identical ion-exchange capacities. The conductivity of the new BMI-AAEM is comparable to the BTM-benchmark AAEM. The fuel cell performance obtained with the BMI-AAEM was, however, significantly poorer due to in situ AAEM degradation. FT-Raman spectroscopic studies on the stability of the two head-groups at 60 °C in aqueous potassium hydroxide (1 mol dm−3) indicates that the BMI-group is intrinsically less chemically stable in strongly alkaline conditions compared to the BTM-benchmark head-group. However, the stabilities of both head-groups are improved when treated at 60 °C in lower pH aqueous carbonate and bicarbonate solutions (1 mol dm−3). Contrary to a portion of the prior literature, there appears to be no real advantage in using anion-exchange polymer electrolytes containing pendent imidazolium groups in highly alkaline systems.

In this paper we exploit the complementarity of inelastic neutron scattering (INS), infrared and Raman spectroscopies with ab initio calculations to generate an updated assignment of the vibrational modes of C(60). We have carried out periodic-DFT calculations of the high temperature face centred cubic phase modelled as the standard structure and also of the low temperature simple cubic phase, the latter for the first time. Our assignment differs from all previous work, however, it is the only one that is able to successfully reproduce the INS spectrum in terms of both transition energies and intensities. In addition to the INS spectrum we are also able to quantitatively simulate the major features of the infrared and Raman spectra in the high temperature phase and the infrared spectrum in the low temperature phase.

A simple aqueous-processable alkaline ionomer (amenable to scale-up) has been developed for enhancing electrode/electrolyte interfaces in clean energy devices (e.g. alkaline polymer electrolyte membrane fuel cells). The water uptake of the alkaline ionomer is tuneable allowing its use as a tool for fundamental studies into these interfaces.