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Synchrotron grazing incidence X-ray diffraction has been used to newly reveal the heating rate dependent oxidation reactions that develop on a polycrystalline nickel-based superalloy. A continuous layer of precursor oxide was shown to form during the heating stage. Their approximate growth rates, their effect on local surface compositions of the alloy substrate, and their degree of interface planarity are considered critical in determining subsequent oxidation reactions when held for extended thermal exposures. The precursor oxides were predominantly nickel or cobalt based (NiO/CoO and Co3O4/NiCo2O4). Following the fastest heating rates (40 °C min−1 and above), the stable Cr2O3 phase formed, inhibiting Ni or Co diffusion to the surface. At slower heating rates (10–20 °C min−1), no evidence of the stable Cr2O3 was found, even after 200 h at elevated thermal exposure, instead continued growth of the precursor oxides was observed. Heating at 5 °C min−1 gave rise to an intriguing zone where sufficient precursor and favourable kinetics enabled the formation of a spinel, NiCr2O4, surface layer. Cross sections observed with electron microscopy confirmed this to be planar and continuous. Heating at the slowest tested 2 °C min−1 contrarily gives a non-protective surface layer comprising an outwardly growing NiO/CoO precursor oxide on top of an inwardly growing mixed oxide. The quantities, interfacial morphologies of oxides of the precursor oxide grown and the possible thermodynamic reactions that lead to their formation are discussed.

The photoelectron spectrum for the two lowest ionisation bands of phenol has been simulated using quantum dynamic methods. A vibronic coupling Hamiltonian was set up consisting of seven vibrational modes and the first two ionised states. Parameters for the model are obtained by fitting adiabatic surfaces to a series of points calculated using ab initio methods. Such a model allows non-adiabatic couplings between the states to be included. CASSCF calculations used in this work provide reliable quantum chemical information for the model and the calculated photoelectron spectrum shows good agreement to experiment. The vibrational fine structure of both bands are reassessed and different assignments to those previously reported are detailed. The existence of a conical intersection between the ionised states is reported and its role in the dynamics of phenol upon ionisation is examined.

Carbon deposition on 20Cr25Ni steel at 700 °C has been investigated in CO2-based gases containing 0.7 vol%, 1.0 vol% and 1.4 vol% CO, each with ∼1000vpm C2H4, at 700 °C. Filamentary carbon deposits were formed at the two lowest CO contents but not at 1.4 vol% CO. TEM analyses have shown that the different CO levels change the propensity for deposition by altering the ratio of Ni:Fe in the nanometre sized catalytic particles produced during oxidation.

Austenitic stainless steel is used as fuel cladding in advanced gas-cooled nuclear reactors (AGR). At elevated temperatures, when the steel is exposed to CO2 based environments filamentary carbon deposits form on the surface of the steel. This filamentary carbon deposition is known to be catalysed by metallic nickel-rich particles. Adding trace amount of carbonyl sulphide (COS) into the gas mixtures suppresses the carbon deposition. In this current work, it has been shown that at 600 °C, the formation of filamentary carbon was suppressed by the addition of 215 ppb COS to a depositing gas mixture (containing approximately 1000 vppm C2H4/1% CO/bal. CO2) which was known to provide the environment suitable for carbon deposition. Samples exposed to the gas mixtures with and without 215 ppb COS were characterised using electron microscopy techniques to understand the formation mechanism of the nickel-rich particles and the inhibition mechanism due to the addition of COS. Electron diffraction study shows that the nickel-rich particles in the oxide layers assume the same crystallography as that of the austenitic metal underneath, regardless of the COS addition. The current observations also show that the metal-oxide interfaces was nickel-rich and a simple model has been proposed to explain the formation of nickel-rich particles within the subsurface oxide. Furthermore, it was found that when COS was added the surface of the nickel-rich particles in the oxide layer was found to be sulphur-rich by energy dispersive spectroscopy (EDS) on a scanning transmission electron microscope (STEM). It is believed that the surface sulphur adsorption onto the nickel-rich particles, rather than bulk sulphide formation, resulted in the inhibition of carbon deformation on the steel.

Spallation of oxides grown on TP347H FG in air-saturated steam at 923 K for 50–1000 hours was investigated using a newly developed technique termed: Simultaneous Thermographic and Optical Recording Media Examination (STORME), recording the temperature disturbance resulting from delamination and spallation, during cooling, using Infra Red and video cameras. For the first time, the radius of the delamination site was measured experimentally at the point of buckle formation and followed during growth to the point of spallation. Collection of the exact spalled fragment was possible. The strain energies at each stage were calculated and a Spallation Map constructed.

The effect of shot-peening on the oxidation in air of the Ni-based superalloy RR1000 has been investigated over the temperature range 700–800 °C. The surface oxide in both peened and un-peened conditions consisted of isolated grains of rutile on the outermost surface beneath which was a protective Ti-doped chromia scale. Internal oxidation of aluminium occurred within the alloy with the formation of alumina particles within a γ ′ (nominally Ni 3 (Al,Ti)) denuded zone but the morphology of the sub-surface oxides differed between the two surface conditions examined. The kinetics of thickening of the chromia layer were sub-parabolic in most cases but closely approached parabolic behaviour for the un-peened surface condition at 800 °C. An enhancement in the rate of chromia growth was found for both surface conditions compared with a Ti-free chromia layer. This enhancement has been attributed to increased Cr ion diffusion as a result of Ti-doping of the chromia layer but the effect is reduced over time because of Ti-depletion in the alloy. At 800 °C, in the un-peened condition, the reduction in growth rate with exposure time is much less marked and this effect seems to be associated with the formation of a (Ti,Ta)O 2 phase beneath the chromia layer.

It is known that fast-growing non-alumina scales in thermal barrier coating (TBC) systems tend to form at features where aluminium depletion is enhanced due to a high surface-area to volume ratio, a phenomenon known as breakaway oxidation. In this work, the influence of breakaway oxidation around protuberances in an MCrAlY bond coat in a TBC system during isothermal oxidation and after cooling is quantified numerically. A finite element approach is used which incorporates elastic, plastic and creep deformation of the bond coat and thermally grown oxide (TGO) and, importantly, the volumetric strains associated with oxide formation during the isothermal exposure. It is shown how volumetric strains which develop during breakaway oxidation can result in the formation of significant (>0.5 GPa) out-of-plane tensile stresses within the yttria-stabilized zirconia top coat at the oxidation temperature. These stresses are located along the flanks of the bond coat protuberances in locations where sub-critical cracks have previously been reported. The magnitude of the stresses increases with bond coat surface roughness, after the initiation of breakaway oxidation and after cooling. Results are also presented for the normal tractions across both TGO interfaces, and the influence of breakaway oxidation on these is discussed.

P-type transparent conductive oxides have potential applications in photovoltaics, transparent electronics, and organic optoelectronics. In this paper, results are presented on the synthesis of Cu 2 SrO 2 thin films, a p-type transparent conducting oxide by a sol–gel route. Cu(II)methoxide and Sr-metal dissolved in anhydrous isopropanol were used as precursor for the sol preparation. For potassium (K) doping, K-acetate dissolved in anhydrous isopropanol was used as the precursor. Films were spin-coated onto substrates and partially pyrolysed in air at 225°C. After partial pyrolization, a two stage annealing sequence was used to achieve the final film microstructure and composition. Although combinations of oxygen pressure, annealing time, and annealing temperature were used to obtain phase pure Cu 2 SrO 2 thin films, X-ray diffraction consistently showed the presence of Cu 2 O as a second phase with Cu 2 SrO 2 −the desired phase. Microstructural studies showed similar phase separation in the films and confirmed the microcrystalline nature. The best conductivities obtained for the undoped and 1% K-doped films were 2 × 10 − 3 and 1.2 × 10 − 2 S/cm, respectively. Both films showed a broad optical absorption edge in the visible range.

The tensile creep properties of a β-rich (Ni,Pt)Al diffusion coating have been determined at various strains over the temperature range 800–1000 °C by deconvoluting the creep response of layered composite specimens under constant stress conditions. It is found that the creep strength of the diffusion coating tends to be higher than that of a similar coating tested previously by Pan et al. [Pan D, Chen MW, Wright PK, Hemker KJ. Acta Mater 2003;51:2205]. Associated with the higher strength is a relatively high creep activation energy (∼600 kJ/mol) and a high stress dependence of creep rate which increases with creep strain from ∼6.8 at 1% strain to ∼9.4 at 9% strain. These high values and the associated high creep strength are attributed to the formation, at the creep temperatures, of a fine dispersion of second-phase particles, presumed to be γ′ and possibly α-Cr, within the β-(Ni,Pt)Al matrix. It is suggested that the extent of this transformation and, hence, the strengthening effect are related to the original aluminium and platinum content of the coating.

A new method is described for the evaluation of the creep properties of as-deposited overlay coatings. The method uses a composite tensile specimen consisting of a core alloy of well-characterised creep properties onto which the overlay coating is deposited. The overall strain/time response of this specimen, tested under constant stress conditions, can then be deconvoluted to obtain the creep characteristics of the coating. The method has the advantage that the coatings are evaluated for the same microstructural conditions as they will be used under, i.e. having the same porosity levels and microstructure. A limited demonstration of the method has been made for an air plasma-sprayed Ni25Cr6AlY coating deposited onto an austenitic steel core and creep tested at 900°C. The creep strength of this coating was surmised to be higher than that of equivalent monolithic samples produced by low pressure plasma spraying.

The ability to predict the onset of spallation of protective oxide layers is an important requirement in evaluating the endurance of high temperature coatings or thin-sectioned components. Oxide spallation tends to occur during cooling, when the oxide layer is usually in compression. Considerable progress has been made in modelling spallation from flat substrates under such conditions, and much of this work is reviewed in this paper. In particular, the results of finite-element modelling of oxide/metal interfacial cracking are presented for both chromia-and alumina-forming substrates. It is shown that creep relaxation in the coating or alloy can retard the growth of the interfacial crack even during fast cooling but the extent of retardation increases with lower cooling rates. When such creep relaxation is extensive, i.e. at low cooling rates or with substrates weak in creep, improved spallation resistance results. For such cases, a simple critical strain-energy approach can be used to predict the onset of spallation.

The current efficiency model of Lillebuen et al. (Electrochim. Acta25, 131, 1980) was reworked and the analytical derivation clarified. As a result, the predicted metal loss differred by nearly 9%.

The dual operating problems of anode effect and sludging, in smelting cells, highlight the central concept of this paper, that is, the electrochemical parameters which determine the rate and efficiency of the electrolysis also control the overall cell heat balance. An additional constraint is present since the material balance, and the necessity of maintaining it through bulk feeding, exerts a strong influence on those same electrochemical parameters. Low concentrations of alumina in the bath result in excessive polarization and anode effect. Overfeeding gives rise to sludging and voltage instability. Even during stable operation the conductivity, decomposition voltage and polarization potentials respond to the electrochemical depletion of the alumina. These interactions place severe limits on the controllability of the batch fed smelting cell so that its operation is essentially dynamic. New technology now emphasizes the concept of continuous or 'point feeding' of the alumina.

The hazards which may arise due to the use of radioactive foils in the gas chromatography detectors are reviewed; they are external radiation, effect of mechanical damage, emission of radioactive gases, the effect of chemical attack and the effect of heat. Overheating of the foils is the principle source of danger to the majority of users, but the other hazards particularly effect those persons who build or service their own apparatus.