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Within the British nuclear inventory, waste is classified into three main categories, including Intermediate Level Waste (ILW). ILW mainly consists of fuel casing metallic swarf, where parts of uranium metal are also expected to have been agglomerated. ILW treatment route includes the material storage in stainless steel drums and subsequent grout encapsulation. The solidified matrix is believed to maintain the radioactive waste fully confined and immobile. Recent inspections revealed mechanical distortion around the steel liner in a proportion of the inspected drums. The distortion has been ascribed to the corrosion of the encapsulated metallic parts. The generated corrosion products occupy greater volume than the parent metal, resulting in an internal volume expansion which imposes stress/strain on the encapsulants. This study attempts to correlate the level of internal corrosion with the magnitude of package degradation in ILW drum–simulant systems by favouring the use of powerful synchrotron X-rays.

The study explores carbon quantum dots (C-dots) as potential candidates for enhancing the signal sensitivity of an electrochemical sensor devised for biologically important molecule, such as uric acid (UA). The C-dots were evaluated for their electrochemical characteristics in combination with Fe3O4 nanoparticles (Fe3O4 NPs), which were applied as the primary electro-catalytic promoter. The hybrid nanocomposite (C-dots/Fe3O4 HCs) formation was achieved by facilitating the adsorption of C-dots over Fe3O4 NPs using amine-carbonyl interactions. Unlike, one pot method, the proposed strategy enables aggregation-free coverage of Fe3O4 NPs with highly conductive layer of C-dots that can act as conduction centres to support ultra-fast electron transfer kinetics to satisfy the need of high signal sensitivity. The hybrid composite demonstrated remarkable signal improvement when tested against the electrochemical oxidation of UA. The heighten current response and lower over-potential values enabled development of a DC-amperometric (DC-AMP) sensor for UA with a linear working range of 0.01 to 0.145 μM and signal sensitivity measurable up to 6.0 × 10−9 M. The said improvement was manifested as a synergetic outcome of active redox couple (Fe (III/II)), larger surface area of Fe3O4 NPs engulfed with a layer of highly conductive C-dots acting as efficient charge sensitisers.

The reaction of unirradiated-U with liquid water was investigated under initial vacuum-contained conditions. Ten samples were examined at varying temperatures and reaction times. Post-corrosion examination of the surfaces was conducted using FIB, SIMS and XRD. Measurements of the reacting water pH and degassing of the samples was conducted after the reaction was stopped. From the analyses, it was concluded that bulk-UH 3 formation occurred on the majority of the samples. It is suggested that UH 3 formation was facilitated by a critical ‘threshold’ headspace pressure ∼0.5bar over which pressure deficiency is observed in the free headspace.

In the UK, the typical route being followed to handle metallic Intermediate Level Waste (ILW) derived from decladding of irradiated nuclear fuel is to primarily deposit it within stainless steel drums/boxes and subsequently encapsulate it into grout. Thus, a monolithic bond between the waste and the encapsulants can be achieved. However, recent inspections have revealed bulges around the circumference in a considerable proportion of the inspected packages. This distortion has been ascribed to the interior metallic corrosion–induced volume expansion, occurring throughout the waste packages storage period. Throughout this period, the volume expansion taking place in the core of the ILW drums has imposed continuously growing levels of strain on the surrounding encapsulants, i.e. grout and steel confinement. As a result, the encapsulants may exhibit considerable damage, in the form of cracks in the grout or/and steel distortion, threatening the integrity of the packages and, consequently, raising safety concerns within the nuclear community. Herein, experimental work performed on ILW drum–simulant packages is described, attempting to evaluate the performance of the packages under an internal corrosion–induced volume expansion.

This study explores the potential of a newly-developed indium tin oxide (ITO) based electrode for the development of an electro-catalytic inhibition sensor system for organophosphorus pesticides. The sensor relies on the redox signal inhibition of pralidoxime chloride (PAM) immobilised over the pimelic acid functionalised CuO nanostructures grown in-situ over an ITO substrate. The in-situ growth enabled on-pot modification and functionalisation of ITO electrodes with the formation of uniform nanostructures possessing high surface area and excellent interface contact. The versatility of the proposed electrode was evident from its excellent electrochemical characteristics evaluated in comparison to bare and slurry-driven glassy carbon electrodes (GCEs). The high structural uniformity and greater surface coverage achieved by in-situ growth provided a uniform surface environment for electrode-analyte interaction, leading to good inhibition signal sensitivity and repeatability. The developed sensor was successful in detecting chlorpyrifos, fenthion and methyl parathion within the concentration range of 0.01–0.16 μM with signal sensitivity reaching down to 1.6 × 10−9, 2.5 × 10−9 and 6.7 × 10−9 M respectively. Moreover, the proposed sensor demonstrated excellent applicability when tested for chlorpyrifos from vegetable extracts using a standard addition method.

This study describes the hydrothermal synthesis of NiO, CuO and Co3O4 nanostructures using acetylsalicylic acid (ASA) as a growth-controlling/directing agent. The as-synthesised nanostructures were shown to possess unique structural features and distinct morphologies, portraying the efficiency of ASA as a suitable growth modifier. The formed metal oxide nanostructures, when used for electrode modification purposes, exhibited excellent electro-catalytic capabilities against the oxidation of nelbuphine hydrochloride (NAL) in aqueous buffer solution. The modified electrodes exhibited distinct electrochemical characteristics, with CuO-based electrodes exhibiting a superior signal sensitivity and lower over-potential value compared to the NiO and Co3O4 nanostructures. The study further explores the variation in the observed electro-catalytic oxidation signal referenced to the distinct morphologies of the metal oxides nanostructures. The CuO-based electrode was selected for the sensitive quantification of NAL in aqueous solution over the linear range 0.001–2.25 μM. The electrode demonstrated excellent working linearity, with signal sensitivity achieved down to 1 × 10− 4 μM. Moreover, the successful quantification of NAL in complex matrices, such as human urine and clinical waste water, further reflected the analytical capability of the proposed sensor.

To accurately predict the initiation and evolution of uranium hydride potentially present in nuclear waste containers, studies of simulated conditions are required. Here, for the first time, the uranium-deuterium reaction was examined in-situ, in real time, whilst within grouted media. A deuterium gas control rig and stainless steel-quartz glass reaction cell were configured on a synchrotron beam line to collect X-ray diffraction and X-ray tomography data. It was found that deuteride formation was limited by the uranium and grout thermal conductivities and deuteride initiation only commenced above a threshold temperature. Strong adherence between uranium oxide and grout was also observed.

Synthetic polygranular graphites of various grades and manufacturing routes are used in nuclear reactors for power generation, and may be used in potential fourth generation and other advanced reactor designs that will operate at higher temperature. Attention is given in this paper to isostatically-moulded synthetic polygranular graphites with porosities in the range 8% to 18%. The lattice parameters a and c for the hexagonal graphite have been measured over the temperature range from room temperature to 800°C by x-ray diffraction. The variation with temperature of the crystal lattice parameters, coherence length (crystallite size) and microstrain are discussed with reference to the microstructure and the relative strength of the bonds in-plane and normal to the graphene layers.

MXene-based hybrid composites are gaining substantial attention due to their impressive chemical and electronic characteristics. Herein, an in-situ engineered heterojunction is constructed using partially-oxidised Ti3C2Tx sheets and photo-active NiWO4 nanoparticles (NPs). The NiWO4 NPs were used to induce partial surface oxidation of Ti3C2Tx, resulting in the formation of a Ti3C2Tx-TiO2/NiWO4 hybrid composite (MX-NiWO4). The electrocatalytic and photo-electrochemical (PEC) characteristics of MX-NiWO4 were studied in reference to the reduced graphene oxide-NiWO4 (rGO-NiWO4) and H2O2-treated Ti3C2Tx (MX-H2O2) hybrids. The MX-NiWO4, based on its in-situ driven configuration, constructed an ideal interfacial arrangement for the electrocatalytic mechanism-based PEC immuno-sensing of prostate-specific antigens (PSA). The developed PEC biosensor was capable of detecting PSA, over a wide detection range of 1.2 fg.mL−1 to 0.18 mg.mL−1, with a detection limit of 0.15 fg.mL-1. The synergic integration of Ti3C2Tx with photo-active NiWO4 offers a superior signal response and practical applicability when used for the quantification of PSA from human saliva samples, anticipating the hybrid’s promising future in clinical detection.

Nuclear graphite has a complex microstructure and displays quasi-brittle fracture characteristics. Multi-scale experimental characterisation (micrometre-scale to centimetre-scale) and numerical modelling were performed for (i) PG25 filter graphite with pores only (52 vol.%); and (ii) Gilsocarbon nuclear graphite with pores and aggregates. Modelling results show that the average mechanical properties and the scatter of the data both decrease monotonically with increase in specimen size. Strain fields and crack patterns were modelled and fit with experimental observations. The benefits of the model as a valuable tool in studying the influence of microstructural parameters on the fracture of nuclear graphites are discussed.

This work reports a highly sensitive electrochemical sensor for organophosphate pesticide (malathion) based on unique and attractive CuO nanostructures. The discussed nanostructures were synthesize ...

During the early years of nuclear industry within the UK, the typical route followed to handle Magnox (Mg-Al alloy) casing after separation from the nuclear fuel has been immersion in water temporarily in specifically-designed water ponds. Over the decades of storage, Magnox has been corroding in water, resulting in the formation of sludge within the ponds; known as Corroded Magnox Sludge. Uranium, which has been also contained within the ponds as a result of faults occurring during fuel-casing separation, is susceptible to corrosion in water-rich environments. Under certain circumstances, uranium corrosion products can be highly pyrophoric during oxidation in air. This raises serious concerns regarding the safety margins of nuclear pond decommissioning. The present study attempts to shed light on the behaviour of uranium in a Magnox sludge-surrogate environment, using X-ray computed tomography at distinct time intervals over an 18-month period. Focus was given onto the uranium-sludge interface to determine metallic corrosion onset and evolution.

A novel, low energy method for coating different nano-particles via electro-deposition to a recyclable carbon glass supporting structure is demonstrated. In the resulting composite, the nano-material is bound to the substrate surface, thereby removing the potential for causing harmful interactions with the environment. Nano-particles were suspended in a salt solution and deposited at low current densities ( −2 ) producing thin (

We have recently undertaken comprehensive computational studies predicting possible crystal structures of the as yet unknown phosphorus carbide as a function of composition. In this work, we report the synthesis of amorphous phosphorus–carbon films by pulsed laser deposition. The local bonding environments of carbon and phosphorus in the synthesised materials have been analysed by x-ray photoelectron spectroscopy; we have found strong evidence for the formation of direct P–C bonding and hence phosphorus carbide. There is a good agreement between the bonding environments found in this phosphorus carbide material and those predicted in the computational work. In particular, the local bonding environments are consistent with those found in the β - InS - like structures that we predict to be low in energy for phosphorus:carbon ratios between 0.25 and 1.

A facile and green seed mediated growth approach for fabrication of well dispersed l -threonine derived nickel nanoparticles (Ni NPs) in an aqueous medium via a modified borohydride reduction method is described. l -Threonine molecules served to organize the nanoscale composites in the form of well dispersed Ni NPs. The basic pH 8.5 was found to favor the formation of spherical and well dispersed Ni NPs as shown in transmission electron microscopy (TEM) micrographs. Freshly prepared Ni NPs possess the nanoscale dimension of 1.68–5.06 nm, as determined from atomic force microscopy (AFM) and TEM data. The Ni NPs thus prepared were used for their catalytic potential in the reduction of congo red (CR) dye selected as a model reagent. The results revealed negligible reduction of dye in the absence of Ni NPs. Conversely the addition of only 0.2 mg Ni NPs produced 100% reduction/degradation efficiency. The used Ni NPs were recovered and reutilized several times for reducing CR without any loss of activity. The current findings are equally extendable for safeguarding the aquatic environment against the pollution caused by other dyes via a facile, highly economical, rapid and efficient reduction/degradation method based on the catalytic potential of Ni NPs.

The study reports mechanical performance of the recycled glass fibres produced from a water-based solvolysis technology, known as the hydrolysis process. The chemical reaction was carried out using sub-critical water to dissolve polyester resin and recover the glass fibres from composites. The effect of temperatures, times, catalyst and water amount on mechanical properties of the recovered glass fibres were investigated. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and time-of flight secondary ion mass spectroscopy (ToF-SIMS) analyses were also employed to examine the fibre surface associated with the polyester resin eliminated level after the hydrolysis reaction. The results revealed that by carefully adjusting the hydrolysis parameters the tensile strength and failure strain of the recycled fibres decrease by approximately 40–70% in comparison with virgin fibres while Young’s moduli remain similar. The relationship between the hydrolysis conditions, recovered fibres and mechanical performance was discussed in this study.

Iron nanoparticles were produced using extracts of green tea leaves (GT-Fe NPs). The materials were characterized using TEM, SEM/EDX, XPS, XRD, and FTIR techniques and were shown to contain mainly iron oxide and iron oxohydroxide. The obtained nanoparticles were then utilized as a Fenton-like catalyst for decolorization of aqueous solutions containing methylene blue (MB) and methyl orange (MO) dyes. The related experiments investigated the removal kinetics and the effect of concentration for both MB and MO. The concentrations of dyes in aqueous solution were monitored using ultraviolet–visible (UV–vis) spectroscopy. The results indicated fast removal of the dyes with the kinetic data of MB following a second order removal rate, while those of MO were closer to a first order removal rate. The loading experiments indicated almost complete removal of both dyes from water over a wide range of concentration, 10–200 mg L−1. Compared with iron nanoparticles produced by borohydride reduction, GT-Fe nanoparticles demonstrated more effective capability as a Fenton-like catalyst, both in terms of kinetics and percentage removal., Birzeit University

Nanosized zero-valent iron (nZVI) is increasingly gaining interest as an efficient sorbent for various types of aqueous pollutants. In this study, nZVI was synthesised by the borohydride reduction method, characterised and then examined for the removal of aqueous Co 2+ ions over a wide range of concentrations, from 1 to 1000 mg/L. The size of nZVI particles was predominantly within the range of 20–80 nm, and only limited oxidation was observed in samples aged for a period of 2 months. The experiments investigated the effects of V / m ratio, concentration, contact time, repetitive loading, pH and aging on the extent of retardation of Co 2+ ions. Iron nanoparticles demonstrated very rapid uptake and large capacity for the removal of Co 2+ ions. Effective uptake was observed even after a number of repetitive trials. The extent of Co 2+ uptake increased with the increasing pH. X-ray photoelectron spectroscopy (XPS) indicate that the fixation of Co 2+ ions takes place through the interaction of these ions with the oxohydroxyl groups on the iron nanoparticle surfaces in addition to spontaneous precipitate formation at high loadings.

Titanium oxide-functionalised MCM 41 materials (Ti-MCM 41) were synthesised by two different methods, namely sol–gel synthesis and post-synthetic grafting, and then TiN-functionalised MCM 41 materials (TiN-MCM 41) were prepared via ammonolysis. X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (p-XRD), CHN microanalysis and infrared (IR) spectroscopy were used for the characterisation of the materials. The changes in the surface properties of the functionalised materials were studied using nitrogen (77 K) and carbon dioxide (198 K) sorption. The p-XRD pattern confirmed that the hexagonal periodicity of the parent MCM 41 materials was maintained upon functionalisation, provided the ammonolysis temperature did not exceed 873 K. Samples ammonolysed at a temperature of 973 K showed a collapse of the hexagonal structure. CHN microanalysis data confirmed the presence of nitrogen in the ammonolysed samples, whereas, the presence of adsorbed NH 4 + and NH/NH2 species were confirmed by IR spectroscopy. The formation of TiN species was confirmed by XPS analysis. The mesoporosity of the Ti-MCM 41 and TiN-MCM 41 samples was confirmed by the Type IV isotherms observed for nitrogen sorption (77 K). Ammonolysis was found to reduce the surface area and pore volume of the materials and this was more marked in the post-synthetically grafted sample. A significant decrease in the surface area (330 m2 g−1) and pore volume (0.24 cm3 g−1), and a slight increase in the average pore diameter (23 to 26 A) suggests sintering of titanium during ammonolysis in the post-synthetically grafted TiN-MCM 41 material. The smaller values of the CO2 monolayer capacity compared with the nitrogen confirms that the sorption of CO2 is localised, i.e., on the polar surface sites of the ammonolysed samples. The lower CO2 monolayer capacity for the ammonolysed samples compared with the un-ammonolysed (parent) material suggests a decrease in the surface polarity, due to the formation of TiN.

We have synthesised 11-A tobermorite hydrothermally, both pure and with increasing isomorphic substitution of aluminium for silicon. The samples were analysed by X-ray photoelectron spectroscopy (XPS). Aluminium was found, on the basis of its Al 2p binding energies, to be tetrahedrally coordinated. We observed no changes in Ca/(Si+Al) ratio upon aluminium substitution, implying that charge balancing does not occur via the incorporation of additional calcium into the tobermorite structure. Aluminium substitution into the silicate structure led to a decrease in Si 2p binding energies. This implies one of two alternatives. Firstly, that charge balancing occurs via substitution of OH− for O2− in the tobermorite structure. Secondly, the presence of aluminium in the tobermorite structure may negatively influence the degree of silicate polymerisation. Further work is required to determine which of these possibilities is the case.

Amorphous hydrogenated carbon–sulfur thin films (a-C:H:S) were deposited from CH yH S gas mixtures by capacitively42 coupled radio-frequency PECVD. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) were used to probe the composition of the films. XPS showed that the sulfur atomic percentage within a film was proportional to the fraction of H S in the H SyCH gas mixture, and that films had been deposited with a sulfur content of up to 27 at.%. SIMS 22 4 showed that the distribution of C and S was homogeneous throughout the films. Ex situ variable angle spectroscopic ellipsometry was used to evaluate the band gap energy variation by three different methods. Values of the E04 band gap for these films were between 1.5 and 2.5 eV, with refractive index values of between 1.8 and 2.1. Laser Raman spectroscopy (514.5 nm) suggested that the addition of sulfur increases the clustering of aromatic six-membered rings. 2003 Elsevier B.V. All rights reserved.

Diamond nanocrystals have been produced by the pulsed laser ablation of graphite at room temperature and pressure in two liquids (water and cyclohexane). This suggests that the mechanism for diamond formation maybe a result of the high-pressure, high-temperature conditions found within the cavitation bubbles in the ablation plume, rather than a chemical route such as etching of non-diamond species by OH.

We have used X-ray photoelectron spectroscopy (XPS) to investigate both tricalcium silicate (Ca3SiO5, C3S) and β-dicalcium silicate (Ca2SiO4, β-C2S), the principal components of cement clinkers. In addition to showing how the two phases may be characterised and differentiated, we show how the sensitivity of these phases to atmospheric carbon dioxide and moisture may, as a result of improper sample preparation, lead to erroneous results. The observed alteration processes of the clinker minerals shed light upon the aging process of cement clinker during storage.

We have prepared a number of crystalline calcium-silicate-hydrate (C-S-H) phases hydrothermally, with calcium–silicon ratios varying from approximately 0.5 (K-phase) to 2.0 (hillebrandite and α-dicalcium silicate hydrate). The phases were then analysed using X-ray photoelectron spectroscopy (XPS). Increasing calcium–silicon ratios resulted in decreased silicon binding energies. Additionally, changes in the O 1s spectra could be explained in terms of bridging (BO) and nonbridging oxygen (NBO) moieties. Finally, the modified Auger parameter has proved particularly useful in determining the extent of silicate anion polymerisation. Of note also are the apparently unusual spectra for 11 A tobermorite. The silicon and oxygen photoelectron spectra indicate a phase with a lower degree of silicate polymerisation than predicted from its composition. The main contributing factor is the intrinsic disorder within the tobermorite structure. This study has shown how XPS may be used to obtain valuable structural information from C-S-H phases, and our analysis of the crystalline phases is the first step towards the analysis of real C-S-H-based cement systems.

Hydrogenated amorphous carbon films were deposited in an RF parallel plate plasma reactor using various values of process pressure (10–50 mTorr) and DC self-bias (0–300 V). The films were then analysed by laser Raman spectroscopy (LRS) at 514.5 nm and X-ray photoelectron spectroscopy (XPS). Values for the ratio of sp 2 :sp 3 bonded carbon in the various films were obtained by suitable fitting of the XPS carbon 1s energy peaks, using a three-curve fitting procedure, which recognises a portion of the peak attributable to CO surface bonding. The sp 3 content was found to depend upon the DC self bias (and hence the ion impact energy) during deposition, peaking at a value of 81% at approximately 150 V. The softer films grown at lower DC bias values still had an sp 3 content of approximately 70%. Microcombustion analysis showed that films deposited with low DC bias contained 7 at.% H compared to less than 2 at.% for films deposited at biases greater than 100 V. This high sp 3 content can be explained by H-termination of dangling bonds, suggesting that sp 3 content alone is not a reliable indication of film properties. Curve-fittings of LRS spectra of the films showed that the Breit–Wigner–Fano lineshape is inappropriate for use with hydrogen containing films. Fitting using a Gaussian profile gave precise values for the FWHM, intensity, and Stokes’ shift of the G and D-peaks. A linear relationship between the intensity ratio of the D to G peaks and the width of the G peak was found for films deposited at high DC bias (with low H content), but not for films deposited at low DC bias. This is consistent with the increased H content of the films causing a change in the elastic constants and/or affecting the stress levels within the films.

A detailed study has been performed of diamond-like carbon films containing high concentrations of phosphorus deposited onto a variety of substrates. These ‘amorphous carbon phosphide’ films have been grown using RF plasma CVD at varying ion impact energies by changing the DC self bias on the powered electrode. X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS) have been used to determine changes in the chemical composition and chemical bonding structure of these films. UV/visible absorption spectroscopy employing the Tauc-plot method has determined the band gap change with varying ion energies. Results show the enhancement of CP bonding ratios with deposition under high average ion energies, and also with the dramatic reduction in contaminant elements (O, H).

a Abstract Radio frequency plasma deposition has been used to deposit phosphorus doped diamond-like carbon (DLC) films on Si and quartz substrates, using a gas mixture consisting of CH with additions of 0-90% PH . XPS studies reveal that the films contain 43

A trial part through-section excavation manual metal arc repair weld, designed to minimise residual stresses was prepared using a critical combination of weld metal strength, bead size and deposition pattern. The repair was in a low alloy ferritic CrMoV steel plate, and the weldment was made using a lower strength C–Mn steel weld metal. Residual stresses have been measured to a high spatial resolution across the weldment using the X-ray diffraction technique with CrKα X-radiation. Peak tensile stresses have been identified in the heat affected zone in the parent plate adjacent to the weld metal. Further measurements have been made using the rosette strain gauge centre hole relaxation and deep hole drilling techniques. The measured residual stress profiles are discussed with respect to comparisons between techniques, the range of microstructures within the weldment and predictions of a finite element model for this particular multi-pass repair weld.

Direct visualisation of adsorbed human plasma proteins on biomaterial surfaces may help the understanding of the performance of implants. The aim of this study was the visualisation of human plasma fibrinogen (HPF) adsorbed on different titanium implants with characterised surface properties. Seven types of titanium samples were used: mechanically polished (P); mechanically ground (G); sand blasted with alumina (B); sand blasted with alumina and etched in HF/HNO3 (BN); sand blasted with alumina and etched in HCl/H2SO4 (SLA); mechanically polished and etched in HCl/H2SO4 (PSLA); and plasma sprayed (TPS). The surface morphology and roughness of these surfaces were analysed by atomic force microscopy (AFM). The surface chemical composition of the implants was analysed by X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). The seven processing methods influenced the roughness and produced distinct morphologies of the implant surfaces. The main chemical constituent of all surfaces was TiO2, with some samples showing the presence of other elements. HPF adsorbed on the titanium surfaces was visualised by AFM phase imaging. Visualisation of the adsorbed HPF was successfully achieved on samples P and G, but not on the other five samples. Differences in the dimensions and in the phase contrast of HPF molecules adsorbed on P and G surfaces were observed and discussed. No correlation between surface topography and morphology of the adsorbed proteins was observed on surfaces P and G. Possible reasons for not detecting HPF with AFM on five of the seven sample types were attributed to the surface physico-chemical properties of these samples.

Undoped CVD diamond films on Si substrates have been chemically treated in order to change the surface termination species. Treatments used include hydrodrogenation, deuteration, oxidation, hydrolysis, amination, chlorination, fluorination, and metallisation, using Na, K and Cs layers. The effect of these treatments upon field emission characteristics has been measured. In general, it is found that emission currents increase and threshold voltages decrease as the electronegativity of the surface species decreases. The best field emission properties were observed for the films with metal layers, with threshold voltages of ∼15 V/μm.

Previous studies have indicated that carbon is deposited on spinel-type oxides containing manganese, iron, nickel and chromium manganese oxides and uranium oxides, especially where rapid electron exchange is possible in mixed valence compounds. In this investigation, characterised magnetite, Fe 3 O 4 , surfaces have been subjected to γ-irradiation under conditions of temperature, pressure and atmosphere similar to those experienced in reactor with the aim of furthering our understanding of the catalytic processes involved in deposit initiation and growth. Although it was not possible to produce large (111) Fe 3 O 4 planes, enhanced carbon deposition was observed on small (111) regions showing the enhanced catalytic effect of these planes for carbon deposition out of the gas phase.

The composition of oxides formed on steel surfaces within power reactors may influence heat transfer efficiency. Previous studies have indicated that carbon is deposited on spinal-type oxides containing manganese, iron, cobalt, nickel and chromium. In this investigation, characterised manganese oxides have been subjected to γ-irradiation under conditions similar to those experienced in reactors in an effort to understand the catalytic processes involved in deposit initiation and growth. Mn3O4 and Mn2O3, under the conditions present in the γ-cell, were reduced to MnO during the time of exposure. Relative carbon deposition rates were observed to follow the trend MnO>Mn3O4≈Mn2O3.

X-ray photoelectron spectra have been recorded from a series of characterised cobalt-iron containing spinels M x Co 1− x Fe 2 O 4 where M = Mn, Fe or Ni and 0 ≤ x ≤ 1. The binding energies of photoelectron peaks observed for the transition metal ions were recorded. Changes in their relative positions were noted and the measured intensities used to determine the surface composition. The observed surface segregation of certain elements were interpreted in terms of kinetic and thermodynamic factors.