Leon Black

Characterisation of crystalline C-S-H phases by X-ray photoelectron spectroscopy

Abstract 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.

Preparation and photoelectron spectroscopy study of UNx thin films

Abstract Thin films of UN and U 2 N 3 were prepared by reactive DC sputtering of U in N 2 -containing atmosphere. The composition of the films was modified by varying the partial pressure of N 2 . 4f-Core-level photoelectron spectra as well as valence-band spectra obtained with HeII and HeI photoexcitation confirm the itinerant character of the 5f-electronic states in UN, showing a high density of states at the Fermi energy. The 4f peaks in U 2 N 3 are shifted towards higher binding energy and are symmetric, indicating a low density of states at the Fermi level. Valence-band spectra show indeed a maximum of 5f emission at 0.8 eV below the Fermi level, but some 5f intensity at the Fermi level is preserved, contradicting full 5f localisation.

X-ray photoelectron spectroscopy of the cement clinker phases tricalcium silicate and β-dicalcium silicate

Abstract 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.

Influence of water vapour and carbon dioxide on free lime during storage at 80 °C, studied by Raman spectroscopy

Micro-Raman spectroscopy has been used to follow the reaction of free lime (CaO) exposed for 24h to moist air at 80 °C under conditions of different relative humidities (10-80% RH). X-ray diffraction and SEM imaging were applied as complementary techniques. The conversion of lime to calcium hydroxide and its subsequent carbonation to various calcium carbonate polymorphs was found to strongly depend on the relative humidity. At low RH (10-20%), only Raman spectroscopy revealed the formation of early amorphous CaCO3 which in the XRD patterns was detected only at ≥40% RH. However, XRD analysis could identify the crystalline polymorphs formed at higher relative humidities. Thus, between 20 and 60% RH, all three CaCO3 polymorphs (calcite, aragonite and vaterite) were observed via XRD whereas at high relative humidity (80%), calcite was the predominant reaction product. The results demonstrate the usefulness of Raman spectroscopy in the study of minor cement constituents and their reaction products on air, especially of amorphous character.

In situ Raman analysis of hydrating C3A and C4AF pastes in presence and absence of sulphate

Abstract Raman spectroscopy has been used to follow the hydration of C3A and C4AF, two of the principal components of ordinary Portland cement (OPC), in the absence and presence of calcium sulphate (gypsum). Raman spectroscopy enabled in situ, real time analysis of the hydrating pastes. Analysis of the pastes by X-ray diffraction complemented the Raman data and confirmed sample composition. Subtle changes in the Raman spectra of the different pastes illuminated differences in hydration behaviour between C3A and C4AF. The similarities and differences between the various systems are discussed. The influence of carbon dioxide on the hydration products has also received attention.

Nature of Lead Patination

AbstractA study of the factors influencing lead patination is reported. Raman spectroscopy has been used to determine the composition of patinas, while weight gain measurements and scanning electron microscopy have followed their physical development. The mechanism of the pati nation process follows a route during which the initially formed oxide film converts to a basic lead carbonate (hydrocerussite, 2PbCO3 . Pb(OH)2 ), which, under the influence of sulphur dioxide, ultimately forms lead sulphate, via intermediate tetrabasic lead sulphate and lead sulphite phases. Levels of atmospheric pollution were observed to play an important role in the rate of formation of the stable end product.

Composition, silicate anion structure and morphology of calcium silicate hydrates (C-S-H) synthesised by silica-lime reaction and by controlled hydration of tricalcium silicate (C3S)

The main product of Portland cement hydration is C-S-H. Despite constituting more than half of the volume of hydrated pastes and having an important role in strength development, very little is known about the factors that determine its morphology. To investigate the relationship between the chemical composition, silicate anion structure and morphology of C-S-H, samples were synthesised via silica-lime reactions and by the hydration of C3S under controlled lime concentrations and with/without accelerators. The silicate anion structure of the samples was studied by 29Si magic angle spinning nuclear magnetic resonance spectroscopy and the morphology and chemical composition by TEM and SEM. All samples prepared via silica-lime reactions with bulk Ca/Si up to 1.5 were foil-like. The hydration of C3S at fixed lime concentration yielded foil-like C-S-H for [CaO]<22 mmol L− and fibrillar C-S-H for [CaO]>22 mmol L−1. A relationship between the silicate anion structure and the morphology of C-S-H was found for the samples fabricated with accelerators.

Interaction of water vapour with anhydrous cement minerals

Abstract Abstract The prehydration of industrial cements (CEM I 52·5 R and API Oilwell Class G) and pure cement clinker minerals (C3S, cubic C3A, orthorhombic C3A, C4AF) has been studied at 60 and 85% relative humidity using in situ X-ray diffraction (XRD), calorimetry, environmental scanning electron microscopy and X-ray photoelectron spectroscopy. This combination of techniques identifies the key components involved in the surface prehydration process. Prehydration of cement leads to dramatic retardation of hydration. in situ XRD shows the retardation of portlandite formation after prehydration, supporting the calorimetry results. X-ray photoelectron spectroscopy and ESEM investigations show surface modification after prehydration for C3S, C3A and doped C3A (4%Na2O). Prehydration of cement leads to modification of the surface area and surface charge, which can strongly influence the reactivity of bulk cements. This is relevant to the quality of cement during storage.

Quantification of Raman Spectra for the Primary Atmospheric Corrosion Products of Lead

In this study laser Raman spectra were recorded for eight lead compounds commonly reported as products from the atmospheric corrosion of lead. The spectra obtained demonstrated that this technique is well suited for the characterization of lead compounds. Moreover, when mixtures of these compounds are being studied, a good correlation can be obtained between sample composition and a characteristic Raman band intensity. This correlation should permit an estimate of the quantity of various compounds present in corrosion products.

SEM–SCA: combined SEM – Raman spectrometer for analysis of OPC clinker

Abstract Obtaining good quality Raman spectra from ordinary Portland cements is not easy, with spectra often being plagued by fluorescence. However, in this paper, the authors present Raman spectra from various points on a cross-sectioned OPC clinker nodule, and show how the different components of the clinker can be readily identified. Samples were analysed using Renishaws structural and chemical analyser (SCA), a combined scanning electron microscope (SEM) and Raman spectrometer. This technique enables topographical information, elemental composition (from EDS) and chemical information (from Raman spectroscopy) from the same spot without sample transfer. This has allowed the authors to confidently relate the Raman spectra from different points on the surface with elemental composition, therefore identifying the various component mineral phases in the clinker nodule unambiguously. The sample was also analysed by X-ray diffraction (XRD) to confirm phase composition.