M. C. Jiménez de Haro

Effect of pollution on polychromed ceramic statues

Abstract Pigments of different colours used to polychrome ceramic statues have been characterized using different experimental techniques. The pigments detected in the painting layers belong to the group of natural minerals widely used in antique paintings. The polluted air and the composition of dust and crust on the ceramic surface have been analysed. Environmental pollution has altered the surface of the ceramic sculptures, destroying the polychrome, so that only small parts covered by crust or dust remain. The environment is responsible for transformation of the chemical components of the pigments. The lead compounds minium and hydrocerussite are altered to anglesite, cerussite, hydrocerussite and lead sulphide. Azurite, forming some blue colour, is hydrated to malachite which is green.Atacamite is formed by the transformation of azurite in the presence of the chloride ion from environmental pollution. The environment supplies a variety of organic compounds—mainly alkanes (produced by petrol combustion)—which are responsible for the black coating on the polychrome., which serves as nutrition for microbiological growth.

Combined x-ray photoelectron spectroscopy and scanning electron microscopy studies of the LiBH4–MgH2 reactive hydride composite with and without a Ti-based additive

A detailed electronic and microstructural characterization is reported for the LiBH4–MgH2 reactive hydride composite system with and without titanium isopropoxide as additive. Surface characterization by x-ray photoelectron spectroscopy combined to a morphological study by scanning electron microscopy as well as elemental map composition analysis by energy dispersive x-ray emission are presented in this paper for the first time for all sorption steps. Although sorption reactions are not complete at the surface due to the unavoidable superficial oxidation, it has been shown that the presence of the additive is favoring the heterogeneous nucleation of the MgB2 phase. Ti-based phases appear in all the samples for the three sorption steps well dispersed and uniformly distributed in the material. Li-based phases are highly dispersed at the surface while the Mg-based ones appear, either partially covered by the Li-based phases, or forming bigger grains. Ball milling is promoting mixing of phases and a good disp...

Study of the gilding technique used in polychromed stones and ceramics by dedicated laboratory-made micro X-ray diffraction and complementary techniques.

This work describes the use of a new dedicated laboratory-made micro X-ray diffraction system for detecting the phases present in cross-sections of artworks. As an example, the phases present in samples from gilding ceramics and stone sculptures from the heritage of Seville (Spain) were successfully detected using this new system, which takes advantage of various devices developed for synchrotron radiation, and is complemented by the information provided by other techniques.

Non-destructive analysis of cultural heritage artefacts from Andalusia, Spain, by X-ray diffraction with Göbel mirrors

The characterization of the phases present in artefacts has been normally carried out using XRD (Bragg-Brentano geometry) that requires sampling from artworks, being a destructive technique. However, X-ray diffraction with Göbel mirrors permits directly to study rough artefacts without sampling. Grazing incidence attachments can be used to characterize as much the superficial layer as the underlying ones in flat samples to obtain information about the depth profile of some samples. The combination of Göbel mirrors and measure at low fixed incidence angles allow to obtain information about the depth profile of bent samples. This work reports the alteration processes on the surface of the following cultural heritage artefacts: a rivet and a nail extracted from Pardon Gateway, located in the North façade of Mosque-Cathedral of Cordoba; a Roman arrow and a button from a Roman jacket obtained from an excavation in Baena (Cordoba); organ pipe from Cathedral of Zaragoza; lead seals from Seville City Hall collection. The main objective of this paper is the study through a totally non-destructive analytical method, X-ray diffraction with Göbel mirrors, of the superficial alteration of some metallic artefacts from cultural heritage. This knowledge allows us the election of appropriate methods to carry out the restoration of these artefacts.

Study of hydration of two cements of different strengths

Main hydration products of two cement pastes, i.e. CSH-gel, portlandite (P) (and specific surface S) were studied by static heating, and by SEM, TEM and XRD, as a function of cement strength (C-33 and C-43) hydration time (th) and subsequent hydration in water vapour.Total change in mass on hydration and air drying, ΔMo, increased with strength of cement paste and with hydration time. Content of water escaping at 110 to 220°C, defined as water bound with low energy, mainly interlayer and hydrate water, was independent on cement strength but its content increased with (th). Content of chemically bound (zeolitic) water in CSH-gel, escaping at 220-400°C, was slightly dependent on strength and increased with (th). It was possibly derived from the dehydroxylation of CSH-gel and AFm phase. Portlandite water, escaping at 400-500°C, was independent on cement strength and was higher on longer hydration. Large P crystals were formed in the weaker cement paste C-33. Smaller crystals were formed in C-43 but they increased with (th). Carbonate formated on contact with air (calcite, vaterite and aragonite), decomposed in cement at 600-700oC. It was high in pastes C-33(1 month) and C-43(1 month), i.e. 5.7 and 3.3%, respectively; it was less than 1% after 6 hydration months (low sensitivity to carbonation) in agreement with the XRD study showing carbonates in the air dry paste (1month), and its absence on prolonged hydration (6 months) and on acetone treatment. Water vapour treatment of (6 months) pastes or wetting-drying increased this sensitivity.Nanosized P-crystals, detected by TEM, could contribute to the cement strength; carbonate was observed on the rims of gel clusters.

Effect of Na+ and NH 4+ Cations on Microstructure Changes of Natural Vermiculite During Heat Treatment

AbstractEmanation thermal analysis (ETA), DTA, SEM, and XRD were applied for the characterization of the effect of Na+ and NH 4+ ions used for saturation of natural Mg-vermiculite on the microstructure during heating. The microstructure changes were characterized by ETA under in situ conditions of samples heating in air in the temperature range 20–1300°C. It was found that Na+ and NH 4+ ions have a significant effect on the microstructure changes during heat treatment of the natural Mg-vermiculite sample saturated with these ions. For Mg-vermiculite and Na+ saturated vermiculite thet emperatures of the onset of the collapse of interlaminar space were determined by ETA. Differences in thermal stability of the microstructure of dehydrated vermiculite samples were observed by ETA: the microstructure of dehydrated Mg-vermiculite, and Na-vermiculite was found stable until 650 and 350°C, respectively. For dehydrated NH4-vermiculite the annealing of the microstructure started at 730°C. The onset temperatures of the formation of new crystalline phases were indicated by ETA as the increase of the radon release rate. The onset temperatures of the ordering of the vermiculite structure or sintering under presence of the glassy stage (for Na-vermiculite), respectively, were determined from the decrease of the radon release rate. The ETA results were confirmed by DTA, XRD and SEM.

Characterization of decayed ceramic sculptures decorating the Pardon portico of Seville cathedral, Spain

The decay of the ceramic sculptures decorating the Pardon portico of Seville cathedral has been studied. The material of the corbels and canopies is alabaster. The presence of dolomite in some black veins initiates the high erosion of the material. The ceramics of the different sculptures show two groups of mineralogical composition: (a) quartz, gehlenite and wollastonite, and (b) illite, calcite and feldspars. The differences in colour of the sculptures are attributed to the firing temperature. The environment, the repair and fixing materials added to the sculptures, and interactions between the ceramic materials and the environment are responsible for the decay.

THE INFLUENCE OF EXCHANGEABLE CATION ON THERMAL BEHAVIOUR OF GROUND VERMICULITE

Grinding and contact with water or salt solution increased the specific surface (ssa) but lowered the first dehydration effect (escaping up to 150°C) and increased the second dehydration effect (150 to 500°C). The dehydroxylation was moved to lower temperatures and was only ΔM(500-1100°C)=3.7±0.3 % as compared to 5.5% in the parent vermiculite (V). Except ΔM(20-150°C), the mass losses measured at the remaining T ranges, were consistent in the ground samples, thus the grinding for 2 min caused the homogenization of the crystal structure of vermiculite [ΔM(150-500°C)=7.6±0.7%]. DTA curves after grinding and cation exchange indicate an important exothermal peak at 795-870°C, its temperature depending on exchangeable cation. It indicates the formation of high temperature phases (enstatite, forsterite, spinel). The lowest temperature of the peak (795°C) was observed in V-gr-Li, here lithium silicate was formed. The highest peak temperature (870°C) was found in V-gr-K, where almost only forsterite developed. These exothermal peaks were very weak in unground V with various exchangeable cations.

AMMONIA RELEASE ON HEATING OF MECHANICALLY TREATED VERMICULITE SATURATED SUBSEQUENTLY WITH AMMONIUM

The differences in thermal behaviour of vermiculite before and after mechanical treatment (sonication and grinding), saturated subsequently with ammonium, were studied by TG, DTA, EGA and IR techniques. Sonication produces only a small modification in the NH4+vermiculite decomposition attributed to a small particle size. Grinding causes an important but different change in the thermal behaviour of NH4-vermiculite. The temperature of ammonium loss is lowered stepwise showing that grinding modifies the bonding energy between and the surface of vermiculite.

Monolithic supports based on biomorphic SiC for the catalytic combustion of hydrogen

Catalytic hydrogen combustion was studied with H2/air mixtures in conditions that simulate the H2 concentration of the exhaust gases from fuel cells (3–4% v/v H2 in air). Pt-impregnated monoliths based on porous biomorphic SiC (bio-SiC) substrates were employed for the first time for this reaction. Capillary forces were exploited for the incipient impregnation of supports with H2PtCl6 solutions. Freeze drying permitted us to obtain a homogeneous distribution of the active phase reducing accumulation at the monoliths outer shell. The supports and catalysts were characterized from a structural and thermal point of view. Catalytic tests were performed in a homemade reactor fed with up to 1000 ml min−1 H2/air mixtures and a diffusional regime (non-isothermal) was achieved in the selected conditions. Catalyst loading was tested in the range of 0.25–1.5 wt% Pt and 100% conversion was achieved in all cases. Temperatures were recorded at different points of the monoliths during the reaction showing anisotropic thermal behavior for selected bio-SiC substrates. These effects are of interest for heat management applications and were explained in correlation with thermal conductivity measurements performed on the supports. Pt-impregnated monoliths were also tested in less than 100% conversion conditions (1% v/v H2 in air) and in powder form in kinetic conditions for comparative purposes.