J. Castaing

The plastic deformation of silicon between 300°C and 600°C

Abstract Constant strain-rate compression of silicon single crystals has been performed under a hydrostatic pressure of 1500 MPa. The crystals were deformed at temperatures as low as 300°C and had resolved flow stress values of up to 1000 MPa. The variation of yield strength with temperature suggests a transition of the mechanism controlling the deformation near 600°C.

Stacking fault energy in sapphire (α-Al203)

Abstract Stacking faults associated with climb-dissociated basal and prism plane dislocations in sapphire (α-Al2O3) after plastic deformation at elevated temperatures have been studied. In both cases, the fault vector is 1 3 〈1010〉 and it is only the cation sublattice which is faulted. The fault energy on and planes are similar, between 0.1 and 0.25 J/m2. Analysis of the geometry of the 1 3 〈1010〉 fault show that one vacancy and two distinct interstitial faults are possible in this structure; one of the interstitial faults is thought to have the lowest energy.

Characterization of illuminated manuscripts by laboratory-made portable XRD and micro-XRD systems

Illuminated Arabic manuscripts have been studied, employing two laboratory-made X-ray diffraction (XRD) systems developed recently in the C2RMF laboratory. The validity of the µ-XRD and XRD portable systems for the study of this type of artworks has been demonstrated. A common observation in all the analyses is the presence of calcite and rutile; also, hematite, goethite, cinnabar, brass, anatase and barite were detected in the various colours. Differences between the results obtained by both techniques due to acquisition mode are discussed. In addition, other techniques such as X-ray fluorescence (XRF) and micro-Raman were used for the complete characterization of the manuscripts.

Point defects and high-temperature creep of non-stoichiometric NaCl-type oxide single crystals I. NiO

Abstract Creep of NiO single crystals has been investigated by compression along 〈100〉 in the temperature range 0·6T m to 0·8T m, for stresses from 25 to 120 MPa and oxygen partial pressures pO2 from 10−5 to 0·2 atm. The data are analysed using the equation for recovery-controlled creep. The stress exponent decreases from a value of 12 to low temperature to 7 at high temperature; the activation energy is in the range 5·4 to 8·5 eV and the pO2 exponent varies from 0 to -0·17. The rate-controlling mechanism exhibits a change at, about 0·7T m which can be interpreted in two different ways. Oxygen diffusion plays a dominant role in the rate-controlling mechanism of creep, and occurs via a vacancy mechanism.

Work hardening and recovery in sapphire (α-Al2O3) undergoing prism plane deformation

Abstract Deformation of sapphire (α-Al23) by slip on the prism planes has been studied in compression. The operative slip system is {1120}〈1100〉 but the large 〈1100〉 dislocations readily decompose into two 1 3 〈2110〉 basal dislocations, especially at high strains. Deformation occurs in three stages—Stage I where the work hardening is low after yielding, Stage II where the work hardening rate is high ( θ ∼ μ 40 ), and Stage III where the work hardening rate decreases and leads to a plateau region. The high work hardening rate is explained in terms of the rapid formation of a forest of basal dislocations which is produced by decomposition of the prism dislocations and hinders further glide on the prism plane. The plateau region is characterized by a balance between this increase in the dislocation density and its decrease due to annihilation in the network by diffusive climb. This recovery process has been modeled by considering the network as a system of linked loops which coarsen either by bulk or pipe diffusion; the latter process is the more probable.

Slip systems and plastic anisotropy in CaF2

An examination was made of the slip planes activated in high-purity CaF2 single crystals with various orientations deformed by compression between 20 °C and 600 °C. It was found that 110 was the most difficult and 100 the easiest to activate. These results are compared to results for UO2 and zirconia.

Deformation mechanisms for high-temperature creep of high yttria content stabilized zirconia single crystals

Abstract Creep of 21 mol.% yttria-stabilized zirconia single crystals has been studied between 1400 and 1800°C. The creep parameters have been determined indicating a change of the controlling mechanism around 1500°C. At higher temperatures recovery creep is found to be the rate controlling mechanism, with a stress exponent ≌ 3 and an activation energy ≌ 6 eV. Transition to glide controlled creep occurs below 1500°C, associated with larger stress exponents (≌ 5) and activation energies (≌ 8.5 eV). TEM observations of the dislocation microstructure confirm this transition. The influence of the high yttria content, which is at the origin of the high creep resistance of these crystals, is discussed for each range of temperatures.

Dislocations and the mechanical properties of stabilized ZrO2

Abstract The dislocation substructures and mechanical properties of cubic ZrO2 single crystals are analyzed. The temperature dependence of the dislocation velocity is complex, the edge segments moving faster than screw segments at low temperatures, while the screws are faster at high temperatures. Using the loop shrinkage technique, the diffusion coefficient of the slowest diffusing species can be determined. The mechanical properties are analyzed in terms of the Peierls mechanism and of interaction of dislocations and point defects.

XRF, μ-XRD and μ-spectroscopic techniques for revealing the composition and structure of paint layers on polychrome sculptures after multiple restorations.

This paper presents the novel application of recently developed analytical techniques to the study of paint layers on sculptures that have been restored/repainted several times across centuries. Analyses were performed using portable XRF, μ-XRD and μ-Raman instruments. Other techniques, such as optical microscopy, SEM-EDX and μ-FTIR, were also used. Pigments and other materials including vermilion, minium, red lac, ivory black, lead white, barium white, zinc white (zincite), titanium white (rutile and anatase), lithopone, gold and brass were detected. Pigments from both ancient and modern times were found due to the different restorations/repaintings carried out. μ-Raman was very useful to characterise some pigments that were difficult to determine by μ-XRD. In some cases, pigments identification was only possible by combining results from the different analytical techniques used in this work. This work is the first article devoted to the study of sculpture cross-section samples using laboratory-made μ-XRD systems.

Material analyses of ‘Christ with singing and music-making Angels’, a late 15th-C panel painting attributed to Hans Memling and assistants: Part I. non-invasive in situ investigations

In cultural heritage science, compositional data is traditionally obtained from works of art through the analysis of samples by means of various bench-top instruments (scanning electron microscope, Raman spectrometer, etc.). Alternatively, the object can be transported to a laboratory where it may be examined, usually by spectroscopic methods working in reflection mode. However, this paper describes how a complementary set of mobile and portable instruments was deployed in situ to gain a comprehensive view on the materials and related ageing compounds of an (almost) unmovable 15th-C polyptych, prior to and in preparation of the extraction of a limited number of samples. In line with the methodological approach discussed, PXRF was first employed as an efficient screening tool. The ensuing elemental data was supplemented by more specific information on both organic as inorganic materials supplied by reflection near- and mid-FTIR spectroscopy and fluorimetry. In completion, a limited number of diffraction patterns were collected with a mobile XRD instrument in order to identify the constituent crystalline phases in pigments, grounding materials and degradation products. In this way, it could be demonstrated how a rich array of colours was obtained by means of a limited palette of pigments: lead white, lead tin yellow, azurite, natural ultramarine, bone black, vermillion, madder lake, and a green copper-organo complex were detected and situated on the panels. Remarkably, next to chalk also gypsum was found in the ground layer(s) of this Western European easel painting. The relatively large surface of the background was covered with gold leaf; the analyses seem to point towards the labour-intensive water gilding technique. The versatility of this combination of analytical techniques was further illustrated by the accurate characterisation of degradation products affecting the readability and conservation of the painting: the overall presence of a calcium oxalate-based film of variable thickness was established. Nevertheless, further analysis of cross-sectioned samples was considered desirable in order to study the stratigraphy, to gain direct access to altered and sub-imposed layers and to allow highly detailed analysis of micrometric degradation products by state-of-the art techniques (i.e. synchrotron radiation).