A morphological and chemical classification of bronze corrosion features from an Iron Age hoard (Tintignac, France): the effect of metallurgical factors

A categorization of corrosion morphologies of archaeological Sn bronzes was carried out on archaeological Iron Age objects. The objects come from a Celtic deposit located in central France (Tintignac, Corrèze) and are dated between 2nd and 3rd cent BC. Being samples of corroded metals taken from a single find spot, parameters connected to the features of the alloy and known to influence the corrosion morphologies were thoroughly considered. Global processes were highlighted, and corrosion mechanisms were characterized with a multi-analytical protocol (SEM-EDS, micro-Raman spectroscopy, image analyses) according to the detected morphology. Elaboration of the results was carried out with a multicomponent approach. Results show the presence of 5 different morphologies correlated to the alloys characteristics of the objects. Alloy composition, microstructure, degree of deformation and grain size were found to influence the corrosion products formed and the morphology of the attack. In particular, the 'tentacle like corrosion', associated to a microbial attack was the most susceptible to the effect of metallurgical features: their occurrence is connected to a higher presence of Fe and Pb in the alloy, a homogeneous deformation and a larger grain size

Successful Experiences and Development of Key Competences in Chemistry Education: the Italian Context

As often teachers underline, textbooks are an essential tool and a good point of reference for students, but they are not sufficient to teach chemistry in a significant way. For this reason, teachers often look for sources from which to get updates on scientific knowledge, but also on teaching methodologies and on successful experiences. These considerations became even more valuable in 2012, when the New National Guidelines of the Italian school system established the framework of key competences for lifelong learning, defined by the European Parliament, as the reference horizon to work towards. The teaching for competences made essential to renew the teaching of disciplines, especially of sciences, away from the previous transmissive teaching and focusing on the action\u201d in situation\u201d of the student. The \u201dChemistry Is All Around Network\u201d project is working to help teachers to update their teaching methodology. The project portal has a database of successful experiences to teach chemistry and provides numerous digital teaching resources, some of them tested in classroom. As an example, the testing of a site dedicated to the periodic table of elements, performed involving 200 students of secondary school, is reported in the second part of this paper

Successful Experiences in Primary School Science Education

The paper deals with two successful experiences to teach basic chemistry contents at primary school. The first one is an interdisciplinary teaching proposal focused on the chemical process of dissolution and based on the laboratorial approach. It is a long and complex path, composed of several activities, starting from the first year of primary school and concluding at the fifth year. The second activity has a similar objective and the work with children starts in a motivating context: the preparation of pickled olives and fruit in syrup. Both the experiences encourage motivation linking what the teacher proposes to students\u2019 experience and daily live and are focused on an active and participatory role of students

Stability fields and structural properties of intra rare earths perovskites.

A stability study of perovskitic LaREO3 oxides (RE = Dy, Ho, Er, Tm, Yb, Lu) as a function of temperature was undertaken. A correlation between the Goldschmidt t value and the perovskitic stability field amplitude was found: the latter widens as t increases. Magnetic measurements, performed on all the perovskitic samples, showed that t is also related to the exchange interactions. LaREO3 oxides were synthesized by thermal decomposition of the corresponding coprecipitated oxalates at temperatures ranging between 600 and 1800 \u25e6C. Simultaneous differential thermal and thermogravimetric analyses showed that all the La\u2013RE mixed oxalates decompose similarly. All the oxides, except LaDyO3, crystallize in the perovskitic form in a temperature range that depends on the ionic size difference between La and the smaller rare earth; above and below the perovskitic stability field, the B or C form, typical of rare earth sesquioxides, is present. Rietveld refinements, carried out on all the LaREO3 samples synthesized at 1200 \u25e6C, showed the occurrence of an orthorhombic distorted perovskitic structure belonging to the Pnma space group

ICP-AES and microRaman corrosion behaviour investigation on Pb, Sb, Bi tellurides in sodium chloride solution

Tellurides are in years considered among the best intermetallic compounds for thermoelectric applications in the low-intermediate- temperature range. The corrosion behaviour of pure Pb, Sb and Bi tellurides is investigated in this work through a spectroscopic approach. The samples are synthesized using a muffle furnace and then placed in 0.1 M NaCl aerated solution at room temperature for 48 days. All samples are characterized, prior to and after immersion, in terms of crystal structure, morphology and phases composition (SEM-EDXS, XRD). A study of the ionic release, using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) analysis, is also carried out. Furthermore, a microRaman spectroscopy study is performed on surface corrosion products. The preliminary results reveal that PbTe and Bi2Te3 show the best corrosion resistances in the considered environment

Thermal properties of the magnetic RuSr2GdCu2O8 superconductor

A thermal study was performed on the RuSr2GdCu2O8 (Ru-1212) magnetic superconductor phase to investigate the effect of the annealingtreatments in flowing O2 on the stability limit of the phase and on its structural, magnetic and transport properties. DTA-TG measurements were utilized to determine the decomposition process and the dependence of the decomposition temperatureon the annealing atmosphere. The decomposition of the Ru-1212 phase was found sensitive to the oxygen partial pressure and increases with PO2 and the annealingtime. The annealing treatments exert a depressing effect on the strength of the magnetic interaction, an enhancement on the superconductiveproperties and the vanishing of the magnetostriction.A decomposition reaction of Ru-1212 phase was proposed and discussed

Search for new superconducting oxides in M4Pn2O phases (M=Ca, Sr, Ba and Pn= As, Sb, Bi)

All the high-Tc oxide superconducors known to date are copper-based oxides (cuprates) in the layered perovskite crystalstructures that contain a planar network of copper and oxygen (CuO2 plane). In searching for possible new superconducting metaloxides without Cu ions, we have examined the layered tetragonalpnictides M4Pn2O (M\ubc Ca, Sr, Ba and Pn \ubc As, Sb, Bi) because their structures are considered as an anti-perovskite with alternate stacking of two kinds of layers; conducting M2Pn2 block layers sandwiched by insulating perovskite-based M2O layers. Compounds were prepared by melting stoichiometric amounts of the components in tantalum tube all sealed under an argon atmosphere. The samples have been characterised by scanning electron microscopy, powder X-ray diffraction (XRD), metallographic examination and electrical resistivity. For these stoichiometric compounds no superconductive transition is observed

Evaluation of the Defect Cluster Content in Singly and Doubly Doped Ceria through In Situ High-Pressure X-ray Diffraction

none5Defect aggregates in doped ceria play a crucial role in blocking the movement of oxygen vacancies and hence in reducing ionic conductivity. Nevertheless, evaluation of their amount and the correlation between domain size and transport properties is still an open issue. Data derived from a high-pressure X-ray diffraction investigation performed on the Ce1-x(Nd0.74Tm0.26)(x)O2- x/2 system are employed to develop a novel approach aimed at evaluating the defect aggregate content; the results are critically discussed in comparison to the ones previously obtained from Sm- and Lu-doped ceria. Defect clusters are present even at the lowest considered value, and their content increases with increasing x and decreasing rare earth ion (RE3+) size; their amount, distribution, and spatial correlation can be interpreted as a complex interplay between the defects' binding energy, nucleation rate, and growth rate. The synoptic analysis of data derived from all of the considered systems also suggests that the detection limit of the defects by X-ray diffraction is correlated to the defect size rather than to their amount, and that the vacancies' flow through the lattice is hindered by defects irrespective of their size and association degree.openArtini, Cristina; Massardo, Sara; Carnasciali, Maria Maddalena; Joseph, Boby; Pani, MarcellaArtini, Cristina; Massardo, Sara; Carnasciali, Maria Maddalena; Joseph, Boby; Pani, Marcell