Materials Science Forum Vols. 514-516

Abstract: A characterisation technique based on the stress determination by X-ray diffraction has been developed. It enables the identification of elastoplastic stress-strain laws on materials presenting an in-depth gradient of mechanical properties on its cross section. This technique is especially suitable to the characterisation of surfaces due to the small X-rays penetration depth. The method was applied in the characterisation of a carbonitrided and shot-peened steel, allowing to evaluate the stress-strain laws of the material at the surface, the intermediate layers and the bulk material. In addition, the in-depth evolution of microhardness, residual stresses, diffraction peak broadening and retained austenite contents were analysed. This allowed to understand the results of the proposed technique.

Abstract: Petrography and X-ray diffraction techniques are used in this work to determine the mineralogical composition of a granite, a gabbro and a quartzite. The experimental difficulties and the results obtained by both methods are described and discussed. The semi-quantitative procedure of XRD analysis used in this work allows an estimate of the relative mineral phase composition of each type of rock. Petrography was found to be crucial in terms of textural analysis.

Abstract: A number of failures of large concrete structures during construction have been reported in the last decades [1]. The overestimation of concrete strength at early ages was one of the reasons for the failures. Consequently, reliable information about early age properties of the material is essential to guarantee life-time performance of structures. Portland cement is a complex heterogeneous particulate material and a full knowledge of kinetics of the hydration reactions, for example, is still missing. Gel constitutes the major phase in the hardening cement paste and the corresponding structure and dynamics represent an important contribution to determine the concrete performance. X-ray diffraction, which is widely used for the study of crystalline cement components, does not give information about the gel, amorphous, phase. Conversely, 1H stray-field magnetic resonance imaging (STRAFI-MRI) technique has proved to be a powerful tool to follow the early hydration and hardening periods of Portland cement (type I) [2-4]. The setting of cement pastes depends on parameters like the initial water/cement ratio, R, or particle size of the powder (G) and the compressive strength can be used to characterize the behaviour of hardening concrete. Water availability at the particle surfaces, which is controlled by R and G, limits cement hydration. At low R, G effects are less important. In general, it is accepted that for R<0.42, unreacted solid remain, as all the free volume is filled with hydration products [5]. For example, hydration of Portland cement pastes as a function of R (0.24-0.48) was studied using by STRAFI-MRI and hydrogen maps, from different types of water (capillary, gel or chemically bound water), enabled a spatially-resolved kinetics to be obtained [4]. Using STRAFI-MRI was now evaluated the influence of G (<70 μm to < 90 μm) on the early stages of hydration and hardening of Portland cement. Portland cement uses extend well beyond construction. For example, a mineral trioxide aggregate is now being applied as a root-end filling material, which was shown to have a similar chemical constitution to that of Portland cement except for the addition of bismuth compounds, seemingly to make the materials radiopaque for dental use [6].

Abstract: Archaeological ceramics Terra Sigillata manufactured in different production centres have been studied by “laser induced plasma spectroscopy” (LIPS). The aim of this work is to demonstrate the capability of LIPS for the classification of pottery shreds in function of their provenance. Characteristic emission spectra of different pottery groups were obtained and simple linear correlation methods were used for grouping samples. In addition, complementary scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDX) analysis were performed to obtain morphological features and to confirm chemical results

Abstract: Roman mortars from the industrial archaeological site of Tróia (Portugal) have been studied by means of chemical, mineralogical and microstructural analysis. The mortars are calcitic aerial lime mortars differing in the type and proportion of aggregates used, including crushed carbonaceous rocks (limestone and dolomite), siliceous sand and crushed ceramics. The results show that although these mortars have been subjected to a very aggressive environment they are still in a very good state of conservation.

Abstract: Portuguese ceramic tiles of different origins from XVIth century to XXth century were studied. In this work we describe microstructural, mechanical and mineralogical characterisation and water absorption studies. Microstructural features (pore size) were determined using Scanning Electron Microscope (SEM) photographs. Mechanical tests (four point bending) were performed and the bending strength was determined from the fracture loads. From water absorption essays the absorption coefficient and the total amount of water retained were obtained and the open porosity was estimated. The maximum water absorbed tends to decrease from XVIth century until XXth century, showing a more pronounced drop for the tiles of the XIXth and XXth centuries. This evolution is also observed in the open porosity values. From image analysis data we also observed that porosity decreases progressively with time and an important drop is observed for XXth century tiles. The bending resistance of tiles from XVIIth to XXth century is almost constant and higher than that of XVIth century samples. This evolution does not correlate with porosity. Advances in ceramic processing, such as higher firing temperatures may lead to the appearance of quartz as almost the only crystalline phase. We consider that an increase in the bending strength is due to a more effective vitrification and a lower porosity.

Abstract: Rare earth oxides have been widely investigated in catalysis as structured and electronic promoters to improve the activity and thermal stability of catalysts. Cerium has an important role in three-way catalysis and fluid catalytic cracking, two significant catalytic processes by their economic relevance and tonnage. Cerium and other rare earths have been studied as possible heterogeneous catalysts at selective oxidation of hydrocarbons. Cerite and monazite are minerals with high concentration of cerium element. Extraction of cerium metal using conventional leaching processes has shown low yields or high costs. The main purpose of this research work is to optimize the parameters in cerium purification stage from this mineral using leaching process. To separate particles with different granulometries, the mineral is ground and fractioned with sieves of 80, 200, 250 and 400 mesh. In order to put off organic components and oxidize cerium(III) to cerium(IV), samples were roasted at 1073K by twenty-four hours. The roasted samples were solubilized by acid attack (leaching) for approximately twenty-four hours; according to the acid used hydrochloric or sulfuric), cerium and other trivalent elements are solubilized as chloride or sulfate solution. Cerium was extracted by selective precipitation at pH~3,4 using ammonium or natrium hydroxide as pH changer. After filtration and drying, the precipitated product was characterized by XRD (x-ray diffraction), and then process efficiency was determined (cerium percentage and the different phases in the powder). Particles granulometry, roasting process (time and temperature), as well as leaching parameters (acid used, time, temperature and concentration of reagents) were the main variables studied.

Abstract: This paper presents the application of stereology methods to the description of morphological properties of nanoboehmite and its nanocomposites. Images of boemithe, fracture and cut surface of composites were obtained using high-resolution electron microscopy technique and atomic force microscopy. Quantitative analysis of the fracture structure images obtained with HRSEM technique, allowed us to explain the mechanism of changes of mechanical and thermal properties of polyurethane nanocomposites, as well as allowed to determine relationships between structure characteristics and properties of examined materials. Quantitative image analysis was also found to be useful in comparative analysis of polyurethane nanocomposites structure and structure of boehmite and products of its modification.

Abstract: This paper presents the results obtained in a series of tests on Pinus Pinaster Ait. timber specimens, using the prEN408:2000, to estimate the local and global Young’s modulus and strength both in bending and compression parallel to the grain. The results obtained are compared with the values presented in the Portuguese Nationally Determined Parameters of Eurocode 5, for the quality classes assign by Portuguese Standard NP4305:1994 by visual grading.

Abstract: In the present study, interrupted mechanical cycles are performed to observe ‘micromemory effect’ for the Ni-rich (Ni51.0at%-Ti) Ni-Ti Shape Memory Alloy (SMA) with different strain rates. In addition, the tensile test is coupled with the four-probe electrical resistivity (ER) measurements. Coupled measurements of stress-strain and electrical resistivity for mechanical cycling (with SIM) have not yet been reported in the literature. The behaviour of the alloy during the interrupted cycles is discussed on the basis of the ER profile