Defect and Diffusion Forum Vol. 365

Abstract: In this study, we present a boronizing treatment on a steel microalloy that was performed according to dehydrated paste-pack boriding. The temperatures conducted were at 1173, 1223 and 1273 K; at various exposure times of 1, 3, 6 and 9 h. As a result of the boriding process, diffusion-controlled growth of the FeB/Fe₂B layers was obtained at the surface of the micro-alloy steel, and the kinetics of the growth process changed parabolically over time. The results of these examination properties of the boride layer as revealed by Optical Microscopy (OP) showed the morphology of the boride layer as a saw-tooth with a thickness ranging from 33 μm to 220 μm depending on the boronizing time. The analysis of Scanning Electron Microscopy (SEM-EDS); showed a distribution of the alloying elements that were detected by Energy Dispersive Spectrometry. The X-ray diffraction (XRD) technique indicated that the surface was a mixture of FeB and Fe₂B borides. The evaluation of adhesion of the layers was determined by the technique of Rockwell-C hardness. Young’s modulus and hardness of the layer were evaluated by a nanoindentation technique with a load of 250 mN. The paste dehydrate boriding of micro-alloy reveal a change of properties on the surface; also the coatings FeB and Fe₂B, to make a sacrificial function in the steels micro alloyed as widely used in pipelines transporting oil.

Abstract: Many physical effects, such as dc conductivity and percolation, depend on the morphology of the silicate structure and its relationship to adsorbed water. These effects play an important role in numerous technological applications, in geology, oil-extracting industry, and other practical fields. In this study, all the samples: natural montmorillonite, kaolinite, and сlinoptilolite with different exchangeable cations in their structures, – were stored in ambient air humidity. The investigation was carried by using two separate techniques, namely Dielectric Spectroscopy and a fractal analysis of electron micrographs. The aims of this work were to analyze the complex relaxation behavior of the relaxation process in temperature range –70°C ÷ +70°C and to determine the fractal dimensions of silicates from the dielectric response at percolation. Dielectric measurements in the frequency range of 1 Hz ÷ 1 MHz were performed using a BDS 80 Dielectric Spectrometer based on an Alpha Impedance Analyzer (Novocontrol). The micrographs were analyzed using a special Matlab based program. The analysis of aspects of the dielectric relaxation spectra related to percolation was used for the determination of the numerical characteristics of geometric heterogeneity of natural silicates. The percolation temperatures of the studied samples were determined. The percolation phenomenon in the silicates is related to the transfer of the electric excitation within the developed network of open pores due to the migration of protons and ions along the surface of connected pores on the outer surfaces of the granules. The analysis of these processes allows one to extract the fractal dimensions associated with the migration of charge carriers within the porous medium. Fractal dimensions of the silicates calculated in two ways: from dielectric spectroscopy study and from fractal analysis of the micrographs, – are in good agreement with each other. It was demonstrated that conventional method of the spatial fractal dimension determination using fractal analysis of electron micrographs leads to overestimation in the case of spatial fractal bounded by a surface fractal. The dielectric spectroscopy method is free from such overestimation.

Abstract: The objective of this paper is to present an experimental study that aimed to establish correlations between primary dendrite spacing (λ₁) and microhardness of a ternary Al-6wt%Cu-8wt%Si alloy solidified under transient heat extraction, using a horizontal unidirectional water-cooled solidification device. To examine the microstructural evolution, solidification thermal parameters (growth rate and cooling rate - V_L and T_R, respectively) were calculated through the application of an experimental method and were then correlated with λ₁ using analytical power functions laws. The correlation between microstructural parameters and the measured microhardness values are presented in the forms of power and Hall-Petch types of equations. The analysis of the microstructure of the investigated alloy indicated that the increasing of T_R and V_L reduced the primary dendrite arm spacing, increasing the microhardness.

Abstract: The present study reports the growth of layers formed in the surface of the boride steel AISI W2; by the application of the dehydrated paste-pack boriding process and using three different temperatures at 1173, 1223 and 1273 K, with 2, 4, 6 and 8 h of exposure. The substrate and the boride Fe₂B were analysed quantitatively and qualitatively. The growth of the boride layer Fe₂B was examined using optical microscopy (OM), scanning electron microscopy (SEM-EDS) and X-ray diffraction (XRD). The properties were mechanically evaluated, using a Vickers indenter with loads of 0.5 and 1 N, with a constant distance of 15 μm and 30 μm. To determine the fracture toughness (Kc) and the adherence of the boride layer Fe₂B, the Rockwell C test method (VDI 3198) was used. The morphology present in the boride Fe₂B layer showed a smooth flat, whit ranged thickness from 13.96 ± 1.61 μm to 79.86 ± 4.13 μm. The presence of boride Fe₂B layers of steel substrate was confirmed by XRD and the distribution of alloying elements by Energy Disperses for Spectroscopy (EDS). The hardness of the boride layers Fe₂B ranged from 157 9± 17 to 1875 ± 25 HV. The fracture toughness of boride Fe₂B layer observed ranged from 4.15 to 4.75 MPam^1/2. The boride layer has a scale delamination H3 to H6. The boride layers formed in the surface have the function to increase the service life of W2 steels used in the industry.

Abstract: It is known that the diffusion of boron atoms on the surface of metals and alloys can increase the hardness, wear and corrosion resistance of engineering components. Boriding is an alternative method of sample treatment when the manual work required in powder boriding needs to be decreased. In addition, its advantage lies in high volumes of work and in selective treatments. Boron carbide consists of B₄C (approximately 76 wt% boron). Using gases or powders as boronizing process gives rise to boride coatings constituted by an inner layer of Fe₂B (hardness 15GPa) and an outer layer of FeB (hardness 25 GPa) [1,2]. Many industrial processes require the use of highly wear-resistant materials, tools steel, hot work being these basic Cr steels in applications such as extrusion dies for light alloys, matrices for pressing, forging dies and for molding plastic.

Abstract: This work describes the implementation of two higroregulated wall base ventilation systems in a church in the North of Portugal for the treatment of rising damp and presents the results of four years of the systems monitoring. It is a work developed by LFC – Laboratory of Building Physics of FEUP, where the main goal is to validate and optimize this treatment technique. It was assessed the functioning and effectiveness of the implemented systems, minimizing the likelihood of condensation inside them and maximizing the drying process through the adoption of higroregulated systems. With the monitoring carried out it is possible to conclude that, for the analyzed climate, it is better to adopt a seasonal operation, where the air is admitted from the exterior, during the warm months, and in the cold months the air is admitted from the interior of the Church.

Abstract: One of the main causes of older and heritage buildings degradation is moisture, in particular the rising damp from the ground. The construction materials which are in contact with water or moist soil are subject to capillarity, which is defined as the phenomenon of a liquid rising through the capillaries of a solid, leading to the emergence of several pathologies.The height of progression of the moist front depends on the climatic conditions of the ambiences, the isolation, the wall thickness, the porosity and porometry of the materials, the presence of salts and the nature of the coating materials.The objective was the study of the interface between layers through the introduction, in the automatic calculation program WUFI-2D, of fictitious layers between the layers of brick and mortar. The fictitious layers correspond to the part of the brick that above and below the joint receives the mortar, and for this reason they are small layers whose thickness and properties are unknown and are intended to be characterized. Through simulations on the WUFI-2D program and using lab results will be possible to reach a function that relates the thickness and the properties of the fictitious layers.

Abstract: The principles and tools for the development of a stochastic data base that can be useful for researchers and practitioners is an objective of this work. This paper explores the construction of that data base, focusing on material properties. Principles for that construction are proposed, including: selected properties, required raw data and deliverable format. These principles are derived from possible applications of the data base and available tools for data analysis. The selection of statistics tools that can be used in the construction of a material data base is addressed. The definition of the statistic distribution for selected properties was pursued. Available raw data was analysed resulting in conclusions on difficulties and opportunities that arise from that.

Abstract: Wood has a strong hygroscopic behaviour, with a strong variation of moisture content and dimension stability caused by modifications of the relative humidity of the surrounding air. The properties that define the behaviour of wood facing temperature and moisture actions were studied in this work. Linear thermal expansion, hygroscopicity, shrinkage (tangential and radial shrinkage coefficient) and hygric expansion were given special attention.An experimental device was designed for testing wood samples, red oak. A series of tests was performed including the determination of hygric expansion coefficient and the definition of the sorption curve. This research made possible the evaluation of dimensional stability of wood in transient conditions of relative humidity.

Abstract: The present work investigates the hydrogenation of CO₂ to methanol via a promoted Cu/ZnO/SBA-15 catalyst. In order to understand the effect of Mn, Zr and Pb promoters on the catalytic activity of Cu/Zn/SBA-15 catalysts, the hydrogenation of CO₂ was performed in a stirred high-pressure reactor at 483K, 22.5bar, and a H₂/CO₂ ration of 3. The physicochemical properties of the catalysts were studied using N₂ physical adsorption, TEM and H₂-TPR. The characteristics of catalysts depended on the type of promoter and it influenced their catalytic performance. The Mn and Zr promoters resulted in a larger surface area of the catalyst and improved catalytic activity and methanol selectivity. However, an opposite effect was found for the Pb promoter. A 10% improvement on the CO₂ conversion and 20% on the methanol selectivity was achieved due to the double promotion effect of Mn and Zr on Cu/ZnO-SBA-15 catalyst.