Defect and Diffusion Forum Vol. 353

Abstract: Random walk is the central concept in the mathematical formalization of the diffusion coefficient and so when asked a year ago to present a talk at a diffusion conference it appeared to be a totally appropriate topic. I spent most of my career studying diffusion and even after twenty years in retirement I believed I could write an interesting story about the importance of random walk to diffusion. Unfortunately when I sat down to write I discovered two problems: in the majority of materials that I investigated atoms did follow a random walk; and the history of random walk has been well documented and shows little connection to diffusion. The phrase was coined in 1905 at a time of rapid changes in physics. Scientists are not accustomed to writing history and as Henry Ford said around the same period of time “History is bunk”. He also remarked, "You can have any color (car) as long as it's black". This essay presents my story (not his- or her- tory) of why the use of the phrase random walk in discussions of diffusion in solids is also bunk.

Abstract: Laser weldability was investigated for advanced high-strength steel sheets for automotive applications. Dual-phase steel (DP780) and martensitic steel (MS1300) sheets were employed as base materials; laser-butt and overlap welding experiments were conducted on combinations of steels with similar and dissimilar strength. The tensile strength and metallurgical morphology were analysed for the butt-welded specimens; tensile-shear strength and bead shapes were analysed for the overlap-welded specimens. Even with laser welding, martensite in the heat-affected zone disintegrated and resulted in a softened, heat-affected zone as compared with the base materials. The tensile strength of a butt weldment was determined by the strength of the heat-affected zone. The tensile-shear strength of an overlap weldment was determined by not only the strength of the heat-affected zone but also bead shapes such as blow holes, underfill, and the bead width at the faying surface.

Abstract: In this paper, we present some distinguished methods of the digital thermograms software treatment which allows the visualization of hidden defects in glass fabric laminates, which are not usually visible in standard raw thermograms. The results of the software treatment are tested on artificial defects in glass laminate plates.

Abstract: Non-destructive techniques are essential to detect common pathologies and analyse the building behaviour. Infrared thermography is a testing technology that has been applied to buildings diagnosis for some decades. However, there are still some applications which are not yet completely explored like the detection of micro-cracks on façade coating materials.

Abstract: Infrared thermography is a non destructive testing technology that has been applied to detect buildings pathologies for some decades. The thermograms are affected by several parameters and it is crucial to fully understand them in order to correctly interpret the temperature readings. The infrared radiation is affected by the radiation emitted by the surface and the radiation reflected and emitted by the surroundings. Therefore there are two kinds of parameters that affect the infrared images: parameters connected to the properties of the material itself and parameters connected with the environmental conditions. In this paper we present a sensibility study of the main parameters involved with infrared thermography evaluations to detect building pathologies. To do so, some simple experiments were carried out at the Building Physics Laboratory (LFC) of the Engineering Faculty of Porto University (FEUP). The sensibility study was performed with LFC’s equipment to evaluate how measurements are influenced by emissivity, reflections, absorptance and the meteorological conditions.

Abstract: To meet the high demands of customers for low temperature boilers, a semi-automatic boiler MAGA PU 25 was developed. One of the main customer requirements is to get the best price-quality ratio. Another very important requirement is to meet emission standards. At the time of development of the boiler PU 25, the European standard STN EN 303-5 was valid in Slovakia. Because this boiler did not satisfy the strictest performance criteria, a new type of the boiler, i.e. boiler MAGA P 20, was designed; as a result of design modifications, this boiler fulfils these criteria. The article compares the designs and the results of testing both the boilers using a test fuel in an accredited laboratory. The article deals with testing a new biomass boiler developed to satisfy the highest safety and emission criteria. It presents the comparison of two boilers, namely the standard biomass boiler PU 20 and the latest P 20 version with specific design modifications. Laboratory tests have shown an increase in combustion efficiency to the desired level.

Abstract: Chromium (VI) is known to be carcinogenic to humans and thus it is important to ensure the removal of Chromium (VI) from aqueous solutions and industrial effluents. The present study introduces a good alternative method for Cr (VI) removal from aqueous solutions at ambient temperature by adsorption, allowing the development of newer, lower operational cost, and more efficient technology than other processes already in use. Adsorption was found to be dependent on pH and initial concentration of Cr (VI) solution. Results of adsorption studies suggest that pristine iron oxide and silicon (IV) oxide removes 72.10% and 24.73%, respectively. The iron oxide – silicon (IV) oxide composite, prepared in this work, removes 93.88% Cr (VI) in 20 minutes from aqueous solution at an initial concentration of 50 mgL^-1 at pH 4.8 ± 0.2. The effect of concentration, contact time, adsorbent dose and solution pH on the adsorption of Cr (VI) were studied in detail in batch experiments. Studies of the sorption kinetics shows that equilibrium adsorption was attained in 20 minutes depending on other experimental conditions. The kinetic data justified Lagergren’s first-order kinetic equation. Adsorption isotherm study showed that the results fulfilled the Langmuir Model of adsorption isotherm. The maximum adsorption (98.28%) was recorded at pH 3 in 90 minutes for the initial Cr (VI) concentration of 50 mg L^-1. Therefore, it can be concluded that iron oxide – silicon (IV) oxide composite is a potential adsorbent for adsorption of Cr (VI) from aqueous solution.

Abstract: Resin Transfer Molding (RTM) is one of the most widely known composite manufacturing techniques of the liquid molding family, being extensively studied and used to obtain advanced composite materials comprised of fibers embedded in a thermoset polymer matrix. Nowadays, RTM is used by many industrial sectors such as automotive, aerospace, civil and sporting equipment. Therefore, the objective of this study is to verify the effect of calcium carbonate mixed in resin in the RTM process. Several rectilinear infiltration experiments were conducted using glass fiber mat molded in a RTM system with cavity dimensions of 320 x 150 x 3.6 mm, room temperature, maximum injection pressure 0.202 bar and different content of CaCO₃ (10 and 40%) with particle size of 75μm. The results show that the use of filled resin with CaCO₃ influences the preform impregnation during the RTM molding, changing the filling time and flow from position, however it is possible to make the composite with a good quality and low cost.

Abstract: This work aims to investigate the infiltration of a CaCO₃ filled resin using experiments and the PAM-RTM software. A preform of glass fiber mat, with dimensions 320 x 150 x 3.6 mm, has been used for experiments conducted at room temperature, with injection pressure of 0.25bar. The resin contained 10 and 40% CaCO₃ content with particle size 38μm. The numerical results were evaluated by direct comparison with experimental data. The flat flow-front profile of the rectilinear flow was reached approximately halfway the length of the mold. It was observed, that the speed of the filling decreases with increasing CaCO₃ content and,the higher the amount of CaCO₃ in the resin, the lower the permeability of the reinforcement that is found. The reduction in permeability is due to the presence of calcium carbonate particles between the fibers, hindering the resin flow in the fibrous media. The computational fluid flow analysis with the PAM-RTM proved to be an accurate tool study for the processing of composite materials.