Optimization of wastes content in ceramic tiles using statistical design of mixture experiments

Mineral extraction and processing industries have been cited as sources of environmental contamination and pollution. The inclusion of wastes into productive cycles represents an alternative form of restoration, which is interesting from both environmental and economic standpoints. In this work, the development of ceramic tile formulations containing kaolin processing and granite sawing wastes was investigated using the statistical design of mixture experiments methodology. Ten formulations using the raw materials, red clay, kaolin processing and granite sawing wastes, were selected and used in the mixture design. Test specimens were fired and characterized to determine their water absorption, linear firing shrinkage and modulus of rupture. Regression models were calculated, correlating the properties with the composition. The significance and validity of the models were confirmed by statistical analysis and verification experiments. The regression models were used to optimize the waste content in ceramic compositions. The results showed that formulations containing up to 62% of waste could be used in the production of ceramic tiles.     

Catalytic activity evaluation for hydrogen production via autothermal reforming of methane

A nickel catalyst (5.75 wt.%) supported on gamma-alumina was evaluated through autothermal reforming of methane (ATR). The reforming process was pointed to hydrogen production, following thermodynamic and stoichiometric predictions. The catalyst was characterised by several methods including atomic absorption spectroscopy (AAS), B.E.T.-N₂, X-ray diffraction (XRD), scanning electron microscope (SEM) and thermal analyses (thermogravimetry, TG; derivate thermogravimetry, DTG; and differential thermal analysis, DTA). Experimental evaluations in a fixed-bed reactor (1023–1123 K, 1.00 bar, 150–400 cm³/min feed) presented methane conversions in the range of 40–65%. The effluent mixtures provided hydrogen yields in the range of 78–84%, carbon monoxide 3–14%, and carbon dioxide 5–18%. High molar H₂/CO ratios, ranging from 8 to 90, were obtained. Operating autothermal conditions (excess of steam, 1023–1123 K, 1.00 bar) provided low coke formation and high hydrogen selectivity (81%) for methane reforming.     

Effect of interpass temperature on microstructure,impact toughness and fatigue crack propagation in joints welded using the GTAW process on steel ASTM A743-CA6NM

Mainly due to their great toughness, martensitic stainless steels are used for manufacturing hydraulic turbines. However, these steels have some restrictions regarding regions recovered by welding, mainly due to the formation of non-quenched martensite, which causes a reduction in toughness. Considering repair of hydraulic turbines, there is a great interest in developing welding procedures that increase impact toughness and avoid post-welding heat treatment (TTPS). This study aims to analyse the influence of interpass temperature on microstructure, impact toughness and fatigue crack propagation in multipass welded joints on martensitic stainless steel CA6NM, using AWS410NiMo filler metal and the gas tungsten arc welding (GTAW) process. In the sample with interpass temperature of 80°C, influence of the interpass temperature on the formation of ferrite δ, with intragranular formation in the two-phase δ field, was observed, while in the sample welded at 150°C, the formation of ferrite δδ occurred mainly in the single-phase field. The change in the formation of ferrite δ, with the low interpass temperature, promoted an increase in impact toughness and a decrease in the fatigue crack propagation when compared with the sample welded with a higher interpass temperature. The results obtained indicate that the TIG process is an excellent alternative for the repair of CA6NM steel, with a significant influence from the interpass temperature.     

Synthesis and Characterization of Nanostructured Cerium Dioxide Thin Films Deposited by Ultrasonic Spray Pyrolysis

Nanostructured thin films of cerium dioxide have been prepared on single-crystalline silicon substrates by ultrasonic spray pyrolysis using cerium acetylacetonate as a metal–organic precursor dissolved in anhydrous methanol and acetic acid as an additive. The morphology, structure, optical index, and electrical properties were studied by X-ray diffraction, scanning electron microscopy, atomic force microscopy, ellipsometry, and impedance spectroscopy. The use of additives is very important to obtain crack-free films. The substrate temperature and flow rate was optimized for obtaining smooth ( R _a<0.4 nm), dense ( n >2), and homogeneous nanocrystalline films with grain sizes as small as 10 nm. The influence of thermal annealing on the structural properties of films was studied. The low activation energy calculated for total conductivity (0.133 eV) is attributed to the nanometric size of the grains.     

Interactions between interfacial water and CO adsorbed on Pt and Pt-Ru alloy surfaces under electrochemical conditions: Density-functional theory study

The structural and electronic properties of interfacial water and adsorbed CO on platinum and platinum/ruthenium alloy have been studied via density-functional theory calculations to gain insight into the water-adsorbate interaction under electrochemical conditions. The computational simulations reveal a new interpretation for the interaction of adsorbed CO and water at the electrochemical interfaces. The new interaction model rationalizes the observed quantitative relationship between infrared intensities for adsorbed bridging CO and water molecules that impart a high-frequency O-H stretch, ca. 3630-3660 cm⁻¹ on pure Pt and 3600-3620 cm⁻¹ on PtRu alloy. The theoretical modeling indicates that the observed feature common to both pure Pt and PtRu alloy surfaces is due to interfacial water molecules firmly hydrogen-bonded to bridging CO.     

Poly(vinylidene fluoride) with zinc oxide and carbon nanotubes applied to pressure sheath layers in oil and gas pipelines

In this work, PVDF composites containing 0.2% (m/m) of carbon nanotubes (MWCNTs), PVDF with 5.0% (m/m) of zinc oxide (ZnO), and composites containing both particles in the same contents in the matrix were melt processed in a mini-extruder machine with double screws, using the counter-rotation mode. Composites were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), dynamic-mechanical analysis (DMA), and contact angle tests (CA). The samples presented the predominance of the α phase, with an increased degree of crystallinity as well as an increase in dimensional stability by incorporating both fillers, showing a synergistic effect between these particles, as shown on FTIR, DSC, and XRD results. SEM images showed a good dispersion of high aspect ratio particles. In general, DMA and TGA analysis showed that composites had not decreased their thermal and mechanical performance when compared to neat PVDF. Results of CA analysis showed an increase in the hydrophobicity of the sample containing MWCNTs. Permeability tests were also performed using a differential pressure system, combining high temperature and pressure, obtaining permeability measures and time lag. This work presents an alternative of composite materials, suggesting its application in the internal pressure sheath layers of oil and gas flexible pipes.     

On arginine-based polyurethane-blends specific to vascular prostheses

Polymer blends based on Tecoflex™ and an experimental aliphatic polyurethane (HMDI-PCL-arginine stands for 4,4 (metylene-biscyclohexyl) isocyanate - poly (ε caprolactone) diol, SPUUR stands for segmented poly(urea)urethanes using amino acid of L-Arginine as chain extender) were obtained by solvent casting, and further studied by fourier transform infrared (FTIR) and Raman spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis, and X-ray diffraction (XRD). Their biological performances were assessed in terms of hemocompatibility and Human umbilical vein endothelial cell (HUVEC) cytotoxicity. Tensile properties of dumbbell specimens were compared to longitudinal and circumferential tensile properties of tubular vascular graft. FTIR showed that as the SPUUR content increased in the blend, absorptions at 2860 cm⁻¹ increased, carbonyl absorptions at 1724 cm⁻¹ broaden and the small peak at 2796 cm⁻¹, typical of Tecoflex™ disappeared. Raman spectroscopy showed that the low intensity carbonyl absorption at 1724 cm⁻¹ also increased with SPUUR content. DSC allowed detection of PCL soft segment melting (T_m = 50°C) in agreement with X-ray reflections at 21.3° and 23.6°, assigned to SPUUR. However, no improvements in thermal stability were detected by TGA by blending. The addition of SPUUR to Tecoflex™ improved hemocompatibility and HUVEC cytotoxicity. The vascular grafts performance showed that 40% SPUUR blends exhibited the highest force in the longitudinal test whereas 50% SPUUR blends showed the highest circumferential force. Pressure burst strength was higher than 1000 mmHg for all blends. Overall, these blends can be used for high caliber vascular grafts.     

Effect of different surface treatments on polypropylene composites reinforced with yerba mate fibers: Physical,mechanical, chemical,and morphological properties

This study presents the preparation of post-consumer polypropylene (r-PP) composites filled with 30 wt% yerba mate (YM) stick particles. To improve the fiber–matrix adhesion, three surface treatments were performed: alkaline treatment with sodium hydroxide (NaOH) and use of 3-aminopropyltriethoxysilane (APTS) and maleic anhydride graft polypropylene copolymer (PP-g-MA) as coupling agents. Mechanical properties including tensile, flexural, and impact resistance were determined, and chemical (Fourier transform infrared spectroscopy [FTIR]), physical (water absorption), and morphological analyses were performed. The main findings show that the treatments were efficient in improving the mechanical properties of the composites, with emphasis on the r-PP/YM30/APTS and r-PP/YM30/PP-g-MA composites, which proved to be superior in tensile, flexion and impact strength and absorption of water compared to the untreated composite. The morphological analysis showed a better interaction between the fiber and the polymeric matrix for the composites with YM/APTS and YM/PP-g-MA, which corroborates the results of tensile and flexural strength, as well as with the spectra of FTIR in which the chemical modification of the fibers is observed. However, the results show that these treatments are promising in obtaining composites with recycled matrix with better properties.     

Changes in optical properties caused by UV-irradiation of aquatic humic substances from the amazon river basin: seasonal variability evaluation

Aquatic humic substances (AHS) isolated from two characteristic seasons of the Negro river, winter and summer corresponding to floody and dry periods, were structurally characterized by 13C nuclear magnetic ressonance. Subsequently, AHS aqueous solutions were irradiated with a polychromatic lamp (290-475 nm) and monitored by its total organic carbon (TOC) content, ultraviolet-visible (UV-vis) absorbance, fluorescence, and Fourier transformed infrared spectroscopy (FTIR). As a result, a photobleaching up to 80% after irradiation of 48 h was observed. Conformational rearrangements and formation of low molecular complexity structures were formed during the irradiation, as deduced from the pH decrement and the fluorescence shifting to lower wavelengths. Additionally a significant mineralization with the formation of CO2, CO, and inorganic carbon compounds was registered, as assumed by TOC losses of up to 70%. The differences in photodegradation between samples expressed by photobleaching efficiency were enhanced in the summer sample and related to its elevated aromatic content. Aromatic structures are assumed to have high autosensitization capacity effects mediated by the free radical generation from quinone and phenolic moieties.