In the present work, synthetic slags (FeO-SiO2-CaO-P2O5-Al2O3-TiO2-V2O5 system) mimicking the composition of the slag inclusions of Ipanema were solidified at different cooling rates. FactSage software was used to calculate the slag’s phase equilibria from 500ºC to 1600°C to guide the microstructural characterisation. The samples solidified with slower cooling rates featured wüstite dendrites and a eutectic-like matrix, with intradendritic (Al,V,Ti)-containing iron spinel precipitates in the wüstite. The rapidly solidified slag showed refined wüstite dendrites surrounded by a Fe-O-Si-Ca-containing amorphous single-phase matrix without intradendritic (Al,V,Ti)-containing iron spinel precipitation. The comparison of the calculated phase diagram with the as-cast microstructures showed a few discrepancies. For instance, the FactSage’s database must be updated to consider the simultaneous solubility of Al, V and Ti in the thermodynamic description of the spinel phases, such as FToxid-SP-V, FToxid-SPINA, FToxid-TiSp and (FeO)2(TiO2)(s). Finally, the intradendritic precipitation of (Al,V,Ti)-containing iron spinel phases in the wüstite of the slag inclusions indicated that an Ipanema’s iron artefact was exposed to high service temperatures between 750 and 1050ºC.

Double-layer Ni-P coatings with low phosphorus content in the inner layer and high phosphorus content in the outer layer and Ni-Mo-P composite coatings are successfully prepared on the surface of AZ91D magnesium alloy by chemical plating process. The microstructures, friction and corrosion resistance of double-layer Ni-P and Ni-Mo-P coatings are studied in comparison. Meanwhile, the deposition and corrosion resistance mechanism for the coatings are investigated. Results convey that both Ni-P and Ni-Mo-P coatings showcase an amorphous structure. The coating possesses denser and more homogeneous structure with the co-doping of Mo. The micro-indentation hardness (859.7 HV) and friction coefficient (0.58) of Ni-Mo-P coatings show that the ternary alloy coating is firmly bonded to the magnesium alloy substrate. Besides, the Ni-Mo-P coatings demonstrate exceptional wear resistance attributed to Mo co-deposition, fostering grain refinement and facilitating the growth of passivation films.

High chromium cast irons (HCCIs) are widely applied in the mining industry as components of equipment for iron ore transportation, in which their surfaces are subjected to abrasive and erosive wear. The present work evaluated the erosion-abrasion behavior of a HCCI possessing different amounts of austenite and martensite, using a laboratory impeller-tumbler wear test apparatus and iron ore pellets as abrasive material. The results showed that the wear dominant mechanism on the worn surface of the as-cast material depends upon the material microstructure. For HCCI destabilized at 930 and 990 °C, the matrix has high martensite/austenite ratio and finely dispersed secondary carbides, offering high abrasion-erosion wear resistance. The absence of fractured eutectic carbides indicates that such matrix has hardness and load bearing capacity, enough for mitigating a significant plastic deformation during the impact pellets. For HCCI destabilized at 1050 °C, the matrix has a low martensite/austenite ratio and coalesced secondary carbides, leading to high wear rates during erosion-abrasion tests.

Membrane technology offers solutions for separation of complex gas mixtures. Therefore, new efficient and durable membranes are required to produce gas permeation modules with high area/volume for CO2 removal from natural gas. This study aims to develop cost-effective zeolite DD3R alumina composite hollow fibers to achieve these process requirements. A porous hollow fiber support from low-cost alumina was prepared via phase inversion followed by thermal treatment. DD3R zeolite seeds were then implanted over the surface of the microporous hollow fibers to form a selective layer by hydrothermal synthesis. The thickness of the selective layer was controlled by the seed concentration, which also affected the crystal intergrowth and competing zeolite phase formation, Sigma-2, which influenced the membrane performance. A reduced-diameter composite DD3R-alumina hollow fiber was obtained with a selectivity of 203 and a CO2 permeance of 5.4 x 10-8 mol m−2 s−1 Pa−1 at a pressure of 2 bar.

Abstract Silicoaluminophosphates SAPO-5 and SAPO-11 were synthesized using the hydrothermal method, 170 ºC with triethylamine and dipropylamine as the structure directing agents, respectively. This work aimed the incorporation of boron into the structures obtained by modifying the composition of the system, using as a reaction equation: Al2O3:P2O5:x SiO2: yB2O3:1,5TEA (or DPA):50H2O, with x, y=0-0.2. The phase was identified by XRD and characterized by FTIR, TGA/DTG, TPD-NH3 and nitrogen adsorption at -196°C. The structure parameters confirmed the obtaining of pure structures, showing a slight contraction in the parameters of the unit cells, indicating the presence of boron in the crystal lattice. The Brønsted sites, were modified up to a maximum of boron (y = 0.1) and for higher content, the acidity was not significant. The modification of weak acidity related to the appearance of isolated BO3 groups, indicating that the silicon atoms were not sufficiently distributed for the formation of sites.

Abstract The aim of this work is to determine effective elastic properties of pultruded Glass Fiber Reinforced Polymer using micro-CT in conjunction with a two-step numerical homogenization technique. The two-step homogenization involves the segmentation of the material’s layers, which was made here by means of a machine learning approach. The segmentation was validated through the comparison between the phase’s volume fractions of samples obtained from the segmented images and laboratory tests. Further, a standard accuracy analysis in a 10-fold cross validation was performed. The samples’ effective axial Young’s modulus obtained by our numerical homogenization were compared to results obtained from experimental tests. For both the experimental tests and the image-based numerical analysis we considered samples extracted from the same profile. The two-step methodology allowed the homogenization of large volumes of the composite corresponding to the whole thickness of the profile, imaged with a high resolution. In addition to the axial effective Young’s modulus, our methodology was also able to successfully provide all the other elastic properties along the three orthogonal directions, even the ones that are arduous to be obtained in laboratory setups.

Abstract The present work is to study the production and characterization of biochar produced at two different temperatures (400 and 900 °C) and its influence on the interaction of biochar with elastomers of different polarity, aiming at the replacement of carbon black in elastomer compounds, based on the rheometric, physical, chemical and mechanical properties. The biochar production temperature of 900 ºC affected the optimum vulcanization time (t90), with compounds containing NR and NBR having the shortest vulcanization times because temperatures above 400 ºC produce an alkaline biochar that accelerates vulcanization. The biochar interacted with the two elastomers, being superior to NBR due to the oxygen concentration. Therefore, the blends with biochar showed a demonstrated reinforcement of the tensile strength, even if the biochar had a surface area of 3 m2.g-1 for the observed irregular surface, in addition to the mechanical properties, analogous to the blends with carbon black.

Abstract Copper oxide (CuO) is a heterogeneous catalyst applied with success in several systems like vegetable oils transesterifications. The Ce-dopoing CuO is a promisor material with a potential improve catalysis performances. In this work, CuO and Ce-doping CuO were synthesized by the microwave hydrothermal method in only 5 min at low temperature (100 oC) without templates or other petroleum dependent organic substances, using only copper and cerium nitrates and sodium hydroxide as a precursors. Both materials were applied as photocatalysts for the degradation of remazol golden yellow dye (RNL). X-ray diffraction analysis showed that CuO and Ce-doped CuO has monoclic copper oxide structure without secondary phases. SEM analysis showed the Ce-doping full modify the CuO powder morphology. The dye RNL degradation rate of Ce-doping CuO was bigger than pure CuO and the expensive CeO2.

Abstract Sustained research in high-entropy alloys (HEAs) has presented opportunities for relatively lighter alloys, specifically the Ti-containing HEAs, having an excellent combination of properties, and a great potential to replace heavier superalloys. We adopted a novel data-driven methodology to sort and select Ti-containing HEAs from the literature for their potential applications in aeroengine turbines by applying multiple-attribute decision-making (MADM). The ranks of the alloys evaluated by diverse MADMs were consistent. The data-driven methodology identified the following top five Ti-containing HEAs: ONS-BCC-Ti17.8 (Al20.4-Mo10.5-Nb22.4-Ta10.1-Ti17.8-Zr18.8), EF-BCC-Cr20-Ti20 (Ti20-Zr20-Hf20-Nb20-Cr20), ONS-BCC-Ti27.9 (Al11.3-Nb22.3-Ta13.1-Ti27.9-V4.5-Zr20.9), ONS-BCC-Ti27.7 (Al5.2-Nb23.4-Ta13.2-Ti27.7-V4.3-Zr26.2), and ONS-BCC-Ti20 (Nb20-Cr20-Mo10-Ta10-Ti20-Zr20); the methodology provides directives for further development of the identified Ti-containing HEAs for potential replacement of legacy superalloys in aeroengine turbines. The top-ranked alloy (Al20.4-Mo10.5-Nb22.4-Ta10.1-Ti17.8-Zr18.8) is lighter than the current industry benchmark, Inconel 718, by ~13%. All the top five Ti-containing HEAs have configurational entropy greater than ~13.3 J/mol K and body-center cubic crystal structure. The potency of the methodology could further be tapped by choosing appropriate weights of the properties for specific aeroengine turbine applications.

Abstract This paper presents the resistance spot welding process test and numerical simulation analysis of medium manganese steel TRIP steel (7MnSteel) and DP590 steel plate. The results show that the failure mode is PF-TT failure, and IF and PF-TT are investigated. At the same time, based on the numerical simulation under the typical welding parameters, the welding plate has the stress concentration at the electrode edge at the beginning of the welding. Along with the welding, there is the stress concentration in the heat-affected zone of the medium manganese TRIP steel, which may also be the reason for the failure of the joint here. The current density is concentrated at the contact surface between the electrode and the weld plate, and the error in the diameter of the nugget measured by simulation and experiment is within 7%, which verifies the accuracy and reliability of the model.

Abstract The Half-Heusler semiconductor alloys can be used efficiently as thermoelectric materials to transform the waste heat into useful electrical energy. The low-cost and large-scale production of suitable half-Heusler alloys are important in the present context. In this work, a nanostructured half-Heusler NbFeSb alloy is obtained by mechanical alloying with 15h of milling. The structural parameters of the sample are investigated by powder X-ray diffraction followed by Rietveld refinement. Differential scanning calorimetry indicates that the NbFeSb phase is stable up to about 420 K. The electrical resistivity is obtained as a function of temperature. A band gap of 0.37(3) eV is obtained from UV-Vis measurements. Density functional theory calculation shows an indirect band gap of 0.52 eV. Analyses of the obtained data indicate that structural defects and nanometric crystallites sizes present in the nanostructured NbFeSb produced by mechanical alloying do not degrade the electrical and optical properties of the compound.

Abstract The magnesia (MgO) hydroxylation behavior in dilute suspensions (below 50% volumetric solid loads) has been extensively studied over the past decades due to its role in refractory castables. However, its equivalent effects on concentrated systems have not been analyzed in such a systemic way, although they are known to be as or more deleterious than those observed in dilute systems. This study focuses on the hydroxylation behavior of different sources of magnesia (sinter and caustic magnesia) in aqueous suspensions prepared at various solids concentrations (17-96 vol%) and shaped by distinct methods. They were analyzed by thermogravimetry, apparent volumetric expansion measurements, X-ray diffraction, scanning electron microscopy, and in situ temperature measurements during curing. The ratio between experimental and theoretical extents of the hydroxylation degree resulted in the reaction yield. A comparison between samples containing the same water amount revealed those with caustic magnesia showed a faster evolution of hydroxylation degree, apparent volumetric expansion, and higher maximum internal temperature during curing. In both systems, the yield levels of compositions of heavier solid loads were higher, despite the small quantity of hydroxylation products formed. Significant differences in the products’ microstructure were observed and related to the ions' mobility toward crystallization nuclei.

Abstract Continuous development, improvement and innovation of ballistic material systems with superior energy absorption performance has been the subject of numerous works nowadays. Some research has been carried out with the objective of replacing traditional metallic and ceramic materials and composites with high-performance polymeric composites. Due to their excellent properties, multi-scale polymer composites have been used in the most varied segments of the industry, being recently researched in applications such as ballistic materials. This work promotes the combination of high-strength three-dimensional woven aramid fiber fabrics with vinyl ester resin to produce a panel through the compression molding process. The resin was reinforced with graphene nanoplatelets (0.1, 0.2 and 0.3% wt). The impact, tensile and flexural strength were evaluated, along with dynamic-mechanical analysis by DMA and by Hopkinson split bar test, indicating a trend of better performance for the composite containing 0.1% of graphene nanoplatelets.

Abstract Although most of the studies presented in the literature are focused on MgAl2O4 formation and its role on alumina-based refractories performance, ZnO has been reported as a promising spinel inducer. Aiming to investigate the influence of ZnAl2O4 (ZA) and MgAl2O4 (MA) generation on the properties of alumina-based castables, three vibratable compositions containing calcium aluminate cement or hydratable alumina as binders and 1 wt% of silica fume, were evaluated in this work. Flexural strength, apparent porosity, hot elastic modulus, corrosion cup-tests, thermodynamic simulations, were carried out to analyze the performance of such ceramics. The results indicated that ZnAl2O4 was mainly formed above 800 °C, favoring an earlier sintering of the samples. Besides that, the softening of the castables was observed above 1200 °C, which resulted in the elastic modulus decay of the samples during their first heating cycle due to the formation of SiO2-rich liquid phase in the resulting microstructure. Cement-free samples obtained after calcination (600 °C for 5h) presented enhanced corrosion resistance when placed in contact with molten slag at 1500°C. Although, silica fume addition to the castables negatively affected their corrosion performance, it helped to counterbalance the expansion associated with the spinel and calcium aluminates formation.

Abstract In this work, a thermal plasma-based ablation test system was used to evaluate the ablative performance of the EPDM composite. The system produces a high enthalpy plasma jet generated by a plasma (DC) torch, operating at atmospheric pressure using compressed air as working gas, enabling the variation of the thermal flux concerned with the studied EPDM composites. The samples were characterized using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Fourier-Transform Infrared spectroscopy (FTIR), and Thermogravimetric Analysis (TGA) to investigate the morphology, mass-loss rate, the reaction layer (char formation), and chemical changes of the samples for each thermal flux. For a complete evaluation, the thermal fluxes were varied in 0.30, 0.45, 0.60, 0.75, and 0.90 MW/m2 and for each thermal flux, disk-shape samples remained exposed to the plasma jet for 10s. During the plasma jet exposure time, the temperatures of the surface and the back of the samples were collected to verify the formed char layer's insulator capacity and the samples' thermal diffusivity for each experimental condition. The mass loss is continuous under the thermal fluxes of 0.30 and 0.45 MW/m2, stabilizing at 60% until 0.75 MW/m2. The formed char layer begins to lose its protective capacity, evidenced by the size decrease (from 800 µm to 700 µm), due to the ablation process of the reaction layer from the thermal flux of 0.90 MW/m2.