Abstract The oxidation and deposition of transition metal oxides on porous carbon precursor materials strongly influence the final performance of supercapacitor electrodes. Thus, the influence of oxidation time combined with simple iron oxide deposition was evaluated on a flexible carbon fiber cloth electrode oxidized at three different times and exposed to spontaneous iron oxide deposition. The 140 minutes oxidation time increased by two times the iron quantity deposited on the activated carbon fiber cloth (ACC) and also increased the crystallinity of the carbon matrix. The iron oxide deposition improved the contribution of anions to store energy, enhancing the pseudocapacitive effect in the samples. The optimal oxidation time of the ACC140_Fe sample with the greater iron oxide deposition achieves 116.8 F g-1. The binder-free flexible electrode presents a successful design through pre-oxidation and spontaneous iron oxide deposition on the carbon matrix without expensive and environmentally unfriendly chemical treatments.

Abstract From the first hydraulic fracturing in the 40’s until nowadays, the techniques of each process step have evolved significantly. This study presents a new approach on the development of metakaolin (MK) and geopolymer based proppant with and without nanocarbon materials such as multi-walled carbon nanotubes and graphene oxide. For manufacturing the microspheres, the chosen method was intensive mixing of raw material with dispersed nanocarbons followed by sintering metakaolin and curing the geopolymer using an alkaline medium (NaOH). Compression mechanical tests, bulk density, turbidity, and K&S method analysis were made following API RP 19C standard. The sample containing 4.3 M NaOH to produce alkali-activated metakaolin sintered at 1300 ºC for 2 h presented higher mechanical resistance generating 2.4% of fines at 3 K (3000 psi). The geopolymer samples showed higher crushing strength and lower bulk density when compared to the MK samples without heat treatment. Furthermore, reduced graphene was produced and incorporated into activated MK. Morphology and presence of carbon nanostructures on the proppants were evaluated by scanning electron microscopy. Crushing test reached 3 K enabling it to be used as a ceramic synthetic proppant containing carbon nanomaterials.

Abstract The geopolymers synthesis are based on geopolymerization, a sequence of reactions processed in an alkaline medium through oligomers providing a three-dimensional molecular structure. In this work, the polycondensation of metakaolin was performed with alkaline activators (NaOH and sodium silicate), wood sawdust and other additives. Two different compositions were evaluated after and before sintering at a high temperature (850 °C). The effect of sawdust addition and the thermal treatment of geopolymers were evaluated by scanning electronic microscopy, X-ray diffraction, mechanical properties, apparent density and porosity by different characterization techniques to guide of development of high porous and low-density materials for thermal and noise control application on building/home construction engineering applications.

As massas de tamponamento para furos de corrida de altos-fornos são materiais refratários diretamente ligados a toda logística de produção de ferro gusa, pois é um dos agentes responsáveis pela estabilidade de vazamento destes equipamentos siderúrgicos. Durante a injeção da massa no interior do furo (na operação de tamponamento do forno), toda a escória e gusa remanescentes devem ser conduzidas para dentro do forno, a fim de que o furo seja completamente preenchido. Além disso, este produto deve recompor o cogumelo, que é a parte interior do cadinho do alto-forno, formada principalmente por massa de tamponamento antiga. No momento do vazamento do forno a massa de tamponamento, que foi injetada, curada e sinterizada no furo de corrida, deve apresentar relativa facilidade de perfuração por uma broca conduzida por máquina perfuratriz, proporcionando vazamento estável do forno. Desta forma, a massa de tamponamento é um material refratário monolítico de elevado nível tecnológico, com um conjunto de características que deve atender plenamente a exigências distintas. Ao mesmo tempo em que o produto deve apresentar determinado nível de densificação para suportar o agressivo ataque do gusa e da escória líquidos, deve proporcionar também relativa facilidade de perfuração, com um adequado nível de porosidade após sua sinterização. Além disso, este produto deve suportar condições extremamente elevadas de temperatura e pressão interna do alto-forno. Neste trabalho serão apresentadas técnicas de caracterização das massas de tamponamento para altos-fornos focando o balanço entre suas principais características. Entre estas, serão considerados aspectos ligados à adesão, usinabilidade e densificação do produto. No final será aplicada a metodologia AHP (Processo de Hierarquização Analítico) para priorização e escolha da melhor formulação testada, considerando-se todos os parâmetros envolvidos.

The hot metal production process is very dependent on the performance of the taphole mix, which directly influences the stability of the blast furnace. During the plugging operation the taphole mix must conduct all the metal and slag back into the furnace, thereby filling in and sealing the hole. Additionally it must also adhere to the old mix and recompose the so-called mushroom, which protects the inner part of the furnace hearth. Conversely, for the tapping operation, the mix, which has been cured and sintered, needs to be easily drilled in order to provide a stable and safe tapping? Therefore, the taphole mix is a complex and highly technological refractory product, designed to attend widely different demands. During operation it must be sintered and consolidated in order to attain good corrosion/erosion resistance against slag and hot metal, whereas for the tapping operation it must be soft enough to provide an easy drilling. Moreover, the taphole mix should resist to high temperatures and to the high pressure coming from the inner part of the blast furnace. In this work, a number of tests are presented in order to evaluate the performance of taphole mixes. The experiments were selected according to the most important demands that the mixes need to attain in actual operations: extrusion index, adhesion capacity, drilling resistance, mechanical strength, refractoriness, and others. The results of the tests were assessed according to the AHP (Analytical Hierarchy Process) method, which allows for the selection of the best formulation considering all parameters involved.