Abstract: Nanotechnology is the domain of technological development and application of materials which go from 1 to 100 nm in at least one of their dimensions. The use of nanoparticles in engineering focuses on the development of new materials with special properties, which can be used as filler materials in the welding field. In this context, this study contributes to the stage preceding the deposition of the weld beads. This work aims to insert, using the colloidal processing technique, ceramic nanoparticles (ZrO2) into a Co-based superalloy (Stellite 6) and study the solidification of this “nanocomposite”. 4 filler materials in the shape of compacted cylinders were melted by PTA: Stellite 6 with added Fe carriers with ceramic nanoparticles (ZrO2) (1%, 2.5% and 7.5% volume) and Stellite 6 without any additions. The molten materials were characterized through optical and scanning electron microscopy with field emission (SEM-FEG), XRD and Vickers microhardness. The results show that the colloidal processing technique was effective in adhering the ZrO2 nanoparticles to the carrier Fe particles, which were mixed with Stellite 6, as well as the relationship between microstructure refinement, phases and microhardness after PTA melting.

Flat sintered copper and copper-zirconia substrates, with zirconia nanoparticles contents of 1 and 3 vol%, were produced by aqueous tape casting and controlled sintering. Aqueous suspensions were prepared to a solid content of 58 vol% using 3 wt% commercial binder emulsion. The green tapes were treated at 350 ºC in air to remove organics and sintered at temperatures ranging from 800 to 1000 ºC in atmosphere of Ar/5%H2. Copper tapes reached almost full densification at 900 ºC. Composite with 1 vol% zirconia, sintered at 800 ºC, maintained high density and provided a noticeable increase of the mechanical strength, whereas further additions up to 3 vol% reduced the densification and the resulting mechanical performance became poorer.

RESUMO O processamento coloidal é uma técnica amplamente usada para a produção de componentes cerâmicos. Diversos artigos científicos foram publicados na última década apresentando a possibilidade de se obter suspensões aquosas concentradas estáveis de partículas metálicas a partir do seu controle de pH e uso de dispersantes. Este artigo tem o objetivo de estudar a produção de um aço com microestrutura austenítica usando pós elementares de ferro (Fe) e níquel (Ni) via rota coloidal. Para tanto, foram realizadas medições de potencial zeta entre os pHs 2 e 12 para a composição Fe30Ni em massa. As suspensões aquosas atingiram concentrações de sólidos de até 45% v/v e processadas por colagem de barbotina. Os compactados colados foram caracterizados por densidade (Arquimedes), análise térmica diferencial (ATD) e dilatometria. Após a sinterização aos 900°C e 1100°C/1h, os compactados apresentaram microestrutura com formação de maclas de recozimento, porosidade inferior a 10% em volume e microdureza Vickers aproximada de 160 HV.

ABSTRACT Colloidal processing is a widely used technique to produce ceramic components. Several papers have been published in the last decade presenting the possibility to obtain aqueous concentrate stable suspension of metallic particles from their pH control and using dispersants. This paper aims to study the production of a steel with austenitic microstructure using elemental iron (Fe) and nickel (Ni) powders via colloidal route. For this, Zeta potential measurements were performed between pH 2 and 12 to Fe30Ni wt% composition. Aqueous suspensions reached solids concentrations of up to 45% v/v and processed by slip casting. The compacts were characterized by density (Archimedes), differential thermal analysis (DTA) and dilatometry. After sintering at 900°C to 1100°C/1h, the sintered bodies presented a microstructure with of annealing twins, porosity less than 10 %v/v approximate Vickers microhardness of 160 HV.

RESUMO Resíduos de vidro podem ser reutilizados para o desenvolvimento de materiais alternativos. Uma opção viável são os materiais celulares para isolamentos térmicos já que, apresentando poros isolados, possuem baixa condutividade térmica, baixa densidade aparente e temperaturas de serviço mais altas que a dos materiais isolantes poliméricos. Neste trabalho, foi preparada uma suspensão aquosa com resíduos de vidro previamente moídos, Ágar-ágar (gelificante) e Emustab(r) (emulsificante), a qual foi adicionada diferentes frações de óleo de soja (50, 70 e 90% em massa). Subsequentemente, foi realizada a emulsificação do óleo vegetal no líquido da suspensão por meio de agitação em misturador mecânico de alto cisalhamento. Corpos de prova cilíndricos foram produzidos via colagem por gelificação e queimados a 700 °C/30 min. Os resultados mostraram que os vidros celulares obtidos apresentaram porosidade entre 74 e 93% com poros bem definidos e distribuídos e baixas condutividades térmicas (0,05 a 0,09 W/m.K). Tais resultados indicam que os materiais obtidos são potenciais candidatos para atuarem como isolantes térmicos, como por exemplo, painéis para revestimentos utilizados na construção civil.

ABSTRACT Glass wastes can be reused for the development of alternative materials. A viable option are the cellular materials for thermal insulation since with isolated pores they show low thermal conductivity, low density and service temperatures higher than those of the polymeric insulating materials. In this work an aqueous suspension was prepared with previously milled glass wastes, agar (gelling) and Emustab(r) (emulsifier), in which different soy oil fractions (50, 70 and 90 wt% ) were added. Subsequently, the emulsification of the vegetable oil was carried out in the liquid suspension by stirring in a mechanical mixer at high shear. Cylindrical samples were produced by gelation slip casting and fired at 700 °C/30 min. The results showed that the obtained cellular glasses had porosity between 74 and 93% with well-defined and distributed pores and low thermal conductivity (0.05 to 0.09 W/mK). These results indicate that the obtained materials are potential candidates to act as thermal insulators, such as panels for coatings used in construction.

In this work carbon steel plates were dip-coated with a composite film obtained from a colloidal suspension of Ni-TiO2. Suspensions with different solids contents were used to evaluate the adherence of the film and the microstructural features. The samples were characterized using both optical and scanning electron microscopy, energy dispersive spectroscopy and microhardness. The microstructural analysis revealed that the films have high porosity at the surface. However, an interfacial region was observed demonstrating that there was good adhesion between both materials. This region shows an increased hardness that can be attributed to diffusion mechanism of nickel from the composite film to the steel matrix. Besides the interface, there was an abnormal grain growth, followed by a region of smaller grains of austenite and at longer distances near the center of the plate some colonies of pearlite appear.

In this work the dispersion of iron oxide III particles in aqueous media was studied. To achieve the maximum solid content zeta potential measurements were carried as a function of pH. The influences of two different types of polyacrylates as dispersants were investigated. Suspensions were produced by varying solids concentration up to 30 vol.%. The results showed a strong influence of pH on the size distribution of the particles in suspension. The most efficient dispersant towards particle dispersion was sodium polyacrylate. The maximum solid content in the suspension was optimized to 25 vol % with density values higher than 35% theoretical density with 2 wt.% polyacrylate.

In this study, the influence of mechanical activation by intensive ball milling of a stoichiometric mixture of talc, kaolin, and alumina on the mechanism and kinetics of cordierite (2MgO·2Al2O3·5SiO2) formation was evaluated. The raw materials were characterized by chemical analysis, X-ray diffraction (XRD), laser diffraction, and helium pycnometry. The kinetics and mechanism of cordierite formation were studied by XRD, differential thermal analysis, and dilatometry in order to describe the phase formation as a function of temperature (1000-1400 ºC), time of thermochemical treatment (0-4 h), and grinding time of the mixture (0-45 min). Finally, the optimal conditions of the thermochemical treatment that ensured the formation of cordierite were determined: milling time of 45 min and thermal treatment at 1280 ºC for 1 h.

Ceramic foams were produced from a sludge generated in the aluminum anodizing process by using an industrial polyurethane foam (replication method) with open cell sizes of 10 ± 5 ppi (porosity = 97%) which were impregnated with suspensions containing 50-61 wt.% alumina, 1 wt.% citric acid, 6 wt.% bentonite and fired at 1600 ºC for 2 h. The aluminum anodizing sludge shows a high alumina content (87.5 wt.%) and a low particle size (~1.7 mm) after calcination and milling. The obtained filters show porosity of approximately 70%, filtration capability (mass water flow) of 1.7 kg/s and mechanical strength under compression of 2.40 MPa.

In this work, aqueous suspensions of aluminas with different particle sizes were evaluated. The effect of pH on the electrosteric stabilization using PMAA-NH4 (ammonium polymethacrylate) as deflocculant was studied. The amount of deflocculant was optimized and rheologic properties were determined at four different pH values. Sedimentation was also evaluated. For suspensions with pH 4, an electrostatic mechanism of stabilization was observed, probably due to a flat adsorption of PMMA- on the alumina surface, leading to a small efficiency in relation to steric stabilization. For a suspension with pH 12, the steric mechanism of stabilization prevails. Suspensions with pH 7 and 9 present a higher flocculation degree. In relation to particle size, A-1000 samples present a smaller particle size, leading to a smaller interparticle distance (IPS), making stabilization more difficult.