Abstract Colloidal silica is an important biocompatible, inert and non-toxic material for imaging, therapy, and drug delivery biomedical applications. In this context, the evaluation of colloidal suspensions and their stabilities by a Fiber Optic Quasi-Elastic Light Scattering sensor is proposed. Two different silica nanoparticles were prepared and characterized by scanning electron microscopy and X-ray diffraction, being completely amorphous, with mean diameters of 125 and 159 nm and average specific weight of 1.94 g.cm-3. The nanoparticles were dispersed in deionized water in different concentrations ranging from 0 to 2% (m/m), resulting in suspensions with mean kinematic viscosity of 0.009157 cm².s-1. The sensor showed different sensitivities regarding concentrations and diameters, with an increase in the light intensity dispersion caused by the scattering. A decreasing tendency of the decay rate of the autocorrelation function of the light intensity signal was verified with the variation of pH, and this decay rate also showed an abrupt decrease with the enhancement of the ionic strength, detecting the limits of the colloidal stability. This work presents a simple and reliable methodology for the colloidal assessment in a low-cost and minimally invasive way, easily extendable for different chemical and biological systems.

Important properties in cementitious materials, such as concrete, are related to the presence of additives that influence the rigidity and the physical and chemical resistances. For the evaluation of the additive effectiveness, known as pozzolanic activity, a simple procedure, the Chapelle test, is commonly used, and it essentially consists in a reaction between the additive with calcium oxide in aqueous medium. However, such procedure presents limitations in terms of processing time and lack of information regarding the reactions kinetics. In this sense, a simple method based on the kinetic and thermodynamic principles of chemical reactions is proposed, which can be performed using conventional electronic pH sensors. The study provides an alternative methodology with many advantages over the traditional procedure, such as energy and time-savings, more robustness and more confidence. In this paper, three types of silica nanoparticles that can be used as low-cost additives were characterized in relation to their morphology and crystallinity by XRD and SEM, the particles average diameters were obtained and the particles were used for studying the chemical process that takes place during the Chapelle test. Results and the semi-empirical analysis provided strong evidence that the process is an acid-base 1:1 reaction and it was verified that the mean reaction times varied from 64 to 195 min. It is a remarkable result, since the proposed analysis can be performed with simple, fast and low-cost instrumentation and needs only a worksheet software, whereas the Chapelle test takes 16 hours and provides no dynamic information. Besides the limitation that the methodology is not able to quantify and to elucidate the effects of the specific surface area of the particles, which needs a complete BET study, the research provides a significant contribution for the understanding of the pozzolanic process, of great importance in both concrete and ceramic research.

Atualmente, os adesivos condutivos estão sendo visados como possível alternativa para substituir as pastas de solda convencionais na montagem de componentes eletrônicos em placas de circuito impresso (PCI), por serem menos nocivos ao meio ambiente e pela capacidade de fazer junções fine pitch. No entanto, pouco se conhece sobre o comportamento e propriedades dos adesivos condutivos isotrópicos, na forma de pasta, na montagem de componentes eletrônicos em PCIs. Este trabalho teve como objetivo estudar as propriedades físicas e químicas, assim como o comportamento de alguns adesivos condutivos comerciais, visando a sua utilização na "soldagem" de componentes eletrônicos. Três diferentes adesivos condutivos isotrópicos comerciais (na forma de pasta) foram utilizados. Inicialmente, filmes espessos destes adesivos foram preparados em substrato de vidro com a finalidade de analisar o comportamento de resistividade elétrica em função do tempo e da temperatura de cura. Em uma segunda etapa, os adesivos foram utilizados para fixar diferentes tipos de componentes eletrônicos em PCI. Com o intuito de caracterizar a microestrutura da interface componente/adesivo/placa, amostras foram caracterizadas por microscopia óptica e microscopia eletrônica de varredura. Para verificar a viabilidade do uso desses adesivos, foram feitos testes elétricos funcionais e os resultados obtidos foram comparados aos da solda convencional. Verificou-se que os adesivos condutivos apresentaram propriedades físicas compatíveis aos da pasta de solda convencional.

Recently, conductive adhesives have been considered as alternatives for replacing conventional solders in the mount technology of the electronic components on print circuit board (PCI), due to necessity to look for environment - friendly materials and fine pitch components. However, there is a little information about the behavior and properties of the isotropic conductive adhesives (as paste) for using in the mounting of the electronic components. The objective of this work was to study the physical and chemical properties, as well as the behavior of isotropic conductive adhesives aiming their use in the "soldering" of electronic components. Three different commercial isotropic conductive adhesives were utilized in this study. Firstly, thick films were prepared on glass substrate aiming to analyze the behavior of resistivity as a function of the time and temperature of cure. Secondly, the adhesives were utilized for fixing different kinds of electronic components on PCI. Then, the samples were characterized by optical and scanning electronic microscopy with the purpose of verifing the component/adhesive/PCI interface. Electric tests were realized to verify the viability of the use of these adhesives and the results are compared with the conventional solders. It was observed that the isotropic conductive adhesives showed properties compatible to conventional paste solders.