Abstract Nanoparticles nickel-doped cobalt ferrites [NixCo1-xFe2O4 (x = 0.0, 0.25, 0.50, 0.75 and 1.0 of Ni2+)] were prepared by the microwave combustion synthesis, using a stoichiometric mixture of metal nitrates and urea as the oxidizer and fuel to drive the reaction. The effect of microwave irradiation on the phase composition was favorable to promote the formation of fluffy foams and nanoparticles sizes. The fast internal heating with microwaves leads to a reduction in synthesis time, to only 2 min. The structural, chemical and magnetic properties of the nickel-doped cobalt ferrites were analyzed by XRD, TEM, SEM and BET. The XRD results confirmed the formation of pure and single-phase spinel structure. The crystallite size of the nanoparticles was in the range of 38 - 50 nm. SEM images show nanoparticles with spherical shape and homogenous morphology. The TEM analysis shows necked near-spherical particles with an average size of ~30 - 50 nm, reflecting the highly crystalline nature of these nanoparticles. The magnetic measurements of all the samples were recorded using vibrating sample magnetometer (VSM) at room temperature in 10 kOe. Increasing the nickel content directly affects the structural characteristics of the particles, causing a reduction in the coercive field.

Poly(glycolide-co-lactide) (PLGA) nanospheres containing magnetic materials have been extensively studied because of its biomedical applications. Therefore, it is very important to know thermal properties of these materials in addition to other physical properties. Thermal degradation activation energy (Eα) of PLGA nanospheres with maghemite entrapment (PLGA-Mag), PLGA nanospheres (hollow spheres) (PLGA-H) obtained by an emulsion method and unprocessed PLGA (PLGA-R) were calculated by isoconversional Vyazovkin method based on data of TG analysis in order to evaluate modifications in thermal behavior caused by nanospheres obtainment process or by maghemite entrapment. Both hydrodynamic diameter in the range of 200-250 nm and polydispersity index lower than 0.3 are considered satisfactory. Thermal degradation of PLGA-R begins at higher temperatures than those of PLGA-H and PLGA-Mag, but processed samples presented increase in thermal stability, which was greater before processing by emulsion and in the presence of the magnetic materials. PLGA-Mag presents superparamagnetic behavior at room temperature.

A cada dia se torna mais frequente o uso de aparelhos eletrônicos que, em sua grande maioria, estão baseados em diodos e transistores semicondutores. Compreender alguns conceitos ligados a esses materiais pode ser muito importante para entender e se relacionar melhor com tais aparelhos. Apesar de essa ser uma constatação que aparece também em documentos oficiais e nos parâmetros curriculares nacionais (PCN), o que se observa na prática é um número muito reduzido de propostas neste sentido. Assim, o objetivo desse trabalho foi descrever o uso de uma sequência de quatro vídeos curtos para ensinar tópicos de semicondutores no Ensino Médio. Eles foram aplicados em duas turmas de terceiro ano do Ensino Médio, num total de 72 estudantes. Após cada vídeo, foi entregue um questionário com 16 itens de Likert, a fim de medir as atitudes dos estudantes em relação a alguns conceitos abordados nos vídeos. Analisando os resultados obtidos nos questionários, observou-se que a proposta se mostrou bastante eficaz, principalmente no que diz respeito à motivação dos alunos em estudar o assunto. A maior parte dos conceitos foi bem assimilada, e as poucas dificuldades apresentadas estavam de acordo com a literatura. Isso sugere que o uso de vídeos curtos é uma estratégia que pode ser mais utilizada, principalmente devido à sua versatilidade e à pequena demanda de recursos técnicos.

The daily use of electronic devices, which are mostly based on semiconductor diodes and transistors, has become very common. The understanding of some concepts related to semiconductor materials is very important to achieve a better comprehension of these devices. Although this statement appears in the official documents and in national Brazilian curricular parameters (PCN), in practice there is a small number of proposals in this direction. Thus, the purpose of this article was to describe the use of a sequence with four short videos to teach introductory concepts of semiconductors at high-school level. These videos were shown to two classes of third grade of high school, with a total of 72 students. After each video, we gave the students a questionnaire with 16 Likert items, in order to measure the students’ attitudes regarding some concepts discussed in the videos. Analyzing the questionnaire results, we saw the effectiveness of the proposal, mainly with respect to the students motivation to study this subject. The majority of concepts were well assimilated, and the few difficulties were in agreement with literature. This suggests that the use of short videos is a strategy that can be more used, mainly due its versatility and very limited need of technical resources.

This study evaluates the structural, microstructural, electric and magnetic properties of nickel ferrite samples prepared through the solid state reaction. It was observed that an increase in the sintering temperature produces a higher cation concentration in the A site when compared to the B site. The assessment of magnetic properties showed that an increase in grain size leads to a decrease in the coercive fields verging on superparamagnetic values, while the saturation magnetization increases up to 46.5 Am².kg-1 for samples sintered at 1200 ºC. The dc electric resistivity behavior of samples was attributed to the increase in the cross-sectional area of grains as well as the different oxidation states and distribution of cations amongst the lattice sites of the spinel structure.