The proposal addresses the electrochemical experimentation as a pedagogical instrument for the integral and dynamic student involvement, facilitating the teaching-learning process. The experimental proposal focuses on the conversion of electrical energy to chemical energy and vice versa. The experiments for the two simultaneous energy conversions were designed with simple, easily accessible and inexpensive reagents and materials. The production of hydrogen and oxygen gases in the electrolytic cell, and the consumption of these same gases in the fuel cell, exploits the non-spontaneous and spontaneous electrochemical semi-reactions, respectively, that occur at the anode and cathode. Hydrogen gas production is crucial to the development of fuel cell technology. To facilitate the identification of anodic and cathodic reaction, and the monitoring of electrochemical decomposition of water, black bean extract was used as an alternative indicator. The electrochemical reactions involved in energy conversions are considered fundamental in the teaching-learning process of basic concepts related to water electrolysis and the recombination of hydrogen and oxygen gases. The experiment also corroborates the elucidation of alternative ways to generate electricity to meet the current needs of modern society.

A new study about corrosion behavior of CoCrMo alloy used as implant material exposed to the physiological serum and Hank's solution in different temperatures, electrolyte compositions and immersion time were simulated, using open circuit potential (OCP), potentiodynamic polarization curves (PPC) and electrochemical impedance spectroscopy (EIS.) From the results, it can be concluded that CoCrMo biomaterial is influenced by electrolyte composition and temperature, and the passive films were more protective when formed in presence of physiological serum. Comparing the Ecorr for both solutions, it is possible to verify that the Hank's solution presented values more negative for the two studied temperatures (25 and 37 °C), indicating a greater susceptibility to the corrosion process. Regarding the results of potentiodynamic polarization, the ipass, decreased as function of time, indicating a more protective passive film at 25 °C. In regards to the physiological serum, the highest ipass values at 37 ºC evidenced the formation of a less stable passive film. The different behavior of ipass in Hank's solution may be related to the competitiveness between a possible film of D-glucose and oxides of the alloy metals. EIS studies suggest that the film formed in presence of physiological serum is nobler than that with Hank's solution.

RESUMO Este trabalho investigou o processo de hidrólise química de poli(tereftalato de etileno) (PET) em meio alcalino; especificamente de garrafas incolores e coloridas pós-uso. A reciclagem química de embalagens PET pós-uso ainda é muito pouco explorada no Brasil, não sendo tão diferente do que está sendo praticado em outros países. Dentre variáveis possíveis de investigação, aquelas estudadas neste trabalho foram a concentração de hidróxido de sódio (NaOH) e a cor do PET. A reação de despolimerização do PET pós-uso foi realizada na concentração de 1,0, 3,0, 5,0, 7,5 e 10,0 mol L-1 de NaOH, sendo que em 7,5 mol L-1 foi aquela que mostrou os melhores resultados, relativamente à extensão da reação e à pureza do monômero recuperado, o ácido tereftálico (TPA). A reação também foi feita para PET de cores diferentes, na concentração de 7,5 mol L-1 de NaOH, cujos resultados mostraram um menor desempenho quando comparados com aqueles obtidos para o PET não colorido. Esse resultado sugere ser devido à presença de corantes, que pela estrutura química dos mesmos, competem pelo ataque nucleofílico do íon hidroxila (OH-), durante a reação de hidrólise do PET. As análises por Espectrofotometria no Infravermelho (FTIR), Difração de Raios X (DRX) e Termogravimétrica (TGA/DTG) confirmaram que os produtos de reação resultaram em TPA, uma vez que os espectros foram coincidentes com aqueles do TPA comercial. O crescente consumo de embalagens PET e o descarte ambiental aleatório precisam de soluções rápidas; os resultados do presente trabalho são importantes e corroboram com o avanço da pesquisa para a reutilização de matéria prima.

ABSTRACT This work investigated the chemical hydrolysis process of polyethylene terephthalate (PET) in alkaline medium; specifically, colorless and colored post-consume bottles. The chemical recycling of post-consume PET bottles is still very little explored in Brazil, not being so different from what is being practiced in other countries. Among possible variables of investigation, in this work was studied the sodium hydroxide (NaOH) concentration and the PET color. The post-consume PETdepolymerization reaction was performed at the concentrations of 1.0, 3.0, 5.0, 7.5 and 10.0 mol L-1 NaOH, and in 7.5 mol L-1was the one that showed the best results, regarding the extent of the reaction and the purity of the recovered monomer, terephthalic acid (TPA). The reaction was also made for PET of different colors at the concentration of 7.5 mol L-1 NaOH, whose results showed a lower performance when compared to those obtained for non-colored PET. This result suggests that it is due to the presence of dyes, which, due to their same chemical structure, compete for nucleophilic attack of the hydroxyl ion (OH-) during the hydrolysis reactionof of PET. Infrared Spectrophotometry (FTIR), X-ray diffraction (XRD), as well as Thermogravimetric (TGA / DTG) analysis confirmed that the reaction products resulted in TPA, since the spectra were coincident with those of the commercial TPA. The increasing consumption of PET packaging and aleatory environmental disposal need quick solutions; the results of this work are important and corroborate with the advance of the research for reutilization of raw material.

O experimento, realizado no Laboratório de Hidráulica e Irrigação da UFC, em Fortaleza, de julho a setembro de 2002, utilizou tanques de drenagem de nível freático constante para verificar a relação existente entre o Índice Diário de Estresse (IDS) e componentes de produção em beterraba, cultivar Early Wonder. O delineamento experimental foi inteiramente casualizado, com cinco tratamentos (0; 120; 180; 240 e 300 cm de soma de excesso de água no solo (SEW30)), quatro repetições e parcelas de 48 plantas úteis. O coeficiente de suscetibilidade da cultura (SC) ao encharcamento foi calculado para o primeiro, segundo e terceiro estádios de desenvolvimento, submetendo-se as plantas a um encharcamento de quatro dias de duração com lençol freático à profundidade de 0,10 m, em cada um desses estádios. Avaliou-se o diâmetro médio do hipocótilo (DM), o comprimento da maior folha (CMF) e a produtividade (PT). Somente DM apresentou variação significativa em função do excesso de água, passando de 5,51 quando não houve estresse para 4,71 quando o estresse foi aplicado no último estádio de desenvolvimento. Os valores obtidos para SC para o primeiro, segundo e terceiro estádios de crescimento foram de 0,10; 0,16 e 0,28, respectivamente. O produto do valor ponderado de SC (0,17) juntamente com os respectivos valores de SEW30 (0; 120; 180; 240 e 300 cm) permitiu calcular, para cada tratamento, os valores de índice diário de estresse (IDS), de 0; 20,4; 30,6; 40,8 e 51,0, respectivamente. Somente o tratamento com maior nível de estresse (lençol freático a 5 cm de profundidade) diferiu estatisticamente (p<0,05) da testemunha sem estresse: DM passou de 5,51 na testemunha para 4,00; CMF foi reduzido 43,35 para 26,10 e; a produtividade caiu de 40,4 para 15,8 t ha-1). A estimativa de IDS que produziu os maiores valores para produtividade (41,8 t ha-1) foi de 12,8 cm, obtida através de regressão quadrática (r² = 0,87).

The experiment was conducted in a laboratory at the Federal University of Ceara, in Fortaleza, Ceara State, Brazil, from July to September 2002. Constant water table depth drainage tanks were used to study the relationship between the Stress Daily Index (SDI) and sugarbeet yield (cultivar Early Wonder). The experimental design was completely randomized with five treatments in four replications using 48-useful plant plots. Treatments consisted of 0; 120; 180; 240 and 300 cm as the total of excess water (SEW30). The crop flooding susceptibility coefficient (SC) was calculated for the first, second and third development stage. Plants were submitted to a four-day flooding period by raising the water depth up to 0.10 m, at each stage. The root mean diameter (DM) was evaluated as well as the length of the largest leaf (CMF) and the productivity (PT). Only DM presented significant variation as a result of soil water excess, varying from 5.51 without stress to 4.71 when the stress was applied at the last stage. The values of SC obtained for the first, the second and the third development stages were 0.10, 0.16 and 0.28, respectively. The weighted value of SC (0.17) associated with the respective values of SEW (0; 120; 180; 240 and 300 cm) allowed us to calculate values of stress daily index (SDI), for each treatment: 0; 20.4; 30.6; 40.8 and 51.0, respectively. Only the treatment with highest stress level treatment (water table at 5 cm) presented statistical difference (p<0.05). DM varied from 5.51 to 4.00, while CMF was reduced from 43.35 to 26.10, and the productivity dropped from 40.4 to 15.8 t.ha-1. The estimate of SDI that produced the highest value of productivity (41.8 t ha-1) was 12.8 cm, based on quadratic regression (r² = 0.87).

Independent of the sample form (powder or film), XRD analysis of Ir0,3Ti(0,7-x)Ce xO2, (nominal) mixtures, for x=0, shows the formation of a solid solution phase between IrO2 and TiO2, as well as the rutile phases of IrO2 and TiO2. The presence of the anatase phase of TiO2 is also confirmed. The introduction of 30 mol% CeO2 in the mixture reveals the presence of the CeO2 and Ce2O3 phases, besides the already mentioned ones, in the powder. In the film form, however, an amorphous phase is identified. When all of the TiO2 is substituded by CeO2, for both sample forms, the only phases found are IrO2, CeO2 and Ce2O3. This result suggests cerium oxides are not capable of forming solid solutions with either IrO2 or (Ir,Ti)O2 acting solely as a dispersant matrix for these phases. These results are consistent with the much higher electrochemically active surface area when CeO2 is introduced in the binary Ti/Ir0,3Ti0,7O2 mixture. It was possible to establish a relationship between the electrochemical stability of the supported films and their crystalline structure. The unexpected presence of TiO2 and Ti2O3 in the Ti/Ir0,3Ce0,7O2 (film sample) is attributed to oxidation of the Ti support during the calcination step.