Infrared to visible up-conversion emission in Er3+/Yb 3+ codoped fluoro-phosphate glass-ceramics

Erbium Er3+ and ytterbium Yb3+ codoped fluoro-phosphate glasses belonging to the system NaPO3-YF 3-BaF2-CaF2 have been prepared by the classical melt-quenching technique. Glasses containing up to 10 wt% of erbium and ytterbium fluorides have been obtained and characterized using differential scanning calorimetry (DSC) and UV-visible and near-infrared spectroscopy. Transparent and homogeneous glass-ceramics have been then reproducibly synthetized by appropriate heat treatment above glass transition temperature of a selected parent glass. Structural investigations of the crystallization performed through X-ray diffractometry (XRD) and scanning electron microscopy (SEM) have evidenced the formation of fluorite-type cubic crystals based during the devitrification process. Finally, infrared to visible up-conversion emission upon excitation at 975 nm has been studied on the Er3+ and Yb 3+ codoped glass-ceramics as a function of thermal treatment time. A large enhancement of intensity of the up-conversion emissions-about 150 times- has been observed in the glass-ceramics if compared to the parent glass one, suggesting an incorporation of the rare-earth ions (REI) into the crystalline phase. © 2012 The American Ceramic Society.

Evaluation of degree of conversion and hardness of dental composites photoactivated with different light guide tips

Objective: The aim of this study was to evaluate the degree of conversion and hardness of different composite resins, photo-activated for 40 s with two different light guide tips, fiber optic and polymer. Methods: Five specimens were made for each group evaluated. The percentage of unreacted carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1637 cm-1) against internal standard before and after curing of the specimen: aromatic C-C (peak at 1610 cm-1. The Vickers hardness measurements were performed in a universal testing machine. A 50 gf load was used and the indenter with a dwell time of 30 seconds. The degree of conversion and hardness mean values were analyzed separately by ANOVA and Tukey's test, with a significance level set at 5%. Results: The mean values of degree of conversion for the polymer and fiber optic light guide tip were statistically different (P<.001). The hardness mean values were statistically different among the light guide tips (P<.001), but also there was difference between top and bottom surfaces (P<.001). Conclusions: The results showed that the resins photo-activated with the fiber optic light guide tip promoted higher values for degree of conversion and hardness.

Alkali activated materials based on fluid catalytic cracking catalyst residue (FCC): Influence of SiO2/Na2O and H 2O/FCC ratio on mechanical strength and microstructure

Reuse of industrial and agricultural wastes as supplementary cementitious materials (SCMs) in concrete and mortar productions contribute to sustainable development. In this context, fluid catalytic cracking catalyst residue (spent FCC), a byproduct from the petroleum industry and petrol refineries, have been studied as SCM in blended Portland cement in the last years. Nevertheless, another environmental friendly alternative has been conducted in order to produce alternative binders with low CO2 emissions. The use of aluminosilicate materials in the production of alkali-activated materials (AAMs) is an ongoing research topic which can present low CO2 emissions associated. Hence, this paper studies some variables that can influence the production of AAM based on spent FCC. Specifically, the influence of SiO 2/Na2O molar ratio and the H2O/spent FCC mass ratio on the mechanical strength and microstructure are assessed. Some instrumental techniques, such as SEM, XRD, pH and electrical conductivity measurements, and MIP are performed in order to assess the microstructure of formed alkali-activated binder. Alkali activated mortars with compressive strength up to 80 MPa can be formed after curing for 3 days at 65°C. The research demonstrates the potential of spent FCC to produce alkali-activated cements and the importance of SiO2/Na2O molar ratio and the H2O/spent FCC mass ratio in optimising properties and microstructure. © 2013 Elsevier Ltd. All rights reserved.

A comparative study of glycerol dehydration catalyzed by micro/mesoporous MFI zeolites

The catalytic properties of monomodal microporous and bimodal micro-mesoporous zeolites were investigated in the gas-phase dehydration of glycerol. The desilication methodology used to produce the mesoporous zeolites minimized diffusion limitations and increased glycerol conversion in the catalytic reaction due to the hierarchical system of secondary pores created in the zeolite crystals. The chemical and structural properties of the catalyst were studied by X-ray diffraction, nitrogen adsorption-desorption isotherms, NH3-TPD and pyridine chemisorption followed by IR-spectroscopy. Although the aim was to desilicate to create mesoporosity in the zeolite crystals, the desilication promoted the formation of extra-framework aluminum species that affected the conversion of glycerol and the products distribution. The results clearly show that the mesoporous zeolites with designed mesopore structure allowed a rapid diffusion and consequently improved the reaction kinetics. However, especial attention must be given to the desilication procedure because the severity of the treatment negatively interfered on the Brønsted and Lewis acid sites relative concentration and, consequently, in the efficiency of the catalysis performed by these materials. On the other hand, during the catalytic reaction, the intracrystalline mesopores allowed carbonaceous compounds to be deposited herein, resulting in less blocked micropores and catalysts with higher long-term stability.

Electrochemical behavior of ruthenium-hexacyanoferrate modified glassy carbon electrode and catalytic activity towards ethanol electrooxidation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Degree of conversion and hardness of two different systems of the vitrebond™ glass ionomer cement light cured with blue LED

This study investigated the physicochemical properties of the new formulation of the glass ionomer cements through hardness test and degree of conversion by infrared spectroscopy (FTIR). Forty specimens (n = 40) were made in a metallic mold (4 mm diameter × 2 mm thickness) with two resin-modified glass ionomer cements, Vitrebond™ and Vitrebond™ Plus (3M/ ESPE). Each specimen was light cured with blue LED with power density of 500 mW/cm2during 30 s. Immediately after light curing, 24h, 48h and 7 days the hardness and degree of conversion was determined. The Vickers hardness was performed by the MMT-3 microhardness tester using load of 50 gm force for 30 seconds. For degree of conversion, the specimens were pulverized, pressed with KBr and analyzed with FT-IR (Nexus 470). The statistical analysis of the data by ANOVA showed that the Vitrebond™ and Vitrebond™ Plus were no difference significant between the same storage times (p > 0.05). For degree of conversion, the Vitrebond™ and Vitrebond™ Plus were statistically different in all storage times after light curing. The Vitrebond™ showed higher values than Vitrebond™ Plus (p < 0.05). The performance of Vitrebond™ had greater results for degree of conversion than Vitrebond™ Plus. The correlation between hardness and degree of conversion was no evidence in this study.

Visible to infrared energy conversion in Pr3+-Yb3+ co-doped fluoroindate glasses

Processes involving visible to infrared energy conversion are presented for Pr3+-Yb3+ co-doped fluoroindate glasses. The emission in the visible and infrared regions, the luminescence decay time of the Pr 3+:3P0 → 3H4 (482 nm), Pr3+:1D2 → 3H6 (800 nm), Yb3+:2F5/2 → 2F 7/2 (1044 nm) transitions and the photoluminescence excitation spectra were measured in Pr3+ samples and in Pr3+-Yb 3+ samples as a function of the Yb3+ concentration. In addition, energy transfer efficiencies were estimated from Pr3+: 3P0 and Pr3+:1D2 levels to Yb3+:2F7/2 level. Down-Conversion (DC) emission is observed due to a combination of two different processes: 1-a one-step cross relaxation (Pr3+:3P0 → 1G4; Yb3+:2F7/2 → 2F5/2) resulting in one photon emitted by Pr3+ (1G4 → 3H5) and one photon emitted by Yb3+ (2F7/2 → 2F5/2); 2-a resonant two-step first order energy transfer, where the first part of energy is transferred to Yb3+ neighbor through cross relaxation (Pr3+:3P0 → 1G4; Yb3+:2F7/2 → 2F5/2) followed by a second energy transfer step (Pr 3+:1G4 → 3H4; Yb3+:2F7/2 → 2F5/2). A third process leading to one IR photon emission to each visible photon absorbed involves cross relaxation energy transfer (Pr3+: 1D2 → 3F4; Yb 3+:2F7/2 → 2F5/2). © 2013 Elsevier B.V. All rights reserved.

Transformação do glicerol em compostos de interesse petroquímico catalisada por zeólitas com ordem hierárquica de poros

Pós-graduação em Química - IQ

Síntese e aplicação de catalisadores à base de óxidos de cério, tungstênio e HZSM-5 para a produção do biodiesel

This work presents a study on the production of biodiesel by esterification reaction of oleic acid with methanol using batch reactor and different catalysts based on CeO2 and WO3 and HZSM-5. Acid treatment was performed in order to increase the catalytic activity. Different characterization techniques were performed, among them X-ray diffraction (XRD), Thermogravimetric analysis TGA/DTA, Spectroscopy in the Region in Fourier Transform Infrared (FTIR) and X-ray fluorescence (XRF). The effects of independent variables: temperature, molar ratio of oil: alcohol and the amount of catalyst and their interactions on the dependent variable (conversion of oleic acid to the corresponding ester). Overall, through the results obtained in the characterization was observed that the applied treatments were efficient, however the XRF technique, indicated that tungsten oxide leaching could occur during the preparation of the materials. The treatments performed on HZSM-5 caused no significant changes in the structure indicating that the zeolite was quite resistant to the treatments used. It was evaluated using complete 23 factorial design. For the catalysts investigated, the best reaction conditions were obtained when using higher levels of the independent variables temperature and amount of catalyst. However, for the variable molar ratio the lowest level showed significant yields for most of the synthesized catalyst, obtaining maximum conversion to the OC (67.97%), OW (74.37%), HZSM-5 (61.16%) OC-OW 1 (75.93%), OC-OW 2 (82.57%), OC-OW 3 (79.15%), S/OC-OW 1 (86.90%), S/OC-OW 2 (91.04%), S/OC-OW 3 (88.60%), S/OC-OW/H 1 (92.34%), S/OC-OW/H 2 (100%) and S/OC-OW/H 3 (98.16%). According to the experimental design, the temperature has the biggest influence on the reaction variable for all the synthesized catalysts. Among the catalysts investigated S/OC-OW/H 2 e S/OC-OW/H 3 were more effective. Reuse tests showed that the catalyst activity decreased after each cycle, indicating that the regeneration process was effective. The leaching test indicated that the catalysts are heterogeneous in the evaluated operating range. The catalysts investigated showed themselves promising for the production of biodiesel.

Espumas cerâmicas produzidas pela conjugação dos processos sol-gel, aeração e emulsificação

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A statistical evaluation of the effects of process variables during catalytic hydrogenation of passion fruit (passiflora edulis) seed oil

ABSTRACT: Hydrogenation of passion fruit (passiflora edulis) seed oil was carried out with a commercial nickel/silica catalyst under different experimental conditions. The influence of reaction parameters (reaction temperature, hydrogen pressure, amount of catalyst, agitation rate and reaction time) on the response variable (iodine value) was studied using a central composite rotatable design and six center points for replication. Under the experimental conditions used, the model response equations for the iodine value showed good agreement with the experimental results.

Produção de biodiesel da gordura de murumuru (Astrocaryum murumuru) via catálise heterogênea

Neste trabalho investigou-se a viabilidade da oleaginosa Murumuru (Astrocaryum murumuru) como matéria prima para a produção de biodiesel através do uso de catálise heterogênea básica na transesterificação. O murumuru é um fruto constituído de polpa e amêndoa, sendo que esta produz cerca de 50% de uma gordura branca, inodora, com a vantagem de não rancificar facilmente, pois é rica em ácidos graxos saturados de cadeia curta como láurico e mirístico. O biodiesel convencionalmente é produzido através da rota catalítica básica homogênea. No entanto, essa rota apresenta algumas desvantagens, tais como: a saponificação dos ésteres e a dificuldade de remoção do catalisador. Por outro lado, a rota catalítica heterogênea evita os inconvenientes da catálise homogênea, reduzindo a quantidade de efluentes aquosos gerados no processo e a reutilização dos catalisadores. O catalisador heterogêneo hidrotalcita foi sintetizado e caracterizado através das análises de fluorescência de raios X, difratometria de raios X, análise termogravimétrica, análise textural (método BET) e microscopia eletrônica de varredura. Foi realizado um planejamento fatorial completo utilizando metanol como reagente. As variáveis independentes foram temperatura, razão molar e concentração de catalisador e a variável de resposta foi a conversão, medida através do método espectrofotométrico. Essas reações foram conduzidas em um reator batelada pressurizado. A melhor conversão encontrada a partir do planejamento foi de 88,97% para razão molar de metanol/óleo igual a 12, temperatura de 200ºC e concentração de catalisador igual a 6%, em 1 hora de reação. Para essa condição, foram realizados estudos cinéticos e testada a utilização de etanol, através do estudo cinético pode-se obter uma boa correlação entre as constantes cinéticas e conversão, quando utilizado o modelo que considera reação reversível, reação química como etapa controladora que segue o mecanismo de Eley Rideal.

Estudo da obtenção de biocombustíveis a partir da rota tecnológica de craqueamento utilizando carbonato de sódio e lama vermelha como catalisadores

Neste trabalho foi estudado o processo de destilação do produto líquido orgânico, obtido no craqueamento catalítico do óleo de palma (Elaeis guineensis, Jacq) bruto em escala piloto, empregando os catalisadores carbonato de sódio (Na₂CO₃) e a lama vermelha, variando o percentual de catalisador em 10% m/m e 15% m/m em relação à matéria prima utilizada, sendo fixada uma temperatura operacional de 450ºC, visando obter frações de biocombustíveis (bio-gasolina, bio-querosene e bio-óleo) semelhantes aos combustíveis derivados do petróleo. Os catalisadores foram submetidos a um pré-tratamento de desidratação durante 2 horas em uma estufa à 300ºC, posteriormente foram realizadas as análises de DRX, IR e TG. Quanto à matéria prima, foram realizadas análises físico-químicas, visando à caracterização do óleo de palma. Os produtos líquidos orgânicos (PLOs) obtidos foram submetidos a operações unitárias de separação, decantação e filtração simples em escala de bancada, para posteriormente serem realizadas análises físico-químicas e composicionais. Os PLOs foram destilados em uma coluna Vigreux de seis (06) estágios, e as frações condensadas foram coletadas de acordo com as faixas de destilação da gasolina (60ºC - 190ºC), querosene (190ºC - 235ºC) e diesel (235°C - 370ºC), para posteriormente serem caracterizadas. Verificou-se uma melhor eficiência para o catalisador carbonato de sódio a 15% m/m quanto a redução do índice de acidez, cerca de 1,7 mgKOH/g, assim como uma conversão mássica de 97% do óleo em PLO, notou-se também que, ao aumentar a quantidade de catalisador, isto favoreceu a obtenção de um produto final com uma melhor qualidade. A lama vermelha por outro lado, apresentou rendimentos de até 64% m/m e produtos com baixa acidez cerca de 62,90 mgKOH/g, comparando este resultado com dados encontrados na literatura. A partir dos resultados finais, verificou-se a eficiência dos catalisadores, no qual o catalisador carbonato de sódio forneceu produtos com baixa acidez e com boas características para uso como combustível.

Síntese, caracterização, estudo termoanalítico e cinético do 2-metoxibenzalpiruvato de 'MN', 'FE', 'CO', 'NI', 'CU', e 'ZN', no estado sólido

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)