Recebido em 5/1/04; aceito em 24/8/04; publicado na web em 17/2/05 PREPARATION OF OPTICALLY TRANSPARENT ELECTRODES. A simple experiment for the preparation of transparent conducting glass electrodes by deposition of pure and fluorine doped SnO 2 films is described. This procedure was tested in the undergraduate inorganic course at IQ-UNICAMP. The success in achieving a conducting layer was easily checked using the standard probes of a volt-ohm meter. The optical transmittance and thickness were studied by UV-vis spectrophotometry. To discuss the experimental results we place significant emphasis on molecular orbital and energy band model theories. The undergraduate students can also discuss the concepts related to the electronic properties of solids and to interesting new materials, such as transparent conducting films, which are the subject of significant current research and technological applications.
Recebido em 23/4/04; aceito em 15/10/04; publicado na web em 17/2/05
PREPARATION OF LAMELLAR COMPOUNDS: SYNTHESIS OF THE CRYSTALLINE ZIRCONIUM HYDROGENPHOS-PHATE AND ITS INTERCALATION WITH AMINES. AN EXPERIMENT FOR UNDERGRADUATE STUDENTS.The present paper describes the synthesis of crystalline zirconium hydrogen phosphate by direct precipitation and its intercalation with pyridine and n-butylamine. The simple experiment was tested in the undergraduate inorganic chemistry laboratory course for chemistry students at IQ-UNICAMP using inexpensive reagents. The materials were characterized by powder X-ray diffraction and infrared analyses in order to obtain detailed information of the solid structure changes as a result of the intercalation process. Pyridine and n-butylamine are focused in this work as clear and elucidative examples leading to acid-base interactive processes that result in the well-formed infinite sequence of inorganic lamellar structures.Keywords: intercalation; α-zirconium hydrogenphosphate; undergraduate experiment.
INTRODUÇÃONo estado sólido existem muitos compostos chamados de compostos lamelares ou bidimensionais, que se caracterizam pelo fato dos átomos que os constituem, ligados por forças de natureza covalente, estarem arranjados de modo a formar camadas ou lamelas [1][2][3][4][5] . Em alguns compostos estas camadas são eletricamente neutras e estão unidas entre si por forças fracas do tipo van der Waals. Assim sendo, as forças que mantém as lamelas unidas (forças interlamelares) são bem mais fracas que as forças existentes entre os átomos presentes na lamela (forças intralamelares), causando uma forte anisotropia ao composto 6 . Tal situação possibilita que espécies como íons, átomos ou moléculas entrem no espaço interlamelar, sendo dado a este fenômeno o nome de intercalação 7 . As intercalações são geralmente acompanhadas por um aumento na distância interlamelar da matriz hospedeira (composto lamelar), para que haja uma perfeita acomodação da espécie convidada (espécie que se liga no espaço interlamelar) [8][9][10] . O interesse nas reações de intercalação está exatamente no fato de que elas modificam as propriedades das espécies do novo material formado e tais modificações surgem da alteração na densidade eletrônica entre as espécies envolvidas. Restrições geométricas e espaciais são impostas a ambas. A presença de íons, átomos ou moléculas entre os planos basais da espécie hospedeira certamente terá um impacto sobre as propriedades físicas em seu "bulk", incluindo densidade, condutividade e características ópticas 6 . Um considerável número de compostos inorgânicos de características cristalinas, tais como grafita, argilas, fosfatos, fosfonatos, arsenatos, oxicloretos, sulfetos metálicos, óxidos de metais de transição, etc., desperta elevado interesse em virtude das propriedades químicas inerentes, destacando-se dentre elas, os comportamentos relacionados às trocas iônicas de grupos ácidos da superfície e o processo de intercalação que ocorre no interior da lamela [11][12][13][14][15] ....
This study aimed to identify alterations in gills and hepatopancreas of the crab Ucides cordatus as indicative of environmental contamination in mangrove areas subject to chemical effluents from port activities in Maranhão, Brazil. Samples of gills and hepatopancreas were removed from each animal and fixed in Davidson's solution until the procedure of histological technique. The biometric data (means and standard deviations) of the specimens collected in the study areas indicated that the crabs in the reference area are significantly (P < 0.05) higher and heavier than the crabs collected in the potentially impacted area (port area). Gill alterations (rupture of pilaster cells, dilation of the marginal channel, cuticle rupture and necrosis) and hepatopancreas alterations (abnormal lumen, vacuolized B cells, pycnotic nuclei and necrosis) were significantly (gbn < 0.05) more frequent in crabs collected in the port area than crabs collected in the reference area. These data indicate that the health of crabs is compromised due to the pollutants present in the mangroves that surround the port area in São Marcos’ Bay.
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