Modelagem dos processos químicos em plasmas de misturas gasosas usadas na corrosão de silício. Parte 1: CF4 / O2

The plasma etching of semiconductor surfaces with fluorine-containing compounds has technological interest. Presently, considerable effort is being devoted to understand the chemistry involved. In this work, a numerical modeling analysis of the gas-phase decomposition of CF4/O2 mixtures, in the presence of silicon, was performed. The relative importance of individual processes was determined as well as the effect of the parameters' uncertainties. The results were compared with experimental data. The main etching agent in the system is the fluorine atom. The concentration of the main species, SiF4, CO, CO2 and COF2 depend on the composition of the mixture.

Modelagem dos processos químicos em plasmas de misturas gasosas usadas na corrosão de silício. Parte 2: SF6 / O2

In this work, a numerical modeling analysis of the gas-phase decomposition of SF6 / O2 mixtures, in the presence of silicon, was performed. The relative importance of individual processes and the effect of the parameters' uncertainties were determined. The model was compared with experimental data for the plasma etching of silicon and with the calculated results for the CF4 / O2 system. In both systems the main etching agent is the fluorine atom and the concentration of the major species depends on the composition of the mixture. The etching rate is greater for SF6 / O2.

Hidrólise enzimática de casca de arroz utilizando-se celulases: efeito de tratamentos químicos e fotoquímicos

In the present work we reported the study of rice hull enzymatic hydrolysis using a commercial cellulase preparation. The results showed that previous treatment with light and sodium chlorite inhibits the enzymatic process (31.4 and 11.8%, respectively) while hydrogen peroxide and ozone favoured the enzymatic production of reducing sugars (5.9 and 54.9%, respectively). Studies performed by quimiluminescence showed that the chlorite treatment produced the most significant change in the structure of rice hull. Nevertheless, this treatment did not favour the subsequent enzymatic process. Photomicrographs obtained from rice hull hydrolysates showed that pre-treatment changed mainly the inner epidermis and parenchyma cell and that they did not change cellular organization of the hull.

O dispositivo à corrente diferencial-residual (DR) e sua utilidade em laboratórios químicos

The use of GFCI, ground-fault circuit interrupter, in the chemical laboratory is described, to improve the electrical safety of equipments such as rotary evaporators and constant temperature baths.

Gerenciamento de resíduos químicos em laboratórios de ensino e pesquisa

The generation of chemical residues in both teaching and research laboratories is a serious problem in Brazil. In this article, a Chemical Residues Management Program is presented and discussed. The Program is centered in different hierarchic positions, but driven by minimization. A common ground for discussion and distribution of related information is also proposed as a mean to spread the program throughout Brazilian Universities.

7-Epiclusianona, a nova benzofenona tetraprenilada e outros constituintes químicos dos frutos de Rheedia gardneriana

Phytochemical investigation of the fruits of Rheedia gardneriana led to the isolation of sesquiterpenes mixture, methyl esters of fatty acids (palmitate, estearate, oleate, linoleate, linolenate), sugars (galactose, glucose, fructose), triterpene (oleanolic acid), steroids mixture (stigmasterol and sitosterol) and the new tetraprenylated benzophenone 7-epiclusianone.

Elementos da dinâmica química ao nível da teoria variacional do estado de transição com correções interpoladas

In this article are presented some fundamental elements of the conventional and of the variational transition state theories which are needed to carried out calculations of semi-classical chemical dynamics. Some important bottlenecks in building reliable potential energy surfaces using electronic structure calculations are also discussed. It is put emphasis on the methodology of the variational transition state theory with interpolated corrections (VTST-IC), and its application in the calculations of the rate constants and of the kinetic isotope effect (KIE) of CH4 + Cl « CH3 + HCl reaction.

Análise de cabelo: uma revisão dos procedimentos para a determinação de elementos traço e aplicações

Aspects related to the quality of human hair analysis are presented, such as sample collection, sample preparation, determination of trace elements and application examples. Also the hair morphology, the importance of this analysis and its uses and meanings are discussed.

Constituintes químicos das raízes de Pyrostegia Venusta e considerações sobre a sua importância medicinal

This paper describes the chemical constituents isolated from roots of Pyrostegia venusta. From ethanol extract of the roots allantoin, beta-sitosterol, 3b-O-beta-D-glupyranosylsitosterol and hesperedin were isolated. The structures of these natural products were identified on the basis of spectral data, including 2D NMR of the peracetyl derivative of hesperidin.

Separação e identificação de constituintes químicos polares dos galhos de Porcelia Macrocarpa

This paper describes a methodology to separate and identify polar compounds as flavonoid and lignan glucosides, amino acids, salt of quaternary ammonium amino acid and carbohydrates from branches of Porcelia macrocarpa (Annonaceae).

Dissolução eletrolítica para a determinação de elementos de liga em aço ferramenta por ICP-AES

Different methods have been applied to solve special problems of metal analysis. First, the solid samples of tool steels were analyzed by X-ray fluorescence. Alternatively, an on-line electrodissolution implemented in a flow injection system and conventional dissolution procedure for determination of W, Mo, V and Cr in tool steels by ICP-AES is described. The resulting analyte solutions were compared with conventional dissolution procedure and determination by ICP-AES. The electrolytic procedure presented a good performance characterized by a sample throughput of 164 determinations per hour. Results were in agreement with those obtained by conventional acid dissolution.

Químicos brasileiros esquecidos Adelino Leal: um professor que ensinava no laboratório

Chemistry is a experimental science and should be taught emphasizing the experimental work at laboratories. Brazilian teachers either in secondary level teaching as well at University gave minor attention in laboratory experiments as a tool to improve the quality of the teaching. Adelino Leal published a monograph in 1926 which emphasizes the experimental work in the teaching of Chemistry. The French chemist Jungfleisch had a important influence in the Adelino Leal's work and was the main reference for both his work and published books.

Sobre a aplicabilidade da termogravimetria para a estimativa de parâmetros termoquímicos de compostos de coordenação: os elementos lantanídicos

By using thermochemical data reported for a series of chelates of the type [Ln(thd)3], thd = 2, 2, 6, 6 ­ tetramethyl- 3,5-heptanedione and Ln = La, Pr, Nd, Sm, Gd, Tb, Ho, Er, Tm and Yb, empirical correlations were found involving thermochemical parameters (e.g. dissociation enthalpy) and the thermodynamic temperatures of the beginning of thermal degradation of the chelates, t i. It is shown that t i values are of capital importance in the study of this all class of coordination compounds. Among others, the empirical equation is obtained: r3+ = (-0,013.Z + 1,36)/0,005, that relates the lanthanide cation radius (pm) with the atomic number of the element. The remarkable fact is that this equation is achieved by using thermogravimetric and calorimetric parameters. Is also shown that t i values are related with the P(M) function values, which are very close related with the energy difference, deltaE, between the lowest electronic energy level of the f n s²d¹ configuration and the lowest energy level of the f n+1s² configuration in the neutral gaseous atoms.

Relações da atividade agropecuária com parâmetros físicos químicos da água

Water Quality Index (WQI) was used during summer and winter of 1994 and 1995 in the final section of Onça and Feijão streams, downstream Broa Reservoir (São Carlos/SP) to evaluate agricultural and catlleman effects. In Onça stream water quality was "acceptable" in winter and "inappropriate to conventional treatment" in the summer. In Feijão stream the water had an "excellent" quality in winter and "good" in the summer. A MANOVA (Multivariate Analysis of Variance) has used to discriminate seasons and streams. Correlation (p<0,05) among the variables was tested. Water temperature, turbidity, pH and fecal bacteria are highly correlated and can be one of the factors that cause WQI change by seasons.

Utilização de modelos físico-químicos de adsorção no estudo do comportamento do cobre em solos argilosos

It was evaluated the applicability of Langmuir, Freundlich and Temkin models to copper adsorption in three classes of soils. Fractions of each soil were added to test tubes containing growing concentrations of the metal in solution. The tubes were shaken and the copper concentrations were determined in the extracts by atomic absorption spectrometry (AAS). The models offered a good fit for the experimental data indicating that presence of silicated clay had high influence on copper sorption. The Langmuir isotherm showed high influence of the organic matter in the absorption phenomenon. It was evidenced the importance of further studies related to Temkin model.