| Author (s): |
Lavinel G. Ionescu
|
| Title: |
XORGE ALEJANDRO DOMINGUES MEXICO S FOREMOST ORGANIC CHEMIST |
| Abstract: |
Xorge Alejandro Dominguez, Mexico s Foremost Organic Chemist, was born in Orizaba, State of Veracruz, Mexico on November 12, 1926, and died of a heart attack in Mexico City on May 26, 1991, only hours after he had been awarded by President Carlos Salinas de Gortari Lázaro Cárdenas Medal for his contributions and dedication to the scientific advancement of Mexico.
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| Keywords: |
Xorge Alejandro Dominguez; Mexico.
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| Year: |
1994
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| Initial page: |
1
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| Final page: |
4
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| Link: |
Acessar |
| DOI: |
10.48141/SBJCHEM.v2.n2.1994.4_1994.pdf |
|
|
| Author (s): |
Gaspar Gonzalez; Sandra M. Saraiva; Washington Aliaga
|
| Title: |
EXPERIMENTAL AND PREDICTED ISOELECTRIC POINTS FOR NIOBIUM AND VANADIUM PENTOXIDE |
| Abstract: |
The isoelectric points for niobium and vanadium pentoxides were determined through electrophoretic measurements, and the experimental results were compared with three alternative procedures to predict this parameter. Experimental and predicted results show good agreement for Nb205 that presents a well-defined value for the isoelectric point, but they do not correlate well in the case of V205 that presents a rather high solubility in the isoelectric pH region.
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| Keywords: |
Niobium pentoxide, vanadium pentoxide, electrophoresis, isoelectric points. .
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| Year: |
1994
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| Initial page: |
5
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| Final page: |
20
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| Link: |
Acessar |
| DOI: |
10.48141/SBJCHEM.v2.n2.1994.8_1994.pdf |
|
|
| Author (s): |
Florentin TACHE; Andrei MEDVEDOVICI; George-Emil BAIULESCU
|
| Title: |
MICRO-HPLC SEPARATION OF SOME THENOYLTRIFLUOROACETONATES |
| Abstract: |
Micro-HPLC separation and UV detection of some metal thenoyltrifluoroacetonates has been achieved. Cyano, octadecyl, and HTT A modified silica gels were used as stationary phases. Data about separation and detection parameters optimization are also described.
|
| Keywords: |
micro-HPLC separation; UV detection; thenoyltrifluoroaceto-nates (Cr (III), Al(III), Fe (III), Cu (II), Pb (II), Mn (II), Zn (II), Cd (II), Co (II), Ni (II), Mg (II), Ca (II), Ba (II), Na (I), K (I)); process parameter optimization; HTT A bonded stationary phases. .
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| Year: |
1994
|
| Initial page: |
21
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| Final page: |
31
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| Link: |
Acessar |
| DOI: |
10.48141/SBJCHEM.v2.n2.1994.24_1994.pdf |
|
|
| Author (s): |
Jose Schifino; Matheus A. G. Andrade
|
| Title: |
THERMOGRAVIMETRIC STUDY OF THE OXIDATION KINETICS OF COPPER |
| Abstract: |
The oxidation kinetics of copper in the air has been studied at various temperatures in the range of 500 °C to 924 °C by thermogravimetry. In that range of temperatures, the oxidation leads to copper I oxide, and the system shows diffusion-controlled kinetics according to Wagner s parabolic law. Plots of the square of the variation of the sample weight as a function of time show a good linear correlation and allow the rate constant to be determined Experiments at various temperatures confirm that the system exhibits an Arrhenius behavior and the frequency factor, as well as the activation energy, have been calculated.
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| Keywords: |
Oxidation Kinetics, Thermogravimetry.
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| Year: |
1994
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| Initial page: |
33
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| Final page: |
40
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| Link: |
Acessar |
| DOI: |
10.48141/SBJCHEM.v2.n2.1994.35_1994.pdf |
|
|
| Author (s): |
Arno Mllller; Jorge Luiz S. Barcelos; Lavinel G. Ionescu
|
| Title: |
USE OF SURFACTANTS ADDED TO REFRACTORY SLURRY IN PRECISION FOUNDRY AND INVESTMENT CASTINGS WITH ALUMINUM |
| Abstract: |
The investment casting process, involving wax models invested with clays to give ceramic molds from which metal castings are made, is characterized by the obtainment of parts of high metallurgic quality, especially as far as dimensional aspects the complexity of design and surface finishings are concerned. The high-precision parts have a wide application in the electronic, aeronautical, biomedical, textile, and food industries. Twenty-one different surfactants, added to refractive zirconite slurry, were tested for their efficiency in obtaining wetting and adherence to the surface of the wax and good quality finished aluminum parts. Only five surfactants, including sodium dodecylbenzene sulfonate, sulfonic acid, dioctyl sodium sulfosuccinate, and ethoxylated long-chain alcohols, gave satisfactory results. Analysis of the specimens manufactured from 98% aluminum, poured at 710 °C, by visual observation, rugosity, optical photography, and electron microscopy showed that they were of high quality. The present paper describes the results obtained with sulfonic acid C 8-l6 and sodium dodecylbenzene sulfonate and explains the effect of the surfactants by the formation of a monolayer film or hemi-micelles between the wax and the ceramic slurry.
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| Keywords: |
Investment Casting, Ceramic Slurry, Surfactants, Hemi-Micelles, Sulfonic Acid, Sodium Dodecylbenzene Sulfonate.
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| Year: |
1994
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| Initial page: |
41
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| Final page: |
54
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| Link: |
Acessar |
| DOI: |
10.48141/SBJCHEM.v2.n2.1994.43_1994.pdf |
|
|
| Author (s): |
Claudete J. Valdug; Eunice Valduga; Martha Adaime; Nadia Viaro
|
| Title: |
NIOBIUM AS A POTENTIOMETRIC SENSOR IN REDOX TITRATIONS WITH AND WITHOUT PASSIVATION BY AMMONIUM MOLYBDATE |
| Abstract: |
The Pt indicator electrode has been commonly used for redox potentiometric titrations. In this work the Nb indicator electrode is suggested as an alternative for the Pt indicator electrode for the redox potentiometric titrations of the system Fe(ll)/K2Cr2O7. The utilization of the proposed electrode has been studied with and without passivation. The passivation is made by electrode immersion in oxidising anodic inhibitor of NH4MoO4. The result was an observed increase of the potentiometric leap from 30 mV to 60 mV, allowing better visualization of the equivalence point. The same equivalence point was observed with the conventional and proposed electrode. With the Nb electrode, an inverse potentiometric leap was also obtained.
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| Keywords: |
potentiometric sensor; redox titrations; niobium; passivation; ammonium molybdate.
|
| Year: |
1994
|
| Initial page: |
55
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| Final page: |
59
|
| Link: |
Acessar |
| DOI: |
10.48141/SBJCHEM.v2.n2.1994.57_1994.pdf |
|
|
| Author (s): |
Rodica Mariana ION, Dumitru LICSANDRU, Florin MOISE; Cristina MANDRA VEL
|
| Title: |
THE INFRARED SPECTRA OF METALLOTETRANAPHTYLPORPHYRINS |
| Abstract: |
The infrared spectra of some metallic complexes of tetranaphthylporphyrins [Me(II) TNP (Me(H) = Mg, Zn, Co, Cn, Cd, Pb, Pd, Ni) and Me(III) TNP X(X2).(Me(III)=Fe, Mn, Co, Al; X=Cl, Imidazole)], have been studied over the range 4000-200 cm-1. The main hands have been assigned in this paper. The correlation between the metal-nitrogen or metal-axial ligand frequencies and the photostability for all these porphyrins have also been analyzed in this paper.
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| Keywords: |
tetranaphthylporphyrins, metal.
|
| Year: |
1994
|
| Initial page: |
61
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| Final page: |
70
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| Link: |
Acessar |
| DOI: |
10.48141/SBJCHEM.v2.n2.1994.62_1994.pdf |
|
|
| Author (s): |
E. A. Lissi;E. B. Abuin
|
| Title: |
HYDROPHOBIC EFFECTS IN WATER AND WATER/UREA SOLUTIONS A COMPARISON |
| Abstract: |
The partition of several n-alkanols, from methanol to n-nonanol, between n-hexane and water and between n-hexane and water containing 20 % (w/v) urea has been measured at temperatures ranging from 0 °C to 60 °C. The standard free energy of transfer from water to the urea-containing solution decreases with the length of the alkyl chain, being positive for the small alcohols and negative for the higher alkanols. The same tendency is observed upon all the temperature range considered. On the other hand, the standard entropy of transfer from water to the urea-containing solution increases with the length of the alkyl chain of the alkanol. These results are compatible with a simple description of the urea effect in terms of increasing the entropy of dissolution of the hydrophobic alkyl chain in the aqueous solution.
|
| Keywords: |
Hydrophobie Effects in Water-Urea Solutions.
|
| Year: |
1994
|
| Initial page: |
71
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| Final page: |
82
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| Link: |
Acessar |
| DOI: |
10.48141/SBJCHEM.v2.n2.1994.72_1994.pdf |
|
|
| Author (s): |
N. Garti; A. Aserin; S. Ezrahi
|
| Title: |
An Attempt to Develop a New Fire-Resistant Hydraulic Fluid Based on Water-in-Oil Microemulsions |
| Abstract: |
The strategy for the development of microemulsion-based fire-resistant hydraulic fluids has been expounded. Phase diagrams were constructed for mixtures of water, oil, and nonionic surfactants with and without cosurfactants. From these phase diagrams, the boundaries of the monophasic area were outlined. After the major components had thus been determined, several preliminary formulations were developed by incorporating suitable additives into the oleic ingredient of the hydraulic fluid. These carefully chosen additives considerably improve the performance of the hydraulic fluid. The resulting microemulsion-based compositions complied with most of the requirements set for fire-resistant hydraulic fluids. Model systems pertinent to such formulations were utilized in order to investigate structural factors, which induce enhanced water solubilization. The role played by alcohols in this context was elucidated in terms of an empirical equation. Sophisticated scattering and NMR methods have demonstrated the variations in the microstructure of a high water content model system. Sub-zero differential scanning calorimetry (DSC) techniques have revealed the existence of two types of water (free and bound) and determined their relative concentrations.
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| Keywords: |
Hydraulic Fluid, DSC.
|
| Year: |
1994
|
| Initial page: |
83
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| Final page: |
104
|
| Link: |
Acessar |
| DOI: |
10.48141/SBJCHEM.v2.n2.1994.84_1994.pdf |
|
|
| Author (s): |
Andrei E Danet, Mihaela Oancea, Silviu Jipa and Tanta Setnescu
|
| Title: |
FLOW INJECTION ANALYSIS FOR METHANOL WITH ALCOHOL OXIDASE AND CHEMILUMINESCENT DETECTION |
| Abstract: |
A highly sensitive flow injection system was developed for the methanol determination. The system is based on the oxidation of methanol in the presence of alcohol oxidase to yield formaldehyde and hydrogen peroxide. The concentration of the hydrogen peroxide produced was determined by luminol chemiluminescence. A four-line flow injection assembly was used. The sample was injected into a flow of phosphate buffer at pH 9 that merged with a flow containing alcohol oxidase. The enzymatic reaction takes place in a coiled tube, 2 meters · long and 0.8 mm i.d. Just in front of the chemiluminescence cell, the flow containing the sample merged with a flow of luminol (1.5 mM) and potassium ferricyanide (20 mM). The injected volume was 50 pL and the total flow rate 1.6 mL min·1 The determination range was 5x10"4 -1x10'2 %(v/v) methanol. The throughput was 40 samples per hour. From 20 tested substances, only L-cysteine generated a signal comparable with that of methanol. The others, at concentrations equal to those of methanol, either gave no signal at all (n-butanol, cyclo-hexanol, glycine, L-threonine, L-proline, copper sulphate) or gave signals much smaller than that of methanol.
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| Keywords: |
CHEMILUMINESCENT DETECTION.
|
| Year: |
1994
|
| Initial page: |
105
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| Final page: |
120
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| Link: |
Acessar |
| DOI: |
10.48141/SBJCHEM.v2.n2.1994.106_1994.pdf |
|
|
| Author (s): |
Nadir Ana Wiederkehr
|
| Title: |
REDOX REACTIONS INVOLVING N-ALKYL-DIHYDRONICOTINAMIDES |
| Abstract: |
Electron transfer reactions involving a series of N-alkyl-dihydronicotinamides (R-NAH) as donors were studied in homogenous solvents and in micellar media. In particular, the redox chemistry and kinetics of the reduction of methylene blue and cytochrome-C, by varying the alkyl chain length (R = C4, C8, C12) were investigated The schemes proposed for functionalized surfactants of nicotinamide suggest photochemical conversion based on light-induced electron-transfer reactions.
|
| Keywords: |
Dihydronicotinamide derivatives, functionalized surfactants, photo-redox mechanisms.
|
| Year: |
1994
|
| Initial page: |
121
|
| Final page: |
135
|
| Link: |
Acessar |
| DOI: |
10.48141/SBJCHEM.v2.n2.1994.122_1994.pdf |
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