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- Ionic interactions in phosphate aqueous solutionsPublication . Ferra, Maria Isabel Almeida; Amaro, Albertina; Mendonça, AntónioMean activity coefficients of NaCl have been calculated, by means of the Pitzer theory,in mixed solutions of NaCl and NaH2PO4 and of NaCl and Na2HPO4, with ionic strength lower than 2 mol kg-1, at 25 ºC. Electromotive force measurements, using a silver, silver chloride and a sodium ion selective electrodes, show nernstian response, in those mixed electrolyte solutions.
- Δ8 Labdanes from Halimium VerticillatumPublication . Urones, J. G.; Marcos, I. S.; Moro, R. F.; López Rodilla, Jesus Miguel; Mendonça, António José Geraldes deThree new acids in the form of methyl esters and the acetyl derivative of an alcohol have been isolated from Halimium verticillatum. Their structures have been established by spectroscopic methods and/or chemical correlations as those of methyl 15hydroxy-7-oxo-8-labden-17-oate, methyl 7a,l5-dihydroxy-glabden-17-oate, methyl 7/3,15-dihydroxy-8-labden-17-oate and 17-nor-15acetoxy-7-oxo-8-labdene.
- Application of the Pitzer theory to the evaluation of pH of the phthalate standard solutionPublication . Mendonça, António; Ferra, Maria I.The pH value of the potassium hydrogen phthalate 0.05 mol.kg-1 has been detemined, using the Bates-Guggenheim convention and lhe Pitzer model for the calculation of the chloride íon activity coefficient. A comparison has been made between lhe two approaches.
- Structure of papers and NonwovensPublication . Pereira, Mário José Teixeira; Costa, A. P.; Salvado, Rita; Silvy, Jacques; Fiadeiro, PauloWe characterise the structure of fibrous materials: papers and nonwovens by diffraction and transmission of light. This allows the measurement of the fibres orientation distribution of the sample as a whole or for the surfaces using replicas. Applications of the methods are demonstrated in the case of paper for the control of the curl tendency and for two kinds of nonwoven materials, one used in the tailoring of surgical garments and the other used as components of the baby diapers.
- New method for the measurement of fibres orientation on the paper faces applied to the analysis of hygro-instability in paper sheetsPublication . Pereira, Mário José Teixeira; Costa, A. P.; Trindade, A. C.; Fiadeiro, Paulo; Silvy, Jacques; Tosio, J. M. SerraFor a given change in the humidity of a paper the hygro-instability of the sheet depends of two main factors: the sheet structural parameters which reflects its structure: the sheet porosity, the fibres orientation distribution mainly in the sheet plane and the variations of these parameters across the paper sheet thickness. the water reactivity of the components of the paper sheet which depends mainly of the sheet composition: the cellulosic and the fillers content, the nature of the fibres, softwood or hardwood, their degree of delignification, the beating degree of the pulp, the fines content, the conditions of the sheet drying with a more or less conditions of restraint. In this research initiated at the University of Beira Interior (UBI) with the collaboration of the Ecole Française de Papeterie (EFPG), we have tried to identify these main parameters of the paper hygro-instability. For this purpose we characterise the sheet structural parameters by optical methods developed at the Optical Centre of UBI.
- 3-D Characterisation of Nonwoven Fabrics by means of an optical systemPublication . Pereira, Mário José Teixeira; Salvado, Rita; Fiadeiro, Paulo; Silvy, JacquesThe characterisation of fabric structure by means of quantified parameters is essential for the control of the fabrication processes and the resulting properties of the nonwoven materials. Important parameters of the structure are the porosity, the mean pore size and the pore size distribution, the specific area of the texture, the fibres orientation the last one needing to be characterised in the three dimension of the fabric web. In this research work we intend to evaluate the porous fibres orientation in geotextiles nonwovens using a procedure based on the fibres light conducting and their associated scattering. The interpretation of the phenomena is made through a modelisation concept of the pore fibre interfaces
- Activity coefficients in the evaluation of food preservativesPublication . Mendonça, António; Vaz, Margarida I. P. M.; Mendonça, DinaFood preservatives are used in very low concentrations. However, usually they are used in aqueous high ionic strength solutions. The Pitzer model allows activity coefficient determination in these cases. Without the knowledge of activity coefficients, activity or ‘correct concentration’ cannot be known. In this work, the activity coefficients of sodium chloride, potassium chloride and calcium chloride in pure solutions were calculated by the Debye H¨uckel theory and the Pitzer theory. The calculated values were compared with experimental values. Activity coefficients of pure sodium benzoate in aqueous mixed solutions with potassium chloride or calcium chloride were evaluated using the Pitzer model. The same evaluation can be done to more complex systems once all Pitzer parameters values for the ionic species are known.
- The Double Monochromator Geometric Theory and Compensatlon of AberratlonSPublication . Sokolova, Elena; Mogo, SandraThe light path function for the double monochromator is constructed, and the formulas of account of the members of its expanding in ascending power series adequate for the defocusing and the first order astigmatism aberrations are found. On the basis of results of the minimisation of obtained expressions the opportunity of construction of a double monochromator so that the second monochromator fractionally compensates aberrations of the first one is analysed. It is also noticed, that in the scheme of the double monochromator under certain conditions compensation of an astigmatism of the second order is automatically carried out. It allows to use a deviation angle of the scheme for more complete compensation of other aberrations and to develop double monochromators with the improved performances.
- Determination of Pitzer parameters for sodium benzoate at 298.15 KPublication . Mendonça, António; Vaz, Margarida; Ferra, Maria I.Sodium benzoate is a salt widely used in industry as preserver. Its activity coefficients in aqueous solutions can be estimated by Pitzer theory, once the necessary parameters are known. Electromotive force (emf) measurements on galvanic cells without liquid junction have been used for the determination o f mean activity coefficients of sodium chloride in the ternary system sodium chloride + sodium benzoate (NaB) + water. Pitzer theory has been applied to this system and those data enabled the evaluation of the specific parameters for sodium benzoate at 298.15 K by linear regression. The values obtained f o r / B(0) NaB and B(1) NaB parameters, respectively 0.177 kg mol-1 and 0.34 kg mol-1 are close to those published already for other carboxylic acid salts.
- Paper surface diffraction to characterise the fibre orientation distributionPublication . Pereira, Mário José Teixeira; Fiadeiro, Paulo; Silvy, JacquesMany paper mills use ultrasonic techniques to measure the Tensile Stiffness Index, TSI, of the paper sheet. They then assume that the TSI value is the same as the fibre orientation anisotropy. This is true if the paper is allowed to dry without any internal tension or elongation, but does not apply to paper manufactured in a paper machine. The paper machine introduces tension and elongation as soon as the fibre is placed on the forming fabric. These factors increase through the press section and are accentuated in the drying section. In order to uniquely measure the fibre orientation anisotropy on the surfaces, the proposed method uses replicas of both paper surfaces to produce a laser diffraction pattern. The obtained pattern reveals an elliptical shape, which is related to the fibre orientation anisotropy of the paper surface. By measuring the ellipticity of the diffraction pattern and the deviation with respect to the machine direction, one can quantify the fibre orientation distribution. Different papers from the bench market have been successfully tested with the developed system. This article describes the new developed optical system and its innovative capabilities in the field to produce maps of the fibre orientation of a complete paper sheet surface. A selection of the obtained results to prove its feasibility is also presented.