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- Química geral : reactividade químicaPublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Antunes, Elisa; Leão, HelenaO vídeo trata as reações de oxiredução e as reações de complexação. São explicados e exemplificados os conceitos de redutor, oxidante, elemento de pilha e pilha eletroquímica.
- Validation of a vibrating-wire viscometer: measurements in the range of 0.5 to 135 mPa'sPublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Fareleira, João M. N. A.; Wakeham, William A.The present article describes a novel vibrating-wire viscometer that has been shown to be able to measure viscosities up to 135 mPaâs, after calibration against water at 20 °C, to provide direct traceability to the primary reference for viscosity. For the purpose of validating the instrument, measurements of the viscosity of some selected fluids, including standard reference liquids with viscosity on the order of 100 mPaâs at 20 °C and 2,2,4-trimethylpentane with a viscosity of about 0.5 mPaâs at the same temperature, were performed. The results obtained show that the instrument is capable of performing viscosity measurements with an estimated overall uncertainty better than (0.8% over the range of (0.5 to 135) mPa's.
- An industrial reference fluid for moderately high viscosityPublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Fareleira, João M. N. A.; Fröba, Andreas P.; Harris, Kenneth R.; Leipertz, Alfred; Trusler, J. P. Martin; Wakeham, William A.In industrial practice, there is a demand for a reference standard for viscosity that is established for a readily available fluid to simplify the calibration of industrial viscometers for moderately high viscosities [(50 to 125) mPa · s]. Diisodecyl phthalate (DIDP) has been suggested as that reference fluid, and a number of studies of its properties have been carried out in several laboratories throughout the world, within the auspices of a project coordinated by the International Association for Transport Properties. That project has now progressed to the point where it is possible to collate the results of studies of the viscosity of the fluid by a number of different techniques, so as to lead to a proposed standard reference value which will be included in the paper. To support this recommended value, the various measurements conducted have been critically reviewed, and the sample purity and other factors affecting the viscosity have been studied. Density and surface tension measurements have also been performed. This paper does not describe the individual viscosity determinations carried out in independent laboratories because these are the subject of individual publications, but it does describe the ancillary studies conducted and their relevance to the viscosity standard. In addition, the paper contains recommended values for the viscosity of liquid DIDP. The samples of DIDP to which the recommended values refer are isomeric mixtures available commercially from certain suppliers, with a minimum purity by gas chromatography of 99.8 %. The recommended values result from a critical examination of all the measurements conducted to date and are supported by careful arguments dealing with the likely effects of the isomeric content of the sample as well as of other impurities. The proposed reference standard is intended particularly to serve an industrial need for a readily available calibration material with a viscosity close to that required in practical situations. To that end, the recommended value has an overall relative uncertainty of approximately 1 %. It is therefore not intended to supersede for the reference value for the viscosity of water at 20 °C, which is known much more accurately, but rather to complement it.
- Química geral : velocidade das reacçõesPublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Leão, Helena; Antunes, ElisaA velocidade das reações químicas e a lei da velocidade de uma reação. A equação de Arrhenius e sua confirmação experimental. Através de animação gráfica simulam-se colisões entre moléculas.
- Viscosity measurements of liquid toluene at low temperatures using a dual vibrating-wire techniquePublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Mata, José L. Correia da; Fareleira, João M. N. A.; Wakeham, William A.A recently developed dual vibrating-wire technique has been used to perform viscosity measurements of liquid toluene in the temperature range 213 K ≤ T ≤ 298 K, and at pressures up to approximately 20 MPa. The results were obtained by operating the vibrating-wire sensor in both forced and free decay modes. The estimated precision of the viscosity measurements, in either mode of operation, is ±0.5%, for temperatures above or equal to 273 K, increasing with decreasing temperature up to ±1% at 213 K. The corresponding overall uncertainty is estimated to be within ±1% and ±1.5%, respectively.
- Viscosity measurements of diisodecyl phthalate using a vibrating wire Instrument operated In free decay mode: comparison with results obtained with the forced mode of operationPublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Fareleira, João M. N. A.; Wakeham, William A.Recently, several authors described measurements of liquid viscosities higher than 100 mPa · s, using the vibrating wire technique in the forced oscillation mode of operation. The use of a vibrating wire instrument to measure increasingly higher viscosities poses experimental difficulties due to the consequent decrease of the quality factor of the resonance. This problem affects both modes of operation: in the steady-state, forced oscillation mode, there is a loss of definition of the resonance curve, and in the transient, free decay mode, there is an increase of the decrement of the sinusoidal time response of the vibrating wire. In the present work, we have measured the viscosity of diisodecyl phthalate (DIDP) at 0.1 MPa with a vibrating wire of nominal radius of 190 μm using the free decay mode of operation. The measurements covered a range of viscosities from (64 to 265) mPa · s. The results agreed with those we have obtained with a vibrating wire instrument operated in the forced mode and with the literature data, within the estimated experimental uncertainty (k ) 2) of ( 2 %. The comparisons indicate that the use of the free decay mode of operation does not necessarily imply a significant increase of uncertainty of the viscosity results at moderately high viscosities.
- Viscosity of Di-isodecylphthalate: a potential standard of moderate viscosityPublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Fareleira, João M. N. A.; Wakeham, William A.The paper reports our first measurements of the viscosity of di-isodecylphthalate, which is a candidate for a reference material. At the same time it has a viscosity, which, at room temperature, is around 120mPa · s, so that it can fulfill the need for a reference material more nearly matched to the needs of industry. The present measurements were carried out with a specially designed vibrating-wire viscometer over the temperature range 288–308K and have an estimated uncertainty smaller than ±1.5%, following calibration against the viscosity of toluene. The instrument and results are presented here to encourage other measurements on the same material, by different techniques,which will lead eventually to the establishment of di-isodecylphthalate as a suitable reference material, as well as reference values for its viscosity.
- Diisodecylphthalate (DIDP) — a potential standard of moderate viscosity: surface tension measurements and water content effect on viscosityPublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Fareleira, João M. N. A.; Fernandes, Anabela C.; Serro, Ana P.; Almeida, Inês M. Simões de; Wakeham, William A.Our laboratory, along with several others, has been engaged in a project to determine the suitability of diisodecylphthalate (DIDP) as a standard reference material of viscosity for industrial purposes. As a part of that project, we have undertaken a study of the effects of surface tension and of impurities, of that liquid on viscosity measurements with routine, suspended level capillary instruments. For the former purpose, a set of surface tension measurements is reported here for DIDP and two reference standard mineral oils. In particular, surface tension data for DIDP, obtained using a pendant-drop shape-analysis method, at temperatures from 288K to 308K are presented. The present study suggests that surface tension effects upon viscosity measurements with routine capillary viscometers can be important enough to demand that the surface tension of the reference fluid(s) used for their calibration be specified. It is also evident that the surface tension of materials used for calibration may be relevant to their selection if errors arising from surface tension are to be avoided. In order to fulfil these requirements, the surface tension of the reference material should be included in the definition of the standard. The effect of the water content on the viscosity of a sample of DIDP is assessed as a part of the process of determining its suitability as a standard reference material.
- A new instrument to perform simultaneous measurements of density and viscosity of fluids by a dual vibrating-wire techniquePublication . Oliveira, Carla Padrel de; Mata, José L. Correia da; Fareleira, João M. N. A.; Caetano, Fernando J. P.; Wakeham, William A.A preliminary presentation of a new vibrating-wire instrument for the simultaneous measurement of the viscosity and density of fluids, over wide ranges of temperature and pressure, is made. The new equipment has the capability of measuring modes of oscillation, either in a forced mode or free decay. A theoretical description of both modes enables the simultaneous measurement of the viscosity and density of the fluid, either from an analysis of the resonance curve, or the transient response of the sensor. The consistency of the two approaches, under the same working conditions, and quality of the measuring system, have been assessed with toluene as the test fluid. It is concluded that the new equipment improves the forced mode of operation described earlier and adds a new flexibility to the vibrating-wire method.