Determination Of Oxygen Diffusivity Research Articles

Determination of Diffusion Capability of Oxygen through Brake Pads from the Surface towards the Interior

<div class="section abstract"><div class="htmlview paragraph">The oxidation of raw materials, such as phenolic resin, in the pad during the braking depends on the temperature but also on the oxygen diffusion capability through the pad. Determination of oxygen diffusion is a key point in knowing how deep from the surface tribochemistry can take place. The diffusion of oxygen through the pad is a drawback because it induces the matrix decomposition that contributes to intra-stop CoF instability and consequently worsens NVH. This study is focused on determining the oxygen diffusion through brake pads using oxidized iron sulphide particles as indicator parameter. Iron sulphide has a rough microstructure when it becomes oxide that can be recognized easily, making it a good marker. The oxygen diffusion was determined through the pad characterization, after SAE J2522 and J2707 tests, with SEM and EPMA/WDS techniques. The results show that tribochemistry also takes place beneath the PAD surface during braking due to the oxygen presence and the high temperatures reached. Depending on the testing schedule the temperature profiles on the pad are different and so is the tribochemistry. In pads tested according to SAE J2707, the oxidized particles are found in deeper sections than in pads tested according to SAE J2522. The results of this research will contribute to understanding where the decomposition of the resin starts, and therefore, how reactive compounds such as iron sulphide that also react with oxygen helps to keep the integrity of the matrix by decreasing the decomposition and contributing to the stability of intra-stop CoF, and so NVH properties.</div></div>

Determination of Oxygen Diffusion and Surface Exchange Coefficients of Mixed Ionic-Electronic Conductors by Oxygen Semi-Permeation Methods

The understanding of oxygen transport mechanisms through mixed ionic-electronic conductors is of great interest for the development of electrochemical devices at high temperature for energy conversion applications. This study is focused on the determination of two coefficients—the oxygen diffusion coefficient and the surface exchange coefficient which are key parameters for the electrochemical performance of a material. These coefficients can be largely impacted by the measurement conditions. The oxygen semi-permeation method is an adequate method to determine these two fundamental coefficients close to the working conditions of the material, i.e., under small or large oxygen partial pressure gradients.

Determination of oxygen diffusion in the SnO2/stainless steel interface of thin films by spectrophotometric measurements

Diffusion processes at high temperatures can change the transmittance and reflectance curves of multilayer coatings. These changes can significantly degrade coatings which use optical interference to obtain specific optical properties. This paper describes a study of the oxygen diffusion in SnO2/Sst interfaces using spectrophotometric measurements. A model is developed to optically describe the diffusion process in the multilayer interfaces. The validity of this model is checked experimentally using 16 samples exposed to temperatures between 475 °C and 600 °C for different exposure times: 5, 15, 50 and 120 min. Finally, these measurements are used to estimate the effective thickness of oxide formed at the interface due to oxygen diffusion, and to calculate the corresponding effective diffusion coefficients.

Oxygen Diffusivity in Asphalts and Mastics

Determination of oxygen diffusivity in binders was made by comparing the oxidation rates at the surface and at a solid–binder interface of an asphalt film of known reaction kinetics. For neat asphalts, oxygen diffusivities (D O 2 ) ranged from 10−10 to 10−11 m2/s, with log(D O 2 /T) varying linearly with log(η o *) for both base asphalts and polymer-modified binders (PMBs). For asphalt mastics, oxygen diffusivity was observed to decrease as the filler volume fraction increased. Quantitatively, this effect follows a theoretical estimate of the effect of a dilute suspension of spherical inclusions on diffusivity.

Determination of oxygen diffusivity in tetragonal YBa 2Cu 3O x using a solid state electrochemical method

A solid state electrochemical technique is used to determine the oxygen chemical and component diffusion coefficients in the tetragonal phase of YBa 2Cu 3O x . The measurements are performed at 850 °C, as a function of oxygen partial pressure and oxygen nonstoichiometry. The sample is held in a calcia-stabilized zirconia titration cell. An oxygen ionic current pulse is applied to the cell, and the EMF signal is monitored as a function of time. The diffusion coefficients are evaluated by analyzing the time dependence of the EMF, during and after the current pulse. It is found that the oxygen chemical diffusion coefficient increases weakly with x, with an average value of D ̃ ∼ 5 · 10 −5 cm 2/s at T = 850 °C. The oxygen component diffusion coefficient is found to be independent of nonstoichiometry, with a value of D o ∼ 5 · 10 −5 cm 2/s.

Determination of oxygen diffusion in solid Ag by an electrochemical technique

The measurement of oxygen diffusion in mixed conductors is important in the characterization of materials which are used for applications such as electrodes in ceramic electrochemical reactors and sensors, and membranes for the separation of oxygen from air. It is also important for the determination of the fabrication parameters for materials which depend on the oxygen content for their performance such as the ceramic superconductors. A simple electrochemical technique has been examined in order to determine the diffusivity of oxygen in solid Ag, a well known mixed conductor. The electrochemical cell: Pt, O 2/Bi 1.75Sm 0.25O 3/Ag/ Bi 1.75Sm 0.25O 3/Pt, O 2 and another which uses 8% yttria-stabilized zirconia for the auxiliary electrodes, Pt, O 2/8YSZ/Ag/8YSZ/ Pt, O 2 were employed using dc polarization and impedance spectroscopy. dc polarization gave consistent results for both cells, in agreement with the literature. The oxygen diffusivity was calculated to be: D=4.98×10 −3 exp[ (0.50±0.13 eV) kT ] , where k is the Boltzman constant and T is the absolute temperature. On the other hand, impedance spectroscopy was not successful in the determination of oxygen diffusivity in Ag in the range for which these measurements were performed (temperature: 300–800°C, frequency: 13 MHz-5 Hz). The conditions required for dc polarization to produce valid results are discussed and possible explanations for the lack of success with impedance spectroscopy are presented.

A new EMF-method for the determination of oxygen diffusion in metals

A new EMF-method for the determination of oxygen diffusion in metals