Charles de Izarra

Investigations of GMAW plasma by optical emission spectroscopy

We report on investigations of gas metal arc welding plasma operated in pure argon and in a mixture of argon and CO2 at a dc current of 326?A. The spatially resolved electron densities and temperatures were directly obtained by measuring the Stark widths of the Ar?I 695.5?nm and Fe?I 538.3?nm spectral lines.Our experimental results show a reduction of the plasma conductivity and transfer from spray arc to globular arc operation with increasing CO2 concentration. Although the electron density ne increases while approaching the core of the plasma in the spray-arc mode, a drop in the electron temperature Te is observed. Moreover, the maximum Te that we measure is about 13?000?K. Our experimental results differ from the Haidar model where Te is always maximum on the arc axis and its values exceed 20?000?K. These discrepancies can be explained as a result of underestimation of the amount of metal vapours in the plasma core and of the assumption of local thermal equilibrium plasma in the model.

Study of tribological properties of nanolamellar WS 2 and MoS 2 as additives to lubricants

This work was aimed at studying the tribological properties of nanolamellar tungsten and molybdenum disulfides produced from nanosized W and Mo nanopowders by self-propagating high-temperature synthesis. The prepared WS2 and MoS2 powders were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential thermal analysis (DTA). For tribological tests, oil-based lubricants added with nanolamellar tungsten and molybdenum disulfides were prepared. The tribological tests show that the friction coefficient of the nanolamellar powders is lower than that of commercial powder (µmin = 0.024 and 0.064, resp.). It is also found that the oil-based lubricants with nanolamellar disulfide additives display higher antifriction and antiwear properties compared to commercial powder.

An integral representation for the product of Airy functions

Abstract.An integral representation for the product of Airy functions is given. Particular cases are examined and applications to integrals involving such products are performed.

Calibration and temperature profile of a tungsten filament lamp

The goal of this work proposed for undergraduate students and teachers is the calibration of a tungsten filament lamp from electric measurements that are both simple and precise, allowing to determine the temperature of tungsten filament as a function of the current intensity. This calibration procedure was first applied to a conventional filament lamp (lamp used in automotive lighting) and then tested on a standard tungsten ribbon lamp. The calibration procedure developed was checked by determining the calibration point of the tungsten ribbon lamp with an accuracy of 2%. In addition, for low current intensity, it was observed that the temperature of the filament was not uniform; an explanation is proposed by considering a simple heat transfer model.

Quantitative shadowgraphy on a laminar argon plasma jet at atmospheric pressure

This paper deals with the diagnostics of a dc laminar argon plasma jet operating at atmospheric pressure in ambient air using three techniques. Through the pumping effect of ambient air by the laminar jet, it is possible to observe the UV OH spectrum at 306.357?nm (transition A?2?, ??=?0???X?2?, ???=?0) and to perform emission spectroscopy in order to find the OH rotational temperature close to the thermodynamic temperature of the gas. In addition, measurements of the refractive index are made by considering two different methods: optical interferometry and quantitative shadowgraphy. It is shown that the temperatures obtained by the three diagnostics techniques are very close.

Experimental investigations of the arc MIG‐MAG welding

The type of the applied shielding gas has a strong influence on quality of the welding process. In particular, increase of the percentage of carbon dioxide in argon, causes increase of the transition current value from the globular to spray mode of metal transfer. Observations by fast camera allows to better characterize the arc column shape in the different working modes. The spectroscopic diagnostic of the welding arc is also necessary to understand the observed changes in the mode of droplet transfer. The use of an original diagnostic method allows to estimate the temperature and the electronic density distributions in the plasma without hypothesis on its equilibrium state. Results of this work seem to show that the observed effects could be linked to the microstructural modifications of the anode tip during the MIG‐MAG welding process as a function of the gas composition, and especially to the existence and disappearance of an insulating oxide “gangue” at the wire extremity.

The Ashby and Jephcott interferometer

This paper presents the Ashby and Jephcott laser interferometer that is quite simple to set up. This interferometer is well known in the field of plasma physics and has been employed to measure the electron density in transient ionized gases (plasmas). It is used here to determine both the amplitude and the averaged speed of a loudspeaker membrane moving at a low frequency (500?Hz).

Duration of an elastic collision

With a pedagogical goal, this paper deals with a study of the duration of an elastic collision of an inflatable spherical ball on a planar surface suitable for undergraduate studies. First, the force generated by the deformed spherical ball is obtained under assumptions that are discussed. The study of the motion of the spherical ball colliding with the planar surface allows us to determine the duration of the elastic collision. In order to check the theoretical model, an experiment is proposed to measure the duration of the collision. A more refined model built with masses and springs gives good agreement between theoretical and experimental values.

Quantitative shadowgraphy made easy

This paper is dedicated to the learning of the shadowgraphy technique at graduate and undergraduate levels. It presents an experiment that allows measurement of the refractive index of butane with the help of an affordable quantitative shadowgraphy bench. The paper is constituted of two distinctive parts. The first presents the theory and data processing involved in shadowgraphy, introducing the concept of Abel inversion and modern data computer processing for graduate students. The second focuses on the experimental set-up and results; here, a qualitative interpretation of shadowgrams suitable for undergraduate students is given, as well as a quantitative explanation using a butane gas jet. The refractive index of butane measured with our simple experimental set-up is in close agreement with values available in the literature.

Experimental characterization of an argon laminar plasma jet at atmospheric pressure

This paper deals with a dc laminar pure argon plasma jet operating at atmospheric pressure in ambient air that was experimentally studied in order to obtain temperature and velocity. Plasma jet temperature was evaluated by optical emission spectroscopy and the plasma jet velocity was determined by various methods using a pressure sensor. It is shown that the maximum plasma jet temperature is 15 000 K and the maximum plasma jet velocity is 250 m s−1 at the plasma jet centre. Finally, a study of the ambient air amount entrained into the plasma jet is presented.