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Nonconventional Technologies Review 2013 Romanian Association of Nonconventional Technologies Romania, June, 2013

FLASH LAMPS USED FOR SURFACE TREATMENTS- CASE STUDY

Nederita Victor1, Ciudin Rodica2, Isarie Claudiu3, Titu Mihail4and Petrescu Valentin5 1 “Lucian Blaga” University of Sibiu, ned_vic@yahoo.com

2 “Lucian Blaga” University of Sibiu, rodica.ciudin @ulbsibiu.ro 3 “Lucian Blaga” University of Sibiu, claudiu.isarie@ulbsibiu.ro

4 “Lucian Blaga” University of Sibiu, titu.mihail@gmail.com 5 “Lucian Blaga” University of Sibiu, valentin.petrescu@ulbsibiu.ro

ABSTRACT: Paper presents experimental results showing the effects of flash lamps broad spectrumadiation in order to change the surface characteristics of ebonite samples in different environments, water and air. Results are presented and explained, as well as the benefits of the method used. Presented research results are coming as a need for ebonite surface erosion performed in order to improve chemical and mechanical characteristics. The studies were performed in atmospheric air pressure and water environment, the variables that were determined to play a role in the extent of surface modifications by flash lamp radiation pulses are distance of lamp from the surface, exposure time, pulse radiation intensity, the surface morphology. KEY WORDS: gas discharge lamp, surface treatments, ebonite, material removal rate.

1. INTRODUCTION

Since 1960, when the first working laser was reported the interest for pulsed radiations increased gradually. Based on first experiments in this field the flash lamp used for laser pumping found new applications as a singular source for pulsed radiations that were more and more used in a large scale applications such as: medicine, biotechnology, food industry, military applications also [1]. It has been found that pulsed UV sources can provide the optimum combination of wavelength, distance and duration to produce beneficial changes in the surface energy, surface chemistry and topography of polymers which results in substantial materials improvements [2-3]. Since most materials absorb wide range wavelength radiation energy efficient UV sources are very desirable for stimulating chemical processing. Therefore there is a demand for high-power efficient, low-cost and large area UV sources.

Flash lamps overlap and considerably enlarge the application range of excimer lamps making it possible to carry out surface treatments not only of non-metals but also metal samples. This is because the radiation spectrum is very wide (UV-VIS-IR) and pulse power is much higher than in excimer lamps. The mechanism of processes is based not only on photochemical effects but also on photo-thermal and thermodynamic effect.

2. EXPERIMENTAL EQUIPMENT

In the paper are presented experimental results of surface processing of hard polymers treated by high intensity radiation.

Such a huge interest is due to a lot of advantages provided by the flash lamps for impulse radiation as emitted energy (800kJ), high efficiency (70%), radiation spectrum (200–1100 nm), impulse time (10-3–10-6s), lamp configurations, low environmental impact, compact features.

As optical radiation source a flash lamp ИФП-800 from a laser ОГМ-20 was used. They are filled with gas (usually a noble gas, xenon or krypton) and have two electrodes sealed into the quartz envelope.

An electrical discharge between the electrodes is initiated by the power supply and very large pulsed electrical currents flow through the gas. During this pulsed current flow, intense optical radiation is emitted [4]. The function of the charging power supply is to charge the energy-discharge capacitor.

The installation is made of source radiation-1 (figure 1), placed in side a cylindrical spotlight-3 and the material-4 undergoing the treatment. The source is feed from a set of condensers-2 of a capacity of 700µF which, in its turn, is powered by a high voltage power supply-1 connected to a home network (50Hz, 220V) equipped with a electric signal synchronising device.

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Figure 1. Scheme of the experimental device

Characteristics of IFP 800 (figure 2) are:

• cylindrical shaped lamp Dext.= 10 mm, L = 300 mm;

• filling gas Xenon; • external ignition; • voltage at ignition condenser U>700 V • auto ignition voltage Ua=2500 V.

Figure 2. ИФП-800 Lamp

The lamps functioning is based on the electric discharge between wolfram electrodes in gas environment and plasma emergence which generates through the lamp’s balloon a shiny, glittering flux of radiant energy with a wavelength corresponding to the filling gas [5].

Of all types of filling gas, the most often used is Xe, because it has a high value of changing electric energy into radiant energy. The light emitted from flashlamps contains both discrete line structure and continuum radiation. The line structure arises from transitions between energy levels of the atoms and ions in the discharge. The continuum radiation is blackbody radiation, characteristic of the temperature of the plasma in the discharge. The exact spectral content is complicated, depending in a complex way on the gas type and pressure, the current, the plasma temperature, and the electron density. In addition, the spectral content of the light can change during the course of the pulse [6]. Experiments were performed for ebonite samples having a cylindrical shape. Effects on ebonite hard surface were studied for air environment and water

environment. The loss in weight was monitored and recorded using electronic balance of high performance type ВЛКТ-500 and the results are presented in figure 3 and figure 4. 3. MEASURING THE MATERIAL

REMOVAL RATE (MRR)

The flash lamp was placed inside the ebonite cylinders and fixed at one end to the experimental stand. The radiation intensity was changed according to the tension applied to the condenser terminals and has the value of 800-1000J /pulse and the power of impulse varied between 1kW to 1MW. The plasma’s temperature reaches values of 10000 to 15000K and the radiation wavelength was λ=0,35-0,5µm. It was observed that the erosion process is influenced by the aerodynamics, radiation intensity and interior diameter of the sample or the distance between the lamp and the sample. Radiation intensity performed in this case was varied from 1,0 kV to 1,4 kV. Interior diameter of the sample was changed with 2 to 8 mm. The same experiment was performed in water, a different environment, to study if there are different behaviours or improvements.

Experimental results reveal that the erosion process is influenced by the radiation intensity and the distance between the source (flash lamp) and the ebonite surface and of course the environment (air or water). Hydrodynamics occurred at the impulse radiation to a hard surface, like ebonite, differs from the case to case.

Figure 3. Material removal rate for ebonite according to

intensity of energy: 1- δ = 2 mm; 2- δ = 3 mm; 3- δ = 1 mm; 4- δ = 2 mm; 5- δ = 3 mm; 6- δ = 4 mm;

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Figure 3 shows the intensity of erosion for ebonite samples treated in water environment (curbs 1 and 2) to be much higher than in air (curbs 3 and 6).

Figure 4. Material removal rate for ebonite according to distance between radiation source until the surface of the

ebonite.

In case of samples treated in water cavity effects appear at the surface resulting in high intensity of erosion processes.

Figure 4 shows the erosion zone A to be influenced directly by the distance between the lamp and the sample, and the maximum effect of erosion is in water environment, because the cavitation occurred.

Surface erosion products formed in ambient atmosphere environment. This occurs because of shock wave effect that appears at the interaction of radiation with the surface. Dates of strong acoustic phenomena were recorded. Ablated molecules are responsible for the formation of the shock/blast wave, and might be re-deposited into the substrate. The drag forces, generated by the blast wave, cause the re deposition of the ablation products on the substrate, which are then called debris [7]. Because of its good adherence, debris can be considered as a surface modification, which might be useful.

4. CONCLUSIONS

This method is used to improve surface properties of polymer material materials or polymer composite materials in order to improve mechanical properties and physical-chemical properties according to technological needs or requirements. In many cases flash lamp irradiation method is much more superior to laser treatments. In summary, UV-VIS-IR oxidation and surface activation has the potential for creating a low cost, fast and robust method for surface preparation of polymer, metallic or composite material surfaces in order to improve mechanical and chemical characteristics. The process can be capable of treating any polymer or metallic surfaces, environmental healthy since it does not emit volatile organic compounds. 5. REFERENCES 1. Boyd, I. W.; Zhang, J. Y.,New large area

ultraviolet lamp sources and their applications, Nuclear Instruments and Methods in Physics Research Section B, v. 121, p. 349-356, (1997).

2. Lau K.S., Chan P.W., Wong K.H., Yeung K.W., Chan K., and Gong W.Z., Surface properties of polyester fabrics induced by excimer laser processing. Journal of Materials Processing Technology,vol.63 pp 524, (1997).

3. Murahara M. and Okoshi M., Polymer Surface Modification; Relevance to Adhesion, Part 1(1996)

4. An Overview of Flashlamps and CW Arc Lamps. Technical Bulletin 3, Sunnyvale, CA: ILC Technology, (1986).

5. Koechner, W. Solid-State Laser Engineering. 3rd ed. Berlin and New York: Springer-Verlag, (1992).

6. Chan, K., Yip, J., Sub-micron Surface Structures Induced by Excimer Laser Treatment: Effect on Fabric Properties.: Hong Kong Institute of Textile and Clothing, Hong Kong, (2001).

7. Drzal, L.T., Ultraviolet Light Surface Treatment of Polymers, Metals, and Composites. Technical Session No. 4B. Partners in Environmental Technology Pollution Prevention, Poster No. 171, pp 6-9 (2001).