Tungsten coil

Fast reactions between pure metal powders (A1 + Ni, A1 + Ti and A1 + Ni + Ti) have been studied by Javel etal. (1997) by using time-resolved X-ray diffraction with the help of synchrotron radiation. The sample (20 X 10 X 2 to 3 mm3 was prepared under purified argon by cold pressing the metal powders mixed in the required proportion. It was then placed in a reaction chamber kept under He gas. A mylar window allows the incident and diffracted X-ray beams to pass in and out. Two small heating devices (tungsten coils on alumina supports) were included. The first one was used to keep the sample at a uniform temperature before ignition and the second one to start the self-propagating reaction at one end of the sample. X-rays irradiated the centre of the specimen. 

Combustion synthesis (CS) can occur by two modes self-propagating high-temperature synthesis (SHS) and volume combustion synthesis (VCS). A schematic diagram of these modes is shown in Fig. 1. In both cases, reactants may be pressed into a pellet, typically cylindrical in shape. The samples are then heated by an external source (e.g., tungsten coil, laser) either locally (SHS) or uniformly (VCS) to initiate an exothermic reaction. 

Fig. 2, Laboratory setup for combustion synthesis. 1-reaction chamber 2-sample 3-base 4-quartz window 5-tungsten coil 6-power supply 7-video camera 8-video cassette recorder 9-video monitor 10-computer with data acquisition board 11-thermocouple 12-vacuum pump ...

Tungsten-coil atomizers have to some extent been used in connection with atomic techniques in general and ETA-AAS in particular, and their popularity continues to rise. Their high simplicity and low cost make them attractive alternatives to graphite furnaces for many applications. However, they are much more interference-prone than their graphite counterparts. The interferences experienced by W-coil atomizers have been overcome in various ways, however. Thus, Barbosa et al. [25] avoid the interference from a salt matrix and implement a preconcentration step by electrochemically reducing Pb onto the coil surface. They use a flow injection system to deliver the sample through an anode inserted in the tip of the autosampler and the W-coil itself as cathode. The use of a W-coil as a platform inside a Massmann-type furnace provides no appreciable improvement over wall atomization [26]. 

Peuster M, Pink C, Wohlsein P, et al. (2003) Degradation of tungsten coils implanted into the subclavian artery of New Zealand white rahhits is not associated with local or systemic toxicity. Biomaterials 24 393-399. 

Krivan V., Barth P. and Schnurer-Patschan C. (1988) An electrothermal atomic absorption spectrometer using semiconductor diode lasers and a tungsten coil atomizer design and first applications, Anal Chem 70 3625-3632. 

Lucic M. and Krivan V. (1999) Analysis of aluminium-based ceramic powders by electrothermal vaporization inductively coupled plasma atomic emission spectrometry using a tungsten coil and slurry sampling, Fresenius J Anal Chem 363 64-72. 

Berndt H. and Schaldach G. (1988) Simple low-cost tungsten-coil atomiser for electrothermal atomic absorption spectrometry, J Anal At Spectrom 3 709-713. 

Dittrich K., Berndt H., Broekaert J. A. C., Schaldach G. and Tolg G. (1988) Comparative study of injection into a pneumatic nebuliser and tungsten coil electrothermal vaporisation for the determination of rare earth elements by inductively coupled plasma optical emission spectrometry, J Anal At Spectrom 3 1105—1110. 

Electrodes in fluorescent lamps (coated W or NS-W). Fluorescent lamps are low-pressure mercury discharge lamps which radiate in the UV region. The ultraviolet radiation is converted into light by means of a fluorescent layer (phosphor). Tungsten coils, coated with a mixture of Ca, Ba, and Sr compounds, are used as electrodes (emitter). 

Silva, M.M., Arruda, M.A.Z., Krug, F.J., et al. (1998). On-line separation and preconcentration of cadmium, lead and nickel in a fuUerene (Cgg) minicolumn coupled to flow injection tungsten coil atomic absorption spectrometry. Anal. Chim. Acta, 368, 255-63. 

Small electrically heated tungsten coils have also been used experimentally for the formation of acetylene by cracking methaue.80 At 3000° C. and with a time of contact of 0.0004 second a conversion of 86 per cent has been reported as obtainable from coke-oven gas containing 25.5 per cent methane. The results of this experimental work indicate that higher yidds are possible by the electric arc method. 

Barrett J, Wells 1, Riordan R, Roohottom C (2000) Endovascular embolization of varicMceles resorption of tungsten coils in the spermatic vein. Cardiovasc Intervent Radiol 23 457-459. 

Figure 8.11 SHS Az constant pressure laboratory reactor. (1) Handle, (2) electrical contact, (3) back nut, (4) mitre valve, (5) sealing ring, (6) case, (7) coil holder, (8) initiating tungsten coil, (9) sealing ring from vacuum rubber, (10) viewing window, (11) filtering assembly, (12)...

Rights U., Beoekaeet J. A. C., Tschopel P. and Tolg G. (1991) Comparative study of a Beenakker cavity and a surfatron in combination with electrothermal evaporation from a tungsten coil for microwave plasma optical emission spectrometry (MIP-AES), Talanta 38 863-869. 

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