Cylindrical cathode

For quantitative analysis, the resolution of the spectral analyzer must be significantly narrower than the absorption lines, which are - 0.002 nm at 400 nm for Af = 50 amu at 2500°C (eq. 4). This is unachievable with most spectrophotometers. Instead, narrow-line sources specific for each element are employed. These are usually hoUow-cathode lamps, in which a cylindrical cathode composed of (or lined with) the element of interest is bombarded with inert gas cations produced in a discharge. Atoms sputtered from the cathode are excited by coUisions in the lamp atmosphere and then decay, emitting very narrow characteristic lines. More recendy semiconductor diode arrays have been used for AAS (168) (see Semiconductors). 

The hollow-cathode lamp is shown diagrammatically in Fig. 2.2. As the name suggests, the central feature is a hollow cylindrical cathode, lined... 

The recent model of the Vorce cell has been improved in such a way that an additional cylindrical cathode and diaphragm was placed into the middle of the anode space, so that also the inner surface of the anode was utilized for electrolysis. With this adaptation the electrolyzer can work with nearly twice the load of that of an electrolyzer with one cathode without any increase in dimensions. 

The most useful radiation source for atomic absorption spectroscopy is the hollow-cathode lamp, shown schematically in Figure 28-17. It consists of a tungsten anode and a cylindrical cathode sealed in a glass tube containing an inert gas, such as argon, at a pressure of 1 to 5 torn The cathode either is fabricated from the analyte metal or serves as a support for a coating of that metal. 

Schematic representation of electron transport processes in a discharge between a cylindrical cathode and a coaxial anode in a uniform axial magnetic field.

Another electrolyser is provided with a rotating cylindrical cathode that operates at high current densities causing deposition of metals in the form of a powder, which is removed by a brush and carried away by the streaming electrolyte. The metal powder is separated from the liguid by means of a filter. An industrial type of this equipment is known under the ncune ECO CELL. 

Figure 12. Basic scheme of the electrolyser developed by Akso Zout Chemie Nederland B.V. 1 Rod anode, 2 diaphragm, 3 one of Cu particles in suspension strecuning upward, e cylindrical cathode.

Hollow Cathode Lamps. Hollow cathode lamps are the most widely used radiation sources in the AA technique. A hollow cathode lamp consists of a glass cylinder, and an anode and a cathode (Figure 18). The cylindrical cathode is either made of the analyte element or filled with it. The diameter of the cathode is 3 to 5 mm. The anode is in the form of a thick wire and usually made of tungsten, nickel, tantalum, or zirconium. The glass tube is first evacuated and then filled with an inert gas (argon or neon). The pressure of the inert gas is about 0.5 to 1.3 kPa. 

A second device based on the movement of a cylindrical cathode is the impact rod or rotating tubular reactor [12]. This cell uses a set of rod... 

The setup at the Universitat Rostock utilizes an ACIS to produce a continuous cluster beam (see Fig. 3.9). The metal vapor plasma is created in the cylindrical cathode of target material. The fabricated clusters, neutral and charged are expanded through an exit nozzle and collimated by an aerodynamic lens attached to the source. The clusters then flow through a secondary pumping stage bracketed by two skimmers and are size selected by an electrostatic quadrupole deflector for deposition. 

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