DD289849A5 - A SHAPED, SHIELDED HOLLOW CATHODE LAMP FOR PRODUCING HOT HOLLOWING CHARACTERISTICS FOR EMISSIONS SPECTRAL ANALYSIS OF ELEMENTSPURES - Google Patents

Abstract

The invention relates to a demountable, shielded hollow cathode lamp for generating heiszer hollow cathode discharges for the emission spectral analysis of element traces and is suitable for routinemeszigen element trace analysis, z. B. in the fields of production and control of high-purity chemicals and environmental research. The hollow cathode lamp consists of an anode and a cathode part, in which the Hohlkathodennapf low heat contact to the movable bottom plate and the replaceable, pierced cover plate, the Abschirmplaettchen that receives the upper part of the hollow cathode cup in a separable from austenable, auszen cooled Abschirmhohlraum located. The anode part can be part of a glow discharge lamp according to Grimm or a simplified version modified especially for hollow cathode operation. The use of the hollow cathode lamp allows the formation of heiszer discharges, avoids side discharges and memory effects and reaches high final temperatures and relatively fast heating rates and allows rapid change of Hohlkathodennapfes {hollow cathode lamp; glow discharge; Anode part; Cathode member; Discharge, heisze; emission spectral}

Description

Sample evaporation and therefore not universally applicable for trace analysis. Often occur in the operation also to the

with ablated Napfmaterial covered areas of Abschirmbauteile on side discharges. Fast replacement of these components to prevent breakdowns or contamination is usually not possible.

The shortcoming inherent in the known unshielded devices continues to be too slow Sample change due to lack of quick-release closures and the presence of a relatively large to be evacuated Lamp interior. The known devices are not as an addition to commercially produced glow discharge lamps

suitable.

Object of the invention

ZIoI the invention is to atihaftenden the known devices to eliminate defects that with the possible use of a glow discharge lamp according to Grimm In conjunction with a newly developed cathode part with low device complexity an effective, strong and reliable trace analysis real micro samples is possible.

Explanation of the essence of the invention

The invention has for its object to realize a sturdy, quickly demountable hollow cathode lamp for hot discharge operation with electrically completely outwardly shielded hollow cathode cup while highly wärmeisollerter mounting the same <u, memory effects and contamination should be largely eliminated. According to the invention the object is achieved in that the hollow cathode lamp consists of an anode part for the formation of a shortened, disabled discharge and a demountable into two components and flanged, water-cooled cathode part. The anode and cathode part are designed as rotationally symmetrical metal parts. The vacuum-tightness is produced by the silicone rubber O-rings, which are arranged on the connecting surfaces of the components. The two components of the cathode part form in the closed state of the hollow cathode lamp inside a cylindrical Abschirmhohlraum whose walls consist of a high temperature resistant material (such as graphite, glassy carbon, ceramic or silica glass). In this shield cavity of Hohlkathodennapf is supported with high thermal insulation. On the anode side, the annular front surface of the hollow cathode cup and the top surface of the Abschirmhohlraumes (the outer surface of the interchangeable and pierced Abschirmplättchens) in a plane that is brought very close to the located in the anode part anode tube to realize the lateral obstruction of the discharge.

The outer surface of the Abschirmhohlraumes located in the front (anode side) component of the cathode part, while the bottom plate is located as a movable element in the lower part. Through the bottom plate of the rear pressure of the hollow cathode cup is caused to the shield plate with little thermal contact and the electrical contact of the cup. By attaching the hollow cathode cup in a closed, cylindrical shielding cavity whose single opening receives the hollow cathode cup, no discharge can form on its outer surfaces. Lateral propagation of the discharge is prevented by the anode tube being brought up with a narrow, evacuated annular gap and / or by the design of the shielding plate made of electrically non-conductive material (eg high-temperature ceramic). During operation, inert gas is passed through the interior of the hollow cathode lamp via a throttle point, which is removed by a pump system (consisting of one or two backing pumps). Gas inlet and outlet are controlled so that in the hollow cathode lamp, a working pressure of 600-3000 Pa (depending on the gas and mode) adjusts. The anode part can be formed by a Grimm discharge lamp. The DC power supply is stabilized with adjustable currents (or electrical power) of approx. 60-1000 mA (or 20-600W). After ignition, the Hohlkathodennapfes forms inside the Hohlkathodennapfes without disturbing side charges occur. The heating of the hollow cathode cup to the stable final temperature value takes place relatively quickly in the course of 1-58. The tent for changing the Hohlkathodennapfes is only about 30s, If necessary, the shielding plate can be quickly replaced with a new one.

Ausführungsbeisptel The invention will be explained in more detail below on a Auoführungsbelsplel with reference to the drawing. Flg. 1: shows anode part in the form of a Gllmmentladungslampe after Grimm Flg. 2: shows Anodenteil In modified form otner Gllmmentladungslampe after Grimm Flg.3: shows cathode part.

The anode part made of Cu * Be * bronze or light metal is designed either in the form of a discharge lamp according to Grimm (file 1) or as a modified special configuration (FIG. 2). Spectrographenseltlg these are completed with a quartz window 1. The inert gas flowing in via a needle valve into the anode part at the gas inlet 2 is removed by vacuum pumps via the vacuum connections 4 and 28. In the case of using a Grimm submilluminating lamp (FIG. 1), as usual, two separate vacuum pumps are connected to the anode block 3. When using the stepped configuration (FIG. 2), evacuation across the annular gap at the anode tube 10 is sufficient. The anode tube 10 is suitably made of carbonaceous material (such as glassy carbon) and interchangeable. The provided with water cooling 6 cathode plate 8, which is separated by a Isolatorfolle 6 from the anode block 3 is replaced in the embodiment of FIG. 2 by a Isolatorplatto 7 (ceramic material). The parts of Fig. 1 and Flg. 2 are on the side facing away from the Spekirographers equipped with Schnellverschlüesen 11, In which the Tolle on the cathode part Tolle dos

Quick release 15 can be engaged. In the flanged state, the front part 17 of the cathode part (Flg.3) is thus firmly connected to the rear face of the anode part (Flg. 1 or 2). The centering takes place via annular connecting elements 9 and 13. The vacuum seal at all interfaces is effected by annular silicone rubbers 12. A separation of the front component 17 from the parts of the Flg. 1 or 2 is usually carried out only at relatively long intervals when renewing the Abschlrmplättchens 14 made of temperature-resistant material (graphite or other carbon materials, high temperature ceramics), but it can also be made when changing the hollow cathode cup 20. Inside the front component 17 of the cathode part is a tubular component 18 is permanently installed (10 about 25 mm), which consists of temperature-resistant material (s.o.) and which absorbs the outgoing from the lateral surface of the hollow cathode cup 20 thermal radiation. In the closed state, the rear component 24 of the cathode part (Flg.3) is flanged at the parting line T to the front part 17, the vacuum seal is also here via an O-ring made of silicone rubber 12. Both components 17 and 24 of the cathode part are water cooled (16 or 23) provided and consist In the basic construction of stainless steel. The rear component 24 of the cathode part can be evacuated on the back, wherein via the vacuum flange 28, a connection to one of the existing vacuum pumps of the system takes place. The rear component 24 is attached to a centered guided Preßluftstempel 29 and can be moved through this with a stroke of about 100mm for opening the cathode part (Flg.3), inside of part 24 is a .Druckzylinder "26 with spring element, which is connected via a small graphite rod to the bottom plate 19, which is made of graphite or glassy carbon The pressure exerted on the hollow cathode cup 20 by the pressure cylinder 26 via the bottom plate 19 (movable with a stroke of about 1 mm) is small (some p The bottom plate pushes the hollow cathode cup 20 (A 04-8mm, I01-6mm, I "10-20mm) via a pin 21 with little heat conduction against the shield plate 14. The hollow cathode cup 20 receives its leadership in the central bore of the Abschlrmplättchens the length of this bore is correspondingly reduced in the outside diameter of the hollow cathode cup When flushed, make sure that it is flush with the surface of the Abschlrmplättchens. The shield plate has a reduced wall thickness in the vicinity of the receptacle for the hollow cathode cup (about 1 mm), whereby a small heat release at the front end of the hollow cathode cup is made possible. In order to ensure effective back-pumping, the bottom plate 19 is provided with holes 22. Under the bottom plate 19 is located for heat protection in addition, the base plate 25, dl ·) is firmly installed in the rear component 24. It consists of temperature-resistant material (eg graphite, glassy carbon, high temperature ceramics) and has such a shape that even at the edges of the bottom plate 19 and the tubular member 18 In the closed state of the hollow cathode lamp, the metallic parts are completely covered against heat radiation from Hohlkathodennapf and a spatial connection of the vacuum port 28 with the shielding cavity 27 via the holes 22 and the interior of the impression cylinder 26 is ensured. At the beginning of the course of the analysis, the anode part (FIG. 1 or 2) is fixedly connected to the front component 17 of the cathode part (FIG. 3) containing a functioning shielding plate 14 via the quick-release closures 11 and 15. The hollow cathode cup 20, which contains the dry or dried analyte substance at the bottom, is introduced into the bore of the shielding plate 14 at the back. By pressing the Preßluftetempels 29, the rear member 24 is brought to the front member 17 and pressed. This is the Hohlkathodennapf inside the now closed Abschirmhohlraumes 27; it is held in place in the bore of the Abschlrmplättchens 14 and has only a small direct thermal contact with the environment at its two ends. First, an evacuation via the vacuum ports 4 and 28 to a pressure of less than 40 Pa. Thereafter, the inert gas continuously flows in via the gas inlet 2, adjusting a pressure of about 500 Pa (at Ar as a discharge gas) to about 2000 Pa (at He as a discharge gas). With running water cooling 6,16,23 now the ignition of the discharge takes place with about 1KV DC voltage as ignition voltage. In this case, the anode pressure 3 is positive, whereas the cathode plate 8 and the front and rear components 17, 24 are connected to the hollow cathode cup 20 to negative potential. The positive potential is connected to the earth potential. The stabilized discharge current is gradually regulated within a tent program of initially 100mA up to 1000mA, which finally adjust burning voltages by 400V. The Hohlkathodennapf 20 heats up to white heat in a few seconds. The atoms and ions of the vaporized sample material are excited in the low-pressure discharge to emit characteristic radiation, the registration of the spectra is carried out with a spectrograph or a spectrometer. After the analysis time of 30-9Os, the hollow cathode cup is cleaned by further Ncchbrennen (about 30s at 1000 mA). Before changing the Hohlkathodennapfes the voltage is switched off, further, the valves are closed at 2.4 and 28, the interior is vented, then the Preßluftetempel 29 is moved back together with the rear member 24; As a result, the shielding cavity 27 becomes accessible for the change of the hollow cathode cup.

Highly pure Mlneratsäuren and organic solvents and trace concentrations of extracted samples were analyzed using each 60μΙ sample volume. In the simultaneous analysis for the 20 elements investigated, Al ₁ Ag, Be, B, Bi, Ca, Cu, Co, Cr, Fe, Ga, In, Mg, Mn, Na, Ni, Pb, Sn, Zn in Ar-atmosphere detection limits (3 S-Krlterlum) between 0.1 and 4 ng / ml, an average of about 1 ng / ml (corresponding to 60 pg). When challenged in the He atmosphere, detection limits of between 2 and 20 ng / ml were found for the more challenged elements As, Cl, F, P, Se, Te, with a mean of about 10 ng / ml (equivalent to 600 pg). The hollow cathode lamp not only proved to be reliable, but also suitable for routine use and reliable.

Claims (2)

1. A detachable shielded hollow cathode lamp for generating hot hollow cathode discharges for the emission spectral analysis of element traces, consisting of an anode part in the form of a glow discharge lamp according to Grimm or an analogous structure with an insulator plate instead of the cathode plate and a cathode part, characterized in that the anode tube (10) of the anode part is brought up to 2 to 4 tenths of mm to the shield plate (14) of the cathode part, which consists of two separable, rotationally symmetrical, water-cooled components (17 and 24), of which the front component (17) has a Abschirmhohlraum (27), the is covered with the interchangeable shield plate (14) containing a bore which serves to receive the front part of the hollow cathode cup (20), wherein the annular end face of the hollow cathode cup (20) is flush with the outer surface of the Abschirmplättchens (14) and at the rear component (24) is a e movable with holes (22) provided bottom plate (19) with pin (21) is located. 2. Breakable shielded hollow cathode lamp according to claim 1, characterized in that the tubular member of the Abschirmhohlraumes, the base plate and the bottom plate made of high temperature resistant material, preferably graphite, pyrolytically coated graphite, glassy carbon or high-temperature ceramic. For this 1 page drawings Field of application of the invention The invention relates to a collapsible, shielded hollow cathode lamp for generating hot hollow cathode discharges for the emission spectral analysis of element traces and applies to the extreme element trace analysis of dry residues of pure liquid chemicals and trace concentrates, in particular for solving tasks in microelectronics, environmental protection, chemistry and toxicology. Characteristic of the known state of the art Among the known methods of spectral analysis, the hollow cathode discharge has a particularly high performance in extreme trace analysis (JJ Slevln, W.W. Harrison, Applied Spectroscopy Reviews 1975, 10, 20). An important field of application is the analysis of residuals of microvolumes for dryness of vaporizable liquids, e.g. I. Zilbershtein, Ed., "Spectrochemical Analysis of Pure Substances", Adam Hilger Ltd., Bristol, 173 pp.) In hot hollow cathode discharges, thermal processes dominate upon the material entry of the analytes into the plasma The small amount of sample required (several 10μΙ) favors effective pre-enrichment steps of the initial samples over several orders of magnitude. The known hollow cathode lamps for hot discharges (eg BQA Pevtsov USSR, 18 (1963) 1140) consist of a metal or quartz glass tube body (outer body) with water cooling, which is terminated on the side of the light exit by a quartz glass window Hollow cathode cup containing the sample is placed with its bottom on the End of a molybdenum or tungsten wire attached, which is located in the tube axis and at its other end via electrical feedthroughs firmly connected to the vacuum-tight sealable lid part of the outer body. After evacuation and setting of a low-pressure atmosphere of inert gas In the lamprey gray, the electrical ignition voltage is applied, which leads to the formation of a low-pressure discharge. It is desirable that the main part of the radiation comes from the interior of the hollow cathode cup. At sufficiently high currents in conjunction with a thermally insulated attachment of the hollow cathode cup, a hot discharge with thermal evaporation of the sample is formed. The spectral decomposition and registration of the generated characteristic radiation of the atoms and ions of the sample is carried out with a spectral device. A particular problem is in addition to the rapid, associated with minimal contamination Napfwechsel the electrical shielding of Hohlkathodennapfes against side discharges on its outer surfaces or other surfaces with a corresponding electrical potential. The often used arrangements without shielding U. B. V.Z. Kraallshchlk, Zavodskaya Lab. 31 (1965) 251) show analytical dangers as a result of reduced and fluctuating current leakage in the interior of the hollow cathode wells, at least in the burn-in phase of the discharge. Shielding can be achieved by the sheath of the Hollow Cathode Cup with Temperature Resistant Material ("Glomax Demountable Hollow Cathode Lamp", Barnes Engineering Company, Stamford, Connecticut). Propagation of the charge to the front can be achieved by obstructing it while shortening to eliminate the positive column (for example, BR Mavrodlanu, J. of Research of NBS, 89 (1984) 143), by approaching a tubular anode very closely At the cathode end face, with simultaneous reduction of the pressure in the resulting nip, below which value still electrical breakdowns can occur, the direct cladding of the hollow cathode vaporizer prevents the formation of true hot discharges as a result of the dissipation of heat energy