JPH0484730A - Electric heating atomizing furnace of sample for spectroscope and manufacture thereof - Google Patents

Abstract

PURPOSE: To manufacture an electrothermal atomization furnace having cavity for receiving a sample by jointing two half bodies forming the cavity along a separation face traversing the cavity. CONSTITUTION: At first, two blank parts engaging a flat plane are manufactured. The two blank parts are then machined commonly to form a cavity being traversed by flat planes 12, 14. Each blank part serves as the half body 76 of a furnace 10. Two half bodies 76 of the furnace 10 are then separated and coated individually. The inner surface of the cavity defines the outer surface each of the two half bodies 76 of the furnace 10. The two half bodies 76 of the furnace 10 are then assembled into one furnace 10. More specifically, the furnace 10 comprises two half bodies 76 defining a cavity and abutting along a separation face traversing the cavity.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to an electrothermal atomization furnace for spectroscopic samples having a sample receiving cavity.

A very sensitive quantitative analytical method for determining the expected amount of a given element in a sample is atomic absorption spectroscopy. In atomic absorption spectroscopy, a sample is atomized such that the individual components of the sample exist in one of their atomic states and form an "atomic vapor." A measuring light beam passes through this atomic vapor. This measurement light beam originates from a line-emitting light source that emits characteristic resonance lines of the expected element. Such a measuring light beam is simply absorbed by the atoms of the expected element. The absorption of the measuring light beam in the atomic vapor therefore provides a measurement of the number of atoms of the expected element in the path of the measuring light beam and thus, after appropriate calibration, of the concentration of the expected element in the sample.

For atomization of the sample, a furnace, usually made of graphite, is used, into which the sample solution is introduced and heated to high temperatures by means of a strong electric current.

Thereby, a "cloud of atoms" is generated inside the furnace, through which the measuring light beam penetrates the aligned apertures of the furnace. This is called "electrothermal atomization".

However, it is also known how in such a furnace, in which the sample is heated electrothermally, an outgassing is generated, whereby the sample atoms are excited to emit a characteristic line spectrum.

The present invention relates to such a spectrometer and a furnace for a similar spectrometer.

The invention further relates to a method for manufacturing such a furnace.

BACKGROUND OF THE INVENTION It is known from DE 24 20 546 A1 to coat a furnace made of graphite tubes with a layer of pyrocarbon in carrying out electrothermal decomposition of samples. In contrast to pure graphite, a non-porous surface is thereby provided by such a coating and the penetration of sample liquid into the graphite is prevented. If such ingress of sample liquid into the graphite tube is allowed, atomization of the sample elements is retarded. This reduces the sensitivity and accuracy of the measurement.

Pyrocarbon is a graphite element, here carbon generated by the thermal decomposition of carbides on the surface of a graphite tube. Various methods of providing pyrocarbon layers on the surface of graphite tubes are known. Such a method is described in German Published Patent No. 2420546
listed in the number. Other methods use gaseous carbides such as methane. In a vacuum in which the elements to be coated are placed, argon as a carrier gas supports the methane on the surface to be coated, where the methane being decomposed generates a pyrocarbon coating.

In practice, uniform coating of graphite furnaces with pyrocarbon is often difficult to achieve. This is especially true inside the cavity, ie the bore of the graphite tube, into which the atomizing sample is introduced. The thickness of the layers is difficult to determine. Usually, layer thicknesses that are too small become apparent only in actual operation, ie by premature deterioration of the analytical results. The pyrocarbon layer wears out with use, so that if the layer of pyrocarbon is too small, as described, after a relatively unreliable analysis, the sample liquid will penetrate into the furnace material which is no longer sufficiently covered.

A "graphite tube atomizer" in which the graphite furnace is formed by a graphite tube through which electric current flows in the longitudinal direction is described in DE 27 18 416 A1.

European patent application publication specification box A2-0311761
No. indicates a sample electrothermal atomization furnace with a tubular furnace body provided on the half side with longitudinal contact ribs which are in turn integral with the cylindrical contact piece. A hollow, generally semi-cylindrical platform is provided within the bore of the furnace body extending approximately 180 degrees. This platform is integral with the furnace body, ie it forms an integral element made of graphite with the furnace body, contact ribs and contact pieces. Opposite the platform, the furnace body has a sample inlet opening.

The purpose of the platform is to retard the heating of the sample fed to the platform to reach the atomization temperature compared to the heating of the furnace walls so that the sample is already in thermal equilibrium when it is atomized. This is achieved because the sample on the platform is heated substantially indirectly by thermal radiation from the furnace walls.

From German Utility Model No. 8901529°0, a furnace similar to the one described above is known, in which a hollow, approximately semi-cylindrical platform, which is integral with the furnace, is connected to the furnace body by means of narrow ribs. connected, this narrow rib is located on the platform and only on one side of the longitudinal center plane of the platform.

When the furnace is manufactured according to EP-A-0311761 and German Utility Model No. 8901529.0, there is a relatively large amount of waste when the integral platform is machined.

DISCLOSURE OF THE INVENTION The object of the invention is to design a furnace of the type described above in such a way that it is easy to manufacture.

In particular, waste in furnaces with integral platforms is reduced and coating with pyrocarbon is facilitated.

According to the invention, this purpose is achieved by forming two cavities.
The furnace can be made of graphite and provided with a coating, in particular a coating consisting of pyrolytic graphite. be able to.

A platform for sample storage can be integrated into one of the two halves. The furnace may have a tubular furnace section with a contact piece on an opposite side, the contact piece extending perpendicularly to the axis of the tubular furnace section and in the plane of the current flow therethrough. The furnace section can be passed circumferentially. The furnace is then separated along this plane containing the axis. The two halves of the furnace are held together by a ring attached to the contact piece. A trapezoidal contact rib is integrally arranged between the cylindrical contact piece and the furnace body. A groove from which a cylindrical ring projects is formed in the contact rib around the contact piece.

A method of manufacturing a furnace of the type described above comprises: (a) manufacturing two blank parts that engage each other with a flat surface; (b) machining the two blank parts in common so that the flat surface (C) separating the two halves of the furnace produced in this method; (d) (e) assembling the two halves of the furnace generated in this method into one furnace.

In this method, the coating of the inner surfaces of the furnace takes place while the inner surfaces are freely accessible, ie while they form the outer surface. A better and more uniform coating can thereby be achieved.

In order to reduce waste in furnaces with integrated platforms, the manufacturing process is such that the blank parts of the first joined pair form two, hollow, generally cylindrical platforms within the cavities of the six pairs of blank parts. one platform is integral with one half of the furnace and the other platform is integral with the other half of the furnace and then joined to form the furnace halves. This can be done in such a way that the blank parts of the six pairs of cavities are machined to form continuous holes without an integral platform therewith. In forming the furnace, each of the furnace halves manufactured from the blank portions of the first pair of blank portions and the furnace halves manufactured from the blank portions of the second pair of blank portions are joined.

The production of two halves of a furnace with an integral platform requires the same work steps as the production of a complete furnace with an integral platform.

When machining of the platform causes waste in the blank part from which the furnace halves with integral platforms are manufactured, this waste usually results in only one half of the furnace. The other half of the furnace can be used and can be combined with the other half of the furnace without a platform. A waste element with an integral platform can be reprocessed into a furnace half without an integral platform, if necessary.

According to the statistical waste rate of the furnace halves with an integral platform, the furnace halves without an integral platform can be generated in reduced numbers.

Embodiments of the invention will now be described in detail in conjunction with the accompanying drawings.

Preferred Embodiment of the Invention In FIGS. 1-4, the lower half of furnace 10 is constructed from a graphite plate having an upper flat surface 12 and a lower flat surface 14. A typical graphite plate is provided with recesses 18 and 20 (FIG. 2) symmetrically with respect to the central plane 16, each of which has a respective planar surface 1.
4 and cylindrical surfaces 30 and 32. The two convex cylindrical surfaces are aligned to form a semi-cylindrical outer surface 36, the axis 34 of which is defined by the intersection of the flat surface 12 and the central plane 16.

On the upper side of the plate, a cylindrical surface 38 is provided coaxially to the outer surface 36. In this method, a half-tube 40 is formed which represents a half of a tubular furnace body.

A hollow, generally cylindrical platform 42 is disposed concentrically within this half-tube 40 . As can be seen from FIGS. 1 and 3, the platform 42 is simply connected to the half-tube via the web 42. This web 44 is disposed on an axial projection 46 at one end of the platform 42 and is connected to the half-tube 40 only on one side of the elongated central plane 16.

Contact ribs 48 and 50 are provided adjacent to half-tube 40 on both sides. In plan view, contact ribs 48 and 50 are trapezoidal. Contact pieces 52 and 54 are each integral with a contact rib. The contact piece is semi-cylindrical. The aligned axes of the cylindrical outer surface of the contact piece are located within the planar surface 12 and extend perpendicularly to the axis 34 of the half tube 40. Semi-cylindrical, axial grooves 56 and 58 are also provided in the planar surfaces of the semi-cylindrical contact pieces 52 and 54. Grooves 56 and 58 terminate forward of outer surface 36 of half-tube 40 and traverse recesses 18 and 20 within passage openings 60 and 62.

Recesses 18 and 20 allow half-tube 40 to have contact ribs 4 along its edges with relatively thin bridges 64 and 66.
8 and 50 are connected to thicker portions 68 and 70. The contact pieces 52 and 54 are connected to these upper thicker parts 6
8 and 70, the thickness of which corresponds to the thickness of the plate from which the furnace halves are made. Annular grooves 72 and 7
4 are provided in the thicker parts 68 and 70 of the contact ribs 48 and 50 around the contact piece 52.

The "upper" half 76 of the furnace is substantially identical to the described lower half of the furnace IO. However, upper half 76 does not have integral platform 42.

Half tube 78 (FIG. 3) has a continuous smooth cylindrical inner surface. The upper half of the furnace 76 has a flat surface 80 that corresponds to flat surface I2.

To form a furnace, the lower half of furnace 10 and the upper furnace half 76 are joined with their flat surfaces 12 and 80. Tubular rings 82 and 84 are attached to contact pieces 52 and 54. Cylindrical rings 82 and 84 project into annular grooves 72 and 74. Thereby, the two halves of the furnace are held closely together over a large portion of their length.

FIG. 5 shows, in a similar illustration to FIG. 3, a furnace consisting of two identical halves 86 and 88 of the furnace without a platform.

The furnace halves are coated with pyrocarbon.

The manufacture of the furnace is accomplished as follows. That is, blank parts having the shape of the plates described above with flat surfaces 12 and 80 are joined and fastened together. In that case the plates are machined together. However, in these pairs of plates, neither of the furnace halves or the furnace halves includes an integral platform 40. in fact,
Manufacturing one platform or two platforms requires the same outlay.

The furnace halves obtained in this way are separated and coated with pyrocarbon by known methods. The coating of the furnace halves, in particular in the critical areas of the platform and on the inner walls of the holes, corresponds to an external surface to which the platform and the inner walls of the furnace halves are easily accessible for separation and the coating does not present difficulties. , can be more easily achieved than in conventional furnaces.

Each of the "lower halves" of the furnace 10 with body platforms and the "upper half" of the furnace 76 are then joined together and connected to each other by attachment to rings 82 and 84.

Instead of the connection by rings 82, 84, a connection by bonding can also be provided. Also, the furnace halves remain separated and in operation the furnace can be compressed by contacts with conical contact surfaces between them held in the device. This method can be particularly used in conventional types of gilafite tubes which are held by their end faces between annular contacts and through which current flows longitudinally. Also, such a furnace can advantageously be constructed from two halves of the furnace.

[Brief explanation of the drawing]

1 is a plan view of a laterally heated furnace half with an integral platform; FIG. 2 is a sectional view along line A--H of FIG. 1; and FIG. A sectional view taken along line C--D of FIG. 1 in which the upper half of the furnace is shown with the connecting ring of the furnace halves; FIG. Figure 5 shows the lower half; Figure 3 shows the furnace without an integral platform;
It is a sectional view similar to the figure. In the figure, the symbol IO is the furnace, I 2, 14 is the flat surface, 42
is the platform, 48.50 is the contact rib, 52.54
is a contact piece, 72.74 is a groove, 76 is an upper half body 82.8
4 is a ring. 1. Indication of the case 1990 Patent Application No. 1 98067 2゜Name of the invention Electric thermal atomizing furnace for spectrometer samples and its manufacturing method 3゜Amendment person case and Relationship: Name of patent applicant: Bodenseewerk PerkinElmer Gesellschaft Mitbeschrenktel Hafrang 4, Agent 5, Date of amendment order: Spontaneous 6° Subject of amendment (1) Name of representative of patent applicant (2) Document certifying authority of representation

Claims (11)

[Claims] (1) An electrothermal atomization furnace for spectroscopic samples, characterized in that it consists of two halves forming a cavity, and these halves are joined along a separation plane that crosses the cavity. (2) The electrothermal atomization furnace for spectroscopic samples according to claim 1, characterized in that said furnace is made of graphite and is provided with a coating. 3. The electrothermal atomization furnace for spectroscopic samples according to claim 2, characterized in that each of the two halves of the furnace is provided with a coating of pyrolytic graphite. (4) The electrothermal atomization furnace for spectroscopic samples according to claim 3, characterized in that the platform for accommodating the sample is an integral part of one of the two halves. (5) further comprising a tube furnace section having a contact piece on an opposite side, the contact piece extending perpendicularly to the axis of the tube furnace section; 5. The electrothermal atomization furnace for spectroscopic samples according to claim 4, wherein the furnace lies in a plane along which the two halves of the furnace are joined. (6) The electrothermal atomizing furnace for spectroscopic samples according to claim 5, wherein the furnace is supported together by a cylindrical ring attached to the contact piece. (7) A trapezoidal contact rib is integrally arranged between the cylindrical contact piece and the furnace body, and a groove from which the cylindrical ring projects is formed in the contact rib around the contact piece. The electrothermal atomization furnace for spectroscopic samples according to claim 5. (8) manufacturing two blank parts interengaging with a flat surface and machining the two blank parts in common so that a cavity is formed which is traversed by the plane of said flat surface and said blank part is machined in common; A method for manufacturing a furnace, characterized in that each blank part forms a half of the furnace. (9) further separating the two halves of the furnace so produced, coating said furnace halves separately, the inner surface of the cavity forming the outer surface of each of the two halves of the furnace; 9. A method for manufacturing a furnace according to claim 8, characterized in that it comprises the step of assembling both halves of the furnace produced in this method into one furnace. (10) The machining includes forming two hollow, generally cylindrical platforms in the cavity of each pair of blank parts, one platform being integral with one half of the furnace and the other being integral with one half of the furnace. 9. The method of claim 8, wherein the platform is integral with the other half of the furnace and the machining includes joining each blank portion to form the furnace. 11. The method of claim 8, wherein the machining includes continuous holes joining each pair of blank portions to form a furnace within the cavity of each pair of blank portions.