US3623136A

US3623136A - Light-source lamp for atomic light-absorption analysis

Info

Publication number: US3623136A
Application number: US822360A
Authority: US
Inventors: Sadami Tomita; Akira Hosoya; Hiroshi Okagaki
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1968-05-10
Filing date: 1969-05-07
Publication date: 1971-11-23
Anticipated expiration: 1988-11-23
Also published as: GB1219705A

Abstract

A light source lamp for atomic light-absorption analysis comprising a structure constituted by a molded body of fine metal wires having a relatively high-melting-point which are mechanically closely linked with each other having a metal having a relatively low-melting-point impregnated in the gaps between the fine wires, wherein the metal of a low-melting-point is continuously fed to a hollow portion through the gaps between the fine wires while maintaining the contour of the structure by virtue of the frame composed of the fine metal wires of a highmelting-point, thereby making it possible to produce a high light-intensity resonance line of the low-melting-point metal which is stabilized for a long time.

Description

United States Patent [72] Inventors Sadami Tomita Hitachi-shi; Akira l-losoya, Hitachi-shi; Hiroshl Okagaki, Katsutashi-shi, all of Japan [2]] App]. No. 822,360 [22] Filed May 7, 1969 [45] Patented Nov. 23, 1971 [73] Assignee Hitachi, Ltd.

Tokyo, Japan [32] Priority May 10, 1968 [3 3] Japan [3 l] 43/30883 [54] LIGHT-SOURCE LAMP FOR ATOMIC LIGHT- ABSORPTION ANALYSIS 26 Claims, 10 Drawing Figs.

[52] US. Cl 313/178, 29/25. I 8, 313/209, 313/346, 356/85 [51] Int. Cl G01] 3/12, 1-10 1 j 61/08 [50] Field of Search 313/209. 210. 178, 346; 356/85, 86; 29/25. 1 8

[56] References Cited UNITED STATES PATENTS 2,103,623 12/1937 Kott 313/178X Primary Examiner-Roy Lake Assistant Examiner- Palmer C. Demeo Attorney-Craig, Antonelli & Hill ABSTRACT: A light source lamp for atomic light-absorption analysis comprising a structure constituted by a molded body of fine metal wires having a relatively high-melting-point which are mechanically closely linked with each other having a metal having a relatively low-melting-point impregnated in the gaps between the fine wires, wherein the metal of a lowmelting-point is continuously fed to a hollow portion through the gaps between the fine wires while maintaining the contour of the structure by virtue of the frame composed of the fine metal wires of a high-melting-point, thereby making it possible to produce a high light-intensity resonance line of the lowmelting-point metal which is stabilized for a long time.

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INVENTORS AKIRA Hosoy d HIROSHI okAGAKI gi wwwyawh w ATTORNEYS LIGHT-SOURCE LAMP FOR ATOMIC LIGHT- ABSORPTION ANALYSIS This invention relates to a light-source lamp for atomic light-absorption analysis.

Among methods of quantitatively analyzing a metal salt contained in a solution sample is the atomic light-absorptionanalyzing method utilizing the principle of atomic light absorption.

This analyzing method has recently found extensive use in the fields of medical science, biochemistry, food chemistry, petrochemistry, industrial chemistry and so forth since it is suited to the analysis of a very small quantity of metal in a sample solution.

This atomic light-absorption-analyzing method is an optical method to decompose a metal salt by heat energy of flame to convert it into atomic vapor, and externally transmit a resonance line light through the atomic vapor to cause it to be absorbed by the latter, thus achieving an analysis in accordance with the quantity of light absorbed by the atomic vapor. The basic principles of such method are disclosed in U.S. Pat. No. 2,847,899. In the atomic light-absorption analysis method, only the resonance line or atomic beam having a desired wavelength is absorbed by atomic vapor, and an analysis is performed by virtue of the fact that there is a predetermined relationship between the quantity of the absorbed atomic resonance beam and the density of atoms to be analyzed. Therefore, irrespective of the coexistence of different atoms in the material of the cathode, there occurs no trouble if their absorption lines do not overlap the absorption line of the cathode material.

Thus, it is possible to make the cathode of a suitable alloy or composite material.

ln fact, such a cathode is formed by a fusible material of plural kinds of elemental metal fused to be alloyed to each other, a sintered body consisting of two or more kinds of elemental metal or alloy powder mixed at a suitable rate and pressmolded and thereafter sintered, or a composite sintered body consisting of two or more kinds of elemental metal or alloy powder mixed with each other and press-molded and thereafter sintered which is impregnated with a melt of an elemental metal or metal having a lower melting point.

In an attempt to make a cathode of a fusible material, however, limitation is naturally laid on the selection of metals, because it is required that the overlapping of the resonance lines and the lowering of their light intensities be avoided. Furthermore, some metals cannot be alloyed. Disadvantageously, therefore, such fusible material cannot be utilized in extensive applications.

For example, iron (Fe) and copper (Cu) can be alloyed with each other, but by using a cathode formed by such alloy, either a resonance line having a particular wavelength corresponding to the bright line spectrum of iron (Fe) or copper (Cu) cannot be obtained or even if it is obtained, its quantity is small. Therefore, such a cathode cannot be put to practical use. it is presumed that the reason is that the bright line spectra of iron (Fe) and copper (Cu) are weakened due to the alloying of these metals.

Such elemental metals as Li, Na, K, Zn, Cd, Hg, In, Te, Sn, Pb, P, As, Sb, Bi, Se, Te have a low melting point and/or poor machinability. Therefore, if it is attempted to form a cathode of such elemental metals as for example Se and As by alloying these metals to achieve a high melting point or improved machinability, it is impossible to produce such a cathode by the common fusing method because these metals cannot be substantially alloyed with a metal having a high melting point such as Cu, Ni, Mo, W and the like,.

With a cathode consisting of a sintered body it is possible to realize a high light-intensity as compared with that consisting of a fusible material, since the mixed metals are merely mechanically combined with each other. The method of using a sintered body is effective with respect to metals having relatively close melting points, but it is practically impossible to apply this method to metals the melting point of which tends to be greatly varied because of the sintering temperature range and so forth. In this method, too, difficulty is encountered in the selection of the material.

With a cathode formed by a composite material consisting of a sintered material impregnated with a metal having a lower melting point, on the other hand, it is possible to use the aforementioned low-melting-point metals, but this method is disadvantageous in that the resulting light intensity is low because the low-melting-point metal tends to be fed to the hollow portion between the closely mixed powder grains. Therefore, it is required that atoms for the light emission be incessantly evaporated from the inner wall of the hollow portion in order to produce a resonance line or atomic beam. This means that it is necessary to uninterruptedly feed atoms for the light emission to the inner wall of the hollow portion. With a cathode consisting of the sintered material impregnated with a lowmelting-point metal as described above, however, the permeability for the ligh-emission atoms is insufficient to achieve a high light intensity.

It is a primary object of the present invention to provide an improved light-source lamp including a hollow cathode for atomic light-absorption analysis.

Another object of the present invention is to provide a lightsource lamp for atomic light-absorption analysis which is so designed as to produce an atomic resonance line of a metal element to be analyzed with a high light-intensity.

A further object of the present invention is to provide a light-source lamp for atomicv light-absorption analysis which is capable of producing the resonance line of a elemental metal having a low melting point by which a cathode cannot be formed.

A further object of the present invention is to provide a light-source lamp for atomic light-absorption analysis which is capable of producing any desired number of resonance lines with a high light-intensity.

A still further object of the present invention is to provide a light source lamp for atomic light-absorption analysis which is capable of producing resonance lines with a high light-intensity including the resonance lines of metals which cannot be alloyed with each other or the light intensity of the resonance lines of which tends to be lowered due to the alloying thereof.

In accordance with the present invention, there is provided a light-source lamp for atomic light-absorption analysis, including a cathode the contour of which is defined by mechanically linking fine metal wires having a relatively high melting point with each other, wherein the gaps between the fine wires are filled with a metal having a relatively low melting point, and the low-melting-point metal in uninterruptedly passed to the inner wall of a hollow portion through the gaps between the fine wires.

In the present invention, as the metal having a relatively high melting point, either elemental metals or an alloy may be used. Use may also be made of a combination of plural kinds of fine metal wires each having a different metallic material. The metal having a relatively low melting point may be embedded in the form of a elemental metal or alloy in the gaps between the fine wires of the relatively high melting point metal.

However, it is preferable to avoid such a combination of metals that the resonance lines overlap each other or the light intensity becomes remarkably low.

The use of cathode constituted by a composite body of copper (Cu) and lead (Pb) for the analysis of copper (Cu) is practically impossible because the resonance line of copper occurs at a higher temperature than the melting point of lead. In such case, therefore, copper may be combined with a metal of which the resonance line overlaps that of copper. For example, in the case of a composite body consisting of iron (Fe) and copper (Cu), it is possible to produce the resonance lines of both of these metals, and therefore in such case use of a combination of a composite body with a metal of which the resonance line overlap those of said metals or by which the light intensity is weakened should be avoided.

The relatively low melting point may be combined in the form of fine wires with the relatively high-melting-point metal.

Alternatively, the relatively low-melting-point metal may be filled in the gaps between the fine wires of the relatively highmelting-point metal by such conventional means as impregnation, evaporation or the like.

The fine wire" referred to herein means not only usual wires having a circular section, but also wires 200 microns or less in thickness and 0.5 mm. or less in width. Though the latter are foils in general, the foils are set forth as the fine wires." From the viewpoint of press-molding the fine wires and of the mechanical strength of the molded body, the foilshaped fine wires are more preferable than the usual fine wires because the former tends to be closely entwined with each other to form a strong molded body.

The reason is that with wires 200 microns or greater in thickness and 0.5 mm. or greater in width, the resulting cathode structure tends to be destroyed by a small stress imparted thereto since a close mechanical linkage cannot be established therebetween. However, no limitation is. laid on the length of such fine wires, so that either these fine wires may be cut into a multiplicity of pieces to form the cathode structure or one or a plurality of such fine wires may be regularly entwined with each other to define a predetermined contour.

In accordance with the present invention, there is provided a light-source lamp for atomic light-absorption analysis including an one of the following cathodes.

A first type of cathode is constituted by a body having a predetermined contour defined by intertwining fine wires of a relatively low-melting-point metal having a desired dimension,

the gaps between which are at least partly filled with a predetermined quantity of metal powder having a relatively low melting point.

A second type of cathode is constituted by a body having a predetermined contour defined by a close mechanical linkage between predetennined quantities of fine wires of a relatively high melting point having a desired diameter and fine wires of a relatively low-melting-point metal.

A third type of cathode is constituted by a combination of the first and second ones. The fine wires of the relatively high-melting-point metal may be arranged either regularly or irregularly.

The cathode according to the present invention can effectively be constructed by any of the following methods.

A first type of method is to define a predetermined contour by regularly or irregularly arranging fine wires of a relatively high-melting-point metal and causing these fine wires to be entwined with each other, and impregnate a metal of a relatively low melting point into the gaps between the fine wires.

The impregnation can effectively be achieved either by amethod of immersing a porous structure formed by the high melting point metal in a melt of the low-melting-point metal or an evaporation method of providing vapor of the low-meltingpoint metal in the gaps between the fine wires constituting the structure of the high-melting-point metal and then cooling the vapor.

A second type of method is to press-mold a mixture of fine wires of a metal having a relatively high melting point and powder of a metal having a relatively low melting point.

A third type of method is to regularly or irregularly arrange metal wires of a metal having a relatively high melting point and those of a metal having a relatively low melting point.

It is desirable that powder or fine wires of the relatively low melting point are heated to be fused and mechanically combined with fine wires of the relatively low point after having been molded.

Furthermore, it is desirable that the relatively low-meltingpoint metal is embedded in the gaps between the relatively high-melting-point metal wires mechanically closed linked with each other to define a predetermined contour, in an inert or reductive atmosphere so as to avoid absorption of gas.

This is because if any absorptive gas exists in the cathode constructed, there occurs the tendency that a resonance line of that gas produces a noise signal.

Therefore, it is desirable to take measures to remove any adsorptive gas after the cathode has been constructed.

The cathode according to the present invention may be manufactured by a method corresponding to a combination of the foregoing methods, which comprises the steps of mixing fine wires of a metal having a relatively high melting point and fine wires of a metal having a relatively low melting point with fine wires and powder of a metal having a relatively low melting point, and press-molding the resulting mixture.

Among examples of the cathode manufactured by such a method is one constituted by a Fe-Ni-Cu composite body consisting of a mixture of Fe and Ni fine wires and copper powder.

The cathode thus constructed is capable of standing a high mechanical stress because the contour thereof is defined by a mechanical linkage between fine wires of a metal having a relatively low melting point, and the gaps between the fine wires are made contiguous throughout the cathode since the latter is constituted merely by the mechanical linkage of the fine wires. Thus, the relatively low-melting-point metal is continuously fed to the hollow portion between the gaps of the structure constituted by the high-melting-point metal because of capillary action. As a result, the permeability for atoms is improved so that the atoms of the relatively low-melting-point metal are evaporated in succession, resulting in a stable and strong light emission.

It is to be understood that the present invention can be applied not only to the aforementioned metal having a low melting point such as Fe, Cu, Ni, W, C0, Ag, Al. but also to any other kinds of metals and alloys. Especially, the present invention is effective with respect to elemental metals which are not suited to the forming of a cathode due to the melting point and the machinability thereof.

In an attempt to form a cathode of such low-meltingpolnt metal, the contour of the cathode is previously established by fine wires ofa metal having a relatively higher melting point, and in such case it is desirable to use as the high-melting-point a metal such as for example Fe (m.p. L530 C.), Cu (l,083 C.), Ni l,455 G), M0 (2,620 C.), W (3,400 C.) or the like which has somewhat high strength and is not easily deformed.

Furthermore, it is desired that such a metal as for example Li, Na, K, Hg or the like which cannot be impregnated in the form an elemental metal and formed into fine pieces because of the extremely low melting point thereof be alloyed with a metal such for example as Li (m.p. 179 O), Na (97 C.), K(87 C.), Hg or the like to raise the melting point, before it is impregnated. The melting point of Na can be raised up to 300 to 600 C. by alloying Na with Pb or Sn to form a Na-Pb or Na- Sn alloy. The melting point of K can be raised up to 500 to 700 C. by alloying K with Bi or Pb to form a K-Bi or K Pb alloy. The melting point of Hg can be raised up to 210 C. by alloying Hg with Pb to form a Hg-Pb alloy.

Metals such as Zn (mp. 4l9.7 C.), Cd (320.9 C.), In (156.6 C. Tl (303.6 C. Sn (231.9 C.), Pb (327.3 C.), Sb (630.5" C.), Bi (271 C.) and the like may be directly fused for impregnation. Further, metals such as Pb, Sn, Zn which can be worked into fine wires may be combined with fine wires of a metal having a relatively high melting point after having been formed into fine wires.

Metals such as P, As, Se, Te cannot be fused for impregnation, and therefore they are evaporated to be impregnated into the gaps between the fine wires of a metal having a relatively high melting point.

Other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view showing a lightsource lamp assembly for atomic light-absorption analysis;

FIG. 2 is a view showing the electrode structure of the lightsource lamp assembly;

FIG. 3 is a longitudinal sectional view showing a manufacturing method of the cathode according to the invention;

FIG. 4 shows curves representing the current versus light-intensity characteristics of a light-source lamp assembly including a cathode containing indium (In);

FIG. 5 shows curves representing the current versus light-intensity characteristics of a light-source lamp assembly including a cathode containing lead (Pb);

FIG. 6 shows curves representing the current versus light-intensity characteristics of a light-source lamp assembly including a cathode containing arsenic (As);

FIG. 7 shows curves representing the current versus light-intensity characteristics of a light-source lamp assembly including a cathode containing bismuth (Bi);

FIG. 8 shows curves representing the current versus light-intensity characteristics of a light-source lamp assembly including a cathode containing tin (Sn);

FIG. 9 shows curves representing the current versus light-intensity characteristics of a light-source lamp assembly including a cathode consisting of a compound of copper (Cu) and iron (Fe); and

FIG. is an enlarged sectional side view showing the cathode structure of a light-source lamp for atomic light absorption analysis.

Referring to FIG. 1, there is shown a general form of lightsource lamp assembly for atomic light-absorption analysis devices, wherein numeral 1 represents a cathode adapted to produce a resonance line or atomic resonance beam. This cathode is made of a material containing an element which produces the same light as that produced by the metal to be analyzed, and it is constructed in a cylindrical form including a hollow portion. Numeral 2 denotes the hollow portion where an atomic resonance line or spectral light beam is produced, and 3 is a ring-shaped anode. Discharge occurring between the anode 3 and the cathode 2 results in an atomic resonance line or spectral light beam. Numeral 4 indicates a cathode terminal, 5 an anode terminal, and 6 a discharge preventing disk which may be made of mica, for example. Numeral 7 represents an annular insulating member which may be made of steatite for example, 8 an insulating sleeve for the anode terminal 5, and 9 a metal cylinder fitted over the surface of the cathode 1 except for the hollow portion 2 where an atomic resonance line is produced. The cup-shaped cover 9, which may be fon'ned by nickel for example, is provided for the purpose of preventing the occurrence of discharge between the surface of the cathode 1 except the hollow portion 2 and the anode 3. Numeral l0 denotes a hermetically sealed envelope which is usually formed by transparent glass. Sealed in the envelope 10 is an inert gas such as argon gas or the like. Numeral 11 indicates a base socket, and 12 a member for connecting the base socket 11 and envelope 10 which each other and which may be formed by nickel for example. Numeral 13 indicates an window portion transmissive to atomic resonance lines produced in the sealed envelope l0 and which is commonly fomied by quartz glass.

By energizing the light source lamp having aforementioned construction to cause a current to flow between the cathode l and the plate 3, discharge is caused therebetween so that positive ions (such as He", Ar", Ne*) of the inert gas confined in the envelope 10 are dissociated therefore impinge upon the surface of the hollow portion 2 of the cathode. As a result, the metal atoms of the cathode l are vaporized out of the surface of the hollow portion 2 and excited due to sputtering action, thus resulting in generation of atomic resonance lines.

FIG. 2 schematically shows the electrode portion of the light source lamp for atomic light absorption analysis, wherein an arrow 14 shows the direction of resulting resonance lines.

Usually, discharge between the cathode l and the anode 3 is effected in the normal glow region to restrain the cathode consumption which is caused due to the sputtering action. Preferably, however, it is effected in the neighborhood of the abnormal glow region in order to produce intense resonance lines and yet minimize the cathode consumption. Operation of the lamp at such a low temperature may be made small undesirable affection such as Doppler width due to the thermal movement of luminescent atoms.

Referring now to FIG, 3, there is shown a method for manufacturing a cathode consisting of fine metal wires having a relatively high melting point formed in a predetermined contour by being mechanically closely linked with each other and onto which a metal having a relatively low melting point is evaporated.

In the drawing, numeral 15 represents a quartz glass envelope, and 16 a member having a contour which is defined by a mechanical linkage of fine metal wires having a relatively higher melting point than that of a metal to be evaporated thereonto, and 17 the metal to be evaporated. The quartz glass envelope is closed at one end, the diameter thereof is changed approximately at the midpoint of the length thereof. The inner diameter of the closed end of the envelope is smaller than the outer diameter of the molded member 16, and the diameter of the opposite end thereof is greater than the outer diameter of the molded member 16.

The metal to be evaporated is first inserted in the quartz glass envelope 15. in this case, it is preferable to use ground form of metal as the metal 17 to be evaporated, in order to avoid damage of the quartz glass envelope l5 and to make easy accommodation of the metal.

Subsequently, the molded member 16 is inserted in the quartz glass envelope 15. Preferably, the molded member 16 is disposed in such a manner as to float in the space so that molded member 16 can be satisfactorily impregnated with the evaporated metal. In the illustrated example, the molded member 16 is disposed in a floating manner while being supported at that portion of the quartz glass envelope 15 which has a reduced diameter.

After the metal to be evaporated and molded member have been incorporated in the quartz glass envelope, gasses existing within the quartz glass envelope are removed to obtain a vacuum therein, and then the open end of the envelope is sealed. Numeral 18 indicates the sealed end portion.

Subsequent to completion of the foregoing operation, the quartz glass envelope is erected, with the smaller diameter portion thereof downward, and then it is externally heated at a temperature at which the crushed metal accommodated therein can be vaporized, for a predetermined period of time. Thus, the vaporized metal 17 is deposited in gaps between the fine wires constituting the molded member 16.

EXAMPLE l Cathodes containing indium (In) for use in a light-source lamp for atomic light-absorption analysis were manufactured by the following two methods. The dimensions of the cathode were as follows: Outer diameter 15 mm' b; height 20 mm.; diameter of the hollow portion 4 mm and depth thereof 17 mm. a. Nickel powder having a grain diameter of 4 to 6 microns was press-molded at a molding pressure of 2 tons/cm. into a molded body constituting a cathode structure by the use of a metal mold, and then the resulting molded body was sintered at 550 C. Thus, there was obtained a porous sintered nickel (Ni) body having a porosity of about 60 percent. Thereafter, the sintered nickel body was immersed in molten indium heated at about 400 C. in a graphite crucible, maintained therein for 5 minutes. During the impregnation of the indium, the impregnation system was maintained to a high inert gas pressure in order to impregnate effectively the porous sintered body with the molten indium, and then removed therefrom. By scraping off indium adhered to the outer periphery of the nickel body and hollow portion thereof, a cathode to be compared with the inventive cathode was obtained.

Chemical analysis of the sintered ln-Ni cathode thus obtained showed that about 50 weight percent of In was contained therein.

b. Nickel wires about 80 microns in thickness, 0.4 mm. in width and 4 mm. in length were subjected to annealing treatment while being heated in a hydrogen atmosphere at 700 C. for 1 hour in order to soften the material and make easy the molding of the fine wires. Subsequently, these fine wires were press-molded at a molding pressure of l ton/cm. by the use of a metal mold to obtain a molded body in the form of a cathode, which in turn was heated at 1,000 C. for one hour so as to be sintered. The porosity of the molded body thus obtained was about 60 percent. Then, the molded body was immersed in molten indium heated at 400 C. and held therein for 5 minutes so as to be impregnated with indium. In this case, the molded body was easily impregnated with the molten indium without additional steps to promote the impregnation.

By scraping off an excess amount of indium which adhered to the outer periphery of the composite ln-Ni body and hollow portion thereof, a desired cathode was obtained. Chemical analysis of the ln-Ni composite cathode thus obtained showed that the quantity of indium contained therein was about 50 weight percent.

Each of the cathodes obtained by the above two methods was disposed as shown in FIG. 2, and then incorporated in a light-source lamp assembly having such a construction as shown in FIG. I, with the cup-shaped cover 9 fitted over the surface of the hollow cathode 1. Measurement of light-intensity was carried out with respect to such lamp assemblies.

FIG. 4 shows the intensity of light emitted by each of the cathodes obtained by the methods described above in the items (a) and (b), with respect to light having a wavelength of 3,256 A. which corresponds to the bright line spectrum of indium.

The horizontal axis indicates the current, and the vertical axis indicates the relative light intensity on a logarithmic scale.

As the reference light intensity value, the intensity of light produced by flowing a current of 5 ma. through a cathode constituted by a molded body consisting of fine nickel wires according to the present invention was taken, the value of which was regarded as unity.

As the current increases, the light intensity increases relatively. This is due to the fact that the temperature of the electrodes is elevated because of the current increase so that the quantity of vaporized metal atoms which contribute to glow discharge is increased.

When the current is made higher than a predetermined value, the increasing rate of the light intensity decreases. It is presumed that this phenomenon stems from self-absorption due to the excess amount of nonexcited metal vapor drifting by the anode.

Comparison of the cathode manufactured by the above method (a) which is formed by the sinteredpowder body impregnated with indium and the cathode manufactured by the above method (b) which is constituted by the molded finewire body impregnated with indium according to the present invention shows that in a current range below 30 ma. the intensity of light produced by the use of the latter cathode, i.e., one produced according to the present invention, is about three to live times higher than the intensity of light produced by the use of the former cathode. This proves that by impregnating a molded fine-wire body rather than a sintered powder body with a metal, it is possible to enhance the permeability of the low-melting-point metal to emit spectral light and also the accuracy of an analysis which is achieved by the use of a light-source lamp for atomic light-absorption analyszs.

EXAMPLE 2 Cathodes formed of copper (Cu) containing lead (Pb) having the same dimensions as those described in example 1 were produced by the following three methods.

c. A cathode was obtained by machining an alloy consisting of percent by weight of lead (Pb) and 80 percent by weight of copper (Cu).

d. Lead powder having a grain diameter of about 20 microns and copper powder having a grain diameter of about 30 microns were mixed at a ratio of 2 (Pb): 8 (Cu). Then, the mixture was press-molded into a molded body in the form of a cathode at a molding pressure of 2 tons/cm. by the use of a metal mold. Subsequently, the molded body was sintered at 500 C. for 1 hour.

e. Copper wires about 80 microns in thickness 0.4 mm. in width and 4 mm. in length were subjected to annealing treatment while being heated at 300 C. for 1 hour, and thereafter press-molded into a cathodelike form at a molding pressure of l ton/cm. by the use of a metal mold. The molding operation was easily performed. Subsequently, the molded body thus obtained was heated in a hydrogen atmosphere at 800 C. for l hour so as to be sintered. The porosity of the molded body as about 60 percent. Thereafter, the molded body was immersed in a molten lead heated at 700 C. in a graphite crucible placed in an argon gas atmosphere, held therein for 5 minutes, and then removed therefrom. Then, the extra portion of lead adhered to the outer periphery of the molded body and hollow portion thereof was scraped off. Thus, a desired cathode was obtained. Chemical analysis of the Pb-Cu composite cathode thus obtained showed that the quantity of lead (Pb) contained therein was about 50 weight percent.

Each of the cathodes produced by the aforementioned three methods was disposed in such a manner as shown in FIG. 2, and then incorporated in a light source lamp having such a construction as shown in FIG. 1. Measurement was made of the intensity of light produced by the lamps.

FIG. 5 shows the intensity of light having a wavelength of 2,833 A. corresponding to the bright line spectrum of lead (Pb) measured with respect to each of the cathodes manufactured by the above three methods.

The horizontal axis indicates the current supplied to the cathode, and the vertical axis indicates the relative value of light intensity on a logarithmic scale. As the reference light-intensity value, the intensity of light produced by flowing a current of 5 ma. through the Pb-Cu alloy cathode consisting of the fusible material obtained by the foregoing method (c) was taken which was regarded as unity.

Comparison of the cathode constituted by a molded finewire body impregnated with lead (Pb) by the present method (e) with those obtained by the fusing method (c) and sintering method (d) shows that in a current range below 30 m. the light intensity ratio becomes approximately (c):(d):(e)=l:2:4. From this, it will be seen that the intensity of light produced by the cathode (e) according to the present invention is remarkably high, and therefore that it can be very effectively utilized in a light source for atomic light-absorption analysis.

EXAMPLE 3 Cathodes for use in a light-source lamp for atomic light-absorption analysis having the same dimensions as those of example l were manufactured by the following two methods.

f. A cathode was manufactured by a As-Ag alloy containing 30 atom percent of arsenic (As).

Since arsenic (As) represent a high vapor pressure at an elevated temperature and becomes sublimated before it melts,

the As-Ag alloy was fused by heating the material consisting of As and Ag, with it accommodated in a hermetically sealed quartz glass envelope.

The melting point of silver (Ag) is as high as 960 C., but arsenic (As) was caused to diffuse thereinto by heating them at 600 C. for longer than 4 hours, so that these two metals could be entirely fused. Since the alloy possesses a eutectic composition of As-Ag binary alloy in the vicinity of 30 atoms percent of arsenic (As), it was cooled with water after having been fused. In this way, an As-Ag alloy having a uniform dispersion therein was obtained. The As-Ag alloy thus obtained was machined into a cathode having desired dimensions. lt is noted that the amount of As in the Ag-As alloy is necessarily limited to about 30 percent from the viewpoint of solubility of As in Ag.

g. Copper wires about 80 microns in thickness 0.4 mm. in width and 4 mm. in length, were subjected to annealing treatment while being heated at 300 C. for 1 hour, and thereafter press-molded into a molded body in the form of a cathode at a molding pressure of l ton/cm. by the use of a metal mold. Subsequently, the molded body thus obtained was heated in a hydrogen atmosphere at 800 C. for 1 hour so as to be sintered. The porosity of the molded body thus sintered was about 60 percent.

Thereafter, the molded body 16 and arsenic 17 was inserted in a quartz glass tube closed at one end, as shown in FIG. 3. Subsequently the quartz glass envelope 15 was evacuated and had the open end portion sealed, and then it was heated in a temperature range of 500 to 600 C.

Arsenic (As) 17 was vaporized by the heating so as to be deposited in the gaps between the fine-wire pieces of the molded body 16. Experimentally, it has been confirmed that arsenic (As) is completely impregnated into the gaps of the molded copper body by heating them at 550 C. for 3 hours.

Chemical analysis of the As-Cu composite cathode thus manufactured showed that the quantity of arsenic (As) contained therein was about 50 percent by weight.

Each of the cathodes obtained by these two methods was disposed in such a manner as shown in FIG. 2, and then incorporated into a light-source lamp assembly having a structure such a shown in FIG. 1. Thereafter, measurement was made of the light intensity.

FIG. 6 shows the intensity of light having a wavelength of 1,987 A. corresponding to the bright line spectrum of arsenic (As) measured with respect to each of the cathodes obtained by the methods just described above, wherein the the current is indicated on the horizontal axis and the relative light intensity on the vertical axis on a logarithmic scale. As the reference light intensity, the intensity of light produced by supplying a current of 5 ma. to the cathode constituted by the molded copper body having arsenic (As) deposited thereon in accordance with the present invention was taken which was regarded as unity.

Comparison of the As-Cu composite cathode constituted by a molded copper body having arsenic (As) deposited thereon in accordance with the present invention with the As-Ag alloy cathode formed by the fusible material shows that the intensity of light produced by the use of the former is about ten times as high as that achieved by the use of the latter in a current range below about 30 ma. From this, it will be seen that the cathode according to the present invention can be very effectively applied to a light-source lamp for atomic light-absorption analysis.

EXAMPLE 4 Cathodes for use with a light-source lamp for atomic lightabsorption analysis containing bismuth and having the same dimensions as examplel were manufactured by the following two methods.

h. Nickel (Ni) powder having a grain diameter of about microns and bismuth (Bi) powder having a grain diameter of about microns were mixed with each other at a weight ratio of Ni:Bi=6:4, and then the mixture was press-molded into a molded body in the form of a cathode at a molding pressure of 2 tons/cm. by the use ofa metal mold. Thereafter, the molded body thus obtained was heated at 300 C. immediately above the melting point of bismuth for l hour so as to be sintered.

i. Nickel wires about 80 microns in thickness, 0.4 mm. in length, and 4 mm. in length were subjected to annealing treatment while being heated at 700 C. for 1 hour, and then the fine wires were mingled with bismuth powder having a grain diameter of about 30 microns at a weight ration of Ni:Bi=8:2. Thereafter, the resulting mixture was press-molded into a body in the form of a cathode at a molding pressure of l ton/cm? by the use ofa metal mold. Subsequently, the molded body thus obtained was heated at 300 C. to fill the gaps between the fine nickel wires thereof. In this way, a Bi-Ni composite cathode was obtained.

Each of the cathodes manufactured by the above two methods was disposed in such a manner as shown in FIG. 2, and then incorporated in a light-source lamp having such a structure as shown in FIG. I. Then, measurement was made of the light intensity with respect to each of the cathodes.

FIG. 7 shows the intensity of light having a wavelength of 3,067 A. corresponding to the bright line spectrum of bismuth (Bi) measured with respect to each of the cathodes obtained by the two methods just described above, wherein the current supplied to each cathode is indicated on the horizontal axis and the relative light intensity on the vertical axis in a logarithmic scale.

As the reference light intensity, the intensity of light produced by supplying a current of 5 ma. to the cathode fonned by the sintered powder body in accordance with the method (h) was taken which was regarded as unity. Comparison of the Ni-Bi composite cathode embodying the present invention with the sintered cathode shows that in a current range below 30 ma. the intensity of light produced by the use of the former is about 2.5 times higher than that achieved by the use of the latter. Thus, the cathode according to the present invention can be very effectively applied to a light source lamp for atomic light-absorption analysis.

EXAMPLE 5 Cathodes for use in a light-source lamp for atomic light-absorption analysis containing tin (Sn) and having the same dimensions as example I were manufactured by the following three methods.

j. An alloy consisting of 35 weight percent of tin (Sn) and 65 weight percent of copper (Cu) was machined to obtain a cathode.

k. Copper (Cu) powder having a grain diameter of about 20 microns and tin (Sn) powder having a grain diameter of about 50 microns were mingled with each other at a ratio in weight ofCu:Sn=65:35, and then the mixture was press-molded into a molded body in the form of a cathode at a molding pressure of 2 tons/cm. by the use of a metal mold. Thereafter, the molded body thus obtained was heated at 300 C. for one hour so as to be sintered.

1. Copper wire about microns in thickness 0.4 mm. in width and 4 mm. in length, were subjected to annealing treatment while being heated at 300 C. for 1 hour, and then the fine wires were mixed with tin wires about 25 microns in thickness, 200 microns in width and 5 mm. in length at a ratio in weight of Cu:Sn=65:35. Thereafter, the mixture was press-molded into a molded body in the form ofa cathode at a molded pressure of l ton/cm. by the use of a metal mold. Subsequently, the molded body thus obtained was heated at 300 C. to melt the tin. In this way, there was obtained a Sn-Cu composite cathode having the gaps between the fine copper wires thereof filled with tin.

Each of the cathode manufactured by the three manners just described above was assembled into a light source lamp having such a structure as shown in FIG. 1. Then measurement was made of the light intensity with respect to each cathode.

FIG. 8 shows the intensity of light having a wavelength of 2,839 A. corresponding to the bright line spectrum of tin (Sn) measured with respect to each of the cathodes obtained by the above three methods, wherein the current supplied to each cathode is indicated on the horizontal axis and the relative light intensity on the vertical axis in a logarithmic scale. As the reference light intensity, the intensity of light produced by supplying a current of 5 ma. to the Sn-Cu alloy cathode formed by the alloy material in accordance with the method (j) was taken which was regarded as unity.

Comparison of the cathode consisting of a combination of fine wires obtained by the method (1) of present invention with those obtained by the fusing method (j) and sintering method (k) shows that the intensity ratio becomes approximately (j):(k):(l)=l:4:5 in a current range below 30 ma. From this it will be seen that a very high light-intensity can be achieved by the use of the cathole l embodying the present invention and therefore that it can be very effectively applied to a light source for atomic light-absorption analysis.

EXAMPLE 6 A cathode for use in a light-source lamp for atomic light-absorption analysis consisting of copper (Cu) and iron (Fe) and having the same dimensions example 1 was manufactured by the following method. m.'Copper wires about 80 microns in thickness, 0.5 mm. in width and 8 mm. in length of oxygen-free copper were subjected to annealing treatment while being heated at 300 C. for 1 hour, and iron wires about 80 microns in thickness and 0.5 mm. in width and 8 mm. in length were also subjected to annealing treatment while being heat at 700 C. for 1 hour. Thereafter, the copper and iron wires were mixed with each other at a ratio in weight of Cu:Fe=:5. Subsequently, the mixture thus obtained was press-molded in the form of a cathode at a molding pressure of l ton/cm. by means of a metal mold.

The Cu-Fe composite cathode thus produced was arranged in such a manner as shown in FIG. 2, and then incorporated in a light source lamp having such a structure as shown in FIG. 1. Then, measurement was made of the light intensity.

FIG. 9 shows the intensities of light having a wavelength of 3,248 A. corresponding to the bright line spectrum of copper (Cu) and light having a wavelength of 2,483 A. corresponding to the bright line spectrum of iron (Fe), wherein the current supplied to the cathode is indicated on the horizontal axis and the relative light intensity on the vertical axis in a logarithmic scale. As the reference light intensity, the light intensity of copper achieved at a current of 5 ma. was taken which was regarded as unity. Thus it has been found that both the intensity of light of the copper (Cu) and that of the iron (Fe) are high and therefore that a cathode formed of these metals can be satisfactorily applied to a light source for atomic light absorption analysis.

As described in detail, the light source lamps according to the invention show good characteristics, and especially very much higher light intensities than that of conventional lamps. it is believed that the high intensity of the spectral light beam may be due to a capillary phenomenon which is caused by the gaps between fine metal wires used as a frame body of the hollow cathode.

In a cathode manufactured by powder metallurgy, the gaps difierent from that of the cathode of the invention do not cause such a capillary phenomenon hat contributes to a continuous feed and permeation of the low-melting-point metal contained in the frame body.

P16. 10 shows another embodiment, wherein the lamp includes a cylindrical envelope 40 having a portion transmissive to spectral light as shown in FIG. I, a ring-shaped anode 43 and a hollow cathode 3 disposed in the envelope 40, a pair of refractory insulating disks 45 and 45 for separating electrically the anode and the cathode, a pair of refractory insulating members 52 and 52' for isolating the insulating disks and the anode and cathode, a pair of electrically conducting means 56 and 44 respectively connected with the anode and the cathode, and elongated insulating sleeves 42 surrounding the anode leads 44. The insulating disks have central apertures 54, each having a diameter not smaller than that of the hollow 41 of the cathode. The hollow cathode 3 is covered with a case member comprising a cylinder 46 and a bottom plate 58 of a high melting point and a small sputter rate, such as nickel. The bottom plate 58 is connected with the cathode lead 56 by means of a terminal 59. In this embodiment, the refractory disks 45 and 45' have small affinity for the vapor of the lowmelting-point metal in order to avoid undesirable glow discharge which occurs between the anode and the surface of the disks. If the insulating disks have affinity for the vapor, the surface thereof may tend to be reduced by deposited metal of the low-melting-point metal because the metal is very active in general. From the above point of view, the anode and the cathode should be isolated from the above-mentioned glow discharge by such desirable manner as shown in FlG. 10. That is, the first and second insulating disks 45 and 45' are separated from each other by an annular insulating member 52 and the second insulating disk 45' and the ring-shaped anode 43 are also separated by another annular insulating member 52' and therefore, it is possible to decrease sufficiently the effect of the deposition of the low-melting-point metal on the insulating disk 45.

What is claimed is:

l. A light source lamp for atomic light-absorption analysis comprising a cathode having a hollow portion formed therein, an anode provided adjacent to said cathode, a hermetically sealed envelope containing said cathode and said anode, and an inert gas atmosphere confined in said envelope, wherein said cathode is formed in a predetermined contour by a close mechanical linkage of fine wires of a predetermined dimension consisting of a metal having such a relatively high melting point that it will not be deformed at the operating temperature of said light source lamp, and at least part of the gaps between said fine wires being filled with a predetermined quantity of a metal for irradiating a desired resonance spectral light, which metal has a relatively low melting point compared with the metal forming said fine wires.

2. A light source lamp according to claim 1, wherein said cathode is formed in a predetermined contour by intertwining fine wires of a predetermined dimension consisting of the relatively high-melting-point metal, and substantially all gaps between said fine wires are filled with an impregnation metal of the relatively low-melting-point metal.

3. A light source lamp according to claim 2, wherein the fine wires of the relatively high-melting-point metal are regularly arranged to define the predetermined contour of said cathode.

4. A light source lamp according to claim 2, wherein the fine wires of the relatively high-melting-point metal are irregularly arranged and entwined with each other to define the predetermined contour of said cathode.

5. A light source lamp according to claim 2, wherein said relatively low-melting-point metal is composed of an alloy of an alkali metal element.

6. A light-source lamp according to claim 1, wherein fine wires of a predetermined dimension consisting of the relatively high-melting-point metal are entwined with each other to define the predetermined contour of the cathode, and at least part of the gaps between the fine wires are filled with metal powder of the relatively low melting point metal.

7. A light-source lamp according to claim 6, wherein the gaps between the fine wires of the relatively high-meltingpoint metal are filled with melted metal powder having a relatively low melting point.

8. A light source lamp according to claim 1, wherein the relatively low melting point is made of fine wires, both the fine wires of the high-melting-point metal and the lowmeltingpoint metal being entwined with each other to define the predetermined contour of the cathode.

9. A light source lamp to claim 8, wherein the fine wires of the metal having a relatively high melting point and the fine wires of the metal having a relatively low melting point are arranged in regular relationship to each other to define the contour of the cathode.

10. A light source lamp according to claim 8, wherein the fine wires of the metal having a relatively high melting point and the fine wires of the metal having a relatively low melting point are arranged in irregular relationship to each other.

ll. A light source lamp according to claim 6, wherein the fine wires of the relatively high-melting-point metal are entwined with each other, at least part of the gaps between the fine wires are filled with the powdered metal having a relatively low melting point, and the remaining gaps are filled with an impregnated metal having a lower melting point than that of said powdered metal.

12. A light-source lamp according to claim 8, wherein the fine wires of the relatively high-melting-point metal and fine wires of the relatively low-melting-point metal are entwined with each other to define the predetermined contour of the cathode, and substantially all the gaps between said fine wires are filled with an impregnated metal having a lower melting point than that of said low-melting-point metal.

13. A light source lamp according to claim 8, wherein the fine wires of the relatively high-melting-point metal and the fine wires of the relatively low-melting-point metal are entwined with each other to define the predetermined contour of the cathode, and at least part of the gaps between the fine wires are filled with a powdered metal having a relatively low melting point.

14. A light-source lamp according to claim 1, wherein the fine wires of the relatively high melting point are 200 microns or less in thickness and 0.5 mm. or less in width.

15. A method of manufacturing a hollow cathode of a lightsource lamp for atomic light-absorption analysis comprising the steps of mechanically linking fine wires of a predetermined dimension consisting of a metal having a relatively high melting point with each other to form a predetermined structure, impregnating the gaps between said fine wires with a predetermined quantity of a metal having a relative low melting point, and forming the resultant body into a desired contour for the hollow cathode.

16. A method of manufacturing a hollow cathode according to claim 15, wherein the fine wires of the relatively high-melting-point metal are press-molded into a predetermined structure.

17. A method of manufacturing a hollow cathode according to claim 15, wherein the fine wires of the relatively high melting point are knitted to form a predetermined structure.

18. A method of manufacturing a hollow cathode comprising the steps of mixing fine wires of a predetermined dimension consisting of a metal having a relatively high melting point with a predetermined quantity of powdered metal having a relatively low melting point, and press-molding the resulting mixture into a structure having a predetermined contour.

19. A method of manufacturing a hollow cathode according to claim 18, wherein after having been press-molded, the mixture of the fine wires and powdered metal having a relatively low melting point is heated so that said powdered metal is mechanically bonded to said relatively high-melting-point metal.

20. A method of manufacturing a hollow cathode according to claim 18, further including impregnating gaps between the fine wires and powdered metal with a metal having a lower melting point than that of said powdered metal.

21. A method of manufacturing a hollow cathode comprising the steps of mixing fine wires of a predetermined dimension consisting of a metal having a relatively high melting point with a predetermined quantity of fine wires of a predetermined dimension consisting of a metal having a relatively low melting point. and causing said fine wires to be mechanically tightly linked with each other to form a predetermined structure.

22. A method of manufacturing a hollow cathode according to claim 21, further including, and press-molding the resulting mixture.

23. A method of manufacturing a hollow cathode according to claim 21, in which the fine wires of high-melting-point metal and low-melting-point metal are knitted to define a predetermined structure.

24. A method of manufacturing a hollow cathode according to claim 23, further including heating said structure to fuse and bond the fine wires of the relatively low-melting-point metal, to the fine wires of the relatively high-melting-point metal.

25. A light-source lamp for atomic light-absorption analysis comprising a cathode having a hollow portion formed therein,

an anode provided adjacent to said cathode, a hermetically sealed envelope containing said cathode and said anode, and

inert gas atmosphere confined in said envelope, wherein said cathode is formed in a predetermined contour by a close mechanical linkage of fine wires of a predetermined dimension consisting of such a relatively high-melting-point metal as being not deformed at a temperature to operate said lightsource lamp, and at least part of the gaps between said fine wires are filled with a predetermined quantity of an evaporated element selected from the group consisting of Se, Te P and AS.

26. A light-source lamp for atomic light-absorption analysis; comprising a cathode having a hollow portion formed therein, an anode provided adjacent to said cathode, a hermetically sealed envelope containing said cathode and an inert gas atmosphere confined in said envelope, wherein said cathode is formed in a predetermined contour by a close mechanical linkage of fine wires of a predetermined dimension consisting of such a relatively high-melting-point metal as being not deformed at a temperature to operate said light-source lamp, and at least part of the gaps between said fine wires being filled with a predetermined quantity of an impregnated metal selected from the group consisting of Zn, Cd, In, Sn, Pb, Sb and Hi.

t t i t 4

Claims

1. A light source lamp for atomic light-absorption analysis comprising a cathode having a hollow portion formed therein, an anode provided adjacent to said cathode, a hermetically sealed envelope containing said cathode and said anode, and an inert gas atmosphere confined in said envelope, wherein said cathode is formed in a predetermined contour by a close mechanical linkage of fine wires of a predetermined dimension consisting of a metal having such a relatively high melting point that it will not be deformed at the operating temperature of said light source lamp, and at least part of the gaps between said fine wires being filled with a predetermined quantity of a metal for irradiating a desired resonance spectral light, which metal has a relatively low melting point compared with the metal forming said fine wires.

4. A light source lamp according to claim 2, wherein the fine wires of the relatively high-melting-point metal are irregularly arranged and entwinned with each other to define the predetermined contour of said cathode.

6. A light-source lamp according to claim 1, wherein fine wires of a predetermined dimension consisting of the relatively high-melting-point metal are entwinned with each other to define the predetermined contour of the cathode, and at least part of the gaps between the fine wires are filled with metal powder of the relatively low melting point metal.

7. A light-source lamp according to claim 6, wherein the gaps between the fine wires of the relatively high-melting-point metal are filled with melted metal powder having a relatively low melting point.

8. A light source lamp according to claim 1, wherein the relatively low melting point is made of fine wires, both the fine wires of the high-melting-point metal and the low-melting-point metal being entwined with each other to define the predetermined contour of the cathode.

11. A light source lamp according to claim 6, wherein the fine wires of the relatively high-melting-point metal are entwinned with each other, at least part of the gaps between the fine wires are filled with the powdered metal having a relatively low melting point, and the remaining gaps are filled with an impregnated metal having a lower melting point than that of said powdered metal.

12. A light-source lamp according to claim 8, wherein the fine wires of the relatively high-melting-point metal and fine wires of the relatively low-melting-point metal are entwinned with each other to define the predetermined contour of the cathode, and substantially all the gaps between said fine wires are filled with an impregnated metal having a lower melting point than that of said low-melting-point metal.

13. A light source lamp according to claim 8, wherein the fine wires of the relatively high-melting-point metal and the fine wires of the relatively low-melting-point metal are entwinned with each other to define the predetermined contour of the cathode, and at least part of the gaps between the fine wires are filled with a powdered metal having a relatively low melting point.

15. A method of manufacturing a hollow cathode of a light-source lamp for atomic light-absorption analysis comprising the steps of mechanically linking fine wires of a predetermined dimension consisting of a metal having a relatively high melting point with each other to form a predetermined structure, impregnating the gaps between said fine wires with a predetermined quantity of a metal having a relative low melting point, and forming the resultant body into a desired contour for the hollow cathode.

21. A method of manufacturing a hollow cathode comprising the steps of mixing fine wires of a predetermined dimension consisting of a metal having a relatively high melting point with a predetermined quantity of fine wires of a predetermined dimension consisting of a metal having a relatively low melting point, and causing said fine wires to be mechanically tightly linked with each other to form a predetermined structure.

25. A light-source lamp for atomic light-absorption analysis comprising a cathode having a hollow portion formed therein, an anode provided adjacent to said cathode, a hermetically sealed envelope containing said cathode and said anode, and inert gas atmosphere confined in said enVelope, wherein said cathode is formed in a predetermined contour by a close mechanical linkage of fine wires of a predetermined dimension consisting of such a relatively high-melting-point metal as being not deformed at a temperature to operate said light-source lamp, and at least part of the gaps between said fine wires are filled with a predetermined quantity of an evaporated element selected from the group consisting of Se, Te P and AS.

26. A light-source lamp for atomic light-absorption analysis; comprising a cathode having a hollow portion formed therein, an anode provided adjacent to said cathode, a hermetically sealed envelope containing said cathode and said anode, and an inert gas atmosphere confined in said envelope, wherein said cathode is formed in a predetermined contour by a close mechanical linkage of fine wires of a predetermined dimension consisting of such a relatively high-melting-point metal as being not deformed at a temperature to operate said light-source lamp, and at least part of the gaps between said fine wires being filled with a predetermined quantity of an impregnated metal selected from the group consisting of Zn, Cd, In, Sn, Pb, Sb and Bi.