DE2825424C2 - Silicon-containing tantalum powder, process for its production and its use - Google Patents

Description

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The invention relates to silicon-containing tantalum powder, processes for its production and its Use.

Some of the main uses for tantalum are in electrolytic capacitors and furnace components in High temperature vacuum furnaces. Among the properties of tantalum that make it one of these fields of application make attractive material include a high melting point, high dielectric constant in the oxide film formed by anodic oxidation, high electrical conductivity, excellent ductility and machinability as well as availability in a highly pure form.

It is well known that tantalum becomes brittle when it is itself at relatively high temperatures (over 315 ° C) is briefly exposed to certain gases and vapors. Are oxygen, carbon monoxide and carbon dioxide Examples of contaminating gases to be mentioned, and they are important because they are the products or reaction components involve many physical and chemical reactions that involve the use of Tantalum products, either directly or indirectly, are involved in the electronics, metal and chemical industries is. The brittleness condition described above relates to the loss of proper flexibility without breakage in the intended applications (observed and measured at or near room temperature) as a result of the tantalum being exposed to high temperatures, unsuitable vacuums or contaminants Gases and vapors have been exposed to the lack of the ability to operate at low temperature without rupture after Being able to bend contamination creates serious problems because manufactured tantalum parts contaminate it later the vibration, impact and static forces at or near room temperature to determine finished products or devices during their service life or their processing are exposed.

One of the major difficulties with using tantalum in electrolytic capacitors has been that Tantalum lead wires during sintering of tantalum anode compacts made by pressing and sintering of tantalum powder with tantalum lead wire embedded in the powder compacts, become extremely brittle. That The degree of brittleness is, as is well known, even higher when such tantalum lead wires are contained in tantalum powder a relatively high oxygen content, e.g. more than 1600 ppm.

One method that has been used in an attempt to overcome this difficulty has been to use the surface of the tantalum lead wire to be treated with carbon or a carbonaceous material. The carbon coating tends to react with oxygen in the tantalum powder during the subsequent high-temperature sintering, and thereby the bendability of the lead wire is retained because the oxygen tends to be with it reacted to the carbon coating rather than being absorbed by the tannic lead wire. With this method is however, it is difficult to control the application of carbon in order to achieve uniform behavior and to maintain the necessary flexural strength of the lead wire. In addition, carbon exerts itself on the wire surface an adverse effect on the electrical properties of tantalum by causing an undesirable increase of the DC leakage current is caused through the tantalum oxide dielectric film.

Another method is used to reduce the amount of fragility of tantalum lead wire which consists in using a grain size controlled tantalum lead wire; d. H. a Tantalum wire that exhibits a grain size that will decrease after exposure to the elevated temperatures encountered during the Sintering of the anodes used does not increase significantly. However, this also has grain size controlled In many cases, brace wire does not have the desired resistance to fragility, in particular in those applications where the grain size controlled tantalum lead wire in a highly oxygenated Tantalum powder compact is embedded and in particular where the oxygen content of the tantalum powder is 1600 ppm or above is.

The brittleness of tantalum lead wires is a major problem when working with anodes when they are on the anodizing frame can be welded. The brittleness is especially bad with tantalum lead wire, though this is close to the highly oxygenated powder where the anode lead wire or the riser pipe into the Tantalum powder is embedded. The greatest brittleness is at the point where the wire exits the sintered anode to determine where the oxygen content of the wire is high and the wire is no longer is held. The brittleness of the tantalum lead wires has a strong influence on whether a manufacturing process for a capacitor may or may not be done economically because of failure of the lead wires

to a complete failure during handling the parts can lead. So all the value given to the material during manufacture is lost. A solution to this problem of tantalum lead wire fragility has a profound economic impact Manufacture of capacitors. Usually the problem is brittleness in tantalum capacitor anodes most serious, those pressed and sintered from powders that are proportionately high oxygen content (e.g. 1600 ppm oxygen or above), as well as with powders that have been sintered at temperatures of 1,800 ° C or above.

Furthermore, the brittleness of components made from tantalum semi-finished products in high-temperature furnaces or in other high temperature applications adversely affect the life of the parts. Tantalum materials Cooking temperature applications are adversely affected because they are getters for gases such as carbon monoxide or carbon dioxide, oxygen and nitrogen. Due to the high cost of made from tantalum Parts replacing parts can cause extended downtime due to fragility and high replacement costs to lead. Significant economic benefits can be achieved if the service life is such Tantalum parts can be increased.

A silicon-containing tantalum powder, in particular for electrical capacitors, is described in FR-PS 21 28 820 and 12 98071. While in the first PS no information about the amount of silicon contained According to the second PS, at least 0.81% by weight of silicon is present. A context between break resistance and silicon content cannot be deduced from either patent.

According to DE-OS 27 43 061, in a method for producing a solid electrolytic capacitor anode bodies pressed and sintered from commercially available pure tantalum powder into an anode body containing metal ions Immersed solution, which can also contain silicon ions, among other things. With a subsequent thermal The metals present in the doping solution go through the treatment, and thus also the silicon, different degrees of oxidation. The metal ions are said to have the electrical properties of the tantalum capacitors and can easily be separated from the tantalum during reprocessing.

The solid electrolytic capacitor according to DE-OS 26 38 752 contains the dielectric consisting of tantalum oxide besides a first impurity from a bad metal ion, such as molybdenum in abundance from 100 to 20,000 ppm, a second impurity of a tetravalent metal ion such as silicon.

In DE-AS 11 39 922 a method for producing of anodes for solid electrolytic capacitors, among others. made of tantalum, described using metal powder used, which contains 0.5 to 1.4 wt.% Oxygen and in which one carbon or carbide in one for the Formation of CO adds stoichiometric amount.

In FR-PS 22 09 992 is for a solid electrolytic capacitor an anode body made of sintered tantalum powder with an anode wire made of aluminum is described, in which the aluminum can contain silicon.

The invention is based on the object of a silicon-containing Tantalum powder used in the manufacture of tanlal products enables which remain resistant to breakage even after treatment at high temperatures, and to specify a method for its production and a use of the tantalum powder.

With regard to the silicon-containing tantalum powder, this object is achieved according to the invention in that it made of pure tantalum or at least 80% by weight Tantalum alloy each with less than 300 ppm niobium, less than 50 ppm tungsten, less than 10 ppm molybdenum, less than 30 ppm chromium, less than 20 ppm calcium and less than 200 ppm iron, chromium and Nickel is made together and that its silicon content is 100 to 2000 ppm.

The inventive method for producing the

ίο silicon-containing tantalum powder is characterized that the pure tantalum or the at least 80 wt .-% tantalum alloy and the silicon finely divided and are mixed to a premix and that the premix is pure tantalum or at least 80% by weight tantalum alloy is added in a finely divided state in such an amount that the silicon content of the mixture is in the range of 100 to 2000 ppm.

The silicon-containing tantalum powder according to the invention is used according to the invention for producing fracture-resistant Tantalum material used

Typically, a finely divided silicon powder is mixed with a finely divided tantalum powder in such an amount that a silicon content between 1% and 5% results in the premix. Since silicon volatilizes much more quickly than tantalum, and some of the silicon is lost during high-temperature processing, the premix is then mixed with finely divided tantalum powder in such quantities that a nominal silicon content *. about 2 to 3 times the actually desired silicon content in the final composition. The final mixture is then pressed and sintered to form a dense billet and then processed as desired. To produce tantalum wire, the ingot or ingot is subjected to repeated cold rolling and then repeated wire drawing operations until a wire of the desired diameter is obtained.
The resistance to breakage which is achieved according to the invention is shown by an objective test run under conditions which are similar to actual application conditions. In this test, a test wire made in accordance with the invention is compared with a test wire made in accordance with conventional practice in terms of the number of bends to which each wire can be subjected before it breaks. The details of the test are described below in connection with the specific examples.

example 1

A tantalum / silicon premix was prepared by mixing 3 parts by weight of elemental silicon powder having a particle size of less than 0.074 mm with 97 parts by weight of high purity tantalum powder having a particle size of less than 0.044 mm. The mixture was degassed in vacuo for 3 h at 1325 ° C., comminuted in a jaw crusher, ground and sieved to a particle size of less than 0.044 mm and classified. The above starting mixture and reduced sodium tantalum powder were then mixed to provide a powder mixture with a nominal silicon content of 300 ppm. About 6.35 kg of the powder mixture was then isostatically ^{pressed under a compaction pressure of 2812 kg / cm 2} to form a wire rod of 22.2 × 22.2 mm × 76.2 cm rectangular longitudinal cross-section. The compacted rod was heated by resistance for 3.5 h in a vacuum at a temperature

sintered temperature of 2380 ° C, cooled under vacuum, ^{isostatically pressed again under 5624 kg / cm 2} to increase its density, again sintered by resistance heating for 3.5 h in vacuum at a temperature of 2400 ° C and cooled under vacuum. The double sintered wire rod obtained was analyzed with the following results:

Chemical composition

Carbon 16 ppm

Oxygen 55 ppm

Nitrogen 38 ppm

Hydrogen <5 ppm niobium 40 ppm * · '·

Tungsten 25 ppm

Molybdenum <10 ppm

Iron 100 ppm nickel 75 ppm

Chromium 10 ppm

Calcium <10 ppm

Silicon 150 ppm

Hardness, Bhn 66.8-71.5

Density 15.85 g / cm ³

The double-sintered wire rod of 22.2 × 22.2 mm in cross-section became a rod of square section with rounded corners of 11.2 mm cold-rolled, which is degreased in perchlorethylene, acidic stripped in a nitric acid / hydrogen fluoride / sulfuric acid bath to make it chemically clean To obtain surface, and 60 min in a vacuum at an absolute furnace pressure of 0.1 μπι at 1300 ° C annealed. The 11.2 mm annealed rod then further became a rounded square cross-section of 3.75 mm, whereupon it was wound up. The winding was done by degreasing and subsequent Acid etching, as described above, cleaned and tempered again in a vacuum at 1300 ° C. for 60 minutes. The wire with a rounded square cross section of 3.73 mm was then made using square rolling passes rolled down to a rounded square cross-section of 2.26 mm and in a rounding pass in rollers with a semicircular cross-section to a diameter of 2.11 mm. The wire of this diameter was cleaned by degreasing and acid pickling, and then annealed in a vacuum as previously described. This wire was made using a brand name wire drawing machine to the final wire gauges with diameters of 0.64 mm, 0.51 mm, 0.41 mm and 0.36 mm pulled down. The wire of all final diameters received a slight etch in solution 1300 ml 48% hydrofluoric acid, 450 ml 70% nitric acid, 600 ml 98% sulfuric acid and 2500 ml deionized Water. The wires were then annealed in vacuo at 1300 ° C. for 60 minutes.

The wire of each diameter was spooled and checked for surface quality at a magnification of 10 times, the possible presence of any defects, such as splinters or chips, detachments, scars or uncover cracks or other imperfections that could be detrimental to wire quality.

To determine the resistance to rupture of the wire samples in a capacitor anode, a test was conducted under conditions designed to simulate the brittleness of tantalum wire that can occur during anode manufacture. A total of five samples of each wire diameter were cut to lengths of about 19 mm and the wires were pressed into cylindrical pellets of tantalum powder containing 2735 ppm oxygen. The wires were embedded to a depth of 3.18 mm in the anodes, which had a diameter of 6.35 mm, a height of 8.89 ± 2.54 mm and a weight of 2.0 g each. A Be / .ugs standard wire (without the addition of silicon), the performance data of which had previously been determined according to the test measures, was included in the tests for comparison purposes. The tantalum powder was pressed into these anodes to a density of 7.5 gcm ³ without the addition of a binder. The pressed anodes with the embedded lead wires were placed symmetrically on sintering trays. In each sintered passage were in addition to the test wires containing anodes and anodes with the reference standard wire not intended SiIiciumzusatz contained The anodes were 30 minutes at a temperature of 2050 ± 10 ° C and an absolute pressure of 10 ^-5 Torr vacuum in a sintered wall furnace

The lead wires in the sintered anodes were at a point 3.18 mm above the exit point of the anode bent repeatedly. A nozzle 3.18 mm thick with a hole in the center goes over the lead wire and is used to check the position where the bend occurs during the bending test. The wires were over that 3.18 mm thick nozzle bent by 90 ° and then bent back up to the vertical position. This overall movement is defined as a bend in the wire. Subsequent bending processes were also carried out, but the direction of force was rotated 60 ° between successive bending operations. The number the bending processes before failure of the wires due to breakage was determined. The data became a bending ratio calculates the number of bends to failure of the test wire compared to that of the Comparing standard reference wire of the same diameter under the same conditions (for a satisfactory Test should average the number of times the control wire is bent in the range of 1–5 bends lie). The following table compares the ratio of the flexures before the test wires break of example 1 with that of the control wire:

Tested wire Wire diameter Bending mm misrepresentation Reference wire, 0.635 1.0 control example 1 0.635 2.1 Reference wire, 0.381 1.0 control example 1 0.381 2.3

The test wires with 150 ppm silicon show a clear and considerable improvement in the flex ratio versus the standard reference wire which contained less than 10 ppm silicon.

Example 2

Test results on pressed and double-sintered rods containing various amounts of silicon in the form of a tantalum / 3% silicon premix, as described in Example 1, showed that the amount of silicon added to the rod

to the amount i: n remaining after the double sintering was in the range from about 2: 1 to 3: 1. The decrease in the silicon content in the rods is attributed to the volatilization of silicon monoxide, which is formed as a result of the reaction between the added silicon and the oxygen contained in the tantalum powder. Silicon monoxide is more volatile than elemental silicon at the temperatures used to process powdered tantalum. The main reduction in the silicon content entered, as was found during the first sintering at the bar while it was still fairly porous and permeable, thereby permitting the escape of silicon monoxide during sintering at 2380 ⁰ C. During the second sintering, when the rod approached full density, the silicon loss was insignificant.

In a series of additional tests, a number of additional rods with different silicon contents were carried out manufactured. The silicon was in the form of the tantalum / 3% silicon master alloy described above Amounts added to include 80, 200, 300 (two bars) and 450 ppm added silicon. Then were Rods produced according to the procedure of Example 1. Wire was pulled down to a diameter of 0.635 mm. The wire made from the 300 ppm samples was checked for residual silicon and others Elements analyzed by emission spectrographic analysis. The results were as follows:

Chemical composition

Silicon 110 ppm

Carbon 16 ppm

Niobium 40 ppm

Iron 100 ppm

Molybdenum <10 ppm

Nickel 75 ppm

Chromium <10 ppm

30th

The wires with the various amounts of silicon added were selected from those detailed in Example 1 conditions described are tested for their bending ratio. The results were as follows:

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Silicon additive

Bending ratio
(Average of five tests)

80 ppm
200 ppm
300 ppm
(first sample)
330 ppm
(/ wide sample)
400 ppm

1.5

1.4

1,6,2,1

(two different wires)

1,9,2,4

(two different wires)

2.1

The above data and other tests on a large number of samples show that the average flex ratio increases as the amount of remaining silicon increases, up to an average flex ratio of about 2.0 with a silicon content of about 100 ppm. With higher contents of the remaining For silicon, the average bending ratio remains at roughly the same value, but the "spread" of each one Tests will decrease, giving greater certainty that a given wire will have a bend ratio close to 2.0.

45

50

55

50 8
Example 3

A series of five bars were made with both silicon and carbon added. The silicon additions were made in the form of the tantalum / 3% silicon premix, as described in Example 1, while carbon is added in the form of tantalum carbide powder with a particle size of less than 0.044 mm became. These rods were pressed, sintered twice, and then cut to 0.635 mm in diameter after in Example 1 specified procedure pulled down. Two of the wires were silicon and carbon based analyzed, the other three were fully analyzed. The following table lists the chemical Composition of the wires and shows the remaining content of silicon and carbon of the wires as well as the achieved bending ratios:

Chemical composition [in ppm]

Examples

3a 3b 3c 3d

Silicon

carbon

niobium

iron

aluminum

Molybdenum nickel

chrome

Tungsten 290

115

415

150

130

150

71
77

150 130 60 150

220 208 290 150

<10 130

<10 <10

190 170

14 <10

<50 <50

35 bending ratios 1.9 2.2 2.1 2.2: 2.5 2.2 Example 4

A rod was made comprising 300 ppm silicon in the form of a tantalum / 3% silicon premix with 200 ppm aluminum added as tantalum / 1% aluminum master alloy. The rod was processed by pressing, sintering and wire drawing according to the procedure given in Example 1. Chemical analysis of this wire showed that 170 ppm silicon and 90 ppm aluminum remained in the wire was. The bending ratio of the wire was found to be 1.8.

Another stick was made, the 150 ppm Silicon as tantalum / 3% silicon premix, 100 ppm aluminum as tantalum / 1% aluminum master alloy and 100 ppm carbon has been added as tantalum carbide powder with a particle size of less than 0.044 mm was. The wire made from the rod with a diameter of 0.635 mm, produced according to the example below The procedure described in 1 was found to contain 71 ppm silicon. 59 ppm aluminum and 71 ppm carbon. The bending ratio was 2.4.

Example 5

7 kg of tantalum powder were added with 300 ppm silicon, in the form of a tantalum / silicon premix powder having a particle size of less than 0.044 mm with 3% silicon. A flat piece of about 1.27 cm thick χ 7.62 cm wide χ 91.4 cm long isostatically pressed in a rubber mold of rectangular cross-section. This piece was then im Sintered vacuum, isostatically pressed again and then sintered a second time. The compaction pressures

ίο

and the conditions of the sintering time and temperatures were the same as those for the square bars according to the earlier examples and as detailed in Example 1 described have been applied.

The double-sintered sheet was cold rolled to 0.254 mm thickness, with during processing was started in a suitable manner in between. This sheet was compared with a tantalum sheet, which was made similarly, except without the addition of silicon. Tensile strength properties ίο

were applied over a temperature range to the silicon

containing sheet of this example in comparison with the tantalum sheet containing no impurities added silicon. The tensile elongation for the sample without added silicon rose with increasing temperature to a peak value of about 93% at about 2500 ^° C. and then fell sharply to a value of about 58% at about 3000 ^° C. In contrast, the added silicon-containing sample showed increasing elongation under tension at temperatures up to about 3000 ^° C., a value of 100% being reached at this temperature.

The ultimate tensile strength of the added silicon containing tantalum was also found to be that of tantalum superior without the addition of silicon over the entire temperature range of 538-1649 ° C.

Corrosion sections of the silicon-containing tantalum of this example and of tantalum without added silicon were exposed to 95% sulfuric acid at a temperature of 205 ° C. for 31 days. The following weight losses were determined:

Silicon-containing tantalum 64 10- "g / cm ²
Tantalum without added silicon 75 χ 10- "g / cm ² .

As can be seen in Example 5, the addition of small amounts of silicon leads to tantalum or tantalum-rich Alloys to beneficial effects in addition to increased resistance to brittleness and is at Tantalum compositions useful even when made for end uses, for which excessive brittleness may not be a problem.

According to the invention, 100 to 2000 ppm of silicon are added to tantalum or a tantalum-rich one Composition with at least 80 percent by weight of tantalum considered to be a processed after processing Manufacture product or semi-finished product with about 50 to 700 ppm silicon. A preferred area for silicon is between about 200 and about 900 ppm in the starting composition and about 100 to about 300 ppm in the finished product.

The tantalum-rich alloys to which the invention is generally applicable are those which at least Contains 80 percent by weight of tantalum. A particularly useful class of tantalum-rich alloys, silicon can be added according to the invention are those with up to 14 percent by weight of tungsten and up to to 3 percent by weight of other alloying elements.

The silicon added according to the invention does not have to be in the form of elemental silicon, as in that Example shown. It can be in the form of a silicon compound, such as tantalum silicide. or (albeit with added carbon is desired) can be added in the form of silicon carbide.

It should be noted, as illustrated in Example 3a, that the advantages of the invention in terms of resistance to breakage can be achieved even when there are significant amounts of impurities in the metal. The desire for optimal properties other than break resistance can, however, be proportionate Require low limits on the amounts used for certain metallic impurities can be accepted. For in terms of electrical characteristics in the field of application For example, superior performance from capacitors is desirable to have the following impurities below the values listed in the following table:

Cichali

Niobium <300 ppm

Iron, chromium and nickel in total <200 ppm

Tungsten <50 ppm

Molybdenum <10 ppm

Chromium <30 ppm

Calcium <20 ppm

In the method according to the invention illustrated in the examples, a silicon-containing one is first used Premix with significantly higher silicon content than what is required for the end product, by mixing finely divided silicon into finely divided tantalum or a finely divided tantalum-rich alloy prepared in proportions desired for the premix, whereupon the mixture is volatile to remove Heated impurities and then ground to make it substantially uniform.

The premix is then thoroughly mixed with tantalum or a tantalum-rich alloy in powder form in such Mixed proportions that 2 to 3 times the amount of silicon desired in the finished composition is present, and the mixture is pressed and sintered once or twice before further processing.

The materials used to make the premix should be finely divided into the desired one practical uniformity of the end product. Preferably the materials should be sufficiently finely divided to pass through a sieve with a mesh size of 0.25 mm, in particular preferably to go through a sieve with a mesh size of 0.074 mm.

The silicon content in the premix is not critical. Any content can be useful for ease of use contributes to the preparation of the final mixture. A suitable range for the silicon content in the premix is 1 to 5 percent by weight.

The volatile material stripping temperature used to prepare the premix is preferably maintained at a maximum of about 1500 ° C to avoid partial sintering of the tantalum and the consequent difficulty in milling. Temperatures above 1500 ^° C can, however, be used if Measures are taken to maintain the easy grindability of the product by hydrogenating the tantalum before grinding.

In the foregoing description, tantalum wires have been primarily used for purposes of clarity described. The powders according to the invention are also for the production of sheet metal (Example 5), rods and other semi-finished forms of tantalum and in particular for the production of tantalum heating elements, reflectors and other components for high temperature vacuum furnaces.

Claims (6)

Patent claims: 1. Silicon-containing tantalum powder, in particular for electrical capacitors, characterized in that that it is made of pure tantalum or an at least 80 weight percent tantalum alloy each with less than 300 ppm niobium, less than 50 ppm tungsten, less than 10 ppm molybdenum, less than 30 ppm chromium, less than 20 ppm calcium and less than 200 ppm iron, chromium and nickel is produced together and that its silicon content is 100 to 2000 ppm 2. A method for producing the tantalum powder according to claim 1, characterized in that the pure tantalum or the at least 80 weight percent tantalum alloy and the silicon finely divided and are mixed to a premix and the premix pure tantalum or at least the 80 weight percent tantalum alloy in a finely divided state added in such an amount it is found that the silicon content of the mixture is in the range of 100 to 2000 ppm. 3. The method according to claim 2, characterized in that the premix for the purpose of removal of volatile impurities and then ground into particles of uniform size. 4. The method according to claim 3, characterized in that that the premix is ground to a particle size that passes through a sieve with a clear mesh size of 0.25 mm passes through it. 5. The method according to any one of claims 2 to 4, characterized in that a premix with 1 up to 5 weight percent silicon is formed. 6. Use of the tantalum powder according to claim 1 for the production of fracture-resistant tantalum semifinished products.