EP0082210B1 - Method of selectively dissolving molybdenum in the presence of tungsten - Google Patents

Abstract

1. A process for selectively dissolving molybdenum in the presence of tungsten, particularly for selectively dissolving the tungsten core-wire from tungsten spirals manufactured on a molybdenum core-wire, with an acid solution of 1 or more compound(s) having oxygen in peroxide-oxygen bond, characterized in that one carries out the dissolving with an acid solution which does not contain nitric acid in the presence of 1 or more compound(s) of 1 or more of the elements iron, copper, thallium, silver, lead, chromium, nickel, bismuth, tellurium, cerium, titanium, vanadium, manganese and cadmium as a catalyst(s) which selectively accelerates (accelerate) the dissolving of the molybdenum.

Description

The invention relates to a method for the selective dissolution of molybdenum in the presence of tungsten, in particular for the selective dissolution of the molybdenum core wire from tungsten spirals produced on a molybdenum core wire.

As is known, in the manufacture of the tungsten filament-containing electric light bulbs, the tungsten wire is usually formed by winding or winding onto a molybdenum core wire to form a single or multiple spiral, then these tungsten spirals are heated on the molybdenum core in a protective gas to about 1500 ° C. until the Mechanical stresses in the tungsten wire have largely disappeared, which means that after the chemical dissolution of the molybdenum core, i. H. after its removal, the tungsten coils no longer change their intended original dimensions to any significant extent (do not shrink) and, when heated for the first time without a core to the temperature of the incandescent body, also lose none of their geometric uniformity and correctness.

It is also known that the tungsten wire is spiraled, e.g. H. When winding onto the molybdenum core, small groove-like depressions are pressed into the surface of the molybdenum core, d. H. that the tungsten in this product does not come into contact with the molybdenum along a line but on a considerable part of the surface, which is why when heated together to around 1500 ° C, a clearly detectable amount of molybdenum in significant concentration in the surface parts of the tungsten wire that touch the molybdenum core, diffuses.

In common practice, a mixture of concentrated nitric acid, concentrated sulfuric acid and water, e.g. B. a mixture of 5 parts by volume of concentrated nitric acid, 3 parts by volume of concentrated sulfuric acid and 2 parts by volume of water (see BJAM van Liempt, _" Recueil des Travaux Chimiques des Pays-Bas", Vol. 45 [1926] , Nos. 7/8, 508 to 521), because such a mixture chemically completely dissolves the molybdenum core wire at the spontaneously occurring temperature of loosening the molybdenum core, but only slightly attacks the tungsten wire.

A disadvantage of this known method is that the weight loss of the tungsten spirals of different sizes made of tungsten wires of different thicknesses, which is brought about by loosening the molybdenum core wire with the mixture of nitric acid, sulfuric acid and water, is on average about 4% by weight, so it is still increasing is high, and in particular that its spread is large. This weight loss and its dispersion are due in part to the fact that the composition and temperature of the mixture do not change uniformly with each individual dissolution process, and in part to the fact that the surface part of the spirals made of tungsten wires of different thickness, which comes into contact with the molybdenum, comes into play various masses of molybdenum absorbs from the molybdenum core wire and the tungsten / molybdenum alloys formed in the surface are sensitive to the chemical effect of the mixture dissolving the molybdenum core to varying degrees.

A major disadvantage of the known method mentioned is that nitric acid inevitably produces large amounts of nitrogen oxides during the dissolution of the core and that the so-called nitrous gas consisting of them is an extremely caustic and very harmful product, the neutralization (binding) of which is known to be one only with a great deal of effort and also only a very incompletely solvable task.

Another disadvantageous feature of this process is that the recovery of the valuable molybdenum trioxide content (MoOa content) of the exhausted solution mixture can only be achieved with end-of-solution products that count as impermissible impurities in living water.

It has also long been known that medium concentration aqueous hydrogen peroxide solutions slowly dissolve both molybdenum and tungsten. In the case of the known hydrogen peroxide solutions, however, no such remarkable difference in the dissolution rates was observed which would have made it possible to loosen the molybdenum core without simultaneously attacking the tungsten spiral.

Furthermore, DE-OS No. 2234494 describes a method for dissolving the wire mandrel, for example made of molybdenum, a filament or spool of tungsten in a solution containing nitric acid and water, which in addition to the nitric acid as acids also contains sulfuric acid, hydrochloric acid and / or May contain phosphoric acid and contains an inhibitor against the generation of gaseous nitrogen oxides, known. However, this known method also has the disadvantage that it has to be used with a solution of nitric acid with its disadvantages, albeit to a lesser extent, as is the case, for example, in p. 10, lines 14 to 16 (in example 4) and p. 12, line 8 from the bottom to 6 from the bottom (in example 9), where the release of small amounts of gaseous nitrogen oxides into the air is mentioned, and from page 8, lines 13 to 15 (in example 1), and on page 13, line 8 from the bottom to 6 from the bottom (with reference to Examples 10 and 11) of the cited document, where it was added, stating that there was scarcely any case that gaseous nitrogen oxides were released into the air, that it can happen that gaseous nitrogen oxides get into the air. Furthermore, in the process of DE-OS No. 2234494 when regenerating the molybdenum trioxide content inevitably contaminate the environment (natural waters) waste, eg. B. salts such as sulfates and chlorides. Also in example 1 on page 8, line 13 from the bottom to 10 from the bottom of DE-OS No. 2234494 stated that the metal thread double helix removed from the liquid after the wire mandrel had dissolved showed more or less a deposition on the surface and this had to be removed by acid washing . This disadvantage is also pointed out in DE-AS No. 2359558 by the same patent applicant, in particular in column 4, lines 4 to 10 and in column 4, lines 22 to 28.

Furthermore, from DE-AS No. 2359558 it is known to etch a molybdenum core from a tungsten wire helix with nitric acid or an acid mixture consisting mainly of nitric acid and sulfuric acid with the addition of ammonium peroxodisulfate. This publication also has the disadvantage that it is imperative to use nitric acid, possibly together with sulfuric acid, as the acid. This means that the disadvantages discussed in connection with DE-OS No. 2234494 also apply to the method of DE-AS No. 2359558.

In DE-AS No. 2359558, column 2, lines 7 to 25, the state of the art at the time described the use of nitric acid or acid mixtures containing nitric acid with an addition of hydrogen peroxide for etching or pickling metals. However, the use of hydrogen peroxide is not recommended, since it decomposes easily and thus loses its property that prevents the formation of nitrogen monoxide, which is further compounded by the fact that any additional hydrogen peroxide added during the reaction entails the risk of intermittent boiling.

Column 4, lines 11 to 14 of DE-AS No. 2359558 also speaks of the need to avoid the use of an oxidizing agent consisting of a metal salt. In addition, the word _" or" also speaks optionally of avoiding an oxidizing agent which in turn emits a harmful gas.

Furthermore, DE-OS No. 2425379 describes a solution which consists only of hydrogen peroxide and water for etching molybdenum. However, it has already been shown above that such a solution is disadvantageous, in particular because it is unable to selectively dissolve the molybdenum in the presence of tungsten. In this context it should also be pointed out that DE-AS No. 2359558 also describes the use of hydrogen peroxide together with nitric acid or an acid mixture containing nitric acid as disadvantageous. Because of the fact that the hydrogen peroxide is not selective with respect to molybdenum in the presence of tungsten, it is not surprising that DE-OS No. 2425379 does not speak of the presence of tungsten, but rather of the etching Molybdenum restricted. On page 6, line 16 from the bottom to 11 from the bottom of DE-OS No. 2425379, other standard etching agents, such as hydrochloric acid and sulfuric acid, are mentioned as the state of the art at that time, but only in relation to the etching of molybdenum , d. H. without the presence of tungsten, although its use is also discouraged for molybdenum etching.

Furthermore, DE-OS No. 2532773 discloses a solvent made of nitric acid, optionally together with sulfuric acid or hydrochloric acid, hydrogen peroxide and various organic hydrogen peroxide stabilizers, the purpose of use also being to remove molybdenum cores from tungsten filaments. However, this known method also has the disadvantage that it is imperative to use nitric acid in the solvent.

In addition, DE-OS No. 2848475 discloses solvents for dissolving metals from sulfuric acid, hydrogen peroxide and monohydroxy- or dihydroxy-substituted cycloparaffins or alkylcycloparaffins as activators, optionally together with copper ions. However, the use for the selective dissolution of molybdenum in the presence of tungsten is not even hinted at, rather the etching of copper in the production of printed circuits is specified as a special embodiment. Also in this publication on page 6, line 11 from the bottom to 8 from the bottom, it is mentioned that the use of hydrogen peroxide as a component of etching agents is problematic, the stability of hydrogen peroxide in a sulfuric acid / hydrogen peroxide solution being caused by the The presence of heavy metal ions, such as copper ions, is adversely affected, which in turn shows how critical the use of hydrogen peroxide is.

The same applies analogously to US Pat. No. 3597290, which was dealt with at that time in DE-OS No. 2848475 as prior art. This describes a method for dissolving metals, in particular copper, with a solvent of hydrogen peroxide, a saturated lower aliphatic alcohol and at least 1 of the acids sulfuric acid and phosphoric acid and possibly at least 1 of metal ions with a lower oxidation potential than that of copper, for example silver, are described, there being no question of selective dissolution of molybdenum in the presence of tungsten. Much more, this document focuses exclusively on the dissolving of copper, although in some places there is general talk of dissolving metals. The main field of application of the method of US Pat. No. 3597290 is the etching of copper plates in the production of printed circuits. Table II on page 14 of DE-OS No. 2848475 also shows in particular how unfavorable that the solvent containing no substituted cycloparaffin or alkylcycloparaffin was as stabilizer, in that the hydrogen peroxide decomposed rapidly. Furthermore, on page 8, lines 17 to 20 of DE-OS No. 2848475, it is pointed out that silver ions in hydrogen peroxide / sulfuric acid etching solutions do not yet promote the etching rate to the extent that this would be desirable.

Furthermore, from DE-OS No. 2933430 Dissolving molybdenum in the presence of tungsten only known with solvents from nitric acid, sulfuric acid and water. However, this document does not actually concern the dissolution, but rather the recovery of molybdenum and mixed acid from used mixed acid pickling solutions. This is done in such a way that the dissolved molybdenum is oxidized by adding nitric acid at elevated temperature and the precipitated molybdenum oxide is filtered off at elevated temperature. Also on page 6, lines 12 to 25 of DE-OS No. 2933430 as the state of the art at the time, US Pat. No. 3963823, according to which dissolved molybdenum is recovered from spent mixed acid pickling solutions in such a way that they are combined with ammonium hydroxide solution Adjusted pH from about 1.5 to 3, the resulting solution is heated to a temperature of less than about 95 ° C with stirring and then filtered. A disadvantage of this method is, however, that the ammonium molybdate formed is difficult to filter off and the waste water is additionally contaminated by the ammonium salts formed.

The invention is based on the object, while eliminating the disadvantages of the prior art, a method for the selective dissolution of molybdenum in the presence of tungsten, in particular for the selective dissolution of the molybdenum core wire of tungsten spirals produced on a molybdenum core wire, in which the weight loss of the tungsten is less than in the case of the is known methods and no harmful and polluting substances are created.

The above has surprisingly been achieved by the invention.

The invention relates to a method for the selective dissolution of molybdenum in the presence of tungsten, in particular for the selective dissolution of the molybdenum core wire of tungsten spirals made on a molybdenum core wire, with an acidic solution of 1 or more oxygen in a compound (s) having a peroxide-oxygen bond, which is characterized in that that dissolving with an acidic solution that does not contain nitric acid in the presence of 1 promotes more compound (s) of 1 or more of the elements iron, copper, thallium, silver, lead, chromium, nickel, bismuth, tellurium, ger , Titan, Vana-. dium, manganese and cadmium which dissolve the peroxide oxygen bond as catalyst (s) which selectively accelerate or accelerate the dissolution of the molybdenum.

Hydrogen peroxide and / or 1 or more peracid (s), persalt (s) and / or other peroxides (other peroxide) (superoxides [superoxide]) are or are preferably used as the compound (s) having oxygen in a peroxide-oxygen bond. The use of hydrogen peroxide is particularly preferred. This is advantageously used in the form of a 30% solution.

It has been found that it is expedient in individual cases to adjust the concentration of the hydrogen peroxide or other solvent containing peroxide to the size of the specific surface of the molybdenum body, e.g. B. to choose the thickness of the molybdenum core wire, that is, to determine the most suitable concentration experimentally, and to regulate the severity of the chemical solution process with drop metering. In this case, the oxygen-bonded oxygen compound can be added dropwise to an acidic solution of the catalyst or catalysts containing the body containing the tungsten and the molybdenum, which selectively accelerates or accelerates the dissolution of the molybdenum.

An essential element of the invention is the discovery of catalysts which practically do not increase the dissolution rate of the tungsten in acidic solutions of 1 or more oxygen in compound (s) containing peroxide-oxygen bond, such as hydrogen peroxide solutions, but the dissolution of the molybdenum under the same conditions Accelerate orders of magnitude and thus enable the molybdenum core to be loosened at a practically usable rate even without other solvents in such a way that the tungsten spiral suffers a smaller weight loss than previously, mostly 1 to 2% by weight, which is insignificant for the spiral quality.

As catalysts which selectively accelerate or accelerate the dissolution of the molybdenum, 1 or more iron compound (s), in particular iron (III) compounds, very particularly iron (III) chloride, are preferably in the form of its hexahydrate.

This enables particularly favorable technical conditions to be achieved.

With the choice of the concentration of the compound (s) which accelerate or accelerate the dissolution of the molybdenum, the rate of dissolution of the molybdenum can be varied within wide limits. Concentrations thereof of 0.1 to 6, in particular 0.2 to 4,% by weight are preferably used.

As the acidic solution of 1 or more oxygen in the peroxide-oxygen bond, the compound (s) whose acidity is adjusted with an inorganic or organic acid other than nitric acid can be used.

Preferably, as the acidic solution of 1 or more oxygen in the peroxide-oxygen bond, the compound (s) whose acidity is adjusted to a pH of -0.5 to +2.0 with an acid other than nitric acid is used. It was found that very favorable practical solution conditions can be achieved as a result. Mineral acids other than nitric acid, especially sulfuric acid and / or hydrochloric acid, and / or overchloric acid can suitably serve as acids for this purpose, the use of sulfuric acid is particularly preferred. Of the organic acids, the use of acetic acid and / or tartaric acid is preferred. Acid concentrations of 0.5 to 3, in particular 1 to 3,% by weight are preferably used.

The advantages of the method according to the invention can be further increased if the dissolution of the molybdenum in the presence of an inhibitor, i.e. H. of a substance that prevents the tungsten from attacking. According to an expedient embodiment of the process according to the invention, the acidic solution of 1 or more oxygen in a peroxide-oxygen bond is one which also contains 1 or more perchlorate (s) and / or overchloric acid or 1 or more chromate (s) and / or contains chromic acid as an inhibitor (s) to prevent the tungsten from dissolving. When using overchloric acid, this can also serve to adjust the acidity.

The speed of the process of dissolving the molybdenum according to the process according to the invention is sensitive to the temperature of the dissolving mixture. The temperature is advantageously kept below 45, in particular at 25 to 35, very particularly at 25 to 30 ° C. With such temperatures of the dissolving mixture, the dissolution rate of the tungsten can namely be kept at a negligible value. It turned out to be useful to regulate the temperature of the dissolving mixture by constant cooling. According to an expedient embodiment of the method according to the invention, the dissolution process is carried out in a closed system under excess pressure, as a result of which the loss of peroxide oxygen, which occurs as a result of the spontaneous decomposition of the hydrogen peroxide or the other compound (s) having a peroxide-oxygen bond, is reduced. An extraordinary advantage of the method according to the invention in all its embodiments is that, in contrast to the prior art, i. H. to use a solution mixture of nitric acid, sulfuric acid and water, neither harmful and difficult to remove nitrous gases, nor other polluting gaseous by-products.

A particular advantage of the method according to the invention also lies in the fact that when it is carried out not only no nitrous gases are produced, but also, as the end product of the solution, an exhausted solution which is available for recovering the molybdenum trioxide content and which in the process is not harmful to living water and contains only difficult to remove solutes, can be obtained.

The invention is illustrated by the following examples.

example 1

There were 1000 pieces of tungsten spirals of average size, in which the mass of the molybdenum core was 3 to 4 times the mass of the tungsten spiral, z. B. 40 mg / piece of molybdenum core mass and 10 mg / piece of tungsten spiral mass, in 500 cm ^{3 of} a 30% hydrogen peroxide solution (H ₂ 0 ₂ solution), which 3% by weight sulfuric acid (H _Z S0 ₄ ) and 1.0 wt .-% iron (III) chloride hexahydrate (FeCl ₃ · 6 H ₂ O), introduced. In the solution from room temperature, the dissolution of the molybdenum started with a violent reaction, which was moderated in such a way that the temperature of the solution was kept below 45 ° C. with water cooling. The process was completed in about 15 to 25 minutes. In addition to the tungsten spirals from which the molybdenum core was removed, a solution containing brown peroxymolybdic acid remained. The solution and the spirals were separated and the spirals were washed with dilute acid and water and finally with dilute ammonia and dried. The surface of the spirals was polished. Their weight loss was 2% by weight and the weight spread matched the original weight spread of the spirals.

Example 2

There were spirals of the type described in Example 1 in the amount also described in this in 300 cm ^{3 of} a solution which 1% by weight iron (III) sulfate (Fe ₂ [SO ₄ ] ₃ ) and 2% by weight overchloric acid contained, introduced. With water cooling, 500 cm ^{3 of} a 30% hydrogen peroxide solution were added dropwise at such a rate that the temperature of the solution did not exceed 35 ° C. After the dissolution of the molybdenum had ended, the tungsten spirals were treated as described in Example 1. The surface of the spirals was polished. Their weight loss was 2% by weight and their weight spread matched that of the original spirals.

Example 3

• Lösung a): Eisen(III)perchlorat (Fe[ClO₄]₃)/ Überchlorsäure (HClO₄)
• Lösung b): Eisen(III)chlorid (FeCl₃)/Weinsäure

There were 1000 pieces of tungsten spirals of average size, in which the mass of the molybdenum core was 3 to 4 times the mass of the tungsten spiral, z. B. 40 mg / piece of molybdenum core mass and 10 mg / piece of tungsten spiral mass, each in 300 cm ^{3 of} the following solutions a and b, each containing 1 wt .-% iron (III) ions and 3 wt .-% acid, wherein the iron (III) compounds and acids used can be found in the following information:

• Solution a): Iron (III) perchlorate (Fe [ClO ₄ ] ₃ ) / overchloric acid (HClO ₄ )
• Solution b): Iron (III) chloride (FeCl ₃ ) / tartaric acid

The 30% hydrogen peroxide solution was added dropwise at such a rate that the temperature of the solution did not exceed 35 ° C. After the molybdenum core had been removed, the spirals were treated as described in Example 1. The main parameters observed for the solution processes are summarized in the following table.

Example 4

Spirals of the type described in Example 1 were introduced in the amount also described in this into a 2-liter autoclave equipped with a pressure gauge and a pressure-relieving valve. Then 300 cm ^{3 of} 30% hydrogen peroxide, cooled to at least + 10 ° C., which contained 0.2% by weight of iron (III) chloride (FeCl ₃ .6H ₂ O) and 0.5% by weight of sulfuric acid, admitted. The autoclave was quickly closed and the release process was started by carefully heating the autoclave to 30 ° C. The reaction rate was then regulated as required by cooling or with the pressure-relieving valve so that the excess pressure in the reaction space did not exceed 1 MPa. The reaction was complete after about 20 minutes. After the overpressure had been released, the autoclave was opened and the spirals were treated as described in Example 1. The weight loss of the spirals was 1.4% by weight.

Example 5

There were 1000 pieces of tungsten spirals in which the mass of the molybdenum core was less than that of the tungsten spiral, namely 7 mg / piece of vacuum tungsten spiral mass (mass of a tungsten spiral intended for use in a vacuum) and 3 mg / piece of molybdenum core mass, in 200 cm ^{3 of} a solution that Contained 0.5 wt .-% iron (III) sulfate (Fe ₂ [SO ₄ ] ₃ ) and 1 wt .-% sulfuric acid (H _z S0 ₄ ). Then 300 cm ^{3 of} a 60% ammonium persulfate solution were added dropwise so that the temperature of the solution did not exceed 40 ° C. After the molybdenum triggering reaction had ended (about 20 min), the spirals were separated and treated as described in Example 1. The weight loss of the spirals was found to be 0.8% by weight.

Example 6

Spirals of the type described in Example 1 were used in the amount also described in 500 cm ^{3 of} a solution which contained 0.1% by weight of thallium (III) sulfate (TI ₂ [SO ₄ ] ₃ ) and 0.02% by weight .-% copper (11) sulfate (CuS0 ₄ ) and 3 wt .-% sulfuric acid, introduced. While cooling, 30% hydrogen peroxide was added to the solution at such a rate that the temperature of the solution did not exceed 35 ° C. After the molybdenum triggering reaction had ended (about 30 min), the spirals were separated and treated as described in Example 1. The weight loss was determined to be 3% by weight.

Claims (9)

1. A process for selectively dissolving molybdenum in the presence of tungsten, particularly for selectively dissolving the tungsten core-wire from tungsten spirals manufactured on a molybdenum core-wire, with an acid solution of 1 or more compound(s) having oxygen in peroxide-oxygen bond, characterized in that one carries out the dissolving with an acid solution which does not contain nitric acid in the presence of 1 or more compound(s) of 1 or more of the elements iron, copper, thallium, silver, lead, chromium, nickel, bismuth, tellurium, cerium, titanium, vanadium, manganese and cadmium as a catalyst(s) which selectively accelerates (accelerate) the dissolving of the molybdenum.

2. A process according to Claim 1, characterized in that one uses as compound(s) having oxygen in peroxide-oxygen bond hydrogen peroxide and/or 1 or more peracid(s), persalt(s) and/or another (other) peroxide(s).

3. A process according to Claim 1 or 2, characterized in that one uses as a catalyst which selectively accelerates the dissolving of the molybdenum iron(III)-chloride.

4. A process according to Claims 1 to 3, characterized in that one uses as an acid solution of 1 or more compound(s) having oxygen in peroxide-oxygen bond such the acidity of which has been adjusted by an acid to a pH-value of from -0.5 to +2.0.

5. A process according to Claims 1 to 4, characterized in that one uses as an acid solution of 1 or more compound(s) having oxygen in peroxide-oxygen bond such the acidity of which has been adjusted by sulphuric, hydrochloric, perchloric, acetic and/or tartaric acid.

6. A process according to Claims 1 to 5, characterized in that one uses as an acid solution of 1 or more compound(s) having oxygen in peroxide-oxygen bond such which also contains 1 or more perchlorate(s) and/or perchloric acid or 1 or more chromate(s) and/or chromic acid as an inhibitor(s) for hindering the dissolving of the tungsten.

7. A process according to Claims 1 to 6, characterized in that one maintains the temperature below 45° C.

8. A process according to Claims 1 to 7, characterized in that one maintains the temperature at 25 to 35° C.

9. A process according to Claims 1 to 8, characterized in that one works in a closed system at excess pressure.