Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F1/00—Etching metallic material by chemical means
  • C23F1/10—Etching compositions
  • C23F1/14—Aqueous compositions
  • C23F1/16—Acidic compositions
  • C23F1/26—Acidic compositions for etching refractory metals

Definitions

• 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.
• 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 1,500 ° C. until the Mechanical stresses that have arisen for the most part have disappeared, which means that after the chemical dissolution of the molybdenum core, that is to say after its removal, the tungsten spirals no longer change their intended original dimensions to a remarkable extent (do not shrink) and when heated for the first time without a core do not lose any of their geometric uniformity and correctness on the filament temperature.
• the tungsten wire is spiraled. that is, when winding onto the molybdenum core, small furrow-like depressions are pressed into the surface of the molybdenum core, that is, the tungsten in this product does not come into contact with the molybdenum along a line but on a considerable surface part, which is why when heated together to about 1,500 ° C diffuses an easily detectable amount of molybdenum in significant concentration into the surface parts of the tungsten wire that touch the molybdenum core.
• removal of the molybdenum core wire after heating is generally carried out Mixture of concentrated nitric acid, concentrated sulfuric acid and water, for example 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 for example JAM van Liempt: Recueil des Travaux Chimiques des Pays-Bas, T. 45 [1926], No. 7/8, 508 to 521), because such a mixture chemically completely dissolves the molybdenum core wire at the temperature of the loosening of the molybdenum core, while the tungsten wire is only slightly attacked .
• a disadvantage of this known method is that the weight loss of the differently sized tungsten spirals made of differently strong tungsten wires, which is brought about by dissolving the molybdenum core wire with the mixture of nitric acid, sulfuric acid and water, is on average about 4% by weight, that is to say, still increasing is high, and in particular that its spread is large.
• a major disadvantage of the known method mentioned is that nitric acid inevitably produces large amounts of nitrogen oxides during the dissolving of the core and that the so-called Nitrous gas is an extremely caustic and very harmful product, the neutralization (binding) of which is known to be a task that can only be carried out with great effort and therefore only very incompletely.
• An unfavorable feature of this process is also that the recovery of the valuable molybdenum trioxide content (Mo03 content) of the exhausted solution mixture can only be achieved with those end-of-solution products which pay as impermissible impurities in living water.
• 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 invention relates to a process 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, with an acidic solution, which is characterized in that the dissolving with an acidic solution of 1 or more in part than for the non-selective dissolution of molybdenum together with tungsten known per se in peroxide-bonded compound (s) 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 which dissolves the peroxide oxygen bond as catalyst (s) which selectively accelerates or accelerates the dissolution of the molybdenum.
• hydrogen peroxide and / or 1 or more peracid (s), per salt (s) and / or other [s] peroxide (s) [superoxide (s)] is or are used as the oxygen-containing compound (s) .
• the use of hydrogen peroxide is particularly preferred. This is advantageously used in the form of a 30% solution.
• the concentration of the hydrogen peroxide or other solvent containing peroxide according to the size of the specific surface of the molybdenum body, for example the thickness of the molybdenum core wire, that is to say to determine the most suitable concentration experimentally, and that To regulate the intensity of the chemical dissolving process with drop metering.
• the oxygen in a peroxide-oxygen bond can form a compound containing the body containing the tungsten and the molybdenum of the catalyst or catalysts which selectively accelerate or accelerate the dissolution of the molybdenum are added dropwise.
• An essential element of the invention is the discovery of catalysts which practically do not increase the rate of dissolution of the tungsten in acidic solutions of 1 or more oxygen in a compound (s) containing peroxide oxygen, such as hydrogen peroxide solutions, but accelerate the dissolution of the molybdenum by orders of magnitude under the same conditions and thus the dissolving of the molybdenum core with practically usable speed even without other solvents in such a way that the tungsten spiral suffers a minor weight loss insignificant for the spiral quality than previously, mostly 1 to 2% by weight.
• iron compound (s) in particular iron (III) compounds, very particularly iron (III) chloride, are expediently in the form of its hexahydrate.
• the rate of dissolution of the molybdenum can be varied within wide limits. Concentrations of the same of 0.1 to 6% by weight, in particular 0.2 to 4% by weight, are preferably used.
• the compound (s) whose acidity is adjusted with an inorganic or organic acid can be used.
• the acidic solution of 1 or more oxygen in the peroxide-oxygen-containing compound (s) one whose acidity is adjusted to an pH of -0.5 to +2.0 with an acid is used.
• Mineral acids in particular sulfuric acid and / or hydrochloric acid, and / or also nitric acid and / or overchloric acid can expediently serve as acids for this purpose, the use of sulfuric acid being particularly preferred.
• organic acids the use of acetic acid and / or tartaric acid is preferred. Acid concentrations of 0.5 to 3% by weight, 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 is carried out in the presence of an inhibitor, that is to say a substance which prevents the tungsten from attacking.
• 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.
• overchloric acid this can also serve to adjust the acidity.
• the speed of the process of dissolving the molybdenum by the process according to the invention is sensitive to the temperature of the dissolving mixture.
• the temperature is advantageously kept below 45 ° C., in particular at 25 to 35 ° C., 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.
• the dissolving 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 of its embodiments is that, in contrast to the prior art, that is to say the use of a solution mixture of nitric acid, sulfuric acid and water, it does not produce any harmful and difficult-to-remove nitrous gases, nor any other environmentally polluting gaseous by-products .
• a particular advantage of the method according to the invention is also that not only does no nitrous gases occur when it is carried out, but moreover, as the end product of the solution, an exhausted solution which is available for recovering the molybdenum trioxide content and does not contain any for the living Contains dissolved substances that are harmful to water and difficult to remove.
• Example 1 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 wt .-% iron (III) sulfate (Fe 2 (SO 4 ) 3 ) and 2 wt .-% Contained overchloric acid. 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.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Catalysts (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)

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Citations (6)

• 1981
  • 1981-12-18 DE DE8181110588T patent/DE3169917D1/de not_active Expired
  • 1981-12-18 EP EP81110588A patent/EP0082210B1/fr not_active Expired
  • 1981-12-18 AT AT81110588T patent/ATE12661T1/de not_active IP Right Cessation

Patent Citations (6)

Non-Patent Citations (1)

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