Chemistry of inorganic compounds – Halogen or compound thereof – Plural metal or metal and ammonium containing
Reexamination Certificate
2002-10-02
2004-06-01
Nguyen, Ngoc-Yen (Department: 1754)
Chemistry of inorganic compounds
Halogen or compound thereof
Plural metal or metal and ammonium containing
C148S024000, C148S026000, C228S262510
Reexamination Certificate
active
06743409
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing alkali metal fluorozincate, to the resulting product, and to the use thereof in brazing aluminum.
Alkali metal fluorozincates, such as cesium fluorozincate and particularly potassium fluorozincate, may be used as fluxing agents for brazing aluminum components and components made of aluminum alloys. In this case, these compounds act not only as fluxing agents, but rather they produce a coating of the surface, in that zinc is deposited on the surface of the components. The fluorozincates may also be used together with alkali fluoroaluminates, for example potassium fluoroaluminate and/or cesium fluoroaluminate. These compounds also act as fluxing agents for brazing aluminum. German Published Application 199 13 111 A1 discloses these types of fluxing agents and their use. The production of alkali metal fluorozincates according to this published application is achieved by melting together alkali metal fluoride and zinc fluoride, by reacting alkali metal fluoride and zinc fluoride in aqueous phase, or by reacting zinc oxide with adducts of hydrogen fluoride and alkali metal fluoride.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method for producing alkali metal fluorozincates which is capable of producing products having defined grain distribution ranges.
Another object of the invention is to provide an alkali metal fluorozincate which is especially suited for use as a fluxing agent or fluxing agent component.
These and other objects are achieved in accordance with the present invention by providing a method for producing alkali metal fluorozincate from alkali metal hydroxide, zinc oxide, and alkali metal fluoride or hydrogen fluoride in aqueous phase, wherein:
a) to produce fine alkali metal fluorozincate, alkali metal hydroxide and zinc oxide are mixed into a suspension and hydrogen fluoride is added, or
b) to produce medium fine alkali metal fluorozincate, hydrogen fluoride and zinc oxide are mixed with one another and alkali metal hydroxide is added, or
c) to produce coarse alkali metal fluorozincate, hydrogen fluoride and zinc oxide are mixed with one another and alkali metal fluoride is added.
In accordance with a further aspect of the invention, the objects are achieved by providing a fine alkali metal fluorozincate produced by the method of claim
1
, and having a grain spectrum in which 50% of all particles have a diameter <5 &mgr;m, or a medium fine alkali metal fluorozincate produced by the method of claim
1
, and having a grain spectrum in which 50% of all particles have a diameter <11 &mgr;m, or a coarse alkali metal fluorozincate produced by the method of claim
1
, and having a grain spectrum in which 50% of all particles have a diameter >11 &mgr;m.
In accordance with yet another aspect of the invention, the objects are achieved by providing a method of fluxing an aluminum or aluminum alloy component for brazing, said method comprising applying to said component a fluxing agent comprising an alkali metal fluorozincate produced as described above.
The present invention is based on the recognition that alkali metal fluorozincate having specific grain size properties may be produced as a function of the type of starting compounds and the sequence in which the starting reactants are brought into contact with one another.
The method according to the present invention for producing alkali metal fluorozincate from alkali metal hydroxide, zinc oxide, and alkali metal fluoride or hydrogen fluoride in aqueous phase is distinguished in that
a) to produce fine alkali metal fluorozincate, alkali metal hydroxide and zinc oxide are mixed into a suspension, and hydrogen fluoride is added, or
b) to produce medium fine alkali metal fluorozincate, hydrogen fluoride and zinc oxide are mixed with one another, and potassium hydroxide is added, or
c) to produce coarse alkali metal fluorozincate, zinc oxide and hydrogen fluoride are mixed with one another, and alkali metal fluoride is added.
Instead of zinc oxide, other zinc compounds, e.g., zinc hydroxide, zinc carbonate, or zinc chloride, may be used. However, zinc oxide is preferred.
In the context of the present invention, the term “fine” refers to an alkali metal fluorozincate in which 50% of the particles have a particle size smaller than 5 &mgr;m and 90% of the particles have a particle size of less than 9 &mgr;m; the remaining particles are then the same size or larger than the indicated values. Fine alkali metal fluorozincate is preferably produced in which 50% of all particles have a diameter of <3.8 &mgr;m and 90% of all particles have a diameter of <8 &mgr;m. The size is determined using laser diffraction.
Within the context of the present invention, the term “medium fine” refers to a product in which 50% of the particles of the material produced have a grain size of less than 11 &mgr;m and 90% have a grain size of less than 27 &mgr;m. The diameters of the remaining particles are at or above the listed values. “Medium fine” preferably means that 50% of all particles produced have a grain size of less than 10 &mgr;m and 90% of all particles have a grain size of less than 26 &mgr;m. The particle size analysis is again carried out by laser diffraction.
In the context of the present invention, the term “coarse” means that 50% of all particles have a grain size of less than 22 &mgr;m and 90% have a grain size of less than 40 &mgr;m. The term “coarse” preferably means that 50% of all particles have a grain size of, less than 21 &mgr;m and 90% have a grain size of less than 39 &mgr;m. The diameters of the remaining particles correspond to the recited dimensions or lie below them.
Alkali metal hydroxide, hydrogen fluoride, and alkali metal fluoride advantageously are used in the form of an aqueous solution. The preferred alkali metal is potassium.
In the first variant of the method according to the present invention, fine alkali metal fluorozincate is formed. The fine alkali metal fluorozincate preferably is then isolated and dried. Surprisingly, the resulting product is finer than the product which results according to the method described in German Published Application 199 13 111. For example, alkali metal fluorozincate having a grain spectrum in which 50% of all particles have a diameter of <5 &mgr;m (measured by laser diffraction) may be produced in this way.
Preferably, the procedure starts with potassium hydroxide as an alkali hydroxide and produces potassium fluorozincate. In this case, the potassium hydroxide is preferably used in the form of an aqueous potassium hydroxide solution. The concentration of KOH in this potassium hydroxide solution is advantageously in the range from 10 to 50 weight-percent. KZnF
3
is particularly preferably produced. For this purpose, potassium hydroxide, zinc oxide, and hydrogen fluoride are preferably used in quantities such that the atomic ratio of K:Zn is in the range from 1:1±0.05 and the atomic ratio of (K+Zn):F is in the range from 1:3±0.05. The zinc oxide may also be replaced by a zinc oxide precursor, for example, ZnCO
3
or ZnCl
2
.
A suspension is formed, which then reacts further with hydrogen fluoride to obtain the desired alkali metal fluorozincate. Preferably, a hydrofluoric acid solution is used containing 10 to 99 weight-percent HF, preferably 20 to 40 weight-percent HF.
The suspension of alkali metal hydroxide and zinc oxide is preferably produced at a temperature in the range from 15 to 85° C., particularly at ambient temperature (approximately 20° C.). The resulting intermediate product is advantageously reacted with hydrogen fluoride at a temperature in the range from approximately 20° C. to 90° C.
In the second variant of the present invention, medium fine alkali metal fluorozincate is produced. Hydrogen fluoride and alkali hydroxide are preferably used as an aqueous solution. The preferred concentrations correspond to those of the first variant. Alkali preferably is represented by potassium. Hydrogen fluoride and zinc oxide, whic
Becker Andreas
Frehse Joachim
Seseke-Koyro Ulrich
Crowell & Moring LLP
Nguyen Ngoc-Yen
Solvay Fluor and Derivative GmbH
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