Patent Application
20050205418
Applicants claim priority under 35 U.S.C. §119 of German Application No. 10 2004 013 593.2 filed Mar. 19, 2004 and German Application No. 10 2004 032 260.0 filed Jul. 3, 2004.
1. Field of the Invention
The present invention relates to a cell for gas generation, particularly for the operation of a lubricant dispenser, having two electrodes to be connected to a circuit containing a power source, and an aqueous electrolyte fluid located between the two electrodes, containing an azide having the formula XN3, for electrochemical generation of a gas containing nitrogen (N2).
2. The Prior Art
In practice, it is known to meter the amount of lubricant that is dispensed by a lubricant dispenser by means of a gas-generating cell, whereby the pressure produced using the gas causes a corresponding exit of lubricant from the dispenser. In this connection, the generation of hydrogen or oxygen at the electrodes of a galvanic cell is known, for example from DE 35 32 335 C2. The cell can itself supply a sufficiently great voltage, if necessary with a zinc anode for generating hydrogen, or with a manganese dioxide cathode for generating oxygen. In this way, the electrolyte stream that flows between the electrodes can be regulated by way of an externally adjustable resistor. In addition, a battery can also be provided, which makes better regulation of the current intensity possible.
A gas cell is known from the reference DE 692 26 770 T2, wherein nitrogen is formed from a sodium azide solution, by means of electrolysis. In the electrolysis of an aqueous sodium azide solution, the gas generation rate quickly drops with the increasing formation of nitrogen. This gas generation rate drop arises because the hydroxide ions that are formed during the reaction result in a great increase in the pH of the solution, as the following reaction equation shows:
2 NaN3+2 H2O→3N2+H2+2 NaOH
At high pH values, the formation of free nitrogen does not take place, and only water is decomposed. Usual buffer substances, e.g. phosphates, are unsuitable for solving this problem, since their buffering capacity is too low.
An improvement is possible, by means of adding potassium iodide and potassium thiocyanate, but these are substances that behave aggressively with regard to metals, so that accordingly, precious metals or graphite electrodes must be used.
It is an object of the present invention to provide a cell having the characteristics described initially, which has a good gas generation rate.
These and other objects are achieved in accordance with the invention, by a cell for gas generation in which the electrolyte fluid contains a magnesium salt as an additive, for chemical binding of hydroxide ions that are formed during the electrochemical reaction. It has now been found that magnesium hydroxide formed from the magnesium salt and the hydroxide ions has only a very small solubility product. Accordingly, the magnesium hydroxide is withdrawn from the reaction equilibrium in the electrolyte fluid. Furthermore, magnesium is electrochemically neutral in its compounds, and also the precipitated hydroxide gel, which contains water, does not noticeably influence the ion migration in the electrolyte fluid.
According to the invention, it is possible to keep the pH of the electrolyte fluid constant, within a narrow range, even with an increasing formation of nitrogen. Since the hydrazoic acid formed from the azide at first is a weak and, at the same time, a highly volatile acid, the solution is adjusted to be weakly alkaline right from the start. The electrolyte fluid can have a pH between 8 and 10. Preferably, the pH is 8-9.5. While it is practical if the azide is formed from sodium azide, magnesium sulfate or magnesium perchlorate is preferably used as the magnesium salt. In order to guarantee a sufficient withdrawal, from the electrolyte fluid, of the hydroxide ions that are formed, the magnesium salt is added stoichiometrically or in excess, in proportion to the amount of azide.
The electrolyte fluid can have an anti-freeze agent added to it, which preferably is made up of ethylene glycol and/or dimethyl sulfoxide. In this way, proper operation of the gas cell is guaranteed even at low temperatures. To prevent a hydrogen over-voltage of the electrode forming the cathode, the electrolyte fluid can contain nickel sulfate as an additive. In accordance with the invention, the direct oxidation of azide is possible not only on electrodes made of precious metals, but also on electrodes made of steel, preferably chrome-nickel steel, or graphite. Alternatively, the electrodes can be made of plastic with embedded graphite powder.
Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention.
In the drawings:
2 NaN3+2 H2O→3N2+H2+2 NaOH
causes a clear reduction in the gas generation rate even in low concentrations. As a result, the effectiveness of the cell quickly drops with an increasing production of gas.
2 N3−→3 N2+2 e−,
while a corresponding reduction of hydrogen ions takes place at the cathode 1′:
2 H++2e−→H2
Since hydrogen ions are used up during the reaction, in accordance with the reaction equation that applies for cathode 1′, the concentration of the hydroxide ions clearly increases during the production of nitrogen. In order to avoid an accompanying increase of the pH in electrolyte fluid 4, a magnesium salt has been added to electrolyte fluid 4, for chemical binding of the hydroxide ions that are formed during the electrochemical reaction. Magnesium hydroxide has a very low solubility product. As a result, the magnesium hydroxide formed from the magnesium salt and the hydroxide ions is precipitated from electrolyte fluid 4 in accordance with the equation
Mg2++2 OH31→Mg(OH)2,
which is formed at cathode 1′. The electrolyte fluid according to the invention makes it possible to use conventional materials, such as steel, preferably chrome-nickel steel, or graphite for electrodes 1,1′. Alternatively, electrodes 1, 1′ can also be formed from plastic with embedded graphite powder.
The following electrolyte fluids were produced:
The magnesium perchlorate binds the soda lye that is formed during the reaction, by forming magnesium hydroxide that has low solubility. This magnesium hydroxide is precipitated as a precipitate and is thereby withdrawn from the reaction equilibrium.
The use of magnesium perchlorate has the advantage that the electrolyte fluid remains liquid to below −20° C. As a result, anti-freeze agents need not be added, and the electrolyte fluid can easily be absorbed in a sponge. In this way, a simple separation of gas and electrolyte fluid, independent of the position, is present in practical operation. The disposal of a cell that contains the electrolyte fluid (see
2 NaN3+Mg(ClO4)2+2H2O→3 N2+H2+Mg(OH)2+2NaClO4.
The solution is weakly alkaline, hygroscopic, odorless, not aggressive, and keeps without decomposing. 1 ml of this solution can yield 75 to 100 ml gas (N2 and H2), depending on the experimental conditions.
While a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 013593.2 | Mar 2004 | DE | national |
| 10 2004 032260.0 | Jul 2004 | DE | national |
