Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2001-09-10
2002-12-03
Tung, T. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C205S775000, C200S190000, C200S193000, C200S194000, C116S109000, C116S227000, C324S439000, C340S620000, C422S082020
Reexamination Certificate
active
06488826
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to new fluid electrode system and in particular a fluid electrode system for use in resistive slope sensors. This fluid electrode system consists of a mixture of an electrolyte and a solvent, and due to its favorable properties, permits a wide variety of technical applications.
DESCRIPTION OF THE PRIOR ART
A resistive slope sensor, in particular one for the automotive area, is described in DE 19512374 as having a housing which is partially filled with an electrically conducting fluid. The housing contains electrodes for recording measuring signals which are conducted through the housing wall to the outside, where the measuring signals are fed to a plotting unit. That invention proposes that polyether be used as a fluid to serve the function of a sensor. However, because of the toxicity of the proposed materials, their mass application may be fraught with problems.
FR-A2668824 describes fluid-filled sensors, containing as sensor fluid, mixtures based on ethylene glycol and water in equal parts. As the lower working limit for these sensors, the temperature is given as −31° C., thus, also ruling out these sensors as a possible solution, since the automotive area requires a working temperature range of <−40 to 120° C., as well as a flash point >100° C.
Furthermore, WO 96/27892 and DE 19507610 describe fluids which contain as a main component, at least triethyleneglycodimethylether, a compound having mono- or multi OH-functional groups, and a salt which is dissociated within the mixture. Further mixtures that are suitable as electrolytes are described in U.S. Pat. No. 2,852,646, U.S. Pat. No. 2,387,313 and in U.S. Pat. No. 2,927,987.
The sensor fluid described in DE 19597610 represents the best solution to the problem as stated for that sensor and is based on the marginal conditions for its application described in DE 19512374.
However, the disadvantages of that particular sensor fluid are, possible health hazards effected through triethyleneglycodimethylether (see in connection therewith: RTCS No.: XF0665000 2,5,8,1,1-tetraoxadodecane); a likely formation of peroxide when coming in contact with oxygen, and the difficulty of handling the fluids based on the strongly hygroscopic behavior they exhibit, in conjunction with undesirable changes of the electrical properties that occur with the uptake of water, which makes use of these sensors undesirable.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide an improved sensor fluid-electrode system, obviating the afore-stated drawbacks. In particular, it is the object of the present invention to provide an improved sensor fluid-electrode system for use as a slope sensor which fulfills the marginal conditions as described above and which, at the same time, lacks the problems such as, toxicity, incompatibility with water and formation of peroxide.
Furthermore, the electrode-fluid-system must be able to solve the following technical marginal conditions:
working temperature range −40 to +85° C.
ratio of conducting capacity at the working temperature end points “Factor F”
max. 22; computation: (conducting capacity +85° C./conducting capacity −40° C.)
lowest possible changes in viscosity and level of conductivity though thermal
alteration
no discharge at the electrodes.
In a fundamental solution to the object of the present invention namely, to provide the type of fluid component without the above described disadvantages it has been found that mixing an electrolyte with a solvent provides such an improved fluid-electrode system. Additional components, such as solvent facilitators, stabilizers etc. may also be introduced into the system. Furthermore, the sensor fluid can be made compatible with a particular electrode system of choice.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention as further described.
DESCRIPTION OF THE INVENTION
At the outset, the selection of propylene carbonate as a solvent for a fluid component, as described in WO 96127892, is not considered a solution to the object of the invention, since propylene-based electrolytes do exhibit a comparatively large changes in conductivity relative to temperature (compare Example 1). Other fluid components listed there, are conditioned to a lesser degree on the conductivity changes relative to the temperature.
However, the addition of water to the sensor fluids, in particular, the triethyleneglycol dimethylether-based sensor fluids, causes a dramatic decrease in the conductivity condition, thus requiring water-free conditions for the production of the slope sensor, its application, and throughout the life of the slope sensor. Water free conditions poses high demands on the production effort of the slope senor, and in particular also on sealing of the housing, as described in DE-195 12374, since electrodes must be conducted through the housing and the conduits must be sealed. These adverse properties of the fluid systems are amplified further by the hygroscopic characteristics of the triethyleneglycol dimethylether.
It has surprisingly been found, that when propylene carbonate is used as a sensor fluid base, the addition of water causes only small changes in the conductivity condition between the outer limits of the temperature range as is shown in Example 1. This is surprising, since addition of water to various other organic solvents always leads to considerable changes of this condition. Propylene carbonate thus appears to mask available charge carriers (ions) at high temperatures for water.
Advantageously, it follows, that by using propylene carbonate as a solvent base of the fluid component according to the invention, the electrochemical properties, particularly the conductivity-temperature range condition, are very insensitive to contamination by water.
It appears, that a mixture of tetra-alkylammonium halogenides and propylene carbonate solves this object of the invention. These compounds are soluble within the temperature range from −45 to >+100° C. in propylene carbonate. These solutions exhibit electrical conductivity. For example, a 0.055% solution exhibits at −40° C., a conductivity of 12.5 &mgr;S cm
−1
, at 85° C., a conductivity of 260 &mgr;S cm
−1
. By varying the amount of tetraethylammonium halogenides to be used, conductivity may be adjusted within a wide range of requirements without extensive change of factor F.
To provide a complete solution to the object of the invention, a sensor fluid had to be found which, among others, behaves indifferent to thermal load. As Example 5 illustrates, this is not the case when tetra-alkylammonium halogenides are used as electrolyte.
It has surprisingly been found that the use of sodium iodide as electrolyte solves the above-stated object of the invention. This electrolyte is not taken into consideration at the outset, since electrolytes with metal cations possess the adverse property of reacting with possible disintegration products of the solvent (carbon dioxide) and thereby forming precipitations. However, these disadvantages are alleviated through limiting other conditions during use, and if necessary, by the addition of stabilizers. The examples below illustrate these relations. For example, precipitations occur, at a thermal load above 90° C. over a longer period of time when more than 1.5% water is added to the mixture (compare Example 4). Thus, when dibenzo-18-crown-6 (Cas is added, a precipitation of sodium carbonate can be avoided.
One of the decisive criteria for the technical application of the electrolytes described here, the is the long term stability of the electrolyte. Only slight changes in its properties are permissible to occur during transport, storage, production and application of the electrolyte.
In accordance with the invention, no change occurs in a mixture of propylene carbonate and sodium iodide, unless there are outside influences relative to conductivity, factor F, viscosity, bo
Altmeier Patrick
Konrad Andreas
Day Ursula B.
Feiereisen Henry M.
Tung T.
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