Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
  • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
  • G01N27/06—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a liquid
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/416—Systems
  • G01N27/42—Measuring deposition or liberation of materials from an electrolyte; Coulometry, i.e. measuring coulomb-equivalent of material in an electrolyte
  • G01N27/423—Coulometry

Definitions

• the invention relates to a method for determining the number of dissociable particles (ion pairs) in liquids.
• electrochemical methods for determining ions in liquids are known, which are all based on a conductivity measurement of the liquid.
• an electrical voltage is applied to a pair of electrodes located in the liquid to be examined and the electrical current which then arises is measured by means of a measuring device.
• Disassociable particles represent impurities in liquids and are generally in a dissociated and non-dissociated state.
• the methods mentioned based on a conductivity measurement are therefore not able to exactly determine the number of dissociable particles in liquids, since during such a measurement some of the particles are always in undissociated form and therefore cannot contribute to the conductivity.
• charge carriers are also continuously injected into the liquid, which also falsifies the result.
• the invention is therefore based on the object of specifying a method which enables a simple but very precise determination of the number of dissociable particles in a liquid.
• This object is achieved according to the invention by a method in which an electric field is applied to a pair of electrodes in the liquid which has a low injection capacity for charge carriers,
• the particles already dissociated at the start of the method contribute to the measurement result, but also, since integration takes place over a certain period of time, the particles which are dissociated only later under the influence of the electric field.
• the process is preferably carried out until the current flow practically no longer drops. Since generally certain residual flows always remain, it cannot be waited until the flow comes to a complete standstill. If such residual currents are present, their contribution to the current integral must of course be disregarded.
• passivated electrodes can be used.
• Electrodes are understood to be electrodes whose ability to inject electrodes has been greatly reduced by suitable pretreatment.
• the passivation can be achieved with commercially available brass electrodes, for example, in a very simplified manner as follows.
• the pair of electrodes to be passivated is placed in a cell with propylene carbonate (PC) and a field strength of, for example, 10 kV / c is applied to them. After a while, the electrodes are passivated. In the case of brass electrodes and PC, the passivation can be recognized by the brown discoloration of the electrode surfaces. The electrodes passivated in this way can then be used for the method according to the invention.
• PC propylene carbonate
• Another way of reducing the injectability of commercially available untreated (bare) electrodes is to cover them with ion-exchange membranes in the reverse direction.
• the membrane prevents the ion from escaping into the liquid volume.
• a disc is made up of ceramic, so that the fluid between the two plates is ⁇ and the electrodes of the plates can be fixed to the sides facing away from each of the liquid.
• the present method is preferably carried out by applying a field of a few kV / cm. As a result, the method can be carried out in a sufficiently short time and it can be assumed that all particles capable of dissociation are dissociated.
• the number of dissociable particles can be used to predict the cleaning time for the liquid.
• PC propylene carbonate
• Fig. 1 shows an apparatus for performing the method.
• 2 shows a suitable measuring cell for the method.
• 3 shows the course of the current which arises during the method.
• the measuring cell 1 shown in FIG. 1 serves to hold the propylene carbonate 3 to be examined.
• a pair of passivated electrodes 2 is connected to a voltage source 5.
• a current recording device 4 is connected between one of the electrodes and the voltage source.
• the recorder 6 of the current recording device prints out the temporal Stro veriauf. The start of the process is initiated by closing switch 7.
• the electrodes are at a distance of 0.5 cm from one another, for example.
• the applied voltage is between 100 and 1000 volts.
• the resulting field has a strength of 200 to 2000 volts / cm.
• Fig. 2 shows a specific embodiment for a measuring cell. It can be seen that it is a closed measuring cell 2.
• the electrodes 1 contained therein are covered with ion exchange membranes 3. Alternatively, the passivated electrodes indicated in FIG. 1 could of course be used.
• the current curve in FIG. 3 has a kink in the front area. This is a result of two overlapping processes. Initially, the particles that are already in dissociated form mainly contribute to the current flow. At the beginning, this leads to a high current flow I Q , which drops very quickly with a time constant T->. The current flow is thus brought about by the constantly newly disassociated particles. The decrease in this dominant stream proportion occurs
• the course of the current can easily be determined by leveling out the area enclosed by it.
• the present method has proven to be extremely advantageous when working in connection with the cleaning of propylene carbonate while simultaneously producing passivated electrodes.

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• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Health & Medical Sciences (AREA)
• Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Molecular Biology (AREA)
• Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
• Electrostatic Separation (AREA)

Applications Claiming Priority (2)

Publications (1)

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ID=6413977

Family Applications (1)

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• 1990
  • 1990-09-10 DE DE4028716A patent/DE4028716A1/de not_active Withdrawn
• 1991
  • 1991-09-05 KR KR1019930700731A patent/KR930702671A/ko not_active Application Discontinuation
  • 1991-09-05 WO PCT/DE1991/000717 patent/WO1992004624A1/de not_active Application Discontinuation
  • 1991-09-05 JP JP3514573A patent/JPH06501097A/ja active Pending
  • 1991-09-05 CA CA002091347A patent/CA2091347A1/en not_active Abandoned
  • 1991-09-05 EP EP91915871A patent/EP0548133A1/de not_active Ceased
  • 1991-09-09 CN CN91108794A patent/CN1059966A/zh active Pending
  • 1991-09-25 TW TW080107544A patent/TW240293B/zh active
• 1993
  • 1993-03-09 FI FI931035A patent/FI931035A/fi not_active Application Discontinuation

Non-Patent Citations (1)

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