ELECTRODE FOR REALIZING CONTACT WITH A LIQUID, SUCH AS A REDOX ELECTRODE AND REDOX MEASURING APPARATUS PROVIDED WITH A SUCHLIKE ELECTRODE

Abstract: Electrode for contacting a liquid for instance for measur­ ing a redox potential having an insulating support (1,9), a conductor (3,8) passed through a passage (2,11) in said support and a liquid tight conducting layer (4,12) covering the passage and part of the support, said layer contacting said conductor and being liquid tight adhered to said support.

Description: electrode for realizing contact with a liquid, suc as a redox electrode and redox measuring apparatus Provided with a suchlike electrode. The invention relates to an electrode for realizing contact with a liquid, provided with a support of insulating material and a conductor passed through a passage in said suppprt and to a redox measuring apparatus in which such an electrode is used. Known electrodes, specially those for measuring redox potentials have a number of disadvantages. Namely it has appeared that it is difficult to manufacture such an electrode with sufficient resistance to high tenperatures and/or pressures, whereas further such a smooth cleanable shape that a high degree of sterility can be guaranteed in many cases, for instance in the fermentation industry may be a problem. With known electrodes a wire, for instance of platinum is passed directly through a glass of suitable expansion coefficient, for instance a silicate,lead glass. Such a glass has, however, a relatively low transformation temperature, so that its resistance to high temperatures is very limited. When using other metals, such as gold or silver with redox measurements, it is impossible to mount a wire of these metals directly in the glass such that a good seal is obtained. In these instances one uses a silicon rubber or an epoxy-resin to lute'the wire in the support. Leakage along the passage of the wire may lead to faulty measurements, when the wire at the other side is formed by a conductor of another metal, wherewith the final measurement gives a redox potential which is composed from that one that fits with the metal of the passage wire and that one that fits with the metal to which this wire is connected. This is also the reason why for redox electrodes a normal electro plating of a metal support is not allowed, because sucks a cover in many instances is unsufficiently liquid tight. The invention; aims to eliminate these difficulties. Accordingly it is according to the invention provided, that a liquid tight layer is applied to that side of the support that is intended to contact the liquid, which layer is of a conducting material, covers the passage and at its side away from the liouid engages the conductor passed through the support. Because wit the invention the layer is liquid tight and this layer is applied at the outer side of the electrode as well leakage problems as problems which arise because the liquid contacts the conductor when the latter is of a material differing from that of the layer, are avoided. moreover the outer side of the electrode is completely smooth and it has no corners in which material may stick, se as occur when z wire is lead out of a plane, which simplifies in a high h degree to make or keep the electrode sterile. In this connection is pointed to the fact that sterile electrodes for resox measuremerlts are of great importance in the fermentation industry, in which great damage may arise b insufficiently sterile conditions. according to a further elaboration of the invention it is provided that the end of the conductor is flush with the surface of the support. It has appeared that in this way a sufficient electrical connection between the conductor and the layer can be realized and that the layer at the location of the conductor is undisturbed and remains sufficiently liquid tight. Consequently the conductor itself never contacts the liquid. Of course an additional safety is obtained that the measurement is not wrongly influenced because the conductor contacts the liquid by providing when the conductor and the layer are of the same material. An important advantage of the invention is, that the requirements to be met by the passaJe of the conductor through the support can be considerably lower. This means that use can be made of a glass sort having a high transformation temperature and/or a high chemical rCsistarce, such as for instance boro-silicate glass, so-called pyrex flask of Corning or Duram 50 of Schott. moreover manufacturing is relatively simple, because no passage problems arise and no special lute: : such as an epoxy resin or a silicon rubber are necessary, so that the electrode according the invention not only with respect to thermal and chemical resistance, but also with respect to pressure resistance may include an important improvement with respect to the known art. A further possibi- lity that is obtained with the invention is to make the support of ceramic material. As already mentioned with the known art a platinum wire is directly melted in special glass when manufacturiAg a reàoz electrode, but other metals usable for redox measurements, such as gold or silver were gassed through by means of a lute. By applying the invention this is not necessary any more and a direct passing through of all these metals is possible, also through an insulating material which is not matched to it with respect to the expansion coefficient. A preferred embodiment of the invention provides, that the support has the shape of a cylinder with at its end a partial sphere, the layer covering the partial sphere and the adjoining part of the cylinder, the passage being located in the partial sphere. Another embodiment of the invention provides that the support is a hollow cylinder and that the passage passes through the cylinder wall, the layer covering a preferably ring shaped part of the cylinder wall. In this connection is pointed to it, that the electrode according the invention is not only suitable for redox measurements, but also for for instance conductivity measurements. In this case one can vuit. the electrode indicated above apply a number of spaced apart rings. Therewith it is of course possible to apply the ring shaped layers as ell at the inner side of a cylindrical support, when the liquid is located within the suppoet,as at the outside when the electrode is immersed in the liquid. It has appeared tt L a good method for manufactur1g the invention consists in that the layer a is made by fritting a paste of a rolled mixture of metal, fine glass particles and a binding agent on the support. Such pastes are commercially available and the binding agent normally is a substance which evaporates at the frittin temperature, so that a mixture of glass particles and metal particles remains, which, as experience has shown, forms a homogeneous liquid tight conducting layer. The invention also encompasses a redox measuring apparatus for determining redox potentials at higher temperatures and pressures anor sterile conditions, provided with an electrode as described above. The invention in the following is elucidated on hand of the drawing, in which: Figure 1 schematical rt shows a cross-section through a first embodiment of te invention; and Figure 2 shows 2 schematical cross-section through a second embodiment of the invention. In fig. 1 reference 1 indicates a cylindrical insulating support member ending in a partial sphere. In the centre of the partial spherical portion an opening 2 has been applied through which a conductor 3 passes. This conductor is fixedly connected to a liquid-tight layer 4 which is adhered to the support 1 and provides an absolute liquid seal between the inside of support 1 and the liquid located outside it. In fig. 2 an embodiment has been shown of a redox electrode, with which the redox potential is not measured with respect to a reference electrode but with respect to a pH-electrode. The hollow glass sphere 5 shown at the lower side contains a liquid 6 vit) a pH-value of for instance 7, in which a connecting member protr-udeF which is connect > to a conductor 8. The wall 9 of the cylindrical portion above the pH-electrode part has a hole 11 through which a conductor 10 passes, which ends in a liquid tight layer 12, which has been applied according the invention. With this electrode it is possible to measure the redox potential of the metal of the layer 12 with respect to the pH-potential. The latter is measured via the glass wall 5 which can be considered to be a diaphragma, as is known per se. It will be clear that an electrode as depicted above'may contain a number of rings located above each other, by reason of which the possibility exists to measure potentials in different points of the liquid, for instance for carrying out conductivity measurements or suchlike. The references indicated in the appending claims only serve the purpose of elucidation. In no way they are intended or can be interpreted as a limitation o; the said claims.

Claims: Claims: 1. Electrode for realizing contact with a liquid, provided with a support (1,9) of insulating material and a conductor (3,10) passed through a passage (2,11) in this support, characterized in that a liquid tight layer (4,12) is applied to said support at the side thereof that is intended to engage the liquid, which layer (4,12) is of a conducting material, covers the passage and at its side away from the liquid engages the conductor passed through the support. 2. Electrode according to claim 1, characterized in that the end of the conductor is flush with the surface of the support. 3. Electrode according to claim 1 or 2, characterized in that the conductor and the layer are of the same material. 4. Electrode according to claim 1, 2, or 3, characterized in that the support is of glass sort with a high trans for mation temperature and/or a great chemical resistance such as boro-silicate glass, for instance Pyrex glass of Corning or Duram 50 of Schott. 5. Electrode according to claim 1, 2 or 3, characterized in that the support is of ceramic material. 6. Electrode according to one or more of the preceding claims 1-3, in which the wire is of a material other than platinum or according to claim 4 or 5 characterized in that the wire is attached in the passage without lute means. 7. Electrode according to one or more of the preceding claims, characterized in that the support (1)- has the shape cf a cylinder with at its end a partial sphere, wherewith the layer (4) covers the partial sphere and part of the cylinder adjoining it, the passage (2) being located in the partial sphere. 8. Electrode according to one or more of the claims 1-6, characterized in that the support (9j is a hollow cylinder and in that the passage passes through the cylinder wall, wherewith the layer (12) covers a preferably ring shaped part of the cylinder wall. 9. electrode according to claim 8, characterized in that the layer is located at the outer side of the cylindrical support and the conductor at the inner side thereof. 10. electrode according to claim 8, characterized in that the layer is located at the inner side and the conductor at the outer side of the support. 11. Electrode according to one or more of the preceding claims, characterized in that the layer has been manufactured by fritting a paste of a rolled mixture of metal particles and fine glass particles and a binding agent on the support. 12. electrode according to one or more of the preceding claims, characterized in that the layer is of platinum, gold or silver. 13. Redox measuring apparatus for determining redox potentials at higher temperatures or pressures and/or sterile conditions provided with an electrode according to one or more of the preceding claims.

Inventors: DE JONG, HENDRIK
Applicants: YOKOGAWA ELECTROFACT B.V.
Application year: 1982
Main classification: G01N27
IPC codes: G01N27