GB2235699A - Detecting wear of electrodes for electrolysis - Google Patents

Abstract

In electrolysis apparatus e.g. for electrolysis of chlorine from sea-water, wherein electrodes are at least partially submerged in an electrolyte, wherein each electrode has a substantially solid body with a base surface connected to a support means and an exposed surface arranged to be at least partially in contact with the electrolyte, at least one cavity 23 extends from the base surface 16 into the body of the electrode 15 and each cavity contains a conducting wire separated from the wall of the electrode by an absorbent wick. The cavities are positioned such that, when exposed to the electrolyte, the electrode is at its optimum time for replacement. The sensitivity of the detector is improved by the provision of the wick, which absorbs electrolyte to provide a large conducting surface within the cavities. In order to detect asymmetrical wear, a plurality of cavities are provided, each connected to a control system by means of a common circuit board. <IMAGE>

Description

ELECTRODE FOR ELECTROLYSIS AND AN ELECI:ROLYSIS METHOD BACKGROUND OF THE INVENTION The present invention relates to electrodes for use in electrolysis, in which the electrode is at least partially submerged in an electrolyte. The invention also relates to an electrolysis method.

Electrolysis forms the basis of many separation, purification and plating processes, for example, the elements of hydrogen, oxygen, aluminium, copper, gold, iron and zinc are formed be electrolysis along with compounds such as phosphoric acid, potassium hydroxide and sodium chlorinate.

Electrolysis is also used for generating ions, an example being the production of copper ions to reduce biological fowling of marine equipment.

During electrolysis, electrodes are eroded and contamination or damage may occur if eroded electrodes are not replaced. However, electrodes are often fabricated from expensive materials, such as platinum, therefore, it is desirable to identify the optimum time to replace them, thereby avoiding unnecessary wastage.

A problem with identifying the optimum time to replace an electrode, is that wear is often asymmetrical, therefore, is often difficult to optimise the positioning of means for detecting wear.

It is a object of the present invention to provide an electrode with improved means for optimising the detection of wear.

It is a further object of the present invention to provide an electrode having means for detecting wear with improved sensitivity.

SUMMARY OF THE INVENTION According to the present invention, there is provided an electrode for use in electrolysis apparatus, wherein said electrode is at least partially submerged in an electrolyte, comprising a substantially solid electrode body having: a base surface for connection to a support means; an exposed surface, arranged to be at least partially in contact with said electrolyte; a plurality of cavities extending from said base surface into the body of said electrode; and detection means for detecting the presence of electrolyte in any one of said cavities due to wear of the electrode caused by electrolysis, wherein said cavities are placed at a plurality of positions in said electrode body, allowing wear occuring at substantially any portion of the electrode body to be detected.

An advantage of the present invention is that it allows all types of wear to be detected, thereby indicating the optimum time for replacing the electrode.

According to a second aspect of the invention, there is provided an electrode for use in electrolysis apparatus, wherein said electrode, having a substantially solid body, is arranged to be at least partially submerged in an electrolyte, said electrode comprising: a base surface for connection to a support means; an exposed surface arranged to be at least partially in contact with said electrolyte; a cavity extending from said base surface into the body of said electrode; and a conducting wire placed in said cavity and separated from said electrode by a wick material, in which said wick insulates said wire from said electrode when dry but absorbs electrolyte to provide a large conducting surface when said electrolyte is introduced into the cavity due to wear of the electrode.

An advantage of the second aspect of the invention is that it is very sensitive to detecting the critical threshold of wear.

Preferably, the conducting wire is supported within said cavity by a circuit board fabricated from a laminated material, including a conducting path for providing a signal to an electrolysis control system.

According to a third aspect of the invention, there is provided an electrolysis method, in which current is passed through an electrolyte by means of an electrical potential placed across electrodes of opposing polarity, comprising the steps of, placing conducting wires into a plurality of mutually off-set cavities formed in at least one of said electrodes, wherein each wire is surrounded by a wick material providing a large conducting path between said wire and said electrode when electrolyte enters a cavity, and, on detecting electrolyte in a cavity, disconnecting the electrical potential applied to said electrodes.

The invention will now be described by way of example only with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows an electrode assembly including means for detecting electrode wear; Figure 2 shows examples of wear; in which figure 2A shows idealised symmetrical wear and figure 2B shows more typical asymmetrical wear, Figure 3 details the means for detecting wear shown in Figure 1, including a circuit board for connecting wear detectors; and, Figure 4 shows a top view of the circuit board shown in Figure 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT An electrode assembly is shown in Figure 1, in which an electrode 15 is fabricated from a solid piece of conducting material, such as aluminium, copper or mild steel coated with platinum. A base surface 16 of the electrode 15 is connected to an insulating support means 17 and is secured by a threaded bolt 18, which also provides an electrical contact to the electrode.

The electrode is supported over a container of electrolyte by means of a support flange 19, which may support a plurality of electrodes of the type shown in Figure 1. Bolt 18 is secured to the flange by a nut 20 which is surrounded by a sealed capping means 21. Within the space 22 defined by said capping means, a suitable dessicant is provided, such as a Cortec 101 VCI device, to prevent the build-up of moisture. Moisture occasionally enters this space when the top is open, or when it leaks through the electrical or mechanical seals, and it is important that this moisture is removed to prevent short circuiting and corrosion inside the electrode assembly.

In the example shown, the assembly is for an anode arranged to attract chlorine ions from sea water and has a diameter of eight inches. During electrolysis, platinum is lost and, after an appropriate interval, the anode must be removed before the platinum coating is penetrated and the underline base metal is consumed. Two types of electrode wear are shown in figure 2, in which Figure 2A show the ideal type of wear, which is symmetrical, and Figure 2B shows the more typical type of wear which is asymmetrical. The problem with asymmetrical wear is that electrode replacement optimisation is made much more difficult.

To provide a means for detecting critical wear to the anode of Figure 1, the anode includes four elongated cavities 23, each of which extends from the base surface 16 into the body of the electrode 15. The electrode 15 is of circular cross section and each cavity is positioned around a circle, off-set by ninety degrees from its neighbours. The cavities 23 are placed at positions such that the electrode is ready for replacement when they become slightly exposed, allowing electrolyte to enter therein A cavity is shown in greater detail in Figure 3 and includes means for detecting the presence of electrolyte in the form of a conducting wire 23 separated from the wall of the cavity by a wick 32 of cotton or of similar material.When dry, the wick provides a insolator between the wire and the electrode but, once a small hole is created in the cavity, the wick absorbs electrolyte by capillary action until it becomes completely wet. However, before reaching its saturated condition, the electrical path provided between the electrode wall and the conducting wire 31 is detected, resulting in an alarm been raised or the potential applied to the electrode been cut-off.

The upper end 33 of each wear detector wire 31 enters a hole 34 formed in a circuit board 35 fabricated from laminated thermo setting plastic with a glass cloth base. A top view of such a circuit board is shown in Figure 4 and includes a strong conducting material 41 which, in addition to providing an electrical contact between a detector wire 31 and the board 35 also provides a mechanical washer 42 capable of withstanding compressive force.

In operation, current is passed through an electrolyte of, in this example, sea water from (in accordance with the conventional analysis) the anode to the cathode. At the platinum anode, chlorine ions are stripped of their excess electron and combined to form molecules of chlorine gas. During this process, platinum is slowly lost from the anode, therefore, conducting wires are introduced into mutually off-set cavities formed in the body of the electrodes. The wires are separated from the body of the electrode by an insulating wick, however, when sufficient wear has accured to allow electrolyte into the cavity, the wick absorbs the electrolyte allowing a current to pass through to the detecting wire.

Electrodes embodying the present invention may be used in many applications, in addition to the application detailed above. For example, in a Down's sodium cell, a single graphite anode is provided in combination with a iron cathode, Carbon anodes are also provided in cells for the electrolysis of aluminium, each typically having three anodes. In the mass production of aluminium, a large battery of cells may be provided, each having, typically, twenty-four anodes each.

Claims (10)

1. An electrode, for use in electrolysis apparatus, wherein said electrode is at least partially submerged in an electrolyte, comprising a substantially solid electrode body having: (a) a base surface for connection to a support means, (b) an exposed surface, arranged to be at least partially in contact with said electrolyte, (c) a plurality of cavities extending from said base surface into the body of said electrode, and (d) detection means for detecting the presence of electrolyte in any one of said cavities due to wear of the electrode caused by electrolyses, wherein said cavities are placed at a plurality of positions in said electrode body, allowing wear occurring at substantially any portion of the electrode body to be detected.

2. Apparatus according to claim 1, wherein said detection means includes conducting wires each running the length of its respective cavity, wherein an electrical connection is provided between one of said wires and the body of said electrode when electrolyte enters its respective cavity.

3. Apparatus according to claim 2, in which, in each of said cavities, said wire is separated from said electrode by a wick which is insulating when dry but absorbs electrolyte to provide a large conducting path when electrolyte enters its respective cavity.

4. Apparatus according to claim 1, wherein each detection means is connected to a common circuit board, wherein said board also provides the function of a washer between said detection means and a securing means.

5. An electrode, for use in electrolyses apparatus, wherein said electrode, having a substantially solid body, is arranged to be at least partially submerged in an electrolyte,said electrode comprising: (a) a base surface for connection to a support means, (b) an exposed surface arranged to be at least partially in contact with said electrolyte, (c) a cavity extending from said base surface into the body of said electrode, and (d) a conducting wire placed in said cavity and separated from said electrode by a wick material, in which said wick insulates said wire from said electrode when dry but absorbs electrolyte to provide a large conducting surface when electrolyte is introduced into the cavity due to wear of the electrode.

6. Apparatus according to claim 5, wherein said wick absorbs electrolyte by capillary action and is composed of cotton cord or similar material.

7. Apparatus according to claim 5, wherein said conducting wire is supported within said cavity by a circuit board fabricated from a laminated material, including a conducting path for providing a signal to an electrolysis control system

8. An electrolysis method in which current is passed through an electrolyte by means of an electrical potential placed across electrodes of opposing polarity, comprising the steps of, placing conducting wires into a plurality of mutually off-set cavities formed in at least one of said electrodes, wherein each wire is surrounded by a wick material providing a large conducting path between said wire and said electrode when electrolyte enters a cavity, and, on detecting electrolyte in a cavity, disconnecting the electrical potential applied to said electrodes.

9. An electrode substantially as herein described with reference to Figures 1,3 and 4.

10. An electrolysis method substantially as herein described with reference to Figures 1,3 and 4.