Chemistry: electrical and wave energy – Processes and products
Patent
1983-06-13
1984-10-02
Andrews, R. L.
Chemistry: electrical and wave energy
Processes and products
204420, 204433, 204 141, C25B 100
Patent
active
044746539
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND ART
Methods of electrolytically co-precipitating mixed metal oxides are known from Canadian Patent No. 593,187 and UK Patent No. 864.249. Another method of precipitating or co-precipitating metal compounds, more particularly oxides and hydroxides, in an electrolysis cell is described in Canadian Patent No. 623.339.
It was recognized in the latter patent that the process should be carried out at a specific and as constant as possible pH, and this was achieved by carrying out a preliminary electrolysis to obtain suitable starting conditions and setting the electrolysis currennt at a value corresponding to the rate of supply of a solution of the salts from which the compounds are precipitated. In carrying out these known processes, it has been observed that the particle size and density do not remain constant and this reduces the usefulness of the product. The invention is based on the observation that the uneven particle size and variable density obtained with the known processes are due to variations in the solution pH which occur when following the prior teachings and because of the inherent difficulties in measuring and controlling the pH in an electrolysis cell particularly when gas is bubbled in or is electrochemically generated.
Similar considerations apply to the control of the particle size and density of electrodeposited coatings and to the control of electrophoretic deposition.
DISCLOSURE OF THE INVENTION
According to the invention, the precipitation or the depositing of the particles is controlled by measuring the pH of the solution in the cell using a probe shielded from migrating electric current and adjusting the pH of the solution to a selected value as a function of the measured pH.
Preferably, this is achieved by supplying a first electrical signal representative of the measured pH, comparing the first electrical signal with a reference electrical signal corresponding to the selected pH, and adjusting the pH of the solution as a function of the difference of the first signal and the reference signal to maintain it close to the selected pH.
The pH may be adjusted by acting on any pH-determining parameter such as by bubbling acid vapour or base vapour into the solution or by adjusting the supply of air, in the case where air is supplied as an oxidant. This method of bubbling in a vapour or air is particularly appropriate when a solution of metal salt(s) to be precipitated is obtained by dissolving at least one metal anode.
In another arrangement, the pH is adjusted by varying the electrolysis current. For example a preprepared solution of metal salt(s) is introduced into a compartment of the electrolysis cell in which the particles are precipitated, and the ions liberated by the salt(s) are passed through a separator into another compartment of the cell by passing an electrolysis current at a raate controlled as a function of the measured pH to keep the pH of the solution at the selected value. This arrangement is recommended when it is desired to incorporate a metal such as barium which does not dissolve anodically or manganese which is soluble without the passage of current so that, when connected as an anode, it does not dissolve in proportion to the current passed. However, the arrangement can of course also be used to supply the salts of other metals.
The solution of salts can be introduced into the cell compartment by dripping it in uniformly or by blowing in a fine dispersion of the solution for example with an oxidizing gas, or in any other suitable manner.
It is possible to combine this arrangement with the previous one by providing ions of at least one further metal to be precipitated by dissolving at least one metal anode, and adjusting the pH of the solution by bubbling acid vapour, base vapour or by adjusting the supply of air into the solution when said controlled electrolysis current reaches a threshold value.
It is equally possible, when a preprepared solution of the metal salt(s) is supplied to the electrolysis cell, and whether or not this is combined with diss
REFERENCES:
patent: 2563062 (1951-08-01), Perley
patent: 2607718 (1952-08-01), Suthard
patent: 3214301 (1965-10-01), Pocock et al.
patent: 3869359 (1975-03-01), Beer
European Patent Application 0,026,591, published Apr. 8, 1981.
Beer Henri
Suyberbuyk Ludovicus F. M.
Van Den Keybus Franz A. M.
Andrews R. L.
Skord Jennifer L.
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