Postby dognose » Thu Feb 12, 2015 2:31 pm
PREVENTING THE OXYDATION OF, AND COLOURING METALS.–MESSRS. ELKINGTON AND BARRATT's PROCESSES
In our 811th number we published a full account of the processes of M. Sorel, for the coating of iron and other metals, with zinc, to prevent their oxydation. We now lay before our readers descriptions of some further processes for the same purpose, and for giving iron and steel a brass colour, invented and patented by Messrs. Elkington and Barratt, of Birmingham, which, although they have not been found so effectually to answer the desired purpose, are nevertheless very ingenious, and worthy of the attention of those interested in the matter We may observe, however, that M. Fontainemoreau, in his patent, claims the application of amalgams of zinc, as also alloys of zinc with lead, tin, or bismuth; how far the peculiar processes of Messrs. Elkington and Barratt will enable them to uphold their patent, we will not take upon ourselves to say.
Messrs. Elkington and Barratt's invention consists of certain modes of coating metals with zinc, and zinc and mercury; and a mode of colouring iron and steel.
In order to coat copper and brass with zinc, there are mixed in an earthen vessel seven parts of muriatic acid, (specific gravity about 116.) and one hundred parts of water, both by weight and to these are added four parts of zinc, in the state of powder, or pieces. These articles are allowed to remain twenty-four hours, or until the acid and zinc cease to act upon each other, and the solution thus obtained is poured into a convenient vessel for boiling it, adding a quantity of zinc in powder, or in thin pieces. While boiling, the articles to be acted upon are immersed therein, bringing them in contact with the metallic zinc; and they will speedily become coated therewith. They are then removed, and washed with;, water and dried. In using this solution of zinc, if the articles are of iron or steel, they are previously coated with copper; and this is effected as follows: The articles are first cleansed, or pickled in dilute sulphuric acid, composed of one part concentrated acid to sixteen parts of water; and having prepared a solution of sulphate of copper, commonly called blue vitriol, the iron is immersed therein while cold, for few seconds, and speedily removed and washed. This is repeated one, two, or three times, or until it is found that the iron is perfectly coated; care must be taken not to allow it to remain too long in the solution of copper, or the copper precipitated on the surfaces becomes loose. If a strong coating of zinc be required, the processes of coppering and zincing are repeated, and it has also been found, that if the articles, when of copper, or if of iron, after they have been coppered, are introduced into a dilute solution of nitrate of mercury, and then again boiled in the solution of zinc, that the same object is obtained. The nitrate, or any other convenient solution of copper, may be substituted for the sulphate.
Another process is as follows: Take dilute muriatic acid in about the proportion of one part acid, (the specific gravity 116,) and thirty parts of water, into this introduce a quantity of zinc, in powder or in small pieces. The articles of iron are then to be placed in the acid, and kept in contact with the zinc during the process, which will require from two to five minutes, or until they are evidently coated with zinc; then remove, wash and dry them, as before.
Various metals, as iron, steel, copper, brass, &c., may be coated with the amalgam of zinc, and although this may be effected by using the two metals in almost any proportions, it has been found that six or seven parts of zinc, with one part of mercury, will answer best; these are amalgamated by heat, or by agitating the two metals in contact with dilute muriatic, or other convenient acid; the zinc being previously granulated, or reduced to small pieces. To this amalgamated zinc, when effected by heat, add dilute acid, as before, and then introduce the articles, which may require to be kept occasionally stirred. Instead of using the muriatic acid.some salts are employed, as the muriate, or sulphate of ammoniac, in the proportion of one of salt to thirty ounces of water, or thereabout ; and other acids than the muriatic may be employed, as ascetic sulphuric &c., and which require no other directions than to employ them of about the same strength as directed for the muriatic acid. It is preferable to employ these solutions in a hot or boiling state, as the effect is thereby obtained in a shorter period; but the processes where the free acid is used, may be successfully performed in a cold state, the acid and water to be added occasionally, as the solution becomes reduced in strength or quantity, by the boiling or action upon the metals to be coated.
An amalgam of zinc may be employed in a melted state for some articles, in which case, and particularly if they are of iron, they require to be well pickled or cleaned and also to be immersed in a solution of muriate of ammonia, to induce the perfect adhesion of the amalgam, which amalgam may be varied in almost any proportion of the two metals, but the proportions now given are considered best.
The oxides of the metals may also be used in the same manner, instead of the metals, or in conjunction with them; as, for example, a solution of zinc may be made with the oxide of that metal, instead of using the metal itself, and so also with the oxides of mercury. Messrs. Elkington and Barratt's processes may be applied in connection with the means patented by Messrs. Craufurd and Fontainemoreau, and detailed by us last week.
The process for colouring metals is as follows:–To colour iron and steel to imitate brass; first wet the iron or steel by means of a solution of copper as already described, and having afterwards boiled it in the saturated solution of zinc, having excess of zinc therein, until perfectly covered, remove it and dry it in saw dust and then submit it to heat in a closed oven until the required colour is obtained, and which is easily observed by looking occasionally at the articles during the process. They are afterwards to be pickled in a dilute acid and washed and dried.
A process called "Similoring," from the words "simile l'or," has been before practised for colouring copper and brass, and which consists in obtaining on the surface a thin coating of zinc, and submitting the articles so prepared to the action of heat till a colour approaching to that of gold is obtained. The object of the present invention, so far as it relates to coating copper and brass, is to obtain a good and sufficient coating of zinc on the surfaces, in order to prevent or retard oxidation. The use of heat is omitted, which would be prejudicial to the coating of zinc.
Source: The Mechanics' Magazine - 9th March 1839
Trev.