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ENTERTAINING EXPERIENCES AT HOME
Electrotype. Chemical experiments
Entertaining experiences at home / Chemistry experiments for children A very common electrochemical process is electroplating, i.e., the deposition of a thick, massive layer of metal on the surface of an object whose shape they want to reproduce, copy. Electroplating is used in cases where a metal part has a very complex shape and is difficult or impossible to manufacture using conventional methods (casting or machining). This is how sculptures are sometimes reproduced according to models (Apollo's chariot on the pediment of the Bolshoi Theater is made by galvanoplastics); metal molds are also encoded from the standard recording, in which gramophone records are pressed, exactly reproducing the finest relief of the grooves. If you do not have a solution for copper plating, then cook it again. Take a piece of wax or paraffin and smooth its surface very carefully so that it is as flat as possible. On this smooth area, scratch the inscription, drawing or pattern. We advise you to write your initials - then you will get a monogram. It is most convenient to write with a needle, but please do not leave too deep scratches. Apply electrically conductive powder to the patterned surface with a soft brush. You can, for example, crush the lead of a simple pencil or a graphite battery rod in a mortar. Along the edges of the picture, press thin bare copper wires to the surface covered with graphite (they will serve as down conductors) and connect them together. Hang the wax cast in a glass, pour in the electrolyte, lower the copper electrode and assemble the same circuit as in the experiments with copper plating. But unlike electroplating, a much lower current is needed here, about 5-10 mA. Therefore, you will have to move the rheostat engine or pick up another radio resistance. Turn on the current and be patient, because at this current the copper will be deposited on the graphite surface for at least five hours, if not more, but you do not need to increase the current: the quality of work will be much worse. Open the chain and remove the wax cast from the glass. Carefully dip the wax into hot water - it will melt. And you will have a thin copper sheet with a pattern in your hands. Carefully tear off the down conductor wires from it. An exact copy of the drawing has been obtained. Now you can move on to a very useful thing: the production of unique badges by electroforming. They will only be in your collection! If you make twenty or thirty souvenirs in a mug, they will remind you and your comrades for a long time about a hiking trip, about sports competitions ... We will not give artistic advice: come up with a sketch yourself. There is no need for complex icons: it is more difficult to make, and they look worse. According to the sketch, cut out a template from thin cardboard - it should repeat the outer contour of the icon. Lay the template on thin copper or brass foil and carefully cut out as many blanks on it as you want to make badges. Your workpiece is soft. To make it hard, cover it with a layer of copper in a plating bath. In principle, you already know how to do it; here you will find tips for making badges. Pierce the blanks at the edge with a needle and pass a thin copper wire into the hole. Rinse the workpieces, wipe with gasoline and tooth powder, rinse again and, holding the pendant or with tweezers, dip for half a minute in a dilute, approximately 5% solution of nitric acid. Finally, rinse in running water and hang on a metal rod. Lower the entire suspension into a glass with two copper anode plates (the badges will be cathodes). Foil sheets should be located at different levels so that they do not cover each other. Pour the electrolyte into the glass! 25 g of copper sulfate and 1,5 ml of sulfuric acid per 100 ml of water, preferably distilled. Current source - battery; You can also use a transformer with a rectifier. The current in the circuit is about 10 mA per 1 cm2. The thickness of the copper layer should be 0,5-0,8 mm. When the copper plating is finished, wash the parts. If you decide to make a relief image or inscriptions on the icon, mark them with a needle. Cover that part of the surface that does not need to be covered with a thin layer of BF glue, varnish or paraffin, lower the workpieces into the electrolyte and turn on the current again so that the open areas are covered with a layer of copper - then they will become convex. After that, remove the glue or paraffin. If you can, engrave an inscription or image on the badge, and be sure to solder a pin on the back. Finally, let's give the icon a fancy look. Chemical painting and nickel plating are quite suitable. But the old silver badges look even better. Prepare a 2-3% solution of silver nitrate (you can dissolve a pharmacy pencil in water). Add hydrochloric acid in small portions - three to four volumes per volume of solution. Drain the solution from the precipitated precipitate of silver chloride, rinse the precipitate several times with distilled water, draining the water very carefully, over a glass rod, so as not to lose silver chloride. Add a 30% solution of potassium iodide in small portions to the washed precipitate until the precipitate is completely dissolved. Add water to bring the volume of the solution to the original. You should have the same amount of electrolyte for silver plating as you prepared it for copper plating. Immerse the badges in this electrolyte (they will again be cathodes). Graphite rods can serve as anodes, preferably from batteries, and not from pencils, because their area should be slightly larger than the area of the icons. The current density is low, about 1 mA/cm2. This forms a layer of silver on the badges and, of course, it looks like new. However, it is not such a trick to blacken the badges under the old silver ... Heat an aqueous solution of potassium sulfide of approximately 0,5-1% concentration to 50 ° C. The icons in this solution will gradually change color - they will become first gray, then bluish, and finally black. Rinse the badges and rub them with felt or cloth. Then the convex parts will brighten, the rest of the surface will remain black, and the badges will look exactly like old silver items. Author: Olgin O.M.
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