1. Thermite Welding Base Metal Liquid
Power
Fe2O3 + 2Al > 2Fe + Al2O3 + heat
Base Metal
Chemical reactions are also used in joining materials together. Thermite reactions are exothermic burning of combinations of powders to induce extremely high temperatures. In the burning process, oxides of the filler metal are reduced and this adds filler metal to the weld, While the oxidized powder produces a slag to protect the melt. In order for this process to work, the oxidizing powders must have a lower free energy of formation of its oxide than the oxide power which will provide the filler so that this later power can be reduced and melted. The chemical reaction illustrated here is as follows: metal oxide (in this case iron oxide) + aluminum => aluminum oxide + metal + heat . This process is widely employed in the joining of railroad track and for other emergency repairs. To make the weld, the two pieces of base material are brought within proximity of each other, a dame is formed on each open side and a “hopper” box is provide for powder storage. The powder mixture is place in the joint and within the hopper, the powder is ignited and the reduction and melting occurs with the molten filling the weld joint.
Liquid