Fused metal, hydrogen content

Fluorine cannot be prepared directly by chemical methods. It is prepared in the laboratory and on an industrial scale by electrolysis. Two methods are employed (a) using fused potassium hydrogen-fluoride, KHFj, ill a cell heated electrically to 520-570 K or (b) using fused electrolyte, of composition KF HF = 1 2, in a cell at 340-370 K which can be electrically or steam heated. Moissan, who first isolated fluorine in 1886, used a method very similar to (b) and it is this process which is commonly used in the laboratory and on an industrial scale today. There have been many cell designs but the cell is usually made from steel, or a copper-nickel alloy ( Monel metal). Steel or copper cathodes and specially made amorphous carbon anodes (to minimise attack by fluorine) are used. Hydrogen is formed at the cathode and fluorine at the anode, and the hydrogen fluoride content of the fused electrolyte is maintained by passing in... 

The consumables to be tested are used to deposit a single weld bead which is rapidly quenched. Both the welding and quenching processes are carefully controlled. The specimen so produced is maintained at room temperature for a sufficient time to release its content of diffusible hydrogen, which is measured by volumetric methods and reported on unit mass of either deposited or fused metal (Note 2]. 

The total hydrogen content is defined for the present purposes as the sum of the diffusible and residual contents, the latter being determined by hot extraction at 650 °C under vacuum or in a carrier gas as described below. The results may be expressed in terms of the hydrogen content per unit weight of either deposited metal (i.e. the weld metal deposited on to the test specimen during the test) or fused metal (i.e. the metal deposited plus the parent metal in the test sample which has been melted by the welding operation). 

If it is also desired to determine the amount of fused metal, the cross-section of the bead shall be measured on tracings or photographs of the fractured faces. These measurements are made after hot extraction if the residual hydrogen content is also to be assessed. 

That part of a welded joint which has been melted during welding. It comprises added weld metal and fused parent metal. The term is particularly used in tests to measure weld hydrogen contents and it is usually estimated from the area of fused metal in a weld crqss-section which has been ground and etched. 

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