Citric Acid Pickling
Citric acid pickling is an environmentally friendly weld pickle that uses organic chelating agents to remove iron(III) oxides and free iron. It reduces environmental impact without loss of chemical effectiveness.
Physicochemical Mechanism of Action
Citric acid pickling contains organic chelating agents, such as ethylenediamine-N,N'-bis(3-sulfopropanamine)-hydrocarbon (EDTA), which bond with iron(III) oxides and free iron. These compounds are then removed from the weld, cleaning and improving the microstructure.
Metallurgical Relevance & Welding Risks
Using citric acid pickling reduces the environmental impact through lower emissions of toxic chemicals. It also reduces porosity and improves weld strength. However, excessive use can lead to over-cleaning, which may soften the microstructure and reduce toughness.
Workshop Practice & Instructions
Use citric acid pickling in the same amounts as classic hydrofluoric-nitric acid pickle. Make sure the weld is well cleaned and the pickle is completely dry before starting to weld. Control the application to achieve optimal cleaning without over-cleaning.