The Indirect Determination of Fluorine in Coating of Low Hydrogen Type of Arc Welding Electrode and Its Raw Materials by Separating Precipitated CaF₂ and Atomic Absorption Spectrophotometry

Abstract

An indirect determination of F by atomic absorption spectrophotometry was studied. F was precipitated as CaF₂, and Ca in CaF₂ which was separated by filtering was determined by atomic absorption analysis.
The results are as follows:
(1) The addition of excess CaCl₂ as a reagent for precipitation decreased the solubility of CaF₂ in the solution.
(2) The solution was boiled for formation of CaF₂, and CeCl₃ was added to the solution, after cooling to room temperature F^-dissolved in the solution was precipitated as CeF₃.
(3) When absorbance of Ca²⁺was measured after HClO₄ dryness of CaF₂, and CeF₃, the presence of Ce³⁺in CeF₃ increased absorbance of Ca²⁺.
(4) The amount of F, when 20 mg or over, recovered by both Ca²⁺ and Cf³⁺ was about 96.5% actually, and the amount of F obtained from the absorbance of Ca²⁺, which was increased by Ce³⁺, was indicated twice as much as F (about 1.5%) recovered by Ce³⁺, but the amount of F recovered as CaF₂ was about 95%, and as CeF₃ was about 1.5%. These values were nearly constant so that the effect of the increase of the absorbance was used in that condition for increase of value of F, and F could be determined as the recovery of about 98%.
(5) The method was successfully applied to the determination of F in the coating of the low hydrogen type of electrode, fluorides of alkaline earth metals, and cryolite.