The determination of boron in steels

A thesis submitted in partial fulfilment of the requirements of the Council for National Academic Awards for the degree of Doctor of PhilosophyA method for the rapid determination of boron in mild and low alloy steels containing 0.0005 to 0.010%B has been developed based on the reaction of 1-(arsenophenylazo)-2-hydroxynaphthalene-3, 6-disulphonic acid trisodium salt (Thoron) with boric acid in sulphuric acid. (90% v/v) to produce a fluorescent complex. The method is compatible with dissolution techniques used for the separation of 'soluble' and 'insoluble' boron and was found to be tolerant to the presence of iron and other elements at the levels commonly present in steel. The procedure was automated using the AutoAnalyzer system. The reproducibility at 0.0027oB is better than +0.0001%B. The limit of detection is less than 0.0005%B. - The composition and stability of the complex between boric acid and. thoron were - determined from fluorescence measurements. Only a single complex between one boric acid and one thoron molecule was found. The apparent stability constant in 9076 v/v sulphuric acid and at 250C was found to be 7X 103 M-1 .. 11B n. m. r. spectroscopy showed that at least two borate anions were found to be present in solutionsof H3BO3 in concentrated sulphuric acid, B(HS04)4 appeared to be the predominant species. While in less concentrated acid this species was in equilibrium with rapidly interconverting tetrahedral species of the form B(OH) x(HS04) 4 -X11B n. m. r. has also been used to determine the stability constants of the thoron -boric acid complex and other similar tetrahedrally coordinated boron complexes with a range of 2-hydroxyphenylketones and mono-phenylazochromotropic acid derivatives. These values are consistent with those derived from fluorescence measurements