Chemiluminescent investigations of corrosion of stainless steels

Abstract

DC 620.193 Chemiluminescent systems of luminol are used to design and improve methods for the direct express evaluation of the content of chromium and nickel in corrosive media of stainless steels. By these methods, we can determine nanogram amounts of chromium and nickel in the presence of greater amounts of iron and other components of corrosive media. The methods were approved while testing corrosion of 40KhN steel in a 3% NaCI aqueous solution.In recent years, the chemiluminescent method has been used for the evaluation of the content of iron in corrosive media in the process of mechanical and chemical investigations of steels [1] and in microvolumes of these media at tips of cracks of specimens in studies of corrosion-mechanical strength [2]. As compared with the known electrochemical, photometric, radiometric, X-ray spectral methods [3][4][5][6], the proposed method is characterized by a low detection threshold, broad range of measured concentrations, high speed, and the possibility of automation [7].We studied the possibility of using the chemiluminescent method for the direct determination of nanogram amounts of chromium and nickel in corrosive media of steels. As a basis, we used systems of hydrazide of 3-aminophthalic acid (luminol, H2L ) which are some of the most sensitive systems among the known chemiluminescent methods [8,9]. Experimental Procedure for Chemiluminescent InvestigationTests were carded out in a discrete mode by using a chemiluminescent photometer consisting of the analytic unit with a photomultiplier and a chemiluminescent tray, a high-voltage stabilizer (in the supply circuit of the photomultiplier), an 1-02 digital automatic integrator, a dc voltage amplifier, and an N306 recording potentiometer.The components of the chemiluminescent composition were first separated into two parts with volumes of 10 ml (mixtures I and 11) and placed separately in the chemiluminescent tray and in the pneumatic batcher. The tray was placed in the field of vision of an Ft~U-79 photodetector. The chemiluminescent composition was mixed by opening the shutter. In the diagram of the photodetector, we recorded the intensity of luminescence (I) as a function of time, i.e., kinetic curves. The integrator was used to measure the integral light output for a certain period of time (St) Evaluation of the Content of ChromiumThe sensitivity of evaluation of the content of chromium on the basis of the system of luminol (H2L), hydrogen peroxide (H202), carbonate buffer solution (CBS), and Trilon B (T) is 0.025 ng/ml [81. Trilon B was used for the elimination of the influence of ions of metals. We optimized the method by taking into account the specific nature of the analysis of corrosive media. For the optimal concentrations (8.0.10 -5 M H 2 L, 3.0 9 10 -2 M H202, 1.25 9 10 -2 M NaHCO 3, 1.0 9 10 -3 M T; pH 10.3) [4], we studied the dependence of the integral light output for the first 30 sec of the chemiluminescent reaction ($30) on the content of chromium in pure solutions. We showed that chromium could be detec...