The determination of aluminum in refractories is a complex task. When chemical methods are used for this purpose, the aluminum is very often separated from the other components. This prolongs the analysis and makesit very labor-consuming.The atomic-absorption method is promising as it can be done accurately and at high speed. Many publications [1][2][3][4][5][6][7][8] deal with the atomic-absorption method of determining aluminum. However, the published data are contradictory and they are difficult to use because of the great variety of compositions of the refractories, the use of various types of atomic-absorption spectrophotometers, sources of light, etc.The present paper reports some results of a refinement of the optimum measurement conditions for the atomic-absorption analysis of A1 and a study of the effect of the components involved in the composition of the solutions to be analyzed.We have developed and documented the method of measuring the mass fraction of A1203 in refractory materials.The work was carried out in an AAS-IN atomic-absorption spectrometer (made by CarlZeiss, Jena, GDR) using an acetylene-~itrous oxide flame as the atomizer.The atomic absorption of A1 was measured at a wavelength of 309.3 nm and a slot width of 0.025 mm. The source of radiation was a lamp with a hollow cathode of the LSP-I type. A coupler was used to couple the Soviet-made lamp to the fitting of the device. The current in the lamp was the maximum possible for the spectrophotometer (15 mA). The measurements were made in a regime where there was a once-only passage of the beam through the flame since the use of a threefold passage of the beam introduces additional noise in the atomic-absorption measurements in the case of A1 atomized in a limited region of flame.Sodium in a concentration of 2 g/dm 3 was added as the ionization buffer.The main solution of A1 with a concentration of 1 g/dm 3 was prepared by dissolving metallic A1 (Technical Specification 6-09-3742--74) in HCI. The working solutions were obtained by the appropriate dilution of the main solution.The effect of the composition of the gas mixture on the absorption of A1 was studied with a steady consumption of N20 of 230 liters/h and of acetylene of from 150 to 180 liters/h. It was found that a change in the consumption of acetylene has an intense effect on the analytical signal from A1 and therefore the consumption of acetylene must be maintained strictly constant. With an increase in the consumption of acetylene, the absorption of A1 increases. As the optimal acetylene consumption we took 170 liters/h (height of red zone of flame, i0 mm) since with a further increase in the consumption of acetylene, carbon deposits rapidly form on the burner.In selecting the optimal height of the flame zone we established that when the. burner is raised to its maximum possible position, the atomic absorption of A1 increases.By changing the dimensions of the eccentric roller we were able to raise the burner another i0 mm, and this made it possible to increase significantly the sen...

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Manganese is present in metallurgical slags and enters the refractory as a result of the reaction with slags during service, in various types of furnace [i, 2], and it also exists in the form of impurities in the raw material. The concentration of MnO varies in wide limits, for hundreds of a part to several percentage parts.GOST 2642.12-8 standardizes the determination of MnO for its concentration in magnesia and magnesia-lime refractories from 0.05 to 1.0%. A drawback of existing standard and attestation methods of photometric determination of manganese is that they are laborious and not universal. For the complete analysis of refractories the determiantion of MnO is done with separate samples, which increases the time of the analysis, and the consumption of reagents and of platinum.A prospective method for determining manganese is the atomic-absorption spectroscopic technique. This is highly sensitive, selective, and has good reproducibility.The spectra of manganese contain a number of intense resonance lines which are favorable for observation of the absorption. With a wavelength of 279.5 nm the linearity of the graduation graph is preserved in the concentration range 0-3 ~g/cm3; with a wavelength of 280.1 and 403.1 nm the sensitivity is 2 and 20 times less respectively, but the signal-noise ratio is better [3].Some researchers [3-5] have described methods of atomic absorption for determining manganese, but these have not been extended to refractory materials. Information on the influence of various components in these publications is somewhat contradictory.In this paper we present the results of a study of the precixse, optimum conditions for measuring atomic absorption of manganese and an investigation of the effect of the components present in the solutions being tested. The work was done on the Karl-Zeiss atomicabsorption spectrophotometers, the Jena models AASIN and AAS3, using as the atomizer, acetylene-air flames with a wavelength of 279.5 rim. The source of radiation was a lamp with a hollow cathode. The current on the lamp was 5 mA. The original standard solution of manganese was prepared by dissolving metallic manganese specified by GOST 6008-82 in a mixture of nitric and hydrochloric acids.We established that the linearity of the calibration graph is maintained in the range of concentration 0-7 ~g/cm 3 on the AAS3 and in the range 0-8 ~g/cm ~ on the AASIN. Turning the burner through an angle of up to 90 ~ facilitates measurements of the absorption for solutions with mass proportions of Mn of up to 40 ~g/cm 3.During the analysis of standard specimens Sh2 and R6 we found that we need to use calibrated standard solutions prepared on the basis of flux salts (Table i), but in this case the results are somewhat depressed.

Atomic-absorption spectroscopy is one of the best methods of determining chromium. The sensitivity of the determination and the degree to which the chemical composition in acetylene -,~ air or acetylene-nitrous oxide flames has an effect depend on the valence state of the chromium [I, 2]. Chromium is easily reduced to the atomic state from compounds in which it exists in the form of Cr(lll).The main differences in the behavior of Cr(lll) and Cr(VI) compounds arefound in a reducing flame.With the development of a method for the atomic-absorption determination of chromium in refractory materials, particular attention was paid to the stage of bringing thespecimen into solution and to finding the effect of the state of the Cr ion on the results of the analysis.

Ecological safety is one of the main requirements of any technological process in the manufacture of refractories. An assessment of such safety in relation to the main oxides is shown in Table 1.The most dangerous materials are chromium-containing refractories; dinas takes second place; and tar-dolomite refractories third. The maximum permissible concentration (MPC) is 2 mg/m 3 (third class of danger).At present the refractories industry is producing chromium refractories of various compositions: periclase -chromite, chromite-periclase, fused chrome-spinel, forsterite-chromite, chromite-forsterite, mullite-chromite, chromite-mullite, chromite, and chromium-oxide. Their production involves using natural chromites, fused periclase-chromite, and commercial Cr203. These materials contain ecologically dangerous hexavalent chromium oxide (see Table 1), and so any reduction in its concentration during the manufacture and use of refractories is of real importance.The main thermodynamically stable chromium oxides in such materials are highly refractory trivalent chromium oxide Cr203 (fusing point tfu s = 2330~ boiling point t b = 3000~ hexavalent chromium oxide CrO 3 (tfu s = 187-196~ t b = 723~ Thus, CrO 3 is unstable in relation to Cr203 and CrO 2 [2], and at temperatures above 196~ decomposes with the evolution of oxygen, although it may exist also in the gaseous phase.Moreover, the Cr-O system contains many unstable oxides that are not components of refractories: Cr30, CrO (tfu s = 1723~ Cr304, CrO 2 (decomposition temperature tde c = 477~ Cr5012 (tde c = 547~ Cr205 (tde c = 380~ Cr8021 (tde c = 367~CrO2. 9 (tde c = 237-277~ These oxides, depending on the temperature and partial pressure of the oxygen, change into Cr203 and CrO 3, and the amounts depend on the type of material. The Cr203 and CrO 3 contents in regular refractories, determined by the atomic adsorption method, are shown in Table 2.Natural chromites and fused materials based on them (periclase-chromite, etc.) contain trivalent chromium oxide strongly bonded with magnesium and iron oxides and hexavalent chromium oxide present in water-soluble alkaline chromates. Oxidizing and reducing firing of chromites at 1300~ (2 h) reduces the content of Cr 6+ by a factor of 3-8.The periclase-chromite and chromite-periclase products contain 0.035-0.036% Cr 6+, which is a measure of their ecological danger; fused periclase-chromite (0.061% Cr 6+) is also dangerous. In chromite-mullite refractories the Cr 6+ content equals 0.0031%, that is, one order less than PKIaS and KhPT products. The presence of Cr 6+ in refractories is determined visually by slaking with water the particles of milled material; Cr 6+ is highly soluble in water, which it turns a yellow color; and Cr 3+ is not soluble in water. This method can be used to visually determine the ecological danger of chromium refractories.Furthermore, Cr 6+ contaminates the air in the production of refractories that contain chromium. Thus, in melting periclase-chromite the Cr 6+ content in the gas phase reaches 1.7 mg/m ...