Retarding corrosion during the concn. of sulphuric acid - by using plant made of nickel-iron-chromium-molybdenum alloy

• Main Authors: SCHMOLL,ERICH, FARINA,CARLO,.DR, GRASSINI,UBALDO,.DR, KRATZ,EDUARD, DUCATO,ALDO
• Format: Patent
• Language: English; German
• Published: 19.04.1979
• Edition: 2
• Subjects: CHEMICAL SURFACE TREATMENT; CHEMISTRY; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATIONOR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING MATERIAL WITH METALLIC MATERIAL; COATING METALLIC MATERIAL; DIFFUSION TREATMENT OF METALLIC MATERIAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION INGENERAL; METALLURGY; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLICMATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASSC23 AND AT LEAST ONEPROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25; NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE

The aq. H2SO4 solns. have a concn. of 20-80 wt.% and also contain min. 0.02 wt.% ferric ions, and the concn. of carried out in appts. or plant made of an alloy contg. by wt. 15-30% Cr, 10-60% Ni, 1-10% Mo opt. with the following, all maxima 5% Cu, 1.5% Ti, 0.5% Si, 1% Mn, 0.5% C, the remainder being iron. The pref. aq. acid solns. contain 0.02-0.15% ferric irons, or 0.1-1% ferric ions, in either case added as such, or added as ferrous ions plus air or O2 or another oxidant, viz. HNO3, N2O3, KMnO4, or ch romate ions. The amt. of ferric ions, and thus the corrosion rate, is pref. controlled by measuring the electrochemical potential:-metal/soln.