Inder Singh

Electrochemical behaviour of AISI‐316 stainless steels in sulphuric/nitric acid mixtures

Stainless steels are very unique in that they offer a wide range and combination of resistance to corrosion, resistance to oxidation at high temperature and good mechanical properties at room temperature. With rapid industrialization all over the world, these very properties have led to extensive use of stainless steels in different industries. Austenitic stainless steels containing molybdenum exhibit corrosion resistance in both sulphuric acid and nitric acid. Stainless steel undergoes severe attack in sulphuric acid having concentrations in the range of 20‐85 per cent, whereas they are immune to nitric acid in any concentration. However, sensitized stainless steels are prone to intergranular attack in acids, even in nitric acid. Further, the attack is aggravated in the presence of aggressive ions. Study of the behaviour of stainless steels in a mixture of acids (nitric and sulphuric acid) is lacking in the literature. This paper, therefore, discusses the performance of AISI‐316 and 316‐L in sulphuric acid and nitric acid and a mixture thereof at room temperature. It is observed that the steels are quite resistant to sulphuric acid and nitric acid, but in the acid mixture they are not so resistant, especially in AISI‐316 SS in respect of corrosion resistance, even in acid mixture containing C1‐ and Cu++ ions.

High temperature corrosion‐resistant coating on steel for short‐term application

Relates to the development of high temperature resistant coating applicable in the temperature range of 500°C to 700°C. A12O3, TiO2 and ZrO2 have been incorporated in aluminium phosphate and ivory‐400 used as binders. Aluminium phosphate as a binder has not performed well in comparison to ivory‐400. Aims mainly to study and to highlight the behaviour of the corrosion‐resistant coating at high temperature.

Role of silicon in the corrosion resistance of Cu‐Si alloys in natural seawater

Silicon plays a vital role in the corrosion resistance of Cu‐Si alloys by forming a copper silicide protective layer on the surface of the alloys in natural seawater but, for the higher percentage of silicon content in the alloy (10 wt. per cent), sometimes, with the synergistic effect of the silicide layer along with free silicon, protection takes place. Electrochemical behaviour test using computerized potentiostat/galvanostat (PARC Model No. 273, EG&G, USA) immersion test in natural seawater and X‐ray diffraction analysis using Simons D‐500 diffractometer support the phenomenon.

Corrosion behaviour of silver brazing alloys in different environments

Corrosion data of the widely used silver brazing alloys (BAg‐1 and BAg‐3) of the American Welding Society’s (AWS) specification are scant in literature. Deals with the study of the corrosion behaviour of these alloys in different environments with particular emphasis on the industrial and marine atmospheres.

Electrochemical corrosion behaviour of heat-treated AISI 304 austenitic stainless steel in inorganic acid mixture

Attempts to study the effect of heat‐treated AISI 304 stainless steel in a nitrated‐sulphuric acid environment. Potentiodynamic polarization studies of heat‐treated AISI 304 SS samples were carried out in 75 per cent H2SO4 ‐ 25 per cent HNO3 acid environment using a PARC‐273 potentiostat/galvanostat. For comparison, potentiodynamic polarization studies of untreated AISI 304 SS were also carried out under similar conditions. Potential versus current density were plotted and the values of Ip and Ic were calculated. The curve depicts that the value of Icorr increases with increasing heat treatment temperature and time of exposure. Abrupt changes in Icorr were observed in the sample heat‐treated at 500°C and 600°C for 120 minutes and 60 minutes respectively. Infers that heat treatment temperature and time of exposure to heat accelerated the corrosion in the acid. Attributes this to precipitation of chromium carbide at the grain boundaries.