Corrosion Study of Iron and Copper Metals and Brass Alloy in Different Medium

The corrosion of iron, copper and brass alloy has been investigated in different medium i.e. HNO3, H3PO4, H2SO4, HCl, CH3COOH. The study reveals that corrosion rate increases in the order iron > copper > brass and for the medium the corrosion follows the order HNO3 > H3PO4 > H2SO4 > HCl > CH3COOH. The rate of corrosion increases with increasing concentration of acid and with increase in time.


Introduction
Corrosion [1][2][3] is defined as the destruction or deterioration of material because of reaction with its environment.Some insist there the definition should be restricted to metals but often the corrosion engineers must consider both metals and non-metals.Ceramics, rubber and other non-metallic materials, deterioration of paints and rubber by sunlight or chemicals, fluxing or lining of steel making furnace and attack of solid metal by another molten metal (Liquid metal Corrosion) are all considered to be corrosion.Corrosion can be fast or slow.
Corrosion of metal can be considered as extractive metallurgy.Rusting is a term reserved for steel and iron corrosion, although many other metals form their oxides when corrosion occurs.Practically all environments are corrosive to some degree.Air, moisture, fresh distilled, salt and mine waters, rural or urban and industrial atmosphere, steam and other gases such as NH 3 , Cl 2 , H 2 S, SO 2 , fuel gases, inorganic acids, organic acids, solvents, petroleum oils cause corrosion environment.Inorganic materials are more corrosive than the organics.High temperature and pressure involve more severe corrosion conditions.Anodizing of aluminum is another beneficial corrosion process used to obtain better and uniform appearance in addition to a protective corrosion product on the surface.

Experimental
Acids like HCl, H 2 SO 4, H 3 PO 4 , HNO 3 and CH 3 COOH of different concentrations viz 0.1 N, 0.5 N, 1 N, 4 N, were prepared from commercially available (A.R) grades and were standardized.Similarly bases like NaOH, KOH and NH 4 OH have been used in different concentrations [4][5][6] .Organic acids like benzoic acid and salicylic acid which are sparingly soluble in water their saturated solutions were used for corrosion studies.Small rectangular size metal-alloy plates of the size 8 x 6 x 0.3 cm were used and were dipped in the different solutions for different timings viz 1 to 5 h.The weight loss in different solutions and the emf was measured for each metal by using the respective metal strips as an electrode and calomel electrode as the reference electrode.From the weight loss and the emf observed, a correlative study of the corrosion rate has been done.The summary of the results are given in Table 1  Corrosion rate expression [7][8][9] The expression mile per year has been used as the most desirable way of expressing corrosion rate.The expression is readily calculated from the weight loss of the metal specimen during the corrosion test by the formula given below: 534W mpy = DAT Where, W =Weight loss in mg, D = Density of the Specimen (g/cm 3 ), A = Area of Specimen (sq.inch), T = Exposure time, (hours).In the present study, the corrosion rate is correlated to the weight loss in mg.

Results and Discussion
Corrosion of iron [10][11][12] in the form of small plate has been studied in different medium by weight loss method.Five different concentrations viz 0.1 N, 0.5 N, 1 N, 4 N, were used for different timings viz 1-5 h.From the study the following conclusions have been arrived.i) The rate of corrosion increases with increasing the concentration of the acid.
ii) The rate of corrosion increases with increase in time.
Corrosion rate on iron metal was found almost similar to acetic acid, succinic acid and salicylic acid and more at higher concentrations for oxalic and benzoic acids and it has been found to be comparatively less for bases NaOH, and KOH.The potential (emf) studies have also been carried out in the respective solutions on iron metal as electrode and calomel electrode as the reference electrode.For inorganic acids which show more corrosion, the emf was found to be less, and for bases, the emf was found to be more.The potential studies on Fe shows the following order bases > neutral > organic acids > inorganic acids.This is related to the electrochemical behavior of metals under different concentrations.Similar weight loss and potential studies have also been carried out for Cu and brass alloy.The order of reactivity has been found to be Fe > Cu > brass.Since brass is an alloy of Cu and Zn the coupling effect of metals do not occur and hence the corrosion rate is found to be less.This is in relation to the observed literature [13][14][15] .Solid solution alloys are usually more corrosion resistant than alloys with two or more phases.

Table 1 .
-14.Comparative corrosion study of metals and alloys in different medium in terms of

Table 2 .
Comparative corrosion study of metals and Alloy in different medium in terms of emf (mV)

Table 3 .
Weight loss of Fe in HNO 3

Table 4 .
Weight loss of Fe in H 3PO 4

Table 5 .
Weight loss of Fe in NaOH