,i1u·· dby vanuu:s mt:muus . - .
-- uvvv u1:scuss now the rusting of iron objects can be
. ,ente • .
pre tion of Rusting
even . . . .
rr , wasting of rron objects due lo rusting causes a big loss to the country's economy, so it must be
1lt ,d. Several_ metho_ds ar~ used to protect the iron objects from rusting (or corrosion). Most of the
f""\nvolve coating the iron_
0
bJect wzth 'something' to keep out air and water (which cause rusting). The various
~on methods of preventing the rusting of iron (or corrosion of iron) are given below : . ·
""'"Rusting of iron can be prevented by painting. The most common method ofpreventing the rusting
.t. (or corrosion
':.tJ!Ofl th of iron)
. isd lo coat
. its surface with a paint When a coat of paint is applied to the surface .
J:
• . on object, en arr an mozsture cannot come in contact with the iron object and hence no rusting
:cl,es,
;i,ce. The irOn •~des such as window grills, railings, steel furniture, iron pipes, iron bridges, _railway
ships, and bodies of cars, buses and trucks, etc., are all painted to_protect them from rusting [see
Egure 87(a)J. . . · • · ·· · . .
l Rusting of iron can be prevented by applying grease or oil. When some grease or oil is applied to
ur
the s face of an iron object, then air and moisture
, cannot come in contact with it and hence
. rusting zs
il
prevented· For example, the tools and machine parts made of iron and steel are smeared with grease or o
revent their rusting [see Figure 87(b)]. ·
to p ------, r::
(a) The iron pipe is being paint.ed to (b) Oil is being applied to bicycle (c) This bucket is made of iron sheet
prevent rusting · chain and gear wheel to coated with zinc (galvanised iron
. prevent rusting sheet) to prevent rusting
- . . S
Figure 87. ome me thod~ of preventing
· rusting of iron and steel objects.
.• thin 1 f · c
. lva~isation. The process of depositing a ayer o z~
3. Rusting of iron can be prevented by ga . . . d by dipping an iron ob1'ect in molten zmc
. ti Galvarusation 1s one
metal on iron objects is called galvarusa on. th . bJ'ect This thin layer of zinc metal on the
. th f
8metal. A thin layer of zinc metal 1s en orm
ed all over e rron o •
· . metal does not corrode on exposure to
dUrface of iron objects protects them fr om rus ting because dzmct-bins and sheds (roofs). are galvarused. · to
.
amp au. The iron sheets used for making .buckets,
. . drums,
sed foruswater supply are also galvarused
. . ·t
to preven
Prevent their rusting [see Figure 87 (c)]. The rron pzpes u : . .·
fllsting.
SCIENCE FOR TENTH CLAss .
. Cffc
1
. We wi~l now explain how a more reactive metal zinc is able to pro~ect iro~ from rustin .~
q~te reactive metal. The action of air on zinc metal forms a very thin coating of zmc oxide all g. 2lllc·
zinc oxide· coating is hard and impervious to air and hence prevents the further corrosion it. o:V~r
(becau,se ~ir is not able to pass through this hard zinc oxide coatin~). So, when a layer of zin_:IIJc
d_epos1ted on an iron object, then the zinc oxide coating formed on i_ts sa:face pr?tects the Zin.c :~
zmc layer ~s well as the iron below it. Please note that the galvamsed iron obJect remains
againS t ru~ting even if a break occurs in the zinc layer. This is because z~c is Pro
~ore e~sil~ oxidised than iron. So, wheri zinc layer on the surface of galvarused
rron °bJect is broken, then zinc continues to corrode but iron object does not corrad e
or rust. ·
. 4. Rusting of iron can be prevented by tin-plating and chromium-plating. Tin
and chromium metals are resistant to corrosion. So, when a thin layer of tin metal
(or chromium metal) is deposited on iron and steel objects by electroplating, then
the iron and steel objects are protected from rusting. For example, tiffin-boxes made
of steel are nickel-plated from inside and outside to protect them from rusting. Tin
js ·used for plating tiffin-boxes because it is non-poisonous and hence does not
contaminate the food kept in them. Chromium-plating is done on taps, bicycle handle
bars and car bumpers made of iron and steel to protect them from rusting and give
then:1, a shiny appearance (see Figure 88).
· .,. 5. .Rusting of iron can be prevented by alloying it to make stainless steel.
When iron is alloyed with chromium and nickel, then stainless steel is obtained. Figure 88. This tap
iron (or steel) has
StaJnless steel does not rust at all. Cooking utensils, knives, scissors and surgical chromium-plated to
instnim~nts, etc:,:· are made of stainless steel and do not rust at all. But stainless its rusting and also to ·
steel is to.o expensive to be used in large amounts. Please note that in the 'stainless a shining appearance.
steel fo:rmafion' metho'd of rust prevention, the iron is not coated with anything. .
