MIL-HDBK-1003/11
14.3.3.3
Aluminum,Magnesium,and Their Alloys Alminum,magnesium,and
their alloys are actually used as sacrificial anodes. Alumninum
alloys
with aluminum (duraluminum)become corrosion resistant because of the
rapid formation of a hard aluminum oxide that forms on the surface of the
pure aluminum external surface.
.
14.3.4
Changes of Environment. Surroundings may be changed by any of the
following methods:
14.3.4.1
Water Treatment. Refer to Section 11.
14.3.4.2
Inhibitor. These substances retard corrosion by increasing the
polarization rate at either an anode or cathode metal or bath. They can also
build up electrically resistant films in conduction paths between anodes and cathodes
and cathodes. See Table 16 for inorganic corrosion inhibitors. Organic
inhibitors are, for example, glucosates, amines, phenylhydrazines, and
similar substances
14.3.4.3
Soil Alteration. Replace corrosive soils with sand or treated
soils,or change soil characteristics by providing adequate drainage .
Table 16
Inoganic Inhibitors and Corrosive Systems
Approx. Inhibitor
Concentration
Corrosive Environment
Metallic Systems
Inhibitor
(%)
Small amount
Water systems
Steel.
Glassy phosphates
Iron-brass.
0.05-0.2
Tap water
Potassium dichromate
Steel.
Seawater
Potassium dihydrogen
+ 5.0
phosphate + sodium
nitrite
Aluminum.
0.10
0.30% N NaOH solution
Potassium permanganate
0.03% NaCl solution
Mild steel.
Sodium benzoate
0.5
Sodium carbonate
Small amount
Gas-condensate wells
Iron.
Cooling water
Sodium chromate
Electrical rectifier
0.5
systems.
Sodium chromate
0.07
CaC12 brine
Cu, brass.
Sodium dichromate
Air-conditioning water
Air-conditioning
0.025
equipment.
Sodium dichromate
0.1 + 0.05
Water
Heat-exchangers.
+ sodium nitrate
Sodium hexametaphos-
Water about pH 6
Lead.
0.002
phate
Small amount
Sodium metaphosphate
Ammonia
Mild-steel
Water
Sodium nitrite
0.005
Mild-steel.
Sodium nitrite
20% of seawater
Seawater/distilled
water mixtures.
Water pH 7.25
Sodium orthophosphate
Iron.
1.0
Small amount
Seawater
Sodium silicate
Zn, Zn-Al alloys.
63
Previous Page
