Environmental Engineering Reference
In-Depth Information
and possesses a higher strength-to-weight ratio compared to aluminum and steel.
This provides a distinct advantage in automotive and aerospace industries. How-
ever, in high-temperature applications care should be taken to avoid adsorption
of gases, which makes it brittle.
Commercially pure titanium is well suited to many corrosion applications.
Titanium is alloyed for strength with Al, V, Mn, Cr, and Sn and the alloys have
comparable corrosion resistance. Ti-6Al-4V is a widely used alloy. Titanium
alloys, however, suffer from SCC in many environments, i.e., in halides at tem-
peratures of 287-427
C and at room temperature in NaCl solution, methanol/
HCl solution, N
2
O
4
, and red fuming nitric acid. Ti-0.2Pd and Ti-5Ta alloys have
been developed as special corrosion-resistant materials that are extremely suc-
cessful in handling reducing acids like sulfuric and hydrochloric acid. An alloy
with 30% Mo is also resistant to hydrochloric acid.
The major applications of titanium and titanium alloys in chemical industry
are as follows:
1. Titanium anodes in the chloralkali industry
2. Pressure vessels and columns in chemical, urea, and fertilizer plants
3. Desalination plants
4. Heat exchangers in coastal power stations
5. Synthetic fiber industry
6. Electroplating industry for various tanks used in nitric acid industry, pickling,
nitriding baths, etc.
7. In electrometallurgy plants as anodes for plating of metals
Besides these major uses, titanium is used in automotive parts, in ship building,
as auxiliary anodes in cathodic, protection, and in medical implants and equip-
ment. As titanium gives vivid interference colors when subjected to controlled
oxidation, it is used in fancy applications such as spectacle frames, tennis rackets,
and jewelery.
°
4.2 CONTROL OF ENVIRONMENT
In many cases corrosion can be effectively reduced through the change or modi-
fication of the corrosive environment. This can be achieved by:
1.
A change of operating variables
2.
Removal of corrosive constituent, and
3.
Use of inhibitors
4.2.1 Change of Operating Variables
Temperature, velocity, and pH are the operating variables that can sometimes be
suitably modified to reduce corrosion. Since the rate of corrosion increases at
