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| Properties of Titanium |
◎ Physical properties
Pure titanium has the following physical properties,
1. High melting point: 1,668℃ (slightly higher than iron)
2. Low specific gravity: 4.5 (about 60% that of iron, 1.7 times that of aluminum).
3. Low thermal-expansion coefficient: 6.4*10¯6 /℃ (about half that of 18-8 stainless steel, one-third that of aluminum).
4. Low thermal-conductivity coefficient: 0.041 cal/cm2 /sec/℃/cm (almost the same as that of 18-8 stainless steel).
5. High electrical resistance: 0.55μΩ/cm (higher than any metal except 18-8 stainless steel).
6. Non-magnetic: magnetic permeability is 1.0001
7. Crystal structure: close-packed hexagonal lattice (below 885℃ transformation point); body-centered cubic lattice(above 885℃ transformation point).
8. Young’s modulus: 10,850 kg/mm2 (about one-half that of iron, about 1.5 times that of aluminum).
◎ mechanical properties
Titanium’s high-and low-temperature properties, fatigue strength and creep rupture strength are as shown in the figures below. As seen in the figures, at elevated temperatures, strength decreases as temperature increases; however strength remains at a reasonably high level until 300℃. At low temperatures, ductility little, despite the increase in strength, and low-temperature brittleness is not observed. It can therefore be said that this material is suitable for low temperature application.
◎ Corrosion resistance
1. General
Titanium’s corrosion resistance is derived from the stability of the oxide layer (passive layer) readily formed by the trace amounts of water or a hydroxyl group. This results in high resistance to corrosion by various media such as oxidizing acids, neutral, alkaline and chloride solutions, organic acids and wet gases.
2. Resistance to acids
Titanium shows very resistance to oxidizing acids such as nitric and chromic acid, regardless of concentration or temperature. However, a violent reaction, possibly resulting in ignition, does occur between titanium and fuming nitric acid containing 1% or less water or 6% or more NO2.. Against strong non-oxidizing acids such as hydrochloric and sulfuric acids, titanium shows resistance under low temperatures and concentrations, but becomes severely corroded as the temperature and concentration increase. In cases where strong oxidizing agents such as nitric of chromic acid, or metal ions such as Fe+++ or Cu++ are contained in the solution, however, no corrosion occurs.
3. Resistance to corrosion by sea water
Actual results show that titanium has high resistance to corrosion by flowing sea water at normal temperature. Titanium tubes even show high resistance to corrosion by sea water containing sulfides or drift sand or flowing at high speed, conditions damaging to copper alloy tubes widely used for sea water heat exchangers. For this reason it expected that titanium tubes will see increasing use in this field. Westinghouse Electric Corp. has estimated corrosion resistance and other factors for several materials used for condenser tubes. The results emphasize titanium’s usefulness, provided that care is taken to avoid organic fouling. |
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