Atomic structure
Titanium is located in Group IVB of the periodic table, with an atomic number of 22. The nucleus consists of 22 protons and 20-32 neutrons. The extranuclear electronic structure is arranged as 1S22S22P63S23D24S2. The radius of the nucleus is 5 × 10 - 13 cm.
Physical properties
The density of titanium is 4.506-4.516 g/cm 3 (20 ° C), the melting point is 1668±4 ° C, the latent heat of fusion is 3.7-5.0 kcal / gram atom, the boiling point is 3260 ± 20 ° C, and the latent heat of vaporization is 102.5-112.5 kcal / gram atom. The critical temperature is 4350 ° C and the critical pressure is 1130 atmospheres. Titanium has poor thermal conductivity and electrical conductivity, which is similar to or slightly lower than that of stainless steel. Titanium has superconductivity, and the superconducting critical temperature of pure titanium is 0.38-0.4K. At 25 ℃, titanium heat capacity of 0.126 cal / g · atom of the enthalpy of 1149 cal / gram atom, the entropy of 7.33 cal / g · deg atom, titanium metal is paramagnetic, permeability of 1.00004.
Titanium has plasticity. The elongation of high-purity titanium can reach 50-60%, the reduction of area can reach 70-80%, but the strength is low, which is not suitable for structural materials. The presence of impurities in titanium has a great influence on its mechanical properties, especially the interstitial impurities (oxygen, nitrogen, carbon) can greatly increase the strength of titanium and significantly reduce its plasticity. The good mechanical properties of titanium as a structural material are achieved by strictly controlling the appropriate impurity content and adding alloying elements.
Chemical properties
Titanium reacts with many elements and compounds at higher temperatures. Various elements can be divided into four categories according to their different reactions with titanium:
The first type: halogen and oxygen elements and titanium to form covalent bonds and ionic bond compounds;
The second category: transition elements, hydrogen, antimony , boron , carbon and nitrogen elements and titanium to form intermetallic compounds and limited solid solutions;
The third category: zirconium , hafnium , vanadium , chromium , antimony and titanium form an infinite solid solution;
The fourth category: inert gas, alkali metal, alkaline earth metal, rare earth elements (except for strontium), bismuth, antimony, etc. do not react with or substantially do not react with titanium.
Reaction with the compound:
HF and fluoride
The hydrogen fluoride gas reacts with titanium to form TiF4 upon heating, and the reaction formula is (1); the non-aqueous hydrogen fluoride liquid can form a dense titanium tetrafluoride film on the surface of the titanium to prevent HF from entering the interior of the titanium. Hydrofluoric acid is the strongest flux of titanium. Even a hydrofluoric acid with a concentration of 1% can react violently with titanium, see formula (2); anhydrous fluoride and its aqueous solution do not react with titanium at low temperatures, and fluorides melt only at high temperatures. Significant reaction with titanium.
Ti+4HF=TiF 4 +2H 2 +135.0 kcal (1)
2Ti+6HF=2TiF 4 +3H 2 (2)
HCl and chloride
Hydrogen chloride gas can corrode metal titanium. Dry hydrogen chloride reacts with titanium to form TiCl 4 at >300 °C, see formula (3); hydrochloric acid with concentration <5% does not react with titanium at room temperature, 20% hydrochloric acid at room temperature Titanium occurs in the formation of purple TiCl 3 , see formula (4); when the temperature is high, even diluted hydrochloric acid will corrode titanium. Various anhydrous chlorides, such as magnesium , manganese , iron , nickel , copper , zinc , mercury , tin , calcium, sodium, cesium and NH 4 ions and their aqueous solutions, do not react with titanium, titanium in these chlorides Has good stability.
Ti+4HCl=TiCl 4 +2H 2 +94.75 kcal (3)
2Ti+6HCl=TiCl 3 +3H 2 (4)
Sulfuric acid and hydrogen sulfide
Titanium reacts with <5% dilute sulfuric acid to form a protective oxide film on the surface of titanium to protect the titanium from corrosion by dilute acid. However, >5% sulfuric acid has obvious reaction with titanium. At normal temperature, about 40% sulfuric acid has the fastest corrosion rate to titanium. When the concentration is greater than 40%, the corrosion rate becomes slower when it reaches 60%, and 80% reaches The fastest. The heated dilute acid or 50% concentrated sulfuric acid can react with titanium to form titanium sulfate. See equations (5) and (6). The heated concentrated sulfuric acid can be reduced by titanium to form SO 2 , see formula (7). At room temperature, titanium reacts with hydrogen sulfide to form a protective film on the surface to prevent further reaction of hydrogen sulfide with titanium. However, at high temperature, hydrogen sulfide reacts with titanium to precipitate hydrogen. See formula (8). Powdered titanium begins to react with hydrogen sulfide at 600 ° C to form titanium sulfide. The reaction product is mainly TiS at 900 ° C and Ti at 1200 ° C. 2 S 3 .
Ti+H 2 SO 4 =TiSO 4 +H 2 (5)
2Ti+3H 2 SO 4 =Ti 2 (SO 4 ) 3 +H 2 (6)
2Ti+6H 2 SO 4 =Ti 2 (SO 4 ) 3 +3SO 2 +6H 2 O+202 kcal (7)
Ti+H 2 S=TiS+H2+70 kcal (8)
Nitric acid and aqua regia
Titanium with a smooth surface has good stability to nitric acid. This is because nitric acid can quickly form a strong oxide film on the surface of titanium, but the surface is rough, especially titanium sponge or powdered titanium. Nitric acid reacts, see formula (9), (10). Concentrated nitric acid above 70 °C can also react with titanium, see formula (11); at room temperature, titanium does not react with aqua regia. At high temperatures, titanium reacts with aqua regia to form TiCl 2 .
3Ti+4HNO 3 +4H 2 O=3H 4 TiO 4 +4NO (9)
3Ti+4HNO 3 +H 2 O=3H 2 TiO 3 +4NO (10)
Ti+8HNO 3 =Ti(NO 3 ) 4 +4NO 2 +4H 2 O (11)
In summary, the nature of titanium has an extremely close relationship with temperature and its presence and purity. Dense titanium metal is quite stable in nature, but powdered titanium can cause spontaneous combustion in air. The presence of impurities in titanium significantly affects the physical, chemical, mechanical and corrosion resistance of titanium. In particular, some interstitial impurities, which can distort the titanium lattice and affect various properties of titanium. At normal temperature, titanium has little chemical activity and can react with a few substances such as hydrofluoric acid. However, the activity of titanium increases rapidly when the temperature increases, especially at high temperatures, and titanium reacts violently with many substances. The smelting process of titanium is generally carried out at a high temperature of 800 ° C or higher, and therefore must be operated under vacuum or under an inert atmosphere.
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