Titanium is a chemical element, chemical symbol Ti, atomic number 22, in the periodic table of chemical elements in the fourth cycle, Group IVB. Is a silver-white transition metal, which is characterized by light weight, high strength, with metallic luster, moisture-resistant chlorine corrosion. But titanium can not be used in dry chlorine, even if the temperature below 0 ℃ dry chlorine, there will be a violent chemical reaction, the formation of titanium tetrachloride, and then decomposition of titanium dioxide, or even combustion. Only when the moisture content of chlorine gas is higher than 0.5%, titanium in which to maintain a reliable stability.
Titanium  is considered to be a rare metal, due to its dispersion in nature and difficult to extract. But its relatively rich, in all the elements in the tenth place. Titanium ore mainly ilmenite and rutile, widely distributed in the crust and lithosphere. Titanium is also present in almost all creatures, rocks, water bodies and soil. Extraction of titanium from the main ore requires the use of the Crow method or the Hunt method. The most common compound of titanium is titanium dioxide, which can be used to make white pigments. Other compounds include titanium tetrachloride (TiCl4) (as a catalyst and for the manufacture of smoke screens for aerial cover) and titanium trichloride (TiCl3) (for the production of catalyzed polypropylene).
Titanium has metallic luster and has ductility. Density of 4.5 g / cm3. Melting point 1660 ± 10 ℃. The boiling point of 3287 ℃. Valence + 2, + 3 and +4. The ionization energy is 6.82 eV. Titanium is characterized by a small density, mechanical strength, easy processing. The plasticity of titanium is mainly dependent on purity. Titanium more pure, the greater the plasticity. Has good corrosion resistance, not affected by the atmosphere and sea water. At room temperature, will not be less than 7% hydrochloric acid, 5% sulfuric acid, nitric acid, aqua regia or dilute alkali solution corrosion; only hydrofluoric acid, concentrated hydrochloric acid, concentrated sulfuric acid can only role it.
Titanium is an important alloying element in steel and alloys. The density of titanium is 4.506-4.516 g / cm (20 ° C) higher than that of aluminum and lower than iron, copper and nickel. But the strength is at the head of the metal. Melting point 1668 ± 4 ℃, melting latent heat 3.7-5.0 kcal / gram atom, boiling point 3260 ± 20 ℃, latent heat of vaporization 102.5-112.5 kcal / gram atom, critical temperature 4350 ℃, critical pressure 1130 atmospheric pressure. Titanium thermal conductivity and conductivity is poor, similar or slightly lower than the stainless steel, titanium with superconductivity, titanium superconducting critical temperature of 0.38-0.4K. At 25 ° C, the heat capacity of titanium is 0.126 cards / gram atom, enthalpy 1149 cards / gram atom, entropy is 7.33 cards / gram atom, metal titanium is paramagnetic material, permeability is 1.00004.
Titanium has plasticity, high purity titanium elongation of up to 50-60%, section shrinkage up to 70-80%, but the shrinkage strength is low (that is, the intensity of contraction). Titanium impurities in the existence of its great impact on mechanical properties, especially the gap impurities (oxygen, nitrogen, carbon) can greatly improve the strength of titanium, significantly reducing its plasticity. Titanium as a structural material has good mechanical properties, that is, by strictly controlling the appropriate impurity content and adding alloying elements to achieve.
Titanium reacts with many elements and compounds at higher temperatures. Various elements, according to their different reactions with titanium can be divided into four categories:
The first category: halogen and oxygen elements and titanium covalent bond and ionic bond compounds;
The second category: transition elements, hydrogen, beryllium, boron, carbon and nitrogen elements with titanium to produce intermetallic and limited solid solution;
The third category: zirconium, hafnium, vanadium, chrome, scandium and titanium to generate infinite solid solution;
The fourth category: inert gas, alkali metal, alkaline earth metal, rare earth elements (except scandium), actinium, thorium, etc. do not react with titanium or basically does not react. With the compound HF and fluoride fluoride gas in the heating reaction with titanium to generate TiF4, the reaction is
Ti + 4HF = TiF4 + 2H2 + 135.0 kcal
The non-aqueous hydrogen fluoride liquid can form a dense titanium tetrafluoride film on the titanium surface to prevent the HF from immersing in the interior of the titanium. Hydrofluoric acid is the strongest solvent for titanium. Even if the concentration of 1% of hydrofluoric acid, but also with the titanium reaction:
2Ti + 6HF = 2TiF3 + 3H2
The anhydrous fluoride and its aqueous solution do not react with titanium at low temperatures, and only the fused fluoride at high temperatures reacts significantly with titanium. HCl and chloride The hydrogen chloride gas can corrode the metal titanium and the dry hydrogen chloride reacts with titanium at & gt; 300 ° C to produce TiCl4:
Ti + 4HCl = TiCl4 + 2H2 + 94.75 kcal
Concentration <5% hydrochloric acid at room temperature does not react with titanium, 20% hydrochloric acid at room temperature with the occurrence of melon in the generation of purple TiCl3:
2Ti + 6HCl = 2TiCl3 + 3H2