Physical properties
Titanium has metallic luster and ductility. The density is 4.5g/cm 3 . The melting point is 1668°C. The boiling point is 3287°C. Common valences +2, +3 and +4. The ionization energy is 6.82 eV. The main characteristics of titanium are low density, high mechanical strength, and easy processing. The plasticity of titanium mainly depends on purity. The purer the titanium, the greater the plasticity. It has good corrosion resistance and is not affected by the atmosphere and sea water. At room temperature, it will not be corroded by hydrochloric acid below 7%, sulfuric acid below 5%, nitric acid, aqua regia or dilute alkali solution; only hydrofluoric acid, concentrated hydrochloric acid, concentrated sulfuric acid, etc. can act on it.
Titanium is an important alloying element in steel and alloys. The density of titanium is 4.506-4.516 g/cc (20°C), which is higher than aluminum but lower than iron, copper, and nickel. But the specific strength is at the top of the metal. The melting point is 1668°C, the latent heat of fusion is 3.7-5.0 kcal/gram atom, the boiling point is 3260±20°C, 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 and electrical conductivity, which is similar to or slightly lower than stainless steel. Titanium has superconductivity. The superconducting critical temperature of pure titanium is 0.38-0.4K. At 25°C, the heat capacity of titanium is 0.126 cal/gram atom·degree, the enthalpy is 1149 cal/gram atom, and the entropy is 7.33 cal/gram atom·degree. Titanium is a paramagnetic substance with a magnetic permeability of 1.00004.
Titanium has plasticity. The elongation of high-purity titanium can reach 50-60%, and the reduction of area can reach 70-80%, but the shrinkage strength is low (that is, the strength generated during shrinkage). The presence of impurities in titanium has a great impact on its mechanical properties , especially 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 through strict control of the appropriate impurity content and the addition of alloying elements .
Chemical nature
chemical reaction
Titanium can react 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 category: halogen and oxygen group elements form covalent bond and ionic bond compounds with titanium ;
The second category: transition elements , hydrogen, beryllium, boron, carbon and nitrogen elements form intermetallic compounds and finite solid solutions with titanium ;
The third category: zirconium, hafnium, vanadium, chromium, scandium and titanium form an infinite solid solution;
The fourth category: inert gases , alkali metals , alkaline earth metals, rare earth elements (except scandium), actinium, thorium, etc. do not react or basically do not react with titanium. It reacts with the compound HF and fluoride hydrogen fluoride gas to produce TiF 4 when heated, and the reaction formula is
Ti+4HF=TiF 4 +2H 2 +135.0 kcal
The non-aqueous hydrogen fluoride liquid can form a dense titanium tetrafluoride film on the titanium surface, which can prevent HF from immersing into the titanium. Hydrofluoric acid is the strongest solvent for titanium. Even hydrofluoric acid with a concentration of 1% can react violently with titanium:
2Ti+6HF=2TiF 3 +3H 2
Anhydrous fluoride and its aqueous solution do not react with titanium at low temperatures, only the fluoride that melts at high temperatures reacts significantly with titanium. HCl and chloride hydrogen chloride gas can corrode metal titanium, and dry hydrogen chloride reacts with titanium to form TiCl 4:
Ti+4HCl=TiCl 4 +2H 2 +94.75 kcal
Hydrochloric acid with a concentration of <5% will not react with titanium at room temperature, and 20% of hydrochloric acid will react with titanium at room temperature to produce purple TiCl 3 :
2Ti+6HCl=2TiCl 3 +3H 2
When the temperature is high, even dilute hydrochloric acid will corrode titanium. Various anhydrous chlorides, such as magnesium, manganese, iron, nickel, copper, zinc, mercury, tin, calcium, sodium, barium and NH 4 + ions and their aqueous solutions, do not react with titanium. Titanium is in these chlorine It has good stability in the compound. Sulfuric acid and titanium hydrogen sulfide have obvious reactions with 5% sulfuric acid. At room temperature, about 40% sulfuric acid has the fastest corrosion rate on titanium. When the concentration is greater than 40% and reaches 60%, the corrosion rate becomes slower, 80% Reached the fastest. Heated dilute acid or 50% concentrated sulfuric acid can react with titanium to form titanium sulfate:
Ti+H 2 SO 4 =TiSO 4 +H 2
2Ti+3H 2 SO 4 =Ti 2 (SO 4 ) 3 +3H 2
The heated concentrated sulfuric acid can be reduced by titanium to generate SO 2 :
2Ti+6H 2 SO 4 =Ti 2 (SO 4 ) 3 +3SO 2 +6H 2 O+202 kcal
Titanium reacts with hydrogen sulfide at room temperature to form a protective film on its surface, which can prevent further reaction of hydrogen sulfide with titanium. But at high temperature, hydrogen sulfide reacts with titanium to produce hydrogen:
Ti+H 2 S=TiS+H 2 +70 kcal
The powdered titanium reacts with hydrogen sulfide to form titanium sulfide at 600°C. The reaction product is mainly TiS at 900°C and Ti 2 S 3 at 1200°C . The dense and smooth surface of nitric acid and aqua regia titanium has good stability to nitric acid. This is because nitric acid can quickly form a firm oxide film on the surface of titanium, but the surface is rough, especially sponge titanium or powder titanium. Second, hot dilute nitric acid reacts:
3Ti + 4HNO 3 + 4H 2 O = 3H 4 TiO 4 + 4NO
3Ti + 4HNO 3 + H 2 O = 3H 2 TiO 3 + 4NO
Concentrated nitric acid above 70℃ can also react with titanium:
Ti+8HNO 3 =Ti(NO 3 ) 4 +4NO 2 +4H 2 O
At room temperature, titanium does not react with aqua regia. When the temperature is high, titanium can react with aqua regia to form TiCl 2 .
In summary, the properties of titanium have an extremely close relationship with temperature, its existence form, and purity. The dense metallic titanium is quite stable in nature, but powdered titanium can cause spontaneous combustion in the air. The presence of impurities in titanium significantly affects the physical, chemical, mechanical, and corrosion resistance of titanium. Especially some interstitial impurities, they can distort the titanium lattice and affect the various properties of titanium. The chemical activity of titanium is very small at room temperature, and it can react with a few substances such as hydrofluoric acid, but the activity of titanium increases rapidly when the temperature increases, especially at high temperatures, titanium can react violently with many substances. The smelting process of titanium is generally carried out at a high temperature above 800 ℃, so it must be operated in a vacuum or under the protection of an inert atmosphere. The physical properties of titanium metal titanium (Ti), gray metal. The atomic number is 22 and the relative atomic mass is 47.87. The arrangement of extranuclear electrons in the sublayer is 1s 2 2s 2 2p 6 3s 2 3p 6 3d 2 4s 2 . Metal mobility is between magnesium and aluminum, and it is not stable at room temperature. Therefore, it only exists in a chemical state in nature. Common titanium compounds include ilmenite (FeTiO 3 ) and rutile (TiO 2 ). The content of titanium in the earth's crust is relatively high, ranking ninth, reaching 5600ppm, which is converted into a percentage of 0.56%. The density of pure titanium is 4.54×10 3 kg/m 3 and the molar volume is 10.54 cm 3/mol, the hardness is poor, and the Mohs hardness is only about 4, so the ductility is good. Titanium has good thermal stability, with a melting point of 1668°C and a boiling point of 3287°C. The chemical properties of metallic titanium Titanium has a very strong reducing ability in high temperature environments. It can combine with oxygen, carbon, nitrogen and many other elements, and it can also extract oxygen from some metal oxides (such as alumina). Titanium combines with oxygen at room temperature to form an extremely thin and dense oxide film. This oxide film does not react with nitric acid, dilute sulfuric acid, dilute hydrochloric acid, and the king of acids-aqua regia at room temperature. It reacts with hydrofluoric acid , concentrated hydrochloric acid , and concentrated sulfuric acid .
Titanium is corrosion resistant, so it is often used in the chemical industry. In the past, stainless steel was used for the parts containing hot nitric acid in chemical reactors . Stainless steel is also afraid of the strong corrosive agent-hot nitric acid. This kind of parts must be replaced every six months. Titanium is used to make these parts, although the cost is more expensive than stainless steel parts, but it can be used continuously for five years, but it is much more cost-effective to calculate.
In electrochemistry, titanium is a one-way valve type metal with very negative potential, and it is usually impossible to use titanium as an anode for decomposition.
The biggest disadvantage of titanium is that it is difficult to extract. The main reason is that titanium has a strong ability to combine with oxygen, carbon, nitrogen and many other elements at high temperatures. Therefore, no matter when smelting or casting, people are careful to prevent these elements from "invading" titanium. When smelting titanium, air and water are of course strictly forbidden. Even the alumina crucible commonly used in metallurgy is also forbidden to use, because titanium will take oxygen from the alumina. People use magnesium and titanium tetrachloride to interact in an inert gas- helium or argon to refine titanium.
People take advantage of the extremely strong chemical ability of titanium at high temperatures. During steelmaking, nitrogen is easily dissolved in molten steel. When the steel ingot is cooled, bubbles are formed in the steel ingot, which affects the quality of steel. Therefore, the steel workers add titanium metal to the molten steel to combine with nitriding to become slag —titanium nitride, which floats on the surface of the molten steel, so that the steel ingot is relatively pure.
When a supersonic aircraft is flying, the temperature of its wings can reach 500°C. If the wing is made of relatively heat-resistant aluminum alloy , one to two or three hundred degrees will be overwhelming. There must be a light, tough, and high-temperature resistant material to replace the aluminum alloy. Titanium can meet these requirements. Titanium can withstand the test of more than one hundred degrees below zero. At this low temperature, titanium still has good toughness without being brittle.
The powerful absorption of titanium and zirconium on air can remove the air and create a vacuum. For example, a vacuum pump made of titanium can pump air to only one part of a ten trillion.
Titanium compounds
The oxide of titanium is titanium dioxide , natural TiO 2 is rutile, and pure TiO 2 is a white powder. It is the best white pigment, commonly known as titanium white, which is white when cold and light yellow when hot. In the past, the main purpose of mining titanium ore was to obtain titanium dioxide. Titanium dioxide has strong adhesion and is not easy to undergo chemical changes . It is always white and is an excellent white paint. It has high refractive index, strong coloring, large hiding power and stable chemical properties. Other white paints, such as zinc white ZnO and lead white 2PbCO 3 ·Pb(OH) 2 , do not have these excellent properties of titanium white. Especially valuable is that titanium dioxide is non-toxic. It has a high melting point and is used to make refractory glass [7] , Glaze, enamel , pottery clay, high temperature resistant experimental utensils, etc.
Titanium dioxide is the whitest thing in the world. 1 gram of titanium dioxide can paint an area of more than 450 square centimeters white. It is 5 times whiter than the commonly used white pigment- Lithopone , so it is the best pigment for white paint. Titanium dioxide used as a pigment in the world can reach hundreds of thousands of tons a year. Titanium dioxide can be added to paper to make the paper white and opaque. The effect is 10 times greater than other substances. Therefore, it is necessary to add titanium dioxide to banknote paper and art paper. In addition, in order to lighten the color of the plastic and soften the luster of the rayon, titanium dioxide is sometimes added. In the rubber industry, titanium dioxide is also used as a filler for white rubber.
Titanium tetrachloride is very interesting. Under normal conditions, it is a colorless liquid (melting point: -25°C, boiling point: 136.4°C). It has a pungent odor. It will emit white smoke in moist air—it is hydrolyzed and becomes White hydrogel of titanium dioxide. In water, it is strongly hydrolyzed to metatitanic acid H 2 TiO 3 . In the military, people use the weird temper of titanium tetrachloride as an artificial aerosol. Especially in the ocean, there is a lot of water vapor, and when titanium tetrachloride is placed, the thick smoke looks like a white Great Wall, blocking the enemy's sight. In agriculture, people use titanium tetrafluoride to prevent frost.
TiCl 3 is a purple crystal, and its aqueous solution can be used as a reducing agent. Ti 3+ has stronger reducibility than Sn 2+ .
Barium titanate crystal has the characteristic: when it changes shape under pressure, it will generate electric current, and it will change shape when it is energized. Therefore, when people put barium titanate in ultrasonic waves, it generates electric current when it is pressed, and the strength of ultrasonic waves can be measured by the magnitude of the electric current generated by it. On the contrary, by passing high-frequency current through it, ultrasonic waves can be generated. Barium titanate is used in almost all ultrasonic instruments . In addition, barium titanate has many uses. For example: a railway worker puts it under the rails to measure the pressure when a train passes; a doctor uses it to make a pulse recorder. The underwater detector made of barium titanate is a sharp underwater eye. It can not only see the fish, but also the reefs, icebergs and enemy submarines under the water.
When smelting titanium, it has to go through complicated steps. Turn ilmenite into titanium tetrachloride, put it in a sealed stainless steel tank , and fill it with argon to make them react with metallic magnesium to obtain "sponge titanium". This porous "sponge titanium" cannot be used directly, and it must be melted into a liquid in an electric furnace before it can be cast into a titanium ingot . But it's not easy to make this kind of electric furnace! Except that the air in the electric furnace must be cleaned, what's more troublesome is that there is almost no crucible containing liquid titanium, because general refractory materials contain oxides, and the oxygen in it will be taken away by the liquid titanium. Later, people finally invented a "water-cooled copper crucible" electric furnace. Only part of the central area of this electric furnace is very hot, and the rest are cold. After the titanium is melted in the electric furnace, it flows to the wall of the copper crucible cooled with water and immediately condenses into titanium ingots. This method has been able to produce several tons of titanium blocks, but its cost can be imagined.
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