physical properties

Titanium has metallic luster and ductility. The speed of sound in it is 5090 m/s. The main characteristics of titanium are low density, high mechanical strength and easy processing.

The new titanium alloy has good heat resistance and can be used for a long time at a temperature of 600 ℃ or higher.

Titanium alloys have good low temperature resistance. Titanium alloys TA7 (Ti-5Al-2.5Sn), TC4 (Ti-6Al-4V) and Ti-2.5Zr-1.5Mo are represented by low-temperature titanium alloys, and their strength decreases with temperature. The increase, but the plastic change is not large. It maintains good ductility and toughness at a low temperature of -196-253 °C, and avoids the cold brittleness of metals. It is an ideal material for low-temperature containers, storage tanks and other equipment.

Titanium metal has strong anti-damping performance. After being subjected to mechanical vibration and electrical vibration, its own vibration attenuation time is the longest compared with steel and copper metals. Using this property of titanium, it can be used as a tuning fork, a vibration element of a medical ultrasonic mill and a vibration film of an advanced audio speaker.

Titanium is an important alloying element in steel and alloys, but its specific strength ranks first among metals. The melting point is 1668°C, the latent heat of fusion is 3.7-5.0 kcal/g atom, the boiling point is 3260±20°C, the latent heat of vaporization is 102.5-112.5 kcal/g atom, the critical temperature is 4350°C, and the critical pressure is 1130 atmospheres. Titanium has poor thermal conductivity and electrical conductivity, similar to or slightly lower than stainless steel, titanium has superconductivity, and the superconducting critical temperature of pure titanium is 0.38-0.4K. At 25°C, the heat capacity of titanium is 0.126 cal/g-atom·degree, the enthalpy is 1149 cal/g-atom·degree, and the entropy is 7.33 cal/g-atom·degree.

Titanium has plasticity, the elongation rate of high-purity titanium can reach 50-60%, and the section shrinkage rate can reach 70-80%, but the shrinkage strength is low (that is, the strength generated during shrinkage). The existence of impurities in titanium has a great influence on its mechanical properties, especially interstitial impurities (oxygen, nitrogen, carbon) can greatly improve 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.

Pure titanium is a non-magnetic metal, and it is difficult to be magnetized in a large magnetic field. It is non-toxic and has good compatibility with human tissue and blood, so it is used in the medical field. Titanium alloys are paramagnetic substances with a permeability of 1.00004.

The fact that the tensile strength of titanium is close to its yield strength indicates that its yield-to-strength ratio (tensile strength/yield strength) is high, indicating that the plastic deformation of titanium metal materials is poor during forming. Due to the large ratio of the yield limit to the elastic modulus of titanium, the resilience of titanium during forming is large.

Although the thermal conductivity of titanium metal is lower than that of carbon steel and copper, due to the excellent corrosion resistance of titanium, the wall thickness can be greatly reduced, and the heat exchange between the surface and the steam is dropwise condensation, which reduces the heat group. No scaling can also reduce thermal resistance, so that the heat transfer performance of titanium is significantly improved.

The elastic modulus of titanium is 106.4GPa at room temperature, which is 57% of that of steel.

The following is the ionization energy data of titanium (unit: kJ/mol)

M - M+ 658

M+ - M2+ 1310

M2+ - M3+ 2652

M3+ - M4+ 4175

M4+ - M5+ 9573

M5+ - M6+ 11516

M6+ - M7+ 13590

M7+ - M8+ 16260

M8+ - M9+ 18640

M9+ - M10+ 20830

 Cell parameters:

a = 295.08 pm

b = 295.08 pm

c = 468.55pm

α = 90°

β = 90°

γ = 120°

chemical properties

 chemical reaction

Titanium is a chemically very active metal, but its melting point is as high as 1668°C. Titanium can also react with many elements and compounds at higher temperatures. According to its different reactions with titanium, it can be divided into the following four categories:

The first category: halogen and oxygen group elements and titanium to form covalent bonds and ionic bond compounds;

The second category: transition elements, hydrogen, beryllium, boron, carbon and nitrogen elements form intermetallic compounds and limited solid solutions with titanium;

The third category: zirconium, hafnium, vanadium, chromium, scandium and titanium form 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. With the compound HF and the fluoride hydrogen fluoride gas, it reacts with titanium to form TiF4 when heated, and the reaction formula is

Ti+4HF=TiF4+2H2+135.0 kcal

Titanium has good corrosion resistance and is not affected by the atmosphere and seawater. [11] Under normal temperature, it will not be corroded by hydrochloric acid below 7%, sulfuric acid below 5%, nitric acid, aqua regia or dilute alkaline solution; only hydrofluoric acid, concentrated hydrochloric acid, concentrated sulfuric acid, etc. can act on it. Hydrogen fluoride liquid without water can only generate a dense titanium tetrafluoride film on the surface of titanium, which can prevent HF from immersing into the interior of titanium. Hydrofluoric acid is the strongest solvent for titanium. Even 1% hydrofluoric acid reacts violently with titanium:

2Ti+6HF=2TiF3+3H2

Anhydrous fluoride and its aqueous solution do not react with titanium at low temperature, and only fluoride molten at high temperature reacts significantly with titanium. HCl and chloride hydrogen chloride gas can corrode metal titanium, and dry hydrogen chloride reacts with titanium at >300 ° C to form TiCl4:

Ti+4HCl=TiCl4+2H2+94.75kcal

Hydrochloric acid with a concentration of <5% does not react with titanium at room temperature, and 20% hydrochloric acid reacts with titanium at room temperature to form purple TiCl3:

2Ti+6HCl=2TiCl3+3H2

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 NH4+ ions and their aqueous solutions, do not react with titanium, which is in these chlorides Has good stability. 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. The fastest again. Heated dilute acid or 50% concentrated sulfuric acid can react with titanium to form titanium sulfate:

Ti+H2SO4=TiSO4+H2

2Ti+3H2SO4=Ti2(SO4)3+3H2

Heated concentrated sulfuric acid can be reduced by titanium to generate SO2:

2Ti+6H2SO4=Ti2(SO4)3+3SO2+6H2O+202kcal

At room temperature, titanium reacts with hydrogen sulfide to form a protective film on its surface, which can prevent the further reaction of hydrogen sulfide and titanium. But at high temperatures, hydrogen sulfide reacts with titanium to evolve hydrogen:

Ti+H2S=TiS+H2+70kcal

Powder titanium starts to react with hydrogen sulfide to form titanium sulfide at 600°C. The reaction product is mainly TiS at 900°C and Ti2S3 at 1200°C. Nitric acid and aqua regia compact titanium with smooth surface has good stability to nitric acid, because nitric acid can quickly form a firm oxide film on the surface of titanium, but rough surface, especially sponge titanium or powdered titanium, can be mixed with titanium dioxide. Second, hot dilute nitric acid reacts:

3Ti+4HNO3+4H2O=3H4TiO4+4NO

3Ti+4HNO3+H2O=3H2TiO3+4NO

Concentrated nitric acid above 70℃ can also react with titanium:

Ti+8HNO3=Ti(NO3)4+4NO2+4H2O

At room temperature, titanium does not react with aqua regia. When the temperature is high, titanium can react with aqua regia to form TiCl2.

In summary, the properties of titanium are closely related to temperature, its existing form, and purity. Dense metallic titanium is quite stable in nature, however, powdered titanium can cause spontaneous combustion in air. The existence of impurities in titanium significantly affects the physical, chemical, mechanical and corrosion resistance of titanium. In particular, some interstitial impurities can distort the titanium lattice and affect various properties of titanium. The chemical activity of titanium at room temperature is very small, 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 ° C, so it must be operated in a vacuum or under the protection of an inert atmosphere. Titanium metal has extremely strong reducing ability in high temperature environment, can combine with oxygen, carbon, nitrogen and many other elements, and can also capture oxygen from some metal oxides (such as alumina). At room temperature, titanium and oxygen combine to form a very thin and dense oxide film. This oxide film does not react with nitric acid, dilute sulfuric acid, and dilute hydrochloric acid at room temperature, and the king of acids - aqua regia. It reacts with hydrofluoric acid, concentrated hydrochloric acid and concentrated sulfuric acid.

In electrochemistry, titanium is a one-way valve type metal with a very negative potential, which usually cannot be decomposed by using titanium as an anode.

People take advantage of the extremely strong compounding ability of titanium at high temperature. When steel is made, nitrogen is easily dissolved in molten steel. When the ingot is cooled, bubbles are formed in the ingot, which affects the quality of the steel. Therefore, steel workers add metal titanium to the molten steel to combine it with nitrogen and turn it into slag—titanium nitride, which floats on the surface of the molten steel, so that the ingot is relatively pure.

When a supersonic plane flies, 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 too much. There must be a light, tough, and high-temperature resistant material to replace aluminum alloy, and titanium can just meet these requirements. Titanium can also withstand the test of more than 100 degrees below zero. At this low temperature, titanium still has good toughness and is not brittle.

Titanium gettering mainly refers to the reaction with carbon, hydrogen, nitrogen and oxygen at high temperature. Using the strong air absorption of titanium and zirconium, the air can be removed, creating a vacuum. For example, using a vacuum pump made of titanium, the air can be pumped to only one part in ten trillion.

The biggest disadvantage of titanium is that it is difficult to refine. Mainly because titanium is extremely strong at high temperature and can combine with oxygen, carbon, nitrogen and many other elements. Therefore, care is taken to prevent these elements from "attacking" titanium when smelting or casting. When smelting titanium, air and water are of course strictly forbidden to approach, and even alumina crucibles commonly used in metallurgy are forbidden to use, because titanium will capture oxygen from alumina. People use magnesium and titanium tetrachloride in an inert gas - helium or argon to extract titanium.

Compounds of Titanium

The oxide of titanium is titanium dioxide, which is the highest valence oxide of titanium. Natural TiO2 is rutile, pure TiO2 is snow-white powder, and is the best white pigment, commonly known as titanium dioxide, 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 chemically change. It is always snow-white and is an excellent white paint. It has high refractive index, strong coloring, large hiding power and stable chemical properties. Other white coatings, such as zinc white ZnO and lead white 2PbCO3·Pb(OH)2, etc., 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, clay, and high-temperature laboratory utensils.

Titanium dioxide is the whitest thing in the world. One 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 - zinc barium white, so it is the best pigment for white paint. Titanium dioxide used as a pigment in the world reaches hundreds of thousands of tons a year. Titanium dioxide can be added to paper to make the paper white and opaque, and the effect is 10 times greater than that of other substances. Therefore, titanium dioxide is added to banknote paper and art paper. In addition, titanium dioxide is sometimes added to lighten the color of the plastic and soften the luster of the rayon. In the rubber industry, titanium dioxide is also used as a filler for white rubber.

Titanium hydride is titanium hydride. Titanium hydride is very brittle, so it can be used to make powdered titanium. It is also used for welding. Titanium dihydride is thermally decomposed to release new ecological hydrogen and metallic titanium, which can promote welding and increase the strength of the weld. Can be used as a catalyst for polymerization. [12]

Titanium tetrachloride is very interesting, it is a colorless liquid under normal conditions (melting point -25 ° C, boiling point 136.4 ° C), has a pungent odor, and emits white smoke in humid air - it hydrolyzes and becomes White titanium dioxide hydrogel. In water, it is strongly hydrolyzed to metatitanate H2TiO3. In the military, people use the strange temper of titanium tetrachloride as an artificial aerosol. Especially in the ocean, there is a lot of water vapor, and when titanium tetrachloride is released, the thick smoke is like a white Great Wall, blocking the enemy's sight. In agriculture, people use titanium tetrafluoride to prevent frost.

TiCl3 is a purple crystal, and its aqueous solution can be used as a reducing agent. Ti3+ has stronger reducibility than Sn2+ [7] .

The barium titanate crystal has the following characteristics: when it changes its shape under pressure, it will generate an electric current, and once it is electrified, it will change its shape. Therefore, people put barium titanate in the ultrasonic wave, it will generate current when it is pressed, and the strength of the ultrasonic wave can be measured by the size of the current generated by it. Conversely, by passing a high-frequency current through it, ultrasonic waves can be generated. Barium titanate is used in almost all ultrasonic instruments. In addition to this, barium titanate has many uses. For example: railway workers put it under the rails to measure the pressure of trains passing by; doctors use it to make pulse recorders. The underwater detector made of barium titanate is a sharp underwater eye, which can not only see fish, but also see underwater reefs, icebergs and enemy submarines.