"Son of the Earth"-Titanium
Titanium is a silvery white metal. As early as 179 1, the British scientist William Gregor first discovered this magical element in the suburb of Minahan, England. Four years later, German chemist klapp Lott discovered this element from a red ore in Anick, Hungary, and named it after a hero in Greek mythology. Titanium means "son of the earth". Titanium looks like steel, but it is far harder than steel and weighs only half as much as iron. At room temperature, titanium can safely "lie" in various strong acids and alkalis; Even the strongest aqua regia can't corrode it. Someone once threw a piece of titanium metal into the sea. Five years later, it is still shining without any rust. As the saying goes, "real gold is not afraid of fire." However, the melting point of titanium is more than 600 degrees Celsius higher than that of gold. Because of its extraordinary ability, titanium has a wide range of uses. At present, titanium is an indispensable metal for making airplanes, tanks, warships and submarines. Titanium is also widely used to replace steel in spacecraft and missiles. Titanium nitride and titanium carbide produced by the combination of titanium with nitrogen and carbon are also very hard compounds, and their heat resistance is even higher than that of titanium 1 times. This hard and heat-resistant material can replace super steel to make high-speed cutting tools. Many special properties of titanium are also used in chemical industry, ultrasonic and superconducting technology. But titanium has one of the biggest disadvantages, which is the difficulty in extraction. This is mainly because titanium can combine with oxygen, carbon, nitrogen and other elements at high temperature. So people used to regard titanium as a "rare metal". In fact, the content of titanium is about 6‰ of the earth's crust weight, which is more than the sum of copper, tin, manganese and zinc 10 times. In the world, China has the largest titanium reserves, and Panzhihua in Sichuan accounts for more than 90% of the country's titanium reserves, which is a rare large-scale titanium ore in the world.
Aluminum coating
Putting silvery white aluminum in the air, it didn't take long to form an extremely thin and almost transparent white oxide film.
It's hard to believe that this aluminum coat has the same main components as dazzling rubies and sapphires, both of which are alumina (A 1203). The only difference between them is the crystal structure. However, don't underestimate this humble aluminum coat, which has made outstanding contributions to the use of aluminum!
As we all know, steel is a material with many valuable characteristics. Putting steel in the air will also put on a coat-rust (mainly iron oxide). However, the structure of this layer of steel is very loose. Oxygen, water vapor and carbon dioxide molecules in the atmosphere can penetrate into the steel through the numerous pores of this coat, and constantly turn the steel into rust until the whole steel becomes useless "rotten iron". Therefore, in order to protect steel from corrosion, people often coat steel with a protective coating-antirust substance.
Aluminum coating is different from steel coating. Although thin, it is "seamless" and dense. Even if the aluminum block is stretched, squashed, twisted or bent, it will not loosen or fall off, and it can still be firmly wrapped on the surface of aluminum. Oxygen, water vapor, and carbon dioxide molecules can't do anything about it.
Alumina, the outer layer of aluminum, is insoluble in water and has a melting point as high as 2050℃. When aluminum products are heated to 660℃, metallic aluminum has melted into liquid state, but alumina still covers the surface of liquid aluminum to prevent oxygen from contacting aluminum.
Aluminum coating can be called a pair of armor that is not afraid of flooding and fire, and can protect itself from atmospheric corrosion.
However, aluminum coating also has some shortcomings: first, the naturally formed protective coating is too thin, with a thickness of only two ten thousandths to four ten thousandths of a millimeter, and a piece of ordinary paper is 500 times thicker than it, which cannot withstand mechanical damage; The second is fear of acid and alkali. It would be better if this coat could be thicker, harder, more wear-resistant and more corrosion-resistant.
In order to thicken the coating of aluminum, people think that the coating of aluminum-alumina film is produced by oxidation reaction between pot and oxygen in the air. If an oxidizing substance stronger than oxygen reacts with aluminum, isn't the alumina film thicker?
Therefore, people first use sodium phosphate (Na3PO4), sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and other solutions to wash off the oil stains on the surface of aluminum products, then let them bathe in hot water, and then soak them in the mixed solution of sodium chromate (Na2CrO4), sodium carbonate (Na2CO3) and sodium hydroxide for oxidation. Because sodium chromate is a strong oxidant, the coating of aluminum-alumina film is greatly thickened.
In industry, aluminum products are immersed in electrolyte solution as anode, and direct current is introduced to oxidize aluminum, which also forms a thick aluminum oxide film. The artificially thickened alumina film is more than 80 times thicker than the naturally formed alumina film, reaching 0.015-0.438+07 mm. ..
Interestingly, artificially thickened aluminum coats, like clothes worn by people, can be dyed in various colors. In this way, aluminum products are no longer all dressed in silver, but can be covered with colorful beautiful clothes such as gold, red, sapphire and green. The lovely golden yellow pencil case, colored metal keys, lighters and other aluminum products you see are all covered with dyed alumina coats.
Light bulb chemistry
How much do we know about this assistant when we gently press the switch and light the desk lamp to review?
Think about it. Do you know how ordinary light bulbs glow?
The light bulb can emit light because the current passes through the tungsten wire (also known as tungsten wire) to produce high heat. We choose tungsten wire because it is the metal with the highest melting point (its melting point is 3422oC), and it remains unchanged in the environment above 1000 degrees Celsius, while other metals have already melted in this environment.
Tungsten, like many metals, will be oxidized and burned out quickly at high temperature, so oxygen can't be stored in light bulbs. However, if all the air is pumped out to vacuum the bulb, the high-temperature tungsten will easily evaporate into gas, shortening the life of the bulb. So what should we do? In order to prolong the life of the bulb, inert gas argon will be filled into the bulb, and a little pressure will be added to reduce the chance of evaporation. In addition, iodine was added to the bulb to slow down the evaporation of tungsten. This is because tungsten and iodine will become tungsten iodide around 1000oC, but when tungsten iodide comes into contact with hot tungsten wire, it will become tungsten and iodine again. In this way, the life of the light bulb can be extended a little.
What substances can't be put out by water?
When a fire breaks out, many people are used to using water to put out the fire, but in fact, sometimes they can't. The following fire situations cannot be put out with water, otherwise it will become "adding fuel to the fire".
(1) alkali metals cannot be extinguished with water. Because water reacts with alkali metals (such as potassium and sodium), it can decompose water to produce hydrogen and release a lot of heat, which is easy to cause explosion.
(2) Alkali metal carbide and alkali metal hydride cannot be extinguished with water. For example, potassium carbide, sodium carbide, aluminum carbide and calcium carbide, potassium hydride and magnesium hydride react with water, releasing a lot of heat, which may cause fire and explosion.
(3) Flammable liquids whose density is less than that of water and insoluble in water cannot be extinguished by water in principle.
(4) Melted steel cannot be used in combat. Because the temperature of molten iron and molten steel is about 65438 0600℃, when the steam is above 65438 0000℃, hydrogen and oxygen will decompose, which may cause explosion.
(5) Without good grounding equipment or cutting off current, the fire of high-voltage electrical equipment cannot be put out with water.
Steel and alloy
Steel and alloys are collectively referred to as metallic materials. Metal materials generally use their physical properties, such as ductility, hardness, tensile strength, thermal conductivity, electrical conductivity and so on. Sometimes they also use their chemical properties, such as oxidation resistance, acid and alkali resistance and so on. Except wires, instrument parts, kitchen utensils, etc. Metal simple substance is rarely used, but its alloy is often used because its performance and use value are higher than that of simple substance.
Alloys usually refer to non-ferrous alloys, such as copper alloys and aluminum alloys. In fact, steel is also an alloy. Ordinary steel is an alloy of iron and carbon, so it is also called carbon steel. Besides iron and carbon, other elements are added to steel, which is called alloy steel. Alloy steel containing another element is ternary alloy steel. Such as manganese steel, silicon steel (also known as silicon steel, silicon is the Chinese name of silicon in the past) and so on. In addition, adding two or more elements is called multi-element alloy steel. Alloy steels are usually named according to their uses, such as tool steel, high speed steel and stainless steel.
The iron and steel industry in China has developed rapidly, especially some large iron and steel plants have been completed and put into operation. The annual output of steel has increased rapidly (at present, the annual output of Baosteel is 6 million tons, reaching 6.5438+million tons in 1999), reaching 86.88 million tons in 1993, ranking third in the world.
The following are some important steel grades.
Among carbon steels, there are ordinary carbon steels and high-quality carbon steels. The former is used as building materials such as iron wires, rivets and steel bars with carbon content below 0.4%, wheels and rails with carbon content of 0.4 ~ 0.5%, tools and springs with carbon content of 0.5 ~ 0.6%. Compared with ordinary carbon steel, the latter contains less impurities such as sulfur and phosphorus, and is often used as mechanical parts, which is the most widely used in mechanical manufacturing.
Among alloy steels are manganese steel and silicon steel. Manganese steel generally contains manganese 1.4 ~ 1.8%, which is used to manufacture connecting rod bolts, half shafts, intake valves, machine tool gears, etc. on automobiles and diesel engines. Silicon steel is a kind of steel with high silicon content and high resistance, which is widely used in electrical industry. For example, the transformer steel is silicon steel, with carbon content less than 0.02% and silicon content of 3.8 ~ 4.5%.
Tool steel, high speed steel and stainless steel are common among steels named according to their uses.
Tool steel is an alloy steel, which is used as turning tool, planer, file, saw blade, wire drawing tool and so on. Commonly used are chromium-aluminum tool steel (containing chromium 1.2 ~ 1.5%, aluminum 1.0 ~ 1.5%) and chromium-molybdenum-vanadium tool steel (containing chromium11~/)
High-speed steel, also known as front steel, is an alloy steel containing tungsten, which is used to manufacture high-speed cutting tools. Generally, it contains 8.5 ~ 19% of tungsten, 3.8 ~ 4.4% of chromium and 0/~ 4% of vanadium.
Stainless steel mainly refers to alloy steel containing chromium and nickel. There are many varieties, chromium 17 ~ 20%, nickel 8 ~ 1 1%. If titanium (about 1%) is added, the acid resistance of steel is stronger.
Among the important nonferrous metal alloys, many are copper alloys. These are five of them. Aluminum bronze contains 90 ~ 95% copper and 5 ~ 10% aluminum, and is used as decorations and utensils.
Bronze contains 67-89% copper, 2-33% zinc, 0-9% tin (also known as Wuxi tin bronze) and 0-2% lead, and is used to manufacture mechanical parts. In addition, there are special bronzes, such as phosphor bronze, beryllium bronze and silicon bronze, which have corrosion resistance and high conductivity and are used in instrument industry.
Brass contains 66 ~ 73% copper and 27 ~ 34% zinc, and is often used to manufacture ship mechanical parts.
Aluminum brass contains copper 68 ~ 70%, zinc 27 ~ 3 1% and aluminum 1 ~ 3%, which is used to manufacture the propulsion wing and rudder of ships.
German silver contains 45-62% copper, 20-30% zinc and 0/5-18% nickel. Silver, high hardness, high resistance, used to make decorations and electric heaters.
There are mainly solid aluminum and aluminum-magnesium alloys in aluminum alloys. Solid aluminum contains 95.5% aluminum, 3% copper, 1% manganese and 0.5% magnesium. It is hard and light, and is used to make cars and planes.
Al-Mg alloy contains 90 ~ 94% Al and 6 ~ 10% Mg, which can be used to manufacture instruments and balance wood.
Fusible alloy has casting alloy, babbitt alloy, wood alloy and solder. Casting alloy (also called movable type gold) contains 70% lead, 18% antimony, 10% tin and 2% copper, which is used to make movable type.
Babbitt alloy contains 70-90% tin, 7-24% antimony and 2-22% copper. It is a kind of supercooled liquid containing hard crystals, which will automatically adjust to reduce wear when pressed, and is used to manufacture mechanical bearings.
Wood alloy contains bismuth 38 ~ 50%, lead 25 ~ 3 1%, tin 12.5 ~ 15%, cadmium 12.5 ~ 16%, and has a low melting point (60 ~ 70℃. It is used to make safety valves for steam boilers.
The solder contains 67% lead and 33% tin, and its melting point is 275℃. It is used to weld metals.
In addition, the Ni-Cr alloy containing 60-75% Ni, 12-26% Fe,11-5% Mn and 1-2% Ni-Cr alloy has high resistance and corrosion resistance.
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New metal materials
There are many kinds of new metal materials, all of which belong to alloys.
Shape memory alloy is a new functional metal material. Even if the metal wire made of this alloy is kneaded into a ball, it can be restored to its original state in an instant as long as it reaches a certain temperature. Why can shape memory alloys have such incredible "memory"? The current explanation is that this alloy has martensitic transformation. When the alloy with martensite transformation is heated to the transformation temperature, it can change from martensite structure to austenite structure and completely recover its original shape.
The first successfully researched shape memory alloy is Nitinol, which is called Nitanon. Its advantages are strong reliability and good function, but its price is high. Copper-based shape memory alloys, such as Cu-Zn-Al and Cu-Al-Ni, are only 10% of nickel-titanium alloy, but their reliability is poor. Iron-based shape memory alloy has good rigidity, high strength, easy processing and low price, and has great development prospects. Table 7-3 lists some shape memory alloys and their phase transition temperatures.
Shape memory alloy is widely used in satellite, aviation, bioengineering, medicine, energy and automation because of its special shape memory function.
In the vast space, an American manned spaceship landed slowly on the silent moon. A small group of antennas installed on the spacecraft quickly unfolded and stretched into a hemisphere under the irradiation of sunlight, and began their respective work. Did the astronauts give the instructions, or did some automatic instrument make it unfold? Neither. Because the material of this antenna itself has wonderful "memory ability", it will restore its original shape at a certain temperature.
For many years, people always think that only humans and some animals have the ability to "remember", and it is impossible for abiotic beings to have this ability. However, American scientists discovered by accident in the early 1950s that some metals and their alloys also have the so-called "shape memory" ability. This new discovery immediately attracted the attention of scientists in many countries. Some shape memory alloys have been developed and widely used in aerospace, machinery, electronic instruments and medical devices.
Why don't these alloys "forget" their "prototype"? It turns out that all these alloys have a transition temperature. Above the transition temperature, they have a microstructure, while below the transition temperature, they have another microstructure. Different structures have different properties. The self-expanding antenna on the American moon landing spacecraft mentioned above is made of nickel-titanium alloy and has the ability of shape memory. When the temperature exceeds the transition temperature, this alloy is hard and strong. But below the transition temperature, it is very soft and easy to cold work. Scientists first make this alloy into the required hemispherical deployment antenna, then cool it to a certain temperature to soften it, and then apply pressure to bend it into a small ball, so that it only takes up a small space on the spacecraft. After landing on the moon, using the temperature of sunlight, the antenna was unfolded again and restored to the shape of a large hemisphere.
Since the appearance of shape memory alloy, it has aroused great interest and concern. In recent years, it has been found that the shape memory effect also exists in polymer materials, ferromagnetic materials and superconducting materials. The research and development of this kind of shape memory materials will promote the development of machinery, electronics, automatic control, instrumentation and robotics and other related disciplines.
Superalloy turbine blades are the key components of turbojet engines of aircraft and space shuttle, and the working environment is very harsh. When the turbojet engine works, it sucks air from the atmosphere, compresses it, mixes it with fuel in the combustion chamber, and then is pressed to the turbine. Turbine blades and turbine disks rotate at a high speed of tens of thousands of revolutions per minute, and the gas is sprayed to the tail and ejected from the nozzle, thus generating strong thrust. Among the parts that make up the turbine, the blade has the highest working temperature, the most complicated stress and the most easily damaged. Therefore, there is a great need for new superalloy materials to manufacture blades.
Hydrogen storage alloy hydrogen is one of the new energy sources to be developed in 2 1 century. The advantages of hydrogen energy are high calorific value, no pollution and abundant resources. Hydrogen storage alloys use metals or alloys to form hydrides with hydrogen to store hydrogen. Metal is a closely packed structure with many tetrahedral and octahedral gaps, which can accommodate hydrogen atoms with smaller radius. For example, magnesium-based hydrogen storage alloys such as MgH2, Mg2Ni, etc. ; In order to reduce the cost, a rare earth hydrogen storage alloy, such as LaNi5 _ 5, is introduced, in which mixed rare earth Mm replaces La. Titanium-based hydrogen storage alloys, such as TiH2 and TiMn 1.5. The test of hydrogen storage alloy in hydrogen-powered vehicles has been successful. With the gradual depletion of petroleum resources, hydrogen energy will eventually replace gasoline and diesel to drive cars, and the pollution caused by burning gasoline and diesel will be eliminated once and for all.
Amorphous alloy Amorphous alloy, also known as metallic glass, has excellent properties such as high tensile strength, high strength and hardness, high resistivity, high permeability and high corrosion resistance. Suitable for iron core materials of transformers and motors. Using amorphous alloy as iron core, the efficiency is 97%, which is about 10% higher than using silicon steel, so it is popularized and applied. In addition, amorphous alloys are widely used in pulse transformers, magnetic amplifiers, power transformers, leakage switches, magneto-optical recording materials, high-speed bubble head memories, magnetic heads and VLSI substrates.