The content of aluminum in the Earth's crust is about 7.7%, second only to oxygen and sulfur, and it is the most abundant metal element in the Earth's crust, twice that of iron. Now, aluminum products are everywhere and the price is low. However, as a symbol of historical status and glory, aluminum has always been shrouded in an aura of mystery.
<h1 class="pgc-h-arrow-right" > "noble metal" down the "altar"</h1>
Our ancestors have long known that kaolin is used to make porcelain. In fact, kaolin is an important aluminosilicate. As early as the 17th century, the German chemist Starr realized that a metal contained in alum has properties different from ordinary metals. As for the discoverers of aluminum, they are generally considered to be the Danish chemist Erstez and the German chemist Weiler, because they independently made aluminum from anhydrous aluminum chloride in the 1920s. In 1854, the Frenchman De Vere reduced anhydrous aluminum chloride with sodium and prepared aluminum by industrial methods. But the metal aluminum produced in this method is more expensive than gold.
The French Emperor Napoleon III once made a helmet out of metal aluminum and was called extremely noble. In recognition of Mendeleev's scientific contributions to the discovery of the periodic law of chemical elements, the Royal Society awarded him a special aluminium trophy, a supreme honor.
In 1886, the American chemist Hall and the French chemist Herlot independently invented the aluminum electrolysis method, pushing the precious metal aluminum off the "altar". Advances in aluminum manufacturing technology have plunged the price of metal aluminum, and the application field of metal aluminum has expanded rapidly. By the mid-20th century, world aluminum production exceeded copper production for the first time. Aluminum alloy has a small specific gravity, high strength, and is not easy to rust. It can be widely used in daily cooking utensils, building materials, aerospace, shipbuilding industry and many other fields.
In the civil field, aluminum alloy is widely used in building doors and windows and aluminum alloy structural parts, and is also used in power long-distance transmission systems. In the high-tech field, aluminum alloys can be used as raw materials for the manufacture of satellites and launch vehicles. It is estimated that aluminum alloys account for about 70% of the total weight of the aircraft. Warships made of aluminum alloy are not easily corroded by seawater in addition to their fast speed. Moreover, it is not magnetic and will not be detected by magnetic mines. Therefore, it has important military application value.
<h1 class="pgc-h-arrow-right" > from "alum book" to "alum food"</h1>
In ancient times, the secret method of communication commonly used in the military struggle of the Chinese court was the "Alum Book", that is, the letter written in alum water. Words written in alum water will not leave any handwriting on the paper after drying, but if you dip it in water, the handwriting will appear immediately. The "Alum Book Incident" of the Kangxi Dynasty was caused by the "Alum Book".
Alum, also known as alum, potassium alum, potassium aluminum, potassium alum, etc., is a composite salt containing potassium sulfate and aluminum sulfate containing crystalline water. Alum is one of the earliest widely used salt compounds in China. Even today, it's still the all-rounder in our lives. First of all, alum has an antibacterial effect and can be used for food preservation. For example, eggs are soaked in 6%-7% alum solution for 15 minutes, and storage after removal can prevent eggs from turning yellow; secondly, alum can be used as a starter for fried foods, aquatic products and soy products, such as baking powder commonly used in daily life, which contains alum; third, it can be used to maintain the crispness of food.
Than if the vegetable raw materials after 0.1% of the alum solution soaking treatment, can make the fruit and vegetable products crisp and delicious; fourth, softening effect, we wear leather clothing in winter is particularly easy to harden, if with 1.2% alum solution and 0.8% salt solution for proper treatment, then the leather coat will become soft and comfortable; fifth, water purification, the use of alum for clean water has a long history in China.
The principle is that the metal ions ionized by alum in water are easily hydrolyzed, and the aluminum hydroxide generated can absorb impurities in the water and make the water clear; the sixth is the mordant dyeing method, and all the colors of the royal costumes of the past generations are taken from plants. When southerners dye with plain squares, they need to add alum, green alum or alum to dye silk thread or cloth.
<h1 class="pgc-h-arrow-right" > control aluminum into the fast lane</h1>
Studies have shown that aluminum is not a trace element needed by the human body, and its absorption capacity is not strong. If the long-term excessive intake of aluminum-containing foods, then the accumulation of a certain amount will produce chronic toxicity. Excessive intake of aluminum often leads to damage to the nervous system and may even increase the risk of developing Alzheimer's disease. It has been reported that the aluminum content in the brain tissue of Alzheimer's disease patients is 1.5-30 times that of normal people, and the brain aluminum content in the nerve fiber tangle area is significantly increased. Public health reports from abroad say that in areas with high levels of aluminum in drinking water, the incidence of Alzheimer's disease is high.
In 1989, the World Health Organization (WHO) and the Food and Agriculture Organization of the United Nations (FAO) officially recognized aluminum as a food contaminant and recommended its control. In China, the intake of aluminum in the public diet is not optimistic. As early as 2012, the national food safety risk assessment report said that 40% of China's food has an aluminum content of more than 2-9 times the national standard. According to the World Health Organization (who) standard, the weekly (safe) intake of aluminum per person is 2 mg/kg body weight. In China, however, more than 30 percent of people consume excessive amounts of aluminum. Among them, children aged 4-6 years have the highest intake, which is 2.6 times the safe intake.
Many years ago, the Ministry of Health launched a plan to limit the use of aluminum-containing additives, which is an important measure taken by China to reduce the excessive intake of dietary aluminum by residents. The newly revised "Standards for the Use of Food Additives" intends to revise the regulations on the use of 9 kinds of aluminum-containing food additives, abolish 3 kinds of aluminum-containing food additives and their use regulations, and delete the use of potassium aluminum sulfate and ammonium aluminium sulfate as a fermentation agent in baking flour products. In order to protect children's health, the new standard proposes to eliminate the use of 12 aluminum-containing food additives in puffed foods. Among them, the synthetic colorant varieties involved include erythritol and its aluminum lake, indigo and its aluminum lake, bright blue and its aluminum lake, lemon yellow and its aluminum lake, sunset yellow and its aluminum lake, carmine and its aluminum lake.
<h1 class= "pgc-h-arrow-right" > the "darling" of the low-carbon era</h1>
Although it is necessary to control the convenience of aluminum additives in the food industry, aluminum is still an irreplaceable darling and hero in modern industry.
Aluminum of the metal has many excellent properties, such as low density, good thermal conductivity, good electrical conductivity, good reflectivity, easy processing and other characteristics determine its application value. The application of metallic aluminum in the manufacture of aluminum alloys has played a greater role in modern society. Although pure aluminum is soft in texture, its alloy strength is very high. For example, adding a small amount of copper, magnesium, manganese and other metal elements to aluminum can make extremely hard aluminum alloys.
The emergence of high-speed rail trains in China is closely related to the application of aluminum alloy materials. It is reported that lightweight is one of the key points of the technological breakthrough of high-speed trains, because when the train is running, the traction weight per ton consumes about 12kw of power, and when the train reaches 300km/h, it consumes about 16-17kw of power per ton. In order to reduce the weight of the body and improve its corrosion resistance, the entire body of the high-speed rail "bullet" is coated with aluminum alloy coating. Since the weight of aluminum alloy is much lower than that of steel, it is conducive to reducing the weight and speed of high-speed rail trains, and aluminum alloy can also provide good air tightness.
The application of aluminum alloys in the automotive industry will greatly improve fuel economy. Since aluminum alloys weigh only about one-third of steel, it will bring good fuel economy. According to the World Aluminium Association, fuel consumption can be reduced by 8 to 10 percent for every 10 percent reduction in vehicle weight. At the same time, every 1 kg of aluminum alloy used in the automotive industry can reduce exhaust emissions by 20 kg during the life cycle of the car. Therefore, the application of aluminum alloy has the dual significance of energy saving and emission reduction.