In 1797, the French chemist Walker discovered chromium from what was then called the red Siberian ore. This chromium salt oxidation treatment is an advanced technology that has only been mastered in modern times. It is said that Germany invented and applied for a patent in 1937, and the United States invented it in 1950, and it was realized under a set of complicated equipment and technological processes.
Chromium is a unique metal in China. The bronze sword unearthed in the second pit of Qin Terracotta Warriors and Horses is 86 cm long and has eight facets, which are extremely symmetrical and balanced. They have been unearthed from the ground for 2000 years, but they are as clean as new, without corrosion or rust. Through modern scientific methods, the surface of these bronze swords is covered with an oxide film with a thickness of about 10 micron, which contains 2% chromium.
According to experts' judgment, the following eight characters (inscription of bird seal) are: Gou Jian, the king of Yue, acts as a sword.
Extended data:
When it comes to Gou Jian's sword, several key words will come to mind: bronzes, national treasures, the Spring and Autumn Period and the Warring States Period. This sword is one of our national treasures, not because of its history or its background. However, due to its own strength, it did not rust after being unearthed, and the cold light shone. More than a dozen newspapers have a sword and two paragraphs (this can't be done without careful sharpening).
The sword is 55.7 cm long and 4.6 cm wide. The sword lattice is cast with black diamond-shaped dark lines, and the scabbard is inlaid with blue glass on the front and turquoise pattern on the back. The head of the sword is ring-shaped with 1 1 concentric circles. The overall body of the sword has been vulcanized, and its corrosion resistance and toughness have been greatly improved, which shows that ancient Chinese people have reached a very high level in metal smelting and surface treatment.
It is very difficult to cast such a sword before 2000. At that time, it was absolutely top-notch smelting process. The main manufacturing difficulties focus on "smelting" and "surface treatment". Of course, it is not difficult to make it by smelting process now, and now steel is harder than bronze and its toughness is better than bronze.
It's still sharp after more than 2000 years. You should know that most of the unearthed metal objects are corroded to some extent. Bury or not. Such a high age is still well preserved and rare in the world.
During the period of 1977, the researchers analyzed bronze alloys with different compositions in different parts of the sword: copper, tin, aluminum, iron, nickel and sulfur.
With the continuous development of science and technology, professors who broke out in major scientific research institutes and universities found that the surface of the sword was plated with a layer of chromium-containing metal! The surface metal is slightly oxidized to form a protective film to prevent further oxidation.
References:
Baidu Encyclopedia-Goujian Sword of King Yue
References:
Baidu encyclopedia-chromium