Continued on the table  Precious metals for some chemicals corrosion resistance comparison Reagents and conditions Au Ag Pt Pd Rh Ir Os Ru NaClO solution Room temperature 　 　 A C B 　 D 　 　 　 A D B B D FeCl 3 Room temperature B 　 　 C A A C 　 　 　 　 D A A D Molten Na 2 SO 4 　 A D B C C 　 B Molten NaOH 　 A A B B B B C Molten Na 2 O 2 　 D A D D B C D Molten NaNO 3 　 A D A C A A D Molten Na 2 CO 3 　 A A B B B B B Note: A—no corrosion; B—slight corrosion; C—corrosion; D—severe corrosion The chemical stability of silver and palladium is relatively poor, soluble in nitric acid and hot concentrated sulfuric acid, platinum and gold are only soluble in aqua regia, and the secondary platinum group metal is difficult to dissolve in aqua regia. The corrosion resistance of precious metals is closely related to its existence and use state. All precious metals in the finely dispersed active state are easily dissolved by aqua regia or acidic oxidants, and the aqua regia insoluble materials can be converted into The dissolved compound, after the precious metal is dissolved, in addition to silver and palladium, nitrate or sulfate can exist in a cationic state, and other precious metals and various coordination elements or groups form various complexes with different valence states and different properties. . Laser Welder Cost,Handheld Fiber Laser Welder,Xyz Laser Welding Machine,Stainless Steel Laser Welding Machine Shenzhen You Kong Laser Technology Co., Ltd , https://www.youkonglaser.com
The properties of bismuth and bismuth are very special, the melting point is very high, the density and hardness are very large, and many of their minerals or compounds are not only difficult to oxidize or even dissolve in aqua regia, but the metal state has poor oxidation resistance, and powdery bismuth is at room temperature. It can be oxidized by oxygen in the air to highly volatile osmium tetroxide (OsO 4 ). The powdered ruthenium is also oxidized to slightly volatile ruthenium dioxide (RuO 2 ) when heated above 450 ° C. It is oxidized to a highly volatile ruthenium tetroxide (RuO 4 ) under atmospheric and higher temperatures.
Iridium strongest antioxidant, it is the metal of all metals may be used only to 2300 deg.] C in an oxidizing atmosphere without serious damage. This is followed by platinum, which can be used in an oxidizing atmosphere before melting. Palladium is heated in air and oxidizes at 350-790 ° C, but above this temperature the oxide decomposes and returns to metal. The ruthenium and osmium are oxidized at 600-1000 ° C, and the oxide is decomposed into metal beyond this temperature. [next]
Precious metals, after hydrogen in the chemical element redox potential sequence table, are positively charged metals, that is, they are difficult to lose electrons that are oxidized to cations. However, once converted into a cation, it has a high oxidation potential and becomes a strong oxidant. It is generally an electronegative metal (such as magnesium , aluminum , zinc , iron, etc.), hydrogen and other reducing agents. It is easy to precipitate them out of solution.
All precious metals are prone to form insoluble sulfides.
Some precious metal compounds have strong explosive properties under certain conditions. For example, RuO4 will decompose and explode at 180 °C. Some compounds of silver such as silver-silveramine, silver nitride, silver azide, silver acetylene, gold oxides, hydrogen Oxides, chlorides, etc. react with ammonia and are prone to explosion.
(3) Biochemical properties Precious metals have extremely low abundance in the earth's crust, chemical inertness, poor migration activity, and relatively concentrated distribution. They are difficult to enter the living body through food, water, air, etc., naturally participate in metabolism and element exchange. Their equilibrium concentrations in the biosphere are (ng/g): silver 160, palladium 0.7, gold 0.5, platinum 0.2, 铑0.05, 钌, 锇, 铱 each 0.005, and the total of six platinum group metals is less than 1 ng/g (1g) =109ng), which is a "super trace element" and can be ignored. The precious metals in the metal or alloy state are not obviously toxic and safe to use. The rings, bracelets, necklaces and earrings worn by people are directly in contact with the skin. No poisoning has been found since ancient times. Palladium and its alloys are used in large quantities in dental materials without side effects. However, many precious metal compounds are very toxic, which can cause poisoning damage to living organisms. On the other hand, some compounds can help adjust the imbalanced body and make special drugs to treat difficult diseases.
Silver salt enters the human body and causes anemia and development delay. Entering the digestive tract causes oral irritation, hemorrhagic gastritis, diarrhea, and decreased blood pressure. Long-term intake of a small amount of silver salt causes fatty lesions in the liver and kidney, and a large amount of acute poisoning can be fatal. Some silver compound, such as titanium silver fluoride, silver arsenite acid, alkyl highly toxic silver.
Gold salts are highly toxic, and organic compound gold salts such as alkyl gold are highly toxic. The entry of gold salt into the human body can induce leukocyte and thrombocytopenia, anemia, erythema, exfoliative dermatitis, nephrosteroid necrosis, colitis, uremia and the like.
OsO 4 and RuO 4 are prone to contact with the eyes, and their strong oxidative properties can cause severe conjunctival redness, photophobia, tears, light rays appearing under the lamp, corneal ulcers and even blindness in severe cases. Inhalation of the human body can cause inflammation of the upper respiratory tract.
Platinum salts can cause vomiting, diarrhea, and melena. Contact with the skin can cause squamous erythematous dermatitis and eczema spots, urticaria, persistent flushing, dryness, and cleft palate. Symptoms can extend from the fingers to the neck and face. When the dust concentration of the soluble platinum salt reaches 0.002-0.01 mg/m3, inhalation of the respiratory tract produces obvious irritation and even asthma syndrome.
Palladium salts are irritating to the skin but are not easily absorbed by the digestive tract. There is no report of clinical poisoning caused by palladium salt, but rapid intravenous injection of high concentration palladium salt (0.6 mg/kg) can cause cardiac arrest. Drinking water containing 5 mg of Pd for a lifetime can cause cancer in experimental animals (large mice).