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Cerium, the rare-earth metal with the highest natural abundance


Cerium is a gray and active metal with a density of 6.9g/cm3 (square crystal) and 6.7g/cm3 (hexagonal crystal), melting point 795 ℃, boiling point 3443 ℃, With high ductility. It is the highest natural abundance among lanthanide metals. The bent cerium strip often sparks.

Cerium is easily oxidized at room temperature and loses its luster in the air. It can be burned in the air by scraping with a knife (pure cerium is not prone to spontaneous combustion, but when slightly oxidized or formed into an alloy with iron, it is highly prone to spontaneous combustion). When heated, it burns in the air to produce cerium dioxide. It can react with boiling water to produce cerium hydroxide, soluble in acids but insoluble in alkalis.

1、 The Mystery of Cerium Element

Cerium, with atomic number 58, belongs to the rare earth element group IIIB lanthanide element in the sixth cycle system. The element symbol is Ce, and the elemental substance is a silver gray active metal. The powder is prone to spontaneous combustion in air, soluble in acids, and is a reducing agent. The name cerium comes from the English name of Ceres. The content of cerium in the crust is about 0.0046%, which is the highest abundance among rare earth elements.

In the big family of rare earth elements, cerium is undoubtedly the "big brother". Firstly, the total abundance of rare earths in the crust is 238ppm, with cerium at 68ppm, accounting for 28% of the total rare earth composition and ranking first; Secondly, cerium is the second rare earth element discovered nine years after the discovery of yttrium (1794).

二、The main uses of cerium

1. The most representative application of environmentally friendly materials is automotive exhaust purification catalysts. Adding cerium to commonly used ternary catalysts of precious metals (platinum, rhodium, palladium, etc.) can improve catalyst performance and reduce the amount of precious metals used. The main pollutants in automotive exhaust are carbon monoxide, hydrocarbons, and nitrogen oxides, which can affect human hematopoietic function, form photochemical toxic smoke, and produce carcinogens, causing damage to humans, animals, and plants. The ternary purification catalytic technology can fully oxidize hydrocarbons and carbon monoxide to generate carbon dioxide and water, and decompose nitrogen oxides into nitrogen and oxygen (hence the name ternary catalysis).

2. Harmful metal substitution, cerium sulfide can replace metals such as lead and cadmium that are harmful to the environment and humans as a plastic red colorant, and can also be used in industries such as coatings, ink, and paper. Organic compounds such as cerium rich light rare earth naphthenates are also used in paint drying agents, PVC plastic stabilizers, and MC nylon modifiers, which can replace toxic substances such as lead salts and reduce expensive materials such as drilling salts.

3. Plant growth regulators, mainly cerium based light rare earths, can improve crop quality, increase yield, and enhance crop stress resistance. Used as a feed additive, it can improve the egg production rate of poultry and the survival rate of fish and shrimp farming, as well as improve the wool quality of long haired sheep

三、Common compounds of cerium

1. Cerium oxide - an inorganic substance with the chemical formula CeO2, a light yellow or yellowish brown powder. Density 7.13g/cm3, melting point 2397 ℃, insoluble in water and alkali, slightly soluble in acid. Its performance includes polishing materials, catalysts, catalyst carriers (additives), ultraviolet absorbers, fuel cell electrolytes, automotive exhaust absorbers, electronic ceramics, etc

2. Cerium sulfide - With a molecular formula of CeS, it is a red powdery substance with a yellowish phase inorganic pigment. It is a new green and environmentally friendly red pigment used in fields such as plastics, coatings, paints, and pigments. It is an inorganic pigment with strong coloring power, bright color, good temperature resistance, light resistance, weather resistance, excellent covering power, and non migration. It is an excellent substitute material for heavy metal inorganic pigments such as cadmium red.

3. Cerium chloride - also known as cerium trichloride, is anhydrous cerium chloride or a polyhydrate of cerium chloride, which can irritate the eyes, respiratory system, and skin. Used in industries such as petroleum catalysts, automotive exhaust catalysts, intermediate compounds, and also in the production of cerium metal。