Cesium is a low melting point metal. The pure metal cesium is golden yellow with a density of 1.878, a melting point of 28.4℃ and a boiling point of 669.3℃. Among alkali metals, cesium has the lowest melting point and boiling point, the highest vapor pressure, the strongest positive charge, and the lowest ionization potential and electron work functions. At room temperature, cesium metal burns violently in the air and explodes in pure oxygen to produce cesium peroxide. Cesium reacts violently with water and even ice at-1 16℃ to generate cesium hydroxide and hydrogen. Therefore, cesium must be stored in liquid paraffin under airtight isolation conditions. Cesium reacts with a limited amount of oxygen to produce cesium oxide, which can also react with halogen. Cesium and other alkali metals can form low melting point alloys, such as alloys containing 12% sodium, 47% potassium and 4 1% cesium, with a melting point of-78℃; The melting point of the alloy containing Rb 13% and Cs 87% is-39℃. The melting point of the alloy containing 5.5% sodium and 94.5% cesium is -29℃.

The content of cesium in the earth's crust is relatively small, mainly dispersed in spodumene, lepidolite and zinc-aluminum garnet, and exists in isomorphism with potassium, sodium and lithium in potash feldspar, Tianhe stone, potassium salt and carnallite. The main cesium mineral is cesium garnet (2Cs2O? 2Al2O3？ 9SiO2？ H2O), containing 34.6% of CS2O. There is also boron cesium rubidium ore, containing CS2O 3.5%; Cesium beryl, containing CS2O 1.72 ~ 3.6%, is rare.

Extraction of cesium compounds: There are hydrochloric acid method, chlorination roasting method, salt dissolution method and sulfuric acid method to extract cesium compounds from cesium garnet. Hydrochloric acid method is to grind cesium garnet concentrate (containing 20-30% of CS2O), stir and leach with concentrated hydrochloric acid, convert cesium in the concentrate into cesium chloride, dilute with water, add antimony trichloride hydrochloric acid solution, and precipitate antimony cesium chloride double salt (3CsCl? 2SbCl3). Because the solubility of antimony-cesium double salt in hydrochloric acid solution is less than that of rubidium-potassium double salt, most of rubidium-potassium remains in the mother liquor and is separated from cesium. Adding 10 times the weight of water into antimony cesium double salt, boiling and hydrolyzing to generate white basic antimony chloride precipitate, and the reaction formula is 3CsCl? 2scl3+2h2o → 3cscl+2sbocl ↓+4hcl, cesium chloride re-enters the solution. Introducing H2S gas into the solution to remove residual antimony and other heavy metals. Boiling the refined solution, evaporating and concentrating, cooling and crystallizing, and drying to obtain cesium chloride.

Chlorination roasting method is to mix cesium garnet with calcium carbonate and calcium chloride, roast at 800 ~ 900℃, and then soak it out with water. The salting-out method is to mix cesium garnet with sodium chloride and sodium carbonate, melt at 800 ~ 850℃, and then leach with water. After the leachate of the two methods is purified, it can be extracted with 4- sec-butyl -2(α- methylbenzyl) phenol (BAMBP)- for short)-aliphatic kerosene, and then back-extracted with hydrochloric acid or carbon dioxide and water to obtain cesium chloride or cesium carbonate products.

Preparation of metal cesium: Cesium chloride is usually reduced with calcium by metal thermal reduction method. In this method, the reduction reaction is carried out at 700 ~ 900℃ under vacuum less than 10-3 Torr, and the generated cesium vapor is collected in liquid state after condensation. Molten salt electrolysis method is to electrolyze cesium chloride at 700℃ with liquid lead as cathode and graphite as anode, and obtain lead-cesium alloy containing 8.5% cesium from cathode. The alloy was distilled in vacuum at 600 ~ 700℃ to remove impurities such as lead and prepare pure cesium.

The main industrial uses of cesium are to make photovoltaic cells, photomultiplier tubes and television camera tubes, and to be used as getters for vacuum tubes. Cesium iodide activated by sodium and thallium can be used to manufacture industrial and medical X-ray image amplification plates or fluorescent screens. The artificial cesium ion cloud formed by cesium can propagate and reflect electromagnetic waves. Cesium is used as cocatalyst or catalyst in many organic and inorganic syntheses. Cesium salt is also used to produce laser glass, low melting point glass and fiber lens glass. Cesium can also be used to make cesium atomic clocks. Cesium is used in new energy research such as cesium ion thermoelectric converter, cesium ion engine, magnetic fluid power generation system and supercritical steam power generation system. Various cesium salts are used for microanalysis and as drugs.

Cesium metal is very active. When it burns in the air, it will splash and produce thick alkaline smoke, which is harmful to eyes, respiratory system and skin. Therefore, contact between cesium and air or water must be strictly prevented during production, storage and transportation. When metal cesium is transferred, it is usually carried out in a molten state (65℃). Common methods include syringe suction, siphon, injection of inert gas, pressure delivery or vacuum suction.