The main application of lithium iodide trihydrate

Lithium iodide is a colorless or white cubic crystal system. Easy deliquescence. It is known to have hydrates, halohydrates LiI·1/2H2O, monohydrates LiI·H2O, dihydrates LiI·2H2O, and trihydrates LiI·3H2O. These hydrates are usually stable (the liquid phase composition is the same as the composition of the compound when dissolved, and no decomposition occurs). Commercially available products are usually trihydrate. Lithium iodide (sanshui) : hexagonal crystal system, yellow crystal. The molecular mass is 187.89. Relative density 3.48. Melting point is 73 ℃. At 75 ~ 80℃, one molecule of crystal water is lost and dihydrate is formed. At 80 ~ 120℃, two molecules of crystal water are lost and become monohydrate. It becomes anhydrous at 300℃. Soluble in water, methanol, ethanol, acetone and ester solvents. Solubility in water: 0℃ 151, 60℃ 201.2. LiI·3H2O+Cl2→LiCl4·3H2O. Lithium iodide trihydrate is easily oxidized by oxygen in air to form elemental iodine. At home and abroad, the main methods to prepare lithium iodide trihydrate are hydrogen sulfide reduction, hydrazine, liquid ammonia and neutralization. Hydrogen sulfide reduction method is made of lithium hydroxide, iodine and hydrogen sulfide as raw materials, and water as the reaction solvent. The disadvantages of this method are long reaction time, low yield and need to pay attention to prevent hydrogen sulfide gas leakage caused by safety accidents; The biamine method is prepared with lithium hydroxide, iodine and biamine as raw materials and water as reaction solvent. Although the reaction time of this method is shortened and no harmful gas is produced in the whole production process, it has the disadvantages of complex device and high one-time investment. Liquid ammonia method is to prepare lithium iodide by reaction of ammonia iodide and lithium metal in liquid ammonia. Neutralization method is to prepare lithium iodide by adding hydrogen iodate acid as raw material and neutralizing reaction of lithium carbonate or lithium hydroxide. The preparation of hydrogen iodate acid required by this method is cumbersome and not conducive to large-scale industrial promotion.

Lithium iodide trihydrate is an important basic chemical reagent, which is widely used in fuel cell electrolyte, drug synthesis, catalytic chemistry and photography industry.

1) Application in battery electrolyte
Some researchers have invented a high-quality, inexpensive and reliable timer, which can be used in airplanes, spaceships or other precision instruments with a wide temperature range, compressive and seismic resistance. The key element of the indicator is the electrolyte of the battery. Studies have shown that the electrolyte composed of mercury iodide and other components can hinder the normal operation of the battery because the solution freezes at slightly above 35℃, disabling the instrument, and becomes extremely unstable below 10℃, resulting in system errors. However, the addition of lithium iodide to mercury iodide not only increases the stability of the solution at low temperatures, but also does not produce any system errors. The solution consists of 50-60% lithium iodide trihydrate, 12-18% mercury iodide, and 2-38% distilled water. The results are as follows: (1) 7.5g lithium iodide trihydrate, 2.7g mercury iodide, 10ml distilled water will not form any crystal when the temperature is higher than 1 35℃, and will not condense when the temperature is constant; (2) 9g lithium iodide trihydrate, 2.7g mercury iodide, 10mL distilled water will not condense at a temperature higher than 57℃; ③10g lithium iodide trihydrate, 2.7g mercury iodide and 10mL distilled water will not condense at a temperature higher than 79℃. There will be no system error in the above experimental test results. The third solution is the best mix for current instrument use because its freezing point is just below the limit of instrument failure. Any material that can provide lithium ions can be selected as anode active material for lithium batteries. To prepare a solid electrolyte, lithium nitride, lithium iodide monohydrate, lithium iodide dihydrate, lithium iodide trihydrate powder, a mixture of lithium iodide powder or one of the above lithium iodide powder and alumina monohydrate can be used to conduct lithium ions. The electrolyte composed of the above components can increase the conductivity of lithium ions and the stability of the battery, extending its service life.

2) Application in drug synthesis
Parkinson’s disease has been the focus of medical research, and dopamine drugs have been used to treat it. However, research has shown that dopamine does not cross the blood-brain barrier and therefore cannot eradicate the symptoms of Parkinson’s disease. The amino compounds of dopamine and other alternative anilines, however, do. These compounds stimulate and sensitize the central nervous system, particularly in reducing symptoms of Parkinson’s disease such as stiffness and involuntary tremors. The amides can be synthesized from lithium iodide trihydrate.

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