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Properties of urea

Urea, also known as carbamide, carbamide and urea. Pure urea is white, tasteless, odorless, needle shaped or prismatic crystal, with a melting point of 132.7 ℃ under normal pressure. It is hygroscopic, deliquescent, hydrolyzable, and weakly alkaline. It is made into compound fertilizer with acid fertilizer. Urea is an organic compound composed of carbon, nitrogen, oxygen and hydrogen. It is a white crystal. Urea is one of the simplest organic compounds. The most important use of urea is as fertilizer. Its nitrogen content is more than 46%. After being converted into ammonium carbonate in soil, urea is hydrolyzed and absorbed by plants. It is the nitrogen fertilizer with the highest nitrogen content at present.

Molecular formula of urea: CO (NH2) 2, molecular weight 60.06, density 1.335g/cm ³， The melting point is 132.7 ℃. Soluble in water and alcohol, insoluble in ether and chloroform. It is slightly alkaline. It can react with acid to form salt. It has hydrolysis. Condensation reaction can be carried out at high temperature to produce biuret, triuret and cyanuric acid. Heat to 160 ℃ and decompose to generate ammonia gas and turn into cyanic acid at the same time. Urea can be hydrolyzed into ammonia and carbon dioxide under the action of acid, alkali and enzyme (acid and alkali need to be heated). Unstable to heat, heat to 150 ℃～ 160 ℃ to deamination to biuret. Urea is easily soluble in water, 105g can be dissolved in 100ml water at 20 ℃, and the aqueous solution shows neutral reaction. There are two kinds of urea products: crystalline urea is white acicular or prismatic crystal with strong hygroscopicity; Granular urea is a translucent particle with a particle size of 1~2mm, which has a smooth appearance and improved moisture absorption.

Urea is a physiologically neutral fertilizer, which does not leave any harmful substances in the soil and has no adverse effects after long-term application. However, a small amount of biuret, also known as biuret, will be produced when the temperature is too high during granulation, which has an inhibitory effect on crops. Urea is molecular before conversion and cannot be adsorbed by soil, so it should be prevented from being lost with water; The ammonia formed after conversion is also volatile, so urea should also be deeply covered with soil. Urea is the first synthetic organic substance and widely exists in nature, such as 0.4% urea in fresh human feces.

The new version of national standard GB/T2440-2017 for urea has been officially implemented since July 1, 2018. Compared with the replaced 2001 standard, certain adjustments have been made.

New standard GB/T2440-2017