Properties of Urea

Some properties of urea that are of interest for fertilizer use are as shown in Table 9.1. 

If the product is dedusted and the producer has made good prills with high impact and crushing strengths, it is possible to ship uncoated bulk urea long distances wdth no problems (i.e., Houston to Brazil). 

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Urea has the remarkable property of forming crystalline complexes or adducts with straight-chain organic compounds. These crystalline complexes consist of a hoUow channel, formed by the crystallized urea molecules, in which the hydrocarbon is completely occluded. Such compounds are known as clathrates. The type of hydrocarbon occluded, on the basis of its chain length, is determined by the temperature at which the clathrate is formed. This property of urea clathrates is widely used in the petroleum-refining industry for the production of jet aviation fuels (see Aviation and other gas-TURBINE fuels) and for dewaxing of lubricant oils (see also Petroleum, refinery processes). The clathrates are broken down by simply dissolving urea in water or in alcohol. 

Table 4. Properties of Urea Ammonium Nitrate Nonpressure Solutions...

The nitrate decomposes explosively when heated [1], Prepared in the presence of phosphates, the salt is much more stable, even when dry [2], The manufacture and explosive properties of urea nitrate and its mixtures with other explosives are discussed in detail [3], Explosive properties of the nitrate are detailed [4],... 

Many of the properties of urea plastics are similar to those of the phe nolics, but, unlike phenolics, the urea plastics are not dark and are characterized by pastel and translucent colors as well as slightly superior insulating electric properties. Urea is tetrafunctional. As shown in Figure 15.5, linear and cross-linked network products are readily produced. 

Urea is v sol in ammonia, ethanol, benz ( ), methanol and w si sol in eth insol in C tetrachloride (Refs 13,29a 30a). Table 1 lists the general physical and physicochemical properties of urea... 

U50 000 psi IB, minimum = 60 psi and linear expansion, maximum = 0.25. Properties of all examples given in Table II substantially surpass the comercial standard and also surpass the properties of the PF control boards with respect to linear expansion, thickness swelling, and absorption in the one-hour boil test. Internal bonds, both initial and after the one-hour boil test, and water immersion results of the HDA experimental boards were slightly inferior to results of these tests for the PF control boards. Properties of urea-formaldehyde control boards were similar to the PF control boards excepting in the one-hour boil test where complete failure of all bonding took place in about 15 minutes. 

Adhesive. Urea-formaldehyde water-based dispersions are the most widely used particleboard binders. The low-cost, rapid curing, and colorless properties of urea-formaldehyde adhesives make them the adhesive of choice for most interior particleboard. These adhesives have been continuously improved by the resin manufacturers, resulting in reduced press times without detrimental effects on their storage life or handling characteristics. 

Folklore is rich in references to the healing properties of urea. The Babylonians of about 800 b.c. are known to have used it. In the beginning of this century, urea was employed in the treatment of infections, particularly infected wounds and ulcers, infection of the ears, infected tooth sockets, infected malignant growths, and of burns.4,5... 

Urea is an odorless, white solid that contains 46.65% nitrogen, the most of any ordinarily solid fertilizer. Urea is not flammable, but it will melt and decompose in a fire to give off ammonia. When it is dissolved in water, it hydrolyzes very slowly to ammonium carbamate and eventually decomposes to ammonia and carbon dioxide. Urea dust is not regarded as hazardous. However it is recommended that exposure should be limited to < 10 mg/m3 (8 hr TWA) for inhalable dust and < 5 mg/m3 (8 hour TWA) for respirable dust. Some of the other properties of urea are given in Table 11.1108, no. 

In contrast to urea itself, its N-methylated derivatives enhance water-water interactions, i.e. lower the structural temperature hexa-methylene tetramine produces similar marked effects (Barone et al., 1968). Glycine and /3-alanine appear to be structure breakers (Devine and Lowe, 1971) according to their effect on the viscosity of water (Herskovitz and Kelly, 1973). The viscosities and diffusion properties of urea solutions show striking changes as the concentration increases (MacDonald and Guerrera, 1970). 

TABLE 15.18 Typical Properties of Urea-Formaldehyde-Alpha-Cellulose Moldings... 

Properties of Urea (SECTIONS 223, 224).—(a) Nitrate of urea.—Dissolve a crystal of urea in a drop of water on a microscope slide place near this solution a drop of concentrated nitric acid, and bring the two together by touching with a glass rod. (Eq.) Examine the crystals under the microscope. 

Table 3.15 Properties of Urea-Ammonium Nitrate Solutions [4]...

In 1828 Wohler attempted to synthesize ammonium cyanate via the treatment of silver cyanate with aqueous ammonium chloride. The reaction produced a white crystalline solid that did not possess the properties of ammonium cyanate. Wohler then attempted to synthesize ammonium cyanate using lead cyanate and ammonium hydroxide. This produced the same white powder, but with fewer contaminants so that it could be analyzed. Upon analysis this white powder proved to have the composition and properties of urea, a compound that had been isolated from urine. 

E. Zych, D. Flreniak, W. Strgk, L. Kepinski, K. Domagala, Sintering Properties of Urea-Derived Lu203-Based Phosphors,/. Alloys Compd.. 341, 391-394 (2002). 

C. Adant, M. Dupuis, and J. L. Bredas, Int.J. Quantum Chem., Quantum Chem. Symp., 29, 497 (1995). Ab Initio Study of the Nonlinear Optical Properties of Urea Electron Correlation and Dispersion Effects. 

TABLE 4.21 Properties of Urea-Formaldehyde and Melamine-Formaldehyde Moldings. 

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