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Urea

About: Urea is a research topic. Over the lifetime, 21394 publications have been published within this topic receiving 382444 citations. The topic is also known as: carbamide & carbonic acid diamide.


Papers
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Journal ArticleDOI
TL;DR: In this article, a surfactant-free precipitation method using MgCl2 ·6H2O and NaOH as raw materials, urea and ethanol as assistant additives was used to synthesize hexagonal lamellas.

81 citations

Journal ArticleDOI
TL;DR: In this article, the effects of irrigation, side-dressed application of urea, and urea partially substituted by ammonium sulphate on losses of NH3-N by volatilization in corn crop were evaluated.
Abstract: A field experiment was carried out on a dark-red latosol (Oxisol) of the Centro de Pesquisas Novartis-Seeds, in Uberlândia, State of Minas Gerais, Brazil. The objective of this study was to evaluate the effects of irrigation, side-dressed application of urea, and urea partially substituted by ammonium sulphate on losses of NH3-N by volatilization in corn crop. The fertilizers were applied at 25 and 36 days after planting. The treatments, arranged in randomized complete block design, were: (i) control, (ii) urea, with irrigation before the two applications, (iii) urea, with irrigation after the two applications, (iv) urea + ammonium sulphate (rate N:S = 2.1:1) at the first application, and only urea at the second application, with irrigation before the applications, and (v) with irrigation after applications. Nine samples of volatilized NH3-N were taken, using semi-open static collectors, which were installed after the first N application, at intervals of 4 to 5 days. With irrigation after N application the NH3-N gaseous losses were 40.6% for urea and 23.0% for urea with partial substitution by ammonium sulphate. With irrigation before N application the NH3-N gaseous losses were 42.8 and 38.6%, respectively. Even though the N losses did not show significant differences among the treatments, the partial substitution of urea by ammonium sulphate was positive when the irrigation was performed after the N application. This treatment also showed the largest stalk diameter, the greatest plant high and the highest leaf-N concentration. At harvest, only the fertilized treatments increased yield compared to the control. The relationship between NH3-N volatilized and corn yield established by an inverse linear regression showed that 19.3 kg-1 of grains were lost per every kilogram of volatilized nitrogen.

81 citations

Patent
22 May 1978
TL;DR: Urea granules are prepared by spraying an aqueous urea solution having a urea concentration of 70-99.9% by weight on to fluidized urea nuclei in the form of droplets having a mean drop diameter of 20-120 μm as discussed by the authors.
Abstract: Urea granules are prepared by spraying an aqueous urea solution having a urea concentration of 70-99.9% by weight on to fluidized urea nuclei in the form of droplets having a mean drop diameter of 20-120 μm at a temperature at which the water is evaporated from the solution sprayed on to the nuclei and urea crystallizes on the nuclei to form granules having a desired size.

81 citations

Journal ArticleDOI
TL;DR: In this paper, the role of urea in dissolution of cellulose in aqueous alkali-urea solvent was monitored by differential scanning calorimetry and X-ray diffractometry.
Abstract: To elucidate the role of urea in dissolution of cellulose in aqueous alkali-urea solvent, the dissolution process was monitored by differential scanning calorimetry and X-ray diffractometry. Urea had no direct interaction with cellulose in dissolution process, but promoted the decrease of crystallinity. Moreover, the addition of urea increased the dissolved fraction of cellulose in the solvent by 1.5–2.5 times and improved the thermal stability of the solution. Urea might help alkali hydrate to penetrate into crystalline region of cellulose by stabilizing the alkali-swollen cellulose molecules, leading to an increase in dissolved fraction of cellulose. This stabilization may be due to the local accumulation of urea on the hydrophobic surface, preventing the hydrophobic association of dissolved cellulose molecules.

81 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,000
20221,982
2021433
2020502
2019589
2018557