Papers by Keyword: Urea

Abstract: Potassium silicate is well known as a fertilizer and source of silica for plants growth. This study aims to infiltrate nitrogen from carbamide (urea) into potassium silicate solution to produced silica potassium nitrogen (Si-K-N) matrix by precipitation method using CO₂ as precipitator. Potassium silicate in the range of 3-8% SiO₂ was obtained by extracting silica from geothermal sludge using potassium hydroxide solution. Carbamide is added to the potassium silicate solution allowed by mixing and flowing of CO₂ gas in reactor glass. The result of IR spectra indicated the presence of N-H groups, potassium and silica in the gel matrix produced from precipitation process while no N-H group appears in the gel matrix produced from precipitation in the absence of carbamide. X-ray fluorescence showed the composition of the product Si-K-N in the range of 40 to 50 %SiO₂ and in the range of 50 to 60 %K₂O.

Abstract: Bioplastic composites based on carboxymethyl cellulose (CMC) and urea have been successfully synthesised at various amount of zeolites. Urea inclusion into the bioplastics was supposed to result in nitrogen slow-release composites. The bioplastic composites were prepared by solvent casting the precursor gel containing 0.5 % (w/w) urea in CMC in the petri dishes. The zeolites content was varied at 0.1, 0.5, 1.0, 2.0, and 3.0 % (w/w to CMC). It showed that the addition of zeolites to the bioplastic composites up to 0.5% increased their tensile strength. More addition of zeolites decreased the strain of the bioplastic composite. It could be due to the formation of hydrogen bonds between CMC and zeolites. The amount of urea absorbed in the bioplastics increased as the amount of zeolites increases. It is possibly to be due to the strong interaction between urea and zeolites. The ammonium ions may interact with interchangeable cations in the zeolite. This interaction will also extend the time for the bioplastics to biodegrade. The presence of zeolites in the CMC polymer chains is useful to give nitrogen slow-release composites.

Abstract: The S-doped g-C₃N₄ materials were prepared by heating mixtures of urea and thiourea with various weight ratios at 550 °C, and denoted as x:y SCN, where x:y is weight ratios of urea to thiourea. The obtained samples were characterized by X-ray diffraction, diffuse reflectance ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric differential thermal analysis, scanning electron microscopy and infrared spectra. The results showed that all the x:y SCN materials exhibit the presence of doping S in the structure of g-C₃N₄ and higher capability in the photodegradation of Rhodamin B in aqueous solution under visible light condition than pure g-C₃N₄. Among the SCN samples, 75:25 SCN performed the highest photocatalytic activity, which is believed the presence of the largest amount of doping S in the matrix of g-C₃N₄, leading to reduction of their bandgap. The reduction of bandgap for S-doped g-C₃N₄ materials compared to pure g-C₃N₄ was proved by theoretical calculation.

Abstract: This work demonstrates a simple, reproducible and scalable method of producing a potential slow-release fertilizer material. In this study, oxalate-phosphate-amine metal organic frameworks (OPA-MOFs) powder was synthesized from the hydrothermal treatment of ferric chloride (FeCl3•6H2O), orthophosphoric acid (H3PO4), oxalic acid dihydrate (H2C2O4•2H2O), and a common fertilizer, urea (CO(NH2)2). Being a structure directing agent (SDA)-type of MOF, the material is expected to slowly release urea via cation exchange, and eventually trigger the collapse of the framework, thus resulting to the subsequent release of the phosphates and iron-oxalate complexes. Elemental analysis revealed that the synthesized samples contains a promising amount of incorporated nitrogen and phosphorus. In this particular study, increasing in the amount of urea during the synthesis however revealed minimal change in the %N in the final product which tells us that maximum loading has already been achieved. P and N release experiments shall still be done both in vitro and in actual soil samples to monitor the release delivery kinetics and efficiency of the OPA-MOFs for fertilizer release applications.

Abstract: TiO₂ has become a widely investigated photocatalyst because of its low cost, low toxicity and high photocatalytic activity under UV irradiation that causes photocatalytic decomposition of organic compounds. Impurities dopant and metal are often used to acquire impurities doped or metal doped TiO₂ powder by a sol-gel method. In this paper, we made nitrogen doped TiO₂ by a simple process. TiO₂ (P25) thin films with 80 % of anatase and 20 % of rutile were fabricated on FTO glass by electrophoretic deposition (EPD). These were then doped with nitrogen by using urea and sintered in electric furnace at 500 and 600 degrees Celsius. EPD was superior for film formation at dispersibility. We calculated absorbance spectra of nitrogen doped TiO₂ thin film fabricated on FTO glass. As the result, 600 degrees Celsius is superior sintering temperature at absorbance under visible light than 500 degrees Celsius. Moreover, when the samples sintered at 600 degrees Celsius, each additive amount had different increment of absorbance in specific visible light range. This result indicates the improvement in visible-light response on TiO₂ by the simple process. To further research, it is essential to make nitrogen doped TiO₂ under pressure and measure the photodegradation reaction.

Abstract: Metal foams are a cellular structure that has a solid matrix made of metal and has pores in their structure. Metal foams offer excellent combination of properties which led researchers interested in investigation in recent years. Closed-cell stainless steel (SS316L) foams for biomedical application were prepared by space holder method and the physical and morphological properties of SS316L foams were studied. Stainless steel (SS316L) powders as metallic material, polyethylene glycol (PEG) as a binder and Urea as a space holder material were mixed homogenously to avoid the particle wrecked. This mixture was compacted using uniaxial pressing machine and pressurized to 8 tons to formed the green body. By using tube furnace, the SS316L foams was two-stage sintered, the first phase at 600°C for 2 hours to decompose the urea, and the second phase at 1000°C, 1100°C, and 1200°C respectively to sinter the steel. The porosity and density test was carried out by applying Archimedean principles, while morphological observation was done by using Field Emission Scanning Electron (FESEM). The samples with 40wt.% SS316L composition and sintered at temperature of 1100°C, leads to porosities of about 44.539% and show the potential as the best metal foams.

Abstract: The effect of milling on structure of kaolinite-urea intercalates were studied. Untreated and treated kaolinite samples were examined by Field scanning electron microscopy (FESEM), X-ray powder diffraction (XRPD) and Fourier transform infrared (FT-IR) spectroscopy. The basal spacing of kaolinite measured by X-ray powder diffraction (XRPD) increased from 1.02 to 3.62 nm after intercalation by urea. Significantly, nature of intercalation was reached through formation of hydrogen bonds between urea and both Si-O and AlOH groups of the interlayer surface of kaolinite.

Abstract: The hydrophobicity of starch/PVA blend was improved by crosslinking with boric acid. It was found that the swelling ratio of the boric acid modified starch/PVA matrix decreased as function of boric acid concentration. FTIR spectra and SEM images demonstrated that the urea had been encapsulated in polymer matrix successfully. The urea release characteristic was explained with respect to the swelling ratio and crosslinking density of polymer matrix. In addition, the matrix displayed a good barrier for controlling the release rate of urea from pellet.

Abstract: The objective of this work is to determine the maximum reduction of NO_x emissions by varying the concentrations of urea solution with a reduction catalyst, and optimization of the urea injection by the evaporation of the solution, using the CFD-Fluent solver. An aqueous solution of urea was injected in the engine exhaust pipe for reducing NO_x emissions, in a single cylinder light duty, stationary, four stroke, air cooled DI diesel engine, fuelled with neat diesel and diesel-ethanol blends (10%). The concentration of the urea solution was varied from 30 to 35% by weight with constant flow rates, and tested with a Titanium dioxide (TiO₂) coated catalyst, fitted on the engine exhaust pipe, which controls the by products of ammonia and water vapour. The results indicated that a maximum of 70% NO_x reduction was achieved when the engine was fuelled with diesel-ethanol blends at a constant flow rate of 0.75 lit/hr with an urea concentration of 35%, and also that 66% reduction of NO_x was achieved, using the Titanium dioxide catalyst in the Selective Catalytic Reduction system with neat diesel. From the simulation results,it was seen that only at 75% and 100% load,the evaporation point of the urea solution was higher than that of the boiling point (423 K), due to complete vaporisation of water.

Abstract: Alumina powder dispersions in molten urea medium were prepared using ammonium poly (acrylate) dispersant. The dispersant concentration for achieving very good dispersion of the powder was optimized through rheological measurements. The optimum dispersant concentration for alumina powder dispersion in molten urea (1.25 wt.% of alumina) is higher than that required in aqueous medium (0.35 wt%). The dispersions with alumina loading as high as 55 vol.% having low viscosity could be achieved in molten urea medium at 135 °C. The viscosity and yield stress of the alumina powder dispersions in molten urea is low enough for casting.