Papers by Keyword: Chemical Precipitation

Abstract: Hematite (α-Fe₂O₃) is a low-cost n-type semiconductor with significant absorption of visible light owing to its low bandgap energy of 2.1 eV. The wide applications of hematite in renewable energy and environmental remediation continuously entice more studies. However, the low absorbance of solar energy in the UV-range significantly limits the efficiency of many photocatalytic materials. In this study, we tried to dope α-Fe₂O₃ with silver via chemical precipitation method to lower the bandgap energy and widen its absorbance. The effects of doping hematite with Ag on the structure, morphology, elemental composition, and optical absorbance were determined by characterizing the samples via X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, and UV-Vis spectroscopy, respectively. It was observed from the XRD patterns that the α-Fe₂O₃ crystallizes in hexagonal structure with lattice parameters a = 5.0380 Å and c = 13.7720 Å for the pure α-Fe₂O₃. Doping with 0.1M and 0.2M AgNO₃ leads to a greater value of the lattice parameters indicating successful doping. SEM images show that the hematite formed was composed of particles with irregular shapes that have sizes in the range 0.865-0.883 μm. Excess silver particles were deposited on the surface of hematite. UV-Vis spectra show that there is a red-shift in the absorption band of the Ag-doped hematite. A notable decrease in the bandgap energy of the undoped α-Fe₂O₃ was observed from ~2.2eV to ~2.0eV with the increase in the amount of the dopant in the hematite as determined using Tauc’s plot.

Abstract: In this study, an industrial method is provided for the synthesis of zinc oxide (ZnO) nanoparticles by a simple and economical wet chemical precipitation reaction between Zinc Chloride (ZnCl2) and Sodium Hydroxide (NaOH) at low temperatures less than 80 °C. In first step, Small quantity of ZnO powder is produced in laboratory scale. As-synthesized lab-scale ZnO powders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Orthogonal experiments were performed to find out the optimal conditions for the maximum yield of ZnO powder. In second step, the process flow diagram (PFD), material & energy balance and design of reactor were done on the basis of lab-scale data. Overall, this research work proposes that ZnO powder can be manufactured easy and economical method which can be used for various branches of industry: rubber, pharmaceutical, cosmetics, textile, electronic etc.

Abstract: The possibility of receiving of compositional Ni-P coating modified by potassium polytitanate was analyzed. An aqueous solution to obtain the composite coatings on the basis of nickel-phosphorus alloy modified by K₂О·nTiO₂ onto steel details of the friction knots was developed. The complex oxide K₂О·nTiO₂ represents a layered material from the scaly form nanocrystals with 20-80 nm thick and "diameter" 280 nm. The velocity forming of the modified compositional Ni-P coating was investigated, and the optimal quantity of the introduced potassium polytitanate (8 g/l), as a modified compound into solution, was determined, too. The tribological characteristics and micro-hardness of the resulting coatings depending on the chemical composition of solution and surface state of the rider were investigated.

Abstract: 0.1% Ce³⁺:BaF₂ powders were prepared by coprecipitation method. Then the transparent ceramics were prepared by vacuum sintering. The effectts of sintering temperature and holding time on transparent ceramics were studied. The results show that the 0.1% Ce³⁺:BaF₂ powders prepared by coprecipitation are approximately spherical with the size ranging from 200~300nm and good dispersion. The maximum light transmittance of the 0.1% Ce³⁺:BaF₂ transparent ceramics reaches 69.2% when the sintering temperature is 1275°C. The fluorescence intensity of the transparent ceramics enhances with the increase of the sintering temperature. There are two characteristic f-f transition emission peaks at 610nm and 650nm when the excitation peak is at 290nm. The maximum transparency of 71.4% emerges when the holding time is 6h at 1275°C and the fluorescence intensity reaches the maximum. The 528nm (⁵D₁→²F_7/2) appears when excitated by the 524nm excitation light.

Abstract: Nickel dispersion, which provides total catalytically active metal surface, is significant for partial catalytic oxidation of natural gas to obtain high purpose products yield and productivity in syngas. The interaction of reaction medium under high reaction temperatures during 20-25 hours promotes the increase of total square of active Ni component for block catalysts obtained with self-propagating high-temperature synthesis, which allows achieving productivity in syngas 7.1·10³ cm³ (syngas)/cm³(catalyst)·hour. It is observed that for catalyst systems obtained with precipitation, chemical composition of oxide phase influences the particles size of metal nickel. For granular catalysts obtained through precipitation after 25-hour exploitation, average particle size (according to CSR) metal nickel is 3-4.5 times smaller than Ni in catalysts obtained with self-propagating high-temperature synthesis. This allows achieving productivity in syngas 8.1·10³ cm³/сm³·hour, when there is average temperature decrease over the catalytic layer by ~100°С in comparison with blocks acquired through self-propagating high-temperature synthesis.

Abstract: The marine oil and gas transmission pipelines should be washed by phosphoric acid solution before they were used. The washing wastewater, containing high level of phosphorus, was treated by calcium chloride. The response surface method (RSM) based on Box-Behnken was adopted to consider the impact of n (Ca):n (P), pH and reaction temperature on total phosphorus (TP) removal rate. In this work, the Design-Expert 8.0.6 was employed to design and analyze the results. Then, a quadratic polynomial model was built with TP removal rate as the response value. It was shown that the n (Ca):n (P) and pH have a significant effect on TP removal rate. The interaction of pH and temperature is significant. The optimum conditions were X₁=3.40, X₂=10.97, X₃=38.12. In this condition, the predicted value of TP removal rate is 99.9242% while the average removal rate of verification is 99.9365%, which was shown that the predicted value was identical with experiment value.

Abstract: Hydroxyapatite (HAp) is a kind of bioceramic based material that has been used extensively in many medical applications. Owing to nearly similar mineral contents to natural bone, the material has been accepted as an implant in order to improve the osteointegration with the bone tissue. In this work, an alternative processing route from waste materials, namely clamshell in producing HAp powder is presented. The effects of processing temperatures, ranging from 750°C to 950°C and pH values, ranging from 6.5 to 8.5 on the synthesized HAp prepared via chemical precipitation method were investigated. From the XRD, FTIR and EDX results, it was observed that the lowest pH value of 6.5 with the temperature of 850°C is the optimum parameters to synthesize HAp.

Abstract: The chemical precipitation method was combined with the membrane separation to treat the simulated radioactive wastewater containing strontium in the paper. The calcium carbonate powder was used to prepare the seed and the sodium carbonate was selected as the precipitant. Sr²⁺ and CO₃^2- constantly crystallized on the seed surface in the granulation reactor. FeCl₃ was dosed in the subsequent membrane separator. The average concentrations of strontium in the raw water and in the effluent were 5.046 mg/L and 0.028 mg/L, respectively. The DF increased gradually with the operation time, with an average value of 279. After the test, the formed precipitate was easy to separate from the liquid and was directly discharge after sedimentation for 24 h. The CF was 3170. The membrane specific flux decreased rapidly in the early stage and then declined slowly with the operation time.

Abstract: Leather processing is an important industry in China, and the discharge of chromium waste has been severely circumscribed. Though traditional processes for treating chromium waste have been widely used in tannery plants, technology adopting high efficiency and economic simultaneously is deficient. In order to develop an economic treatment for tannery waste, a mixed alkali of sodium hydroxide and magnesium oxide and diluted mineral acids were tested to improve the sedimentation effect of trivalent chromium from tannery wastewater. The results showed that the most feasible alkali was a mixture of sodium hydroxide and magnesium oxide with a mass ratio of 5:1 to balance the cost performance. The high chromium removal as 99.1% was obtained with a mixed alkali dosage only 0.2 g/L at pH 9.5, with a very low Cr-sludge yield. The effects of various factors on the extraction of trivalent chromium from Cr-sludge using mineral acids were investigated further more, and the results indicated that the feasible condition for chromium recovery from wet chromium sludge was as follows: 4% sulfuric acid as the leaching acid, chromium sludge (dry weight) load 23.55 g/L, extraction time 60 min, and reaction temperature 30°C. A chromium recovery of 20.86 mg/g was obtained under the feasible condition with a recovery rate of 91.8%. The method developed in the present study provided an effective solution to balance the cost performance for tannery waste treatment.

Abstract: Nano SiO₂/ cenoshpere composites were prepared to obtain the core-shell structure by chemical precipitation and heterogeneous nucleation. This kind of composites can be further used to fabricate super-hydrophobic surface. In this study, industrial fly ash cenoshpere and water glass solution were used as raw materials. The aim was to coat a layer of Nano SiO₂ on the surface of cenosphere. By tests of SEM, XRD, FTIR, XPS, the mechanism of coating process was discussed. Treat the composites with KH-570, and then use this kind of particles to prepare super-hydrophobic surface.