Papers by Author: Xiao Xi Li

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Authors: Xiao Xi Li, Ling Chen, Jian Dong Ye, Lin Li, Yan Ran Huang
Abstract: A new consolidation in-situ forming process for high-performance alumina ceramic using acetate starch was investigated. The pasting behavior and thermogelling properties of acetate starch and the effects of different amount of acetate starch and solid loading on the rheologic behavior of the ceramic slip, as well as the linear shrinkage, density, strength and microstructure of the green body were discussed. The results indicate that acetate starch paste has good thermal stability and gelling ability. When the content of acetate starch is about 0.5%~1.5% (mass fraction), the apparent viscosity of alumina slurry, which is always less than 1Pa·s even for 58% (volume fraction) dense suspension, increased with increasing the acetate starch content and solid loading. That results in easier to cast. Moreover, with the increasing of solid loading the linear shrinkage and dry strength of green bodies decreased and the relative density increased. With the increasing starch content, the linear shrinkage rate and the density of the dried body decreased, while the strength of the dried body almost linearly increased. The green body with homogeneously-distributed density and pore size was also obtained in this work. It is concluded that Al2O3 ceramics can be consolidation in-situ formed based on the gelling network of thermally swelled and gelatinized acetate starch.
Authors: Ling Chen, Xu Peng, Yun Huang, Lin Li, Xiao Xi Li
Abstract: Porous ceramic materials usually require an optimal porosity and pore-size distribution to maximize the yield of the required function. In the starch consolidation forming for porous ceramic materials, the porosity and pore size distribution are corresponding closely to the particle size and swelling property of starch. In order to control the porosity and pore size distribution of the porous alumina ceramics, different modified starches with different amounts were added to the alumina slurry with a 58 vol% alumina solid volume loading. The effects of different modified starches and their content on the rheological behavior of the alumina slurry and the porosity, pore size distribution, compressive strength and microstructure of the sintered body were investigated. The results indicated that alumina/starch composite slurry still maintain stable and plastic in suitable condition of slurry preparation. After drying and sintering, materials with ultimate porosities between 22.7 and 68.7% were obtained. The pore of the resulting materials distributed uniformly and the average size was varied from 10 to 40μm. It concluded that the average size was controlled by the modified starch type, amount and the degree of modification. When the amount of the modified starches was reached to 60 vol% the porosities of the sintered samples were varied from 63.5 to 68.7% with different modified starch type and their bending strength varied within the range of 24-32 MPa.
Authors: Ling Chen, Hong Xiang, Xiao Xi Li, Jian Dong Ye, Xiu Peng Wang, Lin Li, Xi Mei Zhang
Abstract: In this study modified starch were used as anti-washout promoters of injectable calcium phosphate cement (CPC) and the effects of the modified starch on the injectability, anti-washout performance, setting time, compressive strength, phase evolution and microstructure of this cement were investigated. The injectability of the cement was improved by adding the modified starch (0.5-2.0%). After mixing with modified starch (0.5-2.0%), the cement showed better anti-washout performance than that without modified starch after immersed and shaken in SBF. Especially, when the content of the modified starch was 1.0%, the remaining percentage of the cement was reached to 92.6%, but only 5.9% of the CPC paste remained and set for the sample without modified starch after shaken for 2 hrs. The compressive strength of cements significantly increased from 44 MPa to 54 MPa when 0.5% of modified starch was added. And a slight increase on the mechanical strength can be observed for other concentrations. Powder X-ray diffraction analysis revealed no significant difference for the conversion of the cement to hydroxyapatite for any concentrations of modified starches. The influence of the modified starch on the microstructure of the set cement was also studied. The results showed the modified starch would reduce the acicular crystal size of hydroxyapatite accompanied with little flaky crystals generation and made a compact structure. It is concluded that modified starch, a suitable anti-washout promoter, improved the performance of CPC.
Authors: Xia Zhang, Lin Li, Jian Rong Huang, Ling Chen, Xiao Xi Li, Guo Qin Liu, Bing Li
Abstract: Naringin esters are paid more attention in medical and functional food industry than naringin due to their higher stability and solubility in lipidic environments. Naringin palmitic acid esters were enzymatically synthesized with naringin and palmitic acid. The effects of solvent type, temperature, concentration and types of enzymes and the molar ratio of substrates on the conversion of naringin were investigated. Novozym 435 performed higher catalytic ability in tert-amyl alcohol in the esterification of naringin with palmitic acid. The conversion yield of naringin increased with the increase of temperature (30-70°C) and of the concentration of enzyme. The structure of the naringin palmitate was characterized by FT-IR, 1H-NMR and HPLC-MS. 1H-NMR spectroscopic analysis indicated the presence of an ester bond on the C-6 of the glucose moiety of naringin molecule.
Authors: Ling Chen, Xiao Xi Li, Lin Li, Bing Li
Abstract: Colon-targeting drug delivery systems (CDDSs) are employed to improve the bioavailability of protein and peptide drugs through the oral route. So it is important to prepare the drug carriers for oral CDDS. In this study, the Enzyme-Resistant starch (RS) was studied for use as a vehicle in oral colon-targeting drug delivery. The characteristics of RS powders were investigated by X-ray diffraction, polarizing microscopy, DSC and SEM, and their film were examined by enzymatic digestion test. The results showed that RS could be a promising film-former for pharmaceutical coatings, having good stability to enzymatic digestion. Furthermore, a novel peroral formulation using RS coating and bovine serum albumin as a model drug was studied for colon-specific drug delivery in vitro. Drug release studies have shown that RS coating could delivery the drug to the colon and the release rate in simulated colonic fluids was dependent on the biodegradation of RS and its coatings. It is indicated that the RS coated tablet is a potential system for oral CDDS.
Authors: Ling Chen, Hong Xiang, Xiao Xi Li, Jian Dong Ye, Xiu Peng Wang, Lin Li
Abstract: Calcium phosphate cements (CPCs) are well-known orthopedic materials for filling bone. However, CPC pastes tend to disintegrate immediately when contacting with blood or other aqueous (body) fluids, which is a main limitation of its clinical applications in bone repairing, reconstruction and augmentation. To improve the anti-washout performance of CPC, modified starches such as pre-gelatinized starch, etherified starch, and esterified starch were added to the liquid phase of CPC in this work. CPC with good anti-washout performance was prepared and the effects of the modified starches on the properties of CPC were investigated. The results showed that the CPC with the modified starches were more stable in simulated body fluid than that without modified starch, especially the CPC with the etherified starch (II). X-ray diffraction analysis revealed that the modified starches did not inhibit CPC components from converting to hydroxyapatite. Furthermore, the anti-washout mechanism of the modified starches in CPC was discussed. It is concluded that the addition of the modified starches such as pre-gelatinized starch, etherified starch, and esterified starch to CPC can improve its anti-washout performance and should be of value in clinical surgery where the cement is exposed to blood.
Authors: Bing Li, Hui Ling Zhong, Hong Jie Li, Ling Chen, Lin Li, Xiao Xi Li
Abstract: Artificial neural networks have been successfully used in classification, formulation optimization, defect diagnosis and performance prediction in ceramic industry. However, an artificial neural network based on the traditional backpropagation (BP) algorithm showed some disadvantages in mapping the nonlinear relationship between the composition and contents of the ceramic materials and their properties. In this paper, a new PSO-Grain (Particle Swarm Optimization Gain) BP algorithm was introduced, and an improved artificial neural network model was employed to predict the properties of an alumina green body. The training performance of the neural network using the PSO-Gain BP algorithm was analyzed and it was indicated the POS-Gain BP based neural network could reduce convergence to local minima and was more efficient than the traditional BP based network. The prediction accuracy of the properties such as linear shrinkage and bending strength using the PSO-Gain BP based neural network was higher than that of the BP based neural network.
Authors: Xiao Xi Li, Ling Chen, Bing Li, Lin Li
Abstract: Zirconia nanopowders were prepared in the ultrasonic field by the sol-gel method and the sonochemical effect on the structure of zirconium hydroxide and the zirconia nanopowder properties were systematically investigated in this work. Ultrasound was introduced into the different stages of the synthesis of zirconia nanopowders in sol-gel reaction system, and zirconium hydroxides and the zirconia nanopowders with different properties were obtained. The results indicated that ultrasonic cavitation could not only disaggregate the agglomerates of zirconia colloidal particles but also reduce the amount of coordinated H2O, free H2O and free hydroxyl groups of the zirconium hydroxide colloidal particles, thus effectively preventing the formation of hard agglomerates in zirconia powders. Moreover, the effects of different ultrasonic output powers and treatment cycles on the structure and properties of ZrO2 nanopowders were studied by TEM, XRD and SAXS. Zirconia nanopowders with an extremely small crystallite size (10.3 nm) and a narrow size distribution were yielded with 520 W ultrasound for 6 treatment cycles on the formation period and 600 W ultrasound for 2 treatment cycles on the washing period. It is concluded that the ultrasonic field is a potential method for nanopowder preparation.
Authors: Yun Huang, Ling Chen, Jian Dong Ye, Xiao Xi Li, Xi Mei Zhang, Chen Hui Ju
Abstract: A modified starch was employed to be the pore former in the in-situ consolidation forming process of porous alumina ceramic. In order to prepare ceramic slurry with high dispersion, high stabilization and high solid volume loading, the effects of modified starch content, dispersant content, alumina solid volume loading, pH value of the slurry and ball milling time on the rheological behavior of alumina ceramic slurry were investigated. The results indicated that the viscosity of the slurry increased with the modified starch content, alumina solid volume loading and ball milling time. When the pH value of the slurry was 9.0, the modified starch-alumina slurry exhibited high fluidity. The modified starch-alumina slurry was a pseudoplastic fluid exhibiting shear thinning behavior. The slurry possessed a desirable plasticity to enable shape forming when adding 50 vol% modified starch and 1.0 wt% dispersant to the alumina slurry at pH 9.0 after 14 h ball milling treatment.
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