Preparation of Hollow Spherical Particles of Strontium Ferrite SrFe12O19 by Spray-Pyrolysis

Refractories and Industrial Ceramics - The synthesis of hollow nanostructured microspheres of strontium ferrite by microspheres is reported. The phase composition, morphology, and particle-size...     

Preparation,characterization and adsorption performance of molecularly imprinted microspheres for erythromycin using suspension polymerization

BACKGROUND: There are few reports on erythromycin molecularly imprinted polymers (MIPs) used as HPLC stationary phase and solid phase extraction matrices. These imprinted polymers are prepared by bulk polymerization, which is tedious and time‐consuming, and they are irregular and possess poor reproducibility and low binding capacity. In this study, molecularly imprinted microspheres for erythromycin were prepared by aqueous suspension polymerization for the first time. RESULTS: Imprinted microspheres for erythromycin were prepared using suspension polymerization in which 1.5% PVA‐water solution is used as continuous phase, and chloroform solution containing erythromycin, methacrylic acid and crosslinker is used as disperse phase. The composition of disperse phase is optimized, and the optimum molar ratio of erythromycin to methacrylic acid was 1:5. Selectivity analysis revealed that the imprinted microspheres can specifically recognize erythromycin from its structure analogues. The binding mechanism between erythromycin and methacrylic acid was investigated by UV‐Vis spectrophotometry. Adsorption kinetics and the adsorption isotherm of the imprinted microspheres indicate that erythromycin can be adsorbed rapidly by the imprinted microspheres and the maximum theoretical static binding capacity is 128.6110 mg g^?1. The imprinted microspheres were used to extract erythromycin from a milk sample and a high recovery rate was obtained. CONCLUSION: Molecularly imprinted microspheres for erythromycin were uniform and possess high adsorption capacity and excellent selectivity. They are therefore a promising extraction and chromatographic media. Copyright © 2011 Society of Chemical Industry     

Novel glass crystal catalysts for the processes of methane oxidation

Novel catalysts were prepared from magnetic microspheres and cenospheres recovered from fuel ashes being formed in combustion of Irsha-Borodinskii lignite and Kuznetskii coal. The specific features of microsphere formation in the coal combustion were discussed. The morphology as well as composition of different magnetic microspheres and cenospheres were studied by SEM, electron probe microanalysis and Mössbauer spectroscopy. The morphology of globules, crystallite size and defect structure of active phase was established to depend on the basicity of the glass phase. It was shown that catalytic activity of magnetic microspheres and cenospheres in the reaction of deep oxidation of methane is determined by the spinel phase and depends on the extent of its accessibility and type of defect structure.     

Study on preparation and process of poly(MMA-St) thermally expandable core-shell microspheres

Thermally expandable microspheres were synthesized by the suspension polymerization of methyl methacrylate (MMA) and styrene (St) in the presence of paraffin blowing agents. The effect of the monomer composition, the initiator, the blowing agent, the polymerization temperature on the morphology and structure of microspheres were studied. The results showed that AIBN initiated the water phase polymerization of MMA to form secondary polymer particles adsorbed on the surface of the microspheres. MMA diffused from the oil phase to the water phase, which accelerated the phase separation and facilitated the formation of core-shell microspheres. However, LPO could not initiate the water phase polymerization, the phase separation was slow and there was an intermediate state with a porous surface. When the boiling point of the blowing agent was lower than the polymerization temperature, the microspheres were porous and there were a large number of holes on the surface.     

相反转乳化—液中干燥法制备线型氯甲基化聚苯乙烯微球

采用相反转乳化—液中干燥法成功制备出在2~40μm粒径可控且分散性较好的线型氯甲基聚苯乙烯(PCM S)微球,考察了搅拌速度、油相/水相比例、乳化分散体系的组成及加入量等因素对微球粒径及粒径分散度的影响;用扫描电子显微镜观察了微球的形貌。研究结果表明,采用相反转乳化—液中干燥法可制备出球形度极好的PCM S微球;搅拌速度、乳化分散体系的组成与加入量对PCM S微球的粒径都有很大的影响,而影响微球粒径分散系数的主要因素是搅拌速度与油相/水相的比例,分散剂的量对分散系数也有很大的影响。     

Preparation of hollow SiC spheres by combustion synthesis

Hollow spherical β-SiC was successfully prepared in argon by combustion synthesis using Si powder and polytetrafluoroethylene (PTFE) powder. The phase composition and morphology of spherical products can be controlled by adjusting the Si/C₂F₄ molar ratio (M_Si/(C2F4)). When M_Si/(C2F4) = 3, the phase content of β-SiC is the highest (up to 85.54%), and hollow spherical products obtained; When M_Si/(C2F4) ≥ 5, the Si/SiC microspheres are solid. The synthesis mechanism of hollow β-SiC microspheres is as follows: Si particles react with PTFE releasing heat. Then unreacted Si absorbs heat to form liquid phase microspheres, which is equivalent to the core template to form β-SiC microspheres by reaction with cracked C. Meanwhile, the silicon diffuses from the core to the shell to form the cavity. This method can synthesize the hollow spherical β-SiC in a simple way without prearranged spherical template and long synthesis cycle.     

Synthesis of biocompatible and degradable microspheres based on 2‐hydroxyethyl methacrylate via microfluidic method

Monodisperse poly(2‐hydroxyethyl methacrylate), p‐HEMA, microspheres in size ranging from 16 to 340 (μm) were synthesized by in situ emulsion photopolymerization of HEMA monomer with polyethylene glycol diacrylate (p‐EGDA) by means of a three‐dimensional microfluidic flow‐focusing device. An aqueous solution of HEMA, p‐EGDA as chain extender and UV‐photoinitiator serving as dispersed phase formed microdroplets in a continuous oil phase mainly consisting of n‐heptane. A downward coaxial orifices design in the device led to confinement of the reaction admixtures thread to central axis of the microchannels. This design strategy could solve the wetting problem of dispersed phase with the microchannels leading to a successful production of monodisperse microspheres with size variation of less than 4%. The effects of concentration of p‐EGDA, surfactant, and flow rate ratios on microsphere size were examined. It was observed that increasing the concentration of p‐EGDA slightly increases the size whereas increasing the flow rate ratios of continuous to dispersed phase effectively decreases the size of microspheres. The rapid continuous synthesis of p‐HEMA based microspheres via the microfluidic route with reliable control over size, size distribution, and composition opens new doors for mass production of biocompatible and degradable polymeric microspheres for enormous biotechnological applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40925.     

Heat-insulating corundum ceramics based on hollow microspheres

A high-temperature heat-insulating porous corundum ceramics is developed based on hollow microspheres produced using the plasma method. The ceramic properties, phase composition, and microstructure of the obtained material are studied. Translated from Steklo i Keramika, No. 3, pp. 15–16, March, 1999.     

膜乳化法与复乳法结合制备粒径均一的PELA载溶菌酶微球

采用快速膜乳化技术与复乳-溶剂去除法制备了尺寸均一的单甲氧基聚乙二醇-聚-DL-乳酸(PELA)载溶菌酶微球,比较了膜材种类和有机溶剂类型对微球中药物包埋率和活性保持的影响. 研究结果表明,该方法能快速制备粒径均一的载药微球,在油相与外水相体积比为1:6的条件下,微球粒径分布系数小于20%,而且该方法对膜材和有机溶剂有很好的普适性. 以PELA为膜材、乙酸乙酯为有机溶剂,采用溶剂扩散法制备的载药微球包埋率高达95.7%,并且能保持高的活性.     

Production of Spherical UO2-UC2 for Nuclear Fuel Applications Using Thermochemical Principles

A process for the fabrication of uranium dioxide-uranium dicarbide microspheres for use as an advanced nuclear fuel is described. The uranium-carbon-oxygen phase diagram was used extensively in applying thermochemical principles to the combined process of uranium carbide synthesis and kernel sintering. Variation of the partial pressure of carbon monoxide during the carbothermic reduction of urania plus carbon allowed the kernel composition and density to be controlled. X-ray diffraction, microstructural examination, and detailed chemical analyses were used to identify the kernel composition. A procedure was developed to convert urania plus carbon microspheres produced by a wet-chemical gelation process to a highly dense UO₂−UC₂ product at 1550°C. Kernels were first treated at 1550°C in Ar-1% CO for 4 h to produce high-density microspheres with a composition of UO₂+UC_x:O_y, (x +y≤1.1). These kernels were then processed at 1550°C for an additonal 4 h in Ar-3% CO to shift the thermodynamic equilibrium from UO₂+UC_xO_y, to the desired UO₂+UC₂. Batches of material containing different initial amounts of carbon were processed to produce high-density microspheres having specific UC₂ contents.     

Monodispersed thermoresponsive hydrogel microspheres with a volume phase transition driven by hydrogen bonding

We report the synthesis and characterization of monodispersed thermoresponsive hydrogel microspheres with a volume phase transition driven by hydrogen bonding. The prepared microspheres, composed of poly(acrylamide-co-styrene) (poly(AAM-co-St)) cores and poly(acrylamide)/poly(acrylic acid) (PAAM/PAAC) based interpenetrating polymer network (IPN) shells, were featured with high monodispersity and positively thermoresponsive volume phase transition characteristics with tunable swelling kinetics, i.e. the particle swelling was induced by an increase rather than a decrease in temperature. The monodisperse poly(AAM-co-St) seeds were prepared by emulsifier-free emulsion polymerization, the PAAM or poly(acrylamide-co-butyl methacrylate) (poly(AAM-co-BMA)) shells were fabricated on the seeds by free radical polymerization, and the core-shell microspheres with PAAM/PAAC based IPN shells were finished by a method of sequential IPN synthesis. The microsphere size increased with increasing both AAM and BMA dosages. The increase of hydrophilic monomer AAM dosage resulted in a better monodispersity, but the increase of hydrophobic monomer BMA dosage led to a worse monodispersity. With increasing the crosslinker methylenebisacrylamide (MBA) dosage, the mean diameter of the microspheres decreased and the monodispersity became better. An equimolar composition of AAC and AAM in the IPN shells of the microspheres resulted in a more complete shrinkage for the microspheres at temperatures lower than the upper critical solution temperature. Both BMA and MBA additions depressed the swelling ratio of the hydrodynamic diameter of the microspheres.     

Flow characteristics of thermo‐responsive microspheres in microchannel during the phase transition

To probe into the flow and aggregation behaviors of thermo‐responsive microspheres in microchannel during the phase transition, the flow characteristics of monodisperse poly(n‐isopropylacrylamide) (PNIPAM) microspheres in microchannel with local heating are investigated systematically. When the fluid temperature in the microchannel increases across the lower critical solution temperature (LCST), the PNIPAM microspheres finish the phase transition within 10 s and are easily get aggregated during the phase transition. The diameter ratio of microsphere to microchannel, number of microspheres, initial distance between microspheres, and flow direction of fluid in microchannel, are key parameters affecting the flow and aggregation behaviors of the microspheres in microchannel during the phase transition. If a proper combination of these parameters is designed, the microspheres can aggregate together during the phase transition and stop automatically at a desired position in the microchannel by local heating, which is what the targeting drug delivery system expected. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

油页岩灰渣制备空心陶瓷微球及机理探讨

以油页岩灰渣为实验原料,利用火焰喷枪熔射法制备了空心陶瓷微球.采用TG-DSC对油页岩灰渣进行热分析,采用SEM和XRD分别对油页岩灰渣和空心陶瓷微球的微观形貌和物相组成进行分析.研究结果表明,利用火焰喷枪熔射法制备的微球绝大多数为球状,极少部分为不规则形状,微球破碎后可发现其为空心结构;空心微球的形成机理为:油页岩灰渣粉末受热熔化、发气物质形成气泡、气泡合并、降温凝固、最终形成空心微球;油页岩灰渣自身疏松的结构、所含充足的发气物质和适宜的熔射温度是形成微球空心结构的重要因素.     

Preparation of polymer‐supported polyethylene glycol and phase‐transfer catalytic activity in benzoate synthesis

The crosslinked polymeric microspheres (GMA/MMA) of glycyl methacrylate (GMA) and methyl methacrylate (MMA) were prepared by suspension polymerization. Polyethylene glycol (PEG) was grafted on GMA/MMA microsphers via the ring‐opening reaction of the epoxy groups on the surfaces of GMA/MMA microspheres, forming a polymer‐supported triphase catalyst, PEG‐GMA/MMA. The Phase‐transfer catalytic activity of PEG‐GMA/MMA microspheres was evaluated using the esterification reaction of n‐chlorobutane in organic phase and benzoic acid in water phase as a model system. The effects of various factors on the phase transfer catalysis reaction of liquid–solid–liquid were investigated. The experimental results show that the PEG‐GMA/MMA microspheres are an effective and stable triphase catalyst for the esterification reaction carried out between oil phase and water phase. The polarity of the organic solvent, the ratio of oil phase volume to water phase volume and the density of the grafted PEG on PEG‐GMA/MMA microspheres affect the reaction rate greatly. For this investigated system, the solvent with high polarity is appropriate, an adequate volume ratio of oil phase to water phase is 2:1, and the optimal PEG density on the polymeric microspheres is 15 g/100 g. Triphase catalysts offer many advantages associated with heterogeneous catalysts such as easy separation from the reaction mixture and reusability. The activity of PEG‐GMA/MMA microspheres is not nearly decreased after reusing of 10 recycles. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Synthesis and characterization of hollow glass–ceramics microspheres

Hollow glass–ceramics microspheres (HGCM), with the diameter from 10 μm to 60 μm and the shell thickness less than 2 μm, were successfully fabricated by a simple technique using polyacrylamide microspheres (PAM) as template. The corresponding HGCM were obtained by a thermal treatment of the core–shell microspheres, which were synthesized with organic template method. The size, morphology and phase composition of synthesized products were determined via XRD, SEM, TGA. The effects of the amount of glass powder, the Hydrophile–Lipophile Balance (HLB) value, the sintering temperature, and the ratios of pre-adsorbed water and the water in the slurry on the morphologies of HGCM have been investigated. The results showed that the agglomeration of HGCM can be reduced by adjusting the HLB value. In addition, the amount of solid beads decreases obviously by reducing ratios and adjusting the HLB value. As the sintering temperature increases, the surface of the HGCM becomes smooth and compact.     

Preparation of Magnetic Porous Microspheres and Their Ability to Remove Oils

Magnetic, porous poly (tripropylene glycol diacrylate) (PTPGDA) microspheres are successfully prepared using a combination of microfluidic emulsification and free‐radical polymerization. The porous structure can be precisely controlled by controlling the amount of the oil‐phase emulsifier polyglycerol polyricinoleate (PGPR). The effects of PGPR content and pH on the contact angle of the microspheres is investigated. The contact angle of the microspheres increases with the raise of PGPR content, and the hydrophobicity of the microspheres remains stable at different pHs. The microstructure, magnetic properties, and oil adsorption abilities of the microspheres are also studied. The as‐prepared microspheres perform adsorption well, the higher the PGPR content, the more pore structures and larger contact angle occurres on the microspheres, which improves the adsorption capacity. In addition, the adsorption capacity of the microspheres for diesel can reach 3.38 g·g^?1 when the mass fraction of PGPR in oil phase is 50% w/v. After adsorbing oil, the microspheres can be separated, recovered, and reused by applying an external magnetic field. The magnetic microspheres have good oil adsorption abilities and recyclability, which shows their potential for use in oil removal.     

Preparation of calcium hexaluminate porous ceramics by gel-casting method with polymethyl methacrylate as pore-forming agent

Calcium hexaluminate (CA₆) porous ceramics were prepared by gel-casting method, with α-Al₂O₃ and CaCO₃ as raw materials and polymethyl methacrylate (PMMA) microspheres as pore-forming agent. The effects of the amount of pore-forming agent PMMA microspheres on the phase composition, bulk density, apparent porosity, flexural strength, microstructure, thermal shock stability and thermal conductivity of CA₆ porous ceramics were systematically studied. The pores of CA₆ porous ceramics are mainly formed by the burning loss of PMMA microspheres and the decomposition of organic matter. Adding an appropriate amount of PMMA microspheres as pore-forming agent has a positive effect on the thermal shock stability of CA₆ porous ceramics. When the amount of pore-forming agent is 15 wt%, the volume density of CA₆ porous ceramics is 1.33 g/cm³, the porosity is 63%, the flexural strength is 13.9 MPa, the thermal shock times can reach 9 times, and the thermal conductivity is 0.293 W/(m·K), which can meet the application in refractory, ceramics or high temperature cement industries.     

A novel SiCN@TiO2 core–shell ceramic microspheres derived from a polymeric precursor

A novel core–shell ceramic microspheres, composed of a SiCN inner core and TiO₂ nanoparticles outer shell, were prepared via emulsion technique and polymer-derived ceramics (PDCs) method. The forming process of SiCN@TiO₂ core–shell ceramic microspheres were controlled by adjusting the ratio of raw material, curing temperature and pyrolysis temperature. The morphology, chemical composition and phase transformation were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). PVSZ@TiO₂ microspheres with good spherical structure and uniform-dispersed TiO₂ surface were fabricated at 200 °C with raw material ratio of 25%. After pyrolyzed at 1400 °C, the obtained SiCN@TiO₂ core–shell ceramic microspheres retained spherical structure. The XRD showed that the products were mainly composed of rutile TiO₂, SiC and Si₃N₄ crystalline phase, which were generated by polyvinylsilazane.     

旋转膜乳化法制备均一魔芋葡苷聚糖凝胶微球

以天然多糖魔芋葡苷聚糖(KGM)为材料,采用旋转膜乳化法结合化学交联法制备均一的魔芋葡苷聚糖凝胶微球,以3种不同粘度的12%(w) KGM水溶液为分散相(水相)、液体石蜡(LP):石油醚(PE)混合油相为连续相,考察了乳化剂种类对KGM乳液稳定性的影响及水相粘度、油相配比和膜管转速对KGM成球的影响. 结果表明,KGM水相粘度越高,相应的最佳油相粘度越低,最佳KGM水相粘度为1548 mPa×s,最佳油相体积比为LP:PE=5:1,最优膜管转速为400 r/min,利于KGM乳液稳定的乳化剂是4%(w) Span 80. 该条件下制得粒径约70 μm、粒径分布系数Span<1.0的均一KGM微球.     

Dependence of morphological changes of polymer particles on hydrophobic/hydrophilic additives

Fairly uniform microspheres of poly(styrene‐co‐methyl methacrylate) were prepared by employing a microporous glass membrane [Shirasu porous glass (SPG)]. The single‐step SPG emulsification, the emulsion composed mainly of monomers, hydrophobic additives, and an oil‐soluble initiator, suspended in the aqueous phase containing a stabilizer and inhibitor, was then transferred to a reactor, and subsequent suspension polymerization followed. The droplets obtained were polymerized at 75°C under a nitrogen atmosphere for 24 h. The uniform poly(styrene‐co‐methyl methacrylate) microspheres with diameters ranging from 7 to 14 μm and a narrow particle‐size distribution with a coefficient of variation close to 10% were prepared by using SPG membrane with a pore size of 1.42 μm. The effects of the crosslinking agent and hydrophobic additives on the particle size, particle‐size distribution, and morphologies were investigated. It was found that the particle size decreased with a narrower size distribution when the additives were changed from long‐chain alkanes to long‐chain alcohols and long‐chain esters, respectively. Various microspheres with different morphologies were obtained, depending on the composition of the oil phase. The spherical poly(styrene‐co‐methyl methacrylate) particles without phase separation were obtained when using an adequate amount of the crosslinking agent and methyl palmitate as an additive. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1013–1028, 2000