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Ultrafine Powder (ultrafine + powder)
Selected AbstractsPolycarbonate microspheres containing tumor necrosis factor-, genes and magnetic powder as potential cancer therapeuticsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Bin Hu Abstract Amphiphilic polycarbonate copolymers including methoxy-terminated poly(ethylene glycol)- co -poly (5,5-dimethyl trimethylene carbonate) [Poly(PEG- b -TMC)] and poly(ethylene glycol)- co -poly(trimethylene carbonate) [Poly(PEG- b -DTC)] were synthesized. The water-in-oil-in-water (W/O/W) solvent evaporation technique was adopted to produce anticancer magnetic Poly(PEG- b -DTC) microspheres containing tumor necrosis factor-, (TNF-,) genes and Fe3O4 magnetic ultrafine powder. Drug release studies showed that the microspheres can sustain a steady release rate of TNF-, genes in 0.1M phosphate buffer saline solution in vitro for up to 60 h. In vitro cytotoxicity assays demonstrated that the microspheres have high inhibition and antitumor action to human hepatocellular carcinoma (Bel-7204) cells in vitro. In vivo inhibition on the growth of hepatic carcinomas and histopathologic observation indicated that the microspheres possess a markedly high antitumor activity to human hepatocellular carcinoma (Bel-7204). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Novel Nanosized Aluminium Carboxylates: Synthesis, Characterization and Use as Nanofillers for Protective Polymeric CoatingsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 1 2007Hans-Jürgen Gläsel Abstract A mixture of novel aluminium carboxylate nanoparticles and aluminium hydroxide ultrafine powder was prepared via precipitation reaction between Al(2-PrO)3 and maleic acid. In this mixture both free primary particles occur (mean geometrical size around 40 nm) together with a secondary agglomerated particle fraction of sizes in the low micrometer region. However, centrifugation processes allowed for the removal of the latter and resulted in the formation of size stable nanopowders. Up to 30 wt.-% of these particles were incorporated into acrylate matrices resulting in low-viscosity formulations with [,],<,1,000 mPa,·,s, which allowed for roller application and even spray coating of these nanocomposites at room temperature. Radiation curing of such coatings was accomplished via UV irradiation. In comparison to the corresponding SiO2 -based nanocomposites and carboxylate alumoxane fillers, the cured coatings revealed significantly improved surface mechanical properties. [source] Influence of the COOH and COONa groups and crosslink density of poly(acrylic acid)/montmorillonite superabsorbent composite on water absorbencyPOLYMER INTERNATIONAL, Issue 9 2001Jihuai Wu Abstract A novel poly(acrylic acid)/montmorillonite superabsorbent composite with a water absorbency of 1100 times its own weight was synthesized by the graft copolymerization of acrylic acid with a cross-linking agent in the presence of montmorillonite ultrafine powder. The influence of the amount of crosslinker and montmorillonite on water absorbency has been investigated. It was found that a crosslinker concentration of 0.03,wt% and 30,wt% montmorillonite gave the best results. The collaborative absorbent effect of sodium carboxylate and carboxylic acid groups was superior to that of sodium carboxylate or carboxylic acid groups alone, and the composite with a ratio of about 2/3 for sodium carboxylate to carboxyl acid groups possessed the highest water absorbence. © 2001 Society of Chemical Industry [source] Solid-State Synthesis of Nanocrystalline BaTiO3: Reaction Kinetics and Powder PropertiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2008Maria Teresa Buscaglia The formation of BaTiO3 nanoparticles by a solid-state reaction between nanocrystalline raw materials BaCO3 and TiO2 was studied as a function of temperature (400°,800°C), time (1,24 h), and titania particle size (15 and 30 nm). The reaction starts at 500°C and a high reaction rate is already observed at 600°C for the finest titania, with up to 90% conversion after 2 h. Two main reaction stages were observed at 600°,700°C. The first step is dominated by nucleation and growth of BaTiO3 at the TiO2,BaCO3 contact points and at the TiO2 surface. Surface diffusion of BaCO3 is, most likely, the prevailing mass transport mechanism responsible for the rapid formation of BaTiO3, even in the absence of a significant contribution from lattice diffusion. The second stage begins when the residual TiO2 cores are completely covered by the product phase. For longer times, the reaction can only proceed by the slower lattice diffusion, resulting in a strong decrease of the reaction rate. Single-phase BaTiO3 nanopowders with a specific surface area of 12,15 m2/g, an average particle size of 70,85 nm, a relative density of 96.5%,98.3%, and a tetragonality of 1.005 were obtained by calcination at 700°,800°C. Critical parameters in the preparation of ultrafine powders by solid-state reactions are the particle size of both raw materials, the absence of large hard agglomerates, and the homogeneity of the mixture. The use of fine raw materials and optimization of the reaction conditions make mechanical activation unnecessary. [source] Crystallite and Grain-Size-Dependent Phase Transformations in Yttria-Doped ZirconiaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2003Arun Suresh In pure zirconia, ultrafine powders are often observed to take on the high-temperature tetragonal phase instead of the "equilibrium" monoclinic phase. The present experiments and analysis show that this observation is one manifestation of a much more general phenomenon in which phase transformation temperatures shift with crystallite/grain size. In the present study, the effect of crystallite (for powders) and grain (for solids) size on the tetragonal , monoclinic phase transformation is examined more broadly across the yttria,zirconia system. Using dilatometry and high-temperature differential scanning calorimetry on zirconia samples with varying crystallite/grain sizes and yttria content, we are able to show that the tetragonal , monoclinic phase transformation temperature varies linearly with inverse crystallite/grain size. This experimental behavior is consistent with thermodynamic predictions that incorporate a surface energy difference term in the calculation of free-energy equilibrium between two phases. [source] | ||||||||||