Formation Of Hard Agglomerates Research Articles

Low-Temperature Synthesis of Hollow β-Tricalcium Phosphate Particles for Bone Tissue Engineering Applications.

β-Tricalcium phosphate (β-TCP) has been extensively used in bone tissue engineering in the form of scaffolds, granules, or as reinforcing phase in organic matrices. Solid-state reaction route at high temperatures (>1000 °C) is the most widely used method for the preparation of β-TCP. The high-temperature synthesis, however, results in the formation of hard agglomerates and fused particles which necessitates postprocessing steps such as milling and sieving operations. This, inadvertently, could lead to introducing unwanted trace elements, promoting particle shape irregularity as well as compromising the biodegradability and bioactivity of β-TCP because of the solid microstructure of particles. In this study, we introduce a one-pot wet-chemical method at low temperatures (between 160 and 170 °C) to synthesize hollow β-TCP (hβ-TCP) submicron particles of an average size of 300 nm with a uniform rhombohedral shape. We assessed the cytocompatibility of the hβ-TCP using primary human osteoblasts (HOB), adipose-derived stem cells (ADSC), and antigen-presenting cells (APCs). We demonstrate the bioactivity of the hβ-TCP when cultured with HOB, ADSC, and APCs at a range of particle concentrations (up to 1000 μg/mL) for up to 7 days. hβ-TCP significantly enhances osteogenic differentiation of ADSC without the addition of osteogenic supplements. These findings offer a new type of β-TCP particles prepared at low temperatures, which present various opportunities for developing β-TCP based biomaterials.

Investigation of the influence of the mode of heat treatment of the initial powder on the efficiency of sintering zirconium ceramics by dilatometry

Using methods of synchronous thermal and X-ray structural analyzes applied to zirconium dioxide powders partially stabilized with yttrium obtained by chemical coprecipitation the processes of dehydration of these powders during annealing in air have been investigated. Using the dilatometry method, the regularities of compaction of powder compacts have been investigated with thermal sintering. It was found that the resulting powders mainly consist of the tetragonal modification zirconium dioxide and are nano-sized. The average particle size was 25 nm. The resulting powders are characterized by a high degree of agglomeration. It is shown that an increase in the thermal annealing temperature from 500 to 700ºС leads to partial baking of individual particles inside the agglomerate, and causes the formation of hard agglomerates, the presence of which complicates the processes of compaction and subsequent sintering. The presence of such agglomerates prevents the production of ceramics with high mechanical characteristics: density and porosity. Thermal annaling temperature increase leads to a decrease in the density of the sintered ceramic and a decrease in itshardness.

Mechanistic Elucidation of Hard Agglomerate Formation from Drying Kinetics in the Integrated Sorption Chamber

The formation of hard agglomerates during drying has impacts on the product quality, particle size distribution, and downstream formulation. Hence, understanding the cause of hard agglomerates and determining a remedy for them or preventing their formation are necessary. The integrated sorption chamber (ISC) has been successfully applied to the study of hard agglomerate formation. The design and development of this ISC are briefly described. The vapor-phase profile of a binary mixture of acetone and water without active pharmaceutical ingredient (API) was predicted using an analytical solution of a batch distillation and verified via mass spectrometry (MS). The drying of the API wet cake, which is very soluble in water, using a starting point of 5 wt % water in acetone was conducted in the ISC. A significant delay in water removal was observed from both the weight measurement and the MS signal. The slow removal of water was attributed to diffusion of water from a thin crust layer induced by the solution o...

PREPARATION AND CHARACTERIZATION OF ATO NANOPARTICLES BY COPRECIPITATION WITH MODIFIED DRYING METHOD

Antimony-doped tin oxide (ATO) nanoparticles were prepared by coprecipitation by packing drying and traditional direct drying (for comparison) methods. The as-prepared ATO nanoparticles were characterized by TG, XRD, EDS, TEM, HRTEM, BET, bulk density and electrical resistivity measurements. Results indicated that the ATO nanoparticles obtained by coprecipitation with direct drying method featured hard-agglomerated morphology, high bulk density, low surface area and low electrical resistivity, probably due to the direct liquid evaporation during drying, the fast shrinkage of the precipitate, the poor removal efficiency of liquid molecules and the hard agglomerate formation after calcination. Very differently, the ATO product obtained by the packing and drying method featured free-agglomerated morphology, low bulk density, high surface area and high electrical resistivity ascribed probably to the formed vapor cyclone environment and liquid evaporation-resistance, avoiding fast liquid removal and improving the removal efficiency of liquid molecules. The intrinsic formation mechanism of ATO nanoparticles from different drying methods was illustrated based on the dehydration process of ATO precipitates. Additionally, the packing and drying time played key roles in determining the bulk density, morphology and electrical conductivity of ATO nanoparticles.

Preparation of nanometer Nd3+, Y3+ co-doped CaF2 powder by coprecipitation-azeotropic distillation technique

The synthesis of Nd3+, Y3+:CaF2 nanopowder was conducted by azeotropic distillation method, which effectively dehydrated hydrous CaF2 and prevented forming hard agglomerates. X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning calorimetries-thermalgravimetry (DSC-TG), Fourier transform infrared spectroscopy (FT-IR) and absorption spectroscopy were performed to characterize the powder properties. The experimental results showed that products obtained by azeotropic distillation were single phased, rather monodispersed, successfully prevented the hard agglomerate formation and effectively removed the residual water inside the as-prepared precipitate than that of the direct drying. The absorption spectra showed a wider and stronger absorption bands around 792 nm, which should be profitable for LD pumping.

The Effects of Water Removal Process on the Properties of Magnesium Aluminate Spinel Nanopowders Synthesized by Co-Precipitation Method

Magnesium aluminate spinel (MgAl2O4) or spinel ceramics have been widely used in engineering fields due to its attractive properties, such as high mechanical strength, good optical properties, and high refractoriness. Precipitation is one of the most common techniques for preparing spinel nanopowders because it offers many advantages including low cost, simple method, and ease of mass production. However, severe agglomeration usually takes place during water removal process, i.e. washing and drying. These hard agglomerates deteriorate sinterability of nanopowders. In this study, spinel nanopowders were prepared by co-precipitation method. The remaining water in the precipitated precursor was removed by washing the precipitated precursor with organic solvents, i.e. ethanol and acetone-toluene-acetone. Conventional drying process was also performed for comparison. The characteristics of the obtained spinel nanopowders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS) method. The results showed that the water removal process did not have any significant effects on phases of the dried precursors and the calcined powders. However, washing the precipitate precursor with organic solvent is the most effective process to prepare spinel nanopowders with low degree of agglomeration. Whereas, removing water by conventional drying process led to the formation of hard agglomerates. Furthermore, the effects of water removal process on sinterability of the spinel nanopowders were also reported.

Azeotropic distillation, ethanol washing, and freeze drying on coprecipitated gels for production of high surface area 3Y–TZP and 8YSZ powders: A comparative study

Coprecipitation is a well-established method for synthesizing yttria-stabilized zirconia (YSZ); however, the hard agglomerates formed during the drying stage make it difficult to obtain high surface area powders. This paper compares azeotropic distillation, ethanol washing, and freeze drying, the most common dehydration methods, and assesses their ability to yield non-agglomerated powders of coprecipitated 3mol% Y2O3 (3Y–TZP) and 8mol% Y2O3-stabilized zirconia (8YSZ). Azeotropic distillation most effectively increased the surface area of the powders, yielding 3Y–TZP and 8YSZ powders with specific surface areas of 94.73 and 109.37m2g−1, respectively, and crystallite sizes between 9 and 10nm. Ethanol washing did not homogenously dry out the precipitate, whereas the freeze drying method promoted the formation of hard agglomerates, as evidenced by the peculiar powder characteristics derived from this technique. Interestingly, the surface area seems to be increased in methods that reduce the crystallization enthalpy on the hydrous zirconia precipitates.

Preparation of nano-sized Al2O3–2SiO2 powder by sol–gel plus azeotropic distillation method

Nano-sized amorphous Al2O3–2SiO2 powder was prepared by a sol–gel method coupled with azeotropic distillation. The structure of the powder was investigated by DTS, BET, TEM, FT-IR, TG-DTA and XRD, showing that n-butanol azeotropic distillation could effectively remove water from the aluminosilicate gels and prevent the formation of hard agglomerates in the drying process. The average particle diameter of the powder was about 70nm. The largest BET specific surface area of the powder was 669m2/g. To examine the alkali-activation reactivity of the powder, alkali-activation tests were performed with the powder reacting with sodium silicate solution. The synthetic powder was found to be highly reactive.

Preparation and characterization of nanosized bismuth doped tin dioxide powders with a novel post treatment process

Bismuth-doped tin dioxide (BTO) nanopowders were prepared by wet chemical co-precipitation method using tin tetrachloride (SnCl 4 ) and bismuth nitrate (Bi(NO 3 ) 3 ) as raw materials. Effects of calcination temperature and post treatment methods on particle size and crystalline phase transition of bismuth tin precursor (BTP) were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric-differential scanning calorimetric instrument (TG-DSC) and X-ray photoelectron spectroscopy (XPS). The optimal calcination temperature of BTP was found to be about 873 K. A novel post treatment process with polyacrylamide (PAM) in the preparation of nanometerials was presented for the first time. Experimental results showed that nonionic PAM is a highly effective additive, which not only speeds up the filtration of precursor, but also effectively reduces the formation of hard agglomerates. The average size of BTO nanopowders prepared using nonionic PAM as a filtration aid and disperser is smaller than 10 nm. We believe this post treatment method will come into wide use for preparation of many nanosized materials.

Preparation and characterisation of nanosized antimony-doped tin dioxide powders with a novel post-treatment process

Bismuth-doped tin dioxide (BTO) nanopowders were prepared by wet chemical co-precipitation method using tin tetrachloride (SnCl4) and bismuth nitrate (Bi(NO3)3) as raw materials. Effects of calcination temperature and post treatment methods on particle size and crystalline phase transition of bismuth tin precursor (BTP) were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric-differential scanning calorimetric instrument (TG-DSC) and X-ray photoelectron spectroscopy (XPS). The optimal calcination temperature of BTP was found to be about 873 K. A novel post treatment process with polyacrylamide (PAM) in the preparation of nanometerials was presented for the first time. Experimental results showed that nonionic PAM is a highly effective additive, which not only speeds up the filtration of precursor, but also effectively reduces the formation of hard agglomerates. The average size of BTO nanopowders prepared using nonionic PAM as a filtration aid and disperser is smaller than 10 nm. We believe this post treatment method will come into wide use for preparation of many nanosized materials.

Preparation of Zirconia Nanopowders in Ultrasonic Field by the Sol-Gel Method

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.

Synthesis of Lanthanum Beta Alumina by the Polymeric Precursor Technique

Lanthanum beta alumina powders were obtained by the polymeric precursor technique using lanthanum nitrate, aluminum nitrate, ethylene glycol and citric acid. The transformations that occur during thermal treatment of the precursor solution were evaluated by thermogravimetric and differential thermal analysis. Fourier Transform Infrared analysis for residual carbon qualitative detection and gas adsorption analysis for evaluating specific surface area, BET method, were carried out in powder specimens heat treated at different temperatures. High calcination temperature leads to the formation of hard agglomerates. The powders calcined at 800°C for 4 h have high specific surface area, ~ 120 m2/g. All processed powders and green pellets sintered at different temperatures were analyzed by X-ray diffraction for structural phase determination. Single phase LaAl11O18 pellets have application as solid electrolytes in disposable electrochemical devices for monitoring dissolved oxygen species in molten steel at very high temperatures, > 1500 °C, during steel production.

Synthesis and surface modification of ZnO nanoparticles

ZnO precursor was prepared by direct precipitation from zinc acetate and ammonium carbonate. ZnO nanoparticles were synthesized by calcination of the precursor at 450 degrees C for 3 h and the calcination after the heterogeneous azeotropic distillation of the precursor, respectively. The synthesized ZnO nanoparticles were characterized by FT-IR, XRD and TEM. It is concluded that the heterogeneous azeotropic distillation of the precursor effectively reduced the formation of hard agglomerates. The surface modification of synthesized ZnO nanoparticles was conducted by capping with oleic acid, and the existence of organic layer can be confirmed by the FT-IR spectra. The lipophilic degree of surface modified ZnO nanoparticles was measured. The ZnO nanoparticle surface was also modified by SiO2, coating. The FT-IR spectrum and XPS clearly showed the formation of an interfacial chemical bond between ZnO and SiO2. In addition, photocatalytic degradation of methyl orange in aqueous solution was performed using ZnO nanoparticles or ZnO/SiO2 nanoparticles as photocatalyst, respectively. The results showed that the ZnO/SiO2 nanoparticles have reduced catalytic activity than that of ZnO nanoparticles. (c) 2006 Elsevier B.V. All rights reserved.

Synthesis and Characterization of NiO-8YSZ Powders by Coprecipitation Route

Nickel oxide – 8 mol% yttria stabilized zirconia (NiO-8YSZ) powders containing 25 to 75 wt% of NiO were prepared by coprecipitation. The entire process includes the reaction of metals aqueous chloride solutions (heated at 95 oC) with ammonium hydroxide, washing steps of the resulting gel, butanol azeotropic distillation treatment to prevent the formation of hard agglomerates, drying, calcination and ball milling. The yield of precipitation of metals was determined by inductively coupled plasma atomic emission spectroscopy analysis (ICP-AES). Powders were characterized by X-ray and laser diffraction, infrared analysis, gas adsorption (BET) and scanning electron microscopy. It was observed that zirconium and yttrium hydroxides are easily precipitated in alkaline medium, while nickel precipitation yield is in the range of 80 to 95% due to the formation of soluble complexes. NiO appears as a second phase in synthesized powders and contributes to decreasing of specific surface area and agglomerate mean size.

Soft- and Hard-Agglomerate Aerosols Made at High Temperatures

Criteria for aerosol synthesis of soft-agglomerate, hard-agglomerate, or even nonagglomerate particles are developed on the basis of particle sintering and coalescence. Agglomerate (or aggregate) particles are held together by weak, physical van der Waals forces (soft agglomerates) or by stronger chemical or sintering bonds (hard agglomerates). Accounting for simultaneous gas phase chemical reaction, coagulation, and sintering during the formation and growth of silica (SiO2) nanoparticles by silicon tetrachloride (SiCl4) oxidation and neglecting the spread of particle size distribution, the onset of hard-agglomerate formation is identified at the end of full coalescence, while the onset of soft-agglomerate formation is identified at the end of sintering. Process conditions such as the precursor initial volume fraction, maximum temperature, residence time, and cooling rate are explored, identifying regions for the synthesis of particles with a controlled degree of agglomeration (ratio of collision to primary particle diameters).

Comparison of different alumina powders for the aqueous processing and pressureless sintering of Al2O3–SiC nanocomposites

Abstract Four different alumina powders, from European and Japanese sources having similar particle size (350–700 nm) were used for the fabrication of nanocomposites. They were compared in terms of green properties, sintering behaviour, microstructure and mechanical properties. The processing route used (attrition milling and freeze-drying) leads to a reduction in green density of the processed aluminas and composites compared to the as-received alumina. All powders had similar green properties except one, which contained a binder from the manufacturer. The presence of this binder led to the formation of hard agglomerates. In this case the pressing did not eliminate, totally, the inter-agglomerate pores, leading to an incomplete sintering. Calcining the powder to remove the binder resulted in similar pressing and sintering behaviour to the other powders and densities >99% were achieved at 1750 °C by pressureless sintering. All the composites exhibited similar microstructures (matrix grain size ∼3 μm) and elastic properties, hardness and fracture toughness. A finer matrix microstructure could be obtained with one of the European powders which achieved ∼99% density at 1700 °C. The presence of 5 vol.% SiC resulted in a mean grain size of ∼2 μm for the alumina matrix compared with 13.9 μm for a monolithic alumina prepared under identical conditions.

Novel azeotropic distillation process for synthesizing nanoscale powders of yttria doped ceria electrolyte

Nanoscale yttria doped ceria powder was successfully synthesized by azeotropic distillation process, which effectively dehydrated hydrous ceria and completely prevented the formation of hard agglomerates. After being calcined at 500°C for 2 h, the average powder size was less than 10 nm. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy were performed to characterize the powder properties. The electrical conductivity of the sintered pellets from this powder was also measured by a.c. impedance spectroscopy, with the values of 0.025 and 0.062 S cm −1 at 700°C and 800°C, respectively.

Combustion Synthesis: Effect of Urea on the Reaction and Characteristics of Ni-Zn Ferrite Powders

The purpose of this study was to evaluate the effect of the urea content (fuel) on the reaction and the characteristics of Ni-Zn ferrite powders obtained by combustion synthesis. Several batches were prepared with different fuel contents, ranging from the stoichiometric composition between 20 and 100% (excess), while the desired molar proportion of the metal precursors was kept constant. The solutions were heated on a hot plate and then transferred to a muffle furnace preheated to 700°C, in which ignition took place. The resulting powders were characterized by XRD, BET, SEM, and sedimentation, aided by rotation measured through an optic light. The crystalline hematite (α-Fe2O3) and Ni-Zn ferrite phases were present in all the compositions studied, and the appearance of the agglomerates varied from soft to hard with increasing urea content. The increased urea content, which promoted a longer flame time, influenced the growth and/or formation of hard agglomerates. After sintering at 1200°C/2 h using the stoichiometric composition, only the spinel structure Ni-Zn ferrite, with homogeneous microstructure, was present.

Sub-micron sized Al2TiO5 powders prepared by high-energy ball milling

High energy ball milling to obtain ultrafine aluminium titanate particles has been investigated. Tempered steel has been selected as material for the containers and balls because the desirable properties of aluminium titanate are not degraded by small amounts of Fe2O3. The starting powders have been milled during different periods (1–60 h) and the evolution of the morphology and crystallinity of the treated powders as well as the extent of contamination from the milling media have been characterised. Different experimental techniques, X-ray diffraction, BET-analysis, chemical analysis, scanning electron microscopy and low and high resolution transmission electron microscopy have been used. High energy ball milling has been proved to be an efficient route to obtain submicron sized (50–100 nm) aluminium titanate powders, but further milling of the powders is accompanied by contamination from the milling media and the formation of hard agglomerates.

Mechanism of Hard Agglomerate Formation in a High Purity Sub-micron .ALPHA.-Alumina Powder.

A high purity, sub-micron, α-alumina powder produced by the hydrolysis of aluminum alkoxide method and a thermally hydrated product of the as-received powder have been investigated. The powders were divided into two particle size range fractions. The intensity of aluminum trihydroxide polymorph bands is larger in the diffuse reflectance infrared Fourier transform (DRIFT) spectra of the large particle size fractions of the as-received, as well as the hydrated product. The amount of aluminum trihydroxide polymorphs in the hydrated powder was large enough to be detected in the X-ray diffraction (XRD) pattern of the powder. Scanning electron microscope (SEM) observation of the powders shows the presence of large agglomerates in the hydrated powder. A smaller amount of agglomerates is also noticeable in the as-received powder. Transmission electron microscope (TEM) images of the as-received and hydrated alumina powders revealed the presence of a surface layer interconnecting neighboring α-alumina particles. It is concluded that Al(OH)3 surface structures of adjacent particles can form hydrogen bonding creating crystalline structures similar to the aluminum trihydroxide polymorphs. These structures are believed to be responsible for the formation of hard agglomerates even in the as-received alumina powder.