[Show abstract][Hide abstract] ABSTRACT: Hydroxyapatite (HAP) nanoparticles were successfully prepared without using organic modifiers by the combination of high-gravity reactive precipitation and hydrothermal method. The influences of the high-gravity level, the total reactant flow rate, the reactant flow rate ratio, and the reactant concentration on the preparation of HAP nanoparticles were systematically explored. The results showed that a high-gravity level of 3808−7774 m/s2, a total reactant flow rate of 120−360 mL/min, a moderate reactant flow rate ratio of 0.6−1.67, and a low reactant concentration of 0.04−0.3 mol/L favored the formation of uniformly small HAP nanoparticles with a mean size of 55−110 nm and a narrow size distribution. The increase of the high-gravity level led to the initial rapid and following slight decrease of the mean particle size. The mean particle size first decreased and subsequently increased with increasing the total reactant flow rate, the reactant flow rate ratio, and the reactant concentration. The uniformity of HAP nanoparticles was mainly determined by the micromixing condition of reactants. It could be envisioned that high-gravity reactive precipitation combined with hydrothermal method would be promising in the commercial production of HAP nanoparticles.
[Show abstract][Hide abstract] ABSTRACT: A microporous tube-in-tube microchannel reactor (MTMCR) was successfully adopted to prepare hydroxyapatite (HAP) nanoparticles. The rodlike HAP nanoparticles with a mean size of 58 nm, a specific surface area of 49.32 m2/g, and a narrow size distribution were obtained in an MTMCR under a high throughput of 3 L/min. The mean particle size sharply decreased with increasing the continuous phase flow rate, while first decreased and subsequently increased with increasing the dispersed phase flow rate and the reactant concentration. The extension of the mixing distance led to the initial rapid and following slight decrease of the mean particle size. The size of HAP nanoparticles was also strongly dependent on the micropore size on the surface of inner tube. Small micropore size was beneficial for producing small particles. For comparison, HAP nanoparticles were also prepared in a stirred tank reactor (STR) and a T-junction microchannel reactor (TMCR), clearly exhibiting the advantages of the MTMCR over the STR and TMCR due to the achievement of uniformly smaller HAP nanoparticles and a high throughput for industrial production.
No preview · Article · Nov 2009 · Industrial & Engineering Chemistry Research
[Show abstract][Hide abstract] ABSTRACT: Novel size-tunable alumina hollow spheres were successfully prepared using colloidal carbon spheres as templates and aluminum nitrate as alumina source. The samples were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD). The influences of the synthesis conditions such as reaction time, reaction temperature, and the concentration of Al(NO3)3 were studied. According to the experiment, the synthesized alumina hollow spheres with a narrow size distribution showed tunable shell thickness and uniform shell. The morphology of the alumina hollow spheres was influenced mainly by the reaction temperature.
Preview · Article · Jun 2008 · ACTA PHYSICO-CHIMICA SINICA
[Show abstract][Hide abstract] ABSTRACT: The viscosity of the suspension evolved to a viscous non-Newtonian fluid during carbonation precipitation of the nano-alumina trihydroxide (ATH). The high viscosity affected mass transfer and carbonation process evidently. At high viscosity, conventional methods improved mass transfer less than viscosity breaking. Therefore, the surfactants were selected by improving the fluidity of nano-ATH filter cake, among which a polycarboxylate plus CTAB led to a concentrated caustic ATH suspension of 40 wt% content with good fluidity under current experimental conditions, i.e. pH > 12 and [Na+] = 2.7 mol L−1. The surfactants in the carbonation reaction strongly reduced the suspension's viscosity, resulting in the shortening of reaction time and the increment of productivity. TGA and FTIR results demonstrated that the nano-ATH adsorbed 1.2 wt% of the surfactants in dry mass, and that the nano-ATH was hexagon-shaped slice with good dispersion and uniform distribution with a size of ca. 100 nm × 10 nm.
No preview · Article · May 2008 · The Chemical Engineering Journal
[Show abstract][Hide abstract] ABSTRACT: Nano-hexagonal platelets of aluminium trihydroxide (ATH) were first time prepared by high-gravity reactive precipitation, and subsequently were modified as precursor by oxalic acid at hydrothermal condition. A new-style nano-flame retardant named modified aluminium hydroxide (MAH) was therefore obtained. The properties of nano-MAH and nano-ATH were characterized and compared using XRD, TEM, TG-DSC and BET. The results indicate that nano-ATH and nano-MAH have similar crystal structure, particle shape and endothermic enthalpy, however, nano-MAH has higher decomposition onset temperature, i.e. 330°C, higher weight loss rate, i.e. 51% and higher specific surface area, i.e. 34.9m2g−1. Therefore, comparing with nano-ATH, nano-MAH can be applied in more polymers with the better dispersibility.
No preview · Article · Feb 2008 · Materials Chemistry and Physics
[Show abstract][Hide abstract] ABSTRACT: A novel flame retardant system composed of nano-kaolin and nano-HAO (nano-sized hydroxyl aluminum oxalate) was used for flame retarding the low density polyethylene (LDPE)/ethylene propylene diene rubber (EPDM) blends. Results of fire testing showed that nano-kaolin and nano-HAO exhibited excellent synergistic effects on the flame retardancy of the LDPE/EPDM composites. When 12wt% nano-kaolin took the place of 12wt% nano-HAO in the composites, the LOI of the composites increased from 31.0% to 35.5% and the composites could meet the UL94V-0 standard. Through thermogravimetric and differential thermal analysis (TG–DTA) it was found that nano-HAO mainly affected the degradation of the experimental composites chemically. Meanwhile, results of scanning electronic microscope (SEM) and Fourier transformation infrared spectra (FTIR) of the composites on the char layer revealed that nano-kaolin mainly affected the transfer process physically by aggregating with nano-HAO and thus the synergistic effect on flame retardancy appeared.
No preview · Article · Jul 2007 · Polymer Degradation and Stability
[Show abstract][Hide abstract] ABSTRACT: Nano-sized hydroxyl aluminum oxalate (nano-HAO) and montmorillonite (MMT) were mixed into low density polyethylene (LDPE)/ethylene propylene diene rubber (EPDM) system via melt compounding method. By means of LOI and UL94 horizontal burning tests, MMT and nano-HAO together exhibited better performance on flame-retarding LDPE/EPDM composites than how they performed individually, which proved that there existed a synergistic effect between MMT and nano-HAO on flame retardancy. Furthermore, through the analysis of Fourier transform IR spectra (FTIR), scanning electron microscope (SEM), and the thermogravimetric and differential thermal analysis (TG–DTA), the mechanism of the synergistic flame retardance was proposed as when MMT was added into nano-HAO/LDPE/EPDM composites, a laminated structure formed in the char layer and thus the transmission speeds of heat, oxygen, flammable mass and vapor were adjusted. So the process of combustion was retarded owing to lack of oxygen and heat.
[Show abstract][Hide abstract] ABSTRACT: Mesoporous alumina has been synthesized first by a traditional precipitation method in a rotating packed bed (RPB) in a scaling experiment. Aluminum nitrate was used as source of aluminum, and poly(ethylene glycol) 1540 was used as the template. The characterization showed that the ordered wormlike pores and narrow pore size distributions were obtained, and the surface area reached about 250 m2/g. The experimental results indicated that the structure of mesoporous alumina was related to the synthesized and assembled rate of precursor which was dominated by those factors (such as concentration of reactant, the addition rate of precipitator, and so on). Specifically, the efficiency of micromixing and dispersion which was the most important condition for the synthesis of mesoporous aluminas has been greatly intensified by the high-gravity environment in RPB. It first provided a feasible technology for volume production of mesoporous alumina.
No preview · Article · Apr 2007 · Industrial & Engineering Chemistry Research
[Show abstract][Hide abstract] ABSTRACT: Flame retardant high impact polystyrene (HIPS) was prepared by melt blending HIPS with nano-modified aluminum trihydrate (nano-CG-ATH) and red phosphorus masterbatch (RPM). Styrene–butadiene–styrene (SBS) was used as a strengthener in this research. The effects of the nano-CG-ATH, RPM, and SBS on properties of HIPS composites were studied using mechanical and combustion tests, and thermogravimetric analysis. The morphologies of fracture surfaces and char layers were characterized through scanning electron microscopy (SEM). The HIPS/nano-CG-ATH/RPM (68/20/12) composite and its combustion residues at various temperatures were characterized by Fourier transform infrared (FTIR) spectra analysis. The results show that the UL-94 rating of the HIPS/nano-CG-ATH/RPM (68/20/12) composite reached V–0 and that its char layer after flame test was well-developed and robust, but that its impact performance was poor. The addition of the SBS improved its impact performance but did not influence its thermal and flame retardant properties, but lowered its tensile strength and flexural modulus to some extent. The FTIR spectra confirm that both P–O–P and P–O–C groups were present in the char.
No preview · Article · Apr 2007 · Fire Safety Journal
[Show abstract][Hide abstract] ABSTRACT: This paper devotes to synthesize a new-style nano inner-modified aluminum trihydroxide (IMATH) flame retardant by carbonation in a rotating packed bed (RPB) reactor and hydrothermal modification. Sodium aluminate (SA) solution was carbonated in RPB reactor to yield nano aluminum trihydroxide (ATH) gels, which subsequently reacted with oxalic acid at the optimum hydrothermal conditions of 1 h and 160 °C to form nano IMATH powders. Factors affecting the explosive nucleation in the carbonation process and the properties of ATH product such as temperature, terminal pH, high gravity level, SA concentration, liquid flux and G/L ratio were mainly studied to achieve the required nano ATH gels, and the hydrothermal modification process was also researched. The as-synthesized nano IMATH was characterized by FESEM, XRD, BET, TG-DSC, FTIR and compared with nano ATH. Experimental results show that nano IMATH starts thermal decomposition at 350 °C and has a weight loss of 51%, both higher than nano ATH. In addition, nano IMATH inherits many characters of nano ATH such as crystal phase, endothermic enthalpy and particle morphology. It is confirmed that carbonation parameters have significant influences on the properties of ATH gels, and therefore further affect the properties of IMATH.
No preview · Article · Feb 2007 · Colloids and Surfaces A Physicochemical and Engineering Aspects
[Show abstract][Hide abstract] ABSTRACT: Ultra thin hexagonal crystallites of nano aluminium trihydroxide (ATH) with 100–200nm in particle size and 20–30nm in thickness have been synthesized by carbonation of sodium aluminate (SA) solution in a rotating packed bed (RPB) reactor, followed by thermal hydrolysis. Due to the intensified absorption of CO2 under high gravity situations, SA solution was acidified rapidly at a fine scale, and thereby nano-scale gelatinous particles of ATH were precipitated from the supersaturated SA solution. This paper mainly discussed the factors of controlling carbonation process such as carbonation temperature, high gravity level, SA concentration, G/L ratio and terminal pH on the properties of precipitated ATH, which were characterized by TEM, XRD and BET. With carbonation temperature lowered to 30°C, ATH size sharply reduced to below 200nm. Higher gravity level and higher G/L favor the absorption of CO2, resulting in higher supersaturation degree of precursor with the lower pH for nucleation stage. But only when pH values were kept steady in the nucleation stage, the formed particles had a minimum size. In order to achieve ATH crystal phase, the final pH should be above 12.0. When SA concentration rose to 2.0mol/L, the productivity of ATH achieved 75%.
No preview · Article · Aug 2006 · The Chemical Engineering Journal
[Show abstract][Hide abstract] ABSTRACT: Mesoporous alumina has been synthesized by traditional precipitation method using aluminum nitrate and aluminum sulfate. Ammonium carbonate was used as precipitator. The characterization showed that the ordered worm-like pores are obtained, surface area reached about 250–300 m2/g, and narrow pore size distributions centered at 6 nm. The experimental results indicated that the structure of mesoporous alumina was related to precursor which was dominated by the source of alumina and pH value. The structure change of precursor and calcination process were discussed. A self-assembly mechanism is proposed for the formation of this materials.
No preview · Article · Jul 2006 · Microporous and Mesoporous Materials
[Show abstract][Hide abstract] ABSTRACT: Ethylene vinyl acetate copolymer (EVA)/alumina trihydrate (ATH) nanocomposites were prepared by melt-blending. Two kinds of interfacial modifiers were used in this research, a titanate coupling agent and maleated ethylene vinyl acetate copolymer (MEVA), which acted as a compatibiliser. The effects of modifiers on the properties of EVA nanocomposites were studied by thermogravimetric analysis, tensile and combustion tests. The dispersion and adhesion patterns of the ATH nano-particles in EVA matrix were characterized through Molau solution test, TEM and SEM. The experimental results demonstrated that the use of untreated ATH could clearly decrease the tensile properties of EVA composites. It was found that the combined addition of the two kinds of interfacial modifiers led to a dramatic increase in tensile and flame retardant properties of the nanocomposites. Also the thermal stability of this system, in terms of the thermal degradation test, was enhanced. These effects would be diminished if only one modifier was used. The improvement in the properties of interfacial modified EVA/ATH nanocomposites is mostly attributed to a better dispersion of surface modified filler and a strong adhesion between the filler and matrix.
No preview · Article · Mar 2005 · Polymer Degradation and Stability
[Show abstract][Hide abstract] ABSTRACT: This paper presents a route of synthesizing nano-fibrillar aluminum hydroxide (AH) by carbonation in a novel rotating packed bed (RPB) reactor and thermal hydrolysis. Carbonation of sodium aluminate (SA) is conducted by introducing CO2 into RPB at room temperature to form AH gel which is subsequently treated by thermal hydrolysis for an optimum time of and temperature of 85°C to yield nano-fibrillar pseudoboehmite (PB) of 1– in diameter and 50– in length. Factors affecting carbonation process such as high gravity level, Gas/Liquid ratio and SA solution concentration are discussed. Experimental results reveal that operating conditions have significant influences on the properties of PB and the morphology of PB is closely related to the unit structure of AH gel. The as-prepared PB is characterized by TEM and XRD and compared with those synthesized by conventional Stirred Tank Reactor (STR). Reaction time in RPB shortens for approximately a half compared with that in STR. It is proven that this route has obvious advantages over STR.
Preview · Article · Feb 2003 · Chemical Engineering Science
[Show abstract][Hide abstract] ABSTRACT: Rotating packed bed (RPB), a novel multiphase contactor, can greatly intensify multiphase mass transfer processes. However, the real-flow situation in a rotating bed which leads to the high mass transfer rates is still not clear. The first part of this paper describes phenomena and results observed by a video camera mounted on a RPB. The camera rotates synchronously with the rotor so that in situ signal of liquid flow can be acquired, and continuous and stable live images are obtained. In the second part of this paper, two electro-conductivity sensors are mounted on a RPB to pick up signals in situ at different positions during rotating. Real RTD in RPB at different operating conditions are obtained. A mathematical model is developed for simulating the velocity profile, and the film thickness of liquid flow on the packing. The calculated residence time in the packing gives an average relative error of 14% in comparison with the experimental results.
Preview · Article · May 2000 · Chemical Engineering Science
[Show abstract][Hide abstract] ABSTRACT: On the basis of the analysis of key engineering factors predominating in a reactive precipitation process, a new method called high-gravity reactive precipitation (HGRP), which means that reactive precipitation takes place in high-gravity conditions, is presented here for the massive production of nanoparticles. A rotating packed-bed reactor was designed to generate acceleration higher than the gravitational acceleration on Earth. The syntheses of nanoparticles of CaCO3, aluminum hydroxide, and SrCO3 were employed to demonstrate the advantages and industrial potentials of this technology, where the typical gas−liquid−solid, gas−liquid, and liquid−liquid multiphase reaction systems were involved. Experimental results show that the mean size of CaCO3 particles can be controlled and adjusted in the range of 17−36 nm through the change of operation conditions such as high-gravity levels, fluid flow rates, and reactant concentrations. Nanofibrils of aluminum hydroxide of 1−10 nm in diameter and 50−300 nm in length as well as nanoparticles of SrCO3 with a mean size of 40 nm were synthesized. The crystal structures of these compounds synthesized in high-gravity conditions were the same as those in gravitational conditions. HGRP technology is believed to be capable of the preparation of nanoparticles with low-cost and high-volume production and therefore to have potential applications in industry.
No preview · Article · Mar 2000 · Industrial & Engineering Chemistry Research
[Show abstract][Hide abstract] ABSTRACT: Hydrodynamics and mass transfer characteristics in a cross-flow rotating packed bed (RPB) were studied. Models describing the liquid film flowing on the wire gauze packing, the liquid droplet size in the voids, the gas pressure drop, the gas pressure and velocity radial distribution and liquid flow direction have been established. Three different types of mass transfer processes in cross-flow RPB were studied. Mass transfer model was established based on surface renewal model. The calculated results agree well with that of experiments. Experiments show that: The gas flow rate can be as high as 15 m/s and even higher, therefore the diameter of RPB can be greatly reduced compared to that of counter-current RPB; For the liquid side controlling processes, the height of mass transfer unit is 2.5–4 cm, which is close to that of countercurrent flow RPB.
No preview · Article · Nov 1997 · Chemical Engineering Science