Water Addition Rate Research Articles

Strategy for control of crystallization of polymorphs

The controlling factor and mechanism of the crystallization of polymorphs were investigated in various systems; i.e. amino acids, inorganic compounds (calcium carbonate), pharmaceuticals and inclusion compounds. The controlling factor depends on the systems (compounds and solvents and additives) and the crystallization methods (cooling crystallization, reactive crystallization and anti-solvent crystallization). The controlling factors for each system were found and a schematic diagram was shown. The mechanism of each controlling factor was investigated and some rules were found. It appears that the establishment of “Ostwald's step rule” depends on the systems. In the cooling crystallization of amino acids (L-glutamic acid and L-histidine), the “Ostwald's step rule” cannot be observed; however, in the crystallization of BPT esters, it is clearly established. The difference of the temperature effect between L-glutamic acid and L-histidine polymorphs may be related to the difference of the molecular conformation between the polymorphs. In the reactive crystallization of calcium carbonate polymorphs, the concentration (supersaturation) of reactant solutions, the mixing rate of the solutions, pH, stirring rate and temperature were found to be the controlling factors for the morphology and the crystallization behavior of polymorphs. As for the effect of additives it should be noted that the additive affects not only one polymorph, but on each polymorph. Then, knowing the relative effect of additives on each polymorph is important for the control. The growth kinetics of polymorphs of L-glutamic acid and the mechanism of morphology change of each polymorph were examined in the presence of L-phenylalanine (as an additive) with batch crystallization and the single crystal method. The growth rate model including the additive concentration was proposed for each polymorph and the method of the selective crystallization of the polymorphs by controlling the supersaturation and the additive concentration was also indicated. In anti-solvent crystallization of pharmaceuticals (BPT) it was shown that the addition rate of anti-solvent, initial concentration of solute and temperature are the controlling factors. With the increase of the addition rate the water composition in the nucleation zone increases, resulting in the preferential crystallization of the hydrate crystals. The transformation from BH to A form was observed, however, the transformation rate increased with a decrease in the water addition rate. It is that even when none of the A form was detected by XRD a small amount of fine crystals (A form) is included within the BH crystals and act as seed crystals for the transformation. Furthermore, the change in the molecular structure is related with a dynamic change of the polymorphic crystallization behavior as observed in L-Glu and L-His systems. The dependence of the polymorphic crystallization behavior on the molecular structure was systematically investigated using the newly synthesized BPT esters. It appeared that the conformational flexibility, the size of alkyl group of the esters and the presence of functional group influences the formation of hydrogen bond and the polymorphism. The solvent effect on the polymorphism was also examined in relation to the molecular structure. The functionality of clathrate crystals and the separation efficiency of isomers by clathrate crystals depend on their polymorphic crystallization behavior. The mechanism of the molecular recognition for the guest isomers by the host molecule is clarified. It was also elucidated that the release process of a guest biocide molecule from clathrate crystals includes polymorphic transformation.

INFLUENCES OF STRUCTURE AND PREPARATION CONDITIONS ON SIZE AND PHOTORESPONSIVE PROPERTIES OF AMPHIPHILIC AZO POLYMER COLLOIDAL SPHERES

Amphiphilic azo polymers with different azo chromophores and degree of functionalization(DF) were synthesized,and colloidal spheres of the polymers were prepared by gradual hydrophobic aggregation in selective solvents.To obtain suspensions of colloidal spheres,the required amounts of water were added into the THF solutions at a certain stirring rate.As the water content reached ca.70 vol%,an excess of water was added into the suspensions to "quench" the formed structures.The obtained suspensions of colloidal spheres were sealed after THF was completely volatilized and were characterized by DLS and UV-Vis spectroscopy.The size and size-distribution of colloidal spheres were measured by using a DLS/SLS-5022F laser light scattering apparatus.Before the measurement,the sample was clarified by a 0.45 μm Millipore filter to remove dust,and all the DLS measurements were carried out with 90° scattering angle.UV-Vis spectroscopy was used to study the azo chromophore structure variation in the colloid formation process by measuring the parameters such as the trans-to-cis photoisomerization rate and the isomerization degree at the photostationary state.In the photoresponse experiments,the sample was irradiated by a 365 nm UV light source,and the light intensity was 7000 mV/cm~2 at a distance of 38 cm and 21000 mV/cm~2 at a distance of 5 cm,respectively.In our experiment,the sample was 15 cm away from the UV light,and the temperature of the environment was 30℃.The influences of molecular structure and preparation conditions on the size and photoresponsive properties of the colloidal spheres were studied in some detail.The result shows that the functional group type and DF as well as the preparation conditions(initial polymer concentration,the rate of water addition,etc.) have significant effects on the size and photoresponsive properties of the colloidal spheres.The size of colloidal spheres increases with the increase of DF and initial concentration,but decreases with the increase of the rate of water addition.The photoinduced isomerization rate of poly{2-[4-(4-ethoxyphenylazo)phenoxy]ethyl acrylate-co-acrylic acid}(PEAPE) colloids is higher than that of poly{2-[4-(4-cyanophenylazo)phenoxy]ethyl acrylateco-acrylic acid}(PCNPE) colloids.The PEAPE colloids with higher DF show a slower photoisomerization rate.The photoinduced isomerization rate of the colloids decreases with the increase of initial concentration and the decrease of the rate of water addition.The possible mechanism for the influence is also discussed based on thermodynamics and kinetics consideration.It is believed that the colloidal spheres form through a self-assembling process controlled by the dynamic conditions.For high initial concentration and slow water dropping rate,more polymer chains tend to aggregate on the compact cores formed from the most hydrophobic chains as the water content is above the critical water content(CWC).Moreover,the polymeric chains had chance to rearrange themselves to form stable and compact structures due to the slow rate of water addition.On the other hand,as the rate of water addition increased,the polymeric chains attached to the cores were quickly "frozen" before they could completely adjust their conformations.Also,they could form new less compact cores so as to weaken the continuous aggregation probability.As a result,the formed aggregates had loose structures,and the photoinduced isomerization rate was relatively fast.

Synthesis and Characterization of Nitrogen‐Doped Group IVB Visible‐Light‐Photoactive Metal Oxide Nanoparticles

The incorporation of main group elements into wide-bandgap semiconductors has attracted significant interest because of the potential for modifying the physical properties of these semiconductors, as well as for applications such as photocatalysis, water splitting, and optoelectronics. Among the main group elements, nitrogen is believed to be the most favorable p-type dopant because of its similar size to oxygen, metastable AX center formation, and small ionization energy. For example, the incorporation of N into ZnO has been found to be a very promising way to make p-type ZnO, which represents a potentially useful alternative to toxic and expensive III–V semiconductors for applications such as light-emitting devices (LEDs). Another exciting example is visible-light-active TiO2, which is a promising material for applications such as water splitting and photocatalysis. Owing to its potential role in solving the inevitable global energy and environment crises, N-doped TiO2 has received a great deal of attention in recent years. Although several theoretical and experimental studies have validated the efficacy of the N doping of TiO2 for a variety of applications, the different approaches used for N doping have raised questions about the origin of the observed photocatalytic activity. In order to increase the understanding of N doping at the nanoscale level, it is imperative to carry out a systematic analysis of the photocatalytic activities of nanoparticles with different N-doping levels and metal oxide matrices to aid the development of a new generation of photocatalysts. However, from a survey of the literature, no such study has been conducted up till now. Here, we present the incorporation of controlled amounts of N into group IVB metal oxide (TiO2, ZrO2, and HfO2) nanoparticles via a reliable wet-chemical procedure under ambient conditions. Furthermore, we present the effects of doping on their optical and photocatalytic properties. The synthesis of N-doped group IVB metal oxides is based on our previously reported sol–gel approach. We have determined from the X-ray photoelectron spectroscopy (XPS) analysis of N-doped TiO2 [9,20] that coordinating the amine precursor to the Ti precursor (usually Ti[OCH2(CH3)2]4) is essential for the efficient N doping of metal oxides. In the present synthetic route, we first attach the amine to the central metal to form an amino-coordinated precursor complex; subsequently, we hydrolyze the precursor solution with distilled water. Under different pH conditions it is possible to obtain TiO2 slurries with different amounts of incorporated nitrogen. In addition, the particle size can be confined to the nanometer regime by controlling the rate of water addition. After washing, the dispersions are centrifuged and the obtained powders are dried under vacuum. The dried powders are yellow to orange in color depending on the doping level. Before characterization, the products are annealed at 200 °C for 1 h under vacuum to remove organic residues from the surface. The morphologies of the products have been studied by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). It has been found that N-doped TiO2 and ZrO2 are mostly amorphous when sintered at temperatures below 400 °C (Fig. 1A–C, lower curves); the XRD pattern of HfO2 shows clear diffraction peaks only at sintering temperatures above 600 °C. Figure 1A–C (upper curves) shows the XRD patterns of the sintered products. The XRD patterns of TiO2–xNx, ZrO2–xNx, and HfO2–xNx particles indicate anatase, cubic, and monoclinic structures for these materials, respectively (Joint Committee on Powder Diffraction Standards (JCPDS) Card Nos. 84-1286, 49-1642, and 78-0050, respectively). However, at these temperatures, the obtained N-doping levels of all the three materials are lower than 1 %, indicating that nitrogen is replaced by oxygen at elevated temperatures. In order to maintain a higher doping level, the sintering temperature has been set at 200 °C. The TEM studies show that the unsintered samples are amorphous and irregular in shape. Regular spherical nanocrystals start to appear when a sintering temperature of 150 °C is used. Therefore, the samples used for the optical and catalytic measurements described below are mixtures of crystalline and amorphous particles. Although we have not been able to completely avoid aggregation of the particles on the TEM grids, the particle size has been controlled in the range from 5 to about 50 nm and the particles are approximately spherical in shape, as shown in Figure 1D–F. The N-doping levels of these metal oxides have been investigated by core-level XPS. Figure 2A–C shows a series of fullscale XPS spectra of N-doped TiO2, ZrO2, and HfO2 nanoparticles. All these spectra show typical TiO2, ZrO2, and HfO2 features, as well as a clear N 1s binding energy peak around C O M M U N IC A IO N

Synthesis and Self‐Assembly of Brush‐Rod Diblock Copolymers in the Mixed Solvent of THF/H2O

AbstractTwo amphiphilic brush‐rod block copolymers, PEGMA37‐b‐MBPS87 and PEGMA37‐b‐MBPS141, were synthesized via ATRP of poly(ethylene glycol)monomethyl ether methacrylate (PEGMA) and (+)‐2,5‐bis[4′‐((S)‐2‐methylbutoxy)phenyl]styrene (MBPS). The self‐assembly of the copolymers in THF/H2O was induced by different methods. Spheres were dominant morphologies of PEGMA37‐b‐MBPS87 regardless of the initial concentration and the rate of water addition. Increase of the length of hydrophobic block, as in PEGMA37‐b‐MBPS141, led to the coexistence of primary spheres, large compound spherical and rod‐like micelles at a slow water addition rate. Injecting water into the THF solution of PEGMA37‐b‐MBPS141 quickly or pouring the THF solution into large amount of water resulted only in the formation of spheres.magnified image

Size Control of Mesoscale Aqueous Assemblies of Quantum Dots and Block Copolymers

Dropwise addition of water to blend solutions of block copolymer-stabilized quantum dots (QDs) and amphiphilic block copolymer stabilizing chains PS(665)-b-PAA(68) (PS = polystyrene, PAA = poly(acrylic acid)) in DMF induces self-assembly to form photoluminescent mesoscale QD/block copolymer colloids in water termed QD compound micelles (QDCMs). Here we demonstrate reproducible kinetic control of QDCM particle size and chain stretching within the external PAA stabilizing layer via changes in the initial polymer concentration and rate of water addition. By increasing the initial polymer concentration or decreasing the rate of water addition for a constant blend composition, larger QDCM particles are obtained. From a combination of transmission electron microscopy and dynamic light scattering, the thickness of the external PAA layer is determined for various QDCM sizes, showing that PAA stretching in the external brush layer increases with increasing particle size, reaching the limit of fully extended chains for sufficiently large particles. The photoluminescence spectra from QDCMs in pure water indicate that photoluminescence properties of the block copolymer-stabilized QD building blocks are retained during self-assembly. The demonstrated control of mesoscale particle size and conformation of the stabilizing PAA layer, among other related structural parameters, via simple variation of experimental conditions is a promising step toward the application of QDCM assemblies in photonics and biolabeling.

Study of the Ignition Overpressure Suppression Technique by Water Addition

The main objective of this study is to gain an understanding of the mechanisms responsible for the suppression of the ignition overpressure observed when water is injected through discrete nozzles into a rocket exhaust. A simplified launch-vehicle/launchpad configuration of relevant importance is selected for this study. This configuration is then numerically modeled using two-phase computational fluid dynamics with a representative motor startup sequence and a series of water addition configurations. The study focuses on the interaction between the ignition overpressure wave and the injected water. Chemical reactions are not included in the model; therefore, the effect of afterburning of fuel-rich exhaust is omitted in this study. A total of 11 water addition configurations were studied. The study demonstrated that ignition overpressure is strongly affected by the cooling of the plume and the amount of obstruction restricting the expansion of the plume. Also, the study suggests the existence of an optimal water addition rate with a weak dependence on the water nozzle pressure drop.

Effect of Temperature on Antisolvent Crystallization and Transformation Behaviors of Thiazole-Derivative Polymorphs

Crystallization of the thiazole-derivative (BPT) was performed by adding water, which is an antisolvent for the solute, to methanol solutions of BPT. BPT has three polymorphs (A, B, C) and two solvates (BH(hydrate) and D(methanolate)). The effect of temperature on the polymorphic crystallization and transformation behavior was investigated in relation to the effect of the addition rate of water and the initial concentration. In the crystallization at temperatures between 333 and 313 K, the stable C form did not crystallize. At 333 K, the metastable A and BH forms crystallized competitively. At low initial concentration and slow addition rate, the A form crystallized preferentially, though at a high initial concentration and high addition rate BH tended to crystallize. It was presumed that the nucleation process of the unsolvated A form is not controlled by the dissociation equilibrium of the BH and D forms but is controlled by the kinetic process. This nucleation behavior of polymorphs at 333 K is very different from that at 323 K, which was reported previously, i.e., at low initial concentration BH crystallized, and at higher concentration the D form crystallized with BH. Furthermore, after crystallization at 333 K transformation from the BH form to the A form was observed, and it was found that the transformation rate decreases with the addition rate and the initial concentration. Such tendency is similar to that observed at 323 K. Conversely, at 313 K, the D form tended to crystallize preferentially. At low concentration the BH form also appeared with the D form, and it transformed to the D form. With a decrease of the temperature to 313 K, the D form becomes much more stable than the A and BH forms. This may accelerate preferential crystallization of the D form at 313 K.

Microgravity does not alter plant stand gas exchange of wheat at moderate light levels and saturating CO2 concentration

Plant stand gas exchange was measured nondestructively in microgravity during the Photosynthesis Experiment Subsystem Testing and Operations experiment conducted onboard the International Space Station. Rates of evapotranspiration and photosynthesis measured in space were compared with ground controls to determine if microgravity directly affects whole-stand gas exchange of Triticum aestivum. During six 21-day experiment cycles, evapotranspiration was determined continuously from water addition rates to the nutrient delivery system, and photosynthesis was determined from the amount of CO2 added to maintain the chamber CO2 concentration setpoint. Plant stand evapotranspiration, net photosynthesis, and water use efficiency were not altered by microgravity. Although leaf area was significantly reduced in microgravity-grown plants compared to ground control plants, leaf area distribution was not affected enough to cause significant differences in the amounts of light absorbed by the flight and ground control plant stands. Microgravity also did not affect the response of evapotranspiration to changes in chamber vapor pressure difference of 12-day-old wheat plant stands. These results suggest that gravity naïve plants grown at moderate light levels (300 micromol m(-2) s(-1)) behave the same as ground control plants. This implies that future plant-based regenerative life support systems can be sized using 1 g data because water purification and food production rates operate at nearly the same rates as in 1 g at moderate light levels. However, it remains to be verified whether the present results are reproducible in plants grown under stronger light levels.

Synthesis and Self-Assembly of Poly(ferrocenyldimethylsilane-b-dimethylaminoethyl methacrylate): Toward Water-Soluble Cylinders with an Organometallic Core

Samples of the asymmetric block copolymer poly(ferrocenyldimethylsilane-b-dimethylaminoethyl methacrylate), PFS-b-PDMAEMA (block ratio ≈ 1:5), with a hydrophobic organometallic block and a hydrophilic organic block have been synthesized via a two-step anionic polymerization methodology. To study the self-assembly of these block copolymers in aqueous media, micelles were prepared by two different methods: selective precipitation involving the addition of water to PFS-b-PDMAEMA in dioxane and directly mixing water with PFS-b-PDMAEMA. In the selective precipitation experiments, the rate of water addition was found to be a crucial factor in determining the morphology of the resulting micellar structures. Rapid addition of water resulted in a monomodal distribution of solid spheres with an overall diameter of 20 nm, while slow addition created vesicle-like structures with a broad size distribution. Direct mixing of water with PFS-b-PDMAEMA led to even more complex micellization behavior. After PFS-b-PDMAEMA was initially dissolved in water, polydisperse spherical micelles with Rh = ∼65 nm were formed. However, over time with constant stirring, a range of morphologies including spheres, rods, cylinders, and hollow structures were identified by electron microscopy, whereas, under quiescent conditions, the diameter of the spherical micelles gradually decreased to ca. 25 nm. Quaternization of the PDMAEMA blocks in PFS-b-PDMAEMA rendered a dramatic simplification to the micellization process. Only spheres were observed after the quaternized block copolymers were directly mixed with water. In contrast, alcohol solvents such as EtOH and iPrOH are able to induce PFS-b-PDMAEMA to self-assemble into cylindrical micelles by simply dissolving the block copolymers in the solvent. Aqueous colloidal solutions of cylindrical micelles could then be prepared via the dialysis of PFS-b-PDMAEMA in ethanol against water. The studies indicated that the solubility characteristics of the PDMAEMA corona chains in the micellization media exert a major influence on the micellization process and the resulting micellar morphologies.

Construction of a low-pressure microwave plasma reactor and its application in the treatment of volatile organic compounds.

Volatile organic compounds (VOCs) containing gases exhausted from industrial processes are highly toxic to human health; therefore, their safe elimination is extremely important. This paper describes how a novel prototype microwave plasma reactor was sequentially improved. The design concepts for each modification are also carefully described. For testing the reactor's performance, ethanol was selected as the target VOC. The decomposing and removal efficiency (DRE) value was used to evaluate the reactor's performance. The final stage of the revamping reactor was evaluated to meet the requirements of both stability and long term, high volume operation. When studying the VOC treatment operations, oxygen, air, and water vapor were used as carrier gases or additives to improve the efficiency of the DRE value and to facilitate the ethanol treatment. A DRE value higher than 99% was obtained under these optimal conditions: an ethanol vapor flow rate of 1730 cm3/min (67 mbar, 150 degrees C), power input higher than 1.5 kW, a frequency of 200 Hz, an air flow rate of 100 cm3/min (4 atm, 25 degrees C), and a liquid water addition rate higher than 0.21 mL/min (1 atm, 25 degrees C). With these conditions, the initial concentration of ethanol vapor mixed with the carrier gas was about 7-10%. Because of high processing efficiency and capacity of this system, it could be a potential alternative tool for treating industrial VOCs.

Anti-solvent crystallization and transformation of thiazole-derivative polymorphs—I: effect of addition rate and initial concentrations

Polymorphous crystals of thiazole-derivative (BPT) were crystallized by adding water (an anti-solvent for the solute) to methanol solutions of BPT. At 323K, the crystallization of the polymorphs was found to depend on the water-addition rate and the initial concentration of the BPT solution. At low initial concentrations, BH crystallized independent of the addition rate of water. However, at higher initial concentrations, the D form crystallized in addition to the BH form, especially at low water-addition rates. The increase in the proportion of the BH form with increasing water-addition rate may have resulted from an increase in the amount of water at the nucleation zone around the water droplet. The appearance of the D form with higher initial concentrations may be due to the hindrance of the hydration of the BPT molecule. The crystallized form was found to transform to several different forms, and the transformation characteristics are dependent upon the initial concentration of BPT. The transformation from the BH to the A form was observed at low initial concentrations. The transformation rate appeared to decrease with the addition rate and the initial concentration. With higher initial concentrations, both the BH and D forms transformed to the A form. At much higher concentrations, the D form transformed into the BH form and the transformation rate decreased with the addition rate. With very low addition rates, the nucleation of the D form occurred preferentially even at low methanol composition.

Effects of solvent composition and temperature on polymorphism and crystallization behavior of thiazole-derivative

The thermodynamic stability and transformation behaviors of the polymorphs (A and C) and solvated crystals (BH (BPT·0.5H 2O) and D (BPT·MeOH)) of the thiazole-derivative (BPT) were investigated. The thermodynamic stability and the transformation behavior were examined in relation with the chemical potential and the solubility of BPT in each crystal. The C form is basically the stable form and the A form is the metastable form at every temperature and methanol compositions ( V MeOH). However, the stability of BH and D forms remarkably changes with temperature and the methanol compositions. At 323 K with methanol compositions of 0.7 and 0.8 A, BH and D forms transformed to the stable form, C. However, at 0.5 of V MeOH A and D forms do not transform to the stable C form directly, but transform to the other metastable form of BH. This result may indicate the preferable nucleation and growth of BH crystals due to the specific solute–solvent interaction in comparison with C crystals. The small chemical potential difference between BH and C forms may also stabilize the BH form. The increase in the stability of D crystals and the decrease in the stability of BH with the methanol composition was related to the dissociation equilibrium of each crystal. At 313 K the BH form transformed to the other metastable form, D, while transforming to the stable form C. The transformation from the hydrated BH to the solvated D crystal seems to be relatively easy because of the similar configurations of carboxylic acid group in BPT. The thermodynamic stability of the solvated crystals of BH and D decreases with temperature. It is considered that the dissociation of both BH and D crystals is accelerated with increase of temperature. In the crystallization on adding water to BPT solution of methanol and water mixture, it became clear only the metastable form of A and B crystallizes and the crystallization of A form is remarkably accelerated by increasing the addition rate of water.

Dependence of Polymorphic Transformation on Anti-Solvent Composition and Crystallization Behavior of Thiazole-Derivative Pharmaceutical.

The transformation and crystallization behaviors of the polymorphs (A and C) and solvated crystals (BH (BPT·0.5H2O) and D (BPT·MeOH)) of the thiazole-derivative pharmaceutical (BPT) were investigated. The solubility of metastable form was measured with the vigorous stirring using a magnetic stirrer. It was found that at 323 K with the volume fraction of methanol (VMeOH) of 0.5, A and D forms dose not transform to the stable C form directly, but transform in two steps via the metastable BH form. The stability of A tended to decrease and the stability of D form increased with the decreased of temperature from 323 to 303 K. The A and D forms also transformed to the metastable BH form at 303 K and 313 K. This is because of the selective nucleation and growth of BH crystals due to the specific solute-solvent interaction in comparison with C crystals. The small free energy difference between BH and C forms also stabilizes BH form.It appeared that the C form is the stable form and A is the metastable form with the methanol composition (VMeOH) ranges of 0.5–0.8 at 323 K. At the methanol composition of 0.7 A, BH and D forms transformed to the stable form, C. With increase of methanol composition the stability of D form is increased and that of BH form decreased. Such tendency may be due to the dissociation of the solvated crystals.In the crystallization at 323 K by adding water as an anti-solvent to BPT solution of methanol and water mixture, it cleared that only the metastable forms of BH and D crystallize and the crystallization ratio of these polymorphs depends on the addition rate of water. Further more, it was found that BH transforms to A by solution-mediated mechanism after the crystallization.

Preparation of micron-sized, monodispersed, monomer-adsorbed polymer particles utilizing the dynamic swelling method with loosely cross-linked seed particles

Influence of the water-addition rate (R w ) (ml/h) on the monodispersity of monomer-adsorbed polymer particles prepared by utilizing the dynamic swelling method (DSM) with 1.9-μm-sized, monodispersed, loosely cross-linked polystyrene/styrene-divinylbenzene copolymer [1/(47.5–2.5), w/w] composite particles was examined theoretically and experimentally. The thermodynamic simulation under a kinetic control state indicates that, at the R w values below 4, the cross-linked composite particles adsorb all styrenes separated from ethanol/water media. The experimental result at the R w value of 2.66 supported it. At the R w values above 5.32 and below 1.33, polydispersed styrene-adsorbed particles were prepared. The former depended on the formation of some pure styrene droplets not containing the composite particle. The latter depended on coalescence among the adsorbed particles by DSM.

Estimation of the Amount of Water Removed by Gap and Atomization Air Streams During Pelletization in a Rotary Processor

ABSTRACTThe purpose of this study was to estimate the amount of water removed by the gap and atomization air streams during pelletization by the wet granulation technique in a rotary processor and to test the hypothesis that the influence of the water addition rate on the pellet size (1,7) mainly originates from differences in the amount of water removed by these air streams. Estimations from flow, temperature, and relative humidity measurements of the air streams, and estimations from moisture content measurements, indicated that approximately 3.6 g of waterImin was removed during spheronization. The estimations from the air streams' characteristics obtained for the water loss during the water addition phase (2.6 g/min) reflected the water removal during the later stages and did not reflect the overall rate of water removal during the total water addition phase as estimated from moisture content measurements (2.0 g/min). This was attributed to the fact that estimations from the air streams' characteristics could not take into account the early stages of the water addition phase. In these early stages, the amount of water removed was very limited. Using the foregoing estimations, differences in amount of water removed by the air streams could be compensated by adding more water when the water addition rate was decreased. This resulted in similar pellet sizes (geometric mean diameter of 800–850 μm) using different water addition rates. Thus, the hypothesis that the major influence of the water addition rate on the pellet size mainly originates from differences in the amount of water removed by the gap and atomization air streams was confirmed.

Chemical synthesis of optical grade ceramic precursors: A spectrophotometric approach for analysis

Extremely controlled hydrolysis of a rapidly water-absorbing alkoxide was performed so as to achieve a gel of high optical transmittance. An aluminium sec-butoxide precursor was structurally modified using ethyl acetoacetate in varying stoichiometric ratios. The sol-gel synthesis of the chelated alkoxide was conducted under closely monitored conditions of humidity, temperature and ultrasonic power and the hydrolysing water was added at extremely slow rates using callibrated micropipettes. Molecular level homogeneity was ensured by adopting an intense, contact mode probe type ultrasonication of the chelated alkoxide in presence of excess alcohol, until the alumina sol sonogelled on the addition of a stoichiometric amount of water. The sonogels were seen to possess an extremely high optical transmittance as a result of the novel processing and synthesis technique proposed and developed by us. Uv-visible spectrophotometric analysis of the sonogelling sol at every water addition was performed and a gel of over 95% transmittance could be obtained at a chelate ratio of 1:2, with 15 ml isopropyl alcohol, at a water addition rate of 0.4 ml h −1 g −1 of alkoxide, under an ultrasonic power of 90 watts.

The Influence of Five Selected Processing and Formulation Variables on the Particle Size, Particle Size Distribution, and Friability of Pellets Produced in a Rotary Processor

A factorial-designed study has been performed to investigate the effect of two formulation variables and three processing variables on size, size distribution, and friability of pellets made in a rotary processor by the wet granulation technique. The first are the microcrystalline cellulose content and the ratio of the amount of added water to the amount of microcrystalline cellulose in the powder mixture; the latter are the rotor speed, the spheronization time after water addition, and the water addition rate. Both formulation variables and the three processing variables have a major influence on pellet size and percentage loss in weight in the friability test. With the exception of the spheronization time, increasing an independent variable results in a wider size distribution. The wet granulation technique in the rotary processor has been judged to be a critical technique. However, if all variables are fully controlled, rather good reproducibility can be obtained

COMPUTER-CONTROLLED FOGGING

Wide variations in temperature and humidity on hot summer days can present problems for conventionalfogging systems. Systems with set water flow rates in liters/hour (gallons/hour) often apply too much moisture at one timeof day, while not enough at other times. Typically, broiler houses use two fogging lines with a 7.6 L/h (2 gal/h) nozzle at6 m (20 ft) intervals. While some newer houses use extra lines sequenced with thermostats, a mismatch often exists duringthe day between the water addition rate and the amount of water the air can actually evaporate. This article describes acomputer-controlled, variable-rate fogging system that had extra lines with a variety of nozzles and a motorized valve inthe discharge of the booster pump. The arrangement gave a wide range of water flow with an almost infinite number ofdiscrete flow rates. Results indicated an ability to maintain interior temperatures at somewhat of a plateau duringmidday. On a hot day with near 38C (100F) and 32% relative humidity, the system could reduce interior temperaturesby as much as 6.6C (12F) below ambient.

Improvement of the material motion in a rotary processor.

The purpose of this paper is to reject or to confirm the hypothesis that the influence of the water addition rate on the size and size distribution of pellets is caused by insufficient spreading of the added water at higher water addition rates. To overcome insufficient spreading of the added water, the agitation in the rotary processor is intensified by improving the spiral, rope-like movement by means of two baffles and a permanent PTFE coating, and by installing a chopper. Improvement of the spiral, rope-like movement moderates the influence of the water addition rate on the pellet size. The chopper has no significant influence on pellet size, pellet size distribution, or percentage of agglomerates for the pellets, which are investigated in this study. Furthermore, the implementation of the technical modifications does not influence the dissolution characteristics of the pellets directly. It is therefore concluded that the water added is well spread over the mass by ensuring an optimal spiral, rope-like movement, so that incorporation of a chopper is superfluous. The remaining influence of the water addition rate on the pellet size can most probably be explained by differences in processing time, resulting in different volumes of air capable of extracting water from the powder mass.

Cryogenic-scanning electron microscopy as a technique to image sol-to-gel transformation in chelated alkoxide systems

Direct imaging of wet sol-to-gel microstructures in chelated alkoxide systems is reported for the first time by using fast-freeze and freeze-fracture techniques for sample fixing. The system chosen for microstructural imaging is that of a chelated alkoxide, in an effort to observe sol-to-gel transformation. The batch composition corresponds to a 1: 1 molar ratio of aluminum sec-butoxide and ethyl acetoacetate made using isopropyl alcohol as a mutual solvent. About 100 μl of samples in varying stages of sonogelation, at a water addition rate of 0.4 ml per hour per gram of alkoxide, were injected between two 300-mesh TEM grids mounted on 0.1 mm copper plates and plunged into melting Freon to bring about a rapid solidification. The sample was cryo-transferred into an SEM, equipped with a cold stage maintained at −170 °C, using liquid N 2. The specimen was fractured and imaged for microstructural detail under the electron beam. The direct imaging techniques developed here have been applied to chelated alkoxides for the first time, showing the morphology and microstructure in unhydrolysed as well as fully hydrolysed sols, which were found to indicate complex shapes that were not previously known to exist in such systems. Thus, more microstructural information could be directly gained as a result of this cryo-SEM technique.