No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Characterization of Organic and Inorganic Chemicals Formed by Batch-Cooling Crystallization: Shape and Size
... For a detailed discussion on the characteristic length measured by the laser scanner instrument it is referred to Vaccaro et al. [Vac06a]. Various studies have been made that compare the FBRM with other sizing techniques [Dow01,Hea02,Abb02,Tei05,Li05a,Pat08]. Thereby, often glass, ceramic beads, Duke standards, BCR quartz powders, PVC, silica and emulsion drops are taken as particulate systems. ...
... In comparison, the laser scanner showed a clear undersizing of the respective sieve cut, as also observed by various other authors [Hea02, Li05a, Pat08, Hu08]. Patchigolla et al. [Pat08] reported differences within the median size of up to 200 µm. The systematic undersizing can be cause by several non-ideal conditions that are described in detail in chapter 5.3.2. ...
Dissertation Zur Erlangung des akademischen Grades Doktoringenieur (Dr.-Ing.) genehmigt durch das Zentrum für Ingenieurwissenschaften der Martin-Luther-Universität Halle-Wittenberg als organisatorische Grundeinheit für Forschung und Lehre im Range einer Fakultät (75 Abs.
... MSG crystallises as pentahydrate at below -0.8°C and looses its crystalline water at 120°C. The crystals used in this study were generated by batch cooling crystallisation, details of which are presented in an earlier research paper [14]. The crystals were sieved into different size rangesa glutamic acid (180 < d ≤ 250 lm), b glutamic acid (90 < d ≤ 180 lm) and MSG (180 < d ≤ 250 lm). ...
A standard method to determine particle shape and size is by image analysis. This paper addresses microscopic image analysis (semi-automated) investigations of two different organic crystalline chemicals generated by batch cooling crystallisation. The results generated from microscopic image analysis were compared with data obtained by dynamic image analysis (automated) because very few contributions are available in the open literature. The chemical systems were polymorphic L-glutamic acid which crystallises into α (prismatic) or β (needle) form and the non-polymorphic mono sodium glutamate which crystallises into needles. The images from these techniques were processed to generate information on crystal shape and size. It has been observed that shape effects can distort the size obtained in size characterization studies.
In this study, comparisons were made of processing time, number of crystals and accuracy between microscopic and dynamic image analysis. For representative microscopic image analysis, 5000 crystals were analysed in an average of eight hours while several hundred thousand crystals were processed using dynamic image analysis within 15 minutes. Using the parameters D10, D50, D90, span and aspect ratio for statistical comparison, it was found that the results obtained for D50 by the two techniques were comparable and in accordance with other measurements (laser diffraction spectroscopy and ultrasonic attenuation spectroscopy) even though these non-spherical particles had different orientations during measurement by the two methods. However, substantial differences in span of the distribution and aspect ratio were returned by the two techniques.
... Crystallization is a production method of particles which precipitate through getting oversaturated in solution and has attracted a lot of current attention for including the capability of controlling the particle properties during the production process. 2,3 There are three common methods in the crystallization: evaporation, cooling, and adding antisolvent method. However, the former two methods have some problems concerning thermal energy in the process of the crystallization. ...
Interfacial crystallization, such as surface crystallization in solution (solid-liquid) and liquid-liquid crystallization, gives us an asymmetric reaction field and is a technique for morphology control of crystals. In the liquid-liquid crystallization, the concentration distribution of solute ions and solvent molecules at the liquid-liquid interface directly relates to nucleation, crystal growth, and crystal morphology. Nonequilibrium molecular dynamics (MD) simulations have been performed at interfaces in NaCl solution/1-butanol and KCl solution/1-butanol system in order to clarify diffusion behavior of solute ions and solvent molecules. As simulation results, the hydrated solute ions were dehydrated with the diffusion of water from solution phase into 1-butanol phase. The different dehydration behaviors between NaCl and KCl solution can be also obtained from MD simulation results. Aggregated ions or clusters were formed by the dehydration near the solution/1-butanol interface. By comparison on the normalized number of total solute ions, the size and number of generated cluster in KCl solution/1-butanol interface are larger than those in the NaCl system. This originates in the difference hydration structures in the each solute ion.
Growing high-quality crystals with ideal properties is of great importance. The morphology of crystal is one key factor reflecting product quality, as it can affect the performance of products and downstream operations. In this work, the current state of crystal morphology modification is reviewed from different perspectives. First, the most widely used crystal growth models are discussed. Then, a variety of crystal morphology control methods, which include adjustment of crystallization operation parameters, addition of foreign molecules, change of different solvents, membrane assistance, the addition of external physical fields and the use of ball milling are summarized. As for applications, the control of crystal morphology has application potential in pharmaceutical and material fields, for example, energetic materials and semiconductor materials. Finally, the future development direction of crystal morphology regulation is discussed.
In situ microscopic imaging is a useful tool in monitoring crystallization processes, including crystal nucleation, growth, aggregation and breakage, as well as possible polymorphic transition. To convert the qualitative information to be quantitative for the purpose of process optimization and control, accurate analysis of crystal images is essential. However, the accuracy of image segmentation with traditional methods is largely affected by many factors, including solid concentration and image quality. In this study, the deep learning technique using mask region-based convolutional neural network (Mask R-CNN) is investigated for the analysis of on-line images from an industrial crystallizer of 10 m³ operated in continuous mode with high solid concentration and overlapped particles. With detailed label points for each crystal and transfer learning technique, two models trained with 70,908 and 7,709 crystals respectively are compared for the effect of training data amount. The former model effectively segments the aggregated and overlapped crystals even at high solid concentrations. Moreover, it performs much better than the latter one and traditional multi-scale method both in terms of precision and recall, revealing the importance of large number of crystals in deep learning. Some geometrical characteristics of segmented crystals are also analyzed, involving equivalent diameter, circularity, and aspect ratio.
In this work, different solvents and mixtures were used to prepare the polymorphs (α and β form) of azelaic acid by cooling crystallization at 308.15–263.15 K, including ethanol, propionic acid, n-butanol, methanol, and ethyl acetate. As a result, the α form was successfully prepared in propionic, while the β form was obtained in ethanol. Then the structures and morphologies of both polymorphs were characterized by various means. Moreover, the dissolving properties of the two forms in water, ethanol, and propionic acid from 263.15 K to 308.15 K were investigated by both experiments and molecular dynamic (MD) simulation for the first time. Results show that solubility of the two forms increase with temperature, which are well fitted by the Modified Apelblat model and NRTL model. What's more, the solubility of each form in ethanol is the highest compared to that in propionic acid and water. Particularly, the solubility of α polymorph is always higher than that of β polymorph from 280.15 K to 308.15 K indicating that the latter should be the stable form. The same results were also obtained through the calculation of molecular interaction in the solid, which are −5.02 kJ/mol of α form and −11.46 kJ/mol of β form. Finally, the diffusion coefficients and solvation free energies were calculated for the α and β conformations in solution, and the results reveal that high diffusion rate and solvation free energy seem stay the same with high solubility in different solvents.
Crystal morphology is known to be of great importance to the end-use properties of crystal products, and to affect down-stream processing such as filtration and drying. However, it has been previously regarded as too challenging to achieve automatic closed-loop control. Previous work has focused on controlling the crystal size distribution, where the size of a crystal is often defined as the diameter of a sphere that has the same volume as the crystal. This paper reviews the new advances in morphological population balance models for modelling and simulating the crystal shape distribution (CShD), measuring and estimating crystal facet growth kinetics, and two- and three-dimensional imaging for on-line characterisation of the crystal morphology and CShD. A framework is presented that integrates the various components to achieve the ultimate objective of model-based closed-loop control of the CShD. The knowledge gaps and challenges that require further research are also identified.
High-Resolution Ultrasonic Spectroscopy (HRUS) is a novel analytical technique for non-destructive material analysis for a wide range of samples and processes. This technique is based on precision measurements of velocity and attenuation of acoustical waves at high frequencies propagating through materials. It has considerable advantages over many alternative technologies because it can be applied to systems that are optically opaque and concentrated without the need of any sample preparation. It provides an unprecedented range of new analytical capabilities for research, product development, quality and process control. Applications of this technique include analysis of solution-phase crystallization, aggregation and gelation phenomena, particle sizing, stability of emulsions and suspensions, microstructural transitions and pharmaceutical manufacturing. Here, we review the theory of the HRUS and its applications on crystallization process.
Laser-backscattering instruments, such as the focused beam reflectance measurement or threefold dynamical optical reflectance measurement, are promising tools to aid crystallization process development, allowing an in situ, real-time, and nondestructive measurement of particle size distributions. Besides the instrument principles, in detail geometrical and optical models are discussed which deconvolute the recorded chord length distribution. Emphasis is thereby laid on the influence of the suspension density on instrument recordings. The application of laser-backscattering devices for determination of kinetic constants is discussed and future directions and perspectives are given.
Taurine crystals (TC) with high fluidity, anticaking, and antisticking properties are commercially required by manufacturers. Crystal size and shape are two main factors controlling these properties. This study investigated the size and shape of TCs produced by a cooling crystallization processing. The addition of activated carbon to decolor the product exhibited negligible effects on the size of TCs. Increasing the crystallization temperature resulted in the formation of small-size crystals, whereas TC size decreased as the stirring rate increased. A careful control of post high-speed stirring aging in a slowly stirred system enabled the preparation of larger crystals. The estimation of optimal crystallization time is crucial as lengthening the crystallization time might not effectively increase the overall size of the crystals. It was found that the shape of the TC was not affected by various operating conditions, delineating a similar inherent molecular arrangement of taurine molecules under the range of operating conditions tested. These findings contribute to the understanding of controlling properties of TCs for industrial manufacturing via the cooling crystallization method.
Particle size and suspension density of urea suspensions were investigated by means of ultrasound, optical reflectance as well as focused-beam reflectance measurement techniques. These techniques provide similar proven nonrealistic results regarding suspension density and crystal size. The resulting data can be explained by the presence of bubbles. The influence of air bubbles on the measurement of different particle size and suspension density monitoring techniques is demonstrated and evaluated. Floating air bubbles as well as crystal-bubble complexes are strongly affecting the results and have to be considered under real conditions. It can be demonstrated that the negative impacts on the measured data can be decreased. Special precautions have, therefore, to be taken into account for calibrations, their validation, and during crystallization monitoring or controlling to avoid faulty measured suspension densities and particle sizes caused by bubbles.
The mean crystal size, the suspension d., and the liq. concn. are the 3 most important process parameters to quantify the progress of industrial crystn. processes. These parameters can be in-line monitored simultaneously by an ultrasonic crystn. monitoring technique (UCM), which will be introduced here in a proof of concept. This process anal. technol. (PAT) differs from the known ultrasonic attenuation spectroscopy (UAS). For the UCM the ultrasonic velocity and attenuation were correlated and related to characteristic events during a crystn. process measured at only one frequency (no spectra of frequencies as it is used for UAS). The results shown prep. the ground to establish the UCM as a simple, less complex, robust, universal applicable, inexpensive, and, therefore, a winning alternative PAT to monitor and control in-line the solid as well as the liq. phase in the industrial crystn. by only one measuring device with 2 sensors.
Quantification of droplet shape in a spray field can elucidate several characteristics and mechanisms of the atomization process such as droplet deformation, breakup, and collision. To identify an optimum parameter for accurate quantification of droplet shape using image-based measurement systems, several parameters from different applications are presented in terms of their mathematical definition, calculation procedure, and characteristics. An experimental investigation using a shadowgraph droplet analyzer is also conducted to provide visual evidence of droplet shape in a spray field. The droplets from this data set are classified based on their shape into three categories, namely, spheres, deformed droplets, and ligaments. The capability of the shape parameters in distinguishing between these droplet groups is investigated using a simulation and the collected droplet images. Many of the parameters have insufficient resolution to distinguish between different droplet shapes. A new scaling parameter is applied to each of the parameters to distinguish droplets that are purely convex (spheres and deformed droplets) from those that have concavity (ligaments). From those investigated, an optimum shape parameter is suggested to distinguish the three droplet groups.
Molecular dynamics simulations have been performed for the design of operating conditions of liquid-liquid interfacial crystallization and clarifying the crystallization mechanism. It was found that solute ions were dehydrated with diffusion of the hydration ions from solution to organic phase. There were a significant difference of the dehydration behaviour between NaCl solution/1-butanol and /2-butanone. Aggregated ions or clusters were formed by the dehydration near the solution/organic solvent interface. The number of cluster generation near NaCl solution/2-butanone interface was larger than that in the 1-butanol system. This difference originates in the interfacial structure in the NaCl solution/the each organic solvent interface.
In this article, particle size distributions (PSDs) measured by different techniques, including image analysis (IA), laser diffraction (LD), ultrasonic attenuation spectroscopy (UAS), and focused-beam reflectance measurement (FBRM), are compared for spherical glass beads and nonspherical silica flakes. It is shown that particle shape strongly affects the results obtained by different techniques. For spheres, the PSDs obtained by IA, LD, and UAS agree well. There is no consistent result among different particle measurement techniques for nonspherical particles. The conversion between PSDs obtained by IA, LD, and UAS has been based on particle shape factors. Caution must be exercised when a measured chord length distribution (CLD) is used to indicate the PSD during a process because the CLD result obtained by FBRM is complex, depending not only on the PSD, but also on particle optical properties and shape.
It is shown that the crystallization process of the polymorphs of L-glutamic acid (α and β) at 45°C is composed of four steps (I, II, III, IV) including the solution-mediated transformation from α to β (II). On the other hand, in the crystallization at 25°C, almost only α nucleates and grows, and the transformation rate is very slow. It appears that the temperature effect on the relative nucleation rates of the polymorphs in the crystallization is much more remarkable than the effect of the supersaturation ratio, i.e. the nucleation rate of α relatively decreases with an increase in temperature at constant supersaturation ratio. This effect suggests that the kinetic coefficient for the nucleation of α decreases with increasing temperature.
Within the framework of routine application of image analysis in a pharmaceutical laboratory, a compromise should be established between the number of particles, the analysis time and the accuracy of the results. In the case of nonacicular particles, 500 particles constitute the minimal set to be analysed to get basic information on size and shape distributions. The best choice is 1000 to 1500 particles. As complex shapes should be described by a set of parameters, statistical data mining techniques allow to globally compare samples from the point of view of their size and morphology. For acicular particles, frequently seen in pharmaceutical powders, an algorithm based on the Hough transform and the Euclidian Distance Map transform has been developed: it allows to estimate the length and the breadth of the particles, even when they are in (limited) contact with one another.
The potential application of ultrasonic attenuation spectroscopy to the in situ examination of solution phase crystallization processes is examined through studies carried out on two organic compounds: urea and (L)-glutamic acid. For this study a commercial ultrasonic spectrometer [Ultrasizer by Malvern Instruments Ltd., F. Alba, U.S. Patent 5,121,629 (1992)] was used. A particle size analysis was carried out in an attempt to monitor the crystal size distributions of the crystals growing within the mother liquor. While this technique was found to be of limited effectiveness for the monitoring of the crystallization of urea, due to the formation of high aspect ratio needle crystals, whose long axial size is beyond the range of the technique (0.01 μ-1000 μ), good results were obtained with prismatic (L)-glutamic acid crystals. The size evolution of the latter during crystal growth was successfully monitored throughout the crystallization process.
The shape of the particles produced by comminution is affected by the kind of breakage action employed. Furthermore, the procedures used to determine product particle size are themselves influenced by shape. Illustrative examples of the effects of shape on particle size analysis and of shape variations in comminuted material are presented. Light scattering size measurements on narrow sieve fractions were found to indicate size distributions that were significantly broader than the sieve size range, especially for irregularly shaped particles. The distributions were also shifted to coarser sizes for the irregular particles but not for spheres. The apparent size shift is attributed to differences in the definition of size, while it is proposed that the apparent broadening of the distribution is a result of orientation effects. It is shown that broadening is relatively insignificant for broad, continuous distributions due to compensation effects. Applications to the determination of composite distributions by combining sieving and light scattering data are described. Distributions of particle shape descriptors, obtained by image analysis of comminution products, are shown to depend on the comminution method used. A slight variation with size was observed for coal particles but not for quartz. The implications of the size/shape interaction on the evaluation of comminution process performance are discussed.
The controlling factor and mechanism of the crystallization of polymorphs were investigated in the various systems. The effect of supersaturation was hardly observed in the polymorphic crystallization of both L-glutamic (α,β) and L-histidine (A,B). The temperature effect appeared intensively in the case of L-glutamic acid polymorphs, however, no effect of temperature was observed for L-histidine polymorphs. Such difference of the temperature effect may be related with the difference of the molecular conformation between the polymorphs. In the reactive crystallization of calcium carbonate polymorphs between the calcium chloride and the sodium carbonate solutions, the effect of the concentration (supersaturation) of reactant solutions, the mixing rate of the solutions and temperature on the morphology and the crystallization of polymorphs (calcite, vaterite and aragonite) was observed. The complicated precipitation behavior and the morphological change may be related with the formation of the precursors. The effect of L-phenylalanine on the growth rate and morphology of L-glutamic acid polymorphs was also investigated by the single crystal method. The relationship between the additive concentration and the growth rate of each polymorphs was presented by the equation of the proposed model. The method of the selective crystallization of the polymorphs by controlling the supersaturation degree and the additive concentration was also indicated.
The β-crystal formation of L-glutamic acid in the seeded solution was investigated; and it was found that the growth rate of the seed crystals in a-axis direction was nearly as large as that of the α-crystal, but the growth rate in b- and c-axes was little recognized. The activation energy of the crystallization process of the β-crystal in a-axis direction was calculated from the growth rate constants determined at various temperatures, and 6-7kcal/mol was obtained. On the assumption that the crystallization of β-crystal growth was controlled by the diffusional operation, the thickness of the laminar film was calculated from the growth rate constant and the estimated value of the diffusional constant. The calculated value of the thickness was much greater than the value reported by Nernst; therefore, the crystallization process should be controlled by the surface reaction. The co-existence of a small quantity of amino acids caused a great reduction in the growth rate of the β-crystal. © 1963, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.
The solubilities of L-glutamic acid crystals in α-form and β-form in water were determined, and the results were formulated as follows.
α-form: Log S=-0.377+0.0174t (t is from 0° to 30°C)
Log S=-0.328+0.0153t (t is from 30° to 70°C)
β-form: Log S=-0.461+0.0159t
The formula obtained for β-crystals showed a fair agreement with that reported by J. B. Dalton et al.
The β-crystal formation of L-glutamic acid in the seeded solution was investigated; and it was found that the growth rate of the seed crystals in a-axis direction was nearly as large as that of the α-crystal, but the growth rate in b- and c-axes was little recognized. The activation energy of the crystallization process of the β-crystal in a-axis direction was calculated from the growth rate constants determined at various temperatures, and 6-7kcal/mol was obtained. On the assumption that the crystallization of β-crystal growth was controlled by the diffusional operation, the thickness of the laminar film was calculated from the growth rate constant and the estimated value of the diffusional constant. The calculated value of the thickness was much greater than the value reported by Nernst; therefore, the crystallization process should be controlled by the surface reaction. The co-existence of a small quantity of amino acids caused a great reduction in the growth rate of the β-crystal.
The effects on the polymorphic crystallization of L-glutamic acid were examined of many substances including amino acids, inorganic salts, surface active agents, and sodium salt or hydrochloride of L-glutamic acid, when contained in the mother liquor.
The co-existence of amino acids, especially of L-aspartic acid, L-phenylalanine, L-tyrosine, L-lcucine and L-cystine contributed to the crystallization of L-glutamic acid in α-form, and these amino acid showed an inhibitory action on the transition of α-crystals as the solid phase in the aqueous solution, to β-crystals.
In the presence of a large amount of L-glutamate or the hydrochloride at the time of nucleation of L-glutamic acid, mostly β-crystals appeared even in the presence of the amino acids named above.
In an aerosol spectrometer the size of a powder grain is measured from the time-of-flight of the fineparticle between two laser beams. Due to the flow conditions, irregularly shaped fineparticles align themselves along the direction of flow of the air stream carrying them across the gap between the laser beams. The size distribution measured therefore varies with the shape of the fineparticles. This fact is demonstrated by comparing size distributions generated by image analysis, electrozone stream counter, diffractometer, and time-of-flight aerosol spectrometer.
Monosodium L-glutamate crystals, which are of fragile needle, were obtained by batch crystallization with a natural cooling mode from aqueous solution. The effect of seeding on the product size was examined over a wide range of seed-loadings. The seed-loading ratio C-s defined as the mass ratio of the added seeds to the theoretical yield per batch, had basically the same effect on the product crystal size as ob-served previously in cooling crystallization of mechanically strong granular crystals such as potassium alum. At high seed-loading ratios as C-s greater than or equal to C-s*, where C-s* is a critical value of C-s, seed crystals grew with practically no secondary nucleation. Crystal breakage due to mechanical impacts brought by an agitator occurred only slightly for the small products. For the large crystals the breakage was significant. The breakage also depended on the type of stirrers used; the anchor stirrer induced less breakage than the turbine stirrer. The transient supersaturation was measured on-line by an electro-conductivity method.
The mechanism of additive effect of L-phenylalanine (L-Phe) on the growth kinetics of L-glutamic acid (L-Glu) polymorphs was investigated. With L-Phe concentration the growth rate of the (101) face of the β crystal decreased and finally stopped at a critical concentration Cp*. As for α crystal the growth rate in the [111] direction was suppressed and the new (110) face appeared, while the growth rate of the (001) face was not influenced by L-Phe. The fluctuation of the growth rates was observed for both polymorphs at the higher concentration of L-Phe. The critical concentration of L-Phe for the (110) face of α is about twice of that for the (101) face of β. At the constant L-Phe concentration each polymorph grew at higher supersaturations than the critical relative supersaturation σ*. The value of σ* for the β crystal was a few times larger than that for the α crystal. The relationship between the growth rates and the concentration of the additive was expressed using the growth model of a curved step in connection with the adsorption density of the additive. The dependence of the growth rate of L-Glu on the L-Phe concentration and the relative supersaturation could be represented by Freundlich-type equations for both polymorphs. The calculated values of the adsorption density and the distance between the adsorbed neighboring L-Phe molecules also showed the preferential adsorption of L-Phe on β crystals. The method to determine the optional supersaturation at the certain concentration of additives was proposed.
Glutamic acid can crystallize in two polymorphic structures depending on the crystallization regime. The study demonstrates an efficient method to preferentially crystallize the non-stable polymorphic structure (the α-form) in the presence of surface active agents. The rate of transformation was found to depend on the rate of growth of β and not on the rate of dissolution of α. The growth rate of β was a function of the supersaturation of the solute in solution. It was shown that the transformation could be inhibited by the addition of surfactants. The surfactants are capable of adsorbing preferentially to the α-growing crystals and solution mediating (retarding) the transformation of the α- to the β-form. It was suggested that the surfactant nature and steric considerations were important for the inhibition of both nucleation and growth of the β-polymorph. A Langmuir approach indicated that the kinetic parameter was related to the volume of surfactant adsorbed at the crystal surface. No changes in crystal morphology were observed, indicating that adsorption was not specific to any crystal face. Different mechanisms of surfactant adsorption were suggested: adsorption of single molecules at low concentrations of surfactant and formation of hemimicelles at higher concentrations.
The effects of five γ-L-glutamyl peptides, two α-L-glutamyl peptides, and L-phenylalanine (L-Phe) on the growth of {111} and {001} faces of the α-form of L-glutaminic acid (L-Glu) crystals were investigated. All the γ-L-glutamyl and α-L-glutamyl peptides and L-Phe had inhibitory effects on the growth of the {111} face, but γ-Glu-Glu, γ-Glu-ϵ-Lys, and Glu-Glu suppressed not only the {111} faces but also the {001} faces. Thus, the distribution of additives on the {111} and {001} faces of L-Glu crystals was analyzed. Results showed that the {001} face of L-Glu crystals had higher concentrations of γ-Glu-Glu, γ-Glu-ϵ-Lys, and Glu-Glu than other peptides. The effect of γ-Glu-Glu on inducing the β-form is considered to be closely related to its specific character of inhibiting the growth of both the {111} and {001} faces of the α-form. These phenomena are discussed on the basis of the crystal structure.
Two of the most widely used methods in sizing particulate materials are the electrical sensing zone method (ESZ) and the laser diffraction (LD). In order to deduce size information from a measurement, it is assumed in the LD technology that the particles are spheres. For real industrial materials, only rarely are the particles spherical. The effects of non-sphericity on different technologies vary, causing discrepancies in results and bias from the true characteristics of the sample. Applications in many fields require information about the shape of the particles in addition to their size. Recently, dynamic image analysis (DIA) has been shown to be able to provide both size and shape information of particulate materials. DIA is not subject to restrictions of the spherical assumption and, therefore, provides a means to study the effect of shape in the results obtained using LD and ESZ. In this study, samples of various shapes were characterized using the three technologies (LD, ESZ, and DIA). Laser diffraction yielded progressively larger mean sizes as well as broader distributions as the shape of the particles deviates more and more from that of a sphere. The ESZ and DIA experiments, on the other hand, produced compatible results much less affected by particle shape. The study suggests that DIA is a powerful tool in characterizing nonspherical particles and that caution needs to be taken when evaluating the sizing results of nonspherical particles using laser diffraction.
Particle shape analysis is one of the most difficult problems in powder technology, and to date there is no general shape factor available which clearly differentiates between all possible kinds of shape. A shape factor for particles has been developed on the basis of two-dimensional particle outlines obtained by image analysis. The proposed shape factor uses the deviations of the two-dimensional particle outline from standard images of a circle, triangle and square, and considers the particle elongation and the number of characteristic corners of the apparent shape. The proposed shape factor has first been evaluated for mathematically defined shapes. A comparison with standard shape factors such as aspect ratio and circularity has shown that the new shape factor can differentiate between these model shapes. Therefore, five test powders with variable shape have been studied. While aspect ratio and circularity failed to identify the underlying particle shape and the differences in shape between the five powders, the proposed shape factor identified both the shape of each particle batch and the sometimes small differences in shape from batch to batch. Although the new shape factor has some limitations, it could improve the definition of shape characteristics of powders.
It is well established that particle size and shape substantially influence the bulk properties of powdered materials. Although these characteristics are closely interrelated, the tendency has been to analyse the particle size independently from particle shape. The aim of this work was the assessment of particle shape through particle sizing data. For this purpose, three different particle shape materials – glass beads (spherical), crushed glass (moderately irregular) and mica (lamellar) – were tested, employing four particle sizers. The shape factor selected was the Wadell's sphericity, which was evaluated utilizing distinct equations. The comparison of the results reveals problems arising from the use of approximations rather than more fundamental equations.
This study was conducted to establish a simple method for evaluating the morphology of fine anisometric particles using size measurement techniques. The size distributions of mica particles and carbon fibers classified into narrower size ranges were measured by gravitational sedimentation and laser diffraction techniques. The ratio of mean diameters determined for flaky particles strongly depended on the aspect ratio, i.e. flatness. The relationship between particle shape and diameter is discussed theoretically. The experimental results were similar to those predicted. The flatness of fine particles can be evaluated by the ratio of the median diameter determined by laser diffraction to that determined by sedimentation.
The absorption of sound in emulsions and suspensions is due to viscous and thermal transport processes occurring at the interface of the nonhomogeneities, as well as to the intrinsic absorption in the materials comprising the system. A complete description of these processes for systems of fluid particles suspended in fluid media was given by Epstein and Carhart [J. Acoust. Soc. Amer. 25, 553 (1953)]. However, subsequent investigators of liquid systems have generally neglected the thermal transport process. We show in this work that the Epstein‐Carhart results provide a good description of our experimental attenuation data in emulsions, and that the thermal transport process can be the major factor in the attenuation. We have here also extended the theory further to include the attenuation in suspensions of solid particles, and good agreement is found between our theory and experimental results for aqueous suspensions of polystyrene spheres.
Carefully sieved crystals of nickel ammonium sulphate are analysed with a Coulter particle size counter. Simple correction factors are proposed to rationalize the two sizing techniques.
The measurement of particle size and distribution are of paramount importance in assessing feed pellet quality. For many years, dry sieving has been used to characterise the particle size distribution but this technique is time-consuming and has not been modernised. Other particle sizing methods, more modern, have been developed, such as methods based on light scattering measurements. The laser diffraction technique (based on Fraunhofer diffraction theory) was compared to sieving, the standard procedure. The discrepancies between the two methods seemed to be attributable to particle shape factors which were dependent on the size fractions examined. The laser diffraction method thus gave sufficient accuracy when applied to products with a small range of particle size.
This paper describes how the formation of particle systems can be investigated by using computer vision techniques, namely effective exact dilations and multiscale skeletonization. By assuming that all particles started to grow at the same time and had the same growth rate, a hypothesis that can be validated later, it becomes possible to infer the shape and distribution of the particles in the initial system configuration. Multiscale skeletons are obtained for each individual particle, and a suitable overall spatial scale, i.e. those best approximating the initial configuration, is determined as that immediately before the smallest particle fades. The thus obtained skeletons provide an estimate of the shape and position of the initial particles before uniform expansion. By using exact dilations, a generalized Dirichlet tessellation reconstruction of the particle system is obtained from these skeletons, and the similarity between this reconstruction and the original system can be used to validate the assumptions about the growth conditions. The proposed methodology is illustrated with respect to KC1 polycrystalline thin films.
The ultrasonic attenuation (UA) technique was developed to measure not only particle size distribution (PSD) but also concentration for on‐line and off‐line analysis of high concentration dispersions. Another significant characteristic along with particle size is particle shape. Particle shape influences the apparent particle size as measured by various instruments. Shape factors have been calculated from microscopic images using conventional image analysis (IA) techniques. Particle sizing data measured by UA is more representative than by IA because much larger samples are used for analysis. In this study UA, laser diffraction (LD) and IA size measurements are compared and the influence of particle shape is investigated.
Data obtained from UA has been combined with information on shape factor from imaging to obtain equivalent particle size distributions. In a previous study [1], the influence of shape on size measurement has been investigated using different sizing techniques for non‐fragile materials. These particles showed significant variation in measured PSD with their different shapes. In this paper, the same phenomenon was observed with evolving polymorphs of L‐glutamic acid crystals (α and β form), oxalic acid, sucrose and monosodium glutamate.
We present a simple technique that can identify suitable data from a noisy signal produced on-line by commercially available image-analysis software. A controller successfully uses this signal to regulate the flow rate of a habit modifier stream to maintain a desired crystal habit. We demonstrate these methods on a simple chemical system: sodium chlorate (NaClO 3 ) crystallization using sodium dithionate (Na 2 S 2 O 6 ) as a habit modifier.
The particle size distribution of particles in liquid-based suspensions and emulsions is an important parameter in a wide variety of industrial applications. Many particle-sizing methods require the transmission of light through a sample of the system, and therefore these particulate systems must be severely diluted. Many systems are unstable on dilution and therefore have to be measured at high volume concentration. Sound waves interact with both the suspending medium and the dispersed phase and are able to propagate through concentrated systems. The development of new ultrasonic transducer technology together with advances in digital signal processing has opened the way for a powerful new analysis termed acoustic attenuation spectroscopy. The technique consists of propagating ultrasonic waves of a range of frequencies through the particulate system and accurately measuring the attenuation at each frequency. This attenuation spectrum can be converted to a particle size distribution and a measure of the concentration of the dispersed phase. It offers the particle technologist the means to monitor and control particle formation and reduction processes.
To elucidate the mechanism of polymorph-selective crystallization of L-glutamic acid (L-Glu) crystals by the additives, the effects of various L-amino acids, carboxylic acids, and a di-peptide, γ-L-glutamyl-L-glutamic acid (γ-Glu-Glu) on the growth of the {1 0 1 }, {0 1 0}, and {0 0 1}, three dominant faces of the β-form of L-Glu crystals have been investigated experimentally and structurally. γ-Glu-Glu and L-phenylalanine (L-Phe) showed nearly the same strong inhibitory effects on the three faces of the β-form in contrast to their different behavior on the two dominant faces of the α-form of L-Glu. These phenomena were explained in terms of the characteristics of the hydrogen bonds of each face and it was found that the β-form has less discriminating capacity than the α-form for the recognition of the molecules. Finally, the cause of the polymorph-selective crystallization by the additives in the L-Glu is attributed mainly to the difference in the inhibitory effects of the additives on the two dominant faces of the α-form.
Using a newly developed batch crystallizer (WWDJ-crystallizer) equipped with a slurry sprinkler named Wall Wetter and a double-deck jacket, a suppression of the solvent-mediated transformation of the metastable polymorphic crystals was attempted. Crystallization of l-glutamic acid was carried out to show an example of the suppression. The target polymorphic crystals, namely the metastable α-form crystals were exclusively obtained from the aqueous solution without transformation to the stable β-form polymorph even at a temperature where the transformation could not be avoided if a conventional batch crystallizer was used. The characteristic size of crystals obtained by WWDJ-crystallizer was large and their size distribution was narrow, comparing with those obtained by a conventional crystallizer.
Many speciality organic chemical products, such as pharmaceuticals are crystals that exhibit multiple morphological forms and habits that are of critical importance not only to the end use properties of the products, but also to their downstream processing, such as in filtration and handling and in transport and storage. It is known that minor changes in operating conditions, such as cooling rates and supesaturation can have significant impact on the product leading to batch-to-batch variation. As a result, precision manufacture of crystalline products demands on-line techniques for real-time measurement of crystal morphology. The use of a non-invasive on-line imaging technique in a batch reactor for monitoring cooling crystallization of (L)-glutamic acid which exhibits two polymorphs, alpha and beta is described. The technique was found to allow real-time observation of some temporal moments that are critical in the crystallization process, in particular the crystallization onset and transformation between the two polymorphs. For validation and benchmarking purpose, an off-line system for particle characterization, the PharmaVision 830, and photo-microscope were also used in the study in parallel with the on-line imaging system. © 2005 American Institute of Chemical Engineers AIChE J, 2005
A systematic account is given of the extant freshwater snail fauna of Oman, based on recent collections made in Dhofar and in the northern mountainous areas. Also included are certain species found in brackish coastal localities. A total of 8 freshwater species is regarded as belonging to the fauna of normal freshwater; 7 have been found alive (Thiara scabra, Melanoides tuberculata, Lymnaea natalensis, Gyraulus piscinarum, Biomphalaria arabica, Bulinus wrighti and Indoplanorbis exustus) and one is known only as shells (Paludestrina glaucovirens). This report of G. piscinarum is the first for Oman and may be the first reliable identification for Arabia. Three taxa from brackish water, Gangetia miliacea, Iravadia quadrasi and Melanoides sp., are new for the fauna of Oman and of the whole Arabian peninsula. The finding of G. miliacea provides the first instance of any member of the Stenothyridae living west of the Gulf of Oman and identified from whole snails rather than empty shells. I. quadrasi is the first member of its genus to be found alive west of the Gulf of Oman.
Single crystals of a new promising nonlinear optical material for the tunable UV harmonic generation, l-pyroglutamic acid 60×20×20 mm3 in size were obtained from aqueous solution by using the temperature-lowering method. Solubility of l-pyroglutamic acid in different solvents was measured. The single crystals showed different morphological characteristics and growth rate in different solvents with different crystallographic orientations. Methanol or ethanol solutions yielded needle-like crystals. In mixed solution such as methanol/H2O or ethanol/ H2O plate-like crystals with a thickness in the direction [0 1 0] were observed. The water as a good solvent, however, produced long prism-like crystals. The two polymorphs of L-pyroglutamic acid (α and β phases) were found for the first time. The growth shapes of α-phase is mainly a prism and β phases is a rhombic plate.The growth rate of α and β phases is mainly a function of the supersaturation of the L-pyroglutamic acid in solution.
Different types of solid bodies (particles) with specific shape and size are needed for industrial processes. For spherical particles, ‘sizer’ measurements are usually reported as sphere diameters. For non-spherical particles, particle shape and especially orientation must be taken into account. Particles of a specific shape will present different views when looked at from different directions.We have employed a Camsizer® instrument to measure the distribution of projected area under different physical conditions for solid cylindrical particles:•Under ‘ideal’ conditions, corresponding to a uniform distribution of particle orientation, measurements agreed with predictions. The celebrated theorem of Cauchy applies only to this case.•For two other situations, measured and predicted results differed. However, from the experimental data it was possible to infer the particle orientations and hence theoretically predict the projected area distribution. Excellent agreement between theory and practice was then restored.
The present paper describes the results of a round robin that has been performed to investigate the influence of particle shape on particle-size distributions measured with commercial particle-size analyzers. The commercial equipment based on the five kinds of measuring principle such as electrical sensing zone, laser diffraction and scattering, X-ray sedimentation, photosedimentation, and light-obscuration methods have been employed for analyzing blocky, flaky and rod-like ceramic particles. It is demonstrated that the particle shape has a strong influence on the particle-size distribution measured by the laser diffraction and scattering and by photosedimentation. The size range of rod-like particles is particularly wide when these methods are applied. It is also shown that the particle-size distributions of anisotropic samples measured by photosedimentation has a tendency to be remarkably scattered in the coarse-size range.
The light scattering properties of twenty-eight particles, spanning four sizes (near the resonance region) and seven related shapes (a 4:1 cylinder, 4:1 and 2:1 prolate spheroids, a sphere, 2:1 and 4:1 oblate spheroids, and a 4:1 disk), are presented for a common index of refraction, m = 1.61-i0.004, representing silicates. Microwave analog and theoretical methods were used to derive the scattered intensity and degree of polarization as a function of the scattering angle along with the extinction. All results refer to an ensemble or a cloud of identical particles because averages have been taken over random particle orientations. The degree of polarization, backscatter, and the radiation-pressure cross section are most sensitive to particle shape, implying that the use of Mie theory may be inappropriate for many applications.
The suspended particles are approximated by spheres and the diffraction problem for a fluid sphere in a fluid medium is solved taking into consideration viscosity and thermal conduction. The results are discussed numerically for water droplets in air and a satisfactory agreement with Knudsen's attenuation measurements in water fog is found.
Comparison of particle size
- D Wilkinson
- K Patchigolla
Wilkinson, D.; Patchigolla, K. Comparison of particle size
Online measurement of crystal size distribution during batch crystallisation
- T Tahti
- M Louhi-Kultanen
- S Palosaari
Tahti, T.; Louhi-Kultanen, M.; Palosaari, S. Online measurement
of crystal size distribution during batch crystallisation. In Proceedings of
the 14th International Symposium on Industrial Crystallization, Cambridge,
U.K., 1999.
Direct measurement of concentration and size for particles of different shapes using laser light diffraction Technique error (%) ) [(Technique mean -Technique converted mean ) × 100 Measurement of the size, shape and orientation of convex bodies
- D J Brown
- P G Felton
- D J Brown
Brown, D. J.; Felton, P. G. Direct measurement of concentration and size for particles of different shapes using laser light diffraction. Chem. Eng. Res. Des. 1985, 63, 125-132. Technique error (%) ) [(Technique mean -Technique converted mean ) × 100]/Technique mean (5) Ind. Eng. Chem. Res., Vol. 47, No. 3, 2008 811 (20) Brown, D. J., et al. Measurement of the size, shape and orientation of convex bodies. Chem. Eng. Sci. 2005, 60 (1), 289-292.
Method and apparatus for determining particle size distribution and concentration in a suspension using ultrasonics
- F Alba
Alba, F. Method and apparatus for determining particle size
distribution and concentration in a suspension using ultrasonics. In U.S.
Patent 5,121,629, 1992.
Part 1: Particle size measurement
Part 1: Particle size measurement. AdV. Colour Sci. Technol. 2002, 5 (1),
1-11.
Technique error (%) ) [(Technique mean - Technique converted mean ) × 100
Technique error (%) ) [(Technique mean -
Technique converted mean ) × 100]/Technique mean (5)
Ind. Eng. Chem. Res., Vol. 47, No. 3, 2008 811
- Particle-Shape
Particle-Shape. Appl. Opt. 1981, 20 (23), 4039-4050.
Direct measurement of concentration and size for particles of different shapes using laser light diffraction
- D J Brown
- P G Felton
Brown, D. J.; Felton, P. G. Direct measurement of concentration
and size for particles of different shapes using laser light diffraction. Chem.
Eng. Res. Des. 1985, 63, 125-132.
Technique error (%) ) [(Technique mean -Technique converted mean ) × 100]/Technique mean (5)
Measurement of the size, shape and orientation of convex bodies Size distribution of needle-shape crystals of monosodium L-glutamate obtained by seeded batch cooling crystallization
- D J Brown
(20) Brown, D. J., et al. Measurement of the size, shape and orientation
of convex bodies. Chem. Eng. Sci. 2005, 60 (1), 289-292.
(21) Doki, N., et al. Size distribution of needle-shape crystals of
monosodium L-glutamate obtained by seeded batch cooling crystallization.
The effect of shape on intermethod correlation of techniques for characterizing the size distribution of powder. Part 2: Correlating the size distribution as measured by diffractometer methods, TSI-amherst aerosol spectrometer, and coulter counter
- H K Brain
- A David
Brain, H. K.; David, A. The effect of shape on intermethod
correlation of techniques for characterizing the size distribution of powder.
Part 2: Correlating the size distribution as measured by diffractometer
methods, TSI-amherst aerosol spectrometer, and coulter counter. Part. Part.
Syst. Charact. 1999, 16, 266-273.
- Endoh S