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| 4. |
- Cerreta, M.K., et al.
(author)
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The structure of aqueous solutions of some dihydrogen orthophosphates by laser Raman spectroscopy
- 1987
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 84:4, s. 577-588
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Journal article (peer-reviewed)abstract
- Powdered crystals and pure, aqueous solutions of ammonium, sodium, and potassium dihydrogen orthophosphates in concentrations ranging from 0.01M to supersaturated were investigated at 30°C using laser Raman spectroscopy between 700 and 1350 cm-1. With increasing solute concentration, the peak position of the 875 cm-1 P-(OH)2 symmetric strech band increased. Extreme asymmetry in the 1075 cm-1 P=O2 symmetric stretch band developed to lower energy. The integrated intensity ratio of the 875 cm-1 band to the 1075 cm-1 band envelope remained constant. These observations are consistent with anion-anion association via hydrogen bonds. Deconvolution of the spectral bands showed only 40% and 20% of the phosphates exist as monomers in saturated potassium and ammonium solutions, respectively, and that anion association does not cease at the dimer. The spectra provided no evidence of quasi-crystalline entities in solution. The necessary breaking and reforming of hydrogen bonds during the growth process can explain rapid z-direction growth, growth activation energy, and the rate-limiting surface growth mechanism.
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| 5. |
- Elankovan, P., et al.
(author)
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Contact nucleation from aqueous dextrose solutions
- 1987
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In: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 33:11, s. 1844-1849
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Journal article (peer-reviewed)abstract
- Contact nucleation studies were performed with the dextrose-water system. Under some conditions two crystallographic phases were formed, which were identified in situ using a laser Raman microprobe. In addition, the growth of the contact nuclei was monitored in situ using photomicroscopy. The results are discussed in the context of contact nucleation and growth models.
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| 6. |
- Elankovan, P., et al.
(author)
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Technique for obtaining Raman spectra of contact nuclei In Situ
- 1986
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In: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 40:5, s. 712-714
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Journal article (peer-reviewed)abstract
- Secondary nucleation, the formation of new crystals due to the prior presence of other growing crystals, is the primary source of new particles in most industrial crystallizers. Of the various types of secondary nucleation possible, contact nucleation, wherein a disturbance of a growing crystal surface results in nuclei, is thought to be the most prevalent.
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| 7. |
- Hartel, R.W., et al.
(author)
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Precipitation kinetics of the titanium isopropoxide hydrolysis reaction
- 1986
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In: Better ceramics through chemistry II. - : Materials Research Society. - 0931837391 ; , s. 633-640
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Conference paper (peer-reviewed)abstract
- The precipitation product of the titanium isopropoxide (TiPT) hydrolysis reaction was followed using photon correlation spectroscopy. This technique followed the mean size of the precipitate as the reaction progressed as well as giving an indication of the number of particles being produced. From this analysis, the induction time for the onset of nucleation, nucleation rate (or the rate of particle production) and mean growth rate were correlated with reactant concentrations. In the concentration ranges studied, the induction time was an inverse function of reactant concentrations. Both nucleation rate and average growth rate increase as reactant concentration increased, with the TiPT concentration being more important. This reaction was also followed using absorbance spectrophotometry in the 500 to 320 nm range. After mixing of the reactants, an absorbance peak was seen between 330 and 335 nm, depending on the conditions. This peak increased slowly during the induction period and then increased rapidly after the onset of nucleation due to increasing turbidity
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| 8. |
- Larson, M.A., et al.
(author)
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Growth rate dispersion in MSMPR crystallizers
- 1985
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In: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 31:1, s. 90-94
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Journal article (peer-reviewed)abstract
- A model is presented which relates the crystal size distribution (CSD) from a mixed-suspension, mixed-product-removal (MSMPR) crystallizer to the distribution of growth rates. This model is based on the assumption that individual contact nuclei have some inherent growth rate which remains constant, but the growth rate may vary from crystal to crystal. The crystal size distribution can be calculated from prior knowledge of the growth rate distribution. A limited knowledge of only the coefficient of variation and the mean growth rate permits an approximation of the expected crystal size distribution. Conversely, estimates of the mean and variance of the growth rate distribution can be determined from the moments of the CSD from an MSMPR crystallizer
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| 9. |
- Liang, B., et al.
(author)
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Effects of raffinose on sucrose crystal growth kinetics and rate dispersion
- 1989
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In: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 35:12, s. 2053-2057
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Journal article (peer-reviewed)abstract
- This work seeks to further the investigation of the effects of raffinose on both the crystallization kinetics and GRD of growing sucrose crystals. Measurements of the widening of the crystal size distribution (CSD) of suspension grown seed crystals, as well as direct photomicroscopic measurements of the growth of these seed crystals, were completed for this study. The range of supersaturation studied was 0.28 to 2.05 g sucrose per 100 g solution with a temperature range of 313 to 333 K. The results of a previous investigation on the solubility of sucrose in raffinose solution were utilized for the kinetic determinations.
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| 10. |
- Liang, B. M., et al.
(author)
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Growth rate dispersion in seeded batch sucrose crystallization
- 1987
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In: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 33:12, s. 2077-2079
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Journal article (peer-reviewed)abstract
- The object of this study was to compare the results of batch suspension and photomicroscopic cell experiments on growth rate dispersion of sucrose seed crystals to determine the relative effects of GRD in the two different environments. This was done by observing the change in CSD of the seed distribution in the batch suspension crystallizer, while simultaneously monitoring the individual growth rates of an identical seed sample in the photomicroscopic cell. It is found that seeds growing in a stirred suspension batch crystallizer also exhibit growth rate dispersion, as evidenced by the increasing width of the CSD with time.
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| 11. |
- Mathis-Lilley, J. J., et al.
(author)
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Contact nucleation from aqueous potash alum solutions
- 1985
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In: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 31:5, s. 865-867
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Journal article (peer-reviewed)abstract
- Based on experimental results, it is concluded that potash alum contact nuclei grow at a size-independent rate in a system where flow does not result in crystal collisions. Both initial size and growth rate distributions are present for contact nuclei of potash alum. Curvature in semilogarithmic population density-size plots from continuous potash alum crystallization studies may be due to growth rate dispersion and not size-dependent growth.
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| 12. |
- McMahon, Paula M., et al.
(author)
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A constant-temperature Raman cell for the study of supersaturated aqueous solutions
- 1986
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In: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 40:2, s. 282-283
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Journal article (peer-reviewed)abstract
- In order that the phenomena of crystal nucleation and growth from solution can be fully understood, the current knowledge of supersaturated solution structure must be extended. Previous studies on Raman spectroscopy of aqueous metal nitrate solutions indicated the presence of solvated ions, solvent separated ion pairs, contact ion pairs, and ion agglomerates as a function of concentration. Unfortunately, the concentration range of these studies did not include supersaturated solutions. It is the purpose of this work to describe an experimental technique which allows the study of supersaturated solutions.
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| 13. |
- Murphy, Vincent G., et al.
(author)
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Modeling growth rate dispersion in a batch sucrose crystallizer
- 1986
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In: Industrial and Engineering Chemistry. Fundamentals. - : American Chemical Society (ACS). - 0019-7874 .- 0196-4313 .- 1541-4833. ; 25:1, s. 174-176
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Journal article (peer-reviewed)abstract
- Growth rate data from experiments on sucrose crystals are analyzed for growth rate dispersion (the variation of crystal growth rates within a population). Two competing models are used in this analysis. Experimental results suggest that carefully designed experiments must be performed to distinguish between the two.
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| 14. |
- Payne, Mark J., et al.
(author)
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Raman spectroscopic studies of titanium aloxides using UV excitation
- 1986
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In: Better ceramics through chemistry II. - : Materials Research Society. - 0931837391 ; , s. 627-631
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Conference paper (peer-reviewed)abstract
- The use of Raman spectroscopy can be this hindered by the presence of fluorescing impurities. In this study, Raman spectra were recorded for various titanium alkoxides (ethoxide, isopropoxide, isobutoxide) as a function of concentration and laser excitation wavelength. Fluorescence can be avoided by using uv-excitation (363. 8 nm). In addition, titanium alkoxides exhibit a preresonance Raman enhancement as the excitation wavelength approaches the UV. This result is confirmed by a uv-visible absorption spectrum of the isopropoxide.
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| 15. |
- Shanks, B. H., et al.
(author)
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Contact nucleation from aqueous sucrose solutions
- 1985
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In: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 31:1, s. 152-154
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Journal article (peer-reviewed)abstract
- Both initial size and growth rate distributions are observed for contact nuclei of sucrose. Results presented indicate sucrose contact nuclei appear to grow at a size independent rate and that the proper method of analysis of the growth rate dispersion present is the 'constant crystal growth' (CCG) model. Curvature in semilogarithmic population density-size plots from continuous sucrose crystallization studies is probably due to growth rate dispersion and not size dependent growth.
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| 16. |
- Shiau, L. D., et al.
(author)
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Growth kinetics of fructose crystals formed by contact nucleation
- 1987
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In: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 33:6, s. 1028-1033
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Journal article (peer-reviewed)abstract
- Despite the large number of recent secondary nucleation and growth rate studies with the sucrose-water system, few data are available on the fructose-water system. Fructose is much more soluble in water than sucrose. Since fructose is a monosaccharide constituting half of the sucrose molecule, it is reasonable to consider that similar phenomena may exist with respect to nucleation and growth in the two systems. It is the objective of this work to perform photomicroscopic experiments on the fructose-water system to study these nucleation and growth characteristics.
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| 17. |
- Shiau, L-D, et al.
(author)
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Model for a cascade crystallizer in the presence of growth rate dispersion
- 1987
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 26:12, s. 2515-2521
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Journal article (peer-reviewed)abstract
- A model is developed based on the population balance to relate the resulting crystal size distribution (CSD) from a cascade of mixed suspension, mixed product removal (MSMPR) crystallizers to the growth rate distributions of each stage. This model employs the constant crystal growth (CCG) model, in which it is assumed that an individual crystal has an inherent, constant growth rate, but different crystals might have different inherent growth rates. An explicit recursion formula between the first three moments of the resulting crystal size distribution and the first three moments of growth rate distributions of each stage is presented for a N-stage MSMPR crystallizer. A computer program has been developed to predict the CSD from a three-stage MSMPR crystallizer with continuous seeding into the first stage and growth in the subsequent stages. The model is solved simultaneously with the mass balance by using power law growth kinetics. The CSD in each stage is assumed as a gamma distribution to compute the mean crystal size, production rate, and coefficient of variance.
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| 18. |
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