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- Cerreta, M.K., et al.
(författare)
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The structure of aqueous solutions of some dihydrogen orthophosphates by laser Raman spectroscopy
- 1987
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 84:4, s. 577-588
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Tidskriftsartikel (refereegranskat)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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- Elankovan, P., et al.
(författare)
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Contact nucleation from aqueous dextrose solutions
- 1987
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Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 33:11, s. 1844-1849
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Tidskriftsartikel (refereegranskat)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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- Elankovan, P., et al.
(författare)
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Technique for obtaining Raman spectra of contact nuclei In Situ
- 1986
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Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 40:5, s. 712-714
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Tidskriftsartikel (refereegranskat)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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- Hartel, R.W., et al.
(författare)
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Precipitation kinetics of the titanium isopropoxide hydrolysis reaction
- 1986
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Ingår i: Better ceramics through chemistry II. - : Materials Research Society. - 0931837391 ; , s. 633-640
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Konferensbidrag (refereegranskat)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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- Larson, M.A., et al.
(författare)
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Growth rate dispersion in MSMPR crystallizers
- 1985
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Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 31:1, s. 90-94
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Tidskriftsartikel (refereegranskat)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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- Liang, B., et al.
(författare)
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Effects of raffinose on sucrose crystal growth kinetics and rate dispersion
- 1989
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Ingår i: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 35:12, s. 2053-2057
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Tidskriftsartikel (refereegranskat)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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