Alum Crystals Research Articles

Crystal growth mechanism of size-dependent systems in a fluidized bed.

Based on the two-step model, surface-integration coefficients of potassium alum crystals below 5 × 10–4 m grown in a well-suspended fluidized bed were found to decrease sharply with decreasing crystal size so that the growth process is controlled by surface integration for small crystals. The mass-transfer coefficient is independent of crystal size and solution velocity. The mass-transfer resistance becomes significant when crystal size increases, and finally the growth rates become constant since both mass-transfer and surface-integration coefficients are constant. For larger crystals, there is no dominating step in the growth process, both resistances being important.The crystal growth behavior of various systems other than potassium alum was also examined. Finally, an experimental method for estimating the order of surface-integration rate is suggested.

Growth kinetics of potassium alum crystal in a well-agitated vessel

Growth rates of potassium alum crystal in a well-agitated vessel were determined from the de-supersaturation curve of the solution. The mass transfer and surface integration coefficients were then estimated using the two-step model. Both coefficients were found to increase with increasing crystal size. Judging from the Damköhler number for crystal growth and the over-all order of the growth rate equation, it is concluded that both mass transfer resistance and surface integration resistance are significant in the growth process.

A method for determination of size‐dependent crystal growth kinetics from batch experiments (II). Two‐experiment estimation

AbstractThe method developed for determining size‐dependent crystal growth kinetics utilizes measurement data obtained in two batch crystallization experiments performed under the same circumstances: (1) size distribution data of the seed and product crystals of a seeded experiment and (2) the equilibrium supersaturation course of an unseeded one. In the latter case, computation is carried out in direction of reversed time thus eliminating the effect of nucleation. The evaluation makes use of the population balance equation transformed by using the assumption that the crystal growth rate is a product of two factors, the first of which depends only on the crystal size whereas the second one on the supersaturation. The application of the method is illustrated by evaluating measurement data of two appropriate experiments with potash alum crystals.

A method for determination of size‐dependent crystal growth kinetics from batch experiments (I). One‐experiment estimation

AbstractThe method developed for determining size‐dependent crystal growth kinetics makes use of the assumption that the linear growth rate is a product of a size‐dependent factor and a supersaturation‐dependent one. The transformed form of the population balance equation, obtained by means of this assumption, is the basis of the evaluation utilizing measurement data from one seeded batch crystallization experiment, namely the size distributions of the seed and product crystals as well as the supersaturation course. The application of the method is illustrated by evaluating an experiment with potash alum crystals.

Dislocation etching of rough crystal faces

A model for the preferential dissolution near the outcrops of dislocations at rough (K, S or F faces above the roughening temperature) crystal faces has been developed. In contrast to F faces below the roughening transition, no lateral flow of steps from the etched dislocation centre occurs and therefore only small etch pits, either not or only barely visible by optical microscopy are expected to be formed. This was confirmed by etching of K, S and F faces of Bi 4(GeO 4) 3, KH 2PO 4 and potash alum crystals.

Evidence for the role of pure edge dislocations in crystal growth

X-ray topographic studies have been made of the formation, propagation and character of growth dislocations in the {100} growth sectors of potash alum crystals grown from cut and polished seeds in a kinetic growth cell. Under the conditions of growth used (supersaturation 0.1–6.4%) all dislocations were found to be of pure edge character. As the sectors propagated, the area of the face initially remained constant but then decreased. As the decrease occurred many of the dislocations intersected the growth sector boundaries and became refracted into the adjacent {111} growth sectors. In parallel with the loss of these dislocations from this sector, the growth rate of the facet decreased and became variable. This association is consistent with the contention that the emergent ends of dislocations of pure edge character can act as nucleation centres for crystal growth. Further, more definite proof for such a role was obtained by examining the growth rates of {100} growth sectors containing different numbers of growth edge dislocations, but in the early, constant growth region. The growth rate was found to increase with increasing edge dislocation density. This evidence confirms that edge as well as screw dislocations play a significant role in the crystal growth process.

Structure and function of the nuclei developed during dehydration of the alums kal(SO 4) 2 · 12H 2O and KCr(SO 4) 2 · 12H 2O

Nuclei developed during the dehydration of the alums KAl(SO 4) 2 · 12H 2O and KCr(SO 4) 2 · 12H 2O have been examined microscopically in detail, to extend a previous kinetic and mechanistic study of this nucleation and growth reaction (A.K. Galwey, R. Spinicci and G.G.T. Guarini, Proc. R. Soc. London, Ser. A, 378 (1981) 477). In the present work it has been observed that the contact interface between reactants and products is coherent and is characterized by no discernible associated crack or pore structure. Reactants and products adhered strongly across this zone of chemical change. The textures observed are described and are entirely consistent with the reaction mechanism proposed previously. In this the rate-controlling process is identified as residual solid product retexturing, promoted by product water temporarily retained within the nucleus, an appropriately structured product assemblage. This conclusion is also consistent with results of a study of an alternative dehydration reaction in which alum crystals were immersed in concentrated sulphuric acid. This reaction was not a nucleation and growth process. Reaction proceeded within an adherent product layer that was initially rapidly established across the entire surface and thereafter advanced inwards at a rapidly diminishing rate.

CRYSTAL DISSOLUTION AND GROWTH IN A LEAN FLUIDIZED-BED CRYSTALLIZER

Dissolution and growth rates of potassium alum crystal were measured in a lean fluidized-bed crystallizer in which the flow rate of solution was set near the settling velocity of seed crystals. The...

On New Results of Cr3+ EPR in Potassium Aluminium Alum Crystals

physica status solidi (b)Volume 141, Issue 1 p. K67-K70 Short Note On New Results of Cr3+ EPR in Potassium Aluminium Alum Crystals K. Bielecki, K. Bielecki Institute of Molecular Physics, Polish Academy of Sciences, Poznań Search for more papers by this authorZ. Kruczyński, Z. Kruczyński Institute of Molecular Physics, Polish Academy of Sciences, Poznań Search for more papers by this authorS. I. Fǎrcaş, S. I. Fǎrcaş Institute of Isotopic and Molecular Technology, Cluj-Napoca Search for more papers by this author K. Bielecki, K. Bielecki Institute of Molecular Physics, Polish Academy of Sciences, Poznań Search for more papers by this authorZ. Kruczyński, Z. Kruczyński Institute of Molecular Physics, Polish Academy of Sciences, Poznań Search for more papers by this authorS. I. Fǎrcaş, S. I. Fǎrcaş Institute of Isotopic and Molecular Technology, Cluj-Napoca Search for more papers by this author First published: 1 May 1987 https://doi.org/10.1002/pssb.2221410149Citations: 9 Smoluchowskiego 17/19, PL 60–179 Poznań, Poland. Grunwaldzka 6, PL 60–780 Poznań, Poland. P.O.B. 700, 3400 Cluj-Napoca 5, Romania. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume141, Issue11 May 1987Pages K67-K70 RelatedInformation

Crystal growth kinetics of the two-step model

The single crystal technique was used to measure the growth rate of the potassium alum (111) face and the magnesium sulfate (110) face. The two-step model was found appropriate to describe the growth kinetics with the surface integration order of two for potassium alum crystal and of one for magnesium sulfate crystal. The individual rate constants, K d and K r, were determined accordingly.

Growth rate dispersion of small ammonium alum crystals

The growth rates of small (below 60 μm) and large (about 1 mm) crystals of ammonium alum was measured during batch crystallization from aqueous solutions. The growth rate distribution of small crystals is close to normal. With increasing supersaturation the growth rate of the large crystals increases more rapidly than that of small crystals.

Investigation of habit changes of alum crystals, KAl(SO 4) 2·12 H 2O, by novel additives to the nutrient

The effect of new additives on the change in habit of alum crystal (from octahedron to cube) was investigated. Compounds related to 3,4,5-trihydroxy-benzoic acid (gallic acid) lead to this change in habit if the distances between the three phenolic groups and the carbonyl group are directly matched to the positions of the two K + and the two Al 3+ ions on the (100) plane. Among various surfactants, only sulfonic acids with chain lengths of 10 or 12 C atoms affect the crystal habit. The sulfuric acid esters were ineffective. Quantitative data on the growth kinetics have been obtained.

Size‐dependent crystal growth—A manifestation of growth rate dispersion in the potassium alum‐water system

AbstractGrowth of potassium alum crystals was characterized by the advance rates of crystals on the leading edge of population distributions and by the advance rates of the modes of these distributions. Growth rates of crystals on the leading edge appeared to follow size‐dependent kinetics, but the observed spread of the distribution about the average size was much greater than would be expected from size‐dependent growth alone. The spread of the distribution was correlated with the extent of growth determined from the net advance of the average crystal size. These quantitative and qualitative results show that what has often been referred to as size‐dependent growth is in fact a manifestation of growth rate dispersion.

Kinetics of dissolution of potassium alum crystals in a flow cell in the presence of Fe++ cations

AbstractDissolution rates of the {111} face of potassium alum crystals have been measured in situ in a flow cell. Dependence of the mass dissolution fluxes on the subsaturation and on the presence of Fe++ cations has been studied. No influence of these cations over the concentration range 0–165 ppm on the dissolution kinetics has been observed. In addition, the dissolution process has been found to be of a purely diffusive character.

Agglomeration of potash alum crystals

AbstractCrystals of potash alum, crystallized in suspension at higher supersaturations, are partially agglomerated. Two sets of experiments have been chosen: batch experiments with precipitation of potash alum from its components and continuous crystallization by cooling. Using three different ways described in the preceding paper the size distribution of potash alum crystals was analyzed and the effect of agglomeration on calculated kinetic data demonstrated.

Effects of bismarck brown R on the growth rates of large and small potassium alum crystals

Experimental data show that Bismarck Brown R, at a concentration of 10 ppm, substantially inhibited growth rates of potassium alum. All faces of the crystal were affected similarly, although there was some evidence that inhibition of the (111) faces was slightly greater. Growth rates of small crystals were inhibited more than larger crystals; this is explained using observations of growth rate dispersion believed due to variations in screw dislocation activities. Data showing time-dependent inhibition of growth was used to support the hypothesis that Bismarck Brown R forms complexes or chelates that completely inhibited growth.

The effect of surface treatments on initial breeding of potassium alum

Abstract Using potassium alum crystals shaken for different durations as seeds, the number N of nuclei produced was correlated with the number of seeds N s and the seed diameter d s. This result was coupled with the density of alum particles adhering to the surface of the seed crystals. It was found that the secondary nucleation was principally due to alum particles broken off from the original crystals by the shaking operation.

Morphology and size distribution of fragments from potassium alum crystals caused by different treatments, of importance to secondary nucleation

Abstract The morphology and size distribution of potassium alum particles potentially causing secondary nucleation were investigated by scanning electron microscopy.

ChemInform Abstract: ELECTRONIC PROPERTIES OF HEXAAQUARUTHENIUM(III): EPR AND OPTICAL SPECTRA OF RU(H2O)63+ IN ALUM CRYSTALS

Chemischer InformationsdienstVolume 15, Issue 39 Physical Inorganic Chemistry ChemInform Abstract: ELECTRONIC PROPERTIES OF HEXAAQUARUTHENIUM(III): EPR AND OPTICAL SPECTRA OF RU(H2O)63+ IN ALUM CRYSTALS P. BERNHARD, P. BERNHARDSearch for more papers by this authorA. STEBLER, A. STEBLERSearch for more papers by this authorA. LUDI, A. LUDISearch for more papers by this author P. BERNHARD, P. BERNHARDSearch for more papers by this authorA. STEBLER, A. STEBLERSearch for more papers by this authorA. LUDI, A. LUDISearch for more papers by this author First published: September 25, 1984 https://doi.org/10.1002/chin.198439003Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume15, Issue39September 25, 1984 RelatedInformation

Microhardness studies in mixed alum crystals

The microhardness of mixed alum crystals of various compositions, (NH4)1−xKxAl(SO4)2: 12H2O, has been determined. It is found that the microhardness varies non-linearly with composition, attaining its highest value for a crystal having nearly equimolar concentration. The observed behaviour is explained using the Kataoka and Yamada model.