Ammonium Sulfate Crystals Research Articles

Structure-activity relationships of mineral dusts as heterogeneous nuclei for ammonium sulfate crystallization from supersaturated aqueous solutions.

Mineral inclusions, present in aqueous atmospheric salt droplets, regulate crystallization when relative humidity decreases by providing a surface for heterogeneous nucleation and thus reducing the critical supersaturation. Although laboratory studies have quantified these processes to some extent, the diverse atmospheric mineralogy presents more chemical systems than practically feasible for direct study. Structure--activity relationships are necessary. To that end, in the present work the interactions of ammonium sulfate with corundum, hematite, mullite, rutile, anatase, and baddeleyite were studied by diffuse reflectance fourier transform infrared spectroscopy (DRIFTS) and by epitaxial modeling. The spectroscopic results show that shifts in sulfate peak positions due to chemisorption are not a correlative indicator of the efficacy of heterogeneous nucleation. In contrast, epitaxial modeling results of unreconstructed surfaces explain the sequence of critical supersaturations for constant particle size. If validated by further work, this computer modeling method would provide an important structure--activity tool for the estimation of heterogeneous nucleation properties of the atmospheric mineralogy.

Microhardness and its related physical constants in solution-grown ammonium sulphate single crystals

Abstract The variation of hardness on (1 0 0) faces of orthorhombic ammonium sulphate crystals, AS [(NH 4 ) 2 SO 4 ], with load were studied. Vickers hardness numbers, H v , were found to increase with the increase in load. Work-hardening index ‘ n ’ was found to be greater than 2 showing soft-material characteristics. Kick’s law has been satisfied after making a correction in the observed diagonal length of the indentation impression. The fracture toughness values ‘ K c ’, determined from measurements of crack lengths, were estimated to be 0.078 and 0.073 MN m −3/2 for (1 0 0) faces at 90 and 100 g, respectively. The brittleness indices ‘ B i ’ were estimated as 1.79 and 2.04 μm −1/2 for the same faces at same loads. Using Wooster’s empirical relation, elastic stiffness coefficient, c 11 , has been calculated from hardness value.

The combined influence of supersaturation and impurity concentration on crystal growth

Supersaturation dependence of crystal growth in the presence of impurity is discussed. The supersaturation dependence was divided conveniently into two types: the case where growth rate is suppressed over a wide range of supersaturation and the case where it is suppressed only in the low range of supersaturation while at the higher supersaturation range the impurity effect disappears completely. The latter case is explained theoretically by assuming slow unsteady state adsorption of impurity species at higher supersaturations. Literature data of the growth rate of an ammonium sulfate crystal are successfully explained. It is pointed out that classification of impurity action into the two types is not essential. The former type is a special case of the second one where the time constant of adsorption process becomes very small even at higher supersaturations.

Hypothetical phase transition, structural disorder and spontaneous polarization in ammonium sulfate crystals

EPR spectra of SeO3 − radicals in ammonium sulfate crystal were studied in the high temperature phase. Two magnetically inequivalent SeO3 − radicals exist in the crystal as a consequence of different coupling to two inequivalent ammonium groups: (NH4)1 and (NH4)11. It is estimated that the distinction between the two SeO3 − radicals would disappear at 585 K, which is interpreted as the hypothetical ferroelastic phase transition. The intensity ratio of the two SeO3 − radicals can be changed by appropriate heat treatment of the sample. It is inferred that the intensity ratio is related to the disorder of protons in the asymmetric potential minima in hydrogen bonds. The unusual temperature dependence of spontaneous polarization was studied in crystals grown from solutions with pH in the range 2.0 to 5.0 as well as in crystals after heat treatment.

The unusual temperature dependence of spontaneous polarization in ammonium sulfate crystals

Abstract EPR spectra of SeO3 radicals in ammonium sulfate crystals were studied in the temperature range (430 – 100) K. Two magnetically inequivalent SeO3 radicals are differently coupled to two crystallographically inequivalent ammonium groups: (NH4)I and (NH4)II. At the ferroelectric phase transition temperature Tc = 223 K, both SeO3 radicals become distorted and displaced from the ab plane towards the polar c-axis. One of these SeO3 radicals and (NH4)I remains temperature independent in the ferroelectric phase, while the other one and (NH4)II change their orientation with temperature in the ferroelectric phase. The unusual temperature dependence of the spontaneous polarization can be attributed to different behavior of (NH4)1 and (NH4)II, which can be studied by EPR of SeO3 radicals.

Modelling of the growth of ammonium sulphate crystals in a DTB crystallizer

A literature review of models used to account for the observation of an apparent size dependent growth rate (SDG) of sub-150 μm is made. Growth rate dispersion (GRD), random fluctuation growth (RF) and a fast-growers slow-growers (FGSG) manner of growth are considered. The models are discussed in terms of their relevance to the modelling of industrial crystallization processes. An empirical SDG function to describe the growth of ammonium sulphate crystals in a 970 1 draft-tube-baffled (DTB) crystallizer is derived, by measuring the growth rate of samples of sub-300 μm crystals removed from the fines line in a 2 1 growth cell. This model is implemented in a model for the overall description of the product crystal size distribution (CSD) from the 970 1 crystallizer.

Size dependent growth behaviour related to the mosaic spread in ammonium sulphate crystals

The growth rate of small (1–120 μm) ammonium sulphate crystals, which were removed from a 970 L crystallizer via a fines classification line, were measured in a 2 L growth cell. An exponential size dependent growth (SDG) curve was used to model the data, revealing a size dependent growth rate up to a size of 220 μm. The same crystals were dried and sieved and the level of internal strain (“mosaic spread”) measured using the high intensity synchrotron radiation source. The results showed that the average mosaic spread and also the spread in mosaic spreads reduced with increasing crystal length. These results are consistent with the SDG rate measured for the small particles in suspension and points to internal lattice strain as being the cause of the SDG.

Effect of defects induced by doping and fast neutron irradiation on the thermal properties of lithium ammonium sulphate crystals

Structural defects were introduced in lithium ammonium sulphate crystals (LAS) either in the process of crystal growth (in the form of foreign ions) or by neutron irradiation. The effect of such defects on the thermal properties of LAS crystals was studied in the temperature range 300–500 K. It was assumed that the doped LAS crystals are composed of a two-phase system having different thermal parameters in each phase. The specific heat at constant pressure, C p, of irradiated samples was found to decrease with increasing irradiation doses. The thermal expansion of LAS crystals was found to be dependent on neutron irradiation, and was attributed to two processes: the release of new species and the trapping process.

Investigations on the existence of a high-temperature phase transition in ammonium sulphate crystals

The existence of a high-temperature phase transition in ammonium sulphate (AS) crystals is discussed. The DC electrical conductivity and the dielectric permittivity in the temperature range 300–460 K are measured and the results are examined trying to detect the proposed phase transition. The results indicate no evidence for a ferroelectric phase transition, but the anomaly observed at 423 K simply is the result of variations in the conduction mechanism which could be attributed to an order-disorder type of phase transition.

Ammonium Sulfate Crystallization in a Cooling Batch Crystallizer

Abstract Crystallization kinetics of ammonium sulfate crystals are determined in a 25-L draft tube baffled, agitated crystallizer from a series of batch cooling experiments performed in an integral mode. The method of s-plane analysis for relative nucleation kinetics and the method of initial derivatives for growth rate kinetics are used to establish conventional kinetic expressions. A simulation technique is developed to calculate the product population density functions for the same system in a seeded cooling batch crystallizer configuration.

X-ray diffraction study of lithium hydrazinium sulfate and lithium ammonium sulfate crystals under a static electric field

X-ray diffraction studies are made on proton conducting polar lithium hydrazinium sulfate and ferroelectric lithium ammonium sulfate. The X-ray rocking curves recorded with in situ electric field along the polar b axis of lithium hydrazinium sulfate (direction of proton conductivity) show a strong enhancement of the 0k0 diffraction intensity. The corresponding 0k0 X-ray topographs reveal extinction contrast consisting of striations parallel to the polar axis. They disappear when the electric field is switched off. The effect is very strong in 0k0 but invisible in h0l reflections. It is present only if the electric field is parallel to the polar axis b. This unusual X-ray topographic contrast is correlated with the proton conduction. It is supposed that, under electric field, an inhomogeneous charge distribution develops, distorting the crystal lattice. Similar experiments on lithium ammonium sulfate also show contrast variations, but of quite different behaviour than before. In this case they result from changes of the ferroelectric domain configuration under electric field.

Purification of bovine liver rhodanese by low-pH column chromatography

We report a purification of bovine liver rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1) using column chromatography under conditions that take advantage of recent information regarding the structure and stability of this enzyme. At low pH (e.g., pH 4–6), rhodanese is stabilized against inactivation processes. By maintaining rhodanese at low pH, column chromatography, and especially ion-exchange chromatography, becomes practical, without loss of enzymatic activity. A purification method involving the sequential use of cation-exchange, size-exclusion, and hydrophobic-interaction chromatography was developed, and rhodanese was purified with good yield to electrophoretic purity and high specific activity. Previous methods for purifying bovine liver rhodanese employ repeated ammonium sulfate fractionations and crystallization of the rhodanese. In these methods, it is difficult to separate rhodanese from yellow-brown contaminants in the final stages of the procedures. Here, yellow-brown contaminants, which copurify with rhodanese on the first two columns, are completely resolved by hydrophobic interaction chromatography. This method can be readily scaled up, requires no special equipment, eliminates the variability inherent in previous methods, and is less dependent upon experience.

Controlled cooling crystallization of ammonium sulfate in the ternary system ammonium sulfate-ammonium nitrate-water

The controlled cooling crystallization of ammonium sulfate in the ternary system: ammonium sulfate-ammonium nitrate-water considering the effect of the cooling rate was studied on the basis of the experimental nucleation and growth kinetics. For this, the solubility of ammonium sulfate in the ternary system was determined, and the maximum allowable undercooling was measured with the variations of the cooling rate and saturation temperature of the solution

Growth process of ammonium sulfate crystals produced by secondary nucleation in stirred-tank crystallizer.

Growth behavior of ammonium sulfate secondary nuclei originated from a seed crystal in a stirred-tank crystallizer was investigated using a Coulter Counter. From the time dependence of the cumulative curves it appeared that the particles can be divided according to growth behavior into two groups. Particles larger than 40 μm grow fast, independently of size (group I), and particles less than 20–30 μm grow at a rate 1–2 orders lower than that of group I (group II). It was also suggested that the secondary nucleation mechanisms of groups I and II are different, and that of group I may be initial breeding. It was observed that for a portion of the group II particles the growth rate increases abruptly during the crystallization. Dissolution rates of group I particles obtained from the cumulative curves were consistent with the values calculated by the mass transfer rates equation, but those of group II were largely lower than the calculated values. The difference in growth behavior between groups I and II was attributed neither to Gibbs–Thomson effect nor to mass transfer rate changes with particle size, but to the difference in the contribution of surface kinetic process. It was found that the growth process of large ammonium sulfate crystals (group I) is much more controlled by volume diffusion than are those of other salts such as potassium sulfate.

The crystal structure of the “open” and the “closed” conformation of the flexible loop of trypanosomal triosephosphate isomerase

Triosephosphate isomerase has an important loop near the active site which can exist in a "closed" and in an "open" conformation. Here we describe the structural properties of this "flexible" loop observed in two different structures of trypanosomal triosephosphate isomerase. Trypanosomal triosephosphate isomerase, crystallized in the presence of 2.4 M ammonium sulfate, packs as an asymmetric dimer of 54,000 Da in the crystallographic asymmetric unit. Due to different crystal contacts, peptide 167-180 (the flexible loop of subunit-1) is an open conformation, whereas in subunit-2, this peptide (residues 467-480) is in a closed conformation. In the closed conformation, a hydrogen bond exists between the tip of the loop and a well-defined sulfate ion which is bound to the active site of subunit-2. Such an active site sulfate is not present in subunit-1 due to crystal contacts. When the native (2.4 M ammonium sulfate) crystals are transferred to a sulfate-free mother liquor, the flexible loop of subunit-2 adopts the open conformation. From a closed starting model, this open conformation was discovered through molecular dynamics refinement without manual intervention, despite involving C alpha shifts of up to 7 A. The tip of the loop, residues 472, 473, 474, and 475, moves as a rigid body. Our analysis shows that in this crystal form the flexible loop of subunit-2 faces a solvent channel. Therefore the open and the closed conformations of this flexible loop are virtually unaffected by crystal contacts. The actual observed conformation depends only on the absence or presence of a suitable ligand in the active site.

The Influence ofγ-irradiation on the thermophysical properties of potassium ammonium sulphate crystals

The effect ofγ-irradiation on the thermal properties of KNH4SO4 single crystals in the temperature range 300–600 K is investigated. The variation ofC P as a function of radiation dose is determined. Analysis of the results indicates that changes induced in the thermal behaviour of KNH4SO4 crystal byγ-irradiation might be due to direct collision with lattice atom and multiple atom displacement.

Growth kinetics of ammonium sulfate in the ternary system ammonium sulfate-ammonium nitrate-water

The growth kinetics of ammonium sulfate crystals in the ternary system ammonium sulfate-ammonium nitrate-water were studied in a laboratory-scale fluidized bed crystallizer. The effects of supersaturation, temperature, crystal size, and solid voidage were investigated. The effect of the solute composition in the ternary system on the growth rate was also investigated. The order with respect to supersaturation was less than unity in the ternary system. It was observed that the growth rate of ammonium sulfate is dependent on the temperature, crystal size, solid voidage, and system composition

Dissociation of the hyperchromate ion into the chromic ion in crystals: An electron spin resonance study

By heating LiCsSO 4 crystals which have been doped with ammonium chromate and γ-irradiated, Cr 3+ species with large zero-field splittings were detected by electron spin resonance (ESR). The Cr 3+ species result from an ammonium-hydrogen-assisted dissociation of the CrO 4 3− and CrO 3 − species produced by irradiation. The same oxygen-stripping effect was observed by ESR in γ-irradiated LiNH 4SO 4 and (NH4) 2SO 4 crystals doped with CrO 4 2−. Dissociation of CrO 4 2− itself into Cr 3− was observed by ESR in CrO 4 2−-doped ammonium sulfate crystals heated at temperatures well below the dissociation temperature of this compound.

Purification and characterization of a novel enzyme, N-carbamoylsarcosine amidohydrolase, from Pseudomonas putida 77.

N-Carbamoylsarcosine amidohydrolase, a novel enzyme involved in the microbial degradation of creatinine in Pseudomonas putida 77, was purified 27-fold to homogeneity with a 63% overall recovery through simple purification procedures including successive ammonium sulfate fractionation, DEAE-cellulose chromatography, and crystallization. The relative molecular mass of the native enzyme estimated by the ultracentrifugal equilibrium method is 102,000 +/- 5000, and the subunit Mr is 27,000. The Km and Vm values for N-carbamoylsarcosine are 3.2 mM and 1.75 units/mg protein, respectively. Ammonia, carbon dioxide, and sarcosine were formed stoichiometrically from N-carbamoylsarcosine through the action of the purified enzyme preparation. N-Carbamoyl amino acids with a methyl group or hydrogen atom on the amino-N atom and possessing glycine, D-alanine, or one of their derivatives as an amino acid moiety served well as substrates for N-carbamoylsarcosine amidohydrolase. N-Carbamoylsarcosine, N-methyl-N-carbamoyl-D-alanine, N-carbamoylglycine, and N-carbamoyl-D-alanine were hydrolyzed at relative rates of 100, 12.8, 9.8, and 7.3, respectively, by the enzyme. N-Carbamoyl derivatives of D-tryptophan, D-phenylalanine, and those of some other amino acids including D-phenylglycine and p-hydroxy-D-phenylglycine were also hydrolyzed by the enzyme. For the L-isomers of all N-carbamoyl amino acids tested there was no production of ammonia, carbon dioxide, or the corresponding amino acids due to the action of the enzyme. Cupric, mercuric, and silver ions inhibited the enzyme strongly, and some thiol reagents were also found to be inhibitory.

Raman scattering study of diglycine sulphate and ammonium sulphate double salt crystals

Raman spectra have been recorded for diglycine sulphate and ammonium sulphate double salt crystals (DGSAS) at room temperature. From a comparison between our results and the i.r. and Raman spectra of the amino acids and ammonium sulphate crystals, the functional groups have been ascribed to particular positions of the bands in the Raman spectra of DGSAS crystals.