Variations In Crystal Morphology Research Articles

Equilibrium properties and crystal growth of D2O + cyclopentane hydrate for sustainable tritium separation

AbstractThis study reports thermodynamic properties and crystal growth observations of D2O + cyclopentane hydrate toward the development of a hydrate‐based tritium separation process. We employed D2O as a host of hydrate with respect to the investigation into the formation of D2O hydrate substrate, which is a core component of the tritium separation process. The hydrate phase equilibrium temperature in the liquid D2O + liquid cyclopentane system was 3.2°C higher than the corresponding H2O hydrate. Experiments on crystal growth were conducted at temperatures ranging from 5.1 to 8.5°C under atmospheric pressure. Under each thermodynamic condition, polygonal hydrate crystals appeared, growing along the D2O/cyclopentane interface. The geometric shape and size of the crystals varied depending on the temperature. The variation in crystal morphology was comparable to that of the H2O + cyclopentane hydrate. Implications based on the obtained results for the hydrate‐based isotopic water separation process design are discussed.

Dehydration behaviour and impurity change of phosphogypsum during calcination

The preparation of β-hemihydrate gypsum is an important approach for large-scale utilization of phosphogypsum (PG) because of the simple production technology by calcination. However, the dehydration behaviour and impurity change during the transformation of PG to β-hemihydrate gypsum at low temperatures are unclear. In this study, the dehydration of PG at different temperatures was investigated by a calcination test and in-situ X-ray diffraction analysis. The variation in crystal morphology and structure of PG was clarified using scanning electron microscopy and Materials Studio software. Furthermore, the change of impurity was analyzed by energy-dispersive spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy measurements. The results show that the dehydration of PG to β-hemihydrate gypsum depends on calcination temperature and time. Moreover, an increase in the calcination temperature could accelerate the dehydration of PG and shorten the dehydration time; meanwhile increasing the calcination time or calcination temperature could make a part of β-hemihydrate gypsum further dehydrate to anhydrite. The morphology and elemental distribution of PG did not dramatically change during calcination, but the grain size decreased and the elemental distribution density increased. It should be noted that the calcination did not decrease the phosphorus and fluorine contents in PG at 120 °C, whereas the contents increased due to the removal of crystal water. The phosphorus impurity form transformed from CaHPO4·2H2O and Ca(H2PO4)2·H2O to CaHPO4 and Ca(H2PO4)2, respectively. Therefore, the calcination could not remove the phosphorus and fluorine from PG, and pretreatment is required to reduce the adverse effects of impurities in the industrial production of β-hemihydrate gypsum.

Synthesis of Hydroxy Sodalite from Coal Fly Ash for Biodiesel Production from Waste-Derived Maggot Oil

Zeolites are aluminosilicate crystalline materials known for their unique characteristics, and have been prominent for nearly half a century due to their wide and important industrial applications. The production of zeolites, however, remains a challenge due to the high cost of commercial reagents conventionally used as feedstocks. In the current study, hydroxy sodalite (HS) zeolite samples were synthesised from coal fly ash feedstock by a direct hydrothermal synthesis method. The effects of hydrothermal crystallisation synthesis time on phase crystallinity, crystal size, and morphology of the formed HS were investigated. The prepared samples were characterised using XRD, SEM, EDS and FT-IR techniques. The XRD results of the samples prepared with varying synthesis times confirmed the formation of HS from low to high phase purity and crystallinity from 11 to over 98%. The SEM results reflected gradual variation in crystal morphology, of which highly crystalline HS samples were associated with hexagonal-cubic and cubic-platelet crystals. The FTIR, depicting zeolite characteristics of T–O and T–O–T stretching vibrations in the molecular framework, further confirmed the formation of HS zeolites for samples obtained above the 24-h synthesis time. These zeolite samples were then evaluated for their catalytic activities in the conversion of maggot oil to biodiesel. The application of the various hydroxy sodalite samples for the transesterification of maggot oil yielded up to 84.10% biodiesel (FAME) with physicochemical properties that were in compliance with the biodiesel specification standards. This study investigated the novel use of a coal fly ash-derived, heterogeneous HS catalyst in biodiesel production from maggot oil, and indicates its potential to enhance biodiesel yield and quality upon process optimisation tests.

Mechanistic insights into CTAB assisted TiO2 crystal growth with largely exposed high energy crystal facets

Pristine anatase titanium dioxide (TiO2) photocatalysts were prepared by a modified hydrothermal method using cetyltrimethylammonium bromide (CTAB) as the capping agent. The so-formed TiO2 crystals showed superhydrophilic behavior in a short irradiation time span, without adopting any modifications to TiO2 like doping or hybridizing with organic monolayers. At an optimum pH of 3, the CTAB molecules were effectively adhered to the high energy facets of TiO2 favoring a crystal growth elongation in [001] direction leading to the exposure of high energy {101}/{100} and {001} facets. Variations in crystal morphology, size and exposing facets are investigated in detail using XRD, Raman and TEM, whereas the optical properties are studied using UV–vis diffuse reflectance spectroscopy, PL and TSCPC techniques. Acetic acid acting as a bridging ligand attaching the Ti centres in a twisted conformation effectively led to the anatase phase of TiO2. The shape and size of the CTAB micelles were greatly dependent on the pH of the reaction system, which in turn decided the exposure percentage of different facets. Anatase TiO2 prepared at optimum pH 3 were ellipsoidal and showed 83% photocatalytic degradation (k = 9.23 × 10−3 min-1) of Methylene Blue as the model dye, and the water contact angle of 17° under UV irradiation. When synthesis is repeated with double the quantity of water, TiO2 shared ellipsoidal and cuboidal morphologies and were superhydrophilic showing contact angle of 9° within 5 min UV irradiation, along with a superior photodegradation of 93% (k = 12.9 × 10−3 min-1).

Diversity and Toxicity of Bacillus thuringiensis from Shifting Cultivation (Jhum) Habitat.

Bacillus thuringiensis (Bt) strains were isolated from jhum-agriculture, jhum-forest, aquatic and fallow soil samples from Mizoram by acetate selection method. Isolates were characterized for biochemical typing, cry gene and protein profiling, growth curve study and toxicity against Culex tritaeniorhynchus. Bt frequency was high in jhum-agriculture land (69.56%) whereas low in jhum-forest soils (31.57%). Bt was found to be abundant in jhum shifting cultivation soil with an index ranging between 0.010 and 0.015. Majority of the isolates from jhum soils produced oval and spherical crystals and showed eleven types of crystal proteins groups. PCR analysis revealed predominance of dipteran-active cry genes (cry4 and cry9). The variations in crystal morphology, cry genes and Cry protein (s) from the isolates of Bt revealed molecular diversity. Higher mortality, lower lethal dose, and lesser time to kill were observed in Bt isolates from jhum soils than aquatic and fallow habitats. Based on the toxicity test, SC1 and HP7 isolates containing cry 4 and cry 9 genes showed higher activity. Growth curve analysis showed significant variations among Bt isolates to reach the sporulating stage. Higher growth index and lower mean generation time were observed in SC1 and HP7 Bt isolates. Bt strains express different endotoxin genes and crystal proteins and their harvesting time also varied from strain to strain. Significant variation was found in Bt isolates from jhum habitats in relation to the cry gene composition, protein profiling and toxicity. Results from this study suggest that novel Bt entomopathogens may complement for regulating mosquito vectors.

Bacillus thuringiensis Isolates from Great Nicobar Islands

Bacillus thuringiensis (Bt) strains were isolated from soil samples of Great Nicobar Islands, one of the "hottest biodiversity hotspots," where no collection has been characterized previously. The 36 new Bt isolates were obtained from 153 samples analyzed by crystal protein production with light/phase-contrast microscopy, determination of cry gene profile by SDS-PAGE, evaluation of toxicity against Coleopteran, and Lepidopteran insect pests, finally cloning and sequencing. Majority of the isolates showed the presence of 66-35kDa protein bands on SDS-PAGE while the rest showed >130, 130, 73, and 18kDa bands. The variations in crystal morphology and mass of crystal protein(s) purified from the isolates of Bt revealed genetic and molecular diversity. Based on the toxicity test, 50% of isolates were toxic to Ash weevils, 16% isolates were toxic to cotton bollworm, 38% isolates were toxic both to ash weevil as well as cotton bollworm, while 11% of the isolates did not exhibit any toxicity. PCR analysis unveiled prepotency of cry1B- and cry8b-like genes in these isolates. This study appoints the first isolation and characterization of local B. thuringiensis isolates in Great Nicobar Islands. Some of these isolates display toxic potential and, therefore, could be adopted for future applications to control some agriculturally important insect pests in the area of integrated pest management for sustainable agriculture.

The Nature and Significance of Variations In Gypsum Crystal Morphology In Dry Lake Basins

Depressions in semiarid regions with a gypsiferous geological substrate commonly contain highly gypsiferous sediments, with gypsum that formed either as a synsedimentary precipitate during perennial or ephemeral lake stages or as a diagenetic precipitate during saline mudflat stages. The dry to ephemeral lake basins of the Monegros region in northern Spain are depressions of this type and provide a unique opportunity to examine whether and how conditions of gypsum formation are reflected by gypsum crystal morphology, yielding information that can contribute to a correct interpretation of the depositional environment of gypsum in ancient and modern formations. In most lake basins of the study area, the sediment fill consists of a similar sequence of three lithological units. The lower unit includes fragmented gypsum crystals in some basins, recording clastic reworking, and in other depressions it contains large lenticular crystals, formed as phreatic diagenetic precipitates. The middle unit typically contains synsedimentary gypsum with a non-lenticular morphology, modified by postdepositional processes, but it also comprises synsedimentary lenticular gypsum in some basins. In the upper unit, separated from the underlying interval by a marked hiatus, both synsedimentary and diagenetic gypsum are present, the former including layered gypsum deposits with features such as grading and variations in crystal morphology. The results show that a non-lenticular crystal habit of gypsum occurring within the groundmass (sediment matrix) indicates synsedimentary precipitation. In contrast, a lenticular crystal habit cannot be used in isolation as an indicator of the environment in which the gypsum initially precipitated. Unambiguously late-diagenetic gypsum includes fine-grained precipitates in voids created by soil fauna. These infillings consist of initially non-lenticular crystals, with a tabular-prismatic habit, recording that conditions promoting lenticular crystal growth do not always prevail outside the groundmass in soil-related settings and illustrating the importance of knowing the context of analyzed gypsum occurrences at the scale of a sample.

Crystal Growth of Clathrate Hydrates Formed at the Interface of Liquid Water and Gaseous Methane, Ethane, or Propane: Variations in Crystal Morphology

This paper reports the visual observations of the formation and growth of clathrate hydrate crystals on the surface of a water droplet exposed to gaseous methane, ethane, or propane. The hydrate crystals formed and grew at the guest−water interface. The nucleation of the hydrate first occurred at a random point on the water droplet and then grew to form a polycrystalline layer covering the surface. We observed the individual crystals that constitute the polycrystalline hydrate layer and classified the morphology of the hydrate crystals depending on the system subcooling ΔTsub, the difference between the system temperature and the guest−hydrate−water three-phase equilibrium temperature corresponding to the system pressure. As a general trend, at ΔTsub≥ 3.0 K, the shape of hydrate crystals is typically swordlike or triangular, and the shape changes to a polygon at ΔTsub from 2.0 to 3.0 K, and then to larger-sized polygons with one side of the polygon typically 0.5−1.0 mm in length. It may be concluded that ...

Effect of coagulation pretreatment on membrane distillation process for desalination of recirculating cooling water

The objective of this work was to study the performance of coagulation pretreatment and the effect of coagulation pretreatment on membrane distillation (MD) process for desalination of recirculating cooling water (RCW). In this study, RCW was desalinated by MD process after pretreated by coagulation, precision filtration, acidification and degassing. Pre-coagulation of RCW with poly-aluminum chloride (PACl) coagulant improves the elimination of total organic carbon (TOC), total phosphorus (TP) substances. The optimized pH value and PACl dosage were 7 and 15 mg/L, respectively. Compared with MD process without coagulation pretreatment, much slighter MD flux decrease was observed when coagulation pretreatment was employed for desalination of RCW using MD process. Compared with the membrane flux of MD process for the RCW without coagulation pretreatment, about 23% improvement of MD flux was obtained by employing coagulation pretreatment after 30 days operation. The variation of crystal morphology on membrane surface and hydrophobic character of PVDF hollow membranes were investigated. The results show that distorted rhombic magnesium-calcite scale formed on membrane surface when coagulation pretreatment was employed. However, the deposited magnesium-calcite on the membrane surface was loosely packed with particles of much smaller size when RCW without coagulation pretreatment was fed. It is because that the coagulation pretreatment removed most of the natural organic matter (NOM) and antiscalant additives in RCW, which act as an inhibitor to calcium carbonate crystal growth in water. After coagulation pretreatment, bigger crystal deposit formed on membrane surface with the increase in CF of RCW. It was rather difficult for bigger crystal to enter membrane pores and thus the formation of bigger crystal reduced partial wetting of membrane, which enhanced trans-membrane flux. The hydrophobic character of PVDF hollow membranes used in MD process can be easily recovered by chemical rinsing using acid–base solutions. The results indicate that the pretreatment with chemical coagulant, PACl, is effective for the desalination of RCW by MD process.

Clathrate hydrate crystal growth in liquid water saturated with a hydrate-forming substance: variations in crystal morphology

This paper reports on our interpretation of our visual observations of the variations in macroscopic morphology of hydrate crystals growing in liquid water saturated with a guest substance prior to the hydrate formation. The observations were made in a high-pressure cell charged with liquid water and gaseous CO2. They revealed distinct variations in the morphology of hydrate crystals depending on the system subcooling ΔT sub, the temperature deficiency inside the cell from the triple CO2–hydrate–water equilibrium temperature under a given pressure. When ΔT sub ≳ 3 K, a hydrate film first grew along the CO2–water interface; then hydrate crystals with dendritic morphology grew in large numbers into the liquid-water phase from that hydrate film. When ΔT sub ≲ 2 K, the dendritic crystals were replaced by skeletal or polyhedral crystals. We present a non-dimensional index for such variations in hydrate crystal morphology. This is based on the idea that this morphology depends on the growth rate of hydrate crystals, and their growth rate is controlled by the mass transfer of the hydrate–guest substance (CO2 in the present experiments), dissolved in the bulk of liquid water, to the hydrate crystal surfaces. The morphology variations observed in the present and previous studies are related to this index.

Causes of variation in crystal morphology in metamorphogenic pyrite deposits of the Cameros Basin (N Spain)

AbstractThe low‐grade metasediments of the Cameros Basin, northern Spain, host a number of deposits of spectacular quality pyrite mineralization. These formed during regional metamorphism and the pyrite crystals exhibit a wide range of morphologies. On the basis of pyrite crystal habit, the deposits can be classified into two groups: Group I comprises deposits with cubic, elongated or platy crystals; Group II comprises deposits characterized by pyritohedra and cubo‐pyritohedra with striated faces, along with blocky crystals and fine‐grained aggregates. Group I deposits are formed in sequences dominated by meandriform fluviatile sediments, while Group II is hosted by deltaic plain and lacustrine metasediments.Temperature differences between deposits and As content are possible causes of the different pyrite morphologies in the deposits, but no significant variation exists between the two groups for either factor. Comparison with experimentally grown pyrite crystals suggests that Group I deposits have morphologies indicative of lower degrees of pyrite supersaturation than pyrite crystals in Group II deposits. The sedimentary facies hosting Group II deposits provides a greater availability of sedimentary sulphur (pyrite and sulphates). Moreover, reactions involving sulphate during metamorphism may have modified fluid chemistry, which would also act to produce higher degrees of pyrite saturation in fluids derived from the sulphate‐rich deltaic plain and lacustrine metasediments hosting the Group II deposits. This hypothesis is confirmed by sulphur isotope data on the pyrites, which show a larger component of34S‐enriched sulphate‐derived sulphur in these deposits. Copyright © 2001 John Wiley & Sons, Ltd.

Role of competitive interactions in growth rate trends of subtilisin s88 crystals

An orthorhombic crystal form of subtilisin BPN’ variant s88 exhibits a systematic variation in growth rates of its three unique faces, resulting in pronounced variations in crystal morphology as a function of the ionic strength (Gallagher et al., J. Crystal Growth 193 (1998) 665). We have sought to explain these observations by performing energetics calculations using the full structural details of the protein. The approach of correlating growth rates with the strength of interactions of molecular pairs in the crystal proved unsatisfactory. The attachment of protein molecules to growing crystal faces is a stochastic process: a protein molecule samples numerous configurational (orientational and translational) states before attaching to the crystal in a configuration consistent with the crystal symmetry. This search-and-bind process determines the rate of crystal growth. We present a simplified approach that mimics this dynamical process: we perform docking of a protein molecule with another protein molecule or a cluster of molecules. An analysis of the bound configurations reveals the presence of orientations that are incommensurate with the crystal symmetry but in which a protein molecule can also bind strongly to the crystal face. Such improperly oriented molecules can be thought of as competitive inhibitors, and their presence is shown to affect the growth rate. Thus procedures aimed at decreasing the effect of such competitive inhibition, or conversely increasing the specificity of protein–protein interactions forming the crystal, are expected to offer better control of crystal growth rates.

Laminar flow, immiscibility and segregated fractionation in the Mt Townsend lamprophyric tephrite dyke, New South Wales: Does flow change activities in the melt?

A vertical 1 m‐wide ocellar dyke on the eastern slopes of Mt Townsend, New South Wales, is a member of a dispersed Iamprophyric dyke swarm within the Carboniferous Snowy Mountains Batholith. The dyke has a bulk composition of primitive melanephelinite, but crystallised as a monchiquite due to high levels of magmatic CO2 and H2O. Despite extreme variations in crystal morphology and relative phase abundances, compositions of silicate minerals are relatively constant across the dyke, and from host to ocelli. Whole‐rock analyses show that the dyke has a constant bulk composition, precluding lateral transport of components. More than ten thin flow zones have a dramatic increase in the volume of ocelli (5 to 35%). In the dyke core these are replaced by a pronounced clustering of minerals. The chemical constraints indicate that the ocelli‐rich zones are not caused by a temperature profile, a fractionation profile, flow migration of ocelli, multiple injection, magma retraction, or mixing of related or unrelated m...

Polymorphism, twinning and morphology of crystals of 2,4,6-trinitrotoluene grown from solution

Crystals of 2,4,6-trinitrotoluene (TNT) have been grown from a wide range of organic solvents under various conditions. The structural nature and morphology of these crystals were systematically characterised using a number of techniques. The crystals were found to exist in two basic forms having monoclinic and orthorhombic structures. The monoclinic modification was the stable form from ambient temperature to the melting point and showed extensive twinning: the twin law was defined and the structural origin of twinning determined. The variation in crystal morphology with growth conditions for the monoclinic modification was attributed to the small differences in reticular areas for morphological forms other than {100}. The structural perfection of monoclinic crystals was shown to be dominated by impurity-related defects.

Properties of ZnO ‐ B 2 O 3 ‐ SiO2 Glasses for Surface Passivation

Two glasses, glass A (, , weight percent [w/o]) and glass B (,, ), were prepared for the purpose of passivating high voltage silicon devices. Their physical and electrical properties were compared using DTA characteristics, SEM observations, x‐ray diffraction patterns, thermal expansion coefficients, and surface charge densities, as a function of firing temperature. Reverse characteristics of semiconductor devices passivated with these glasses were also investigated. Differences in the variation of properties with firing temperature between the two glasses were found to originate mainly from differences in the variation of crystal morphology in the glasses as a function of firing temperature.

The crystal morphology of plagioclase feldspar produced during isothermal supercooling and constant rate cooling experiments

AbstractThe crystal morphology of plagioclase feldspar in seven mafic rocks has been studied by isothermal supercooling and constant rate cooling experiments at 1 atmosphere using the ‘wire-loop’ suspension method. There is a systematic variation in crystal morphology with supercooling (−ΔT), but the transitions between the different morphologies are gradual, and consecutive forms sometimes occur together. As −ΔT increases, the sequence of plagioclase morphology is generally laths → skeletal forms → fan spherulites. During isothermal supercooling the position of the plagioclase morphological fields is shown to be dependent on −ΔT, superheating (+ΔT), and also on time to a greater or lesser degree. Variations in melt composition and viscosity affect the position and slope of the boundaries of the fields. In the constant rate cooling experiments, the morphological type is dependent on the cooling rate and can be used to a limited extent as an indicator of the range of supercooling over which the first crystals nucleated and grew.