Framboid Microcrystal Growth

2021 ◽  
pp. 235-261
Author(s):  
David Rickard
Keyword(s):  
Crystal Growth ◽  
Crystal Surface ◽  
Normal Growth ◽  
Hydrothermal Systems ◽  
Hydrothermal Conditions ◽  
Sedimentary Environments ◽  
Surface Nucleation ◽  
Growth Modes ◽  
Cubic Forms ◽  
Nucleation Growth

Framboid microcrystals grow through surface reaction of S2(-II) or H2S with =FeS moieties at defect sites on the pyrite crystal surface. The surface energies of pyrite vary from the most stable cubic through octahedral to pyritohedral and dodecahedral surfaces. Microcrystals commonly develop as truncated octahedra as the supersaturation decreases during crystal growth in sedimentary environments, although cubic forms may be favored under hydrothermal conditions. Screw dislocation growth followed by surface nucleation growth are the normal growth modes in sediments, whereas surface nucleation growth is likely to dominate in hydrothermal systems. The rate of crystal growth of framboids is unknown but appears to be very fast and normally diffusion-limited. Linear approximations to the diffusion equations show that average 6 μ‎m diameter framboids form in five days in sediments, and formation times increase exponentially from a few hours for ca. 2 μ‎m framboids to three years for the largest 250 μ‎m framboids.

Mineral Redox Buffers and The Stability of Organic Compounds Under Hydrothermal Conditions

1996 ◽  
Vol 432 ◽  
Author(s):  
J. S. Seewald
Keyword(s):  
Organic Compounds ◽  
Active Species ◽  
Hydrothermal Systems ◽  
Hydrothermal Conditions ◽  
Sulfur Species ◽  
Sedimentary Environments ◽  
Mineral Assemblages ◽  
Catalytically Active ◽  
Chemical Conditions ◽  
The Stability

AbstractOrganic compounds play an integral role in numerous geochemical process in subsurface environments. To evaluate factors that regulate the stability of ethane, ethene, propane, and propene in hydrothermal systems a series of experiments were conducted at 300 to 325°C and 350 bars. The experiments contained the mineral assemblages pyrite-pyrrhotite-magnetite, hematite-magnetite-pyrite, and hematite-magnetite to buffer fO2, aH2(aq) and aH2S(aq) at geologically reasonable values.Results of the experiments suggest that under appropriate physical and chemical conditions, metastable redox dependent thermodynamic equilibrium involving liquid water and inorganic iron-bearing mineral assemblages may regulate the relative abundance of short chain alkanes and their corresponding alkenes. In addition, alkenes represent an important intermediary in the conversion of n-alkanes to methane and oxidized species such as carbon dioxide, ketones alcohols, and organic acids.The rates of redox dependent organic reactions during the experiments were strongly influenced by the presence of sulfur. Under relatively oxidizing conditions greater catalytic activity due to the presence of dissolved sulfur species was observed. Fluid speciation calculations suggest that oxidized aquous sulfur compounds represent the catalytically active species.These results suggest that redox conditions and the presence or absence of dissolved sulfur species in natural sedimentary environments may strongly influence the stability of hydrocarbons. Accordingly, models used to predict the stability of oil and the formations of natural gas need to account for chemical processes that involve both organic and inorganic sedimentary components.

scholarly journals Faceted-rough surface with disassembling of macrosteps in nucleation-limited crystal growth

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Noriko Akutsu
Keyword(s):  
Crystal Growth ◽  
Rough Surface ◽  
Crystal Surface ◽  
Point Contact ◽  
Surface Model ◽  
Crossover Point ◽  
Growth Changes ◽  
Step Step ◽  
Surface Crystal ◽  
Nucleation Growth

AbstractTo clarify whether a surface can be rough with faceted macrosteps that maintain their shape on the surface, crystal surface roughness is studied by a Monte Carlo method for a nucleation-limited crystal-growth process. As a surface model, the restricted solid-on-solid (RSOS) model with point-contact-type step–step attraction (p-RSOS model) is adopted. At equilibrium and at sufficiently low temperatures, the vicinal surface of the p-RSOS model consists of faceted macrosteps with (111) side surfaces and smooth terraces with (001) surfaces (the step-faceting zone). We found that a surface with faceted macrosteps has an approximately self-affine-rough structure on a ‘faceted-rough surface’; the surface width is strongly divergent at the step-disassembling point, which is a characteristic driving force for crystal growth. A ‘faceted-rough surface’ is realized in the region between the step-disassembling point and a crossover point where the single nucleation growth changes to poly-nucleation growth.

Molecular Dynamics Studies of Surface Nucleation and Crystal Growth of Si on SiO2 Substrates

2005 ◽  
Vol 899 ◽  
Author(s):  
Byoung-Min Lee ◽  
Hong Koo Baik ◽  
Takahide Kuranaga ◽  
Shinji Munetoh ◽  
Teruaki Motooka
Keyword(s):  
Thin Film ◽  
Molecular Dynamics ◽  
Crystal Growth ◽  
Surface Energy ◽  
Md Simulations ◽  
Lower Surface ◽  
Surface Nucleation ◽  
Lower Surface Energy ◽  
Potential Parameters ◽  
Si Thin Film

AbstractMolecular dynamics (MD) simulations of atomistic processes of nucleation and crystal growth of silicon (Si) on SiO2 substrate have been performed using the Tersoff potential based on a combination of Langevin and Newton equations. A new set of potential parameters was used to calculate the interatomic forces of Si and oxygen (O) atoms. It was found that the (111) plane of the Si nuclei formed at the surface was predominantly parallel to the surface of MD cell. The values surface energy for (100), (110), and (111) planes of Si at 77 K were calculated to be 2.27, 1.52, and 1.20 J/m2, respectively. This result suggests that, the nucleation leads to a preferred (111) orientation in the poly-Si thin film at the surface, driven by the lower surface energy.

scholarly journals Ideas and perspectives: Development of nascent autotrophic carbon fixation systems in various redox conditions of the fluid degassing on early Earth

2019 ◽  
Vol 16 (8) ◽  
pp. 1817-1828 ◽  
Author(s):  
Sergey A. Marakushev ◽  
Ol'ga V. Belonogova
Keyword(s):  
Carbon Fixation ◽  
Hydrothermal Systems ◽  
System Model ◽  
Early Earth ◽  
Hydrothermal Conditions ◽  
Oxidation Of Methane ◽  
The Earth ◽  
Autotrophic Metabolism ◽  
Metabolic Systems ◽  
Hydrothermal Environments

Abstract. The origin and development of the primary autotrophic metabolism on early Earth were influenced by the two main regimes of degassing of the Earth – reducing (predominance CH4) and oxidative (CO2). Among the existing theories of the autotrophic origin of life in hydrothermal environments, CO2 is usually considered to be the carbon source for nascent autotrophic metabolism. However, the ancestral carbon used in metabolism may have been derived from CH4 if the outflow of magma fluid to the surface of the Earth consisted mainly of methane. In such an environment, the primary autotrophic metabolic systems had to be methanotrophic. Due to the absence of molecular oxygen in the Archean conditions, this metabolism would have been anaerobic; i.e., oxidation of methane must be realized by inorganic high-potential electron acceptors. In light of the primacy and prevalence of CH4-dependent metabolism in hydrothermal systems of the ancient Earth, we propose a model of carbon fixation where the methane is fixed or transformed in a sequence of reactions in an autocatalytic methane–fumarate cycle. Nitrogen oxides are thermodynamically the most favorable among possible oxidants of methane; however, even the activity of oxygen created by mineral buffers of iron in hydrothermal conditions is sufficient for methanotrophic acetogenesis. The hydrothermal system model is considered in the form of a phase diagram, which demonstrates the area of redox and P and T conditions favorable for the development of the primary methanotrophic metabolism.

Phase evolution and crystal growth of VO2 nanostructures under hydrothermal reactions

RSC Advances ◽  
2016 ◽  
Vol 6 (9) ◽  
pp. 7113-7120 ◽  
Author(s):  
Weilai Yu ◽  
Shuai Li ◽  
Chi Huang
Keyword(s):  
Crystal Growth ◽  
Phase Evolution ◽  
Hydrothermal Conditions ◽  
Hydrothermal Reactions ◽  
First Time

The phase evolution and crystal growth of VO2 nanostructures under hydrothermal conditions was comprehensively investigated and the feasibility of the Ostwald's step rules towards VO2 polymorph evolution was for the first time demonstrated.

scholarly journals Crystal-plane-dependent effects of antifreeze glycoprotein impurity for ice growth dynamics

2019 ◽  
Vol 377 (2146) ◽  
pp. 20180393 ◽  
Author(s):  
Yoshinori Furukawa ◽  
Ken Nagashima ◽  
Shunichi Nakatsubo ◽  
Salvador Zepeda ◽  
Ken-ichiro Murata ◽  
...  
Keyword(s):  
Crystal Growth ◽  
Growth Rates ◽  
Space Station ◽  
Supercooled Water ◽  
Normal Growth ◽  
Crystal Plane ◽  
Impurity Effect ◽  
Crystal Formation ◽  
Ice Crystal ◽  
Antifreeze Glycoprotein

An impurity effect on ice crystal growth in supercooled water is an important subject in relation to ice crystal formation in various conditions in the Earth's cryosphere regions. In this review, we consider antifreeze glycoprotein molecules as an impurity. These molecules are well known as functional molecules for controlling ice crystal growth by their adsorption on growing ice/water interfaces. Experiments on free growth of ice crystals in supercooled water containing an antifreeze protein were conducted on the ground and in the International Space Station, and the normal growth rates for the main crystallographic faces of ice, namely, basal and prismatic faces, were precisely measured as functions of growth conditions and time. The crystal-plane-dependent functions of AFGP molecules for ice crystal growth were clearly shown. Based on the magnitude relationship for normal growth rates among basal, prismatic and pyramidal faces, we explain the formation of a dodecahedral external shape of an ice crystal in relation to the key principle governing the growth of polyhedral crystals. Finally, we emphasize that the crystal-plane dependence of the function of antifreeze proteins on ice crystal growth relates to the freezing prevention of living organisms in sub-zero temperature conditions. This article is part of the theme issue ‘The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets’.

Effect of Phosphate and Silica on the Rate of Crystallization of Sucrose

2005 ◽  
Vol 1 (5) ◽  
Author(s):  
Ms. Aamarpali Ratna Puri ◽  
S. Kaur
Keyword(s):  
Growth Rate ◽  
Crystal Growth ◽  
Mother Liquor ◽  
Crystal Surface ◽  
Mass Transfer Process ◽  
Sugar Solution ◽  
Local Conditions ◽  
Concentration Difference ◽  
Different Temperatures ◽  
Sucrose Crystals

Sucrose Crystallization is a mass transfer process. Sucrose molecule's migration from solution to crystal is driven by concentration difference between the mother liquor and the crystal surface; the coefficient of super saturation is the most important parameter for the process. Supersaturation of sugar solution depends on the purity and brix of the mother liquor. It has large influence on product's quantity and quality (crystal yield, crystal size and size distribution) and on the cost of production i.e output/hour and energy consumption. However there is still no generally applicable theory, which permits an accurate prediction of the effects of all the factors that govern the industrial processes of crystallization from solution. The crystal growth depends on the viscosity, which further depends on the nature and amount of impurities. If the local conditions are favourable, localized layers of molecules of impurity can statistically remain on the surface for a period of time. On the other hand, if the interaction between the impurity and the layer is weak, then there will be competition between impurity and sucrose molecules thus affecting the sucrose crystal growth rate. In the present study, the growth rate of sugar crystals was studied, using two-litre automatic laboratory vacuum pan, under controlled conditions in the presence of impurities. The effect of phosphate and silica (adding one at time) on the growth rate of sugar crystals was studied at two different temperatures 328 and 338K and with two different seed sizes of sucrose (850 and 600µm). The growth rate was studied at two degrees of supersaturation (1.10 and 1.15). The growth rate of sucrose crystals (with or without added impurities) showed significant increase with the 10°C rise in temperature. The growth rate of sucrose crystals increased with the increase in the level of phosphate but decreased with the increase in the level of silica in sugar solution.

scholarly journals Effects of Fluoride on the Interactions between Amelogenin and Apatite Crystals

2008 ◽  
Vol 87 (1) ◽  
pp. 39-44 ◽  
Author(s):  
K. Tanimoto ◽  
T. Le ◽  
L. Zhu ◽  
J. Chen ◽  
J.D.B. Featherstone ◽  
...  
Keyword(s):  
Crystal Growth ◽  
Crystal Surface ◽  
Titration Calorimetry ◽  
Carbonated Hydroxyapatite ◽  
Protein Assay ◽  
Binding Rate ◽  
Apatite Crystals ◽  
Sds Page ◽  
Initial Binding

Fluorosed enamel is more porous and less mineralized, possibly related to altered amelogenin-modulated crystal growth. The purpose of this study was to examine the role of fluoride in interactions between amelogenin and apatite crystals. Recombinant human amelogenin (rh174) was bound to carbonated hydroxyapatite containing various amounts of fluoride, and analyzed by protein assay, SDS PAGE, and AFM. Interactions between rh174 and fluoride were assayed by isothermal titration calorimetry (ITC). The initial binding rate of rh174, as well as total amount of rh174 bound to fluoride-containing carbonated hydroxyapatite, was greater than that in the control carbonated hydroxyapatite. Fluoride in solution at physiologic (5.3 micromolar, or 0.1 ppm) concentrations showed no significant effect on binding, but higher fluoride levels significantly decreased protein binding. ITC showed no interactions between fluoride and rh174. These results suggest that fluoride incorporation into the crystal lattice alters the crystal surface to enhance amelogenin binding, with no direct interactions between fluoride and amelogenin.

Sign in / Sign up

Export Citation Format

Share Document