scholarly journals Parasitic crystallization of colloidal electrolytes: growing a metastable crystal from the nucleus of a stable phase

Soft Matter ◽  
2021 ◽  
Author(s):  
Ignacio Sanchez-Burgos ◽  
Adiran Garaizar ◽  
Carlos Vega ◽  
Eduardo Sanz ◽  
Jorge R. Espinosa
Keyword(s):  
Crystal Growth ◽  
Stable Phase ◽  
Nucleation Barrier ◽  
Lower Stability

Despite its lower stability and higher nucleation barrier, a metastable charge-disordered colloidal phase manages to parasitically crystallize from nuclei of the stable charge-ordered phase due to its enhanced kinetic crystal growth.

PO4 adsorption on the calcite surface modulates calcite formation and crystal size

2019 ◽  
Vol 104 (10) ◽  
pp. 1381-1388
Author(s):  
Yuki Sugiura ◽  
Kunio Ishikawa ◽  
Kazuo Onuma ◽  
Yoji Makita
Keyword(s):  
Crystal Growth ◽  
Crystal Size ◽  
Medical Science ◽  
Bone Substitutes ◽  
Stable Phase ◽  
X Ray Diffraction ◽  
Calcite Crystal ◽  
X Ray ◽  
Fine Structures

Abstract Calcium carbonate (CaCO3) and particularly its stable phase, calcite, is of great geological significance in the deep carbon cycle since CaCO3 from biomineralized shells and corals form sedimentary rocks. Calcite also attracts attention in medical science and pharmacy as a primary or intermediate component in biomaterials because it possesses excellent biocompatibility along with suitable physicochemical properties. Calcite blocks have already been used during surgical procedures as a bone substitute for reconstructing bone defects formed by diseases and injury. When producing CaCO3 biomaterials and bioceramics, in particular, in vivo control of the size and polymorphic nature of CaCO3 is required. In this study, we investigated the effects of PO4 on calcite formation during the phase conversion of calcium sulfate anhydrate (CaSO4, CSA), which is sometimes used as a starting material for bone substitutes because of its suitable setting ability. CSA powder was immersed in 2 mol/L Na2CO3 solution containing a range of PO4 concentrations (0–60 mmol/L) at 40 °C for 3 days. The treated samples were investigated by X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray fluorescence spectroscopy, and thermal analysis. In addition, the fine structures of the treated samples were observed by field-emission scanning electron microscopy, and the specific surface area was measured. We found that PO4, which is universally present in vivo, can modulate the calcite crystal size during calcite formation. A fluorescence study and calcite crystal growth experiments indicated that PO4 adsorbs tightly onto the surface of calcite, inhibiting crystal growth. In the presence of high PO4 concentrations, vaterite is formed along with calcite, and the appearance and stability of the CaCO3 polymorphs can be controlled by adjusting the PO4 concentration. These findings have implications for medical science and pharmacology, along with mineralogy and geochemistry.

Unidirectional Partial Melting and Solidification of SmBCO Superconductor

1997 ◽  
Vol 12 (8) ◽  
pp. 1979-1989 ◽  
Author(s):  
M. Sumida ◽  
Y. Nakamura ◽  
Y. Shiohara ◽  
T. Umeda
Keyword(s):  
Growth Rate ◽  
Crystal Growth ◽  
Partial Melting ◽  
Composite Fiber ◽  
Stable Phase ◽  
Microstructure Formation ◽  
Molten Mixture ◽  
Planar Crystal ◽  
Formation Behavior ◽  
Melting And Solidification

Microstructure control of the SmBCO superconductor was carried out using the floating zone partial melting and solidification method. It is generally recognized that finely and uniformly dispersed nonsuperconductive high temperature stable phase (Sm211) particles included in the superconductive Sm123 matrix act as effective pinning centers. Microstructure formation of the partial molten mixture (Sm211 particles and BaO–CuO liquid) by decomposition of the precursor Sm123 on melting and solidification of Sm123 from the mixture have to be controlled concurrently to fabricate the 123/211 composite fiber with the optimum microstructure. During unidirectional solidification, planar crystal growth which provides the single crystal growth of Sm123 becomes unstable with increased growth rate. During unidirectional melting, the mean diameter of aligned Sm211 particles behind the melting interface decreases with increased growth rate and with decreased temperature gradient at the melting interface. Initial composition of the precursor significantly affects the formation behavior of Sm211 particles. The contribution of process parameters to the microstructure formation is also briefly discussed.

Calcium Sulfate Scale Formation: A Kinetic Approach

1978 ◽  
Vol 18 (02) ◽  
pp. 133-138 ◽  
Author(s):  
George H. Nancollas ◽  
Atal E. Eralp ◽  
Jasbir S. Gill
Keyword(s):  
Crystal Growth ◽  
Ionic Strength ◽  
Specific Surface ◽  
Calcium Sulfate ◽  
Scale Formation ◽  
Phase Changes ◽  
Field Conditions ◽  
Stable Phase ◽  
Calcium Sulfate Dihydrate ◽  
Solid Phases

Abstract The growth and phase transformation of calcium sulfate dihydrate and hemihydrate crystals were studied at temperatures from 70 to 130 deg. C. At 70 deg. C the second-order rate constant for dihydrate crystal growth did not change by more than 20 percent over a pH range of 3.2 to 9.2. It was also independent of ionic strength up to 2.0M. Growth in stable supersaturated calcium sulfate solution was completely inhibited by 7 x 10-7 M phytic acid for about 24 hours at 70 deg. C. The seeded crystallization of calcium sulfate hemihydrate at temperatures from 90 to 140 deg. C and The phase changes from a- to beta-hemihydrate were investigated by X-ray diffraction, specific surface area analysis, and scanning electron microscopy. Organic phosphonates were found to be effective inhibitors of crystal growth of all the phases at high temperatures. Introduction The phases that form during the crystallization of many sparingly soluble salts evidently are determined much more by kinetic factors than by thermodynamic considerations. Thus, in the case of calcium phosphate crystal growth, an amorphous precursor is formed rapidly at the beginning of the precursor is formed rapidly at the beginning of the reaction and undergoes slow transformation to the thermodynamically stable phase, hydroxyapatite. Significant changes with time are observed in such factors as chemical composition, crystallinity, and specific surface areas of the solid phases. The simple equilibrium studies do not reveal the factors that may be important in determining whether these phases will precipitate in the field. phases will precipitate in the field. The case of calcium sulfate, which is important in desalination, geochemistry, and petroleum engineering, is complicated further by the fact that it can crystalize from aqueous solutions in three forms- dehydrate (CaSO4 - 2H2O), hemihydrate (a-CaSO4 1/2 H2O or beta-CaSO4 - 1/2 H2O), and anhy-drite (CaSO4). These phases may be stable or unstable depending on temperature or ionic strength, and they have decreasing solubilities with increasing temperatures above about 40 deg. C. To understand the formation of these scale minerals, high-temperature laboratory methods must be used for the kinetic studies, allowing both solutions and solid phases to be sampled without spurious temperature effects. The kinetics of transformation of one hydrate to another is particularly important in determining the nature of the scale formed under field conditions as a function of both temperature and background electrolyte concentration. This investigation studied the formation and dissolution of calcium sulfate phases under some typical field conditions. Kinetic investigations were emphasized since these frequently can be used to predict the nature of the phases formed under specific conditions of concentration or temperature. Moreover, unlike the results of spontaneous precipitation experiments, such studies are highly reproducible. The effects of factors such as ionic strength, temperature, supersaturation, and effectiveness of scale inhibitors may be studied quantitatively. In addition, the influence of the nature of the seed crystal phase and morphology on the subsequent growth process can be investigated. The morphology of the crystals comprising scale deposits may be particularly important in determining whether they pack together as hard, destructive scale or remain as a sludge to be swept away by the liquid phase. Seeded-crystal growth processes are better models than are spontaneous processes are better models than are spontaneous precipitation studies for the scale formation reactions precipitation studies for the scale formation reactions in which the solid phase is formed heterogeneously either on a foreign substrate or on crystals of scale already present. The growth rate of calcium sulfate dihydrate seed crystals is independent of the fluid dynamics in the system, suggesting that the rate is not diffusion-controlled but depends on a surface reaction rate. This has particular significance for the formation of scale in the oil well because the scaling rate is expected to be independent of the dynamics of fluid flow at the metal surface. SPEJ P. 133

Characterization of Coherent, Ordered Precipitates in Nickel-Base Alloys

1973 ◽  
Vol 31 ◽  
pp. 144-145
Author(s):  
B. H. Kear ◽  
J. M. Oblak
Keyword(s):  
Stable Phase ◽  
Nickel Base Superalloy ◽  
Alloy 718 ◽  
Commercial Alloy ◽  
Precipitate Morphology ◽  
Continuous Precipitation ◽  
Nickel Base ◽  
Base Superalloy ◽  
Strengthening Precipitate

A nickel-base superalloy is essentially a Ni/Cr solid solution hardened by additions of Al (Ti, Nb, etc.) to precipitate a coherent, ordered phase. In most commercial alloy systems, e.g. B-1900, IN-100 and Mar-M200, the stable precipitate is Ni3 (Al,Ti) γ′, with an LI2structure. In A lloy 901 the normal precipitate is metastable Nis Ti3 γ′ ; the stable phase is a hexagonal Do2 4 structure. In Alloy 718 the strengthening precipitate is metastable γ″, which has a body-centered tetragonal D022 structure.Precipitate MorphologyIn most systems the ordered γ′ phase forms by a continuous precipitation re-action, which gives rise to a uniform intragranular dispersion of precipitate particles. For zero γ/γ′ misfit, the γ′ precipitates assume a spheroidal.

Montmorillonite Dendrites

1974 ◽  
Vol 32 ◽  
pp. 454-455
Author(s):  
Necip Güven ◽  
Rodney W. Pease
Keyword(s):  
Crystal Growth ◽  
Growth Mechanism ◽  
Growth Front ◽  
Morphological Features ◽  
Dendritic Crystal ◽  
Crystal Growth Mechanism

Morphological features of montmorillonite aggregates in a large number of samples suggest that they may be formed by a dendritic crystal growth mechanism (i.e., tree-like growth by branching of a growth front).

Lorentz microscopy study of magnetic domain walls in Fe-Cr-Co alloys

1978 ◽  
Vol 36 (1) ◽  
pp. 462-463
Author(s):  
Yalcin Belli
Keyword(s):  
Domain Walls ◽  
Magnetic Domain ◽  
Microscopy Study ◽  
Ferromagnetic Phase ◽  
Stable Phase ◽  
Magnetic Domains ◽  
Lorentz Microscopy ◽  
Magnetic Hardening ◽  
Electron Microscopes ◽  
Co Alloys

Fe-Cr-Co alloys have great technological potential to replace Alnico alloys as hard magnets. The relationship between the microstructures and the magnetic properties has been recently established for some of these alloys. The magnetic hardening has been attributed to the decomposition of the high temperature stable phase (α) into an elongated Fe-rich ferromagnetic phase (α1) and a weakly magnetic or non-magnetic Cr-rich phase (α2). The relationships between magnetic domains and domain walls and these different phases are yet to be understood. The TEM has been used to ascertain the mechanism of magnetic hardening for the first time in these alloys. The present paper describes the magnetic domain structure and the magnetization reversal processes in some of these multiphase materials. Microstructures to change properties resulting from, (i) isothermal aging, (ii) thermomagnetic treatment (TMT) and (iii) TMT + stepaging have been chosen for this investigation. The Jem-7A and Philips EM-301 transmission electron microscopes operating at 100 kV have been used for the Lorentz microscopy study of the magnetic domains and their interactions with the finely dispersed precipitate phases.

TEM and cathodoluminescence of precipitates in II-VI semiconductors

1988 ◽  
Vol 46 ◽  
pp. 488-489
Author(s):  
Joanna L. Batstone
Keyword(s):  
Crystal Growth ◽  
Band Gap ◽  
Local Strain ◽  
Wide Band ◽  
Optoelectronic Device ◽  
Wide Band Gap ◽  
Bulk Crystal Growth ◽  
Transmission Electron ◽  
Device Applications ◽  
Stoichiometry Control

Interest in II-VI semiconductors centres around optoelectronic device applications. The wide band gap II-VI semiconductors such as ZnS, ZnSe and ZnTe have been used in lasers and electroluminescent displays yielding room temperature blue luminescence. The narrow gap II-VI semiconductors such as CdTe and HgxCd1-x Te are currently used for infrared detectors, where the band gap can be varied continuously by changing the alloy composition x.Two major sources of precipitation can be identified in II-VI materials; (i) dopant introduction leading to local variations in concentration and subsequent precipitation and (ii) Te precipitation in ZnTe, CdTe and HgCdTe due to native point defects which arise from problems associated with stoichiometry control during crystal growth. Precipitation is observed in both bulk crystal growth and epitaxial growth and is frequently associated with segregation and precipitation at dislocations and grain boundaries. Precipitation has been observed using transmission electron microscopy (TEM) which is sensitive to local strain fields around inclusions.

STM studies of crystal growth

1991 ◽  
Vol 49 ◽  
pp. 374-375
Author(s):  
M. G. Lagally
Keyword(s):  
Crystal Growth ◽  
Molecular Beam ◽  
Chemical Vapor ◽  
Sputter Deposition ◽  
Field Of View ◽  
Scanning Tunneling ◽  
Wide Field ◽  
Tunneling Microscopy ◽  
Wide Field Of View ◽  
The One

It has been recognized since the earliest days of crystal growth that kinetic processes of all Kinds control the nature of the growth. As the technology of crystal growth has become ever more refined, with the advent of such atomistic processes as molecular beam epitaxy, chemical vapor deposition, sputter deposition, and plasma enhanced techniques for the creation of “crystals” as little as one or a few atomic layers thick, multilayer structures, and novel materials combinations, the need to understand the mechanisms controlling the growth process is becoming more critical. Unfortunately, available techniques have not lent themselves well to obtaining a truly microscopic picture of such processes. Because of its atomic resolution on the one hand, and the achievable wide field of view on the other (of the order of micrometers) scanning tunneling microscopy (STM) gives us this opportunity. In this talk, we briefly review the types of growth kinetics measurements that can be made using STM. The use of STM for studies of kinetics is one of the more recent applications of what is itself still a very young field.

Cristal-growth dynamics of n-doped gaAs

1992 ◽  
Vol 50 (2) ◽  
pp. 1544-1545
Author(s):  
Pham V. Huong ◽  
Stéphanie Bouchet ◽  
Jean-Claude Launay
Keyword(s):  
Crystal Growth ◽  
Spatial Resolution ◽  
Epitaxial Layer ◽  
Outer Surface ◽  
Gaas Substrate ◽  
Structural Modification ◽  
Growth Dynamics ◽  
Argon Laser ◽  
High Anisotropy ◽  
Crystal Gaas

Microstructure of epitaxial layers of doped GaAs and its crystal growth dynamics on single crystal GaAs substrate were studied by Raman microspectroscopy with a Dilor OMARS instrument equipped with a 1024 photodiode multichannel detector and a ion-argon laser Spectra-Physics emitting at 514.5 nm.The spatial resolution of this technique, less than 1 μm2, allows the recording of Raman spectra at several spots in function of thickness, from the substrate to the outer deposit, including areas around the interface (Fig.l).The high anisotropy of the LO and TO Raman bands is indicative of the orientation of the epitaxial layer as well as of the structural modification in the deposit and in the substrate at the interface.With Sn doped, the epitaxial layer also presents plasmon in Raman scattering. This fact is already very well known, but we additionally observed that its frequency increases with the thickness of the deposit. For a sample with electron density 1020 cm-3, the plasmon L+ appears at 930 and 790 cm-1 near the outer surface.

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