A Mechanistic Study on the Nucleation and Growth of Au on Pd Seeds with a Cubic or Octahedral Shape

ChemCatChem ◽  
2012 ◽  
Vol 4 (10) ◽  
pp. 1668-1674 ◽  
Author(s):  
Guannan He ◽  
Jie Zeng ◽  
Mingshang Jin ◽  
Hui Zhang ◽  
Ning Lu ◽  
...  
Keyword(s):  
Nucleation And Growth ◽  
Mechanistic Study

The solid state dehydration of d lithium potassium tartrate monohydrate is complete in two rate processes I. The deceleratory diffusion-controlled first reaction

1994 ◽  
Vol 347 (1682) ◽  
pp. 139-156 ◽  
Keyword(s):  
Activation Energy ◽  
Vacancy Concentration ◽  
Nucleation And Growth ◽  
Crystalline Hydrate ◽  
Rate Equations ◽  
Mechanistic Study ◽  
Crystal Thickness ◽  
Potassium Tartrate ◽  
Diffusion Controlled ◽  
Rate Processes

A kinetic and mechanistic study of the dehydration of d lithium potassium tartrate monohydrate has been undertaken. Water evolution is completed through two separate rate processes. The first reaction is the deceleratory, diffusion-controlled release of water from the superficial zones of the reactant crystals. The yield of this process corresponds to the dehydration of a superficial layer of crystal, thickness 10 µm. About 4% of the constituent water was evolved from the single crystals studied, rising to 50% from crushed powder reactants. The second reaction, reported in Part II, is a nucleation and growth process yielding the crystalline anhydrous salt. Gravimetric measurements for the first reaction identified three distinct dehydration processes. The first step was the rapid release of loosely bonded superficial water. The subsequent two deceleratory stages are characterized as diffusive loss of H 2 O molecules from a crystal zone that is at first ordered but later becomes disordered as the water-site vacancy concentration increases. Rate measurements based on water evolution measured the activation energy of this third step as 153 + 4 kJ mol -1 . Irreproducibility of rate data is ascribed to variations in numbers and distributions of imperfections between individual crystals. The extent and rate of the first reaction increased when initiated in small pressures of water vapour. Electron microscope observations identified a structural discontinuity ca. 1 µm below reacted crystal faces, evidence of superficial retexturing of the reactant. Rates of powder dehydrations were more reproducible than those of crystals but the kinetic behaviour was similar. The same rate equations were obeyed and the activation energy was unaltered. Water loss during the first reaction of this crystalline hydrate gives a comprehensive layer of extensively dehydrated material across all surfaces. Subsequently, in or under this water depleted layer, salt is recrystallized and dehydration continues as a nucleation and growth reaction (part II, following paper).

Mechanistic Study of Sn Electrodeposition on TiO2 Nanotube Layers: Thermodynamics, Kinetics, Nucleation, and Growth Modes

2009 ◽  
Vol 113 (48) ◽  
pp. 20568-20575 ◽  
Author(s):  
Ilie Hanzu ◽  
Thierry Djenizian ◽  
Gregorio F. Ortiz ◽  
Philippe Knauth
Keyword(s):  
Nucleation And Growth ◽  
Tio2 Nanotube ◽  
Mechanistic Study ◽  
Growth Modes

The solid state dehydration of d lithium potassium tartrate monohydrate is complete in two rate processes II. The nucleation and growth second reaction and dehydration mechanism

1994 ◽  
Vol 347 (1682) ◽  
pp. 157-184 ◽  
Keyword(s):  
Water Loss ◽  
Vacancy Concentration ◽  
Preceding Paper ◽  
Nucleation And Growth ◽  
Mechanistic Study ◽  
Water Losses ◽  
Water Release ◽  
Kinetic Measurements ◽  
Potassium Tartrate ◽  
Rate Processes

A kinetic and mechanistic study has been undertaken of the nucleation and growth reaction that is the second of the two consecutive rate processes that occur during the dehydration of d lithium potassium tartrate monohydrate. Electron microscopic examinations of the cleaved surfaces of partly reacted crystals show the development of three-dimensional nuclei that are composed of small crystals of the anhydrous product and above 450 K there is evidence of intranuclear melting. Consistent with this model, the second reaction obeys the Avrami-Erofe’ev equation {[ — ln (1 — α)] 1/2 = kt }. Overall rates of the dehydrations of single crystals and of crushed powder samples were closely similar. The activation energy for dehydration was 150-160 kJ mol -1 for both first (reported in part I, preceding paper) and second reactions and for both single crystal and crushed powder reactants. The addition of product crystallites to the reactant reduced sharply, or eliminated, the induction period to the nucleation and growth process. From consideration of the kinetic characteristics, together with the textural changes observed microscopically, we conclude that the following mechanism very satisfactorily accounts for our results. The first reaction proceeds to the dehydration of all crystal surfaces, representing water losses from a layer ca . 10 µm thickness. This deceleratory process occurs initially in a structure resembling that of the reactant but later the increasing water site vacancy concentration results in increasing reactant disorder and possibly includes fusion of the outer layer. When the first reaction water evolution has slowed, recrystallization to the structure of the anhydrous product occurs at a limited number of sites to generate germ nuclei that effectively act as seed crystals for nucleus growth. During the second reaction the reactant—product contact interface is identified as a zone of diffusive water loss, similar to that described for the first reaction. Here, however, the product crystallites promote reorganization of dehydrated material, thereby opening channels for water escape and continually exposing new hydrate surfaces at which dehydration continues. This product recrystallization enables advance of the nucleus interface to be maintained, so that rates of both first and second reactions are subject to control by diffusive loss of water from an active boundary of the reactant. Product reorganization removes the inhibiting character of accumulated product layer by introducing escape channels for water loss so that interface advance continues and, although spasmodic, this migrates forward at a constant average linear rate. The work is of interest because kinetic measurements have been obtained for both of the consecutive rate processes that contribute to the overall reaction. The controls of both are shown to be closely similar. The reaction model proposed here provides insight into the structure of the dehydration interface and the mechanism of water release.

Study of the nucleation and growth of antibiotic labeled Au NPs and blue luminescent Au8 quantum clusters for Hg2+ ion sensing, cellular imaging and antibacterial applications

Nanoscale ◽  
2015 ◽  
Vol 7 (47) ◽  
pp. 19985-20002 ◽  
Author(s):  
Puneet Khandelwal ◽  
Dheeraj K. Singh ◽  
Subha Sadhu ◽  
Pankaj Poddar
Keyword(s):  
Antibacterial Activity ◽  
Nucleation And Growth ◽  
Cellular Imaging ◽  
Mercury Ion ◽  
Mechanistic Study ◽  
Au Nps ◽  
Ion Sensing ◽  
Quantum Clusters

We report a mechanistic study for AuNPs and Au8QCs synthesis by cefradine (an antibiotic) molecule, and their application in mercury ion sensing, imaging and antibacterial activity.

The kinetics and mechanism of the thermal decomposition of copper(II) malonate

1986 ◽  
Vol 404 (1826) ◽  
pp. 101-126 ◽  
Keyword(s):  
Thermal Decomposition ◽  
Solid State ◽  
Growth Process ◽  
Nucleation And Growth ◽  
Mechanistic Study ◽  
Gas Evolution ◽  
Exponential Equation ◽  
Marked Diminution ◽  
Partial Fusion ◽  
Fractional Reaction

A kinetic and mechanistic study of the thermal decomposition of copper(II) malonate has been completed in which the rate measurements have been complemented with microscopic and analytical observations for salt that was partly decomposed to various known extents. Plots of the fractional reaction ( α ) against time for the isothermal reactions were approximately sigmoid but were distorted by a significant diminution in rate at the half-way stage ( α ≈ 0.5). Microscopic observations gave evidence that local fusion occurred soon after the onset of reaction, so that the initial acceleratory behaviour cannot be ascribed to a solid-state nucleation and growth process. From analytical measurements it is concluded that decomposition proceeds to completion by two distinct reactions, involving a stepwise cation reduction: Cu 2+ →Cu + →Cu 0 . The relatively slower rate of the second reaction accounts for the marked diminution in slope of the α -time plots after α = 0.5. The first reaction, copper(II) malonate decomposition, is characterized by a prolonged acceleratory process that obeys the exponential equation (In α = kt ). This is explained by autocatalytic behaviour in which anion breakdown is promoted by acetate, a reaction product, thus (d α /d t ) = kα . Separate experiments confirmed that added copper(II) acetate accelerated the reaction. The decomposition of copper(II) malonate was accompanied by partial fusion, and gas evolution within the viscous melt resulted in the development of an intracrystalline froth-like texture. Such partial melting was, however, localized within the reactant and the sizes and shapes of crystallites did not change markedly during reaction, so that product particles were pseudomorphic with those of the reactant. The final, short deceleratory phase of the first reaction overlapped with the onset of the second reaction.

scholarly journals Cover Picture: A Mechanistic Study on the Nucleation and Growth of Au on Pd Seeds with a Cubic or Octahedral Shape (ChemCatChem 10/2012)

ChemCatChem ◽  
2012 ◽  
Vol 4 (10) ◽  
pp. 1441-1441
Author(s):  
Guannan He ◽  
Jie Zeng ◽  
Mingshang Jin ◽  
Hui Zhang ◽  
Ning Lu ◽  
...  
Keyword(s):  
Nucleation And Growth ◽  
Mechanistic Study

AEM analysis of crystallization in Ti-based amorphous alloys

1983 ◽  
Vol 41 ◽  
pp. 270-271
Author(s):  
A.R. Pelton ◽  
A.F. Marshall ◽  
Y.S. Lee
Keyword(s):  
Magnetic Properties ◽  
Amorphous Alloys ◽  
Amorphous Materials ◽  
Isothermal Annealing ◽  
Amorphous Matrix ◽  
Nucleation And Growth ◽  
Current Interest ◽  
Amorphous Films ◽  
Electrical And Magnetic Properties

Amorphous materials are of current interest due to their desirable mechanical, electrical and magnetic properties. Furthermore, crystallizing amorphous alloys provides an avenue for discerning sequential and competitive phases thus allowing access to otherwise inaccessible crystalline structures. Previous studies have shown the benefits of using AEM to determine crystal structures and compositions of partially crystallized alloys. The present paper will discuss the AEM characterization of crystallized Cu-Ti and Ni-Ti amorphous films.Cu60Ti40: The amorphous alloy Cu60Ti40, when continuously heated, forms a simple intermediate, macrocrystalline phase which then transforms to the ordered, equilibrium Cu3Ti2 phase. However, contrary to what one would expect from kinetic considerations, isothermal annealing below the isochronal crystallization temperature results in direct nucleation and growth of Cu3Ti2 from the amorphous matrix.

Observations oh Nucleation and Growth of Voids in Nickel

1970 ◽  
Vol 28 ◽  
pp. 414-415
Author(s):  
J. L. Brimhall ◽  
H. E. Kissinger ◽  
B. Mastel
Keyword(s):  
High Purity ◽  
Growth Stage ◽  
Elevated Temperatures ◽  
Early Growth ◽  
Nucleation And Growth ◽  
Pure Nickel ◽  
Different Temperatures ◽  
Total Fluence ◽  
Neutron Exposure ◽  
Growth Of Voids

Some information on the size and density of voids that develop in several high purity metals and alloys during irradiation with neutrons at elevated temperatures has been reported as a function of irradiation parameters. An area of particular interest is the nucleation and early growth stage of voids. It is the purpose of this paper to describe the microstructure in high purity nickel after irradiation to a very low but constant neutron exposure at three different temperatures.Annealed specimens of 99-997% pure nickel in the form of foils 75μ thick were irradiated in a capsule to a total fluence of 2.2 × 1019 n/cm2 (E > 1.0 MeV). The capsule consisted of three temperature zones maintained by heaters and monitored by thermocouples at 350, 400, and 450°C, respectively. The temperature was automatically dropped to 60°C while the reactor was down.

Electrochemical nucleation and growth of copper on iron and aluminum: A TEM study of industrial copper cementation

1978 ◽  
Vol 36 (1) ◽  
pp. 454-455
Author(s):  
L.E. Murr ◽  
V. Annamalai
Keyword(s):  
Metal Surface ◽  
Copper Deposit ◽  
Nucleation And Growth ◽  
16Th Century ◽  
Electrochemical Reactions ◽  
Mine Shaft ◽  
De Re ◽  
Copper Precipitation ◽  
Electrochemical Nucleation ◽  
Interesting System

Georgius Agricola in 1556 in his classical book, “De Re Metallica”, mentioned a strange water drawn from a mine shaft near Schmölnitz in Hungary that eroded iron and turned it into copper. This precipitation (or cementation) of copper on iron was employed as a commercial technique for producing copper at the Rio Tinto Mines in Spain in the 16th Century, and it continues today to account for as much as 15 percent of the copper produced by several U.S. copper companies.In addition to the Cu/Fe system, many other similar heterogeneous, electrochemical reactions can occur where ions from solution are reduced to metal on a more electropositive metal surface. In the case of copper precipitation from solution, aluminum is also an interesting system because of economic, environmental (ecological) and energy considerations. In studies of copper cementation on aluminum as an alternative to the historical Cu/Fe system, it was noticed that the two systems (Cu/Fe and Cu/Al) were kinetically very different, and that this difference was due in large part to differences in the structure of the residual, cement-copper deposit.

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