scholarly journals The mechanism of porosity formation during solvent-mediated phase transformations

2010 ◽  
Vol 467 (2129) ◽  
pp. 1408-1426 ◽  
Author(s):  
Christophe Raufaste ◽  
Bjørn Jamtveit ◽  
Timm John ◽  
Paul Meakin ◽  
Dag Kristian Dysthe
Keyword(s):  
Solid Solution ◽  
Pore Structure ◽  
Phase Transformations ◽  
Solid Phase ◽  
Ex Situ ◽  
Bulk Solution ◽  
Product Phase ◽  
Long Time ◽  
Transformation Mechanisms

Solvent-mediated solid–solid phase transformations often result in the formation of a porous medium, which may be stable on long time scales or undergo ripening and consolidation. We have studied replacement processes in the KBr–KCl–H 2 O system using both in situ and ex situ experiments. The replacement of a KBr crystal by a K(Br,Cl) solid solution in the presence of an aqueous solution is facilitated by the generation of a surprisingly stable, highly anisotropic and connected pore structure that pervades the product phase. This pore structure ensures efficient solute transport from the bulk solution to the reacting KBr and K(Br,Cl) surfaces. The compositional profile of the K(Br,Cl) solid solution exhibits striking discontinuities across disc-like cavities in the product phase. Similar transformation mechanisms are probably important in controlling phase-transformation processes and rates in a variety of natural and man-made systems.

The use of transmission and analytical electron microscopy in studying reactions and phase transformations in thin film

1993 ◽  
Vol 51 ◽  
pp. 842-843
Author(s):  
K. Barmak
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Phase Transformations ◽  
Analytical Electron Microscopy ◽  
Ex Situ ◽  
Multilayer Thin Films ◽  
Absolute Concentration ◽  
Analytical Electron ◽  
Deposition Step

Generally, processing of thin films involves several annealing steps in addition to the deposition step. During the annealing steps, diffusion, transformations and reactions take place. In this paper, examples of the use of TEM and AEM for ex situ and in situ studies of reactions and phase transformations in thin films will be presented.The ex situ studies were carried out on Nb/Al multilayer thin films annealed to different stages of reaction. Figure 1 shows a multilayer with dNb = 383 and dAl = 117 nm annealed at 750°C for 4 hours. As can be seen in the micrograph, there are four phases, Nb/Nb3-xAl/Nb2-xAl/NbAl3, present in the film at this stage of the reaction. The composition of each of the four regions marked 1-4 was obtained by EDX analysis. The absolute concentration in each region could not be determined due to the lack of thickness and geometry parameters that were required to make the necessary absorption and fluorescence corrections.

scholarly journals Структурные фазовые превращения при твердофазной реакции в тонких двухслойных пленках Al/Pt

2018 ◽  
Vol 60 (7) ◽  
pp. 1397
Author(s):  
Р.Р. Алтунин ◽  
Е.Т. Моисеенко ◽  
С.М. Жарков
Keyword(s):  
Thin Films ◽  
Electron Diffraction ◽  
Phase Transformations ◽  
Solid Phase ◽  
Structural Phase ◽  
Solid Phase Reaction ◽  
Phase Reaction ◽  
Formation Heat ◽  
Structural Phase Transformations

AbstractA sequence of phases forming during the solid-phase reaction in Al/Pt bilayer thin films has been investigated by in situ electron diffraction. It is shown that the amorphous PtAl_2 phase forms first during the solid-phase reaction initiated by heating. Upon further heating, PtAl_2, Pt_2Al_3, PtAl, and Pt_3Al crystalline phases sequentially form, which is qualitatively consistent with an effective formation heat model. The content of phases forming during the reaction has been quantitatively analyzed and the structural phase transformations have been examined.

scholarly journals Severe Plastic Deformation and Phase Transformations in High Entropy Alloys: A Review

Crystals ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 54
Author(s):  
Boris B. Straumal ◽  
Roman Kulagin ◽  
Brigitte Baretzky ◽  
Natalia Yu. Anisimova ◽  
Mikhail V. Kiselevskiy ◽  
...  
Keyword(s):  
Solid Solution ◽  
Plastic Deformation ◽  
Severe Plastic Deformation ◽  
Phase Transformations ◽  
Single Phase ◽  
Materials Science ◽  
Bulk Solution ◽  
Second Phase ◽  
High Entropy Alloys ◽  
High Entropy

This review discusses an area of expertise that is at the intersection of three large parts of materials science. These are phase transformations, severe plastic deformation (SPD), and high-entropy alloys (HEA). First, SPD makes it possible to determine the borders of single-phase regions of existence of a multicomponent solid solution in HEAs. An important feature of SPD is that using these technologies, it is possible to obtain second-phase nanoparticles included in a matrix with a grain size of several tens of nanometers. Such materials have a very high specific density of internal boundaries. These boundaries serve as pathways for accelerated diffusion. As a result of the annealing of HEAs subjected to SPD, it is possible to accurately determine the border temperature of a single-phase solid solution area on the multicomponent phase diagram of the HEA. Secondly, SPD itself induces phase transformations in HEAs. Among these transformations is the decomposition of a single-phase solid solution with the formation of nanoparticles of the second phase, the formation of high-pressure phases, amorphization, as well as spinodal decomposition. Thirdly, during SPD, a large number of new grain boundaries (GBs) are formed due to the crystallites refinement. Segregation layers exist at these new GBs. The concentration of the components in GBs differs from that in the bulk solid solution. As a result of the formation of a large number of new GBs, atoms leave the bulk solution and form segregation layers. Thus, the composition of the solid solution in the volume also changes. All these processes make it possible to purposefully influence the composition, structure and useful properties of HEAs, especially for medical applications.

In-Situ Transmission Electron Microscopy of the Solid-Phase Epitaxial Growth of GaAs: Sample Preparation and Artifact Characterization

1997 ◽  
Vol 480 ◽  
Author(s):  
K. B. Belay ◽  
M. C. Ridgway ◽  
D. J. Llewellyn
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Sample Preparation ◽  
Epitaxial Growth ◽  
Solid Phase ◽  
Ion Beam ◽  
Ex Situ ◽  
In Situ Tem ◽  
Transmission Electron

AbstractIn-situ transmission electron microscopy (TEM) has been used to characterize the solidphase epitaxial growth of amorphized GaAs at a temperature of 260°C. To maximize heat transfer from the heated holder to the sample and minimize electron-irradiation induced artifacts, non-conventional methodologies were utilized for the preparation of cross-sectional samples. GaAs (3xI) mm rectangular slabs were cut then glued face-to-face to a size of (6x3) mm stack by maintaining the TEM region at the center. This stack was subsequently polished to a thickness of ~ 200 ýtm. A 3 mm disc was then cut from it using a Gatan ultrasonic cutter. The disc was polished and dimpled on both sides to a thickness of ~15 mimT.h is was ion-beam milled at liquid nitrogen temperature to an electron-transparent layer. From a comparison of in-situ and ex-situ measurements of the recrystallization rate, the actual sample temperature during in-situ characterization was estimated to deviate by ≤ 20°C from that of the heated holder. The influence of electron-irradiated was found to be negligible by comparing the recrystallization rate and microstructure of irradiated and unirradiated regions of comparable thickness. Similarly, the influence of “thin-foil effect” was found to be negligible by comparing the recrystallization rate and microstructure of thick and thin regions, the former determined after the removal of the sample from the microscope and further ion-beam milling of tens of microns of material. In conclusion, the potential influence of artifacts during in-situ TEM can be eliminated by the appropriate choice of sample preparation procedures.

scholarly journals Investigating Processes of Nanocrystal Formation and Transformation via Liquid Cell TEM

2014 ◽  
Vol 20 (2) ◽  
pp. 425-436 ◽  
Author(s):  
Michael H. Nielsen ◽  
Dongsheng Li ◽  
Hengzhong Zhang ◽  
Shaul Aloni ◽  
T. Yong-Jin Han ◽  
...  
Keyword(s):  
Direct Evidence ◽  
Nucleation And Growth ◽  
Ex Situ ◽  
Bulk Solution ◽  
Dynamic Information ◽  
Transmission Electron ◽  
Classical Models ◽  
Liquid Cell ◽  
Temporal And Spatial

AbstractRecent ex situ observations of crystallization in both natural and synthetic systems indicate that the classical models of nucleation and growth are inaccurate. However, in situ observations that can provide direct evidence for alternative models have been lacking due to the limited temporal and spatial resolution of experimental techniques that can observe dynamic processes in a bulk solution. Here we report results from liquid cell transmission electron microscopy studies of nucleation and growth of Au, CaCO3, and iron oxide nanoparticles. We show how these in situ data can be used to obtain direct evidence for the mechanisms underlying nanoparticle crystallization as well as dynamic information that provide constraints on important energetic parameters not available through ex situ methods.

Size-dependent Phase Transformations During Point Loading of Silicon

2000 ◽  
Vol 15 (8) ◽  
pp. 1754-1758 ◽  
Author(s):  
A. B. Mann ◽  
D. van Heerden ◽  
J. B. Pethica ◽  
T. P. Weihs
Keyword(s):  
Phase Transformations ◽  
Strong Dependence ◽  
The Body ◽  
Ex Situ ◽  
Stress Fields ◽  
Rhombohedral Structure ◽  
Size Dependent ◽  
Transmission Electron ◽  
Contact Size

Using a unique combination of in situ electrical and acoustical measurements and ex situ transmission electron microscopy, the phase transformations of silicon during point loading were shown to exhibit a strong dependence on the size of the deformed volume. For nanometer-size volumes of silicon, the final phase was the body centered cubic structure BC8, but for larger volumes it was amorphous. The size dependence was explained by considering how shear stress fields vary with contact size and how interfacial effects between the silicon substrate and the BC8 phase determine its stability. For both small and large contacts the presence of a nonmetallic phase (assumed to be the Rhombohedral structure R8) was observed.

scholarly journals Mechanistic In Situ and Ex Situ Studies of Phase Transformations in Molecular Co‐Crystals

2020 ◽  
Vol 26 (64) ◽  
pp. 14645-14653
Author(s):  
Alexander E. Clout ◽  
Asma B. M. Buanz ◽  
Yuying Pang ◽  
Wing‐Mei Tsui ◽  
Dongpeng Yan ◽  
...  
Keyword(s):  
Phase Transformations ◽  
Ex Situ

A Study of Substrate Orientation Dependence of the Solid-Phase Epitaxial Growth of Amorphised GaAs

1998 ◽  
Vol 523 ◽  
Author(s):  
K. B. Belay ◽  
D. J. Llewellyn ◽  
M. C. Ridgway
Keyword(s):  
Epitaxial Growth ◽  
Rutherford Backscattering Spectrometry ◽  
Solid Phase ◽  
Liquid Nitrogen Temperature ◽  
Amorphous Layer ◽  
Orientation Dependence ◽  
Ex Situ ◽  
Cross Sectional ◽  
Substrate Orientation

AbstractIn-situ transmission electron microscopy (TEM) has been utilized in conjunction with conventional ex-situ Rutherford backscattering spectrometry and channeling (RBS/C), in-situ time resolved reflectivity (TRR) and ex-situ TEM to study the influence of substrate orientation on the solid-phase epitaxial growth (SPEG) of amorphised GaAs. A thin amorphous layer was produced on semi-insulating (100), (110) and (111) GaAs substrates by ion implantation of 190 and 200 keV Ga and As ions, respectively, to a total dose of 1e14/cm2. During implantation, substrates were maintained at liquid nitrogen temperature. In-situ annealing at ∼260°C was performed in the electron microscope and the data obtained was quantitatively analysed. It has been demonstrated that the non-planarity of the crystalline-amorphous (c/a)-interface was greatest for the (111) substrate orientation and least for the (110) substrate orientation. The roughness was measured in terms of the length of the a/c-interface in given window as a function of depth on a frame captured from the recorded video of the in-situ TEM experiments. The roughness of the c/a-interface was determined by the size of the angle subtended by the microtwins with respect to the interface on ex-situ TEM cross-sectional micrographs. The angle was both calculated and measured and was the largest in the case of (111) plane. The twinned fraction as a function of orientation, was calculated in terms of the disorder measured from the RBS/C and it was greatest for the (111) orientation.

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