Understanding metastable phase transformation during crystallization of RDX, HMX and CL-20: experimental and DFT studies

2016 ◽  
Vol 18 (34) ◽  
pp. 23554-23571 ◽  
Author(s):  
Mrinal Ghosh ◽  
Shaibal Banerjee ◽  
Md Abdul Shafeeuulla Khan ◽  
Nirmala Sikder ◽  
Arun Kanti Sikder
Keyword(s):  
Phase Transformation ◽  
Relative Stability ◽  
Molecular Conformation ◽  
Metastable Phase ◽  
Metastable Phases ◽  
Dft Studies ◽  
The Stability

The relative stability of metastable phases of RDX, HMX and CL-20 in solution has been revealed by experimental and DFT studies. Molecular conformation during prenucleation clustering and lattice barrier essentially determines the stability of metastable phases during crystallization.

DFT STUDIES ON THE STABILITY OF THE TRANS AND CIS ISOMERS IN THE SQUARE PLANAR PALLADIUM(II) COMPLEXES Pd(I)(PPh3)(η3-XCHC(Ph)CHR) (X = CMe3, CO2Me, P(O)(OMe)2, AND SO2H; R = H, Me)

2008 ◽  
Vol 07 (04) ◽  
pp. 505-515
Author(s):  
LIQIN XUE ◽  
GUOCHEN JIA ◽  
ZHENYANG LIN
Keyword(s):  
Density Functional Theory ◽  
Electronic Properties ◽  
Relative Stability ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Dft Studies ◽  
Functional Theory ◽  
Square Planar ◽  
The Stability ◽  
Cis Isomer

The relative stability of the trans and cis isomers in the square planar palladium(II) complexes Pd ( I )( PPh 3)(η3- XCHC ( Ph ) CHR ) ( X = H , Me , CMe 3, CO 2 Me , P ( O )( OMe )2, and SO 2 H ; R = H , Me ) was investigated with the aid of the B3LYP density functional theory calculations. We examined how the substituents X, with different electronic properties, of the η3-allyl ligands affect the relative stability of the trans and cis isomers. Through the investigation, we were able to explain the trans/cis relative stability derived from the experimentally measured trans/cis isomer ratios in the palladium(II) complexes.

Microstructural Changes of Welded Zn-AI Alloy

1994 ◽  
Vol 367 ◽  
Author(s):  
Yao Hua Zhu
Keyword(s):  
Phase Transformation ◽  
Early Stage ◽  
Dendritic Structure ◽  
Metastable Phases ◽  
Grain Structure ◽  
Al Alloy ◽  
Cast State ◽  
Microstructural Changes ◽  
Fine Grain ◽  
Ageing Processes

AbstractExtruded eutectoid Zn-Al alloy was welded by a melt of the same eutectoid alloy. Two different microstructures were observed in the joint part and the bulk of the welded alloy. Typical dendritic structure of as cast Zn-Al alloy was observed in the joint part of the welded alloy. The bulk ofthe welded Zn-Al alloy appeared as fine grain structure. Two different metastable phases η'T decomposed from η's of chilled as cast state and η'E of extruded state were found to be unstable during early stage of ageing. A four phase transformation occurred after the decompositions of these two metastable phases of η'T. Microstructures of both joint part and bulk of the welded alloy were investigated parallely during ageing processes.

The search for formal electrostatic effects on molecular conformation and crystal packing: crystal structure of 2,2′′-disubstituted (HversusPPh2) 1,1′-(1,2-phenylene)bis(3-methyl-1H-imidazol-3-ium) bis(trifluoromethanesulfonate)

2016 ◽  
Vol 72 (3) ◽  
pp. 198-202
Author(s):  
Carine Duhayon ◽  
Yves Canac ◽  
Laurent Dubrulle ◽  
Carine Maaliki ◽  
Remi Chauvin
Keyword(s):  
Crystal Structure ◽  
Electrostatic Interactions ◽  
Molecular Conformation ◽  
Crystal Packing ◽  
Relative Orientation ◽  
Electron Delocalization ◽  
Electrostatic Effects ◽  
Conformational Freedom ◽  
The Stability ◽  
Bond Character

Electrostatic interactions between localized integral charges make the stability and structure of highly charged small and rigid organics intriguing. Can σ/π-electron delocalization compensate reduced conformational freedom by lowering the repulsion between identical charges? The crystal structure of the title salt, C14H16N42+·2CF3SO3−, (2), is described and compared with that of the 2,2′′-bis(diphenylphosphanyl) derivative, (4). The conformations of the dications and their interactions with neighbouring trifluoromethanesulfonate anions are first analyzed from the standpoint of formal electrostatic effects. Neither cation exhibits any geometrical strain induced by the intrinsic repulsion between the positive charges. In contrast, the relative orientation of the imidazolium rings [i.e. antifor (2) andsynfor (4)] is controlled by different configurations of the interactions with the closest trifluoromethanesulfonate anions. The long-range arrangement is also found to be specific: beyond the formal electrostatic packing, C—H...O and C—H...F contacts have no definite `hydrogen-bond' character but allow the delineation of layers, which are either pleated or flat in the packing of (2) or (4), respectively.

scholarly journals Phase Transformation of Cr(VI)-Adsorbed Ferrihydrite at Different pH in The Presence of Mn(II): Fate of Mn(II) and Cr(VI)

2021 ◽  
Author(s):  
Zecong Ding ◽  
Fenglian Fu ◽  
Guangzhao Sun ◽  
Chujia Ye
Keyword(s):  
Phase Transformation ◽  
Heavy Metal Ions ◽  
Solid Phase ◽  
Transformation Products ◽  
Transformation Process ◽  
Toxic Heavy Metal ◽  
Chromium Vi ◽  
Initial Ph ◽  
The Stability ◽  
Mn Concentration

Abstract Ferrihydrite is an important sink for the toxic heavy metal ions, such as chromium(VI). As ferrihydrite is thermodynamically unstable and gradually transforms into hematite and goethite, the stability of Cr(VI)-adsorbed ferrihydrite is environmentally significant. This study investigated the phase transformation of Cr(VI)-adsorbed ferrihydrite at different pH in the presence of aqueous Mn(II), as well as the fate of Mn(II) and Cr(VI) in the transformation process of ferrihydrite. Among the ferrihydrite transformation products, hematite was dominant, and goethite was minor. The pre-adsorbed Cr(VI) inhibited the conversion of ferrihydrite to goethite at initial pH 3.0, whereas little amount of adsorbed Mn(II) favored the formation of goethite at initial pH 7.0. After the aging process, Cr species in solid phase existed primarily as Cr(III) in the presence of Mn(II) at initial pH 7.0 and 11.0. The aqueous Mn concentration was predominantly unchanged at initial pH 3.0, whereas the aqueous Mn(II) was adsorbed onto ferrihydrite or form Mn(OH)2 precipitates at initial pH 7.0 and 11.0, promoting the immobilization of Cr(VI). Moreover, the oxidation of Mn(II) occurred at initial pH 7.0 and 11.0, forming Mn(III/IV) (hydr)oxides.

scholarly journals Metastable phases and macroheterogeneous composites

2021 ◽  
Vol 29 (1) ◽  
pp. 65-68
Author(s):  
O. V. Sukhova
Keyword(s):  
Phase Diagram ◽  
Composite Materials ◽  
Abrasive Wear ◽  
Metastable Phase ◽  
Interfacial Reactions ◽  
Metastable Phases ◽  
Metastable Phase Diagram ◽  
Rapid Dissolution ◽  
Strong Adhesion ◽  
Stable And Metastable Phases

The way to control the interfacial reactions that processes during infiltration of macroheterogeneous composite materials is suggested. The idea is to combine the stable and metastable phases in the filler’s structure which dissolves at a different rate in the molten binder. To prove this approach, the structure and gas-abrasive wear of macroheterogeneous composite materials with Cu–20Ni–20Mn binder reinforced by Fe–(9.0–10.0)B–(0.01-0.2)C filler (in wt. %) cooled at 10–20 K/s or 103–104 K/s are studied. It is shown that the wear resistance of the investigated composite materials can be enhanced by accelerating interfacial reactions between the filler and the molten binder. Therefore, the composite materials produced from a rapidly cooled Fe–B–C filler show a higher resistance to gas-abrasive wear due to formation of Fe–Fe2(B,C) metastable eutectics in its structure. This eutectics crystallizes under metastable phase diagram due to the suppression of stable Fe2(B,C) phase formation and saturation of the rest of liquid by iron in the filler cooled at 103–104 K/s. As a result of rapid dissolution of the eutectics in the molten binder during infiltration, the strong adhesion at the interfaces of the composite materials is achieved which prevents the filler from spalling out under the impacts of abrasive.

Mechanochemical Polymorphic Transformation of Photocatalyst Material TiO2 and its Dependence on the Milling Operation

2011 ◽  
Vol 675-677 ◽  
pp. 283-286
Author(s):  
Guo Min Mi ◽  
Fumio Saito
Keyword(s):  
Phase Transformation ◽  
Titanium Dioxide ◽  
Polymorphic Transformation ◽  
Metastable Phase ◽  
Planetary Mill ◽  
Wet Grinding ◽  
Dry Grinding ◽  
Milling Operation ◽  
Lower Temperature ◽  
Tumbling Mill

Some dry and wet grinding experiments have been respectively conducted on titanium dioxide which is a noble photocatalyst material in a mortar, a tumbling mill and a planetary mill. Anatase is apt to transform to rutile via a metastable phase brookite in every kind of mills in the case of dry grinding. And it hardly takes place for phase transformation from rutile to other forms. It is shown that the kind of mill has not decisive effect on the mechanochemical polymorphic transformation of titanium dioxide, which merely influences the rate of phase transformation. On the other hand, the addition of other liquid media, such as water and acetone, is helpless for phase transformation of anatase. Only anatase can transform to metastable phase brookite by wet grinding. When ground titanium dioxide is heated, the amorphous phase is easier to transform to rutile than metastable phase brookite at lower temperature.

Hydrothermal Synthesis and Phase Formation Mechanism of TiO2(B) Nanorods via Alkali Metal Titanate Phase Transformation

2018 ◽  
Vol 283 ◽  
pp. 23-36 ◽  
Author(s):  
Yothin Chimupala ◽  
Rik Drummond-Brydson
Keyword(s):  
Phase Transformation ◽  
Intermediate Product ◽  
Intermediate Phase ◽  
Metastable Phase ◽  
Exchange Process ◽  
Titanium Isopropoxide ◽  
Growth Direction ◽  
Proton Exchange ◽  
Transformation Mechanism ◽  
Synthesis Conditions

Titanium dioxide (B phase) with 1-D structures was successfully fabricated via a hydrothermal method with a subsequent ion-exchange process and calcination. P25, titanium isopropoxide (TTIP), rutile and also anatase were used as Ti precursors in the alkali hydrothermal system. TTIP promoted an elongation of nanorod morphology whereas the other precursors produced short nanorod structures. The different types of titanium precursors did not have any influence on the phase transformation during the fabrication process. Na2Ti6O13 was the primary intermediate product after washing the hydrothermal sample. H2Ti3O7 was the secondary intermediate phase obtained following proton-exchange of Na2Ti6O13 in HNO3 solution. Finally, the TiO2(B) phase was the product of calcination of the secondary intermediate product at 400°C for 5 hr. A phase transformation mechanism is presented based on an investigation of products at each of the steps. The effects of the synthesis conditions on tailoring of the crystal morphology are discussed. The growth direction of the TiO2(B) nanorods was investigated by HR-TEM and SADP. Finally, the metastable phase of TiO2(B) was shown to be transformed to anatase during thermal treatment at temperatures higher than 400°C.

Structure-induced metastable phase transformation in Cu6Sn5 intermetallics

2019 ◽  
Vol 249 ◽  
pp. 124-127 ◽  
Author(s):  
Z.H. Zhang ◽  
C.W. Wei ◽  
H.J. Cao ◽  
J.J. Han ◽  
Y. Zhang
Keyword(s):  
Phase Transformation ◽  
Metastable Phase

Interdiffusion Behavior in γ-Phase U-Mo Alloy versus Al-6061 Alloy Couples Fabricated by Friction Stir Welding

2007 ◽  
Vol 266 ◽  
pp. 131-148 ◽  
Author(s):  
Dennis D. Keiser
Keyword(s):  
Friction Stir Welding ◽  
Research Reactor ◽  
Metastable Phase ◽  
Al Alloy ◽  
Friction Stir ◽  
Point Analysis ◽  
Interdiffusion Process ◽  
Composition Profiles ◽  
Point To Point ◽  
The Stability

To better understand interactions between fuel and cladding in research reactor fuels, diffusion couples between γ-phase U-7 wt% Mo and U-10 wt% Mo alloy fuels and a Si-bearing, Al alloy were fabricated using a friction stir welding technique. The advantage of such a fabrication technique is that it can potentially reduce the amount of aluminum-oxide that might be present at the diffusion couple interface. The presence of oxides at the interface can affect the interdiffusion process. These couples were annealed and characterized using a scanning electron microscope equipped with energy-dispersive and wavelength-dispersive spectrometers. Images were taken of the developed diffusion structures; x-ray maps were generated to identify partitioning behavior of the various components; and, point-to-point analysis was employed to generate composition profiles and to determine phase compositions. To try and determine how the presence of Si in an Al alloy affects the interdiffusion behavior of fuel and cladding components in research reactor nuclear fuels, the results from this study were compared to those from earlier diffusion studies using U-Mo alloys and Al. The formed diffusion zones in some samples annealed for 30 minutes are comprised of Si-rich aluminide phases that appear to be (U,Mo)0.9(Al,Si)4 and (U,Mo)(Si,Al)2, based on composition. The diffusion rates observed and the types of phases that form can be correlated to the stability of the γ-U phase, which is a metastable phase. For a sample annealed for a much longer time, large diffusion structures formed and no Si-rich phases were observed.

scholarly journals Stability of an RNA•DNA–DNA triple helix depends on base triplet composition and length of the RNA third strand

2019 ◽  
Vol 47 (14) ◽  
pp. 7213-7222 ◽  
Author(s):  
Charlotte N Kunkler ◽  
Jacob P Hulewicz ◽  
Sarah C Hickman ◽  
Matthew C Wang ◽  
Phillip J McCown ◽  
...  
Keyword(s):  
Relative Stability ◽  
Triple Helix ◽  
Multiple Factors ◽  
Dna And Rna ◽  
Helix Formation ◽  
Canonical Base ◽  
Triple Helix Formation ◽  
Triple Helices ◽  
Dna Triple Helix ◽  
The Stability

AbstractRecent studies suggest noncoding RNAs interact with genomic DNA, forming an RNA•DNA–DNA triple helix that regulates gene expression. However, base triplet composition of pyrimidine motif RNA•DNA–DNA triple helices is not well understood beyond the canonical U•A–T and C•G–C base triplets. Using native gel-shift assays, the relative stability of 16 different base triplets at a single position, Z•X–Y (where Z = C, U, A, G and X–Y = A–T, G–C, T–A, C–G), in an RNA•DNA–DNA triple helix was determined. The canonical U•A–T and C•G–C base triplets were the most stable, while three non-canonical base triplets completely disrupted triple-helix formation. We further show that our RNA•DNA–DNA triple helix can tolerate up to two consecutive non-canonical A•G–C base triplets. Additionally, the RNA third strand must be at least 19 nucleotides to form an RNA•DNA–DNA triple helix but increasing the length to 27 nucleotides does not increase stability. The relative stability of 16 different base triplets in DNA•DNA–DNA and RNA•RNA–RNA triple helices was distinctly different from those in RNA•DNA–DNA triple helices, showing that base triplet stability depends on strand composition being DNA and/or RNA. Multiple factors influence the stability of triple helices, emphasizing the importance of experimentally validating formation of computationally predicted triple helices.

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