scholarly journals The α–β phase transition in volcanic cristobalite

2014 ◽  
Vol 47 (4) ◽  
pp. 1205-1215 ◽  
Author(s):  
David E. Damby ◽  
Edward W. Llewellin ◽  
Claire J. Horwell ◽  
Ben J. Williamson ◽  
Jens Najorka ◽  
...  
Keyword(s):  
Phase Transition ◽  
Ambient Temperature ◽  
Volcanic Ash ◽  
Phase Identification ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Β Phase ◽  
The Stability ◽  
First Time

Cristobalite is a common mineral in volcanic ash produced from dome-forming eruptions. Assessment of the respiratory hazard posed by volcanic ash requires understanding the nature of the cristobalite it contains. Volcanic cristobalite contains coupled substitutions of Al3+ and Na+ for Si4+; similar co-substitutions in synthetic cristobalite are known to modify the crystal structure, affecting the stability of the α and β forms and the observed transition between them. Here, for the first time, the dynamics and energy changes associated with the α–β phase transition in volcanic cristobalite are investigated using X-ray powder diffraction with simultaneous in situ heating and differential scanning calorimetry. At ambient temperature, volcanic cristobalite exists in the α form and has a larger cell volume than synthetic α-cristobalite; as a result, its diffraction pattern sits between ICDD α- and β-cristobalite library patterns, which could cause ambiguity in phase identification. On heating from ambient temperature, volcanic cristobalite exhibits a lower degree of thermal expansion than synthetic cristobalite, and it also has a lower α–β transition temperature (∼473 K) compared with synthetic cristobalite (upwards of 543 K); these observations are discussed in relation to the presence of Al3+ and Na+ defects. The transition shows a stable and reproducible hysteresis loop with α and β phases coexisting through the transition, suggesting that discrete crystals in the sample have different transition temperatures.

scholarly journals Phase Transition and Melt-Recrystallization Behavior of Poly(Butylene Adipate) Investigated by Simultaneous Measurements of Wide-Angle X-Ray Diffraction (WAXD) and Differential Scanning Calorimetry (DSC)

Polymers ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 75
Author(s):  
Mengfan Wang ◽  
Weiyu Cao
Keyword(s):  
Phase Transition ◽  
Differential Scanning Calorimetry ◽  
Heating Process ◽  
Wide Angle ◽  
Melt Crystallization ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Β Phase ◽  
Simultaneous Measurements

Simultaneous measurements of wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) were carried out to investigate the phase transition and melting behaviors of poly(butylene adipate) (PBA). Thermal expansion changes along the a and b axes of the β form unit cell are different from each other during the heating process. At the beginning of the β to αH (high-temperature α phase) phase transition, the β phase melts very fast, while the recrystallization of the αH phase is delayed and slowed. With the further increment of the temperature, the melting rate of the β phase slows down, while the recrystallization of the αH phase accelerates. The diffraction peak intensity ratios of the β(020):β(110) and αH(020):αH(110) diffraction peaks during the first heating process have similar value. However, the above value is different from the value of α(020):α(110) during the following melt-crystallization process. This difference comes from the different orientations of the crystal lattices of the α and αH(β) crystals to the substrate plane, which indicates that the αH phase inherits the orientation of the β phase during phase transition and the orientation of αH form crystals is different from the α form crystals that crystallized from the melt.

Synthesis of VO2(A) Nanostructures by a Hydrothermal Method and their Transition to VO2(M)

2011 ◽  
Vol 295-297 ◽  
pp. 368-372 ◽  
Author(s):  
Ya Lan Zhong ◽  
Yi Fu Zhang ◽  
Xin Liu ◽  
Xing Hai Liu ◽  
Chi Huang ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Phase Transition ◽  
Transmission Electron Microscopy ◽  
Differential Scanning Calorimetry ◽  
Hydrothermal Method ◽  
Scanning Calorimetry ◽  
Facile Hydrothermal Method ◽  
X Ray ◽  
Transmission Electron ◽  
First Time

VO2(A) nanobelts have been synthesized using V2O5, H2O2, ethanol, H2O as the starting materials through a facile hydrothermal method. The as-obtained products were characterized by X-ray powder diffraction (XRD), X-ray photoelecton spectroscopy (XPS), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). Some parameters, such as, the reaction time, reaction temperature and the ratio of EtOH/H2O, have greatly influenced on the phases and morphologies of the final products. It was found that VO2(A) can be converted to VO2(M) at 700 °C for 2 h for the first time. Furthermore, the phase transition properties of VO2(A) and VO2(M) phases were respectively studied.

scholarly journals Peritectic Phase Transition of Benzene and Acetonitrile and Formation of a Cocrystal Relevant to Titan, Saturn’s Icy Moon

2020 ◽  
Author(s):  
Christina McConville ◽  
Yunwen Tao ◽  
hayden evans ◽  
Benjamin A. Trump ◽  
Jonathan B Lefton ◽  
...  
Keyword(s):  
Organic Molecules ◽  
Binary Phase Diagram ◽  
Polar Space ◽  
Scanning Calorimetry ◽  
Chemical Laboratory ◽  
X Ray ◽  
Composition And Structure ◽  
Reliable Model ◽  
The Stability

Benzene and acetonitrile are two of the most commonly used solvents found in almost every chemical laboratory. Titan, Saturn’s icy moon, is one other place in the Solar system that has even larger amounts of these compounds, together with many other hydrocarbons. On Titan, organic molecules are produced in the atmosphere and carried by methane rainfall to the surface, where they either dissolve in the lakes, deposit as sandy dunes, or solidify as minerals with complex composition and structure. In order to untangle these structural complexities a reliable model of the phase behavior of these compounds at temperatures relevant to Titan is crucial. We therefore report the composition–temperature binary phase diagram of acetonitrile and benzene, and provide a detailed account of the structure and composition of the phases. This work is based on differential scanning calorimetry and in situ powder diffraction analyses with synchrotron X-ray radiation and supported by theoretical modeling. Benzene and acetonitrile were found to undergo a peritectic reaction into a cocrystal with a 1:3 acetonitrile:benzene stoichiometry. The crystal structure was solved and refined in the polar space group, R3, and the solution was confirmed and optimized by energy minimization calculations. To mimic the environment on Titan more accurately, we tested the stability of the structure under liquid ethane. The diffraction data indicate that the cocrystal undergoes further change upon contact with ethane. These results provide new insights into the structure and stability of a potential mineral on Titan, and contribute to the fundamental knowledge of some of the smallest organic molecules

scholarly journals Peritectic Phase Transition of Benzene and Acetonitrile and Formation of a Cocrystal Relevant to Titan, Saturn’s Icy Moon

2020 ◽  
Author(s):  
Christina McConville ◽  
Yunwen Tao ◽  
hayden evans ◽  
Benjamin A. Trump ◽  
Jonathan B Lefton ◽  
...  
Keyword(s):  
Organic Molecules ◽  
Binary Phase Diagram ◽  
Polar Space ◽  
Scanning Calorimetry ◽  
Chemical Laboratory ◽  
X Ray ◽  
Composition And Structure ◽  
Reliable Model ◽  
The Stability

Benzene and acetonitrile are two of the most commonly used solvents found in almost every chemical laboratory. Titan, Saturn’s icy moon, is one other place in the Solar system that has even larger amounts of these compounds, together with many other hydrocarbons. On Titan, organic molecules are produced in the atmosphere and carried by methane rainfall to the surface, where they either dissolve in the lakes, deposit as sandy dunes, or solidify as minerals with complex composition and structure. In order to untangle these structural complexities a reliable model of the phase behavior of these compounds at temperatures relevant to Titan is crucial. We therefore report the composition–temperature binary phase diagram of acetonitrile and benzene, and provide a detailed account of the structure and composition of the phases. This work is based on differential scanning calorimetry and in situ powder diffraction analyses with synchrotron X-ray radiation and supported by theoretical modeling. Benzene and acetonitrile were found to undergo a peritectic reaction into a cocrystal with a 1:3 acetonitrile:benzene stoichiometry. The crystal structure was solved and refined in the polar space group, R3, and the solution was confirmed and optimized by energy minimization calculations. To mimic the environment on Titan more accurately, we tested the stability of the structure under liquid ethane. The diffraction data indicate that the cocrystal undergoes further change upon contact with ethane. These results provide new insights into the structure and stability of a potential mineral on Titan, and contribute to the fundamental knowledge of some of the smallest organic molecules

scholarly journals Design, Preparation and Thermal Characterization of Polystyrene Composites Reinforced with Novel Three-Cages POSS Molecules

Molecules ◽  
2020 ◽  
Vol 25 (13) ◽  
pp. 2967
Author(s):  
Ignazio Blanco ◽  
Francesco Agatino Bottino ◽  
Gianluca Cicala ◽  
Giulia Ognibene ◽  
Claudio Tosto
Keyword(s):  
1H Nmr Spectroscopy ◽  
In Situ Polymerization ◽  
Thermal Characterization ◽  
Scanning Calorimetry ◽  
Single Cage ◽  
The Stability ◽  
First Time ◽  
Thermal Stability Of

Novel polystyrene (PS)/polyhedral oligomeric silsequioxanes (POSSs) nanocomposites were designed and prepared by in situ polymerization, using, for the first time, three-cage POSS molecules. The synthesized compounds were first characterized by Fourier transform infrared spectroscopy (FTIR) and 1H NMR spectroscopy to verify the obtaining of the designed products before their thermal performance was evaluated and compared with those of pristine PS and the corresponding single-cage POSSs nanocomposites. The thermal behaviour was checked by the means of the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) was also used to confirm the hypothesis about the dispersion/aggregation of the POSS molecules into the polymer matrix. The parameters chosen to evaluate the thermal stability of the investigated compounds, namely temperature at 5% of mass loss (T5%) and solid residue at 700 °C, showed a significant increase in the stability of the polymers reinforced with the three-cages POSS, in comparison to both PS and single-cage POSS reinforced PSs, which therefore turn out to be promising molecular fillers for nanocomposite production.

scholarly journals A Superhydrophobic, Antibacterial, and Durable Surface of Poplar Wood

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1885
Author(s):  
Xinyu Wu ◽  
Feng Yang ◽  
Jian Gan ◽  
Zhangqian Kong ◽  
Yan Wu
Keyword(s):  
Stearic Acid ◽  
Antibacterial Properties ◽  
Alkali Resistance ◽  
Poplar Wood ◽  
X Ray Diffraction ◽  
X Ray ◽  
Different Temperatures ◽  
Acid And Alkali Resistance ◽  
The Stability

The silver particles were grown in situ on the surface of wood by the silver mirror method and modified with stearic acid to acquire a surface with superhydrophobic and antibacterial properties. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray energy spectroscopy (XPS) were used to analyze the reaction mechanism of the modification process. Scanning electron microscopy (SEM) and contact angle tests were used to characterize the wettability and surface morphology. A coating with a micro rough structure was successfully constructed by the modification of stearic acid, which imparted superhydrophobicity and antibacterial activity to poplar wood. The stability tests were performed to discuss the stability of its hydrophobic performance. The results showed that it has good mechanical properties, acid and alkali resistance, and UV stability. The durability tests demonstrated that the coating has the function of water resistance and fouling resistance and can maintain the stability of its hydrophobic properties under different temperatures of heat treatment.

scholarly journals Phase Transition and Coefficients of Thermal Expansion in Al2−xInxW3O12 (0.2 ≤ x ≤ 1)

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4021
Author(s):  
Andrés Esteban Cerón Cerón Cortés ◽  
Anja Dosen ◽  
Victoria L. Blair ◽  
Michel B. Johnson ◽  
Mary Anne White ◽  
...  
Keyword(s):  
Phase Transition ◽  
Thermal Expansion ◽  
Thermal Shock ◽  
Monoclinic Phase ◽  
Ceramic Materials ◽  
Precipitation Method ◽  
Scanning Calorimetry ◽  
Orthorhombic Crystal ◽  
Co Precipitation

Materials from theA2M3O12 family are known for their extensive chemical versatility while preserving the polyhedral-corner-shared orthorhombic crystal system, as well as for their consequent unusual thermal expansion, varying from negative and near-zero to slightly positive. The rarest are near-zero thermal expansion materials, which are of paramount importance in thermal shock resistance applications. Ceramic materials with chemistry Al2−xInxW3O12 (x = 0.2–1.0) were synthesized using a modified reverse-strike co-precipitation method and prepared into solid specimens using traditional ceramic sintering. The resulting materials were characterized by X-ray powder diffraction (ambient and in situ high temperatures), differential scanning calorimetry and dilatometry to delineate thermal expansion, phase transitions and crystal structures. It was found that the x = 0.2 composition had the lowest thermal expansion, 1.88 × 10−6 K−1, which was still higher than the end member Al2W3O12 for the chemical series. Furthermore, the AlInW3O12 was monoclinic phase at room temperature and transformed to the orthorhombic form at ca. 200 °C, in contrast with previous reports. Interestingly, the x = 0.2, x = 0.4 and x = 0.7 materials did not exhibit the expected orthorhombic-to-monoclinic phase transition as observed for the other compositions, and hence did not follow the expected Vegard-like relationship associated with the electronegativity rule. Overall, compositions within the Al2−xInxW3O12 family should not be considered candidates for high thermal shock applications that would require near-zero thermal expansion properties.

scholarly journals Pressure-induced Jahn-Teller Switch in the Homoleptic Hybrid Perovskite [(CH3)2NH2]Cu(HCOO)3: Orbital Reordering by Unconventional Degrees of Freedom

2021 ◽  
Author(s):  
Rebecca Scatena ◽  
Michał Andrzejewski ◽  
Roger D Johnson ◽  
Piero Macchi
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Coordination Polymer ◽  
Degrees Of Freedom ◽  
X Ray Diffraction ◽  
X Ray ◽  
Hybrid Perovskite ◽  
Jahn Teller

Through in-situ, high-pressure x-ray diffraction experiments we have shown that the homoleptic perovskite-like coordination polymer [(CH3)2NH2]Cu(HCOO)3 undergoes a pressure-induced orbital reordering phase transition above 5.20 GPa. This transition is distinct...

scholarly journals Direct TEM observation of the “acanthite α-Ag2S–argentite β-Ag2S” phase transition in a silver sulfide nanoparticle

2019 ◽  
Vol 1 (4) ◽  
pp. 1581-1588 ◽  
Author(s):  
S. I. Sadovnikov ◽  
E. Yu. Gerasimov
Keyword(s):  
Electron Microscopy ◽  
Phase Transition ◽  
Transmission Electron Microscopy ◽  
Silver Sulfide ◽  
Transmission Electron ◽  
Silver Sulfide Nanoparticles ◽  
Microscopy Method ◽  
Electron Microscopy Method ◽  
First Time

For the first time, the α-Ag2S (acanthite)–β-Ag2S (argentite) phase transition in a single silver sulfide nanoparticles has been observed in situ using a high-resolution transmission electron microscopy method in real time.

scholarly journals High temperature structural study of decagonal Al-Cu-Rh quasicrystal.

2014 ◽  
Vol 70 (a1) ◽  
pp. C94-C94
Author(s):  
Pawel Kuczera ◽  
Walter Steurer
Keyword(s):  
Structural Changes ◽  
Configurational Entropy ◽  
Lattice Vibrations ◽  
X Ray Diffraction ◽  
Stabilization Mechanism ◽  
X Ray ◽  
Comparative Structure ◽  
The Stability

The structure of d(ecagonal)-Al-Cu-Rh has been studied as a function of temperature by in-situ single-crystal X-ray diffraction in order to contribute to the discussion on energy or entropy stabilization of quasicrystals (QC) [1]. The experiments were performed at 293 K, 1223 K, 1153 K, 1083 K, and 1013 K. A common subset of 1460 unique reflections was used for the comparative structure refinements at each temperature. The results obtained for the HT structure refinements of d-Al-Cu-Rh QC seem to contradict a pure phasonic-entropy-based stabilization mechanism [2] for this QC. The trends observed for the ln func(I(T1 )/I(T2 )) vs.|k⊥ |^2 plots indicate that the best on-average quasiperiodic order exists between 1083 K and 1153 K, however, what that actually means is unclear. It could indicate towards a small phasonic contribution to entropy, but such contribution is not seen in the structure refinements. A rough estimation of the hypothetic phason instability temperature shows that it would be kinetically inaccessible and thus the phase transition to a 12 Å low T structure (at ~800 K) is most likely not phason-driven. Except for the obvious increase in the amplitude of the thermal motion, no other significant structural changes, in particular no sources of additional phason-related configurational entropy, were found. All structures are refined to very similar R-values, which proves that the quality of the refinement at each temperature is the same. This suggests, that concerning the stability factors, some QCs could be similar to other HT complex intermetallic phases. The experimental results clearly show that at least the ~4 Å structure of d-Al-Cu-Rh is a HT phase therefore entropy plays an important role in its stabilisation mechanism lowering the free energy. However, the main source of this entropy is probably not related to phason flips, but rather to lattice vibrations, occupational disorder unrelated to phason flips like split positions along the periodic axis.

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