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1.
Recent X-ray diffraction studies on α-quartz (SiO2) by Kingmaet al [1], have shown the occurrence of a reversible, crystalline-to-crystalline, phase transition just prior to amorphization
at ≈ 21 GPa. This precursor transition has also been confirmed by our recent molecular dynamics simulation study [2]. In order
to investigate the possibility of a similar behaviour in other isostructural compounds, which also undergo pressure induced
amorphization, α-GeO2 and α-AlPO4 (berlinite form) were studied using energy dispersive X-ray diffraction. In either of these materials, no such phase transition
is detected prior to amorphization. The onset of amorphization and its reversal is found to be time dependent in GeO2. 相似文献
2.
A new approach to calculating the equilibrium characteristics of the adsorption of noble gases on the amorphous surfaces of
adsorbents was developed and applied to the Ar−TiO2(rutile) system. Intermolecular adsorbate-adsorbate interactions are taken into account for the nearest neighbors in the quasi-chemical
approximation. The lattice energy parameters of all interactions of the model are determined from the Lennard-Jones potential
(12-6). The formation of amorphous TiO2(rutile) surface includes completion of the surface layers and partial removal of the surface oxygen ions. The quality of
the amorphization procedure was confirmed by the experimentally measured heats and isotherms of adsorption of the system under
study.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1109–1118, June, 1997. 相似文献
3.
Mura P. Maestrelli F. Cirri M. Furlanetto S. Pinzauti S. 《Journal of Thermal Analysis and Calorimetry》2003,73(2):635-646
The interactions of trimethoprim, sulphadiazine and sulphamethoxazole with natural (a- b-, g- ) and amorphous (RAMEB) or crystalline
(DIMEB) methylated b-cyclodextrins were investigated both in aqueous solution (using phase-solubility analysis) and in the
solid state (using DSC supported by X-ray analysis). In particular, DSC studies enabled determination of the relative degree
of crystallinity of each drug in its physical and ground mixtures with the different cyclodextrins on the basis of the variation
of its heat of fusion in comparison with that of the pure drug. In all cases, the host cavity size was a prevalent factor
for the inclusion complexation in liquid state. On the contrary, it had a negligible effect on solid-state interactions in
terms of drug amorphization. DIMEB and RAMEB exhibited similar performances in aqueous solution, showing that the presence
of methyl-groups improved the complexing and solubilizing properties of b-cyclodextrin. However, DSC studies revealed that
RAMEB was clearly more active in performing solid-state interactions, i.e. drug amorphization, and as stabilizing agent for
the amorphous state brought forth.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
I. Waclawska 《Journal of Thermal Analysis and Calorimetry》1997,48(1):145-154
The effect of mechanical treatment on the thermal decomposition of calcium borate, colemanite — Ca2B6O8(OH)6·2H2O was studied by means of XRD, FTIR, SEM and thermal analysis methods. Grinding of colemanite causes the solid-state amorphization of this mineral, as a result of the destruction of its structure along the cleavage plane. The decrease in the particle size of the original material and the increase in its internal structural disorder affect the temperatures and the magnitudes of the thermal effects accompanying the processes of dehydration and dehydroxylation. The diminishing values of the enthalpies of these processes may be a quantitative measure of the degree of amorphization of colemanite.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthdayThe author is grateful to Professor L. Stoch for helpful discussions.Support for this work was provided by the Polish Committee for Scientific Research (KBN) — Grant No. 3 P407 034 06. 相似文献
5.
E. V. Gert 《Cellulose (London, England)》1996,3(1):217-228
For preparation of various modified forms of microcrystalline cellulose, an optional combination is proposed of hydrolytic activity with other properties of nitric acid such as, adduct forming ability (manifested as Knecht compound formation), oxidizing, bleaching and nitrating. The manifestation of a chosen acid function is reached by variation of the reaction conditions: concentration, temperature, time, etc. The sole-reagent continuous procedure involving several operations made in a predetermined sequence allows the use of a more simple technological scheme and saves energy, time and materials. The features of transformation of fibrous and microcrystalline forms of native cellulose into cellulose-II through the Knecht compound are discussed. Purely acidic transformation schemes of native cellulose into microcrystalline cellulose hydrate and amorphous low-nitrate powder cellulose according to the above scheme are considered. Morphological features as well as distinguishing properties — enhanced hydrophilicity, sorption activity and degree of whiteness — of the prepared materials are pointed out. The possibility of obtaining uniformly oxidized forms of powder cellulose according to this scheme and the outlook for the use of nitrogen(IV) oxide as a multifunctional reagent are discussed. 相似文献
6.
Yujia Xu Weijing Zhang Tonglai Zhang Wei Guo Yongjun Lü 《Journal of computational chemistry》2020,41(10):1026-1033
Metal azides have attracted increasing attention as precursors for synthesizing polymeric nitrogen. In this article, we report the amorphous polymerization of nitrogen by compressing cupric azide. The ab initio molecular dynamics simulations show that crystalline cupric azide transforms into a disordered network composed of singly bonded nitrogen at a hydrostatic pressure of 40 GPa and room temperature. The transformation manifests the formation of a π delocalization along the disordered Cu-N network, thus resulting in a semiconductor–metal transition. The estimated heat of formation of the amorphous polymeric nitrogen system is comparable to conventional high-energy-density materials. The amorphization provides an alternative route to the polymerization of nitrogen under moderate conditions. 相似文献
7.
Dr. Aleksandra Mitrović Stefan Wild Vicent Lloret Michael Fickert Dr. Mhamed Assebban Dr. Bence G. Márkus Prof. Ferenc Simon Dr. Frank Hauke Dr. Gonzalo Abellán Prof. Andreas Hirsch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(10):3361-3366
Two-dimensional (2D) black phosphorus (BP) represents one of the most appealing 2D materials due to its electronic, optical, and chemical properties. Many strategies have been pursued to face its environmental instability, covalent functionalization being one of the most promising. However, the extremely low functionalization degrees and the limitations in proving the nature of the covalent functionalization still represent challenges in many of these sheet architectures reported to date. Here we shine light on the structural evolution of 2D-BP upon the addition of electrophilic diazonium salts. We demonstrated the absence of covalent functionalization in both the neutral and the reductive routes, observing in the latter case an unexpected interface conversion of BP to red phosphorus (RP), as characterized by Raman, 31P-MAS NMR, and X-ray photoelectron spectroscopies (XPS). Furthermore, thermogravimetric analysis coupled to gas chromatography and mass spectrometry (TG-GC-MS), as well as electron paramagnetic resonance (EPR) gave insights into the potential underlying radical mechanism, suggesting a Sandmeyer-like reaction. 相似文献
8.
Chao Liu Jing Wang Jingjing Wan Yan Cheng Rong Huang Chaoqi Zhang Wenli Hu Guangfeng Wei Chengzhong Yu 《Angewandte Chemie (International ed. in English)》2020,59(9):3630-3637
Amorphous metal–organic frameworks (aMOFs) are an emerging family of attractive materials with great application potential, however aMOFs are usually prepared under harsh conditions and aMOFs with complex compositions and structures are rarely reported. In this work, an aMOF‐dominated nanocomposite (aMOF‐NC) with both structural and compositional complexity has been synthesized using a facile approach. A ligand‐competition amorphization mechanism is proposed based on experimental and density functional theory calculation results. The aMOF‐NC possesses a core–shell nanorod@nanosheet architecture, including a Fe‐rich Fe‐Co‐aMOF core and a Co‐rich Fe‐Co‐aMOF shell in the core–shell structured nanorod, and amorphous Co(OH)2 nanosheets as the outer layer. Benefiting from the structural and compositional heterogeneity, the aMOF‐NC demonstrates an excellent oxygen evolution reaction activity with a low overpotential of 249 mV at 10.0 mA cm?2 and Tafel slope of 39.5 mV dec?1. 相似文献
9.
将晶态Mg、Zn、Al元素粉末混合,用机械合金化方法制备了Mg-Zn、Al-Mg合金玻璃。用X射线衍射技术测定了不同球磨时间样品的X射线衍射图谱,分析考察了非晶化的过程及其影响因素,讨论了重新晶化的现象. 相似文献
10.
S. B. Fisher 《辐射效应与固体损伤》2013,168(3-4):173-177
The various factors influencing the nucleation of radiation damage in the HVEM are reviewed. A method for obtaining quantitative information from observations is given. The effect of reirradiation at room temperature on the damage formed at elevated temperatures is shown. This effect may give experimental information concerning the strain fields surrounding large dislocation loops. 相似文献