Search results for "Crystallinity"

1979

2D NMR spectra have been measured at variable temperatures between −100°C and +110°C in a sample of melt crystallized deuterated polyethylene (PE). The line shape could be decomposed into a central part originating from deuterons in the amorphous regions and outer parts from crystalline regions of PE. The “NMR crystallinity” determined from this separation was 72% in agreement with the X-ray crystallinity of 74%. Changes of the crystalline NMR line shape were interperted in terms of oscillations around the chain axis, the r.m.s. oscillation amplitude varying from 5° at 40°C to 12° at 110°C. The central part of the NMR line shape indicates the existence of a “narrow” and a “medium” component…

1974

The temperature dependences of the absolute small angle X-ray scattering powers and of the unit cell spacings of a series of 1,3,5-trioxane—1,3-dioxolane copolymers were measured. From a comparison of these data and of the specific volume values measured by Wilski it is concluded that values of crystallinity calculated in a conventional manner provide meaningful parameters when discussing the microstructure of these materials. The measurements were made on annealed samples. At temperatures below the original annealing temperatures changes in small angle scattering power, long periods and crystallinities of the samples were observed. These changes were reversible with temperature and were to…

Raman spectroscopy characterization of 10-cash productions from the late Chinese emperors to the Republic

2017

[EN] The use of Raman spectroscopy for discriminating monetary emissions, a recurrent problem in much archaeological studies, is described. The method involves the record of Raman signatures of tenorite and crystalline and defective cuprite in the patina based on the idea that subtle, mint-characteristic variations in the composition and metallography of the base metal during the manufacturing process are reflected in the variation in depth of the composition and crystallinity of the corrosion patina. The technique was applied to a series of 10-cash copper coins produced around the transition between the Kuang Hsu and Hsuan Tung last Chinese emperors and the first Republic whose averaged co…

Effect of sisal and hydrothermal ageing on the dielectric behaviour of polylactide/sisal biocomposites

2017

[EN] The dielectric properties of virgin polylactide (PLA) and its reinforced composites with different weight amounts of sisal fibres were assessed at broad temperature (from - 130 degrees C to 130 degrees C) and frequency ranges (from 10(-2)-10(7) Hz), before and after being subjected to accelerated hydrothermal ageing. The synergetic effects of both the loading of sisal and hydrothermal ageing were analysed by means of dielectric relaxation spectra. The relaxation time functions were evaluated by the Havriliak-Negami model, substracting the ohmic contribution of conductivity. The intramolecular and intermolecular relaxations were respectively analysed by means of Arrhenius and Vogel-Fulc…

Crystal Growth of HgSe by the Cold Travelling Heater Method

2002

We report on the low-temperature synthesis and growth of HgSe crystals making use of the cold travelling heater method. Ingots so obtained are analyzed by means of scanning microscopy, including EDAX and backscattered electron modes, and X-ray diffraction techniques.

Growth temperature influence on the GaN nanowires grown by MOVPE technique

2011

GaN nanowires (NWs) were successfully grown by Vapor-Liquid-Solid (VLS) growth mechanism on GaN template using metal-organic vapor phase epitaxy (MOVPE) with diameters ranging from 20 to 200 nm and length up to few microns. The characterization by scanning electron microscopy (SEM) reveals an optimum growth temperature at 790°C and X-ray diffraction (XRD) investigations indicates oriented crystallinity of grown NWs.

Microstructural analysis (Voigt function method) of mullite in whiteware triaxial porcelains

2020

Triaxial porcelains were produced of two whiteware blends containing kaolin B (of “high-crystallinity” kaolinite) or halloysitic kaolin M (also with “low-crystallinity” kaolinite) in two different industrial firing cycles (fast or slow) with final temperatures 1270 °C, 1300 °C, 1320 °C and 1340 °C. The crystalline microstructure of mullite in all porcelain samples was studied by X-ray diffraction through analysing 110 and 001 reflections using the Voigt function method and by optical and electron microscopy. Mean crystallite sizes were determined independently for both 110 and 001 diffraction directions as principal semi-quantitative characteristics for all sixteen specimens. They illustrat…

Crystallization kinetics of iPP: Influence of operating conditions and molecular parameters

2007

An analysis of the crystallization kinetics of different grades of isotactic polypropylene (iPP) is here presented. To describe the crystallization kinetics as a function of molecular and operating parameters, the methodological path followed was the preparation of quenched samples of known cooling histories, calorimetric crystallization isotherms tests, differential scanning calorimetry cooling ramps, wide angle X-ray diffraction (WAXD) measurements, and density determination. The WAXD analysis performed on the quenched iPP samples confirmed that during the fast cooling at least a crystalline structure and a mesomorphic one form. The diffractograms were analyzed by a deconvolution procedur…

Electron diffraction, X-ray powder diffraction and pair-distribution-function analyses to determine the crystal structures of Pigment Yellow 213, C23…

2009

The crystal structure of the nanocrystalline alpha phase of Pigment Yellow 213 (P.Y. 213) was solved by a combination of single-crystal electron diffraction and X-ray powder diffraction, despite the poor crystallinity of the material. The molecules form an efficient dense packing, which explains the observed insolubility and weather fastness of the pigment. The pair-distribution function (PDF) of the alpha phase is consistent with the determined crystal structure. The beta phase of P.Y. 213 shows even lower crystal quality, so extracting any structural information directly from the diffraction data is not possible. PDF analysis indicates the beta phase to have a columnar structure with a si…

Inorganic gels as precursors of TiO2 photocatalysts prepared by low temperature microwave or thermal treatment

2008

Abstract A simple procedure for preparing active TiO2 photocatalysts is presented. The starting materials were unusual TiO2 gels formed from TiCl4. The use of microwaves for a very short time enhanced the TiO2 crystallinity preventing an increase of particle size and minimizing the decrease of specific surface area. This result makes this preparation very attractive. The formation of the gels was monitored through measurements of viscosity. All the samples were characterized by means of X-ray diffraction, diffuse reflectance spectroscopy and BET specific surface area measurements. The photoactivity of the samples was evaluated using the photodegradation of 4-nitrophenol in liquid–solid regi…