Search results for "crystallinity"
showing 10 items of 248 documents
Thermal and X-ray powder diffraction studies of aliphatic polyester dendrimers
2004
The syntheses and thermal and X-ray powder diffraction analyses of three sets of aliphatic polyester dendrimers based on 2,2-bis(hydroxymethyl)propionic acid as a repeating unit and 2,2-dimethyl-1,3-propanediol, 1,5-pentanediol, and 1,1,1-tris(hydroxymethyl)ethane as core molecules are reported. These dendritic polyesters were prepared in high yields with the divergent method. The thermal properties of these biodendrimers were evaluated with thermogravimetric analysis and differential scanning calorimetry. The thermal decomposition of the compounds occurred around 250 °C for the hydroxyl-ended dendrimers and around 150 °C for the acetonide-protected dendrimers. In addition, the crystallinit…
Nanocomposites of bacterial cellulose/hydroxyapatite for biomedical applications.
2008
In the present work, a nanocomposite material formed by bacterial cellulose (BC) networks and calcium-deficient hydroxyapatite (HAp) powders was synthesized and characterized. The HAp nanoparticles were previously prepared by a wet chemical precipitation method, starting from aqueous solutions of calcium nitrate and di-ammonium phosphate salts. Energy-dispersive spectroscopy reveals that the prepared HAp corresponds to calcium-deficient hydroxyapatite. BC-HAp nanocomposites were prepared by introducing carboxymethylcellulose (CMC) into the bacteria culture media. HAp nanoparticles were then introduced and remained suspended in the culture medium during the formation of cellulose nanofibrils…
An Approach on the Hydrogen Absorption in Carbon Black after Gamma Irradiation
2013
In this work, different samples of an industrial carbon black are used to study the hydrogen intake from an over pres-surized atmosphere and its changes due to alteration of its level of crystallinity produced by ¿-irradiation. The monitor-ing of the hydrogen adsorption was made by means of thermogravimetric analysis and by measurements of some elec-trical parameters as the Seebeck coefficient. X-ray diffraction shows that the irradiation diminishes the level of crystal-line perfection. These results show interesting possibilities to use carbon black as cheap hydrogen absorbers.
Synthesis of Nanofibrillated Cellulose by Combined Ammonium Persulphate Treatment with Ultrasound and Mechanical Processing
2018
Ammonium persulfate has been known as an agent for obtaining nanocellulose in recent years, however most research has focused on producing cellulose nanocrystals. A lack of research about combined ammonium persulfate oxidation and common mechanical treatment in order to obtain cellulose nanofibrils has been identified. The objective of this research was to obtain and investigate carboxylated cellulose nanofibrils produced by ammonium persulfate oxidation combined with ultrasonic and mechanical treatment. Light microscopy, atomic force microscopy (AFM), powder X-Ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and Zeta potential measure…
Synthesis and characterization of α-hopeite, Zn3(PO4)2·4H2O
1999
Orthorhombic α-Zn3(PO4)2·4H2O, α-hopeite, was synthesized from an aqueous solution of zinc acetate and orthophosphoric acid. The synthesis from these starting materials yielded best results with respect to purity and crystallinity. Structural characteristics of the compound were investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), and thermogravimetric/differential thermal analysis (TG/DTA). Supplemental data came from surface area, particle size distribution, and density measurements. The obtained compound proved to be highly crystalline and stoichiometric. Dehydration of α-hopeite is accompanied by at least two endothermic effect…
Structural Characterisation of Complex Layered Double Hydroxides and TGA-GC-MS Study on Thermal Response and Carbonate Contamination in Nitrate- and …
2015
Layered double hydroxides (LDHs) are versatile materials used for intercalating bioactive molecules in the fields of pharmaceuticals, nutraceuticals and cosmetics, with the purpose of protecting them from degradation, enhancing their water solubility to increase bioavailability and improving their pharmacokinetic properties and formulation stability. Moreover, LDHs are used in various technological applications to improve stability and processability. The crystal chemistry of hydrotalcite-like compounds was investigated by X-ray powder diffraction (XRPD), automated electron diffraction tomography (ADT) and thermogravimetric analysis (TGA)-GC-MS to shed light on the mechanisms involved in io…
Effect of uniaxial deformation on the optical scattering losses of a semicrystalline fluorocopolymer.
1997
Both small- and wide-angle light scattering as well as transmission measurements have been used to investigate the optical scattering losses of a vinylidene difluoride–tetrafluoroethylene–hexafluoropropylene copolymer crystallized from the melt. The main origin of the scattering loss is the wide-angle light scattering from the spherulitic superstructure. Uniaxial deformation transforms this structure into a fiber morphology. The attenuation of fibers has been measured for light propagating both parallel and perpendicular to the orientation axis. For both directions, the attenuation decreases with increasing draw ratio. Annealing of the fibers while keeping their ends fixed is an effective m…
Atomic layer deposition of WO3 thin films using W(CO)6 and O3 precursors
2012
Here we report a new atomic layer deposition (ALD) process for WO3 thin films based on W(CO)6 as a tungsten source and ozone as a source of oxygen. A narrow ALD temperature window is found at 195–205 °C for WO3 with a deposition rate of 0.23 A per cycle. As-deposited films are partially crystalline with root mean square (rms) roughness values of 4.7 nm for 90 nm thick films; annealing the films at 600–1000 °C under oxygen or nitrogen atmospheres enhances the degree of crystallinity considerably. Our results show that the straightforward ALD chemistry of carbonyl compounds and ozone is applicable to the deposition of WO3 thin films.
The role of micro-structural and mechanical properties in the framework of the model for damage inception and growth from air-filled voids in Polyeth…
2007
An innovative, physical, aging and life model for polymeric insulation systems, founded on damage inception and growth at the level of microscopic cavities, was developed previously by the authors. This paper is focused on the role played by micro-structural and mechanical properties (such as crystallinity and Young's modulus) in the framework of such model. These concepts are applied to the case of LDPE, HDPE and XLPE matrixes. The relevant estimates of damage growth rate and time-to-failure as a function of void size and applied electric field in typical working conditions for HVDC power cables are performed. The results show that, under the assumptions made, the crystallinity level itsel…
Bio-inspired consolidants derived from crystalline nanocellulose for decayed wood
2018
Abstract Novel bio-inspired materials derived from crystalline nanocellulose (CNC) have been tested as wood consolidants. A suspension of CNC, produced by acid hydrolysis of cellulose and used as such or mixed with lignin and/or siloxane derivatives (PDMS), was applied on rotted wood samples of Norway spruce. X-Ray diffraction analysis on CNC powder showed high crystallinity index. Dynamic light scattering (DLS) measurement indicated a nearly uniform particle size distribution with an average hydrodynamic diameter for pure CNC smaller than that in the mixtures. Raman and FTIR spectroscopies suggested interactions between lignin, PDMS and CNC components. The storage modulus of wood samples, …