A study of melting of low density polyethylene by in situ WAXD

Analysis of low density polyethylene using in situ wide-angle X-ray diffraction shows that the melting process takes place over a broad temperature range with continuous destruction of lamellar laterals. This process exhibits decreasing rate as the temperature increases, indicating that in general each lamellae has less order in outer regions than in central ones. The shifts in angular position of the amorphous halo as a function of the temperature show that the amorphous phase in a semicrystalline sample is less disordered compared to that in an overall melted sample. As the temperature increases the unit cell parameter a increases, generating a crystalline phase density reduction.     

A study on the kinetics of thermal decomposition of CaCO3

By means of TG, the thermal decomposition of the powdered CaCO₃ was tested with its various dispersities, range of size, and the different content of CO₂ in flowing nitrogen. Formulae for calculating the rate and time of decomposition were obtained.     

X-ray spectral study of a material containing BN nanostructures

The multicomponent substance obtained by laser evaporation of the BN target under nitrogen was studied by X-ray fluorescence and X-ray absorption spectroscopy. The BK _α spectra of the substance and boroncontaining compounds rh-BN, B₂O₃, and α-B were measured on a laboratory instrument using an ethyleneglycol distearate crystal as an analytical element; X-ray absorption spectra near the boron and nitrogen K edge were recorded on a BESSY synchrotron radiation station. The contents of the components in the synthesized substance were evaluated by decomposing the BK _α spectrum into the spectra of the test boron-containing compounds. A comparison of the X-ray absorption spectra near the NK edge of the substance and rh-BN revealed that BN nanostructures obtained by laser evaporation were defective.     

Numerical study of melting and solidification in a wavy double-pipe latent heat thermal energy storage system

Journal of Thermal Analysis and Calorimetry - The objective of this paper is to develop the influences of channel waviness on the performance of a latent heat storage system during phase change...     

Nucleation and growth of CaCO3 mediated by the egg-white protein ovalbumin: a time-resolved in situ study using small-angle neutron scattering

Mineralization of calcium carbonate in aqueous solutions starting from its initiation was studied by time-resolved small-angle neutron scattering (SANS). SANS revealed that homogeneous crystallization of CaCO 3 involves an initial formation of thin plate-shaped nuclei which subsequently reassemble to 3-dimensional particles, first of fractal and finally of compact structure. The presence of the egg-white protein ovalbumin leads to a different progression of mineralization through several stages; the first step represents amorphous CaCO 3, whereas the other phases are crystalline. The formation and dissolution of the amorphous phase is accompanied by Ca (2+)-mediated unfolding and cross-linking of about 50 protein monomers showing the characteristic scattering of linear chains with a large statistical segment length. The protein complexes act as nucleation centers for the amorphous phase because of their enrichment by Ca (2+) ions. SANS revealed the sequential formation of CaCO 3 starting from the amorphous phase and the subsequent formation of the crystalline polymorphs vaterite and aragonite. This formation from less dense to more dense polymorphs follows the Ostwald-Volmer rule.     

Comparative bioelectrochemical study of core-shell nanocluster films with ordinary layer-by-layer films containing heme proteins and CaCO3 nanoparticles

Negatively charged heme protein hemoglobin (Hb) or myoglobin (Mb) at pH 9.0 and positively charged poly(diallyldimethylammonium) (PDDA) were alternately adsorbed on the surface of CaCO(3) nanoparticles, forming core-shell CaCO(3)-[PDDA/(protein/PDDA)(m)] ([protein-m]) nanoclusters. Oppositely charged [protein-m] and poly(styrenesulfonate) (PSS) were then assembled layer by layer on various solid substrates, forming {[protein-m]/PSS}(n) films. In the meantime, ordinary layer-by-layer films of heme proteins with CaCO(3) nanoparticles ({protein/CaCO(3)}(n)) were also grown on solid surfaces. Transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) spectroscopy, quartz crystal microbalance (QCM), and cyclic voltammetry (CV) were used to characterize the nanoclusters and monitor the growth of the two types of films. Both kinds of protein films assembled on pyrolytic graphite (PG) electrodes exhibited well-defined, nearly reversible CV reduction-oxidation peaks, characteristic of heme Fe(III)/Fe(II) redox couples, and were used to catalyze the electrochemical reduction of hydrogen peroxide. The {[protein-m]/PSS}(n) films demonstrate distinct advantages over the {protein/CaCO(3)}(n) films due to their larger fraction of electroactive proteins, higher catalytic efficiency, and better thermostability. The penetration experiments of the electroactive probe into these films indicate that the {[protein-m]/PSS}(n) nanocluster films possess more pores or channels than the simple {protein/CaCO(3)}(n) films, which may be beneficial to counterion transport in the charge-hopping mechanism and helpful for the diffusion of catalysis substrates into the films. In addition, the electrochemical and biocatalytic activity of protein nanocluster films can be tailored by controlling the number of bilayers assembled on the nanoparticle cores (m) as well as the film thickness or the number of nanocluster layers on the electrodes (n).     

A quasi-time-resolved CryoTEM study of the nucleation of CaCO3 under langmuir monolayers

Calcium carbonate biomineralization uses complex assemblies of macromolecules that control the nucleation, growth, and positioning of the mineral with great detail. To investigate the mechanisms involved in these processes, for many years Langmuir monolayers have been used as model systems. Here, we descibe the use of cryogenic transmission electron microscopy in combination with selected area electron diffraction as a quasi-time-resolved technique to study the very early stages of this process. In this way, we assess the evolution of morphology, polymorphic type, and crystallographic orientation of the calcium carbonate formed. For this, we used a self-assembled Langmuir monolayer of a valine-based bisureido surfactant (1) spread on a CaCl2-containing subphase and deposited on a holey carbon TEM grid. In a controlled environment, the grid is exposed to an atmosphere containing NH3 and CO2 (the (NH4)2CO3 diffusion method) for precisely determined periods of time (reaction times 30-1800 s) before it was plunged into melting ethane. This procedure allows us to observe amorphous calcium carbonate (ACC) particles growing from a few tens of nanometers to hundreds of nanometers and then crystallizing to form [00.1] oriented vaterite. The vaterite in turn transforms to yield [10.0] oriented calcite. We also performed the reaction in the absence of monolayer or in the presence of a nondirective monolayer of surfactant containing an oligo(ethylene oxide) 2 head group. Both experiments also showed the formation of a transient amorphous phase followed by a direct conversion into randomly oriented calcite crystals. These results imply the specific though temporary stabilization of the (00.1) vaterite by the monolayer. However, experiments performed at higher CaCl2 concentrations show the direct conversion of ACC into [10.0] oriented calcite. Moreover, prolonged exposure to the electron beam shows that this transformation can take place as a topotactic process. The formation of the (100) calcite as final product under different conditions shows that the surfactant is very effective in directing the formation of this crystal plane. In addition, we present evidence that more than one type of ACC is involved in the processes described.     

A study on immobilization of 14CO2 using inorganic materials

Journal of Radioanalytical and Nuclear Chemistry - Activated carbon wastes from the air cleaning system in a nuclear facility contain a long half-life value of 14C (5700 years). This 14C...     

Biosynthesis of CaCO3 crystals of complex morphology using a fungus and an actinomycete

The biosynthesis of CaCO3 by reaction of aqueous Ca2+ ions with a fungus, Fusarium sp., and an actinomycete, Rhodococcus sp. (both plant organisms), is described. In the case of the fungus, cruciform-shaped calcite crystals are obtained (SEM picture A) while the actinomycete yielded the unstable polymorph of CaCO3, vaterite (SEM picture B). Specific proteins secreted by the microorganisms are responsible for the morphology and crystallography control observed. A highlight of this approach is that the microorganisms also provide CO2 for reaction with the Ca2+ ions, making the crystals completely biogenic.     

Study of the glass transition on viscous-forming and powder materials using dynamic mechanical analysis

The investigation of the glass transition in materials that become too viscous or are difficult to prepare in a solid compact form, is not straightforward using dynamic mechanical analysis, DMA. In this work, metallic pockets are used to envelop samples in order to resolve the loss factor peak, tan δ, in the region of T_g. Experiments with indium were carried out at different heating rates in order to correct the temperature in such isochronal measurements. The proof of concept of the utility of such methodology was done by investigating the glass transition dynamics of poly(d,l-lactic acid), PDLLA, a biodegradable amorphous polyester widely investigated for biomedical applications. The glass transition peaks obtained at scanning rates below 4 °C min^?1 shifted to the same temperature region after correction. DMA tests on PDLLA at different frequencies allowed construction of a relaxation plot where the glass transition dynamics followed Vogel–Fulcher–Tamman–Hesse behaviour. Inclusion complexes, ICs, of PDLLA with α-cyclodextrin were obtained, exhibiting a very organized arrangement at the nano-scale level. DMA experiments on the ICs powder packed in the metallic pocket revealed a loss factor peak located at a higher temperature as compared with PDLLA, indicating that the segmental mobility of the polymer chains is highly restricted in this supra-molecular organization.     

Development of high ionic-conductive Li1.5Al0.5Ge1.5(PO4)3 glass-ceramic solid electrolyte sheet at low temperature using glass/powder composite

Journal of Solid State Electrochemistry - Because of some drawbacks of the organic electrolytes, such as high toxicity and flammability, inorganic electrolytes have attracted attention regarding...     

Synthesis of carbapenems with carbon substituents at C-3 using a wittig approach

Reaction of ketone 2 with phosphorane 4 produced a mixture of endocyclic and exocyclic carbapenem esters 5 and 6. Hydrogenolysis of these gave carbapenems 7 and 8 or carbapenams 9 and 10.     

Optical band gap and spectroscopic study of lithium alumino silicate glass containing Y3+ ions

The effect of different amounts of Y2O3 dopant on lithium alumino silicate (LAS) glass has been studied in this work. Glasses having 14.8Li2O-20Al2O3-65.2SiO2 (wt%) composition accompanied with Y2O3 dopant were prepared by normal melting process. In order to calculate the absorption coefficient of samples, transmittance and reflectance spectra of polished samples were measured in the room temperature. Optical properties i.e. Fermi energy level, direct and indirect optical band gaps and Urbach energy were calculated using functionality of extinction coefficient from Fermi-Dirac distribution function, Tauc's plot and the exponential part of absorption coefficient diagram, respectively. It has been clarified that variation in mentioned optical parameters is associated with the changes in physical properties of samples i.e. density or molar mass. On the other hand, increasing of Y3+ ions in the glassy microstructure of samples provides a semiconducting character to LAS glass by reducing the direct and indirect optical band gaps of glass samples from 1.97 to 1.67 and 3.46 to 2.1 (eV), respectively. These changes could be attributed to the role of Y3+ ions as the network former in the track of SiO4 tetrahedrals.     

Unsaturated hyperbranched polyester as a surface modifier of CaCO3 and enhanced effect on mechanical properties of HDPE/CaCO3 composites

The unsaturated hyperbranched polyester (UH20) based on Boltorn™ H20 (H20) end‐capped with methacrylate groups and carboxylic acid groups was introduced to treat calcium carbonate (CaCO₃) as a new type of surface modifier by a wet‐coating technique. The interaction between CaCO₃ and modifier was proven to be due to the ionic character by FT‐IR after the extraction with acetone. The maximum amount of tightly bonded UH20 modifier was determined to be around 9% by thermogravimetric analysis (TGA). The incorporation of CaCO₃ coated with UH20 into high‐density polyethylene (HDPE) decreased the mechanical performance of HDPE/CaCO₃ composite in comparison with CaCO₃ coated with stearic acid. In the presence of a small amount of dicumyl peroxide (DCP), a greatly improvement of the notched impact strength as well the tensile strength of HDPE/CaCO₃ coated with UH20 composite was obtained. An enhanced effect in the mechanical performance of the composite between CaCO₃ coated with UH20 and HDPE matrix in the existence of DCP was suggested. Moreover, the morphological structures of impact fracture surface of the HDPE/CaCO₃ composites were studied by scanning electron microscopy (SEM) to confirm the possible mechanism for explaining the improvement of mechanical properties of the composite. Copyright © 2005 John Wiley & Sons, Ltd.     

Uptake of Ba2+ ions by natural bentonite and CaCO3: A radiotracer, EDXRF and PXRD study

Ba²⁺ uptake by natural bentonite, CaCO₃ in addition to a number of bentonite-CaCO₃ mixtures with variable compositions as a function of pH and Ba²⁺ concentration was studied. Radiotracer method, EDXRF, and PXRD were used. The results of radiotracer experiments showed that the uptake of Ba²⁺ by CaCO₃ was larger than its uptake by natural bentonite samples, particularly at low initial concentrations of Ba²⁺ and higher pH values. This finding was supported by the EDXRF results. According to the sorption data, the apparent DG° values of sorption were in the range -9±1 to -13±3 kJ/mol. The PXRD studies revealed the formation of BaCO₃ upon sorption of Ba²⁺ on pure CaCO₃ and on some of the bentonite-CaCO₃ mixtures.     

A preliminary study of milk powder hydration using TEDSpiL continuous wave NMR

Moisture content of foodstuffs are typically assessed by Titration or Near Infrared Spectroscopy, which are labour-intensive as a manual measurement or costly when automated. Magnetic resonance offers a method for moisture evaluation but is also normally costly. In this work, we revisit Look and Locker's “Tone Burst” experiment with a marginal oscillator to evaluate moisture content of powdered–skimmed milk subjected to increased humidity. We refer to this technique as the Transient Effect Determination of Spin–Lattice (TEDSpiL) relaxation times. Moisture content in the samples ranged from 0–12% as determined from the weight gained by the dry powder when re-suspended in water to reach a concentration of 40% w/v. The relaxation properties of re-hydrated samples were measured with a CW NMR sensor. Solutions made up from powders with a higher retained moisture content provided lower measured relaxation values providing a method of measuring the moisture content of the powder. This technique provides a moisture measurement in under 5∼s compared with several minutes for the equivalent pulsed method using low-field hardware.     

Bioleaching of low grade uranium ore containing pyrite using A. ferrooxidans and A. thiooxidans

A process of uranium extraction from ore containing 3.1 % pyrite by bacterial leaching was investigated in shaken flasks during 90 days. The highest uranium recovery amounting to 85.1 % was obtained using binary mixture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans that was exceeding results obtained by traditional acid leaching technique up to 27 %. High uranium recovery was founded to be due to the high degree of pyrite dissolution that can be readily achieved by bacterial leaching (up to 98.0 %).