Bulk density of polymer solid granules in vane cylinder

Polymer granules are conveyed and plasticized using an innovational vane extruder composed of several vane plasticizing and conveying units (VPCUs). This study developed a mathematic model to analyze the bulk density of polymer granules in a VPCU, as well as conducted an experiment to investigate the effects of device geometry, polymer properties, and operating conditions on the model. By comparing the theoretical model data with the experiment data, the proposed model of bulk density is found to be aligned with actual conditions, thus providing a basis for device and process optimization. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 842‐850, 2013     

Ferroelectricity in AgNbl-xTaxO3 solid solutions

Existence of the ferroelectric phase in AgNb_l-xTa_xO₃ solid solutions was confirmed. Temperature of the ferroelectric phase transition decreases from 348K for AgNbO₃ to 140K for AgNb_0.4Ta_0.6O₃ with increasing Ta concentration. Investigations of spontaneous polarization P_s, total pyroelectric coefficient p_t and dielectric permittivity were carried out for ceramic samples (0 ≤ X ≤ 0.6). Values of P_s, p_t and ε_max increase with increaseing Ta concentration. Values of P_s are of the order of 0.1 μC/cm².     

Thaumasite-ettringite solid solutions in degraded mortars

The thaumasite form of sulfate attack (TSA) has been observed in mortar prisms made from Portland-limestone cements after laboratory storage in 1.8% magnesium sulfate solution at 5 °C for 5 years. The prisms all showed evident signs of degradation, which increased with increasing limestone content. X-ray powder diffraction indicated that a solid solution was formed in all the prisms, which was based on the crystal structure of thaumasite, but extended towards the chemical composition of ettringite. The prism made from the cement with the highest level (35%) of limestone replacement gave the greatest amount of the thaumasite solid solution and had a composition close to the thaumasite end member, whereas those cements with lower (15%, 5% and 0%) levels of replacement gave reduced amounts of the solid solution and had greater lattice parameters. The solid solutions that have been observed are compared with those reported by Barnett et al. for synthetic thaumasite samples grown from sucrose solution.     

Microwave dielectric properties of forsterite-based solid solutions

Recently forsterite has been reported as an excellent dielectric material for millimeter wave application. However, its temperature variation of the resonant frequency (τ_f) is relatively large which precludes its immediate use in practical applications. In this paper, we report the effect of substituting Ca and Mn for Mg on the microwave dielectric properties of forsterite. The composition 0.975Mg₂SiO₄–0.025Mn₂SiO₄ showed excellent Q × f value of 180,000 GHz with a τ_f of −71 ppm/°C. The end member Mn₂SiO₄, showed a Q × f of 50,000GHz, ɛ_r of 8.52 and τ_f  =  −90 ppm/°C. In the case of Ca substitution for Mg, τ_f shifted to high negative value with increasing amount of Ca. However, Q × f did not show much change in its value. It is suggested that the increase of τ_f towards a more negative value is related to the ionic radii of the substitutes.     

Strength and morphology of solid bridges in dry granules of pharmaceutical powders

This is an experimental study of the tensile strength of solid bridges between primary particles comprising granules of lactose or mannitol. We report on two systems: granules prepared with ethanol granulating solutions, in which the base powders were at most sparingly soluble, and aqueous granulating solutions, in which the base powder solubility was large. Both systems were studied with and without hydroxypropylcellulose (HPC) or polyvinylpyrrolidone (PVP) or surfactants (Triton-X100, sodium lauryl sulfate or polysorbate 80) added to the granulating solution. The interparticle bridge strength was determined from the granule crush strength with a simple model that assumes that solid bridges form by evaporation of solvent from liquid bridges that maintain their shape during drying.Lactose granules prepared with pure ethanol are very weak, with crush strength comparable to that predicted by JKR theory, consistent with its negligible solubility. Mannitol, which is sparingly soluble, forms granules with bridge strength similar to the theoretical (Griffith) strength of a pure mannitol. Addition of HPC or PVP to the granulating solution produces bridges with strength comparable to that of pure polymer films. In comparison, the behavior of granules prepared with aqueous granulating solutions was much more complex due to the high saturation concentration of base powder. Granules produced with pure water had bridge strength approximately 20% of the theoretical strength. Addition of HPC or PVP to lactose granules increased the bridge strength modestly, but the strength was much smaller than that of the corresponding pure polymer films. Addition of HPC to mannitol granules had little effect on bridge strength, while PVP reduced bridge strength by approximately 30%. Addition of surfactants to the granulating solution also reduced dry bridge strength. These results reflect the complex microstructure and resulting mechanical properties of dry bridges produced by coprecipitation of the sugars and polymers (or surfactants).     

Inversion of quartz solid solutions at cryogenic temperatures

Quartz solid solution crystals of six different compositions were obtained from crystallization of glass powders belonging to the Li₂O–Al₂O₃-SiO₂ (LAS) system. They were analyzed in situ by laboratory-based X-ray diffraction down to cryogenic temperatures (−190°C). Temperature-resolved analysis of their lattice parameters allowed determination of the critical inversion temperature T_c in these materials, marking the displacive phase transition from a high-quartz- to a low-quartz-like lattice. Integrating available data from other literature sources, an updated phase diagram for the occurrence of high and low quartz solid solution phases is provided for the LAS system; these data are expected to support future development of functional materials relying on these crystalline phases.     

Stability of rhombohedral structure and improved dielectric and ferroelectric properties of Ba,Na, Ti doped BiFeO3 solid solutions

A study of the (1-x)BiFeO₃-(x)Ba_1/2Na_1/2TiO_2.75 (BFO-BNT) solid solutions obtained using the solid state reaction method, for different molar relative concentration of Ba_1/2Na_1/2TiO_2.75 in the 0.0 ≤ x ≤ 0.12 composition range, is presented. The crystal structure and the dielectric and ferroelectric properties are studied in detail. Results of the Rietveld refinement of the X-ray diffraction data demonstrate that the system is single phase with R3c symmetry up to x = 0.09 while for x = 0.12, a small quantity of a secondary phase with P4mm symmetry appears. Scanning electron microscopy demonstrates that BNT presence promotes grain growth resulting in larger grains. Raman spectroscopy shows that, with increasing x, some of the A and E Raman modes slightly reduce their intensity while shifting in frequency, evincing the structural changes caused by the Ba, Na, and Ti incorporation on the BFO lattice. The X-ray photoelectron spectroscopy study confirms the successful substitution and gradual structural distortion in the samples. The improvement in dielectric properties with increasing BNT concentration can be attributed to stable dipole moment formation. Compared with pure BFO ceramics, doped BFO samples exhibit remarkably enhanced ferroelectric properties.     

Pressure-induced phase transitions in PZ-xBMN binary solid solutions

Solid solutions of (1−x)PbZrO₃-xBa(Mg_1/3Nb_2/3)O₃ (PZ-xBMN, x = 0.02, 0.03, 0.04, and 0.05) were prepared, and their microstructures, electrical properties, and phase transition behaviors under hydrostatic pressure were investigated. It was found that the incorporation of BMN into PZ can provide improved ferroelectric properties, leading to the formation of antiferroelectric/ferroelectric phase boundaries in PZ-xBMN ceramics when the value of x is between 0.02 and 0.03. It was also demonstrated that the ferroelectric phases exhibit excellent temperature stability in the remanent polarization. Importantly, complete depolarization was observed in the PZ-xBMN solid solution due to the hydrostatic pressure-induced ferroelectric-antiferroelectric phase transition. The resultant properties and phase transition behaviors of PZ-xBMN ceramics under pressure will benefit their application in pulsed power supplies.     

ESR study and copolymer analysis of acrylamide-methacrylamide solid solutions

When acrylamide-methacrylamide mixed crystals are irradiated by ultraviolet (UV) rays, a copolymeric sample is obtained containing both monomeric constituents. For identification and quantitative analysis of these copolymers, a modified form of UV spectroscopy was used. The greatest advantage of UV spectroscopy for copolymer analysis lies in its rapid application. A comparison of the spectrum of the unknown compositions with spectra of known systems by using a calibration curve and the shifts in absorption maxima in different concentrations are valuable aids in establishing the composition. Electron spin resonance (ESR) provides a correlation between the obtained copolymer composition and the shape of the signal of the responsible radical. ESR spectra obtained for UV-irradiated acrylamide-methacrylamide mixed crystals reveal that during polymerization both radicals are present. As methacrylamide percentage increases in the mixture, the signal becomes similar to the 9-line spectrum of pure methacrylamide. When there is 90% methacrylamide present in the original mixture, a 5-line signal is observed, with even-numbered peaks in the methacrylamide signal appearing now as shoulders. When the methacrylamide percentage is about 16%, a characteristic 3-line signal of acrylamide is dominant. As the methacrylamide percentage increases in the original mixture of the copolymers, ESR signals indicate a decrease in the rate constant values for second-order decay at 60°C. The stability of the formed radicals was studied by admitting oxygen to the copolymeric samples as well as to the homopolymeric systems. Since the peroxidic radicals are more active in the hydrogen abstraction process, they decay more rapidly than the macro radical itself by a bimolecular termination reaction. As the methacrylamide percentage increases in the copolymeric mixtures, the peroxide radical formation becomes more difficult. This indicates that polymethacrylamide brings more stability in copolymerization reactions with acrylamide. The polymerization rate of both monomers and their mixed crystals were enhanced by adding chlorine gas before irradiation. Chlorine acts as an agent for slowing down the radical decay as well as accelerating the radical initiation reactions.     

Phase formation of zirconia-based solid solutions synthesized from peroxides

A finely crystalline powder of the tetragonal solid solution based on zirconia with a crystal size of less than 40 nm is synthesized from zirconium and cerium peroxides. The amorphous phase formed as an intermediate product upon decomposition of the peroxides is characterized by structural disordering and involves chemical defects (OH^-, H₂O). Crystallization of (Zr_{1 - x}Ce_x)O₂ solid solutions (x = 0–0.2) and the sequence of phase and structural transformations of precursors upon heating are investigated. It is found that, during heat treatment at temperatures in the range 500–1200°C, recrystallization and growth of grains occur very slowly (from 5 to 60 nm). This makes it possible to obtain nanomaterials for different applications.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Glushkova, Lapshin, Vershinin, Podzorova, Polikanova.     

Thermal properties of ZrB2-TiB2 solid solutions

Zirconium diboride ceramics were prepared with additions of up to 50 vol.% TiB₂. The resulting (Zr,Ti)B₂ ceramics formed complete solid solutions based on x-ray diffraction. The addition of TiB₂ resulted in grain size decreasing from 22 μm for nominally pure ZrB₂ to 7 μm for ZrB₂–50 vol.% TiB₂. The thermal conductivity at 25°C ranged from 93 W/m⋅K for nominally pure ZrB₂ to 58 W/m⋅K for ZrB₂–50 vol.% TiB₂. Thermal conductivity was as high as 67 W/m⋅K for nominally pure ZrB₂ at 2000°C, but dropped to 59 W/m K with the addition of 50 vol.% TiB₂. Electrical resistivity measurements were used to calculate the electron contribution to thermal conductivity, which was 76 W/m⋅K for nominally pure ZrB₂ decreasing to 57 W/m⋅K when 50 vol.% TiB₂ was added. The phonon contribution to thermal conductivity did not change significantly for ≤10 vol.% TiB₂. Additions of ≥25 vol.% TiB₂ reduced the phonon contribution to nearly zero for all temperatures.     

Synthesis and characterization of nanometric yttrium-doped hafnia solid solutions

Nanometric-sized yttrium doped HfO₂ powders were obtained by applying metathesis and combustion reactions. The tailored composition of solid solutions was: Hf_1?xY_xO_2?δ with concentration “x” ranging from 0 to 0.2. HfCl₄ was used as a source of hafnium whereas Y(NO₃)₃·6H₂O was used as a source of yttrium. The obtained powders were annealed at different temperatures in order to induce crystallization of HfO₂. The influence of dopant concentration, annealing temperature and annealing time on powder properties was examined. The XRD analysis revealed that the crystal structure of HfO₂ depends on the dopant concentration. The samples doped with 20 mol% of yttrium and annealed at 1500 °C had high-temperature, cubic structure even after cooling to room temperature. The presence of relatively large amount of dopant was beneficial in stabilizing highly desirable cubic phase of HfO₂. It was found that the crystallite size lies in the nanometric range (<10 nm).     

Oxidation of solid gold in chloroform solutions of cetyltrimethylammonium bromide

Oxidation of solid gold was studied in chloroform solutions of cetyltrimethylammonium bromide (CTAB). We observed that, upon sonication, solid gold is oxidized and cetyltrimethylammonium tetrabromo aurate is formed. The Br⁻ ions act as a nucleophile that lowers the reduction potential of gold and molecular oxygen from the air acts as an oxidant. Addition of hydrazine to the sonicated solution leads to the formation of gold nanoparticles dispersed in chloroform.     

On the thermodynamics of solid solutions of polymer and salt

Solid solutions of poly(ethylene oxide) of different molecular masses (M_η from 6 × 10⁵ to 4 × 10⁶ g mol^?1) and lithium perchlorate (LiClO₄) were prepared by solution casting method. Salt concentrations of solutions vary between around 2 and 13 wt%. Thermodynamic properties of these solutions are reported in the range of low salt content. The solutions represent two‐phase systems mostly not in equilibrium at room temperature. They consist of neat crystalline PEO and an amorphous mixture of salt and polymer. Crystallinity of PEO in salt solutions stays constant with increasing salt content and is independent of molecular mass. Crystallinities serve determining share and composition of the amorphous phase. Glass transition temperature increases linearly with salt content in the amorphous phase. Depression of equilibrium melting points by addition of salt provides activity coefficients in solutions and allows for estimation of degrees of dissociation. Rate of crystallization of poly(ethylene oxide) depends exponentially on inverse undercooling. In that way, it is also coined by equilibrium melting point depression. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Range of solid solutions of silica in spinel type phase

Abstract

Al₂O₃–SiO₂ mixed gel of varying compositions has been synthesised by using aluminium nitrate nonahydrate (AR) and tetraethyl orthosilicate (BDH) by coprecipitation technique. Phase evolution studies of these gels have been made by X-ray diffraction technique and ²⁹Si MAS NMR analysis. The lattice parameter of intermediate Al–Si spinel phase has been measured. The calculated data indicate that the composition of spinel phase does not alter irrespective of the composition of mixed gels chosen. Results demonstrate that slightly <28 wt-%SiO₂ is likely to be present as solid solution with γ-Al₂O₃ in Al–Si spinel structure. Mullitisation reactions of mixed gels of compositions on two sides of mullite stoichiometry are described.     

Effect of reactant dispersion on formation of PZT solid solutions

The reactions in the formation of PZT solid solutions were studied with particular reference to changing the dispersion of the reactants by altering the mixing conditions. The final homogenisation step was studied in detail. The effect on the electromechanical properties of the PZT ceramics were measured. The results of these studies are discussed.