Phase equilibrium in systems based on oxides of zirconium,lanthanum and samarium

According to the results of the samples studied by X-ray diffraction and microstructural analyzes the phase equilibria in the binary La₂O₃ – Sm₂O₃ and ternary ZrO₂ – La₂O₃ – Sm₂O₃ systems were studied. The boundaries of the phase fields of the binary system are specified and an isothermal cross section of the ternary state diagram of the ZrO₂ – La₂O₃ – Sm₂O₃ system at a temperature of 1500 °C is constructed. No new phases have been identified in the studied systems. It is established that in the ternary system ZrO₂ – La₂O₃ – Sm₂O₃ at 1500 °C fields of solid solutions on the basis of cubic (F) modification with structure of fluorite type, tetragonal (T) modification of ZrO₂, monoclinic (B) modifications of Sm₂O₃, hexagonal (A) are formed. La₂O₃, as well as an ordered phase with a structure of the type of pyrochlore Ln₂Zr₂O₇ (Py). The boundaries of the phase fields and the parameters of the unit cells of the formed phases are determined. A characteristic feature of this isothermal cross section is the formation of a continuous series of solid solutions based on the phase of the pyrochlore type La₂Zr₂O₇ (Sm₂Zr₂O₇). The limiting solubility of Sm₂O₃ in the ordered phase La₂Zr₂O₇ is 16 mol. % along the section Sm₂O₃- (67 mol.% ZrO₂ - 33 mol.% La₂O₃). The solubility of La₂O₃ in the solid solution Sm₂Zr₂O₇ is slightly less and is 11 mol. % along the section La₂O₃- (67 mol.% ZrO₂ - 33 mol.% Sm₂O₃). The isothermal cross-section of the state diagram of the ZrO₂ – La₂O₃ – Sm₂O₃ system at 1500 °C is characterized by the presence of three three-phase (Py + T + F), (A + Py + B), (Py + F + B) and eight two-phase (A + Py), (B + A), (B + Py), (F + B), (T + F), (Py + T), (F + Py-two) areas.     

Phase relationships,important working properties,and classification of ceramic and other bonding systems

Conclusions A range of volume phase characteristics is proposed for suspensions, semifinished articles, and materials based on them, which will facilitate the determination and objective assessment of a variety of materials.A direct link is demonstrated between the chemical nature of the oxide solid phase, typical ionic potential, and the phase composition of the suspension, and the state of the disperse medium, and also the nature of rheological behavior.A number of principles are formulated for obtaining heat-resistant cements, and their classification is proposed, based on the volume proportion of liquid chemically bonded during the setting of the system.A new principle is proposed for obtaining heat-resistant cements based on incorporating in the composition of low-active (with high ionic potential values) materials, small additions of highly active materials. Castings of corundum composition were obtained with _bend after drying in the range 5–15 MPa.Translated from Ogneupory, No. 6, pp. 49–60, June, 1982.     

Phase transformations in sodium zinc silicate glasses containing PbS nanocrystals

The phase composition and the kinetics of formation of the lead sulfide crystalline phase at the late stages of heat treatments of sodium zinc silicate glasses have been investigated using small-angle X-ray scattering and X-ray powder diffraction. It has been established that, after the completion of the precipitation of the PbS crystalline phase, the reaction PbS + ZnO = PbO + ZnS begins to proceed on the surface of nanocrystals. This reaction results in a decrease in the volume of the PbS phase and the precipitation of ZnS nanocrystals. The size effect has been revealed: PbS nanocrystals with a radius larger than approximately Å are stable, whereas nanocrystals with smaller sizes initiate the reaction PbS + ZnO = PbO + ZnS.     

Collapse of structure in sepiolite and other layered silicate systems

Collapse of structure due to removal of water from sepiolite and other layered silicates was studied. Data from three systems - sepiolite, hydrated C₃S, and hydrated portland cement - are presented. Changes in mechanical properties and helium flow characteristics were correlated with collapse processes in sepiolite. Similarities in helium flow characteristics of the three systems are discussed to elucidate the role of decomposition processes in microstructural collapse. The sepiolite system appears to have potential as a model for the study of collapse processes in other cementitious systems.     

Phase relationships of rigid rod polymer/flexible coil polymer/solvent ternary systems

Phase diagrams of two types of rigid rod polymer/flexible coil polymer/methanesulfonic acid (MSA) ternary systems were determined by polarized optical microscopy at ambient conditions. The rigid rod polymer is a wholly aromatic high temperature resistant (no measurable T_g) poly (p-phenylenebenzobisthiazole) (PPBT). One of the flexible coil polymers is a wholly aromatic high temperature resistant poly (2,5′(6′) benzimidazole) (ABPBI), the other is a thermoplastic poly[2,2′ -(1–4-phenylene)-6,6′ -bis (3-phenyl-quinoxaline)] (PPQ) with T_g of 359°C. The solvent is methane-sulfonic acid (MSA). The experimentally determined critical concentration points, C_cr, are in excellent agreement with Flory's recent theory. Total phase segregation between the polymer pair in ternary solution was predicted and observed at C > C_cr. Different decomposition mechanisms of phase separation were observed as a function of concentration.     

Eu3+-doped transparent potassium lanthanum silicate (KLaSiO4) glass-ceramic nanocomposites: Synthesis,properties and application

The preparation of Eu³⁺-doped novel K₂O-La₂O₃-Al₂O₃-SiO₂ (KLAS)-based glass and transparent KLS (KLaSiO₄) glass–ceramic (GC) nanocomposites is reported. Nanostructures of the transparent GCs were analyzed by FE-SEM, H(R)-TEM and SAED techniques. The average size of the crystallites is calculated using XRD data and found to be in the range 13–19?nm which is matched well with the average particle size observed from TEM images in the range 5–18?nm. Photoluminescence spectra of Eu³⁺ ions exhibit emission transitions of ⁵D₀?→?⁷F_j (j?=?0 and 1–4) under the excitation at 394?nm. The emission spectra reveals up to 3-fold enhancement of luminescence performance of the KLS GC nanocomposites compared to as-prepared glass. This enhancement is caused due to entering of Eu³⁺ ions into the KLS crystal sites by replacing the La³⁺ ions. Such luminescence properties of KLS glass-ceramic nanocomposites could be a promising candidate as laser host for many laser devices.     

Phase formation of Mn-doped zinc silicate in water at high-temperatures and high-pressures

Phase formation of Mn-doped zinc silicate (Zn₂SiO₄:Mn²⁺, ZSM) in high-temperature and high-pressure water was studied by in situ observations with a hydrothermal diamond anvil cell (HDAC). Precursor was prepared with zinc oxalate dihydrate, manganese oxalate, and silica, where the Zn/Mn/Si molar ratio was 192/8/120 to 199/1/120. Conditions of particle formation were at temperatures up to 650 °C and at pressures up to 1250 MPa. Precursors dissolved at temperatures of 145–203 °C and needle-like particles formed through homogeneous nucleation at temperatures from 357 to 374 °C, close to the critical point of water. The needle-like particles grew at growth rates of 0.5–3.8 μm/s and were identified to be ZSM as evident from their green luminescence. ZSM synthesized in supercritical water (400 °C for 180 min) by batch reactions had comparable luminescence with that of ZSM produced by solid-state reaction (1200 °C for 240 min) using the same precursor. The key finding in this work is that the precursors can be made to dissolve in near-critical water and that this allows ZSM to form via a homogeneous nucleation process.     

Structure-property relationships in elastomer-modified terpolymer systems

A number of terpolymers, incorporating as the elastomer phase polybutadiene, polyisoprene, poly-2,3-dimethylbutadiene, poly(butadiene-co-styrene), and poly(butadiene-co-2-methyl-5-vinypyridine), were studied. Matrices were composed of poly(styrene-co-acrylonitrile) (SAN), poly(α-methylstyrene-co-acrylonitrile), and poly(styrene-co-acenaphthylene). At constant elastomer content and elastomer molecular weight in systems employing a SAN matrix, Izod impact resistance was found to vary inversely with rising elastomer-glass transition temperature. In systems of various matrix composition, using a polybutadiene elastomer, heat deflection temperatures were found to very directly and impact resistance inversely with rising matrix-glass transition temperature. In acrylonitrile–butadiene–styrene (ABS), systems of constant matrix composition and elastomer content, varying the elastomer molecular weight from 0.6 to 2.6 × 10⁵ resulted in increasing the Izod impact resistance from 0.67 to 12.8 ft-lb/in. of notch.     

Phase interaction and oxygen transport in oxide composite materials

Abstract

The oxygen permeability of oxide composite membranes containing similar volume fractions of the components, including (La_0.9 Sr_0.1)_0.98 Ga_0.8 Mg_0.2 O_3-δ(LSGM)–La_0.8 Sr_0.2Fe_0.8Co_0.2O_3-δ (LSFC), LSGM–La₂Ni_0.8Cu_0.2O_4+δ (LNC), SrCoO_3-δ–Sr₂Fe₃O_{6.5 ±δ}, Ce_0.8Gd_0.2O_2-δ (CGO)–LSFC and CGO–La_0.7Sr_0.3MnO_3-δ (LSM), was studied at 973–1223 K. In most cases, oxygen transport is substantially affected by component interaction, decreasing ionic conductivity due to cation interdiffusion, and formation of intermediate phases and/or blocking layers at grain boundaries. This interaction is maximised in systems where the phase components have similar structure and thus may form continuous solid solutions, for example LSGM–LSFC, or intermediate compounds such as Roddlesden–Popper phases in LSGM–LNC composites. The results show that, in addition to knowledge of the transport properties and volume fractions of percolating phases, analysis of ionic conduction in oxide composite materials requires assessment of phase interaction and grain boundary processes.     

Phase relationships and properties of the phase composition periclase-spinel

Conclusions We investigated the phase composition and properties of the compositions periclase-spinel bond in the system MgO-Mg (Al_1–xCr_x)₂O₄, where x=0–1, using spinel-phase concentrations of from 5 to 30% by weight.The essential feature of the phase inversions consists in the development and decomposition of solid solutions of spinel constituent in the periclase. With an increase in the content of magnesiochromite in the spinels, their absorption by the periclase increases. After cooling, the concentration of spinel phase in the solid solution with the periclase is about 5%.An increase in the concentration of the spinel phase from 5 to 30%, and also change in its composition in the direction from magnesio-alumina spinel to magnesiochromite (x1) impairs the thermalshock resistance, strength and porosity.To improve the properties of magnesite articles, it is desirable to use 5–15% by weight of magnesio-alumina spinel as the bond, or chromitic ore, the spinel of which contains a large quantity of magnesia-alumina constituent (MgAl₂O₄).Translated from Ogneupory, No. 5, pp. 42–50, May, 1967.     

Mass transport and surface reactions in microfluidic systems

We provide analysis of different regimes of diffusion and laminar flow convection combined with bimolecular surface reactions relevant to biochemical assays performed in microfluidic devices. Analytic solutions for concentration fields are compared to predictions from two-dimensional finite element simulations for the various operation regimes. The analytic and numerical results extend the transport models beyond the models commonly used to interpret results from surface plasmon resonance (SPR) experiments. Particular emphasis is placed on the characterization of transport in shallow microfluidic channels in which the fully developed transport regime dominates rather than the mass transfer boundary layer transport typically encountered in SPR. Under fast reaction and diffusion conditions, the surfaces saturate following moving front kinetics similar to that observed in chromatographic columns. Two key parameters relevant to on-chip biochemical assays and microfluidic sensors are studied and compiled: the capture fraction of the bulk analyte at the surface and the saturation time scale of the reactive surfaces. The physical processes in the different regimes are illustrated with data from the relevant microfluidics literature.     

Raman and Si NMR spectroscopic characterization of lanthanum silicate electrolytes: Emphasis on sintering temperature to enhance the oxide-ion conductivity

Enhancement of oxide-ion conductivity has been investigated with emphasis on the high sintering temperature of apatite-type structure lanthanum silicate (La₁₀Si₆O₂₇) as a potential electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The influence of the sintering temperatures 1500, 1550, 1600 and 1650 °C as a function of ionic conductivity of the La₁₀Si₆O₂₇ electrolyte synthesized via a diethylamine (DEA) precipitation process has been characterized using impedance spectroscopy. The ionic conductivity of the La₁₀Si₆O₂₇ electrolyte sintered at 1650 °C revealed a higher value (1.22 × 10⁻² S cm⁻¹ at 700 °C) of one order of magnitude than the pellets sintered at lower temperatures. The sintered La₁₀Si₆O₂₇ pellets have been characterized by ²⁹Si NMR and Raman spectroscopy. The ²⁹Si NMR data showed the characteristic secondary peak at 81.2 ppm, which confirmed the interstitial oxygen content contributing to high oxide-ion conduction. The Raman spectra revealed the appearance of a new resolved band centered at 861 cm⁻¹ for the pellet sintered at 1650 °C compared with lower temperatures sintered pellets. The results confirmed the possibility of local structural distortion to create additional pathways for interstitial oxide-ion conduction between channels leading to higher conductivity for the pellets sintered above 1600 °C. Thus, the conduction pathway may be determined by the co-operative displacements of the SiO₄ substructure units formed at elevated sintering temperatures for high oxide-ion conductivity.     

Calcium hydroxide distribution and calcium silicate hydrate composition in tricalcium silicate and β-dicalcium silicate pastes

Pastes of tricalcium silicate (C₃S) and β-dicalcium silicate (C₂S) 23 years old were studied by electron probe microanalysis. In both cases, regions consisting entirely or largely of calcium hydroxide and of CSH were distinguished on a scale of 2–50 μm. The regions high in CSH accounted for 75–80 percent of the whole in the C₃S paste and about 96 percent in the C₂S paste; these values are much higher than those initially occupied by anhydrous starting materials. Within the high CSH areas, no compositional variation was detected that could have corresponded to the so-called inner and outer hydrates. The ratio of mean Ca to mean Si in the high CSH areas was found to be 1.72 for the C₃S paste and 1.78 for the C₂S paste with an exciting beam energy of 10 keV.     

Nomenclature for transport phenomena in electrolytic systems

The document deals with the transport phenomena of importance to electrochemists and electrochemical engineers. In the absence of a report on mass transport at large, the first section presents general definitions of mass flux, of flux density and of phenomonological coefficients, as appearing in the relationships of irreversible thermodynamics, which express the proportionality between the driving forces and the fluxes. the main part is concerned with electrolytic systems, in particular with ideal dilute solutions. Mass transport by diffusion, by convection and by migration of ions under the influence of an electric field is considered. The diffusion coefficient of a species is distinguished from that of an electrolyte. A section is devoted to the transport of charges, including transport numbers, the flow of current through the solution and through the electrode, current efficiency, and current distribution. The report also discusses the precise meaning of concepts related to mass transport, such as the Nernst diffusion layer, mass transport control, interfacial concentrations, concentration overpotential, mass transport coefficients and diffusion potentials. However, the diffusion in solid electrolytes and surface diffusion are not treated.Recommendations for symbols and definitions are given. In many cases, it is endeavoured to clarify by a brief discussion the concept itself.