Preferential mineralization of CaCO3 layers on polymer surfaces from CaCl2 and water‐soluble carbonate salt solutions supersaturated by poly(acrylic acid)

CaCO₃ was mineralized from solutions supersaturated only by poly(acrylic acid) (PAA), without bubbling any CO₂ gas in the solution. For example, a layer of CaCO₃ was built up on the surface of a chitosan membrane from a supersaturated aqueous solution containing CaCl₂, Na₂CO₃, and PAA. In this newly developed method, the PAA alone suppresses the precipitation of CaCO₃ from the bulk solution, and therefore, increases the supersaturated concentration. This concentration is estimated to be the same order as that attained in the method in which both CO₂ gas and PAA were used. At the same time, PAA supplies nucleation fields by forming a polymer complex with chitosan. The crystal system obtained was different from those obtained when using CO₂ gas. Self‐organization of aragonite crystallites led to the formation of uniform, concentric, or branching patterns in the surface‐domain structure. These patterns had morphologies similar to those discovered by other researchers, typically in the crystallization of ascorbic acid. Thicker layers of CaCO₃ could be formed on chitosan membranes, the surfaces of which had been converted to a polyelectrolyte complex (PEC) by exposure to PAA solution before the onset of mineralization. Under certain conditions, the CaCO₃ layer had a small spherical curvature, similar to a half‐lens, and generated Newton's ring pattern from the interference fringes of visible light. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:3627–3634, 2004     

Pseudo Phase Diagram and Microwave Dielectric Properties of Li2O–MgO–TiO2 Ternary System

Li₂O–MgO–TiO₂ ternary system is an important microwave dielectric ceramic material with excellent properties and prospect in both scientific research and application. A phase diagram of the Li₂O–MgO–TiO₂ ternary system was established in this article, based on earlier research results and our present work. Microwave dielectric properties with compositions in different regions of the phase diagram have been analyzed. We found that the 0.33 Li₂MgTi₃O₈–0.67 Li₂TiO₃ ceramics sintered at 1200°C exhibited excellent dielectric properties: Q × f value = 80 476 GHz (at 7.681 GHz), ε_r = 24.7, τ_f = +3.2 ppm/°C. We also designed two ceramic systems in the Li‐rich region of the Li₂O–MgO–TiO₂ ternary system, which received little attention in the past decades, because many excellent single‐phase ceramics, such as Li₂MgTiO₄, Li₂MgTi₃O₈ and MgTiO₃, have been found in the Ti‐rich region. The ceramic systems have low sintering temperatures but also relatively poor dielectric properties.     

An ESDIRK method with sensitivity analysis capabilities

A new algorithm for numerical sensitivity analysis of ordinary differential equations (ODEs) is presented. The underlying ODE solver belongs to the Runge–Kutta family. The algorithm calculates sensitivities with respect to problem parameters and initial conditions, exploiting the special structure of the sensitivity equations. A key feature is the reuse of information already computed for the state integration, hereby minimizing the extra effort required for sensitivity integration. Through case studies the new algorithm is compared to an extrapolation method and to the more established BDF based approaches. Several advantages of the new approach are demonstrated, especially when frequent discontinuities are present, which renders the new algorithm particularly suitable for dynamic optimization purposes.     

TTT and CHT curing diagrams of water‐borne polycondensation resins on lignocellulosic substrates

Lignocellulosic substrates such as wood were found to have a marked modifying influence on both lower temperature and higher temperature zones of TTT and CHT diagrams during hardening of phenol–resorcinol–formaldehyde (PRF) and melamime–urea–formaldehyde (MUF) polycondensates. Although the modifying influence of the substrate on the higher temperature zone of CHT diagrams presented the same trend of what was already reported for phenol–formaldehyde (PF) and urea–formaldehyde (UF) polycondensates, marked differences from what reported in the literature were recorded for TTT diagrams of all these polycondensates as well for the lower temperature zones of the CHT diagrams on lignocellulosic substrates, both of which had not been investigated previously. The chemical and physical mechanisms of the interactions of the resins, the substrate, and the water carrier causing such marked variations are presented and discussed. Although in the higher temperature zones both substrate and water carrier play an important role, in the lower temperature zone the presence of water appears to be the dominant factor causing the observed variations. The generalized modified CHT and TTT diagrams characteristic of the behavior of these water‐borne polycondensates on lignocellulosic substrates can be used to describe the behavior and complex changes of phase the formaldehyde‐based polycondensation resins undergo when used as wood adhesives during their curing directly in the wood joint. The results also show that diagrams obtained with pure resin cannot be used to predict the behavior of the polycondensate when this is markedly modified by the presence of interacting solvents and substrates. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2128–2139, 2001     

An improved algorithm for the three‐fluid‐phase VLLE flash calculation

The VLLE flash is important in water and hydrocarbons mixtures, hydrocarbon and CO₂ rich mixtures, and hydrocarbon methane rich mixtures that are encountered in reservoir performance and recovery studies. A robust VLLE flash algorithm is proposed. The equilibrium and mass balance equations are solved as a constrained minimization problem. An inverse barrier function is used to handle the inequality constrains to solve for the phase fractions. It warrants always arriving to the solution. The challenging cases analyzed showed that the initialization procedure proposed, together with successive substitution iteration in the outer loop, is a good method for a stable VLLE flash algorithm, even near critical points. Whenever the result is in the region outside the three‐phase physical domain, the solution suggests that the system has fewer phases. In one of the cases analyzed, a region with three liquid phases was encountered and the algorithm found two different solutions with positive phase fractions. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3081–3093, 2015     

一种新的感度试验与分析方法

介绍了一种新的感度试验设计与分析方法，即Ｎｅｙｅｒ法。它利用最大似然估计来选择下一个试验水平，利用似然比试验可计算任意置信区间，并以Ｃｒａｍｅｒ－Ｒａｏ理论为基础，可以分析所有感度试验结果。     

Enthalpies of formation in the scandia‐zirconia system

The scandia‐zirconia (ScZ) solid solutions have been attracting attention from the communities interested in solid‐oxide fuel cells because they possess the highest ionic conductivity among zirconia‐based materials. However, this system shows a relatively large number of polymorphs with lack of thermodynamic data to enable comprehensive phase control for property optimization. In this work, the enthalpy of formation of the ScZ system within the range 0–20 mol% Sc₂O₃ is determined by combining the surface energy values with enthalpy of drop solution data obtained from high‐temperature oxide melt solution calorimetry. The heats of formation, a key data for understanding phase stability, for five polymorphs: monoclinic (m), tetragonal (t), cubic (c), and rhombohedral (β and γ) are reported for the first time.     

Effect of temperature and span series surfactant on the structure of polysulfone membranes

A macrovoid structure was found in polysulfone membranes formed by the wet‐inversion method using N‐methylpyrrolidinone (NMP) and water as the solvent/nonsolvent pair. The addition of Span series surfactants in the casting solution was found to inhibit the macrovoid formation. Sorbitan monooleate (Span‐80) was more effective in inhibiting macrovoids than was sorbitan monolaurate (Span‐20). The phenomenon of macrovoid suppression became more prominent at higher temperature. The cloud‐point shift might account for the temperature effect. But there was no simple explanation for the effect caused by Span‐80. The cloud‐point position, the demixing rate, and the viscosity of the casting solution were measured. None of them could explain the effect of macrovoid inhibition by the addition of Span‐80. However, the penetration test indicated that the penetration of a nonsolvent into a surfactant‐free casting solution was caused by a convective flow, but that into Span‐80 was through diffusion. It was found that the retardation of nonsolvent penetration was the major cause of macrovoid inhibition. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 166–173, 2002     

Harnessing the Melting Peculiarities of Ultra‐High Molecular Weight Polyethylene Fibers for the Processing of Compacted Fiber Composites

Summary: Compacted fiber composites offer unique properties due to their lack of an extraneous matrix. The conditions of processing ultra‐high molecular weight polyethylene (UHMWPE) fibers were simulated in a heated pressure cell. In situ X‐ray diffraction measurements were used to follow the relevant transitions and the changes in the degree of crystallinity during melting and crystallization. The results strongly support the suggestion that the hexagonal crystal phase, in which the chain conformation is extremely mobile on the segmental level, constitutes the physical basis of compaction technologies for processing UHMWPE fibers into a single‐polymer composite. This report suggests that using a pseudo‐phase diagram outlining the occurrence of different phases during slow heating and the degree of crystallinity can provide valuable insight into the technological parameters relevant for optimal processing conditions.

Degree of crystallinity as a function of pressure and temperature in a region relevant to compaction processes.