Behavior of acrylic acid–itaconic acid hydrogels in swelling,shrinking, and uptakes of some metal ions from aqueous solution

An experimental research of the absorption properties of metal ions onto synthetic hydrogel obtained by solution polymerization of acrylic acid and itaconic acid in presence of N,N′‐methylenebisacrylamide as crosslinking agent was carried out. The swelling behavior in aqueous salt solutions was studied as a function of divalent cation concentration (Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺, Cd²⁺, Pb²⁺, Hg²⁺) in the external solution ranging from 10^?5 to 1M, at 25°C. The ability of these hydrogels to bind cations was measured at different pH values and metal ion concentrations. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 530–536, 2003     

Some Mechanical Properties of Poly[(acrylic acid)‐co‐(itaconic acid)] Hydrogels

Two series of hydrogels of poly[(acrylic acid)‐co‐(itaconic acid)] have been prepared by copolymerization in solution using tetrafunctional N,N′‐methylenebisacrylamide (NMBA) as cross‐linker. The resulting polymer was swollen in water at 298 K to yield homogenous transparent hydrogels. These hydrogels were characterized in terms of swelling and compression‐strain measurements. The influence of the comonomer composition and concentration of cross‐linking agent on volumetric swelling and the mechanical properties of these hydrogels were investigated. Inefficient cross‐linking is indicated by the small values of ν_e relative to the theoretical cross‐linking densities.

Dependence of measured affective cross‐linking density (ν_e) on the theoretical cross‐linking density (ν_t) for acrylic acid/itaconic acid hydrogels prepared at a fixed composition of AA80/AI20 wt.‐%, but at different concentrations of NMBA.     

Effects of Addition of Na2O, Sb2O3, CaO, and ZrO2 on the Properties of Lithium Zinc Ferrite

Some effects of CaO, Na₂O, Sb₂O₃, and ZrO₂ additions on Li_0.3Zn_0.4Fe_2.3O₄ ferrite were studied to improve its density and other material properties. The densification behavior of the ferrite depended on the amount and type of additive. A relative density of ∼98.5% was achieved with the addition of CaO. The grain size decreased with the addition of Na₂O, CaO, and Sb₂O₃. The permeability and electrical resistivity increased with additives. CaO remarkably increased resistvity, whereas, ZrO₂ increased permeability. Na₂O and Sb₂O₃ increased the Curie temperature, whereas CaO and ZrO₂ decreased it. These effects were attributed to mainly additive segregation on the grain boundaries, which suppressed grain-size development during the sintering of lithium zinc ferrite.     

Bipolar membranes in forward bias region for fuel cell reactors

Three bipolar membranes, two home-made composed of commercial cation (DuPont) and anion (FuMA-Tech) exchange membranes (called Nafion/FT-FAA and Nafion/FT-FAS) and a commercial one, BP-1 from FuMA-Tech, were investigated in order to characterize their suitability to use in a H₂/O₂ fuel cell intended to produce hydrogen peroxide on the cathode instead of water. The Nafion/FT-FAA and Nafion/FT-FAS membranes were prepared using a hot-pressing method. The optimal hot-pressing conditions were determined by measuring the ionic conductivity of the membranes. The latter was observed to depend on the relative humidity of the bipolar membrane. Of the studied bipolar membranes, Nafion/FT-FAA showed the best performance. The transport number of protons measured in a concentration cell was observed to depend on the direction of the proton diffusion flux through these membranes so that transport numbers of ca. unity were obtained when the cation exchange side faced the solution with higher proton concentration. In the opposite case, when the higher concentration faced anion exchange side, the transport number of proton was clearly lower, indicating the usefulness of the bipolar membranes for hydrogen peroxide production in the fuel cell.     

The Crystal Structure of Tobermorite 14 Å (Plombierite), a C–S–H Phase

The crystal structure of tobermorite 14 Å (plombierite) was solved by means of the application of the order–disorder (OD) theory and was refined through synchrotron radiation diffraction data. Two polytypes were detected within one very small crystal from Crestmore, together with possibly disordered sequences of layers, giving diffuse streaks along c ^*. Only one of the two polytypes could be refined: it has B 11 b space group symmetry and cell parameters a =6.735(2) Å, b =7.425(2) Å, c =27.987(5) Å, γ =123.25(1)°. The refinement converged to R =0.152 for 1291 reflections with F _o>4σ( F _o). The characteristic reflections of the other polytype, F 2 dd space group, a ≈11.2 Å, b ≈7.3 Å, c ≈56 Å, were recognized but they were too weak and diffuse to be used in a structure refinement. The structure of tobermorite 14 Å is built up of complex layers, formed by sheets of sevenfold coordinated calcium cations, flanked on both sides by wollastonite-like chains. The space between two complex layers contains additional calcium cations and H₂O molecules; their distribution, as well as the system of hydrogen bonds, are presented and discussed. The crystal chemical formula indicated by the structural results is Ca₅Si₆O₁₆(OH)₂·7H₂O.     

Waterloss Detection in Water Distribution Networks using Wavelet Change-Point Detection

The work presented herein addresses the automatic detection of water losses in water distribution networks (WDN), through the dynamic analysis of the time series related to water consumption within the network and the use of a wavelet change-point detection classifier for identifying anomalies in the consumption patterns. The wavelet change-point method utilizes the continuous wavelet transform (CWT) of time-series (signals) to analyze how the frequency content of a signal changes over time. In the case of water distribution networks the time-series relates to streaming water consumption data from automatic meter reading (AMR) devices, at either the individual consumers’ level or at an aggregated district meter area (DMA) level. The wavelet change-point detection method analyzes the provided time-series to acquire inherent knowledge on water consumption under normal conditions at household or area-wide levels, to then make inferences about water consumption under abnormal conditions. The method is demonstrated on several abnormal WDN operating conditions and anomaly detection cases.     

Geometric Methods for Invariant‐Zero Cancellation in Linear Multivariable Systems with Application to Signal Rejection with Preview

This work deals with zero cancellation in linear multivariable systems with possible feedthrough terms from the inputs to the outputs. A methodology for the synthesis of a minimal‐order feedforward compensator preserving key properties of the original system while cancelling minimum‐phase invariant zeros is derived by means of the basic tools of the geometric approach. The properties maintained in the feedforward compensation scheme are stabilizability and right‐invertibility. Duality arguments show how to modify the devised method so as to achieve zero cancellation with a cascade filter retaining detectability and left‐invertibility. Continuous and discrete‐time systems are considered in a unified framework exploiting the common structural features. An original application of zero cancellation to signal rejection with preview is presented. A novel feedforward control scheme is devised, avoiding the steering along minimum‐phase zero techniques that are at the basis of well‐settled solutions.     

Relation between PVT measurements and linear viscosity in isotactic and syndiotactic polypropylenes

Pressure-Volume-Temperature (PVT) data of an isotactic and a syndiotactic PP are fitted to a modification of the Simha-Somcynsky equation of state (S-S), to calculate characteristic parameters, such as V^∗, T^∗, P^∗ and the solubility parameter δ. The hole fraction of the S-S model and the free volume are deduced from these parameters. The application of a modified Doolittle equation and a modified Berry-Fox equation to estimate viscosity, leads to extract novel conclusions on the differences between both types of PPs. An equation which accounts for the effect of temperature on the characteristic ratio of syndiotactic PP is presented.