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PubMed2005

Effect of ion exchange of glazed dental glass ceramics on strength parameters.

Ion exchange treatments can significantly increase the strength of dental glass ceramic core materials by induced compressive residual stresses. However, the core materials of dental restorations need to be veneered or at least to be stained and glazed for esthetic and functional reasons. The objective of this study was to determine the effect of different ion exchange treatments on the strength parameters of stained and glazed glass ceramics. Batches of specimens made of a leucite reinforced dental glass with and without staining and glazing layer, untreated, single ion exchanged (KNO3), and dual ion exchanged (1. KNO3/27, 2. 30 mol% NaNO3/70 mol% KNO3) were tested. The strength of the core material was increased from 117 to 213 MPa by single ion exchange. Staining and glazing increased the strength up to 165 MPa. Single ion exchange of the stained and glazed core caused only a slight additional strength increase up to 173 MPa. The dual ion exchanged stained and glazed core exhibit a strength of 195 MPa and decreased the large strength scatter because of a well-designed residual stress profile. We conclude that dual ion exchange treatments could significantly increase the mechanical reliability of stained and glazed glass ceramic restorations.

Dental Porcelain↗
PubMed1994

Purification of viruses and macromolecular assemblies for structural investigations using a novel ion exchange method.

We describe a novel ion exchange chromatographic technique suitable for large-scale preparation of viruses and other biomacromolecular assemblies in highly purified form. The method, which utilizes anion exchange on either of two commercially available cellulose cartridges, is applied to the Escherichia coli bacteriophage PRD1. Viral particles eluted from both QMA and DEAE cartridges retain infectivity and exhibit greater homogeneity of composition, as judged by gel electrophoresis and electron microscopy, than particles purified by rate zonal sucrose gradient centrifugation. The ion exchange protocols are rapid, requiring less than 15 min elution time, and permit retrieval of the purified viral particles at high concentration in aqueous media without centrifugal pelleting. The present method is particularly well suited to the preparation of milligram to decigram quantities of virus, sufficient for many biophysical structural analyses, including investigations by solution spectroscopic and crystal diffraction techniques. The feasibility and advantages of the ion exchange chromatographic procedure are demonstrated by application of laser Raman spectroscopy to ion exchange purified PRD1 virions and subviral assemblies.

Centrifugation, Zonal↗
PubMed1998

Transport of drugs across porous ion exchange membranes.

Porous ion exchange membranes have potential applications for drug delivery systems. Permeability of these membranes can be controlled by environmental factors like pH and ionic strength but also the drug properties have an important role in the permeation process. In this paper the influence of the drug charge, lipophilicity and molecular weight on the diffusional drug flux is demonstrated. The membranes under study were poly(acrylic acid) (PAA) grafted porous poly(vinylidene fluoride) (PVDF) membranes which are cation selective due to the partial ionization of carboxyl groups in grafted PAA chains. At low pH the membrane pores are open and the drugs can diffuse through the membrane quite easily. However, at pH 7 the grafted chains partially block the pores and the diffusional flux of bigger drug molecules (Mw9400) decreases five orders of magnitude and also the flux of smaller molecules is clearly reduced. When the influence of the drug charge on the diffusion of the drugs across the membranes was studied, it turned out that the PAA-PVDF membranes facilitate the transport of cationic drugs and repel anionic ones. The presented mathematical model, based on Donnan drugs equilibrium and measured transport number data, predicted the observed trends reasonably well.

Biological Transport↗
PubMed2006

Recycling asymmetric hydrogenation catalysts by their immobilization onto ion-exchange resins.

Ion-exchange resins can be used as supports for the preparation of single-site, heterogenised asymmetric hydrogenation catalysts. The immobilised catalysts obtained can be efficiently and conveniently recovered and recycled. This article reviews the significant contributions in the field including the main concepts behind the design and the applications of this type of catalyst.

Journal Article↗
PubMed2005

Local structures of ions at ion-exchange resin/solution interface.

The local structures of Cl- and Br- in anion-exchange resins have been studied by X-ray absorption fine structure (XAFS), and separation selectivity is discussed on the basis of results. When two different anion-exchange resins having trimethylammonium and dimethylammonium groups as anion-exchange groups are employed for ion-exchange experiments, slightly higher Br- selectivity has been obtained with the former. XAFS has indicated that the average hydration numbers for a given anion is not affected by the structure of the ion-exchange group, but that the extent of ion-association between the anion and the ion-exchange groups depends on the type of the ion-exchange group. Shorter interaction distance (and in turn stronger ion-association) has been confirmed for the dimethylammonium-type resin, and is consistent with lower Br- selectivity of this resin.

Anion Exchange Resins↗
PubMed1999

Combined Water and the Ion Exchange Characteristics of Manganese Dioxide Produced by Ozonation.

The change in ion exchange properties of manganese dioxide produced by ozonation (OMD) was studied with respect to its preheated temperature. This was performed by heating samples to different temperatures and later, saturating a part of them in aqueous cadmium sulfate solutions. Analyses were practiced on both the cadmium ion exchanged and un-ion exchanged samples. Results showed that the ion exchange reaction followed a stoichiometric relation between the hydrogen and cadmium ions, promoted by the combined water. The molar ratio of combined water to exchanged cadmium was found to be five. X rays and photographs taken in the scanning electron microscope showed that the structure and morphology of the OMD were not modified by the insertion of the cadmium during ion exchange. From the X rays, the structure of the OMD was determined to be of the gamma type. When the samples were heated to 400 and 500 degrees C, the crystal structure changed to beta and finally to Mn2O3, respectively. However, the changes in structure alone apparently did not affect the ion exchange. The surface area, measured by the BET technique, diminished linearly with the preheat temperature. The ion exchanged cadmium and the surface area showed a nonlinear relationship. However, the surface area and the quantity of combined water in the OMD were both linearly affected by preheating and are directly related to the ion exchange capacity. Copyright 1999 Academic Press.

Journal Article↗
PubMed2006

An electrical impedance spectroscopic (EIS) study on transport characteristics of ion-exchange membrane systems.

This study aimed at investigating ion-exchange membrane systems using impedance spectroscopy. Nyquist plots showed that the impedance obtained in this study described the ion-exchange membrane system well, as consisting of (i) an ion-exchange membrane immersed in solution, (ii) electrical double layers at the membrane surface, and (iii) diffusion boundary layers arising from the interface between the ion-exchange membrane and the electrolyte solutions. Taking into account the physical and electrochemical understanding of the ion-exchange membrane system, an equivalent circuit was suggested to quantitatively analyze each component of the ion-exchange membrane system. To confirm the reliability of the proposed equivalent circuit, the resistance and capacitance were estimated from the impedance data and the values were compared with other experimental results (e.g., I-V curves). The comparison showed good agreement and validated the equivalent circuit. Moreover, the impedance measurements made it possible to confirm the electroconvective effects in the over LCD region.

Journal Article↗
PubMed2005

Towards high capacity latex-coated porous polymer monoliths as ion-exchange stationary phases.

The preparation of high capacity agglomerated monolithic ion-exchangers for capillary ion chromatography is described. Post-modification of reactive monoliths was investigated as an alternative to co-polymerisation of a suitable functional monomer with an overarching goal of increasing ion-exchange capacity. Direct sulfonation of poly styrene-co-divinyl benzene monoliths using concentrated sulfuric acid or chlorosulfonic acid was unsuccessful even for monoliths containing as low as 8% crosslinker. In contrast, chemical transformation of reactive monoliths containing glycidyl methacrylate was used to increase the ion-exchange capacity by up to more than thirty-fold with ion exchange capacities of 14-29 microequiv g(-1) achieved. Three different reactions were considered, including reaction with 4-hydroxybenenesulfonic acid under basic conditions; reaction with thiobenzoic acid followed by transformation to a reactive thiol and the subsequent oxidation to the sulfonic acid; and direct sulfonation with sodium sulfite. Of these, the reaction with sodium sulfite resulted in the most significant increase in the capacity and the best separation performance. In the isocratic mode separation efficiencies of over 13,500 plates m(-1) were observed (for iodate). The separation of seven inorganic anions was also demonstrated using a hydroxide gradient.

Chromatography, Ion Exchange↗
PubMed2005

Adsorption of gaseous formaldehyde and carboxylic acids by ammonium-ion-exchanged alpha-zirconium phosphate.

Ammonium-ion-exchanged alpha-Zr(HPO(4))(2)H(2)O (alpha-ZrP) was obtained as a single phase with the interlayer distance of 9.4 A by the ion-exchange of proton with ammonium ion. The ammonium ion-exchanged alpha-ZrP could adsorb ill-smelling gases, such as formaldehyde and carboxylic acids (formic acid, acetic acid, propionic acid, and butyric acid). The adsorption amounts of carboxylic acids increased in the order, butyric acid<propionic acid<acetic acid<formic acid, whereas the adsorption amount of formaldehyde was the same as that of butyric acid. It was cleared that the adsorbed formaldehyde was partially decomposed to formic acid and methanol by self oxidation-reduction reaction in the interlayer region as evidenced by solid-state NMR. Thereby the interlayer distance after the adsorption of formaldehyde expanded to 14.4 A. In the case of formic acid, it was cointercalated into the interlayer region, and the interlayer distance expanded to 11.1 A. On the other hand, the interlayer distance of the other carboxylic acid-adsorbed compounds decreased to 7.6 A due to release by the evacuation.

Acetic Acid↗
PubMed2002

Kinetics of adsorption of Co(II) removal from water and wastewater by ion exchange resins.

The capacity of ion exchange resins, IRN77 and SKN1, for removal of cobalt from aqueous solution has been investigated under different conditions namely initial solution pH, initial metal-ion concentration, and contact time. The equilibrium data obtained in this study have been found to fit both the Langmuir and Freundlich adsorption isotherms. The adsorption of Co(II) on these resins follows first-order reversible kinetics. The film diffusion of Co(II) in these ion exchange resins was shown to be the main rate limiting step. The studies showed that these cation exchange resins can be used as efficient adsorbent material for the removal of Co(II) from aqueous solutions.

Adsorption↗
PubMed2005

Kinetics study on separation of cadmium from tellurium in acidic solution media using ion-exchange resins.

The feasibility of using ion-exchange resins to separate cadmium from tellurium in acidic solutions of the two metals was investigated. We studied the competitive adsorption of cadmium and tellurium in such resins under varying acid strengths and contact time. We found that low sulfuric acid strength (i.e., 0.5 M) was most effective in removing cadmium from solutions. Different ion-exchange resins were tested for their affinity for cadmium and tellurium ions. In the selected systems, the ion-exchange rate of cadmium was rapid in the first 20 min, and reached equilibrium within 2 h. The Lagergren first-order model described the kinetic data with high coefficient of determination and correlation values. At room temperatures the ion-exchange for cadmium onto the resin followed the Freundlich isotherm model. The maximum removal of cadmium obtained from batch studies using resin A was 91%. Column studies with the same resin showed a removal of cadmium of 99.99% or higher.

Adsorption↗
PubMed1989

[Evaluation of the effectiveness of ion exchange on strengthening of dental porcelain].

This study evaluated the effectiveness of ion exchange on strengthening of porcelain used in metal ceramic. The paste for ion exchange was painted directly on the porcelain surface, dried, and heated at 450 degrees C in the porcelain furnace. The bending strength of porcelain test samples (6.5 x 1.5 x 20 mm), the compressive strength of porcelain-fused-to-metal (PFM) crowns, which were cemented on the metal dies of upper central incisor by an adhesive luting resin 'Panavia EX', and the color change of porcelain test samples (phi 10 x 4 mm) were measured before and after ion exchange. The conclusions were: 1. It was confirmed by X-ray analysis that the compressive stress layer generated by ion exchange for 30 minutes was 150-200 microns in thickness. However, further elongation of time of ion exchange elicited no significant argumentation in the strength. 2. 34 or 57 percent increase of the mean compressive strength of PFM crowns was observed after ion exchange for 30 minutes when the load was applied in the direction of 45 degrees lingually to the tooth long axis or of the tooth long axis, respectively. 3. No significant decrease was found when parts of the incisal edge or the lingual surface of PFM crowns which were strengthened by ion exchange for 30 minutes were reduced by 200 microns. 4. There was so slight difference in the color of dental porcelain before and after ion exchange that the influence seemed to be negligible in its clinical application.

Dental Porcelain↗
PubMed2005

Ion exchange sorption of Pb2+ ions on CrPO4.

The chromium(III) phosphate was observed to have a high affinity towards Pb2+ ion and the sorption capacities were found to be in the order: Pb2+ > Cu2+ > Cd2+ > Ni2+. Different characterization methods i.e. FTIR, SEM and EDX were employed to investigate the sorption mechanism of Pb2+ by chromium(III) phosphate, which showed that no new solid phases were present in the residue after sorption of Pb2+. The exchange between protons from the surface and Pb2+ from solutions was found to be responsible for Pb2+ sorption by chromium (III) phosphate.

Adsorption↗