Preparation and reactivity of lead zirconate-titanate solid solutions produced by precipitation from aqueous solutions

A process for preparation of PZT by precipitation from butoxide precursors is described. The reactivity of the powders during low temperature firing (calcining) has been determined using weight loss, x-ray diffraction, and DTA-TGA techniques.     

Coprecipitation of 60Co from aqueous solutions with solid phases of various coordination compounds

Coprecipitation of ⁶⁰Co from aqueous solutions with solid phases of various coordination compounds was studied. Microamounts of ⁶⁰Co do not noticeably coprecipitate with solid phases of [M(CE)]BPh₄ (M = Na⁺, Cs⁺; CE = 12-crown-4, 15-crown-5, 18-crown-6) and of CsBPh₄. ⁶⁰Co can be efficiently removed from aqueous solutions containing 0.1 and 4.0 M NaNO₃, 0.1 M EDTA, or 1.0 M H₂C₂O₄ by coprecipitation with the KFe[Fe(CN)₆] solid phase formed by successive addition of K₄[Fe(CN)₆] and Fe(NO₃)₃ into these solutions. The degree of ⁶⁰Co removal varies from ～80 to ～99.9% depending on the experimental conditions. This procedure allows simultaneous removal of ¹³⁷Cs from the same solution with no less than 97% efficiency.     

Composition of precipitates of barium and strontium nitrates crystallizing from nitric acid solutions

The chemical compositions of Ba(NO₃)₂ и Sr(NO₃)₂ precipitates obtained by precipitation from HNO₃ solutions of various concentrations were determined using an inert tracer. The data of chemical analysis and IR spectroscopy suggest the presence of HNO₃ in the precipitates of barium and strontium nitrates and of their solid solutions, formed from concentrated nitric acid solutions. The IR spectra of 0 to 23.5 M aqueous HNO₃ solutions were measured and compared to the spectra obtained by subtraction of the spectra of dry barium or strontium nitrate from the spectra of the wet crystals. The IR spectra and structure of the double salt K₂Ba(NO₃)₄ were also examined; they were found to differ from those of the components. The results of X-ray diffraction analysis are indicative of the formation of the precipitates with the structure similar to that of the dry salts, with simultaneously occurring changes in the texture of the precipitates formed from concentrated HNO₃. It was suggested that barium and strontium nitrates could form unstable adducts with HNO₃.     

Nucleation studies in supersaturated aqueous solutions of urea and thiourea doped with inorganic dopants

Induction periods were measured for various supersaturated aqueous solutions of urea doped separately with NH₄NO₃ and NaNO₃ and thiourea doped separately with NaCl and KCI by the direct vision method. Based on classical theory for homogeneous crystal nucleation various critical nucleation parameters were calculated and the results are reported and discussed. In all the cases, the critical nucleation parameters increased with increase in doping concentration.     

Electron-beam-induced deposition of gold from aqueous solutions

Focused electron-beam-induced deposition (EBID) using bulk liquid precursors is a novel approach to nanofabrication that has shown improvements in purity compared to EBID with gas-phase precursors. Here we report the first EBID of gold using bulk liquid precursors. We study the differences in gold deposited from three different aqueous solutions containing chloroauric acid (HAuCl(4)), sodium tetrachloroaurate (NaAuCl(4)), and the disulfitoaurate complex ([Au(SO(3))(2)](3-)). We also examine the dependence of threshold dose upon precursor concentration and demonstrate high-resolution patterning with a pitch as small as 50 nm. Finally, we show that the purity of gold deposited using these liquid precursors is significantly improved in comparison with deposits from metal-organic gaseous precursors.     

Nucleation of supercooled water on solid surfaces

Heterogeneous nucleation of water was investigated using molecular dynamics simulation. Solid with fcc (111) surface was placed at the bottom of a cell consisting of 864 water molecules. ST2 model with NPT ensemble was used. The pressure and temperature were set to be 0.1 MPa and 275 K, respectively. The interaction between water and the solid was based on the equations proposed by Spohr. Exception was made on the lattice constant which was slightly modified to fit with that for ice structure. The shape of the solid surface was considered. It was found that the only one layer of water molecules was adsorbed in a case of a flat surface, whereas ice nucleation occurred by removing some of the atoms from the surface. Spohr's interaction was also modified so that the dipole moment of water became anti-ferroelectric. It was found that the modification increased the ice growth, further. The effect of lattice constant of solid on nucleation was also investigated. It was found that the variation on lattice constant with a few percent from that of ice was acceptable for nucleation, especially on shrinking side. On expanding side, however, it gave some gaps for water molecules to fit in other than that for ice structure, and it prevented the growth of ice. Hence, a guideline for the selection of ice nucleus material was obtained.     

Removal of As(V) and Cr(VI) from aqueous solutions using solid waste from leather industry

This study evaluated the feasibility of using a solid waste from the leather industry as an adsorbent for removal of Cr(VI) and As(V) from aqueous media. The adsorbent material was characterized by chemical analyses, infrared spectroscopy, and scanning electronic microscopy (SEM) prior to reaction in order to assess its surface properties. Langmuir and Freundlich equations were used for analyzing the experimental data, which showed a better fit to the Langmuir model, thus suggesting a monolayer adsorption process in the surface of the adsorbent. The high amounts of Cr(VI)-133 mg g(-1) and As(V)-26 mg g(-1) adsorbed demonstrates the great potential for using this solid waste from the leather industry as a low-cost alternative to the traditionally used adsorbent materials.     

Adsorption of zinc from aqueous solutions to bentonite

The adsorptive properties of natural and Na-enriched bentonite in zinc rich aqueous environment have been studied. The results show that adsorption behavior of both bentonites was strongly depending on the pH. At low pH values, the mechanisms that govern the adsorption behavior of bentonites are dissolution of crystal structure and competition of the metal ions with the H+. Between pH 4 and 7, the basic mechanism is an ion exchange process. The alkaline and alkaline earth metals located in the exchangeable sites of bentonites are replaced with Zn2+ cations present in the aqueous solution. At higher pH values (i.e. pH 8), formation of zinc hydroxyl species may result either participation to the adsorption or precipitation onto the bentonites. Therefore, a rapid increase in the equilibrium removal of zinc was obtained above pH 7. Increase in the initial metal ion concentration led to the increase in equilibrium adsorption to a certain degree; then, a plateau was obtained at higher concentrations. The rate of zinc removal depends also on the solid concentration of the suspension. Reducing the slurry concentration allows particles to get in the more dispersed form, resulting higher available sorption sites for zinc. As a result, the adsorption performance of Na-enriched bentonite is better than the natural bentonite in all physical and chemical changes. The data were fitted both Langmuir and Freundlich isotherms.     

Removal of phosphate from aqueous solutions by electro-coagulation

The aim of this paper was to investigate the feasibility of the removal of phosphate from aqueous solution by electro-coagulation (EC). The current density (CD) between 2.5 and 10 mA cm(-2) and duration in the limits of 5-20 min were tried for different concentrations. In order to determine optimal operating conditions, the EC process used for the phosphate removal was examined in dependence with the CD, initial concentrations and time. The results of the experimental batch processing showed high effectiveness of the EC method in removing phosphate from aqueous solutions.     

Adsorption of cadmium from aqueous solutions by perlite

The present study examined the use of perlite for the removal of cadmium from aqueous solutions. The effects of pH and contact time on the adsorption process were examined. The optimum pH for adsorption was found to be 6.0. Residual cadmium concentration reached equilibrium in 6h and the rate of cadmium adsorption by perlite was rapid in the first hour of the reaction time. Ho's pseudo-second-order model best described the kinetics of the reaction. Batch adsorption experiments conducted at room temperature (22+/-1 degrees C) showed that the adsorption pattern followed the Freundlich isotherm model. The maximum removal of cadmium obtained from batch studies was 55%. Thomas model was used to describe the adsorption data from column studies. The results generally showed that perlite could be considered as a potential adsorbent for cadmium removal from aqueous solutions.     

Removal of cadmium from aqueous solutions by palygorskite

The sorption characteristics of palygorskite with respect to cadmium were studied with the aim of assessing its use in water purification systems. Using a batch method the influence of time (0.5-48 h), initial Cd concentration (5-150 mg/l or 0.044-1.34 mmol/l), ionic strength ([Ca(II)]: 0-0.1 mol/l), pH (3-7) and mineral dose (1-20 g/l) on Cd removal was evaluated. The sorption of Cd on palygorskite appeared as a fast process, with equilibrium being attained within the first half an hour of interaction. This process could be described by the Langmuir model and gave a maximum Cd sorption of 4.54 mg/g. This sorption capacity value was greatly affected by both pH and ionic strength. Thus, Cd sorption decreased as initial pH lessened, especially at proton concentrations similar to those of Cd, at which competition for variable charge sites (silanol groups on palygorskite surface) appeared to be important. High competing electrolyte concentrations also decreased significantly (close to 60%) the amount of sorbed Cd, suggesting a great contribution of replacement of exchange cations in this metal removal by palygorskite. The increase of mineral dose provoked a Cd removal raise; removal values in the range 85-45% were attained for Cd initial concentrations of 10-150 mg/l (0.089-1.34 mmol/l) when a palygorskite dose of 20 g/l was employed. Column studies were also performed in order to estimate the potential of palygorskite to be used in continuous flow purification systems, showing the effectiveness of this mineral to purify down to the legal limit of waste moderate volumes of Cd-containing solutions with a similar concentration (50mg/l or 0.445 mmol/l) to those mostly found in the upper range of concentrations usually present in industrial wastewaters.     

Removal of nickel from aqueous solutions by sawdust

The main parameters influencing Nickel (II) metal sorption on maple sawdust were: initial metal ion concentration, amount of adsorbent, and pH value of solution. The maximum percent metal removal was attained after about 1h. The greatest increase in the rate of adsorption of metal ions on sawdust was observed for pH changes from 2 to 5. An empirical relationship has been obtained to predict the percentage Nickel (II) removal at any time for known values of sorbent and initial sorbate concentration. The experimental results provided evidence for chelation ion exchange as the major adsorption mechanisms for binding metal ions to the sawdust. The adsorbent can be effectively regenerated using 0.1 M strong acid and reused.     

Recovery of 60Co from EDTA-containing aqueous solutions

The possibility of recovering radioactive cobalt from EDTA-containing aqueous solutions using oxidation (O₃) and photooxidation (UV/H₂O₂) methods was examined. The optimal amounts of reagents ensuring complete decomposition of EDTA and recovery of radioactive cobalt were determined. The procedures developed for oxidative decomposition of EDTA and for recovery of radioactive isotopes from aqueous media were tested with real liquid radioactive solutions.     

Preparation of PLZT powders from several aqueous solutions

Fine, soft agglomerate and chemically homogeneous PLZT powders were prepared from nitrate, chloride and alkoxide precursors. The preparation is based on a coprecipitation method in which the aqueous clear solution of multicomponent systems is reacted with ammonia gas at the liquid surface. As-dried powder characteristics — the microstructure of agglomerates, colour and X-ray diffraction structure — were similar in all cases; however, the properties of calcined powders and of two-stage sintered pellet were affected not only by precursors, but also by postprecipitation processing: (a) washing with organic solvent, (b) drying and ageing, (c) calcining. A novel lattice behaviour, i.e. decomposition and recovery of perovskite structure of calcined powders regardless of precursors, was found over a wide temperature range from room temperature to 1150° C. Transparent ceramics were fabricated by sintering the acetone washed-aged powder derived from TiO(NO₃)₂ precursor.     

Precipitation of magnesium ferrite from MgO-FexO solid solutions

Debye-Scherrer X-ray powder photographs and photomicrographs of samples in the MgO-Fe _x O system have revealed the possible presence of spinodal decomposition.Samples of MgO doped with 4.99 cation % iron were quenched from high temperature into water. Debye-Scherrer photographs taken after quenching revealed the presence of satellite lines located adjacent to the main diffraction lines. These lines can be interpreted as due to a periodic fluctuation in lattice parameter. This periodic fluctuation has been described as one of the distinguishing features of spinodal decomposition.Microstructures of the samples in correlation with electrical conductivity measurements revealed two different types of precipitation depending on sample heat-treatment. The first type reveals MgFe₂O₄ precipitates at grain-boundaries. The second reveals a grainy precipitate network permeating the structure. The grainy network could be due possibly to growth of precipitates following an initial decomposition of the spinodal type.Based on a thesis submitted by S. K. Evans for the Ph.D. degree in ceramic engineering, University of Utah, September 1965.