Precipitation Of Inorganic Salts Research Articles

A new precipitation technique provides evidence for the permeability of Casparian bands to ions in young roots of corn (Zea mays L.) and rice (Oryza sativa L.)

ABSTRACTUsing an insoluble inorganic salt precipitation technique, the permeability of cell walls and especially of endodermal Casparian bands (CBs) for ions was tested in young roots of corn (Zea mays) and rice (Oryza sativa). The test was based on suction of either 100 µm CuSO4 or 200 µm K4[Fe(CN)6] into the root from its medium using a pump (excised roots) or transpirational stream (intact seedlings), and subsequent perfusion of xylem of those root segments with the opposite salt component, which resulted in precipitation of insoluble brown crystals of copper ferrocyanide. Under suction, Cu2+ could cross the endodermis apoplastically in both plant species (although at low rates) developing brown salt precipitates in cell walls of early metaxylem and in the region between CBs and functioning metaxylem vessels. Hence, at least Cu2+ did cross the endodermis dragged along with the water. The results suggested that CBs were not perfect barriers to apoplastic ion fluxes. In contrast, ferrocyanide ions failed to cross the mature endodermis of both corn and rice at detectable amounts. The concentration limit of apoplastic copper was 0.8 µm at a perfusion with 200 µm K4[Fe(CN)6]. Asymmetric development of precipitates suggested that the cation, Cu2+, moved faster than the anion, [Fe(CN)6]4–, through cell walls including CBs. Using Chara cell wall preparations (‘ghosts’) as a model system, it was observed that, different from Cu2+, ferrocyanide ions remained inside wall‐tubes suggesting a substantially lower permeability of the latter which agreed with the finding of an asymmetric development of precipitates. In both corn and rice roots, there was a significant apoplastic flux of ions in regions where laterals penetrated the endodermis. Overall, the results show that the permeability of CBs to ions is not zero. CBs do not represent a perfect barrier for ions, as is usually thought. The permeability of CBs may vary depending on growth conditions which are known to affect the intensity of formation of bands.

Precipitation of Inorganic Salts inside Hollow Micrometer-Sized Polyelectrolyte Shells

Hollow polymer shells formed by layer-by-layer adsorption of oppositely charged polyelectrolytes onto micrometer-sized colloidal particles with subsequent decomposition of the colloidal core were employed as a model system for the study of inorganic crystallization reactions in restricted volumes. The size-selective permeability of shells is used for spatially controlling the precipitation of inorganic salts CaCO3 and BaCO3 into the shell interior. Outside the shells the precipitation was suppressed by the polymers, which are unable to penetrate the shell wall. The precipitates were studied by scanning electron microscopy and atomic force microscopy. The fundamental and applied aspects of research on spatially confined synthesis of inorganic particles are under discussion.

A micro-mechanical model for the rate of aggregation during precipitation from solution

This paper collates approximately 10 years of research by our group on the subject of aggregation during precipitation of inorganic salts from aqueous solutions. We show that by considering the aggregation rate constant to be the product of a collision rate constant and an efficiency we may describe all our results (for one vessel) as a dependence of the efficiency on a dimensionless number, M. The formulation of M arises from our previously published hypothesis that new aggregates must cement themselves together fast enough to withstand the (periodic) hydrodynamic force acting to disrupt them. The new analysis presented here shows that our previous deduction of an internal mass transfer limit in the cementing process is incorrect. We are, by means of this analysis, now able to propose simple, physically based, and apparently general, kinetic equations for aggregation.

Water‐Based Gelcasting of Surface‐Coated Silicon Nitride Powder

A layer of Y2O3–Al2O3, used as a sintering aid, was coated onto the surface of Si3N4 particles by the precipitation of inorganic salts from a water‐based solution containing Al(NO3)3, Y(NO3)3, and urea. The electrokinetic and colloidal characteristics of the Si3N4 powder were changed significantly by the coating layer. As a result, dispersion of the Y2O3–Al2O3‐coated Si3N4 powder was significantly greater than that of the original powder. Furthermore, the Y2O3–Al2O3 coating layer prevented the hydrogen‐gas‐discharging problem that occurred during gelcasting of the original Si3N4 powder because of reaction between the uncoated powder and the basic aqueous solution in suspension. Surface coating, as well as the gelcasting process, significantly improved the microstructure, room‐temperature bending strength, and Weibull modulus of the resulting ceramic bodies.

Seasonal variations of nanofiltration (NF) foulants: identification and control

Studies were conducted to develop correlation between nanofiltration (NF) membrane fouling, feed water quality, and membrane characteristics. The water quality of the three seasonal NF feed samples was characterized by UV, DOC, HPLC-0UVA-DOC, XAD, IC and ICP. Surface charge, specific flux variation at different pH and ionic strengths, molecule weight cut-off (MWCO), and functional groups of the NF 200 membrane surface were determined. The extent of fouling was significantly dependent on water quality, membrane properties, and operational conditions. Higher flux decline was observed at high DOC, high divalent cations, high alkalinity and low temperature. Temperature strongly affected the specific flux and natural organic matter (NOM) rejection. Inorganic salt precipitation was proven by FTIR, X-ray diffraction, X-ray fluorescence and SEM. NOM fouling was observed during long run pilot tests at relatively high temperature while scale fouling was observed at both high and low temperatures. Due to the decrease in solubility of CaCO 3(s) and CaSO 4(s) at high temperature, homogeneous crystallization occurred that led to less flux decline. At low temperature, in spite of the increased solubility, heterogeneous crystallization with NOM absorption was observed. This is due to an increase in pH and formation of nucleus components induced by a temperature decrease. Heterogeneous crystallization caused more significant flux decline than homogeneous crystallization.

Homogeneous (co)precipitation of inorganic salts for synthesis of monodispersed barium titanate particles

Various processes of coprecipitation or crystallization of inorganicsalts of barium and titanium from homogeneous solutions were studiedin this work. In particular, barium hydroxide and barium chloridesalt as well as titanium tetrachloride were used as the startingmaterials for dielectric-tuning homogeneous precipitation in mixedsolvents of isopropanol and water. Hydroxypropylcellulose was used asa steric dispersant. Evaluations of size, shape, and composition ofsynthesized particles were made using scanning electron microscopy,high-temperature X-ray diffractometry, and differential thermalanalysis. Results show that salt concentration, pH, and reaction timeare important in determining the morphology and composition of thefinal powder. The titania particles from dielectric-tuningprecipitation are perfect microspheres with narrow size distribution(near monodispersed), while the particles from barium salts areflake-like, irregular in shape and size. Instead of particlescontaining uniform compositions of barium and titanium compounds,dielectric-tuning coprecipitation yielded powders of two separatedphases, i.e., monodispersed titania microspheres (∼1 μm) coated onbarium chloride salt flakes. Titanium-rich barium titanate wasobtained after calcination of coprecipitated powders. However,preliminary results show that the titania particles obtained bydielectric-tuning precipitation can be hydrothermally converted toBaTiO3 particles that are fully crystallized after calcination above950°C.

One-step sol-gel synthesis of sulfated-zirconia catalysts

Sulfated-zirconia catalysts were prepared by a one-step sol-gel method. Two different protocols were studied in which sulfuric acid is introduced either with the hydrolysis water, or in the zirconium alkoxide solution inn-propanol. After calcination at 923 K these two materials were compared with sulfated-zirconia prepared in two steps by post-sulfation of zirconium hydroxide obtained either by the sol-gel method or by precipitation of inorganic salts. The sulfated-zirconias prepared by the one-step protocol are the most active catalysts for the hydroconversion ofn-hexane. Moreover, the sample prepared by adding sulfuric acid through the hydrolysis water exhibits different textural properties and enhanced activity forn-hexane conversion. These different behaviours cannot be explained by the sulfur content.

Theoretical foundations of a method of precipitation of inorganic salts in water under the influence of a dispersed solid (silica)

A method of precipitation of inorganic salts is proposed based on NMR-spectroscopic investigations and calculations of the structure of water in contact with silica particles, as well as on estimates of the content of metal ions in the water.

Periodic nucleation processes in emulsion polymerization systems

Under special circumstances, Liesegang rings, which are normally associated with the periodic precipitation of inorganic salts, can be observed in emulsion polymerization systems. A quantitative theory is presented for the formation of these polymer rings, based on the numerical solution of coupled reaction-diffusion equations describing their temporal and spatial evolution. The autocatalytic step required for periodic phenomena is identified as arising from the coagulative nucleation mechanism for latex particle formation. In this mechanism, precursor particles, formed by either micellar entry or homogeneous nucleation, coagulate to give latex particles. An initial spatial inhomogeneity in the latex particle concentration grows and induces a depletion region adjacent to it. Another maximum in the latex concentration subsequently appears, separated from the initial one by a region where few latex particles have been nucleated. This type of periodic structure is shown to evolve only if the nucleation rate is an increasing function of time. Such a function is derived from extended Müller-Smoluchowski coagulation kinetics involving precursor and latex particles. Excellent agreement is obtained between the theory, using physically reasonable parameters, and the spacing between the two rings in unstirred emulsion polymerization systems.

Synthesis and Characterization of Monosized Doped TiO2Powders

Monosized spheroidal doped TiO2 particles with an average diameter of 0.3 to 0.7 μm were prepared by the controlled cohydrolysis of mixtures of titanium alkoxide and either niobium or tantalum alkoxide. An inorganic salt precipitation technique was used to put Ba, Cu, or Sr onto the surface of singly doped TiO2 particles. Chemical analyses by several methods demonstrated the reproducibility and reliability of the doping procedures

Precipitation of calcium surfactants. Part 3

The precipitation of calcium surfactants has been shown to proceed by the same mechanisms that apply to the precipitation of inorganic salts. As the rates of precipitation of the latter are retarded by the addition of polyelectrolytes it was expected that they may have a similar effect on surfactant precipitation. In this paper the influence of polyelectrolytes and non-ionic surfactants on the precipitation of calcium dodecyl sulphate were investigated. The precipitation was affected by polymeric additives, only through interaction between the polymers and the precipitating species in solution. No evidence was found for adsorption of the polymers on specific growth sites of the crystals. This may have been a result of the adsorption energy arising mainly from hydrophobic rather than electrostatic forces.Non-ionic surfactants also have no specific effect on the precipitation of calcium surfactants, except through the normal mixed micelle formation. In the absence of mixed micelle formation, non-ionic surfactants have no influence on the precipitation of calcium dodecyl sulphate.