Basic Suspensions Research Articles

Effects on Addition of Metal Oxides with Low Workfunctions on the Ca-Sr-Ba Oxide Cathodes for VUV Ionizers

There are several manufacturing techniques for developing thermionic cathodes for vacuum ultraviolet(VUV) ionizers. The triple alkaline earth metal emitters(Ca-Sr-Ba) are formulated as efficient and reliable thermo-electron sources with a great many different compositions for the ionizing devices. We prepare two basic suspensions with different compositions: calcium, strontium and barium. After evaluating the electron-emitting performance for europium, gadolinium, and yttrium-based cathodes mixed with these suspensions, we selected the yttrium for its better performance. Next, another transition metal indium and a lanthanide metal neodymium salt is introduced to two base emitters. These final composite metal emitters are coated on the tungsten filament and then activated to the oxide cathodes by an intentionally programmed calcination process under an ultra-high vacuum(~10-6 torr). The performance of electron emission of the cathodes is characterized by their anode currents with respect to the addition of each element, In and Nd, and their concentration of cathodes. Compared to both the base cathodes, the electron emission performance of the cathodes containing indium and neodymium decreases. The anode current of the Nd cathode is more markedly degraded than that with In.

Influence of phenylalanine dispersant on colloidal processing of alumina particles

This paper reports the adsorption behavior of phenylalanine (PHA) onto alumina surfaces in a wide pH range of 3.6–9.5, rheology and packing densities of concentrated alumina suspensions with PHA, and mechanical properties of consolidated alumina compacts with and without PHA. A small amount of PHA was adsorbed on both the positively and negatively charged alumina surfaces and enhanced zeta potential of alumina particles in acidic and basic suspensions. However, the adsorbed and free PHA provided little influence on the dispersibility of primary particles. In the neutral and basic suspensions, the apparent viscosity decreased with addition of PHA because of the formation of weakly coagulated particle clusters, leading to the increase in the packing density for neutral alumina suspensions. During drying of wet alumina compacts, PHA remaining in the alumina compacts relaxed the applied compressive stress. However, added PHA provided no influence on Young׳s moduli and compressive strengths of alumina compacts after calcination.

Anodic aqueous electrophoretic deposition of titanium dioxide using carboxylic acids as dispersing agents

The dispersion of anatase phase TiO 2 powder in aqueous suspensions was investigated by zeta-potential and agglomerate size analysis. The iso-electric point (IEP) of anatase was determined to be at pH 2.8 using monoprotic acids for pH adjustment. In comparison, it was found that the use of carboxylic acids, citric and oxalic, caused a decrease in zeta-potential through the adsorption of negatively charged groups to the particle surfaces. The use of these reagents was shown to enable effective anodic electrophoretic deposition (EPD) of TiO 2 onto graphite substrates at low pH levels with a decreased level of bubble damage in comparison with anodic EPD from basic suspensions. The results obtained demonstrate that the IEP of TiO 2 varies with the type of reagent used for pH adjustment. The low pH level of the IEP and the ability to decrease the zeta-potential through the use of carboxylic acids suggest that the anodic EPD of anatase is more readily facilitated than cathodic EPD.

Photocatalytic degradation of reactive orange 16 dye over Au-doped TiO<SUB align=right>2 in aqueous suspension

The effect of nanosized Au deposits on TiO2 particles for the photocatalytic degradation of reactive orange 16 dye (RO 16) as model compound was investigated. The deposition of Au on TiO2 was carried out by deposition-precipitation (DP). The catalysts were characterised by XRD, TEM, and XPS analyses. The photocatalytic experiments were carried out under a radiation source of low-pressure mercury vapour lamp (6 W) emitting ultraviolet light with maximum intensity at 253.7 nm. The Au deposits significantly enhanced the degradation rate of the dye. The significant enhancement of the Au/TiO2 photocatalyst can be ascribed to the trapping of photogenerated electrons by nano-sized gold particles, which subsequently increase the lifetime of the photogenerated hole for oxidation process and also increased light absorption by crystalline defects. The catalytic activity was found to be dependent on the metal content on TiO2 and showed a maximum at 2 wt% Au. The amount of catalyst was optimised as 2.5 g/L. The photocatalytic activity was strongly dependent on the initial pH of the suspension; pH values in the range 5-10 showed better activity, whereas highly acidic and basic suspensions resulted in a considerable decrease in the activity.

Effect of pH on Carbon Dioxide Hydrate Formation in Mixed Soil Mineral Suspensions

We investigated the effect of pH on CO2 hydrate formation in the presence of phyllosilicate mixtures. Different pH conditions of phyllosilicate suspensions (Na-montmorillonite-rich and phyllosilicate-rich suspensions) with and without NaCl (3.5%) were prepared and controlled by the addition of an acid or base before the dissolution of CO2. The formation of CO2 hydrates was observed in all phyllosilicate suspensions (30 bar and 273.45 K). The temperature-time plot results showed that hydrate formations were suppressed more in acidic mineral suspensions than in basic suspensions. The fastest hydrate induction time can be observed in Na-montmorillonite-rich and phyllosilicate-rich suspensions with and without NaCl at near neutral conditions (pH 6-8), followed by basic (approximately pH 12.0) and acidic (approximately pH 2.0) pHs. Hydrate induction time can be significantly affected by various chemical species forming under different suspension pHs. The distribution of chemical species in each mineral suspension was estimated by a chemical equilibrium model, PHREEOC, and used for the identification of hydrate formation characteristics in the suspension. Particle-particle and particle-water interactions may possibly contribute to the delay of hydrate formation. NaCl was not an efficient inhibitor but a possible promoter for hydrate formation when pH-dependent solid surfaces were present in the system.

Electrical Properties, Rheology and Packing Density of Colloidal Alumina Particles

The mobility of positively and negatively charged alumina particles in concentrated suspensions was analyzed with monitoring the electrical conductivity of the suspensions. The decreased mobility (u) at a lower charge (Q) was due to increased attractive interaction. The increase of volume fraction of moderately charged particles resulted in the decrease of u value because of the increased repulsive interaction with decreased interparticle distance. Too strong repulsive interaction between highly charged particles suppressed the migration of dispersed particles. The mobility of negatively charged particles was lower than that of positively charged particles at a similar Q value because of a stronger effect of chemical bonding between hydrated particle surface. The apparent viscosity of acidic suspensions was lower than that of basic suspensions. This result was also discussed based on three important effects of charge, concentration and nature of hydrated surface of alumina particles. The green densities of alumina compacts consolidated by filtration through gypsum molds were higher for the acidic suspensions than for the basic suspensions.

Adsorption of polyethyleneimine from aqueous solutions on bentonite clays

The adsorption of the cationic polymer, polyethyleneimine (PEI), on bentonite clay particles was investigated. The adsorption rates for the bentonite suspensions are very fast. The high affinity type of interactions between PEI and bentonite samples is attributed to the electrostatic interaction between the clay particles in ambient basic suspensions and the positively charged high molecular weight polyelectrolyte. The adsorption capacity and the influence of the polyelectrolyte on the rheological behavior change with the exchangeable ions, i.e. Na and Ca ions of the bentonite samples.

Reaction between SiC surface and aqueous solutions containing Al ions

The dissolution behavior of α-SiC coated with amorphous SiO 2 films 0.67 ± 0.34 nm thick and the adsorption of Al ions onto SiC surface were studied in 1.0 vol.% solid suspensions containing 0.37 or 3.7 mM of Al(NO 3) 3 at pH 3–10. In the suspension at pH 3–7, the SiO 2 films and H 2O interacted to form soluble H 4SiO 4. The amount of SiO 2 dissolved in the SiC suspensions was dominated by the solubility limit of surface SiO 2 films and increased at pH 10 due to the formation of H 3SiO 4 − and H 2SiO 4 −2 ions. The addition of Al(NO 3) 3 to the neutral and basic suspensions suppressed the dissolution of the SiO 2 films. The neutral SiC surface near the isoelectric point (pH 3.1) adsorbed no Al 3+ ions or just a trace. The negatively charged SiC surface adsorbed 1.13 μmol of Al 3+ ions m −2 at pH 4. In the pH range 5–8, negatively charged SiC particles coexisted with positively charged Al(OH) 3 precipitate was charged negatively at pH 10 because its isoelectric point was pH 9.0 and some Al(OH) 3 dissolved as Al(OH) 4 − ions.

Factors affecting M13 bacteriophage inactivation by methylene blue photosensitization.

We have investigated the factors that affect the virucidal activity of methylene blue (MB) photosensitization. The M13 bacteriophage was more rapidly inactivated at higher temperatures (6 degrees C < 24 degrees C < 38 degrees C). Rate constants for inactivation were 0.072, 0.139 and 0.260 (log10 inactivation)/ (J/cm2) at 6 degrees C, 24 degrees C and 38 degrees C, respectively. On the other hand, dye penetration into virus particles, which was monitored by the fluorescence of YOYO-1, was unchanged with incubation temperature. These data suggest that temperature dependency of M13 inactivation was due to factors other than dye permeability. The pH of the virus suspension also affected the rate of M13 inactivation by MB. The M13 bacteriophage was inactivated faster in basic suspensions and slower in acidic suspensions compared with neutral buffers. These results suggest that temperature and pH are factors that influence the extent of MB photosensitization, and hence, the control of these factors will be necessary for MB phototreatment of plasma products in transfusion medicine.

Improvement of the floc resistance to a centrifugal shear field by polymer adjunction

The hydrodynamic behaviour of suspended colloid aggregates is studied in three centrifugal separators. The experiments outline the effects of the residence-time duration and of the bowl geometry on the aggregate shear thinning. The floc destruction is stated either from the decrease of their average size d t with time, or from the production of microflocs, the statistical diameter of which, d MF , may be compiled from the floc size distribution. They both extend towards equilibrium values: d min, the final average size of the aggregates that depends on the shear rate, and d MF , the indestructible microfloc average diameter that may be considered as a physicochemical character. The equilibrium average sizes of the flocs as well as of the microflocs are reproducible at different geometric scales. Lastly, the kinetics of floc shear thinning might be approximated as a function of d min and d MF as was checked in the centrifugation tests of MnO 2 colloidal suspensions: d(d t) d t =k 2·d MF· 1−: d t d min Three different colloidal suspensions: MnO 2, Ru-Mo and dissolution juices of irradiated fuel are flocculated through hydrosoluble polymer addition. The comparisons of d min and d MF values measured for each initial suspension, then for the flocculated suspensions conclude that flocculant adjunction enables the improvement of the floc toughness to the shear rate, but also modifies their ordering into bigger and indestructible microflocs. Lastly, the obvious effect of the flocculant ionicity, observed on basic suspensions as well as on acid suspensions, claims that the nature of the acting interparticle forces entirely defines the aggregate structure and therefore their cohesion.

Effects of Addition of Polyacrylic Ammonium on Dissolution of α-Alumina in Solutions Containing Mg2+ Ions

Dissolution behavior of high purity α-alumina particles and adsorption of Mg2+ ions onto α-alumina surface were studied in 5vol% solid suspensions containing polyacrylic ammonium (PAA). The amount of alumina dissolved was higher in acidic suspensions than in neutral or basic suspensions. The solubility of alumina in the wide pH range from 2.5 to 9.3 decreased with the addition of PAA. The amount of Mg2+ ions adsorbed onto alumina surface depended on two factors of pH and PAA content of suspensions. Negatively charged alumina surface in the pH range from 7.6 to 9.3 adsorbed Mg2+ ions of 17.5μmol/m2-alumina surface. Positively charged alumina surface adsorbed little Mg2+ ions in acidic suspensions. The amount of Mg2+ ions adsorbed onto alumina surface increased in acidic or neutral suspensions and decreased in basic suspensions by addition of PAA.

Photoassisted hydrogen production from a water-ethanol solution: a comparison of activities of AuTiO 2 and PtTiO 2

A comparison of the photocatalytic activity for H 2 generation between AuTiO 2 and PtTiO 2 has been made. The deposition of Au and Pt was carried out using TiO 2 powders in aqueous suspensions containing HAuCl 4·4H 2O or H 2PtCl 6·6H 2O by deposition-precipitation (DP), impregnation (IMP), photodeposition (FD) and, in the case of Au, by mixing TiO 2 with colloidal gold suspensions (MIX). The main reaction products obtained from the irradiation of an aqueous 5 M C 2H 5OH suspension containing AuTiO 2 or PtTiO 2 were hydrogen, methane, carbon dioxide and acetaldehyde. Small amounts of acetic acid were also detected. The overall activity of Au samples was generally about 30% lower than that of Pt samples. The activity of Au samples strongly depended on the method of preparation and decreased in the order AuTiO 2-FD>AuTiO 2-DP>AuTiO 2-IMP>AuTiO 2-MIX. The activities of the platinum samples were less sensitive to the preparation method and decreased in the order PtTiO 2-FD>PtTiO 2-DP≈PtTiO 2-IMP. Gold and platinum precursors calcined in air at 573 K showed the highest activity towards H 2 generation, followed by a decline in activity with increasing calcination temperature. The H 2 yield was found to be dependent on the metal content on TiO 2 and showed a maximum in the ranges 0.3–1 wt.% Pt and 1–2 wt.% Au. The exposed surface area of gold had only a small influence on the rate of hydrogen generation. On the other hand, the rate of H 2 production was strongly dependent on the initial pH of the suspension. pH values in the range 4–7 gave better yields, whereas highly acidic and basic suspensions resulted in a considerable decrease in the H 2 yield.

Dissolution Behavior of α-Alumina in Solutions Containing Mg&lt;sup&gt;2+&lt;/sup&gt; Ions

Dissolution behavior of high-purity α-alumina particles was studied in acidic solutions (pH 2.6-5.5) and basic solutions (pH 7.2-9.3) containing Mg2+ ions at room temperature. The amount of dissolved α-alumina was dominated by the solubility limit of aluminium hydroxide formed on the surface of α-alumina. The α-alumina in an acidic suspension of 5 vol% solids dissolved to increase pH of the suspension and to produce a supersaturated solution of Al3+ ions in which nucleation and growth of aluminium hydroxide proceeded until the Al3+ concentration reached the solubility limit of aluminium hydroxide. Little adsorption of Mg2+ ions onto the positively charged alumina surface (<0.5μmol/m2) was examined in the acidic suspensions at pH 4.1-4.3. The amount of alumina dissolved in the basic suspensions was less than that in the acidic solutions. Weakly charged negative alumina surface of 1m2 in the basic suspension at pH 7.9 adsorbed Mg2+ ions of 1.9μmol.

Coagulation and dispersion of red mud suspensions

Red mud is a waste stream the Bayer process for alumina production. This paper deals mainly with the influence of pH on the coagulation and dispersion of red mud suspensions. For the purpose of understanding the coagulation and dispersion phenomena of dilute red mud suspensions, the relationship between zeta potential of red mud and pH is measured, and the phenomena in the case of basic suspensions are analyzed by using the experimental data of zeta potential and the DLVO theory. It is shown that the theory agrees fairly well with the experimental results. Furthermore, measurements of the specific volume of sediment, the zeta potential, the mass fraction of less than 2 μm in red mud and the apparent viscosity of some kinds of slurries, show that in order to entirely disperse red mud suspensions, the addition of a dispersing agent to the suspensions is necessary.