Kazuhiko Kandori

The preparation of spherical calcium phosphate particles by aging a solution containing CaSO4 and NaH2PO4 at 80 and 100 degrees C in the presence of urea (1 mol/dm(3)) and a surfactant [cetyltrimethylammonium chloride; CTAC] (1.0 x 10(-2) mol/dm(3)) has been investigated, and their properties were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning and transmission electron microscopy (SEM and TEM), N-2 and H2O adsorption measurements, and thermogravimetric-differential thermal analyses (TG-DTA). The size and shape of the particles produced strongly depended on the concentration of the reactants and the aging temperature. Spherical calcium hydroxyapatite particles were precipitated only within a narrow concentration domain of reactants after aging at 100 degrees C for 3 h. The spherical calcium hydroxyapatite particles produced at [CaSO4] = 2.0 x 10(-3) mol/dm(3) and [NaH2PO4] = 7.9 x 10(-4) mol/dm(3) were agglomerates of small platelet particles and were B-type carbonate hydroxyapatite in which 4.8 wt % of CO32- ions are substituted for PO43- ions. The results of chemical analysis and TG identified the formula of the particles as Ca8.5Na1.5(PO4)(5.4)(CO3)(0.8)(OH)(0.7).1.2H(2)O. The texture and crystallinity of the spherical calcium hydroxyapatite particles were sustained up to 1000 degrees C, and the particles showed the selective adsorption of H2O molecules. This selective adsorption was more pronounced after calcining the samples in air.

Examination was made of the effects of size and shape of the particles of four iron oxides, α-FeOOH, β-FeOOH, γ-FeOOH and α-Fe₂O₃, on the soiling of and their removal from a textile fabric. Nylon taffeta was soiled by an aqueous dispersion of iron oxide particles. The relationship between reflectance of the soiled fabric and particle content was determined. By application of this relationship in conjunction with Rees's equation, cover and association data on the particles on the fabric obtained.<BR>γ-FeOOH which is small in size and thin plate has a high degree of coverage and easy to associate. β-FeOOH which is large in size and rectangular lod has a low degree of coverage and hard to associate. α-Fe₂O₃ which is small in size and octahedron has a high degree of coverage and hard to associate. α-FeOOH which is large in size and needle has a low degree of coverage and easier to associate than the rectangular lod and the octahedron particles. The removal of γ-FeOOH and especially α-FeOOH was more difficult than in the case of α-Fe₂O₃ or β-FeOOH.<BR>It follows from the present results coverage depends on particle size, association depends on particle shape, and removal depends on both size and shape of particle.

Calcium hydroxyapatite (HAP) was prepared by homogeneous precipitation using formamide and acetamide. The particles formed under various conditions were characterized by XRD, FT-IR, TEM, SEM, ICP, TG-DTA and N2 adsorption. The crystallinity and morphology of the products depended on the kind and concentration of amides and the ageing time. The large rod-like well crystallized HAP particles were obtained in the presence of acetamide. Acetamide hydrolysed more slowly than formamide, forming a smaller quantity of nuclei resulting in larger HAP particles. However, the excess acetamide interfered with the formation of HAP.

The adsorption of N2, H2O, CH3OH, CCl4, C6H6, and C6H5Cl on microporous hematite with well-defined slit-shaped pores of a width of 0.8 nm has been measured at relative equilibrium pressure from 10(-5) to ca. 0.7. The difference among the initial slopes of the isotherms of these adsorbates can be interpreted based on the adsorption potential in the slit-shaped micropore, the molecular size and polarity of the adsorbates, and the chemisorption. The results of in situ FTIR indicated that the surface Fe-OH groups function as adsorption sites.

The surface and pore structures of the materials resulting on outgassing the colloidal delta-FeOOH particles at different temperatures in the range 50-300-degrees-C have been investigated by a variety of techniques. The FTIR spectrum of the particles outgassed at 100-degrees-C has a weak broad band at 3650 cm-1 and a strong band at 3150 cm-1 which are assigned to the surface and bulk OH groups of delta-FeOOH, respectively. When outgassed above 150-degrees-C three bands appear at 3665, 3635 and 3400 cm-1. The former two bands and the latter one can be assigned to the surface OH groups and the H2O molecules adsorbed in the micropores, respectively. Increasing the outgassing temperature develops the microporosity of the products. The t-plots of the samples treated above 150-degrees-C indicate the formation of micropores with a 0.8 nm width as confirmed by transmission electron microscopy (TEM).

The adsorption isotherms of H2O, CCl4, n-C6H14 and CH3OH on the synthetic gamma-FeOOH particles have been measured at different temperatures from -5 to 35-degrees-C. The isotherms of H2O, CCl4 and n-C6H14 exhibited a step below their monolayer adsorption capacity, while no step appeared in the isotherm of CH3OH. The isosteric heats of adsorption of H2O, CCl4 and n-C6H14 showed a maximum at an adsorption coverage of 0.6, 0.8 and 0.75, respectively. The surface fractal dimension was close to 2, indicating that the gamma-FeOOH surface is homogeneous. It can be concluded that the step-like isotherms reflect the two-dimensional condensation of these molecules on the chemically and geometrically homogeneous surface of gamma-FeOOH.

The effects of silicate and phosphate ions on the formation of alpha- and beta-FeOOH particles were studied. The formation and crystallization of alpha-FeOOH particles were inhibited by both the anions, and their particle size decreased with increasing concentration of the anions added. This inhibition was caused not only by complexing with ferric ions but also by adsorption on the particle surface. For alpha-FeOOH the amorphous particles were formed at a higher concentration of these anions. On the other hand, in the case of beta-FeOOH the effects of both the anions were little, especially for silicate ions. This difference between alpha- and beta-FeOOH particles could be explained by the difference between their preparation pH. The alpha-FeOOH particles prepared in the presence of these anions showed a microporosity.

The formation mechanism of monodispersed water-in-oil (W/O) emulsions by a Shirasu-Porous-Glass (SPG) filter emulsification method was investigated using various kinds of SPG filters of different pore diameters and copolymer-type surfactants. The size of the water droplets in the resulting emulsions and their dispersion stability strongly depended on the interfacial tension between water and oil phases, and stable monodispersed W/O emulsions were produced at an interfacial tension below 1 dyn cm-1. However, the sizes of the water droplets were smaller than the average pore diameters of each SPG filter used. It was suggested from calculations based on the mechanism of the drop volume (DV) method, one of the methods for determining the interfacial tension, that the size of the pore outlets of a filter is an important factor for determining the water droplet size rather than the average pore diameters determined by mercury porosimetry. This prediction was confirmed by the agreement of the outlet sizes of the pores calculated by the DV method and those estimated experimentally by a scanning electron microscope.

The amorphous ferric oxide hydroxide particles, prepared by the forced hydrolysis reaction of ferric chloride solution in the presence of citrate ions, adsorbed H2O molecules much more than CH3OH, CCl4, and N2. This selectivity of H2O adsorption was enhanced dramatically with increasing the concentration of residual citrate ions in these particles. The strong adsorption interaction of the polar adsorptives such as H2O and CH3OH was identified by the large hysteresis loops which do not close until low relative pressure. Consequently, the selective adsorption of H2O could be interpreted by penetration of polar H2O molecules into the amorphous particle and coordination to the citrate-Fe complexes. Such selectivity was varied with changing the content of citrate ions in the particles, the outgassing temperature, and the aging period. It was further found that the micropores with narrow size distribution are simply formed in these amorphous particles by raising the outgassing temperature and/or extending the aging period.

The effects of citrate ions on the formation of beta- and alpha-FeOOH particles were investigated using various techniques. The formation and crystallization of both particles were inhibited by citrate ions, and their particle sizes decreased with increase in the concentration of these ions. Finally, aggregated amorphous particles were formed. The effects of citrate ions appeared to be more significant for beta-FeOOH than for alpha-FeOOH. This difference could be explained by the pH dependence of the affinity of citrate ions to Fe3+ ions. The amorphous beta-FeOOH particles prepared in the presence of &gt; 10 mol% citrate ions selectively adsorbed water molecules.

The preparation of fine and monodispersed water-in-oil (W/O) emulsions by using the Shirasuporous-glass (SPG) filter emulsification technique with a copolymer type surfactant was investigated. W/O emulsions were prepared by two kinds of SPG filter emulsification techniques using batch and continuous methods. Highly monodispersed W/O emulsions were formed from this new technique and there was no difference in the size of the water droplets produced by these two methods. The dispersion stability of W/O emulsions prepared by this technique with a concentration of copolymer type surfactant above 7.5 wt% was extremely good. This remarkable stability was ascribed to the low interfacial tension in addition to the formation of a viscoelastic adsorbed film of copolymer type surfactants on the water droplets.