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Beta-FeOOH particles were synthesized in the presence of Ti(IV), Al(III), and Cr(III) at metal/Fe atomic ratios of 0-0.1 by the following two methods: hydrolysis of aqueous FeCl3 solutions added to the hydrolysis products of these metal ions (subsequent hydrolysis, SH) and hydrolysis of aqueous FeCl3 solutions dissolving these metal ions (combined hydrolysis, CH). On increasing Al/Fe the particle size of the products with AlCl3 by SH method steeply rose at a low Al/Fe and then fell. The similar increase of particle size was seen in SH method with Ti(SO4)2 though the addition of TiCl4 decreased the particle size. In CH method, Ti(IV) markedly impeded the beta-FeOOH formation but Al(III) and Cr(III) showed no influence. The particles prepared by CH and SH methods contained a large amount of Ti(IV) but a few Al(III) and Cr(III). The large spindle-shaped and rod-shaped particles produced by SH method with AlCl3 and Ti(SO4)2 were highly microporous and poorly crystallized, indicating that the particles consist of fine primary particles and the aggregation of fine particles would be promoted by SO4(2-). The different influences of the metal ions on the beta-FeOOH formation were explained by their hydrolysis characteristics.

The poorly crystallized steel rusts have been prepared by hydrolysis of aqueous solutions dissolving Fe(III) and different metal ions such as Ti(IV), Cr(III), Ni(II) and Cu(II) at varied atomic ratios in metal/(Fe+metal). The precipitates formed by the hydrolysis were frozen with liquid N 2 to inhibit crystallization and particle growth. The rusts produced were poorly crystalline and nanosized particles with sizes of 4–10 nm and the rust formed without adding metal ions was assigned to ferrihydrite. The crystallite size decreased from 1.1 to 0.7 nm with increasing the added metal ions. It was shown by extended X-ray fine structure and Mossbauer spectroscopy that the short-range structure of poorly crystalline rusts was disturbed by adding Ti(IV).

The objective of this study was to examine the effects of acetonitrile (AN) on the adsorption behavior of bovine serum albumin (BSA) onto calcium hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 , Hap] materials by combining the ultraviolet (UV) and circular dichroism (CD) measurements of BSA solution. The structural change of BSA molecules with addition of AN was investigated by UV and CD spectroscopy measurements prior to studying adsorption behavior of BSA onto Hap. The CD spectra revealed that the fraction of α-helical content of BSA is remarkably decreased at AN concentrations above 30 vol.%, while β-sheet content is increased. On the other hand, the percentages of random coil and turn contents were decreased only slightly. In addition to this secondary structural change of BSA, the UV spectra suggested that the tertiary structure of protein molecules was also changed by the addition of large amounts of AN; BSA molecules associate to form molecular aggregates at [AN]≥40 vol.%. From the adsorption of BSA onto Hap particles (ca. 30 nm in the particle length) from a water–AN mixed solution, it was revealed that the adsorption behavior of BSA strongly depends on the change of secondary and tertiary structures of BSA by addition of AN. The contraction of BSA molecules at low AN concentrations (10–20 vol.%) gave their small cross-sectional area, providing a large amount of adsorption ( n BSA ), although n BSA was decreased above 30 vol.% AN by enlargement of BSA molecules with solvation and unfolding some α-helix domains. The n BSA values of the systems with AN exhibited a maximum; n BSA was increased at a lower BSA concentration region, although it was decreased at a higher BSA concentration due to self-association. Accompanying the change of n BSA with AN addition, the maxima of electrophoretic mobility (em) of the Hap particles were observed for the systems with AN, although the em of Hap particles was normally increased and saturated with increase in protein coverage for the native structure on the system without AN. On the other hand, because the aggregated BSA molecules could be cooperatively bound, the adsorption of BSA onto the Hap particles with large size (108 nm in the particle length) was enhanced in the presence of AN.

The surface structure and properties of synthetic calcium hydroxyapatite (CaHap) treated with different concentrations of F − ions at neutral pH were investigated by a variety of techniques. The adsorption isotherm of F − ions on CaHap below 0.03 mol dm −3 exhibited the Langmuir type and the saturated amount was estimated to be 1.7 ions nm −2 . This value is lower than 2.88 ions nm −2 of surface OH − number calculated from the crystal structure of CaHap, proving that all the surface OH − ions are not replaced with F − ions. The deuteration of column OH − ions of CaHap was interfered with F − ions replaced for OH − ions in the entrance of OH − columns along c -axis, that is, on a b face. When the samples were treated above 0.04 mol dm −3 , the surface phase of CaHap was dissolved to produce calcium fluorapatite, so that, the deuteration of column OH − ions of CaHap was more promoted than the materials treated below 0.03 mol dm −3 . The surface H 2 PO 4 − and HPO 4 2− ions of CaHap were not replaced with F − ions.

To elucidate the role of anti-corroding alloying metals in weathering steels, the γ-FeOOH and Fe 3 O 4 particles were prepared by air-oxidation of FeSO 4 solutions containing different amount of Ti(IV), Cr(III), Cu(II) and Ni(II). The crystallinity and particle size of γ-FeOOH were lowered by adding Cr(III), Cu(II) and Ni(II) but not influenced by Ti(IV). All the metal ions impeded the crystallization and particle growth of Fe 3 O 4 in a similar manner. The results on γ-FeOOH and Fe 3 O 4 were compared with those on α- and β-FeOOHs previously reported to know the comprehensive effects of metal ions on the formation of rusts.

Rod-like calcium hydroxyapatites (Hap) with micrometer size were produced by supplying Ca(CH 3 COO) 2 and NH 4 H 2 PO 4 solutions into a CH 3 COONH 4 solution by varying their feeding rate at 85±5 °C and pH 7.4±0.2 under nitrogen atmosphere and vigorously stirring. The size of the Hap particles was increased with increase in feeding time ( t F ) of the solutions; with increase in the t F the mean particle width and lengths were increased from 0.02 to 0.47 μm and from 0.12 to 5.21 μm, respectively. All these particles were highly crystallized and exhibited a single crystal and Ca-deficient natures with Ca/P atomic ratios of 1.50–1.59. TG and chemical analyses indicated that the chemical composition of the particles can be expressed to Ca 10− x − y (HPO 4 ) x (PO 4 ) 6− x (OH) 2− x −2 y · n H 2 O. The amount of adsorbed bovine serum albumin (BSA) onto the synthesized micrometer-sized Hap particles is strongly dependent upon their mean particle length ( L p ), while that of lysozyme (LSZ) onto the Hap particles exhibited a minor dependence on the L p . This protein adsorption behavior observed in the present paper provided a definitive evidence that the C sites exposed on ac or bc crystal faces are the adsorption sites for BSA.

The effect of poly(ethylene glycol) (PEG) on the formation of spherical hematite particles from a forced hydrolysis reaction in acidic FeCl3 solution was examined. Spherical hematite particles were precipitated under all of the conditions studied, and the diameters of the particles increased from 400 to 1500 nm (1.5 μm) with increasing PEG concentration. The rate of phase transformation from β-FeOOH to hematite was decreased considerably at higher PEG concentrations as a result of the adsorption of PEG onto both β-FeOOH and primary polynuclear particles. The hematite particles formed with PEG were hydrohematite with a crystal lattice distortion, and they exhibited a polycrystalline nature. The nanoporous hematite particles were produced in the presence of PEG acting as a prominent templating agent. This study indicates that the forced hydolysis reaction in the presence of PEG is a successful and simple route for producing micrometer-scale nanoporous hematite particles.

The effect of polyvinyl alcohol (PVA) on the formation of spherical hematite particles from a forced hydrolysis reaction of acidic FeCl3 solution was examined. With increasing the PVA concentration, the shape of hematite particles was varied from spherical to disk-like by reducing their thickness. TEM and SEM observations clearly revealed that the disk-like hematite particles with average diameters of ca. 500 nm and aspect ratios of about 2 are consisting of aggregated cluster particles with a diameter of ca. 5–10 nm. The hematite particles formed with PVA were hydrohematite with a crystal lattice distortion and exhibited a polycrystalline nature. These particles changed from microporous to mesoporous after elimination of residual PVA molecules adsorbing on cluster particles by evacuating the samples above 300 °C. This result supports the fact that hematite particles produced by the forced hydrolysis reaction are aggregates, as we further revealed recently by using simultaneous temperature programmed desorption, mass spectroscopy and thermogravimetric measurements (Phys. Chem. Chem. Phys., 2001, 3, 2949). It was suggested that the large voids between the cluster particles filled with PVA molecules within the disk-like particles produce mesopores after eliminating the PVA molecules.

Lead–calcium hydroxyapatite solid solutions with different Pb/(Pb+Ca) molar ratios (XPb) were prepared by a wet method using acetamide (AA). The crystal phase and structure of the products depended on the aging period (ta), Pb/(Pb+Ca) molar ratio ([XPb]), and AA concentration ([AA]) of the starting solution. At [AA]=1.6 mol dm−3 and ta=6 days, the large needle-like PbCaHap particles were formed from solutions at [XPb]=0–0.6 and 0.9–1. Under the other AA concentrations and aging periods, pure PbCaHap particles could be obtained in a narrower region of [XPb]; e.g., PbCaHap was formed from solutions at [AA]=0.8 mol dm−3, ta=6 days, and [XPb]= 0–0.1, 0.4–0.5, and 0.9–1.

Fe-Ti mixed oxide nanoparticles with different atomic ratios in Ti/(Fe + Ti) from 0 to 1.0 have been prepared by hydrolysis of aqueous solutions containing Fe(III) and Ti_(IV) ions and a freezing method with liquid N_2, which inhibits crystallization and particle growth. The particles produced were poorly crystalline according to XRD and the product, in the absence of Ti_(IV), was assigned to 2-line ferrihydrite. The products had a high specific surface area of 369-460 m^2 g^(-1), corresponding to a mean particle size of 3-4 nm. These nanosized particles were composed of crystallites of about 1 nm size. It was found by Mossbauer spectroscopy that the particles produced were superparamagnetic and their blocking temperature and inner electric field decreased with increasing Ti_(IV) content.

β-FeOOH particles were synthesized from aqueous FeCl 3 solutions added with different metal ions of Ti(IV), Cr(III), Cu(II) and Ni(II) at varied atomic ratios (metal/Fe) of 0–0.1. Ti(IV) was much more incorporated into the formed particles than Cr(III), Cu(II) and Ni(II). Ti(IV) drastically influences the crystallization and particle growth of β-FeOOH, whereas the other metal ions exhibited no marked effect. This result is available for interpretation of the function of Ti in raising resistance to atmospheric corrosion of steels in chloride environments.

The textures of the rusts formed by exposing various kinds of weathering steel to different environments for 17 years were investigated by the adsorption of N2 and H2O. The specific surface area determined by N2 adsorption decreased with the increase of sodium chloride (NaCl) content in the exposure situations, indicating that the rusts formed at the coastal site were agglomerates of large particles and had large pores. This result is consistent with the fast corrosion rate on the coast. The high surface area obtained by H2O adsorption on the rusts generated on the coast can be attributed to the tunnels of akaganeite (β-FeOOH) crystals accessible to H2O but not to N2.

Well-crystallized needle-like cadmium hydroxyapatite (CdHap) particles were prepared by a two-steps wet method with acetamide (AA). Cd 5 H 2 (PO 4 ) 4 ·4H 2 O, which is a precursor of CdHap, was synthesized from aqueous solutions containing Cd(NO 3 ) 2 ·4H 2 O, (NH 4 ) 2 HPO 4 and AA in the first step and then transformed into CdHap by dissolution and recrystallization in the second step. The crystal phases of the products depended on the synthetic conditions, such as AA concentration of the starting solution in the first step ([AA]) and aging period (t a ), solution pH and solution volume (V s ) in the second step. CdHap particles, obtained at [AA] = 8.0 mol dm −3 , t a = 7 days, pH 9.0 and V s = 500 cm 3 , were agglomerates of needle-like particles with ca. 10 μm width and ca. 100 μm length and had a Cd/P molar ratio of 1.69. The transformation from the precursor into CdHap was completed at [AA] ≥ 6.0 mol dm −3 , t a ≥ 7 days, pH = 9–9.5 and V s ≥ 500 cm 3 .

Electrorefining of aluminium was carried out at 750 °C using bipolar electrode cells with centre holes 2, 10 or 20 mm in diameter. Through the centre holes liquid electrorefined aluminium rises to the electrolyte surface. The bipolar electrode cell consists of graphite cathodes, Al–Cu–Fe–Mn or Al–Cu–Fe–Zn alloy anodes and a BaCl2–NaCl–AlF3–NaF electrolytic melt. The centre hole size of more 20 mm in diameter is required to continuously float up the aluminium electrodeposited onto the electrolyte surface, while the current efficiency of the cell decreases with increase of the centre hole size, from 97% at 2 mm diameter to 92% at 20 mm diameter. Aluminium of 99.97% purity precipitates at the cathode. Iron, manganese and zinc included in the alloy as impurities are hardly deposited and the concentrations of these elements in the deposit are 100, 80 and 170 ppm, respectively. In this process aluminium can be produced with an energy consumption of about 4.9 × 103 kWh(t-Al)−1, which is one-third smaller than that of the Gadeau process.

The deuteration of synthetic calcium hydroxyapatite (CaHap) and the effect of fluoridation on the deuteration were investigated by in situ Fourier transform infrared spectroscopy to elucidate the surface structure of CaHap particles. The deuteration of column OH- ions of CaHap was reduced by the fluoridation, indicating that the deuteration does not happen in the columns of which the entrance is closed with F- ions replacing OH- ions. The 2680-cm-1 band observed on the deuterated CaHap was assigned to the surface OD- ions which react with CO2 molecules. The 2633-cm-1 band due to the column OD- ions was not influenced by CO2 adsorption. The fluoridated CaHap did not give rise to the surface OD- band, because the surface OH- ions were replaced with F-.

The roles of metal (Me) ions (Cu(II) and Cr(III)) in the morphologies and structures of hematite particles, produced from a forced hydrolysis reaction of FeCl3−HCl at various concentrations of metal ions ranging from 0 to 0.8 in the Me/(Fe + Me) atomic ratio (XMe), were investigated by separation of the reaction into two steps: precipitation of β-FeOOH and phase transformation from β-FeOOH to hematite. The metal ions inhibited the particle growth of β-FeOOH at a lower concentration region, while they promoted the particle growth at a higher concentration region with incorporation of these ions into the crystal lattice. The β-FeOOH particles produced with metal ions exhibited high specific surface areas and microporosities. It was suggested that the phase transformation from β-FeOOH to hematite is strongly affected by the metal ions incorporated into β-FeOOH particles but not by those adsorbed on the particle surface.

Synthetic calcium hydroxyapatite (CaHap) particles were modified by ionexchange with Al(III), La(III) and Fe(III) by the coprecipitation and immersion methods. The growth of CaHap particles was observed on substituting with these metal ions by coprecipitation. The exchange ratios of Ca(II) with the metal ions revealed that Fe(III) replaces Ca(II) as hydroxo ions and the substitution with La(III) accompanies OH − -deficiency. In the substitution with immersion the exchange ratios for all the metal ions were less than 1.5 of the theoretical ratio, verifying the exchange with metal hydroxo ions. IR spectra of the CaHap particles substituted with Al(III) by both the methods gave rise to several bands due to surface Al-OH besides the surface P-OH bands, whereas the CaHap substituted with La(III) showed no surface La-OH band. The surface Fe-OH was found on the CaHaps substituted by the coprecipitation but not on those substituted by the immersion.

Competitive and cooperative adsorptions of bovine serum albumin (BSA) and lysozyme (LSZ) on synthetic calcium hydroxyapatite (CaHap) were investigated at 15 °C in deionized distilled water of pH 6 by using a liquid chromatography method. The adsorption rate of LSZ was faster than that of BSA due to its larger diffusion coefficient, though the saturated adsorption amount of LSZ was less than that of BSA. The rates of BSA adsorption onto CaHap did not change by the addition of LSZ, while those of LSZ were considerably reduced by addition of BSA with forming (BSA-−LSZ+) agglomerates in the solution. The cooperative adsorption behavior of LSZ was observed in the presence of lower amounts of BSA due to the preferential adsorption of the larger (BSA-−LSZ+) agglomerates. However, in the case of higher BSA content, the adsorption of LSZ was inhibited by capturing the LSZ molecules in the (BSA-−LSZ+) agglomerates. The similar cooperative adsorption behavior of BSA was also observed on all systems examined in the p...

The effects of chloride ions on the morphology and structure of hematite particles, produced from a forced hydrolysis reaction of acidic Fe(III) solution, were investigated. Spherical hematite particles were precipitated under all conditions employed which changed the molar fraction of coordinative Cl^- to non-coordinative N0_3^- ions to Fe(III) ions in the solutions. The size of the particles was increased with increase in the molar fraction of FeCl_3, FeCl_3/[FeCl_3 + Fe(N0_3)_3 (X_(FeCl_3)) although no remarkable change was observed in varying that of HCl, HCI/(HCl + HNO_3) (X_(HCI)). TEM and XRD measurements suggested that the hematite particles formed at X_(FeCl_3) < 0.2 exhibited a single-crystal nature, although those produced at X_(FeCl_3) > 0.4 are polycrystalline with an enlarged c edge length in a unit cell possessing OH^- ions in the lattice. The rate of phase transformation from Beta-FeOOH to hematite decreased with increase in X_(FeCl_3) and was closely related to the crystal lattice distortion. The results obtained were explained by an aggregation mechanism taking into account the difference in the coordination properties of Cl^- and N0_3^- ions to Fe(III) ions. The hydrolysis reaction of Fe(III) was slowed in the presence of Cl^- by its strong coordination to produce electrically neutral, extremely low molecular weight polynuclear (PN) species, [Fe0_(2/3)(OH)_(4/3)(H_2O)_xCl_(l/3))_p. Therefore, this system gave a large spherical particle through the aggregation of the neutral small PNs with less mutual electrostatic repulsion force. In contrast, N0_3^- ions exhibited a fast hydrolysis reaction owing to their non-coordinative nature and produced positively charged, high molecular weight PNs, [Fe0_(2/3)(OH)_(4/3)(H_20)_X)^(p/3)+_p,resulting in less aggregated small hematite particles owing to their repulsion force. This aggregation mechanism was further confirmed by gas adsorption, TEM and addition of NaCI.

Synthetic calcium hydroxyapatite, Ca_10(PO_4)_6(OH)_2 (CaHap), prepared by a wet method was evacuated at various temperatures up to 900 C and the influence of thermal treatment on the structure of this material was investigated by FTIR, determination of concentration of surface P-OH groups, adsorption of H_2O and heat of mersion in water. The number of surface P-OH groups was 2.6 groups nm^(-2) and the ionic ratio of surface (PO_4)^(2-) - to H_2PO_4 - was 31: 69. The surface P-OH groups were essentially dehydroxylated by outgassing above 400 C to produce surface P-O-P species. The heat of rehydroxylationper one P-O-P group was determined to be 1.43 x 10^(-16) J group^(-1). When outgassed above 600 C, CaHap was rehydrated via the reaction: (1- x)Ca_10(P0_4)_6(OH)_2 + 3xbeta-Ca_3(P0_4)_2 + xH_2O → Ca_l0-x(P_2O_7)_x(P0_4)_6-2x(OH)_2.

The adsorption of myoglobin (MGB) onto various kinds of colloidal synthetic hydroxyapatite[X_10(PO_4)_6(OH)_2, noted CaHap, SrHap and CaSrHap for X = Ca, Sr and Ca + Sr, respectivelyJ particles was investigated at 15 °C in a 1 x 10^(-4) mol dm^(-3) KCl solution of pH 6.0. The adsorption rate of MGB onto CaHap was comparable to that of lysozyme (LSZ) and was faster than that of bovine serum albumin (BSA). This distinction was explained by the difference in the molecular mass of these proteins (MGB: 17800 Da, LSZ: 14600 Da, BSA: 67 200 Da); the diffusion rates of the smaller MGB and LSZ molecules to the CaHap surface are faster than that of the larger BSA. The adsorption isotherms of MGB onto these synthetic hydroxyapatites (Haps) exhibited the Langmuir type and the surface charge of the MGB-covered Haps showed almost constant negative value and was independent of the MGB concentration for all the Haps. The values of the saturated amounts of adsorbed MGB for CaHap were independent of the Ca : PO_4 molar ratio of the materials, supporting less importance of an electrostatic interaction between MGB and Haps because MGB molecules are electrostatically neutral at pH 6. It was presumed that MGB molecules are adsorbed onto phosphate ions exposed on ac and bc crystal faces by the van der Waals attractive force without taking advantage of the electrostatic interaction.

The influence of Ti(IV) on the formation and structure of alpha-FeOOH particles was investigated by characterizing the coprecipitation products of Fe(III) with Ti(IV) at different atomic ratios (Ti/Fe) in the range 0-0.1. The particle width of the products increased as Ti/Fe was increased. At Ti/Fe>0.05 the crystallite size of alpha-FeOOH increased with increase of Ti/Fe while the XRD peaks decreased in intensity. Thermal analysis and Mossbauer spectroscopy showed that the alpha-FeOOH phase diminishes upon doping with Ti(IV) and that less crystalline regions composed of agglomerates of fine particles develop. EXAFS revealed that the doped Ti(IV)disturbs the nearest coordination structure surrounding Fe(III). According to N_2 adsorption, micropores are formed in the particles upon addition of Ti(IV). It is deduced from the obtained results that the addition of Ti(IV) produces double domain particles consisting of an alpha-FeOOH core and a porous poorly crystalline shell.

The oxidation products of Fe (OH)2 formed in the presence of Co2, Cu2 and Cr3 were characterized by various means. Co2 and Cu2 produced pure Fe3O4 by inhibiting the generation of a-FeOOH, whilst Cr3 promoted the a-FeOOH formation and interfered with the Fe3O4 formation. The Fe3O4 particles produced with Co2 exhibited high Fe2 content, electrical conductivity and stability to oxidation. Mossbauer spectroscopy demonstrated that the excess Fe2 replaced for Fe3 in B-sites of Fe3O4. A small quantity of metal Fe formed in addition to Fe3O4 on adding Co2.

Grafting of oleylphosphate (OP) molecules to the surface of calcium hydroxyapatite particles (HAP) was carried out by a coprecipitation method with a Ca(OH)2–H3PO4 system in the presence of disodium oleylphosphate (DSOP). All the particles exhibited a single-crystal nature with rod-like shape and were elongated along c-axis from 36 to 122 nm in particle length with an increase in the concentration of DSOP. It was suggested that 0∼84% of the phosphate ions exposed on the ac or bc faces of the HAP particles are exchanged with phosphate ions of DSOP molecules directing oleyl groups outward. The hydrophobicity of OP-grafted HAP particles was enhanced with an increase in the DSOP concentration. This high surface hydrophobicity was further confirmed by water adsorption experiments. The materials with the surface oleyl groups adsorbed much less water than the HAP particles produced without DSOP.

The adsorption of bovine serum albumin (BSA) and lysozyme (LSZ) to oleyl phosphate(OP)-grafted calcium hydroxyapatite (OP-CaHAP) with different degrees of hydrophobicity, ranging the number of surface oleyl group per unit nm2 (nO) from 0 to 2.60, was investigated. The pronounced effects of the hydrophobic moiety of adsorbent on protein adsorption were observed. The saturated amount of adsorbed BSA (ns) was increased up to nO = 0.6 by an enlargement of hydrophobic interaction between hydrophobic CaHAP particle and proteins. However, ns decreased at nO >/= 1.3 by increasing the electrostatic repulsive force between negatively charged BSA and OP-CaHAP particles. On the other hand, the ns value of LSZ was continuously increased up to nO = 2.0 and saturated by increasing either the hydrophobic interaction or the electrostatic attraction of positively charged LSZ and negatively charged OP-grafted CaHAPs. The BSA adsorption experiment revealed that the effect of positively charged adsorption sites on the exposed ac or bc crystal faces (C-sites) of the CaHAPs is screened by the OP-groups grafted on their particle surfaces. Copyright 1999 Academic Press.

Calcium hydroxyapatite (CaHAP) was prepared by homogeneous precipitation from aqueous solutions in the presence of formamide (FA) and Cl− ions. The structures and compositions of the particles formed under various conditions were examined by various methods. The crystal phase and morphology of the particles depended on the concentrations of the reagents, especially FA, in the starting solutions. Spherical, Ca-deficient CaHAP particles with diameters less than 800 μm were obtained with 3–7 mol/dm3 FA and consisted of needle-like particles growing in a radial manner. Cl− ions contributed to the crystal growth of these CaHAP particles.

Lead hydroxyapatite (PbHAP) particles were prepared by a homogeneous precipitation reaction of Pb(NO 3 ) 2 and (NH 4 ) 2 HPO 4 using acetamide (AA) in aqueous media. The particles obtained under different conditions were examined by various methods, including XRD, FTIR, SEM, ICP, TG-DTA and N 2 adsorption. The crystal phase of the products depended on the concentration of AA ([AA]) and the ageing period (t a ). Large highly crystalline needle-like PbHAP particles were formed by ageing at [AA]=0.4-1.6 mol dm –3 and t a ≥1 day. At [AA]≥3.2 mol dm –3 a mixture of PbHAP and α-Pb 3 (PO 4 ) 2 was generated. The transformation of α-Pb 3 (PO 4 ) 2 to PbHAP in solution at [AA]≥3.2 mol dm –3 was hindered by CH 3 COOH, produced by hydrolysis of AA.

Recently, several fiber-reinforced plastic (FRP) posts have been applied for abutment build up; however, it is still unclear what type of build up is preferable for a funnel-shaped root canal. The purpose of this study was to evaluate the effect of a new abutment build-up method which combined an FRP post and metal core for a funnel-shaped root canal.As the tooth for abutment build up, an epoxy artificial maxillary lateral incisor was used. The artificial tooth was cut in the cervix part and a funnel-shaped root canal was formed in the root. As the materials for abutment build up, a glass fiber-reinforced plastic post, core resin and gold-silver-palladium alloy were used. Abutment build up was performed using the following three methods: 1. Combination of an FRP post and core resin by the direct method (FP); 2. Conventional metal core by casting (MC); 3. Combination of an FRP post, core resin and coronal metal core (FM). In addition, as a control, an artificial tooth prepared for abutment (ET) was used. A destruction test was carried out to measure the destruction strength and observe the destruction aspect.The destruction strength of FP was about 160N, significantly lower than that of MC, FM and ET. The destruction strength of FM showed the highest value of about 240N, but there was no significant difference among those of MC, FM and ET. When observing the specimen after the destruction test, FP, FM and ET were fractured or cracked near the cervix of the tooth, whereas MC was fractured near the center of the root.

The growth of microcrystalline (µc-) Si:H:Cl films was studied using a high-density and low-temperature microwave plasma source and a spoke antenna of a SiH2Cl2–H2 mixture. Spectroscopic ellipsometry and cross-sectional transmission electron microscopy revealed that the µc-Si:H:Cl films with a small volume fraction of void were synthesized from SiH2Cl2 rather than µc-Si:H from SiH4 at a high deposition rate of 20 A/s. These originated from the chemical reactivity of SiHxCly in high-density microwave plasma. The excessive crystallization was suppressed with a small volume fraction of void in SiH2Cl2 plasma compared with that synthesized from SiH4. The fine structure of µc-Si:H:Cl was studied and compared with that of previously studied µc-Si:H synthesized from SiH4 [Jpn. J. Appl. Phys. 38 (1999) 6629].

Colloidal calcium hydroxyapatite (CaHAP) particles were modified with Ni 2+ , Cu 2+ , Co 2+ and Cr 3+ ions by ion-exchange and coprecipitation. The CaHAPs doped with these ions were characterized by various methods including FTIR, XPS, TEM and ICP. The atomic ratio, metal/(Ca+metal), of the surface phase ( X s ) of the particles modified with Ni 2+ and Cu 2+ by coprecipitation was much less than the atomic ratio of the whole particle ( X w ), while X s of the particles modified with Cr 3+ approximated to their X w . In the modification by ion-exchange, X s was larger than X w except for the Ni 2+ -substituted samples where X s was identical to X w . The surface P–OH groups were decreased by cation-exchange of the protons of the P–OH groups with Ni 2+ , Cu 2+ and Co 2+ in both the modification methods. On the other hand, Cr 3+ ions were doped in the surface phase by anion-exchange of the surface phosphate ions with hydrated chromium hydroxide anions.

The surfaces of calcium hydroxyapatite (CaHAP) particles with different Ca/P atomic ratios, synthesized by the precipitation method, were characterized and the adsorption mechanism of CO2 on CaHAP ...

The surface of synthetic calcium hydroxyapatite Ca10(PO4)6(OH)2 (CaHAP) particles was treated by repeated modification with hexamethyldisilazane [(CH3)3Si]2NH (HMDS) in hexane and thermal treatment and the surface of the modified CaHAP was characterized by various means. No remarkable change in XRD patterns or in particle shape by the modification was observed. The width of the CaHAP particles gradually increased with repeating the modification. FTIR results indicated that HMDS reacted with surface P-OH groups of CaHAP to yield surface Si-(CH3)3 groups. The surface of the modified CaHAP was hydrophobic. The surface Si-(CH3)3 groups turned to three kinds of surface Si-OH groups by treating the modified materials at 500 degreesC in air. These formed surface Si-OH groups and the remaining surface P-OH groups reacted with HMDS by repeating the modification, resulted in the increase of the surface Si atoms. The modified material having surface Si-(CH3)3 or Si-OH groups adsorbed much less CO2 than the unmodified one. Copyright 1998 Academic Press.

Calcium alkyl phosphates (CaAP) synthesized by the reactions of Ca(OH)2 with hexyl, octyl and decyl phosphates in aqueous systems were characterized by various means. X-ray diffraction patterns of CaAP showed a strong diffraction peak and two weak ones below 2θ=15°. The d values of these peaks increased in proportion to the carbon number of the alkyl phosphates. The plate-like CaAP particles prepared using hexyl phosphate give rise to lattice patterns with uniform alternating spacings of about 1.3 and about 2.2 nm. When treated at 700°C in air, CaAP transformed into β-Ca2P2O7. The molar ratios Ca/P and alkyl groups/P of CaAP approximated to unity. The chemical formula could be shown as ROPO3Ca·1.7H2O. These facts suggest that CaAP is composed of alternating bimolecular layers of alkyl phosphates and a dicalcium phosphate dihydrate (DCPD)-like phase.

The products of the reactions of ferric oxyhydroxides ( α -, β - and γ -FeOOH) with ferrous species in O 2 -free aqueous systems containing Cl − were characterized by XRD, FTIR and TEM. The reactions using all the FeOOH gave Fe 3 O 4 at 25–100°C and a wide pH range from 3 to 13, accompanying a depletion of FeOOH. The yield of Fe 3 O 4 depended on the molar ratio of OH\Fe(II) in the suspensions, showing a maximum at OH\Fe(II) = 2. The maximum yield of Fe 3 O 4 was in the order of β -FeOOH> γ -FeOOH≫ α -FeOOH. It was revealed that Fe 3 O 4 is formed by the reactions of the dissolved species of Fe(OH) 2 with those of FeOOH.

Influences of various kinds of divalent and trivalent metal ions on the formation, sizes, and pore structures of spherical aluminum phosphate particles were investigated. The addition of metal ions dramatically decreased the size of the spherical particles. A remarkable particle size reduction was observed in the systems doped with trivalent Fe3+ions compared with those doped with divalent Co2+, Zn2+, and Mn2+ions. Incorporation of Fe3+ions into the crystal lattice to give solid solutions with a chemical composition of Al1-xFexPO4·nH2O was observed in the systems doped with trivalent Fe3+ions, though no substitution to yield particles with a chemical composition of AlPO4·nH2O occurred for divalent ions. The divalent metal ions were adsorbed onto primary fine particles to interfere with particle growth. The divalent metal ions residing among the primary particles in secondary spherical aluminum phosphate particles were eliminated by rinsing and produced highly mesoporous materials without altering the particle morphology. A similar mechanism was depicted for particle formation in the presence of Fe3+ions and incorporation into the crystal structure. The spherical aluminum phosphate particles produced with Co2+ions exhibited an electrically neutral surface in the aqueous medium, while those formed with Fe3+ions manifested an acidic surface due to phosphate ions exposed on particle surfaces.

The effects of dimethylformamide (DMF) on morphology and texture of hematite particles produced from a forced hydrolysis reaction of FeCl3–HCl solution were investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), thermogravimetry and differential thermal analysis (TG-DTA), N2and H2O adsorption, and zeta potential measurements. The morphology of synthetic hematite particles was concentration dependent; they changed from large sphere with a diameter of ca. 600 nm to diamond-like shape with increasing DMF concentration in the aging solution accompanying a reduction of their size to 80 nm without incorporation of DMF in the particles. This fact was explained by an acceleration of phase transformation from β–FeOOH to hematite with an elevation of the solution pH owing to dimethylamine produced from a hydrolysis of DMF at an elevated temperature. TEM and XRD suggested that the diamond-like hematite particles formed above 6–10 vol% DMF possess a single-crystal nature. Gas adsorption technique revealed that the particles produced above 10 vol% DMF possess a high thermal stability. TG and FTIR indicated that the hematite particles produced with DMF contained small amounts of OH_ions in the lattice though they provided a single-crystal nature.

The effects of dioxane (DX) on morphology and texture of haematite particles produced from a forced hydrolysis reaction of FeCl3–HCl solution were investigated by TEM, XRD, XFS, FTIR, TG-DTA, N2and H2O adsorption, and zeta potential measurements. The spherical shape of haematite particles produced below the DX concentration of 10 vol% (diameters: 600–1000 nm) was changed to cubic for particles produced at more than 12 vol% DX (mean edge lengths: 900–1200 nm). The rod-like β-FeOOH particles were precipitated as cubic particles at the DX concentration ≥28 vol%. TEM and XRD suggested that the haematite particles formed in the presence of DX are polycrystalline with an enlargedcdimension in a unit cell. TG and FTIR indicated that the haematite particles produced with DX are hydrohaematite possessing OH−ions in the lattice. The results obtained in the present study revealed that variation of the polarity of the medium with addition of DX is a determining factor of the particle size and shape rather than the interfacial tension of the medium and the particles.

Particles of δ-FeOOH doped with various divalent metal ions such as Ni(II), Cu(II) and Co(II) were generated by oxidation of Fe(OH)2 containing various amounts of these ions by H2O2. The particle sizes were not influenced by doping Co(II) but reduced by Ni(II) and Cu(II). The t-plot and the pore size distribution obtained from N2 adsorption isotherms showed that micropores develop in the particles doped with Ni(II) and Co(II) on outgassing above 200°C. All the materials with and without doping gave rise to a similar maximum specific surface area of 140–160 m2 g−1 despite their different particle sizes from 0.2 to 2 μm. It was inferred that the thermal decomposition products are agglomerates of thin plate-shaped microcrystals with a constant thickness. The microporous materials doped with Ni(II) and Co(II) in an atomic ratio of 0.333 were ferrimagnetic ferrites.

Calcium hydroxyapatite (CaHAP) particles were prepared by precipitation reactions of Ca(OH)2 and H3PO4 at different pH. Incorporation of CO2 into CaHAP during the preparation was investigated mainly by FTIR spectroscopy. The amount of CO32− ions contained in the formed CaHAP was increased by raising the solution pH. IR bands of the CO32− ions incorporated into CaHAP were assigned by means of CO2 adsorption. The 1414, 1447 and 1500 cm−1 bands were assignable to CO32− ions in OH− sites of the CaHAP crystals and the 1457 and 1550 cm−1 bands to CO32− ions in PO43− sites. This assignment is different from those in the literature. FTIR results demonstrated that the inclusion of CO32− ions in PO43− sites is maximum for CaHAP formed at pH 5.94 and that in OH− sites increases as the solution pH rises.

Fe_3O_4 particles prepared by oxidation of Fe(OH)_2 precipitated from FeCl_2 solutions containing different amounts of Ni^(2+) from 0 to 30 mol% were examined by various means. The thermogravimetry (TG) results show that the addition of Ni^(2+) raised the air-oxidation temperature of Fe_3O_4 particles from ca. 200 to ca. 400°C, which means that the Fe_3O_4 particles were stabilized to air-oxidation by the doped Ni^(2+). Fe^(2+) content of the materials obtained at Ni/(Ni + Fe)>0.1 mol% was significantly greater than the theoretical Fe^(2+) content of Fe_30^4.Fe^(57) Mossbauer spectra indicated that Fe^(3+) ions in B sites of the Ni-doped Fe_3O_4 are exchanged in part by Fe^(2+). The dc electrical conductivity was increased from 10^(-4) to 10^(-2) S cm^(-1) by Ni^(2+) loading.

溶融塩を用いたTiの電解採取や還元製造のための原料塩であるK2TiCl6の合成におけるKClと TiCl4の反応特性を検討した.K2TiCl6の合成反応実験では, 種々の粒径のKCl粒子を用い, 過剰のTiCl4ガスと683Kで接触させた.その結果, 反応速度は反応進行に伴って急速に低下し, 反応は完了前に実質的に停止することが判明した.生成粒子断面のEPMA分析結果から, 反応の停止がK2TiCl6の粒子外殻層形成に起因し, 層厚さが5～6μmに達すると起こることがわかった.さらに, これらの結果が生成物層内のTiCl4ガスの拡散律速を仮定した未反応核モデルにより説明できることを明らかにした.