Akaganeite, β-FeOOH, a natural ferric oxyhydroxide mineral, has a structure containing tunnel-like cavities in which chloride ions reside. Analogs of akaganeite in which carbonate or sulfate groups replace the chloride ions have also been synthesized. Both akaganeite and its substituted analogs are known to be precursors for active hydrocracking catalysts. We present powder X-ray diffraction (XRD) and X-ray absorption fine-structure spectroscopy (XAFS) data confirming the synthesis of new ferric oxyhydroxides having structures similar to akaganeite, but contain molybdate and tungstate oxy-anions. We also present a new hydrothermal method to prepare this family of materials.

The technique of precipitation from homogeneous solutions was used in this study to simulate the formation of iron(III) hydroxides under conditions similar to those at the redox boundary in natural waters. The technique allowed the precipitation of iron(III) hydroxides to occur when the precipitant iron(III) was slowly generated by the oxygenation of iron(II) and subsequently hydrolyzed. During the precipitation, no pH heterogeneity occurred locally as it was usually observed in the conventional preparation of iron(III) hydroxides in the laboratory. Thus, the rapid hydrolysis of ferric ions and the subsequent polymerization of iron(III) hydroxides were effectively prevented. The iron(III) precipitates formed in this way are more representative of the iron(III) particles occurring at the redox boundary in natural waters than those formed by the conventional procedure in the laboratory. The effect of solutes (e.g., H4SiO4) on the structure, size and shape of the iron(llI) hydroxides formed has also be studied.

A method for the preparation of aminosilane coated, chemically stable, agglomerate-free superparamagnetic iron oxide nanoparticles (ferrites, e.g. Fe3O4 and γ-Fe2O3) has been developed. These nanocomposite particles posess core-shell structure. The well crystallized core particles are prepared by precipitation from aqueous salt solutions (primary particle size 10 nm). The surface modification of the weakly agglomerated core particles with aminosilane (e.g. γ-aminopropyl- triethoxysilane) leads to deagglomerated particles, covered by a thin polymerized aminosilane shell. A strong dependency of the particle/agglomerate size on the silane/iron oxideratio as well as on the disintegration time was found. A ratio of aminosilane to iron oxide of 0.8 (weight ratio) and a disintegration time of 72h result in overall particle sizes in the range of 10–15 nm. After surface modification, aminogroups are present on the particle surface (IEP of 9.5). The particles show superparamagnetic behaviour (saturation magnetization 68 EMU/g) and aqueous suspensions are stable against agglomeration. A desorption of the coating in aqueous suspensions (pH 3 to 11) is not observed.

To characterize particle size/magnetic property relationships, 9 to 50 nm in diameter barium hexaferrite, BaFe12O19 (BHF), particles were prepared using a new synthesis route. By replacing the conventional 50 to 100 nm particles of goethite with nanocrystalline goethite produced via the microwave anneal method of Knight and Sylva [1], nanocrystalline BHF was synthesized using the hydrothermal method. Evolution of particle size and morphology with respect to concentration and heat treatment time is reported. Hysteresis properties, including coercivity (0.2 – 1.0 kOe), magnetization saturation (0.1 – 33.4 emu/g), and magnetization remanence (0.004 – 22.5 emu/g) are discussed as a function of particle size. The magnetization saturation and remanence of the 7 nm particles is nearly zero, suggesting the superparamagnetic threshold size for BHF is around this size. In addition, the equilibrium morphology of BHF crystals was calculated to be truncated hexagonal prisms which was verified by experiment, and the isoelectric point, pH of 4.1, was measured for 18 nm BHF particles.

Monodisperse hematite cubes about 30nm in size have been prepared by aging a refluxing acidified aqueous solution of FeCl3 in an open vessel. The as grown nano cubes were determined to be single crystalline hematite in perfect cubic shapes using transmission electron microscope and electron diffraction. The nano cube is one of the equilibrium shapes of hematite, which is resumed to be formed by preferential growth in certain crystallographic directions through the species diffusion in the aqueous solutions.

Some self-assembly prototypes have been observed, such as the short range ordered buildup consisting of several brick-like hematite nano cubes and the nano box consisted of square plates of hematite nanocrystals. The drive force for the formation of the above assemblies is assumed to be the unique magnetic feature of the single crystalline hematite nano cubes.

The perfect shape and the self-assembly feature give a possibility to fabricate bulk ceramics orderly assembled using hematite nano cubes.

Hydroxyapatite (HA), specifically, calcium hydroxyapatite, is the main inorganic compound of human bone and teeth. The utilization of synthetic powders of this material in dental and medical implants has increased in the recent days.

In this paper, synthetic hydroxyapatite powder was prepared by a precipitation method, compacted and sintered at 800, 900, 1000, 1100, 1200 and 1300° C. The powder and its ceramics were analysed by X-ray diffraction, infra-red spectroscopy and scanning electron microscopy. The influence of experimental conditions on the microstructure and densification is discussed.

Some measurements of the hydroxyapatite ceramics obtained in this work were compared with those of the hydroxyapatite ceramics produced from a commercial powder. It was shown that calcium hydroxyapatite is probably the only phase present for the precipitated samples sintered below 1100° C.

BaxSr1-xTiO3 (BST) thin films and powders were processed below 100°C by hydrolyzing Ti metal-organic precursors and TiO2 powder in alkaline Ba/Sr containing aqueous solutions. Film and powder stoichiometries were examined by x-ray diffraction (XRD), and powder stoichiometries were measured by wavelength dispersive spectroscopy (WDS). Both XRD and WDS results showed that Sr cations were more readily incorporated in BST than Ba cations. A thermodynamic model is introduced to predict BST stoichiometry for pH and solution composition. The model is demonstrated for carbonates that also form hydrothermally with Ba and Sr in solid solution, showing good agreement with experimentally measured stoichiometries and confirming a higher reactivity of the Sr cation.

To improve the processing of silicon nitride, boehmite and yttrium oxide were coated on silicon nitride particles by an aqueous sol-gel method. It is shown that boehmite and Y2O3 can be coated on Si3N4 particles from aqueous solutions. However, the Y2O3 coating is not as complete as boehmite coating. The coating of a yttria coating followed by a boehmite coating was attempted and the TEM showed a coating twice as thick as the Y2O3 or AlOOH coating. Hydrothermal treatment of yttrium nitrate hydrous hydroxide results in the formation and growth of Y(OH)3 fibers which can be calcined and transformed into Y2O3 fibers at 500°C.

Gas-aerosol chemical reactions between dilute SO2 and alkali-metal hydroxides have been explored using elastic and inelastic (Raman) light scattering. Single charged particles of NaOH, KOH, and Ca(OH)2 were levitated electrodynamically in a reaction chamber and exposed to humid nitrogen. Particles that were not water soluble remained crystalline while water soluble compounds deliquesced into solution microdroplets. The resulting solids or solutions were reacted with dilute SO2 in humid N2. Elastic scattering measurements and Raman spectra were taken during the gas-aerosol reactions, and results indicate that reaction products and sorbent utilization are highly dependent on the water content of the particle.

Microporous nickel oxides consisting of nano-sized particles have been utilized as active electrode materials for ultracapacitors. Both the physical adsorption of ions near the charged surface of these particles and surface oxidation/reduction reactions play a role in the capacitative charge storing mechanism. These are therefore appropriately referred to as pseudo-capacitors since they rely on mechanisms in addition to double layer charging in order to store energy. In this study, it has been shown that surface hydration contributes to the formation of an initial compound which participates in the electrochemical reactions of ultracapacitors. The specific capacitance of this material is ranging from 60 to 120 F/g depending upon the types of electrolyte solution used in the ultracapacitor.

We have studied the co-adsorption of Cu(II) and an organic ligand, 2,2′-bipyridine (bipy), on amorphous silica (am-SiO2) and γ-Al2O3 (γ-alumina). This study focuses on two fundamental questions: (1) how bipy affects the macroscopic uptake behavior and molecular-scale characteristics of Cu(II) sorption complexes formed on each oxide; and (2) how and why the uptake behavior and the characteristics of Cu(II) sorption complexes differ for the two oxides. Solution uptake experiments and X-ray Absorption Fine Structure (XAFS) spectroscopy were used to answer these questions.

In the absence of bipy and at a surface loading of approximately 0.05 μM/m2, Cu(II) adsorbs predominantly as a dimeric complex on am-SiO2 surfaces but as a monomeric complex on γ-Al2O3. At low Cu(II) to solid ratio, bipy shifts the pH of Cu(II) sorption on am-SiO2 to lower values, but it shifts the pH of Cu(II) sorption on γ-Al2O3 to higher values. Uptake experiments and XAFS measurements on the wet sorption samples indicate that sorption of aqueous Cu(bipy)2 on γ-Al2O3 displaces one bipy from the aqueous Cu(bipy)2 complex, while sorption on am-SiO2 does not disrupt the complex. More detailed XAFS analysis suggests an innersphere Cu(bipy)1 complex on γ-Al2O3 and a stronger Cu-surface oxygen interaction when Cu(bipy)2 adsorbs on γ-Al2O3 than am-SiO2.

Surface precipitation is a critically important process in many systems of scientific and technological importance, such as modeling the segregation of contaminants from aqueous to solid phases in groundwater and the dispersion of active phases on catalyst supports. XAFS and TEM studies of Co(II) sorbed on Al2O3 indicate clearly that surface precipitates have formed from solutions that are undersaturated with respect to any known bulk solid Co-bearing phase. These studies indicate that the structure of the precipitates is similar to that of Co(OH)2(s), but it is disordered and has a high concentration (about 30%) of Co vacancies. Using the FEFF 6.011 multiple-scattering code, we have been able to model the XANES spectrum of the precipitate phase by making small modifications to the structure of Co(OH)2(s). The formation of this precipitate phase is consistent with the coprecipitation of Co(II) with Al(III) derived from dissolution of the substrate, forming a double hydroxide. The existence of a phase that is less soluble than the Al(OH)3 and Co(OH)2 endmembers was proved by forming a colloidal coprecipitate from a mixture of Al(III) and Co(II) aqueous solutions, at the same pH and concentration as in the sorption samples; this material was shown to have Co-XAFS similar to that of the sorption samples. We conclude, therefore, that the surface precipitation observed in the Co(II)/Al2O3 system is due to the the formation of a ternary hydroxide of Al and Co. Successful quantitative models of metal-ion transport in groundwater should include the possibility of forming ternary and higher order precipitates that include ions derived from sparingly soluble solids. For the impregnation of catalysts, the process of surface coprecipitation will make it more difficult to produce a well dispersed precursor material.

Silver-manganese oxide ores are present in western United States, Mexico, South America, and Sumatra. The amount of silver varies between a few parts per million (ppm) to thousands of ppm. However, these ores are not compatible with conventional metallurgical treatment for the extraction of silver. This research is the study of the nature of silver binding with one model manganese oxide phase, cryptomelane. Cryptomelane is widely present in the United States and in parts of Colorado, with silver-bearing cryptomelane ore bodies containing up to a maximum of 1 wt% of silver. In order to better understand the nature of silver binding in cryptomelane, synthetic samples of cryptomelane were prepared and characterized, and then used for silver sorption experiments. The silver uptake appears to be a function of the solution chemistry conditions, pH and potassium nitrate concentration. The sorption of silver was found to increase with decreasing pH and at a fixed pH value, the sorption density was higher at a lower potassium nitrate concentration. Kinetics and equilibrium sorption data from lithium and sodium nitrate background electrolyte demonstrates three main results: firstly, most of the uptake of silver is compensated by release of potassium; secondly, the exchange for silver with protons and potassium ions is almost stoichiometric; and lastly, the importance of tunnel sites for the sorption reaction in cryptomelane. An ion-exchange model for the uptake of silver onto cryptomelane will also be discussed.

Hydrous metal oxide (HMO) materials are inorganic ion exchangers which have many desirable characteristics for catalyst support applications, including high cation exchange capacity, anion exchange capability, high surface area, ease of adjustment of acidity and basicity, bulk or thin film preparation, and similar chemistry for preparation of various transition metal oxides. Cation exchange capacity is engineered into these materials through the uniform incorporation of alkali cations via manipulation of alkoxide chemistry. Specific examples of the effects of Na stoichiometry and the addition of SiO2 to hydrous titanium oxide (HTO) on ion exchange behavior will be given. Acid titration and cationic metal precursor complex exchange will be used to characterize the ion exchange behavior of these novel materials.

The growth of the passive film on tungsten in phosphate buffer solution has been described in terms of the Point Defect Model (PDM). The steady-state current and passive film thickness have been measured as a function of voltage, with the film thickness being obtained from an analysis of capacitance and reflectance data. The observed data cannot be accounted for by the High Field Model (HFM) in its classical form, but can be understood in terms of the PDM. Diagnostic criteria that have been derived from the PDM were used to identify the majority charge carriers in the passive film. The Point Defect Model was employed, together with Mott- Schottky analysis to explore the crystallographic defect structures of the passive films, whereas their electronic structures have been studied using photoelectrochemical impedance spectroscopy (PEIS). The experimental results demonstrate that these structures are strongly coupled with the vacancies acting as the dopants.

New methods of forming corrosion resistant inorganic coatings on Al and Al alloys are required due to environment and work safety hazards associated with the currently used Cr-based coatings technologies. In this paper we report on certain specific aspects of Al surface film formation that can be exploited to form highly corrosion resistant coatings. The aspects discussed include: formation of hydrotalcite surface films, Li2[Al2 (OH)6]2 CO3nH2O, by exposure to Li-salt solutions, elimination of unwanted Cu compounds that accumulate surface films formed on Cubearing Al alloys, and generation of high corrosion resistance by precipitating transition metal oxides on to alkaline hydrotalcite coated surfaces.

The chemical nature of Si(100) and (111) surfaces during immersion in dilute hydrofluoric acid (HF) solution and water was investigated “in-situ” and in real time using infrared absorption spectroscopy in the multiple internal reflection geometry. We demonstrate that in dilute HF solution, Si surfaces are not perfectly terminated by hydrogen, but are covered in part with hydrogen-associated Si fluorides, such as SiH2(SiF). We find that the hydrogen coverage of the surface during storage in dilute HF solution depends on the HF concentration of the solution. It is shown that rinsing in water following HF treatment leads to complete hydrogen termination of the surface. We also show that hydrogen exchange reaction occurs on the hydrogen-terminated Si surface during storage in water.

Many ancient Chinese bronze mirrors have survived with a patina that leaves the delicate relief surface decorations intact. The microstructure of these ancient mirrors is two-phase and consists of acicular α-phase (Cu-rich) regions encased in a δ-phase (Sn-rich) matrix. At the surface, there is evidence of selective dissolution of the α-phase; the α-phase regions are replaced pseudomorphically by a mineral product with the δ -phase remaining metallic. Electrochemical polarization has been used to drive the copper dealloying process in modern, cast bronze. Synchrotron x-ray diffraction was employed to compare the ancient samples with those that were prepared potentiostatically. Poorly crystallized tin oxide (SnO2) was found in the α - replacement products of both sample types. The corrosion-resistance of the potentiostatically-treated bronze samples was tested by atmospheric exposure. Comparison with exposed, untreated samples indicated that the treatment was protective.

Batch experiments were conducted at varying proton concentrations on a representative tropical soil in order to investigate its dissolution behavior over a 12h period. The release kinetics of Al, Fe, Si and C were investigated over a 2 to 6 pH range. The pH-dependence exhibited a “point of minimum dissolution” at pH ≈ p.z.n.c. Light scattering measurements on supernatant solutions indicated that colloids were dispersed mainly at pH > p.z.n.c. These results suggested a two-pathway dissolution process, with organic matter playing a role in both pathways. High-resolution X-ray diffraction as well as electron spin resonance and diffuse reflectance spectroscopies, were applied to characterize solid-phase transformations in the course of dissolution. With the exception of quartz, all mineralogical phases (kaolinite, and minor phases such as Fe-, Al- and Ti-oxides) remained unchanged or were slightly affected. A significant loss of quartz (about 10% by mass) was observed after a 12h dissolution at pH 2. Minor phases might have played an important role in stabilizing kaolinite, and dissolved silica may have hindered the dissolution of minor phases.

Poly(acrylic acid), poly(vinylsulfonate), and poly(styrene sulfonate) are incorporated between the positively-charged sheets of double hydroxide layers M1-xAlx(OH)2+ (M = Mg, Ca, Co) and Zn1-xM' x(OH)2+ (M' = Al, Cr) to form layered nanocomposites. The resulting nanocomposites contain the LDH sheet structures separated by 7.6 – 17.0 Å, which is sufficient to accommodate polymer bilayers between the LDH sheets.

Phase and morphological changes during thermolysis of the nanocomposites with poly(styrenesulfonate) (PSS) are studied by X-ray powder diffraction, scanning and transmission electron micrography, (SEM and TEM) and thermal analyses. Mg4Al2(OH)12CO3·nH2O and the associated PSS / MgAl-LDH nanocomposites show comparable thermal stabilities: the layered structure is lost above 300 °C with the nucleation of MgO and MgAl2O4 phases at approximately 400 and 800 °C, respectively. The PSS / ZnAl-LDH nanocomposite shows complete oxidative pyrolysis of the polyanion at 500 °C, indicating a catalytic effect of zinc oxide on thermolysis. Crystalline oxide products are obtained at approximately 300 °C lower temperature than from thermolysis of Zn6Al2(OH)16CO3·nH2O. SEM and TEM images show that the thermolysis of LDH carbonates produces dense aggregates containing microcrystalline particles, whereas materials obtained from the PSS / MgAl-LDH nanocomposites exhibit a macroporous framework structure.