Oxides hydrous

Forced hydrolysis of metal salts can be used to prepare colloidal metal 

The idea of separation between a non-hydrated solid and a liquid (Fig. 18.7) must be replaced by a structural or defect gradient related to the presence of protons in the bulk, e.g. 2M-OH instead of M—O-M bonds, inducing microporosity (0.1 nm scale) which is linked to macroporosity (10 pm scale) thus water invades the pores until it becomes part of the lattice and develops particular properties due to hydrogen bonding. Additional water molecules can occupy inter-particle space producing a connected viscous liquid region that permeates the composite solid . A protonation equilibrium exists between the outer particle surface and the interparticle liquid . 

The adsorption and exchange properties of hydrous oxides have been extensively studied the attempts to understand the local structure on the 0.1-1 nm scale, however, are quite recent. Hydrous oxides are known for multivalent metals (Be, Mg, Zn, Fe, Al, Mn, La, Bi, Cr, In, Sb, Si, Sn, Th, Zr), most of them being amorphous - 

Antimonic acid can be obtained, similarly to Zr(HP04)2. nHjO, with different water content and degree of crystallinity. Almost amorphous 

Infrared spectra show that the main kinds of protonic species exist as chain fragments of the H30 (H20) type and isolated H30 /H20 species which are hydrogen bonded to the rigid framework. A smaller contribution consists of protons trapped in the Sb40n network in equilibrium 

---

Matijevi i E 1976 Preparation and oharaoterization of monodispersed metal hydrous oxide sols Prog. Colloid Polym. Sol. 61 24-35... 

Scandium is not an uncommon element, but is difficult to extract. The only oxidation state in its compounds is -I- 3, where it has formally lost the 3d 4s electrons, and it shows virtually no transition characteristics. In fact, its chemistry is very similar to that of aluminium (for example hydrous oxide SC2O3, amphoteric forms a complex [ScFg] chloride SCCI3 hydrolysed by water). 

Metal organic decomposition (MOD) is a synthesis technique in which metal-containing organic chemicals react with water in a nonaqueous solvent to produce a metal hydroxide or hydrous oxide, or in special cases, an anhydrous metal oxide (7). MOD techniques can also be used to prepare nonoxide powders (8,9). Powders may require calcination to obtain the desired phase. A major advantage of the MOD method is the control over purity and stoichiometry that can be achieved. Two limitations are atmosphere control (if required) and expense of the chemicals. However, the cost of metal organic chemicals is decreasing with greater use of MOD techniques. 

Fluorozirconate Crystallization. Repeated dissolution and fractional crystallization of potassium hexafluorozirconate was the method first used to separate hafnium and zirconium (15), potassium fluorohafnate solubility being higher. This process is used in the Prinieprovsky Chemical Plant in Dnieprodzerzhinsk, Ukraine, to produce hafnium-free zirconium. Hafnium-enriched (about 6%) zirconium hydrous oxide is precipitated from the first-stage mother Hquors, and redissolved in acid to feed ion-exchange columns to obtain pure hafnium (10). 

Hafnium dioxide is formed by ignition of hafnium metal, carbide, tetrachloride, sulfide, boride, nitride, or hydrous oxide. Commercial hafnium oxide, the product of the separation process for zirconium and hafnium, contains 97—99% hafnium oxide. Purer forms, up to 99.99%, are available. 

The hydrous oxide, Hf02 xH20, is precipitated from acidic solutions by addition of ammonium hydroxide or dilute alkaline solutions. However, the hydrous oxide exhibits a limited solubihty in strongly alkaline solutions (65). The existence and relative stabiUty of soluble alkaline peroxy compounds has been demonstrated (66). 

Two pigment production routes ate in commercial use. In the sulfate process, the ore is dissolved in sulfuric acid, the solution is hydrolyzed to precipitate a microcrystalline titanium dioxide, which in turn is grown by a process of calcination at temperatures of ca 900—1000°C. In the chloride process, titanium tetrachloride, formed by chlorinating the ore, is purified by distillation and is then oxidized at ca 1400—1600°C to form crystals of the required size. In both cases, the taw products are finished by coating with a layer of hydrous oxides, typically a mixture of siUca, alumina, etc. 

Adsorption of Metal Ions and Ligands. The sohd—solution interface is of greatest importance in regulating the concentration of aquatic solutes and pollutants. Suspended inorganic and organic particles and biomass, sediments, soils, and minerals, eg, in aquifers and infiltration systems, act as adsorbents. The reactions occurring at interfaces can be described with the help of surface-chemical theories (surface complex formation) (25). The adsorption of polar substances, eg, metal cations, M, anions. A, and weak acids, HA, on hydrous oxide, clay, or organically coated surfaces may be described in terms of surface-coordination reactions ... 

Purification actually starts with the precipitation of the hydrous oxides of iron, alumina, siUca, and tin which carry along arsenic, antimony, and, to some extent, germanium. Lead and silver sulfates coprecipitate but lead is reintroduced into the electrolyte by anode corrosion, as is aluminum from the cathodes and copper by bus-bar corrosion. 

Hydrous Oxides and Hydroxides. Hydroxide addition to aqueous zirconium solutions precipitates a white gel formerly called a hydroxide, but now commonly considered hydrous zirconium oxide hydrate [12164-98-6], 7 0 - 112 0. However, the behavior of this material changes with time and temperature. 

The gels precipitated as described above are not useful in ion-exchange systems because their fine size impedes fluid flow and allows particulate entrainment. Controlled larger-sized particles of zirconium phosphate are obtained by first producing the desired particle size zirconium hydrous oxide by sol—gel techniques or by controlled precipitation of zirconium basic sulfate. These active, very slightly soluble compounds are then slurried in phosphoric acid to produce zirconium bis (monohydrogen phosphate) and subsequently sodium zirconium hydrogen phosphate pentahydrate with the desired hydrauhc characteristics (213,214). 

Common methods of preparation include direct combination of metallic antimony with air or oxygen, roasting of antimony trisulfide, and alkaline hydrolysis of an antimony ttihafide and subsequent dehydration of the resulting hydrous oxide when heated too vigorously in air, some of the Sb(III) is converted to Sb(V). 

Excess NaOH is used to start the reaction and not over 35% of the chromium is added as dichromate. At the end of the reaction, the thiosulfate is removed by filtration and recovered. The hydrous oxide slurry is then acidified to pH 3—4 and washed free of sodium salts. On calcination at 1200—1300°C, a fluffy pigment oxide is obtained, which may be densifted and strengthened by grinding. The shade can be varied by changes in the chromate dichromate ratio, and by additives. 

A dichromate or chromate solution is reduced under pressure to produce a hydrous oxide, which is filtered, washed, and calcined at 1000°C. The calcined oxide is washed to remove sodium chromate, dried, and ground. Sulfur, glucose, sulfite, and reducing gases may be used as reducing agent, and temperatures may reach 210°C and pressures 4—5 MPa (600—700 psi). 

Acceleration modifies the surface layer of palladium nuclei, and stannous and stannic hydrous oxides and oxychlorides. Any acid or alkaline solution in which excess tin is appreciably soluble and catalytic palladium nuclei become exposed may be used. The activation or acceleration step is needed to remove excess tin from the catalyzed surface, which would inhibit electroless plating. This step also exposes the active palladium sites and removes loose palladium that can destabilize the bath. Accelerators can be any acidic or alkaline solution that solubilizes excess tin. 

SnO exists in several modifications. The commonest is the blue-black tetragonal modification formed by the alkaline hydrolysis of Sn salts to the hydrous oxide and subsequent dehydration in the absence of air. The structure features square... 

SnO and hydrous tin(II) oxide are amphoteric, dissolving readily in aqueous acids to give Sn" or its complexes, and in alkalis to give the pyramidal Sn(OH)3 at intermediate values of pH, condensed basic oxide-hydroxide species form, e.g. [(OH)2SnOSn(OH)2] and [Sn3(OH)4] +, etc. Analytically, the hydrous oxide frequently has a composition close to 3Sn0.H20 and an X-ray study shows it to... 

When produced by such dry methods it is frequently unreactive but, if precipitated as the hydrous oxide (or hydroxide ) from aqueous chromium(III) solutions it is amphoteric. It dissolves readily in aqueous acids to give an extensive cationic chemistry based on the [Cr(H20)6] ion, and in alkalis to produce complicated, extensively hydrolysed chromate(III) species ( chromites ). 

Anions with 8, and probably 16-18, Mo atoms also appear to be formed, before increasing acidity suffices to precipitate the hydrous oxide. It is clear from the above equation that the condensation of M0O4 polyhedra to produce these large polyanions requires large quantities of strong acid as the supemumary oxygen atoms are removed in the form of water molecules. Careful... 

Oil and hydrocarbon leaks that return with the condensate coat heat-exchange surfaces and cause FW system fouling and deposit binding. These materials must be removed or they will reenter the boiler to produce nonwettable boiler surfaces, and create serious problems. Oil in condensate should be removed by the use of an inline pre-coat filter. The pre-coating should be either aluminum hydroxide ox ferric hydroxide becaue both these hydrous oxide gels have an affinity for oil. 

Hydrous Oxides and Hydroxides in the Lanthanide and Actinide Series, Final Report June 1, 1969-May 31, 1972. U.S. AEC Report 0R0-3955-3, Oak Ridge Operation Office, Oak Ridge, TN, 1972. 

Electrochemistry of Hydrous Oxide Films Burke, L. D. Lyons, M. E. G. 18... 

---