Mixed metallic hydroxides

Mixed metal hydroxides demonstrate the following advantages in drilling ... 

Mixed metal hydroxide drilling muds have been successfully used in horizontal wells in tunneling under rivers, roads, and bays for drilling in fluids for drilling large-diameter holes with coiled tubing and to ream out cemented pipe. 

Mixed metal hydroxides can be prepared from the corresponding chlorides treated with ammonium [276]. Experiments done with various drilling fluids showed that the mixed metal hydroxides system, coupled with propylene glycol [469], caused the least skin damage of the drilling fluids tested. 

Thermally activated mixed metal hydroxides, made from naturally occurring minerals, especially hydrotalcites, may contain small or trace amounts of metal impurities besides the magnesium and aluminum components, which are particularly useful for activation [946]. Mixed hydroxides of bivalent and trivalent metals with a three-dimensional spaced-lattice structure of the garnet type (Ca3Al2[OH]i2) have been described [275,1279]. 

J. L. Burba, III and G. W. Strother. Mixed metal hydroxides for thickening water or hydrophylic fluids. Patent US 4990268,1991. 

C. K. Deem, D. D. Schmidt, and R. A. Molner. Use of MMH (mixed metal hydroxide)/propylene glycol mud for minimization of formation damage in a horizontal well. In Proceedings Volume, number 91-29.4th CADE/CAODC Spring Drilling Conf (Calgary, Canada, 4/10-4/12) Proc, 1991. 

Subsequent heating removes water, converting the mixed-metal hydroxide to the oxide YBa2Cu3Og 5, which is then oxidized to YBa2Cu307 by heating in 02 gas. 

New developments in the use of silicates to improve flame retardancy have arisen from the use of synthetic anionic clays that correspond to the family of lamellar mixed metal hydroxides, commonly named layered double hydroxides (LDH) or hydrotalcite-like compounds.17... 

Just as with hydrothermal synthesis, it is possible to carry out the reaction in non-aqueous media, it is possible to form micelles using alcohol as the polar phase. Using ethanol as the polar phase, it is possible to further tailor the solubihties of metal hydroxides. In the SrFei20i9 hexaferrite, simply coprecipitation strontium and iron to make the mixed metal hydroxide results in a mixed-oxide phase. Sr(OH)2 has such a high solubUity... 

The mechanism for the formation of metal hydroxide surface precipitates is not clearly understood. It is clear that the type of metal ion determines whether metal hydroxide surface precipitates form, and the type of surface precipitate formed (i.e., metal hydroxide or mixed metal hydroxide) is dependent on the sorbent type. The precipitation could be explained by the combination of several processes (Yamaguchi et al., 2001). First, the electric field of the mineral surface attracts metal ions (e.g., Ni) through adsorption, leading to a local supersaturation... 

Hydrotalcites are a class of two-dimensional materials consisting of mixed metal hydroxide sheets interspersed with interlayer anions. It is known in the chemistry of hydrotalcites, that it is difficult to synthesize single-phase copper containing hydrotalcites while copper is an important clement explored for various selective oxidation reactions. However, it is also known that Cu-containing hydrotalcites can be synthesized with an addition of another bivalent metal ion. which by itself can independently form hydrotalcites. 

Challier and Slade [175] reported the synthesis of nanocoinposite materials consisting of polyaniline molecules encapsulated between ultra-thin mixed metal hydroxide sheets which are propped apart by spacers of terephthalate or hexacyanoferrate(II) ions acting as pillars. The layered double hydroxides (LDHs) were prepared by the method of Drezdon [176] which were refluxed with aniline to synthesize aniline intercalated LDHs. In thermo-gravimetric studies, terephthalate/Cu/Cr LDHs as well as hexa-cyanoferrate(lI)/Cu/Al LDHs showed weight losses in two steps attributed to the removal of trapped water and thermal breakdown of the intercalated systems. The former material exhibited somewhat better thermal stability than the latter one. 

Precipitation at increasing pH A simple way to prepare a mixed metallic hydroxide consists of carrying out a potentiometric titration of a mixed metallic salts solution with a l sic solution of an alkali metal hydroxide or alkali metal carbonate (Ross, and Kodama 1967 Hemandez-Moreno, Ulibarri, Rendon, and Serna 1985 Yamaoka, Abe, and Tsuji 1989). We have recently prepared by the addition of a NaOH solution at a constant rate to a mixed solution of ZnCl2 and CrCla, and NiCh and CrCls,... 

Coprecipitation processes tend to be more effective than adsorption processes at removing aqueous heavy metal ions from solution. This could be due to a much larger effective surface area becoming available as various "layers" of the colloid form. Alternatively, it may result from the formation of mixed metal hydroxide complexes (either in solution or as a solid) that exhibit greater adsorption characteristics than those of the individual metal ions. 

Unlike LiCo02 cathode material that is synthesized via a relatively simple solid state process, the LiNii.y.zMnyCoz02 compounds are usually prepared using a multistep process based on the modified mixed-hydroxide approach. The first step is predpitalion of a mixed metal hydroxide, Nii.y.zMuyCoz(OH)2, which is then reacted with a lithium salt in air or oxygen, with the optimum temperature of 800-900 C. The mixed metal hydroxide precipitation (alternatively, mixed metal carbonate) is a crucial step, requiring rigorous parameters control (Fig. 1.4). 

This biosensor was based on the immobilization of PPO within layered double hydroxides (LDHs), which are known to be efficient immobilization matrices for this enzyme [26]. LDHs are synthetic solids with positively charged bracite-like layers of mixed metal hydroxides separated by interlayered hydrated anions. 

Zinc-tin and zinc-boron materials are discussed along with their oxides in the metal oxides section below. Very few other metal or mixed metal hydroxides seem to be used commercially as flame retardants or smoke... 

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