Brucite, properties

Simple Models. The surface chemical properties of clay minerals may often be interpreted in terms of the surface chemistry of the structural components, that is, sheets of tetrahedral silica, octahedral aluminum oxide (gibbsite) or magnesium hydroxide (brucite). In the discrete site model, the cation exchange framework, held together by lattice or interlayer attraction forces, exposes fixed charges as anionic sites. 

A formal description of a mineral presents all the physical and chemical properties of the species. In particular, distinctive attributes that might facilitate identification are noted, and usually a chemical analysis of the first or type specimen on which the name was originally bestowed is included. As an example, the complete description of the mineral brucite (Mg(OH)2), as it appears in Dana s System of Mineralogy, is presented as Appendix 3. Note the complexity of this chemically simple species and the range of information available. In the section on Habit (meaning shape or morphology) both acicular and fibrous forms are noted. The fibrous variety, which has the same composition as brucite, is commonly encountered (see Fig. I.ID) and is known by a separate name, nemalite. ... 

Natural sources of ATH (Gibbsite extracted from Bauxite) and magnesium hydroxide (Brucite) are available but generally have large particle size as a result of grinding operations and contain significant amounts of impurities. In wire and cable applications, finer particles sizes are utilized for higher FOI values, improved mechanical properties, lower brittleness temperatures, and smoother surface characteristics despite the drawback of increased mixture viscosity.75... 

Although the unit cell of talc was initially reported to be monoclinic [18], further studies have concluded that the unit cell is triclinic [19-21]. The material is composed of a brucite (MgO) sheet between silicon-oxygen layers, as shown in Figure 1. Each layer is electrically neutral and adjacent layers are held together by weak van der Waals forces. The slippery property of talc is the result of these layers sliding over one another. 

It can be obtained by the electrochemical precipitation of NiCNOjJj- water of hydration is an integral part of this compound and is believed to be responsible for the much larger distance between the hydroxide layers when compared to that in jS-Ni(0H)2, which does not contain water and is denoted as the brucite or C6-type structure. Another form of nickel hydroxide, known as the y-modification, can be prepared from concentrated KOH, leading to the incorporation of potassium ions into the lattice. The inclusion of K and other species as well can alter considerably the physicochemical properties of the otherwise pure... 

Brucite, which was named after Archibald Bruce (1777-1818) in 1824, who discovered it in Hoboken, New Jersey, occurs typically as tabular crystals. Less commonly it can occur in acicular, fibrous, and scaly form. Its color can range from white, pale green, gray, gray-blue, and blue. It can also have a transparent, pearly, waxy, or vitreous appearance see Table 2.5, which displays a variety of physical properties of brucite. 

The physical and chemical properties of magnesium oxide are primarily governed by the source of the precursor, that is, derived from magnesite or precipitated from brine or seawater. Other important factors include time and temperature of calcination and the presence of trace impurities. Electron microscope studies have revealed that the precursor particle morphology has a large impact on the morphology of the final MgO particle. It has been shown that when brucite and magnesite crystals are thermally decomposed at low temperatures, pseudomorphs of a size and shape similar to the parent crystal are formed. 

The work of Barnes and Ernst (1963) provides some information on this, because they experimentally determined the position of the brucite-periclase equilibrium not only in pure water but in 5m and 12.5m NaOH solutions. The NaOH does not enter the reaction in any way except to dilute the water, so that we can compare the experimental and theoretical curves, and thus determine the activity of water in 5m and 12.5m NaOH solutions at the P and T values determined by Barnes and Ernst. This comparison is made in Figure 13.8 and Table 13.5, where we see that, as pointed out by Barnes and Ernst, water and NaOH mix in a fairly ideal way under these supercritical conditions, the activity coefficient of water being generally about 0.7 to 0.8. Despite the value of these results, we should point out that if the mixing properties of water-NaOH solutions is the primary interest (it was only one of several goals for Barnes and Ernst), determination of displaced univariant curves is not the most direct way of proceeding. One would normally want to perform experiments on the densities of these solutions, and extract fugacities as described in Chapter 11. This is more easily said than done, however. 

This study deals with the preparation, properties and reactivity of high-surface-area Ni/Mg/Al mixed oxides featuring different Ni g ratios obtained from HT anionic clays. In HT precipitates all cations are present inside the brucite- pe layers, therefore the specific properties of each element may be evidenced without any interfraence due to phase segregation and/or physical dishomogeneity. 

Metallic Ni or Ni compounds are known to effectively catalyze hydrogenation of unsaturated bonds. As described previously, Ni ions can be readily incorporated into the brucite-like layer and well dispersed with various other cations. The calcination of Ni-containing LDHs in a reducing atmosphere, e.g., H2 or CO, leads to the reduction of Ni ions with the simultaneous formation of LDO. Such prepared hydrogenation catalysts feature fine Ni particles divided by the spinel and/or mixed oxides (LDO). Moreover, the catalytic performance can be optimized by varying the compositions, i.e., the properties of the accompanied spinel and/or mixed oxides (LDO), as shown later. 

Zhang etalP showed that the surface covered with dendritic gold clusters, which was formed by electrochemical deposition onto indium tin oxide (ITO) electrode modified with a polyelectrolyte multilayer, showed superhydrophobic properties after further deposition of an -dodecanethiol monolayer. The chemical bath deposition (CBD) has also been used to make nanostrucmred surfaces, thus, Hosono etaL fabricated a nanopin film of brucite-type cobalt hydroxide (BCH) and achieved a contact angle of 178° after further modification of lauric acid (LA). Shi et al7 described the use of galvanic cell reaction as a facile method to chemically deposit Ag nanostructures... 

As described previously, the cations in LDHs are evenly distributed in the brucite-like layers. Thus, in principle, the catalytic activity of LDHs can be well controlled by varying the cation ratio and incorporating diffCTent cations. Catalytically active constituents of LDH include the hydroxide groups and the metal ions themselves, especially if these are redox active. The introduction of catalytically active anions, such as polyoxometalates (ROMs), can further modify the properties of LDHs. Thermal decomposition (calcination) of LDH gives mixed basic oxides of high surface area and catalytic activity. Finally, the reduction of LDH can give rise to finely divided catalytically active metal and to the prospect of metal/base bifunctional catalyst. 

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