Direct synthesis from component powders

Notice that in the synthesis of these compounds, and of similar phases, a relevant role is certainly played by the high volatility of the pnicogen component. 

Synthesis of sulfo-selenide Chevrel phases Phases ofM Mo x xSex composition (M = Cr, Mn) were prepared by the reaction of stoichiometric mixtures of MoS2 and MoSe2 binary powders with Mo and Cr, or Mn, metallic powders (Mantjour-Billah and Chevrel 2004). The mixtures were pressed into pellets and then (inside an alumina crucible) sealed in evacuated silica tubes. After heating to 800°C and then to 1000°C for 24 hours, two further grinding and annealing (at 1000°C) treatments were performed. Powder X-ray diffraction methods were used to study the solid solutions, the trend of the lattice parameters, etc. 

Direct formation of fj-FeSiy A preparation method for 3-FeSi2 was proposed by Oikawa and Ozaki (2002) to activate the interfacial reaction between Fe and Si powders through a heat process in a sealed ampoule. The mechanism of the reaction process was investigated by using sputtered Fe films on Si substrate (and on sapphire substrates). It was found that Si vapour reacts, in sealed ampoules, with solid Fe, and it is saturated to form e-FeSi. Reaction of FeSi with solid Si then takes place to form FeSi2. It was suggested that this process has a potential interest in the activation of reactions with Si of other refractory metals. 

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Finally, mechanochemical synthesis offers a solvent-free route for the preparation of MOFs by ball milling of starting components [23-28]. Sufficient amounts of pure material for broad-range testing can be easily obtained from this method. Furthermore, the solid-solid reaction typically produces quantitative yields and leads directly to products in powder form. Hence, the materials are ready for various applications without the need for time-consuming treatments. Mechanochemistry as an approach for the synthesis for one-, two-, and three-dimensional metal-organic compounds is currently employed by several groups, who mainly focus on the synthesis of new structures. 

When refractory compounds are produced by the solid-phase synthesis from powder components, the direct contact area of the particles is small and therefore the synthesis is performed at elevated temperatures to enhance the mutual diffrision. If any of the components is transferred to the solution by means of transport reactions, the effective contact area is increased many-fold and the synthesis temperature and time are reduced considerably. This, in turn, allows producing fine particles of refractory compounds. 

In preparing fine particles of inorganic metal oxides, the hydrothermal method consists of three types of processes hydrothermal synthesis, hydrothermal oxidation, and hydrothermal crystallization. Hydrothermal synthesis is used to synthesize mixed oxides from their component oxides or hydroxides. The particles obtained are small, uniform crystallites of 0.3-200 jim in size and dispersed each other. Pressures, temperatures, and mineralizer concentrations control the size and morphology of the particles. In the hydrothermal oxidation method, fme oxide particles can be prepared from metals, alloys, and intermciallic compounds by oxidation with high temperature and pressure solvent, that is, the starting metals are changed into fine oxide powders directly. For example, the solvothermal oxidation of cerium metal in 2-mcthoxycthanol at 473-523 K yields ultrafine ceria particles (ca 2 nm). 

The term pharmaceutical is used for chemicals that are produced for medical purposes. A pharmaceutical is typically composed of one or more active ingredients and many additional components (binder, stabilizers etc). The latter are present to provide a certain form of donation, for example, to integrate the active ingredient into a tablet, a powder, an ointment, or a solution. The active ingredients are produced using chemical synthesis, biological methods (such as fermentation or biocatalysis), or sequences of both. In addition, several active ingredients are obtained directly from plant extraction (e.g., morphine) or from chemical transformations of plant extracts (e.g., codeine). 

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