Synthesis Solid State

An old, simple and still widely used method to perform a solid-state reaction is to mix together the powdered reactants, possibly press them into a pellet and then, generally under a controlled atmosphere, heat it in a furnace for prolonged periods. In a number of cases, especially if fine, well mixed, and compacted component powders are used, this treatment will be sufficient to obtain a complete reaction. In other cases more complex treatments will be necessary (for instance to pulverize the partially reacted pellet and to mix, compact and heat it again). 

Intermetallic compound formation may be observed as the result from the diffusion across an interface between the two solids. The transient formation of a liquid phase may aid the synthesis and densification processes. A further aid to the reaction speed and completeness may come from the non-negligible volatility of the component(s). An important factor influencing the feasibility of the reactions between mixed powders is represented by the heat of formation of the desired alloy the reaction will be easier if it is more exothermic. Heat must generally be supplied to start the reaction but then an exothermic reaction can become self-sustaining. Such reactions are also known as combustion synthesis, reactive synthesis, self-propagating high-temperature synthesis. 

Some examples of reactions between solid-state components and of their different uses and applications are reported in a few paragraphs in the following. 

Cluster formation under such conditions is still poorly understood. Thus far, perhaps the most complete glimpse of a cluster nucleation process was granted in the investigation of a lower temperature route to tungsten iodide clusters (55). 

Parent Solids Formed by High-Temperature Solid-State Routes 

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Wallace C H 1998 The rapid solid-state synthesis of group III and transition metal nitrides at ambient and high pressures PhD Dissertation University of California, Los Angeles... 

Table 6.1. Early solid state synthesis studies.

The initial studies on nickel-aluminide synthesis defined a number of important issues in shock-induced solid state synthesis. This work was extended to the influence of powder particle morphology in recent work of Thadhani and... 

Solid-state synthesis, of polyimides, 304 Solid stating technology, 530 Solid waste disposal, 27 Solubility, 3... 

Recently, some hght was shed on these and other compounds as well as on their structures and properties. Today it may be considered that some of the mistakes made earher could have been avoided by the availability of elements or compounds of higher purity, and thereby have prevented the incorporation of unexpected impurities. In this context it is important to note some experimental principles of solid-state synthesis that should be considered In solid-state synthesis, great attention should be always dedicated to the purity of the starting materials, the purity of the container material (and gas atmosphere) used in the reaction, and the control and adjustment of the reaction conditions in order to finally obtain a high yield product... 

Exploratory solid state synthesis seems to be the only workable route to new phases because of a general inability to predict relative phase stabilities and thence structures or compositions , published in K4La6li40s A new Structure Type for Rare-Earth-Metal Cluster Compounds that Contain Discrete Tetrahedral K4l Units. S. Uma, J.D. Corbett, Inorg. Chem. 1999, 38, 3831-3835. 

Traditional solid-state synthesis involves the direct reaction of stoichiometric quantities of pure elements and precursors in the solid state, at relatively high temperatures (ca. 1,000 °C). Briefly, reactants are measured out in a specific ratio, ground together, pressed into a pellet, and heated in order to facilitate interdiffusion and compound formation. The products are often in powdery and multiphase form, and prolonged annealing is necessary in order to manufacture larger crystals and pure end-products. In this manner, thermodynamically stable products under the reaction conditions are obtained, while rational design of desired products is limited, as little, if any, control is possible over the formation of metastable intermediates. ... 

Low-temperature solid-state synthesis is preferred in most cases, where appropriate, for obvious reasons such as energy and cost economy and process safety or for critical concerns regarding the accessibility of compounds that are stable only at low temperatures or non-equilibrium phases, i.e., compounds thermodynamically unstable with respect to the obtained phase (e.g., a ternary instead of binary phase). The use of low-temperature eutectics as solvents for the reactants, hydrothermal growth... 

We have presented spinel synthesis because these systems were studied first and can be understood in a simple manner. Various silicate systems have also been studied and it has been determined that they are more representative of the general case involving solid state synthesis reactions than spinel. Let us examine the following simple silicate reaction ... 

Ester aminolysis, in general, occurs under harsh conditions that require high temperatures and extended reaction periods or the use of strong alkali metal catalysts. An efficient solid state synthesis of amides from nonenolizable esters and amines using KO Bu under the action of microwave irradiation [97] has been described. The reaction of esters with octylamine was extensively studied to identify possible micro-wave effects [98] (Eq. (45) and Tab. 3.20). 

An interesting solid-state synthesis of amides has also been reported in a MW oven that uses potassium tert-butoxidc and easily accessible reagents, nonenolizable esters and amines [83]. 

Solid-state synthesis of /J-nitrostyrenes has been reported by Varma et al. in a process that uses readily available styrene and its substituted derivatives and inexpensive clay-supported nitrate salts, clayfen and clayan (Scheme 6.50) [170], In a simple experiment, admixed styrene with clayfen or clayan is irradiated in a MW oven (-100-110 °C, 3 min) or heated in an oil bath (-100-110 °C, 15 min). For clayan intermittent heating is recommended with 30-s intervals to maintain the temperature below 60-70 °C. Remarkably, the reaction proceeds only in solid state and leads to the formation of polymeric products in organic solvent. 

According to the aggregation state of the component elements and the method selected for starting and performing their reaction, several preparative procedures can be considered, such as melting (direct reaction in the liquid state), solid-state synthesis (mechanical alloying), combustion synthesis, etc. 

S.K. Konovalov, B.M. Bulychev, The P,T-state diagram and solid state synthesis of aluminium hydride, Inorg. Chem. 34 (1995) 172-175. 

Scheme 10.13 Topochemically controlled solid-state synthesis of bisadduct 61 and subsequent cyclopropanation to give [2 4]-hexakisadduct 62. (i) 180°C, 10 min (ii) 40 equiv. diethyl bromomalonate, 40 equiv. DBU.

Crystal Growth and Solid State Synthesis of Oxide Superconductors... 

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