Powder Synthesis and Treatment

Preparation of Solid State Electrolytes 17.3.7.3. Zircronia-Based Ceramic Electrolytes. 17.3.7.3.1. Powder Synthesis and Treatment. 

As early as 1963 Markl prepared the first representatives of this class of compounds via multi-step synthesis l,l-diphenyl-X -phosphorin 118 ( 1,1-diphenyl-phosphabenzene ) and 1,l-diphenyl-2,3-benzo-X -phosphorin i20 ( 1,1-diphenyl-phospha-naphthalene ). Neither compound could be obtained in crystalline form. Instead, treatment of the crystalline phosphonium salts iiP and 121 with aqueous alkali affords very reactive, air-sensitive yellow or orange powders 118 and 120). Acid treatment leads back to the phosphonium salts. 

Gas phase ceramic synthesis is the subject of several review papers. The treatment here is analogous to that in Magan [1], Friedlander [2], and Pratsinis and Kodas [3] but instead of using the traditional aerosol nomenclature, this chapter uses the nomenclature developed in Chapter 3 on population balances for educational continuity. Each of the gas phase powder synthesis methods is summarized in Table 7.1. The maximum temperatures are also listed. The adiabatic flame temperature is the maximum possible temperature achieved in flame synthesis and will depend on the concentration of reactants in the feed. Powder synthesis in a furnace uses conduction, convection, and radiation, giving a maximum temperature of 2300 K. A plasma is an ionized gas. High velocity electrons remove other electrons from the neutral gas molecules present in the plasma, thereby producing ions and electrons that sustain the plasma. 

The third main step of combustion synthesis technologies is postsynthesis treatment. This step is optional, since not all products require additional processing after synthesis. Powder milling and sieving are used to yield powders with a desired particle size distribution. Annealing at elevated temperatures (800-1200°C) removes residual thermal stress in brittle products. The synthesized materials and articles may also be machined into specified shapes and surface finishes. 

Hydrogen reduction of oxides as well as gasification reactions, solid-state synthesis, and surface treatment processes can be focused on a thin layer of a flat surface and stimulated by non-thermal plasma (Te > To). Similar to the powder-related cold plasma processes, thin-layer processes in cold gas can also be limited by surface temperature. Again, VT nonequilibrium (Te > Tv > To) in this case can provide surface temperatures (Tg) significantly exceeding the gas temperatme (To), because surface VT relaxation is much faster than that in the gas phase. The non-equilibrium heating of a thin layer can be accomplished by... 

During the thermal treatment, behavior of CaP is affected by various factors, like, atmosphere of sintering, ratio of Ca/P, method and conditions of powder synthesis, type and amount of impurities, sample size, particle size, etc. 

FIGURE 8.35 Solubility of PPy-DBSA powder before and after heat treatment under an inert and ambient atmosphere. (From Song, K.T., Synthesis of electrically conducting soluble polypyrrole and its characterization. Ph.D. thesis, 2000. With permission.)... 

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