Specific features of the phase transformations occurring during the sintering process of the beta-alumina based ceramics and their properties

Abstract

The studies carried out during the last two decades on the sodium-sulfur electrochemical system showed that the ceramics based on sodium-containing beta-alumina are most suitable for producing the cell separators and the solid electrolytes of the storage batteries owing to the exceptionally high conductivity with respect to the sodium ions [i]. In such elements, the solid electrolyte is usually used in the form of long thin-walled ceramic tubes.The material of the solid electrolyte must be absolutely resistant to the aggressive environment at high temperatures and must possess sufficiently high strength characteristics. It was established that the density, the microstructure, the chemical composition, and the phase constitution of the ceramic electrolyte have a significant effect on its ionic conductivity, mechanical properties, and efficiency.

A Review on the Role of Amorphous Aluminum Compounds in Catalysis: Avenues of Investigation and Potential Application in Petrochemistry and Oil Refining

“…Thus, it was shown in [33] (Table 4) that amorphous aluminum hydroxide and basic salt transformed into amorphous alumina at temperatures above 400 • C, which remains stable up to 750 • C. The stability of the amorphous structure of the oxide is due to the presence of residual acid anions (e.g., nitrates) in the samples, which stabilizes it. Some other researchers [33,[41][42][43][44][45][46] identified the transformation of amorphous aluminum compounds into amorphous alumina by differential scanning calorimetry (DSC). An endothermic peak of water was observed in the curve, in the temperature range of 250-500 • C, which was due to the slow dehydration of hydroxide to oxide due to the disordered structure.…”

“…High-purity aluminum hydroxides with a large surface area, which are used for the preparation of catalysts and supports, are synthesized mainly by the expensive but very efficient sol-gel method (alcoholate technology) [41][42][43][44][45][46]. This technology allows for the achievement of high purity boehmite and bayerite.…”

“…Currently, amorphous compounds play an ambiguous role in petrochemistry [4][5][6][7][8][9][10][11][14][15][16][17]19,[26][27][28][29][41][42][43][44][45][46][47][48][49]54,62,[66][67][68][69][70][71][72][73][74][75][76][77][78][79]. They are often considered as an undesirable component of heterogeneous alumina catalysts, since they are inevitably formed during the synthesis methods of aluminum hydroxides (precipitation and alcohol technology) [6,9,11,17,37,45,58,…”

“…They are often considered as an undesirable component of heterogeneous alumina catalysts, since they are inevitably formed during the synthesis methods of aluminum hydroxides (precipitation and alcohol technology) [6,9,11,17,37,45,58,67,68,70]. Amorphous aluminum compounds are gel-like, therefore, it complicates the washing and filtration phases of aluminum hydroxides synthesized by precipitation [11,43]. Moreover, amorphous compounds differ in their thermostability from crystalline hydroxides (different temperatures of phase transformation), which is important for the phase inhomogeneity of the obtained catalyst [7,12,25,32,33].…”

Microstructure Changes of Beta Alumina Sintering at Lower Temperature

“…β'' -phase is more desirable since the phase has higher electrical conductivity than β-phase. Most literatures suggested that β'' -phase was yielded after sintered at temperature as low as 1200 o C [2][3][4][5][6][7][8]. For casual, we name this temperature as β''phase starting temperature.…”