Chemical Preparation Routes and Lowering the Sintering Temperature of Ceramics

Abstract

Chemically and thermally stable ceramics are required for many applications. Many characteristics (electrochemical stability, high thermomechanical properties, etc.) directly or indirectly imply the use of refractory materials. Many devices require the association of different materials with variable melting/decomposition temperatures, which requires their co-firing at a common temperature, far from being the most efficient for materials prepared by conventional routes (materials having the stability lowest temperature determines the maximal firing temperature). We review here the different strategies that can be implemented to lower the sintering temperature by means of chemical preparation routes of oxides, (oxy)carbides, and (oxy)nitrides: wet chemical and sol–gel process, metal-organic precursors, control of heterogeneity and composition, transient liquid phase at the grain boundaries, microwave sintering, etc. Examples are chosen from fibers and ceramic matrix composites (CMCs), (opto-)ferroelectric, electrolytes and electrode materials for energy storage and production devices (beta alumina, ferrites, zirconia, ceria, zirconates, phosphates, and Na superionic conductor (NASICON)) which have specific requirements due to multivalent composition and non-stoichiometry.

Raman spectroscopy potentiality in the study of geopolymers reaction degree

“…Alkali-activated materials (AAMs), including those classified as geopolymers, [1] have been intensively studied and promoted in the last decades as low-carbon binder alternatives to Portland-based cements, in response to growing global concerns over CO 2 emissions from the construction sector. [2][3][4][5][6][7][8][9] AAMs can be generated from a variety of industrial minerals such as kaolinite and feldspars and from industrial solid residues or wastes such as fly ashes, metallurgical slags, and mine wastes. [2,6,10] Thus, their versatility and local adaptability make them a powerful tool in the development of worldwide sustainable construction industry.…”

Sol–gel synthesis and characterization of lithium aluminate (L–A–H) and lithium aluminosilicate (L–A–S–H) gels

“…It combines several advantages, such as high purity, lower sintering temperature, a high degree of homogeneity, small processing time, cost effectiveness, and environment friendliness. 16 This method employs two stages, first the preparation of a gel as precursor, and second the thermal treatment (calcination) of the gel to form the final product, which involves significant structural transformations. Several gel syntheses for preparing LAS glass-ceramics or ceramics have been described in the literature.…”

“…However, the most extensively studied method is the sol‐gel process, which is generally applicable to the production of glasses, glass‐ceramic and ceramics. It combines several advantages, such as high purity, lower sintering temperature, a high degree of homogeneity, small processing time, cost effectiveness, and environment friendliness 16 . This method employs two stages, first the preparation of a gel as precursor, and second the thermal treatment (calcination) of the gel to form the final product, which involves significant structural transformations.…”

“…It is noted that, strictly, a glass‐ceramic is defined as a material whose production involves the controlled crystallization of a parent glass. However, in the context of sol‐gel synthesis routes, also the materials with crystalline phases in an amorphous (glassy) matrix, obtained by heat‐treatment of the precursor gels, have been called glass‐ceramics 16,18,20 . The latter, less restrictive use of the term “glass‐ceramics” will be applied in the present study.…”

Nanoscale Piezoelectric Properties and Phase Separation in Pure and La-Doped BiFeO3 Films Prepared by Sol–Gel Method

“…Most of the materials prepared by sol–gel are have improved properties and broadly used in modern technologies [ 19 , 20 , 21 ]. During the synthesis of multicomponent sol–gel materials, the difficulties associated with different reaction rates for various elements similar to those described in [ 22 , 23 , 24 ] must be solved. In this work, a modified sol–gel process, in which the initial components are dissolved separately to form homogeneous organic solutions, followed by hydrolysis and polycondensation of the reaction products, leading to the formation of sol, and then to the final colloidal phase was used.…”