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3 Nanoparticles
Published in Odireleng Martin Ntwaeaborwa, Luminescent Nanomaterials, 2022
S.J. Mofokeng, F.V. Molefe, L.L. Noto, M.S. Dhlamini
The current study focuses on the use of conventional solid-state reaction for preparation of ZnTiO3 nanomaterials for luminescence applications dueto outstanding results accrued [13,15]. Conventional solid-state reaction is a top-down process frequently used to produce complex oxides using simple oxides, carbonates, nitrates, hydroxides, and various metal salts. An overview of conventional solid-state reaction is shown in Fig. 9.5 [28]. Preparation of complexes entails chemical decomposition reactions in which solid reactants are mixed by ball miller prior calcination at higher temperatures to promote interdiffusion of the cations. The final product and rate of solid-state reaction relies on many components such as reaction conditions, structural properties of the reactants, surface area of the solids, reactivity, and thermodynamic free energy [29]. This method is preferred because it is cost effective and large production can be achieved in relatively simple manner.
Synthesis of Perovskite Oxides
Published in Gibin George, Sivasankara Rao Ede, Zhiping Luo, Fundamentals of Perovskite Oxides, 2020
Gibin George, Sivasankara Rao Ede, Zhiping Luo
The traditional method to synthesize perovskite oxides is the solid-state reaction. Perovskite materials are successfully synthesized by heating the salts of the individual elements correspond to the A- and B-sites of the perovskite structure at a high temperature. The precursor materials for solid-state synthesis can be nitrates, carbonates, oxides, and acetates. The term solid-state reaction is used to represent the reactions in which the starting materials and the final products are in solid-state. In a typical solid-state reaction, the solid raw materials at a stoichiometric ratio are thoroughly mixed by making them as fine powders to increase the surface area of the reactants and thereby maximizing the contact between reactants. Pelletizing is also performed in several instances to affirm the contact between reagent particles. The reagents are then heated to an intermediate temperature, where all the volatile part or the reagents are eliminated. At the same time, all the salts are converted to the respective oxides. If the precursors are salts, such as carbonates or nitrates, defects are introduced during their decomposition process prior to the actual reaction. The presence of such defects can increase the rate of reaction in the further processing. Since the reagent crystals have different orientations and each plane of orientations have different reactivity or diffusion rates, the mixing of reagents in every possible way is needed to increase the reaction rate to obtain the final phase.
Synthesis of Solids
Published in Elaine A. Moore, Lesley E. Smart, Solid State Chemistry, 2020
Elaine A. Moore, Lesley E. Smart
Despite its widespread use, the simple ceramic method has several disadvantages. High temperatures are generally required, typically between 500°C and 2000°C, and this requires a large input of energy. This is because the coordination numbers in these ionic binary compounds are high, varying from 4 to 12, depending on the size and charge of the ion, and it takes a lot of energy to overcome the lattice energy so that a cation can leave its position in the lattice and diffuse to a different site. In addition, the phase or compound desired may be unstable or decompose at such high temperatures. Reactions such as this can be very slow; increasing the temperature speeds up the reaction as it increases the diffusion rate of the ions. In general, the solids are not raised to their melting temperatures, so the reaction occurs in the solid state. Solid-state reactions can only take place at the interface of two solids, and once the surface layer has reacted, the reaction continues as the reactants diffuse from the bulk to the interface. Raising the temperature enables the reaction at the interface and the diffusion through the solid to be faster than at room temperatures; a rule of thumb suggests that a temperature of about two-thirds of the melting temperature of the solids gives a reasonable reaction time. Even so, diffusion is often the limiting step. Because of this, it is important that the starting materials are ground to give a small particle size and are very well mixed to maximise the surface contact area and minimize the distance that the reactants have to diffuse.
Synergy of grain boundary and interface diffusion during intermediate compound formation
Published in Philosophical Magazine, 2023
Andriy Gusak, Anastasiia Titova
Recently the formation kinetics of technologically important spinel during the solid-state reaction between ZnO and amorphous was revisited [1]. The process is controlled mainly by interface diffusion (at the stage of nucleation and lateral growth) and later by the grain-boundary diffusion across the growing compound layer. In general, solid-state reactions in nanomaterials, or leading to the formation of nanomaterials, often proceed at comparatively low temperatures when the bulk diffusion is practically frozen, and all mass transport proceeds via grain boundaries or/and interphase interfaces. Often this transport proceeds simultaneously with the migration of these boundaries and interfaces (Cellular Precipitation – CP, Diffusion-Induced Grain-boundary Migration DIGM [2,3], Diffusion-Induced Recrystallisation, Cold Homogenisation [4–6]) and Liquid Film Migration (LFM). Close to such phenomena is a Flux-Driven Ripening of scallops during soldering, when the scallops are growing and coarsening due to fast diffusion along moving liquid channels which appear due to wetting of grain-boundaries between grains of by liquid tin and at practically frozen bulk diffusion within scallops. [7–10]. Even more complicated combination of interface and surface diffusion with simultaneous formation of porous, sponge-like was discussed and modelled in [11]. Also, as suggested first in [12], the lateral grain growth may be induced by the deposition flux during the thin film deposition.
High concentration of vacancies induced by β″ phase formation in Al–Mg–Si alloys
Published in Philosophical Magazine Letters, 2020
Koji Inoue, Ken Takata, Kenji Kazumi, Yasuharu Shirai
Vacancies are among the most fundamental crystal lattice defects and play an extremely important role in many material properties and processes [1,2]. The mechanical properties of materials are sensitive to the presence of vacancies because vacancies interact with dislocations. Diffusion processes, which are responsible for many solid-state reactions, are largely controlled by the migration characteristics of vacancies. Thus, both the static and dynamic properties of vacancies are crucially important in many areas of materials science.