The Role of the Activator Additives Introduction Method in the Cold Sintering Process of ZnO Ceramics: CSP/SPS Approach

Abstract

The great prospects for introducing the cold sintering process (CSP) into industry determine the importance of finding approaches to reduce the processing time and mechanical pressure required to obtain dense ceramics using CSP. The introducing zinc acetate into the initial ZnO powder of methods, such as impregnation, thermovapor autoclave treatment (TVT), and direct injection of an aqueous solution into a die followed by cold sintering process using a spark plasma sintering unit, was studied. The effect of the introduction methods on the density and grain size of sintered ceramics was analyzed using SEM, dynamic light scattering, IR spectroscopy, and XRD. The impregnation method provides sintered samples with high relative density (over 0.90) and significant grain growth when sintered at 250 °C with a high heating rate of 100 °C/min, under a uniaxial pressure of 80 MPa in a vacuum, and a short isothermic dwell time (5 min). The TVT and aqueous solution direct injection methods showed lower relative densities (0.87 and 0.76, respectively) of CSP ZnO samples. Finally, the development of ideas about the processes occurring in an aqueous medium with CSP and TVT, which are subject to mechanical pressure, is presented.

Ethylenediaminetetraacetic Acid (EDTA) Assisted Single Step Densification of Li2TiO3/PTFE Composites at Ultralow Sintering Temperature to Realize a High-Performance Ku-Band Antenna

“…Although dissolution− precipitation was initially approved as the general mechanism of mass transfer in CSP, it was shown later that dissolution− precipitation is only a surface event, and more complex mechanisms, which are not fully understood, are involved in it. 49 This was demonstrated by cold-sintering of ZnO with crystalline Zn(Ac) 2 •2H 2 O as the transport phase 15 and amorphous calcium phosphate in the presence and absence of transient liquid (water). 50 The possible mechanism of densification of LT-PTFE without any additional solvent can be similar to that of HA, as explained by Shen et al 13 The IR spectrum of LT indicates the presence of adsorbed water.…”

“…In the present study, we could fabricate a 0.5LT-0.5PTFE composite with high relative density (>95%) in a single step by applying a uniaxial pressure of 350 MPa at 130 °C for 30 min without an added liquid phase. Although dissolution–precipitation was initially approved as the general mechanism of mass transfer in CSP, it was shown later that dissolution–precipitation is only a surface event, and more complex mechanisms, which are not fully understood, are involved in it . This was demonstrated by cold-sintering of ZnO with crystalline Zn­(Ac) 2 ·2H 2 O as the transport phase and amorphous calcium phosphate in the presence and absence of transient liquid (water) .…”

Preparation of Densified Fine-Grain High-Frequency MnZn Ferrite Using the Cold Sintering Process

“…Due to the greater chemical potential in the contact area between the particles, the particles diffuse through the liquid phase and precipitate at locations away from the force contact area. During the holding process, the solid transfer accelerates, the supersaturation increases significantly as the transient solvent evaporates, and small particles begin to grow, which leads to larger grains [25,26].…”

Impact of PTFE particle size in designing BaTiO3 dielectric composites under the cold sintering process

“…The Cold Sintering Process (CSP) has attracted much attention because of the ability to densify at low temperatures between 100 °C to 300 °C for a number of important functional ceramics such as BaTiO 3 , [1][2][3][4][5] ZnO, [6][7][8][9][10][11] V 2 O 5 , [12][13][14] SnO, 15) Li 2 MoO 4 , 16,17) Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP), [18][19][20] Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP), 20) and β-alumina, 21) and (K, Na)NbO 3 (KNN). [22][23][24] Under conventional sintering conditions, these ceramics must be densified at significantly higher temperatures, so one major interest is the potential that CSP can provide an alternative route to a sustainable production process.…”