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Ultralow-Temperature Densification of Ceramic, Ionic, and Hybrid Materials Via Cold Sintering and Cold Flow.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Ultralow-Temperature Densification of Ceramic, Ionic, and Hybrid Materials Via Cold Sintering and Cold Flow./
作者:	Lowum, Sarah M.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
面頁冊數:	198 p.
附註:	Source: Dissertations Abstracts International, Volume: 83-03, Section: B.
Contained By:	Dissertations Abstracts International83-03B.
標題:	Aqueous solutions. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28841727
ISBN:	9798460447398

Ultralow-Temperature Densification of Ceramic, Ionic, and Hybrid Materials Via Cold Sintering and Cold Flow.
Lowum, Sarah M.

Ultralow-Temperature Densification of Ceramic, Ionic, and Hybrid Materials Via Cold Sintering and Cold Flow. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 198 p.

Source: Dissertations Abstracts International, Volume: 83-03, Section: B.

Thesis (Ph.D.)--The Pennsylvania State University, 2021.

This item must not be sold to any third party vendors.

Ceramic sintering is an ancient process dating back to the Paleolithic era 25,000 years ago. Sintering transforms ceramic powders into dense, robust parts for structural, mechanical, electronic, and decorative applications. Typically, this requires temperatures around two-thirds the material melting temperature, which is greater than 1000°C for most ceramics. As technology has progressed, so has demand for improved material properties, facile material integration, engineered microstructures, and more environmentally-friendly manufacturing processes. Ultimately, this has resulted in a large body of scientific work examining techniques to suppress sintering temperatures. These include application of pressure, such as in hot pressing, application of electric fields, such as in spark-plasma sintering or field-assisted sintering, or use of a liquid phase to promote diffusion, such as in liquid phase sintering, hydrothermal sintering, and cold sintering. Cold sintering is a relatively new technique that has gained growing interest in the past decade. A secondary mass transport phase, generally an aqueous solution of an acid, base, or salt, is added to the ceramic powder, along with moderate pressures on the order of hundreds of MPa, to promote ceramic densification at 300°C or below through a proposed dissolution-precipitation process. Sintering temperatures an order of magnitude below those used in traditional solid-state sintering have enabled many unique opportunities: nanostructured ceramics, ceramic-polymer composites, sintering of thermally unstable materials, and extensive microstructure engineering. Given the recency of the work and the complex nature of the process, the precise mechanisms of cold sintering are not well understood, limiting the technique to a select group of materials and inhibiting the process from being implemented on a wide scale. This dissertation details work investigating densification mechanisms involved in the cold sintering process through modification of the mass transport phase. As discussed in Chapter 3, in situ process monitoring revealed for the first time that liquid water is not required to facilitate densification during cold sintering. Hence, cold sintering using crystalline transport phases with only structural water or small quantities of adsorbed water was performed. This led to the invention of a novel ceramic processing technique: hydroflux-assisted densification (Chapter 4). This approach is similar to cold sintering, although it uses alternative flux-based transport phases that are solid at room temperature. Small quantities of water are added to these fluxes to form "hydrofluxes", which have altered solvent properties and suppressed melting points, enabling their use in cold sintering temperature regimes. Hydroflux transport phases significantly expand the materials spectrum amenable to densification below 300°C and also reveal mechanisms other than dissolution-precipitation, such as water-enhanced diffusional processes, may contribute to densification. In addition to densification mechanisms, properties of cold-sintered materials were investigated and compared to traditionally sintered materials. Chapter 5 details hydrofluxassisted densification of BaFe12O19, a widely used permanent magnet, and demonstrates that magnetic properties of samples sintered at 300°C are comparable to properties of samples sintered at temperatures > 1000°C. Chapter 6 presents mechanical strength data for ZnO cold-sintered with aqueous-based transport phases. Measured strength values were slightly lower than values for traditionally sintered ZnO, indicating grain boundaries in cold-sintered materials may not be as strongly bonded as those in materials densified at high temperatures via bulk diffusional processes. Reports on the chemical and structural nature of the grain boundaries in cold-sintered materials are sparse, so this topic needs to be addressed further in future work. The second half of this dissertation discusses low-temperature densification of ionic materials via a plastic deformation-driven process called cold flow. Chapter 7 presents cold flow studies in NaCl. Highly dense (~100%), transparent NaCl samples can be formed under high applied pressures without the need for any added mass transport phase. It was concluded that densification proceeds primarily by plastic flow of NaCl particles to fill pores, but small quantities of water also enhance densification. Chapter 8 expands on this work, demonstrating both cold flow and cold sintering in the hybrid organic-inorganic perovskite MAPbBr3. Hybrid perovskites are a new material class that has garnered interest in the electronics and photonics communities due to useful optoelectronic properties for solar cells and high energy radiation detectors. Successful densification, microstructural tailoring, and opportunities for single-step device fabrication are demonstrated, establishing an important new application space for ultralow-temperature densification.

ISBN: 9798460447398Subjects--Topical Terms:

3681511
Aqueous solutions.
Subjects--Index Terms:

Ceramics

Ultralow-Temperature Densification of Ceramic, Ionic, and Hybrid Materials Via Cold Sintering and Cold Flow.
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520 $a Ceramic sintering is an ancient process dating back to the Paleolithic era 25,000 years ago. Sintering transforms ceramic powders into dense, robust parts for structural, mechanical, electronic, and decorative applications. Typically, this requires temperatures around two-thirds the material melting temperature, which is greater than 1000°C for most ceramics. As technology has progressed, so has demand for improved material properties, facile material integration, engineered microstructures, and more environmentally-friendly manufacturing processes. Ultimately, this has resulted in a large body of scientific work examining techniques to suppress sintering temperatures. These include application of pressure, such as in hot pressing, application of electric fields, such as in spark-plasma sintering or field-assisted sintering, or use of a liquid phase to promote diffusion, such as in liquid phase sintering, hydrothermal sintering, and cold sintering. Cold sintering is a relatively new technique that has gained growing interest in the past decade. A secondary mass transport phase, generally an aqueous solution of an acid, base, or salt, is added to the ceramic powder, along with moderate pressures on the order of hundreds of MPa, to promote ceramic densification at 300°C or below through a proposed dissolution-precipitation process. Sintering temperatures an order of magnitude below those used in traditional solid-state sintering have enabled many unique opportunities: nanostructured ceramics, ceramic-polymer composites, sintering of thermally unstable materials, and extensive microstructure engineering. Given the recency of the work and the complex nature of the process, the precise mechanisms of cold sintering are not well understood, limiting the technique to a select group of materials and inhibiting the process from being implemented on a wide scale. This dissertation details work investigating densification mechanisms involved in the cold sintering process through modification of the mass transport phase. As discussed in Chapter 3, in situ process monitoring revealed for the first time that liquid water is not required to facilitate densification during cold sintering. Hence, cold sintering using crystalline transport phases with only structural water or small quantities of adsorbed water was performed. This led to the invention of a novel ceramic processing technique: hydroflux-assisted densification (Chapter 4). This approach is similar to cold sintering, although it uses alternative flux-based transport phases that are solid at room temperature. Small quantities of water are added to these fluxes to form "hydrofluxes", which have altered solvent properties and suppressed melting points, enabling their use in cold sintering temperature regimes. Hydroflux transport phases significantly expand the materials spectrum amenable to densification below 300°C and also reveal mechanisms other than dissolution-precipitation, such as water-enhanced diffusional processes, may contribute to densification. In addition to densification mechanisms, properties of cold-sintered materials were investigated and compared to traditionally sintered materials. Chapter 5 details hydrofluxassisted densification of BaFe12O19, a widely used permanent magnet, and demonstrates that magnetic properties of samples sintered at 300°C are comparable to properties of samples sintered at temperatures > 1000°C. Chapter 6 presents mechanical strength data for ZnO cold-sintered with aqueous-based transport phases. Measured strength values were slightly lower than values for traditionally sintered ZnO, indicating grain boundaries in cold-sintered materials may not be as strongly bonded as those in materials densified at high temperatures via bulk diffusional processes. Reports on the chemical and structural nature of the grain boundaries in cold-sintered materials are sparse, so this topic needs to be addressed further in future work. The second half of this dissertation discusses low-temperature densification of ionic materials via a plastic deformation-driven process called cold flow. Chapter 7 presents cold flow studies in NaCl. Highly dense (~100%), transparent NaCl samples can be formed under high applied pressures without the need for any added mass transport phase. It was concluded that densification proceeds primarily by plastic flow of NaCl particles to fill pores, but small quantities of water also enhance densification. Chapter 8 expands on this work, demonstrating both cold flow and cold sintering in the hybrid organic-inorganic perovskite MAPbBr3. Hybrid perovskites are a new material class that has garnered interest in the electronics and photonics communities due to useful optoelectronic properties for solar cells and high energy radiation detectors. Successful densification, microstructural tailoring, and opportunities for single-step device fabrication are demonstrated, establishing an important new application space for ultralow-temperature densification.
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