An official website of the United States government
Cold sintering is an emerging non-equilibrium process methodology that densifies ceramic powders at significantly reduced temperatures. This study proposes a fundamental framework to investigate its densification kinetics. By controlling four densification process variables including the transient chemistry, sintering temperature, uniaxial pressure and dwell time, the anisothermal sintering kinetics of highly densified ZnO is identified and phenomenologically modeled for its relative activation energetics.
more »
« less
This content will become publicly available on March 17, 2026
Mass transport in low‐temperature ceramic sintering and printing assisted by pressure and water
Ceramic processing through the combined use of pressure and water offers a promising approach to achieve accelerated mass transport between ceramic particles at reduced temperatures, providing a sustainable and low‐temperature method for ceramic synthesis and three‐dimensional printing. While previous studies have explored the roles of pressure and water in the fusion and densification of ceramic particles, the underlying mechanisms, especially for micro‐sized ceramic particles, are still debated. This paper aims to propose a potential mechanism for the fusion and densification of micro‐sized ceramic particles under the effect of pressure and water. Using a multi‐phase level‐set simulation model, our results suggest that stress‐assisted fracture and dissolution of interparticle contact points can be key factors driving the densification of micro‐sized ceramic particles in the presence of pressure and water.
more »
« less
- Award ID(s):
- 2236905
- PAR ID:
- 10580375
- Publisher / Repository:
- Wiley Periodicals LLC
- Date Published:
- Journal Name:
- Journal of the American Ceramic Society
- ISSN:
- 0002-7820
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Cold sintering densification and coarsening mechanisms are considered from the perspective of the nonequilibrium chemo-mechanical process known in Earth Sciences as pressure solution creep (or dissolutionprecipitation creep). This is an important mechanism of densification and deformation in many geological rock formations in the Earth’s upper crust, and although very slow in nature, it is of direct relevance to the cold sintering process. In cold sintering, we select particulate materials and identify experimental processing parameters to significantly accelerate the kinetics of dissolution-precipitation phenomena, with appropriate consideration of chemistry, applied stress, particle size and temperatures. In the theory of pressure solution, pressure-driven densification is considered to involve the consecutive stages of dissolution at grain contact points, then diffusive transport along the grain boundaries towards open pore surfaces, and then precipitation, all driven by chemical potential gradients. In this study, it is shown that cold sintering of BaTiO3, ZnO and KH2PO4 (KDP) ceramic materials proceeds by the same type of serial process, with the pressure solution creep rate being controlled by the slowest kinetic step. This is demonstrated by the values of activation energy (Ea) for densification, which are in good agreement with the existing literature on dissolution, precipitation, or coarsening. The influence of pressure on the morphology of ZnO grains also supports the pressure solution mechanism. Other characteristics that can be understood qualitatively in terms of pressure solution are observed in the in systems such as BaTiO3 and KDP. We further consider activation energies for grain growth with respect to the precipitation process, as well as evidence for coalescence and Ostwald ripening during cold sintering. For completeness we also consider materials that show significant plastic deformation under compression. Our findings point the way for new advances in densification, microstructural control, and reductions in cold sintering pressure, via the use of appropriate transient solvents in metals and hybrid organic-inorganic systems, such as the Methylammonium lead bromide (MAPBr) perovskite.more » « less
-
Abstract The contribution of a hollow structure on the rheological behavior of granular suspensions remains un‐investigated due to the challenge of water impermeability. Here starch is used to fabricate water‐permeable hollow particles, as a model for granular suspensions and investigated the resulting microstructures and rheological behavior. The hollow structure is fabricated based on a bottom‐up method by assembling micron‐sized building blocks into a superstructure. A Pickering emulsion is heated to fuse the starch interface, then, upon antisolvent precipitation, the polymer strands interlock to form a rigid shell around the oil template. When the template is removed a hollow particle remained. These particles exhibited a specific volume >5‐times higher than unmodified starch and consequently a higher viscosity. Larger particles showed higher viscosity but are also more fragile. The template structure can be manipulated to fine‐tune their functionality. These micro‐sized building blocks made from edible materials can be used as the next generation of texturizers. Additionally, these water‐permeable colloidosomes present an innovative approach to understanding how micro‐architectures impact the rheological behavior of granular suspensions.more » « less
-
Cold sintering is an unusually low-temperature process that uses a transient transport phase, which is most often liquid, and an applied uniaxial force to assist in densification of a powder compact. By using this approach, many ceramic powders can be transformed to high-density monoliths at temperatures far below the melting point. In this article, we present a summary of cold sintering accomplishments and the current working models that describe the operative mechanisms in the context of other strategies for low-temperature ceramic densification. Current observations in several systems suggest a multiple-stage densification process that bears similarity to models that describe liquid phase sintering. We find that grain growth trends are consistent with classical behavior, but with activation energy values that are lower than observed for thermally driven processes. Densification behavior in these low-temperature systems is rich, and there is much to be investigated regarding mass transport within and across the liquid-solid interfaces that populate these ceramics during densification. Irrespective of mechanisms, these low temperatures create a new opportunity spectrum to design grain boundaries and create new types of nanocomposites among material combinations that previously had incompatible processing windows. Future directions are discussed in terms of both the fundamental science and engineering of cold sintering.more » « less
-
Cold sintering of surface‐modified iron compacts results in a co‐continuous phosphate interphase between iron particles that provide both enhanced green strength and green density similar to the process that has been successfully introduced in low‐temperature densification of ceramic materials. Relative density as high as 95% along with transverse rupture strength of ≈ 75 MPa, which is almost six times that of conventional powdered metal iron compact and 2.5 times that of warm compacted controls, is achieved. Dilatometry study at different pressures shows a small but significant improvement in densification process during cold sintering relative to the larger densification of warm compacted control. Strength model based on microstructural analysis as well as in situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments reveals the nature of the interphase that imparts the large cohesive strength under the cold sintered assisted warm compaction. The process is conducive to produce iron compacts for green machining. Furthermore, the samples when subjected to high‐temperature sintering yield a fully sintered iron compact with density > 7.2 g cm−3and transverse rupture strength as high as 780 MPa. All in all, there are major new opportunities with the cold sintered assisted warm compaction of powdered metals that will also be discussed.more » « less
