[ { "id": "authors:nz65p-gqy77", "collection": "authors", "collection_id": "nz65p-gqy77", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210604-111533773", "type": "article", "title": "Coarsening of dendrites in solution-based freeze-cast ceramic systems", "author": [ { "family_name": "Arai", "given_name": "Noriaki", "orcid": "0000-0002-3040-2997", "clpid": "Arai-Noriaki" }, { "family_name": "Stan", "given_name": "Tiberiu", "clpid": "Stan-Tiberiu" }, { "family_name": "Macfarland", "given_name": "Sophie", "orcid": "0000-0001-8488-7363", "clpid": "Macfarland-Sophie" }, { "family_name": "Voorhees", "given_name": "Peter W.", "orcid": "0000-0003-2769-392X", "clpid": "Voorhees-Peter-W" }, { "family_name": "Muyanja", "given_name": "Nancy S.", "orcid": "0000-0002-3394-5452", "clpid": "Muyanja-Nancy-S" }, { "family_name": "Shahani", "given_name": "Ashwin J.", "orcid": "0000-0002-6157-840X", "clpid": "Shahani-Ashwin-J" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "abstract": "The morphologies of freeze-cast materials are typically controlled and tuned by adjusting the freezing front velocity and temperature gradient. Recently it has been demonstrated that coarsening, similar to that commonly practiced in alloy systems, is also effective for morphological control in freeze-cast materials. However, the underlying coarsening mechanisms and their effect on microstructure evolution are largely unknown. In this study, frozen preceramic polymer/cyclohexane solutions were coarsened at 2 \u00b0C and 4 \u00b0C for up to 5 h, and the resulting morphologies were characterized using scanning electron microscopy, mercury intrusion porosimetry, and X-ray computed tomography. During coarsening the microstructure evolved from dendritic (primary and secondary pores) to honeycomb-like (large open channels with flat walls). The size of both primary and secondary pores increased linearly with the cube root of coarsening time, consistent with dendritic coarsening in alloy systems. Other important metrics such as primary dendrite spacing, dendrite growth directionality, and the effect of coarsening on the pore-ceramic interface area are reported. These findings provide novel insights into coarsening of freeze-cast systems and can lead to new avenues for microstructure tailorability.", "doi": "10.1016/j.actamat.2021.117039", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2021-08-15", "volume": "215", "pages": "Art. No. 117039" }, { "id": "authors:82afh-mep05", "collection": "authors", "collection_id": "82afh-mep05", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210128-095301970", "type": "article", "title": "Interface pinning causes the hysteresis of the hydride transformation in binary metal hydrides", "author": [ { "family_name": "Weadock", "given_name": "Nicholas J.", "orcid": "0000-0002-1178-7641", "clpid": "Weadock-Nicholas-J" }, { "family_name": "Voorhees", "given_name": "Peter W.", "orcid": "0000-0003-2769-392X", "clpid": "Voorhees-Peter-W" }, { "family_name": "Fultz", "given_name": "Brent", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B" } ], "abstract": "Hydriding and dehydriding transitions in bulk and nanocrystalline binary metal hydrides were studied using the Pd-H model system by measuring pressure-composition isotherms with in situ x-ray diffractometry. Nanocrystalline Pd showed a smaller pressure hysteresis, solvus hysteresis, and hysteresis in lattice parameter, compared to bulk Pd. The time-dependence of pressure equilibration was measured after dosing with aliquots of hydrogen, giving equilibration times that were much faster in the single-phase regions than in the two-phase plateaus. In the broad two-phase plateaus, the pressure relaxations were exponential functions of time. An explanation of hysteresis is developed that is based on a dissipative potential barrier that impedes the motion of the interface due to interactions between lattice defects and the two-phase interface. The exponential pressure relaxations and hysteresis are consistent for this mechanism. For a simple model of the pinning potential, the potential barrier maximum is an order of magnitude less than typical grain boundary energies. These pinning effects are substantially different in the nanocrystalline Pd, suggesting differences in the hydriding mechanism.", "doi": "10.1103/PhysRevMaterials.5.013604", "issn": "2475-9953", "publisher": "American Physical Society", "publication": "Physical Review Materials", "publication_date": "2021-01", "series_number": "1", "volume": "5", "issue": "1", "pages": "Art. No. 013604" }, { "id": "authors:bb3rk-r2c39", "collection": "authors", "collection_id": "bb3rk-r2c39", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20171026-133814643", "type": "article", "title": "Suspension- and solution-based freeze casting for porous ceramics", "author": [ { "family_name": "Naviroj", "given_name": "Maninpat", "orcid": "0000-0001-9426-6990", "clpid": "Naviroj-Maninpat" }, { "family_name": "Voorhees", "given_name": "Peter W.", "orcid": "0000-0003-2769-392X", "clpid": "Voorhees-Peter-W" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "abstract": "Freeze casting of traditional ceramic suspensions and freeze casting of preceramic polymer solutions were directly compared as methods for processing porous ceramics. Alumina and polymethylsiloxane were freeze cast with four different organic solvents (cyclooctane, cyclohexane, dioxane, and dimethyl carbonate) to obtain ceramics with \u223c70% porosity. Median pore sizes were smaller for solution freeze casting than for suspension freeze casting under identical processing conditions. The pore structures, which range from foam-like to lamellar, were correlated to the Jackson \u03b1-factor of the solvent; solvents with low \u03b1-factors yielded nonfaceted pore structures, while high \u03b1-factors produced more faceted structures. Intermediate \u03b1-factors resulted in dendritic pore structures and were most sensitive to the processing method. Small suspended particles ahead of a solid\u2013liquid interface are hypothesized to destabilize the dendrite tip in suspension freeze casting resulting in more foam-like structures. Differences in processing details were highlighted, particularly regarding the improved freezing front observation possible with solution-based freeze casting.", "doi": "10.1557/jmr.2017.133", "issn": "0884-2914", "publisher": "Cambridge University Press", "publication": "Journal of Materials Research", "publication_date": "2017-09-14", "series_number": "17", "volume": "32", "issue": "17", "pages": "3372-3382" }, { "id": "authors:a22zm-6mb70", "collection": "authors", "collection_id": "a22zm-6mb70", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:WALprb03", "type": "article", "title": "First-principles calculation of the effect of strain on the diffusion of Ge adatoms on Si and Ge(001) surfaces", "author": [ { "family_name": "van de Walle", "given_name": "A.", "orcid": "0000-0002-3415-1494", "clpid": "van-de-Walle-Axel-Brown" }, { "family_name": "Asta", "given_name": "M.", "orcid": "0000-0002-8968-321X", "clpid": "Asta-Mark" }, { "family_name": "Voorhees", "given_name": "P. W.", "orcid": "0000-0003-2769-392X", "clpid": "Voorhees-Peter-W" } ], "abstract": "First-principles calculations are used to calculate the strain dependencies of the binding and diffusion-activation energies for Ge adatoms on both Si(001) and Ge(001) surfaces. Our calculations reveal that the binding and activation energies on a strained Ge(001) surface increase and decrease, respectively, by 0.21 and 0.12 eV per percent compressive strain. For a growth temperature of 600\u00b0C, these strain-dependencies give rise to a 16-fold increase in adatom density and a fivefold decrease in adatom diffusivity in the region of compressive strain surrounding a Ge island with a characteristic size of 10 nm.", "doi": "10.1103/PhysRevB.67.041308", "issn": "0163-1829", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2003-01-15", "series_number": "4", "volume": "67", "issue": "4", "pages": "Art. No. 041308(R)" } ]