Extrusion of YAG Tubes Shows that Bottom‐up Processing is Not Always Optimal

Abstract

Liquid-feed fl ame spray pyrolysis provides easily dispersed, unaggregated nanopowders with average particle sizes of 20-70 nm depending on the processing conditions. Their chemical compositions can be controlled to ppm levels via control of the initial precursor solution. In this paper, Y 3 Al 5 O 12 composition nanopowders are produced that are atomically mixed but offer a hexagonal crystal structure rather than a YAG structure. Y 2 O 3 and δ -Al 2 O 3 nanopowders are also produced and mixed to evaluate reactive sintering. It is shown that nanopowder/polymer mixtures permit the extrusion of tubes that retain their shape on debindering and sintering to ≥95% theoretical density. More importantly, the sintering behavior of hex-Y 3 Al 5 O 12 is compared with that of tubes formed using 3:5 Y 2 O 3 : δ -Al 2 O 3 mixtures to test the so-called bottom-up paradigm, which suggests that mixing on the fi nest length scales should provide optimal control of sintering rates, fi nal densities, and grain sizes. Instead, it is found that reactive sintering is faster and offers better control of fi nal grain sizes. Dense sintered tubes are translucent, and dimensional uniformity is maintained from extrusion through sintering.

Phase Evolution in the Transformation of Atomically Mixed Versus Ball‐Milled Mixtures of Nanopowders in the Formation of Composite MO·3Al 2 O 3 Spinels: Bottom‐Up Processing is Not Always Optimal

“…As noted above, we are interested in the microstructural evolution of MO . 3Al 2 O 3 (M = Mg, Co, and Ni) using nanopowders that offer a homogeneous composition at atomic length scales versus, mixtures of nanopowders of the same composition but with homogeneity defined by ball‐milling of the same ratios of the two component nanooxide powders . In all instances, the nanopowders used offer APSs of ≈30–40 nm.…”

“…In two recent papers, we described studies along these lines designed to explore the concept of “bottom‐up” processing in Y 3 Al 5 O 12 compositions made both from atomically mixed nanopowders and ball‐milled mixtures of Y 2 O 3 and Al 2 O 3 nanopowders, and nanopowders with a final composition of NiO·3Al 2 O 3 . Our findings were that the bottom‐up concept was either not the optimal route to the targeted materials with controlled microstructures or gave the same microstructures despite significant differences in levels of mixing.…”

The Bottom Up Approach is Not Always the Best Processing Method: Dense α‐Al2O3/NiAl2O4 Composites

“…A related paper on processing atomically mixed Y 3 Al 5 O 12 vs ball milled 3:5 mixtures of Y 2 O 3 and Al 2 O 3 also provides results that greatly contrast with the bottom‐up axiom …”

Ce-Substituted Nanograin Na3Zr2Si2PO12 Prepared by LF-FSP as Sodium-Ion Conductors

“…Na 3 Ce x Zr 2– x Si 2 PO 12 ( x = 0, 0.1, 0.2, 0.3) NPs were synthesized using LF-FSP methods described in detail elsewhere. ,− As-prepared NPs were dispersed in ethanol with 3 wt % poly­(acrylic acid) as the dispersant. Na 3 Ce x Zr 2– x Si 2 PO 12 NPs were ground and then sieved through a 80 mm nylon mesh, uniaxially pressed at a WC die (12 MPa, φ 14.2 mm).…”