Low-Temperature Sintering of Seeded Sol—Gel-Derived, ZrO2-Toughened Al2O3 Composites

Seeding a mixture of boehmite (AIOOH) and colloidal ZrO₂ with α-alumina particles and sintering at 1400°C for 100 min results in 98% density. The low sintering temperature, relative to conventional powder processing, is a result of the small alumina particle size (∼0.3 μm) obtained during the θ-to α-alumina transformation, homogeneous mixing, and the uniform structure of the sol-gel system. Complete retention of pure ZrO₂ in the tetragonal phase was obtained to 14 vol% ZTA because of the low-temperature sintering. The critical grain size for tetragonal ZrO₂ was determined to be ∼0.4 μm for the 14 vol% ZrO₂—Al₂O₃ composite. From these results it is proposed that seeded boehmite gels offer significant advantages for process control and alumina matrix composite fabrication.     

ZnO-activated formation of phase pure perovskite Pb(In1/2Nb1/2)O3-Pb(Zn1/3Nb2/3)O3-PbTiO3 powder

This paper reports on the phase formation of perovskite Pb(In_1/2Nb_1/2)O₃-Pb(Zn_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PZN-PT) powder when doped with 0.04 to 0.83 mol% ZnO. Air calcination of undoped powder mixtures for 4 hours at 800°C resulted in a mixture of Pb₂Zn_0.29Nb_1.71O_6.565 pyrochlore, PIN-PZN-PT perovskite, and In₂O₃. ZnO dopant concentrations as low as 0.04 mol% increased the rate of perovskite formation and resulted in near phase pure perovskite powder of 0.5 μm particle size when heated at 800°C in air. In all cases PbTiO₃ and Pb(In_1/2Nb_1/2)O₃ formed prior to PIN-PZN-PT formation. ZnO doping promotes perovskite phase formation by increasing the reactivity of the intermediate pyrochlore phase by substituting Zn²⁺ on Nb⁵⁺ sites and forming oxygen vacancies when heated in air. Heating in high resulted in an incomplete reaction and a mixture of perovskite and pyrochlore whereas low resulted in phase separation into a mixture of rhombohedral perovskite, tetragonal perovskite, and pyrochlore. The sensitivity clearly shows that oxygen vacancies due to ZnO-doping are critical for synthesis of phase pure PIN-PZN-PT powder.     

Texture Measurements in 〈001〉 Fiber-Oriented PMN–PT

Textured (1- x )(Mg_1/3Nb_2/3)O₃– x PbTiO₃ (PMN–PT) ceramics obtained by the templated grain growth process possess a significant fraction of the piezoelectric properties of Bridgman-grown single crystals at a fraction of the cost. However, for integration of these materials into transducer and actuator designs, a more comprehensive characterization of texture quality than possible with Lotgering analysis is needed. In this study, X-ray diffraction (XRD) and electron backscatter diffraction techniques were used to characterize the fiber texture in 〈001〉-oriented PMN–28PT. The March–Dollase equation was fitted to the intensity data to describe the texture in terms of the texture fraction, f , and the degree of texture of the oriented fraction using the March parameter, r . Although each of the techniques used was quantitatively in agreement, XRD rocking curve collection and analysis was the most time-efficient technique for making a comprehensive measurement of texture ( f =0.69, r =0.29, FWHM=13.9°) for fiber-oriented PMN–28PT.     

Effect of Preparation Conditions on Phase Formation, Densification, and Microstructure Evolution in La-β-Al2O3/Al2O3 Composites

In situ development of La-ß-Al₂O₃(LBA) platelets in alpha-Al₂O₃was studied as a function of the preparation method: a conventional solid-state reaction of commercial Al₂O₃powder and La(NO₃)₃as well as a sol-gel method starting with boehmite and the same La₂O₃precursor. In both cases, homogeneous distribution of the reinforcing phase was achieved, and a noteworthy inhibition of Al₂O₃grain growth resulted. However, samples prepared by solid-state reaction densified more easily than those prepared via sol-gel, but the formation of the LBA phase occurred at a lower temperature in samples prepared by the sol-gel approach. Results on the correlation of the onset of LBA grain growth and densification to microstructure are discussed.     

A comparative study of the effect of gold seed particle preparation method on nanowire growth

Highly controlled particle-assisted growth of semiconductor nanowires has been performed for many years, and a number of novel nanowire-based devices have been demonstrated. Full control of the epitaxial growth is required to optimize the performance of devices, and gold seed particles are known to provide the most controlled growth. Successful nanowire growth from gold particles generated and deposited by various different methods has been reported, but no investigation has yet been performed to compare the effects of gold particle generation and deposition methods on nanowire growth. In this article we present a direct comparative study of the effect of the gold particle creation and deposition methods on nanowire growth characteristics and nanowire crystal structure, and investigate the limitations of the different generation and deposition methods used.      

Dispersion and rheology for direct writing lead-based piezoelectric ceramic pastes with anisotropic template particles

Controlling the rheology of direct writing pastes is essential for producing high quality printed ceramics. Ceramic pastes were formulated to explore the relation between surface chemistry and rheology of complex pastes of Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PMN-PT) powder, large BaTiO₃ (BT) platelet particles, and a commercial poly(acrylic) acid-based binder system. Zeta potential of the ceramic powder, the conformation of the poly(acrylic) acid, and the effect of these factors on rheology were evaluated as a function of suspension pH. Effective dispersion and amenable rheology for direct writing were achieved at mixing pH 5. Additions of 0.3 to 2.6 vol% BT tabular particles dramatically altered the rheology of the pastes due to the shear alignment of the BT particles. Powder-organic interactions and the size and concentration of BT platelet particles can be tailored to direct write either space-filling filaments to form dense ceramics or non-flowing filaments to form spanning ceramic structures.     

Seeding of Perovskite Lead Magnesium Niobate Crystallization from Pb-Mg-Nb-EDTA Gels

The addition of BaTiO₃ seed particles (50 nm in diameter) to a Pb-Mg-Nb-EDTA solution (where EDTA represents ethylenediamine tetraacetic acid) reduces the formation temperature from 700°C to 600°C during combustion synthesis, because of epitaxial effects. The lower perovskite formation temperature eliminates the formation of pyrochlore at the surface of the precursor bed and allows for the direct crystallization of ∼98% perovskite lead magnesium niobate (PMN) during combustion synthesis. Increasing the nucleation density of the seed particles in the seeded precursor decreases the precursor volume that is associated with each perovskite nucleus and, thus, reduces the PMN particle size from 1 µm to 0.2 µm. The influence of BaTiO₃ seeding is discussed in terms of the thermodynamics of perovskite formation, the influence of BaTiO₃ seed concentration, and epitaxial nucleation.     

Flowering and Seed Production across the Lemnaceae

Plants in the family Lemnaceae are aquatic monocots and the smallest, simplest, and fastest growing angiosperms. Their small size, the smallest family member is 0.5 mm and the largest is 2.0 cm, as well as their diverse morphologies make these plants ideal for laboratory studies. Their rapid growth rate is partially due to the family’s neotenous lifestyle, where instead of maturing and producing flowers, the plants remain in a juvenile state and continuously bud asexually. Maturation and flowering in the wild are rare in most family members. To promote further research on these unique plants, we have optimized laboratory flowering protocols for 3 of the 5 genera: Spirodela; Lemna; and Wolffia in the Lemnaceae. Duckweeds were widely used in the past for research on flowering, hormone and amino acid biosynthesis, the photosynthetic apparatus, and phytoremediation due to their aqueous lifestyle and ease of aseptic culture. There is a recent renaissance in interest in growing these plants as non-lignified biomass sources for fuel production, and as a resource-efficient complete protein source. The genome sequences of several Lemnaceae family members have become available, providing a foundation for genetic improvement of these plants as crops. The protocols for maximizing flowering described herein are based on screens testing daylength, a variety of media, supplementation with salicylic acid or ethylenediamine-N,N′-bis(2-hydroxyphenylacetic acid) (EDDHA), as well as various culture vessels for effects on flowering of verified Lemnaceae strains available from the Rutgers Duckweed Stock Cooperative.     

Templated Grain Growth of Barium Titanate Single Crystals

BaTiO₃ single crystals were grown via templated grain growth (TGG), which is a process in which a single-crystal "template" is placed in contact with a sintered polycrystalline matrix and then heated to migrate the single-crystal boundary into the matrix. Millimeter-sized, stoichiometric single crystals of BaTiO₃ were produced by heating polycrystalline matrix with a relative density of 97% and a Ba/Ti ratio of <1.00, which was bonded to a BaTiO₃ single crystal, at temperatures above the eutectic temperature. Growth rates of 590–790, 180–350, and 42–59 μm/h were observed for {111}-, {100}-, and {110}-oriented single-crystal templates, respectively. Lower-surface-energy facets were formed for {111}- and {100}-oriented templates, whereas {110} crystals maintained a {110} growth front, which indicated that this plane orientation was the lowest-energy surface in this system. SrTiO₃ also was shown to be a suitable substrate for TGG of BaTiO₃.     

Comparison of Texture Analysis Techniques for Highly Oriented α-Al2O3

Texture measurements were performed on liquid-phase-sintered alumina textured by a templated grain growth process from 1250° to 1650°C. Texture distributions were measured using X-ray pole figures, rocking curves, Rietveld refinement, and stereology. The March–Dollase equation fitted the measured distributions very well and gave quantitative values of the degree of texture and the texture fraction. The fitting parameters of the X-ray diffraction measurements were comparable to those measured by stereology. Rocking curve analysis was found to be straightforward and to give accurate characterization of texture in the alumina system of this study in a relatively short time.