3-D Microparticles of BaTiO3 and Zn2SiO4 Via the Chemical (Sol-Gel, Acetate, or Hydrothermal) Conversion of Biological (Diatom) Templates

Cai, Yuanqiang; Weatherspoon, Michael R.; Ernst, Eric M.; Haluska, Michael S.; Snyder, Robert L.; Sandhage, Kenneth H.

doi:10.1002/9780470291375.ch6

Cited by 6 publications

(13 citation statements)

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“…Alternatively, a coatingbased approach has been utilized to generate barium titanate replicas of silica diatom frustules [13]. Ongoing research is aimed at investigating the syntheses of other titanate materials with further RF interest which are voltage-tunable dielectric materials (e.g., for steerable devices) with relatively high permittivities and low losses [14].…”

Section: Conversion Of Bioclastic Particles To Rf Ceramics With Definmentioning

confidence: 99%

“…The TiOF 2 was then converted into anatase TiO 2 replicas through the selective removal of fluorine by reaction with either oxygen (reaction (2a)) or water vapor (reaction 2(b)) [13]. Such titania replicas have then been converted into barium titanate replicas through hydrothermal reaction with barium hydroxide-bearing aqueous solutions, as indicated by the reaction below [13].…”

Section: Conversion Of Bioclastic Particles To Rf Ceramics With Definmentioning

confidence: 99%

“…The Sandhage group has invented and developed the BaSIC (Bioclastic and Shapepreserving Inorganic Conversion) process for converting rigid biomineralized (bioclastic) structures into replicas comprised of non-silica-based oxides [11][12][13]. For example, Unocic, et al have converted silica-based diatom frustules into nanocrystalline titania replicas through the use of the following gas/solid reactions [12]: 2TiF 4 (g) + SiO 2 (s) => 2TiOF 2 (s) + SiF 4 (g) (1) TiOF 2 (s) + 1/2O 2 (g) => TiO 2 (s) + F 2 (g) (2a) TiOF 2 (s) + H 2 O(g) => TiO 2 (s) + 2HF(g) (2b)…”

Section: Conversion Of Bioclastic Particles To Rf Ceramics With Definmentioning

confidence: 99%

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Novel polymer-ceramic composites for conformable RF applications

Hansford

Sandhage

2007

2007 IEEE Antennas and Propagation Society International Symposium

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IntroductionMany current and proposed applications of RF antennas and related circuitry bring requirements that require the development of novel materials for dielectric components. Included in these requirements are high permittivity with low losses, the ability to conform to curves and complex surfaces, and the ability to operate in a wide variety of environmental conditions. As antennas are increasingly used on smaller and more mobile vehicles, such as UAVs, these requirements become more difficult to satisfy. Currently available conformal antennas are printed on rigid, curved, laminated substrates that are difficult to incorporate directly into prefabricated structures.Polymers are increasingly being used for electronics applications, from printed circuit boards to conductors for reduced cost components. While polymers have been identified for these applications, their modest dielectric properties have limited their use for antenna and circuit substrates. Polymer-ceramic composites have previously been demonstrated with large permittivities, but often with high losses [1,2]. These high permittivities and losses are based on the use of ferroelectric materials (e.g. PVDF and PZT), which is appropriate for packaging applications, but non-ideal for antenna and circuit applications.The potential for polymer-ceramic composites as antenna materials has yet to be fully realized. The use of lower loss materials for composites presents both opportunities and disadvantages: the lower loss materials maintain this beneficial property in composites, but at the expense of lower permittivities, unless a high volume fraction of ceramic particles is present. In this paper, we review two areas of interest for the fabrication of polymer-ceramic composites for high permittivity conformable devices: polymer-ceramic mixing rules and the production of controlled geometry ceramic particles via chemical conversion of bioclastic precursors. Mixing and effective propertiesFor polymer-ceramic composites, the primary source of the effective permittivity is due to the interaction of the ceramic particles with the external field of the polymer matrix. The exact formulation of theoretical mixing equations for composites comes from the understanding of the field properties through the mixture, the interaction of particles within the mixture, particle geometry, and several other variables. Depending on the role of field perturbation, scattering, material anisotropy, dispersion anisotropy, polarization density, and requirements of formulaic symmetry, there are many different mixing rules that can be applied to predict the effective permittivity of a composite. A classical mixing approach yields the Maxwell Garnett equation, an effective medium approach yields the Bruggeman equation, and an approach that focuses on the effective material for the polarization density (instead of matrix material) yields the Coherent Potential equation. Many other models exist, including power laws, differential, periodic lattice, and random medium models [4]. To c...

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Section: Conversion Of Bioclastic Particles To Rf Ceramics With Definmentioning

confidence: 99%

Section: Conversion Of Bioclastic Particles To Rf Ceramics With Definmentioning

confidence: 99%

Section: Conversion Of Bioclastic Particles To Rf Ceramics With Definmentioning

confidence: 99%

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Novel polymer-ceramic composites for conformable RF applications

Hansford

Sandhage

2007

2007 IEEE Antennas and Propagation Society International Symposium

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“…Weatherspoon, et al synthesized the first freestanding barium titanate-based microshell structures by using a sol-gel process to generate a conformal and continuous BaTiO 3 coating at 700°C on chemically compatible magnesia-converted microshell replicas (formed through reaction with magnesium gas [48][49][50]52 ). 56,62,65 Selective dissolution of the underlying magnesia then yielded freestanding phase-pure BaTiO 3 structures that retained the 3D microshell shape. 56 In this paper, a combination of gas/solid and liquid/ solid reactions is examined for the low-temperature syntheses of BaTiO 3 replicas of diatom microshells.…”

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confidence: 97%

“…Nonetheless, both reactions have been successfully conducted at modest temperatures (i.e., ഛ350°C) with flowing oxygen or moist air. 51,[54][55][56] Coating-based approaches may also be used to alter the chemistries of diatom microshells. [58][59][60][61][62][63][64][65][66] If the coating is thin, continuous, conformal, rigid, and chemically robust, then silica-free structures (e.g., zirconia or polymer 60,64 ) possessing the external shape of the starting microshell can be produced upon selective dissolution of the underlying silica microshell (note: if the internal and external surfaces of the microshell are coated, then dissolution of the silica will yield a hollow wall structure).…”

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confidence: 99%

Enhanced hydrothermal conversion of surfactant-modified diatom microshells into barium titanate replicas

et al. 2007

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The three-dimensional nanostructured SiO 2 -based microshells of diatoms have been converted into nanocrystalline BaTiO 3 via a series of shape-preserving reactions. The microshells, obtained as diatomaceous earth, were first exposed to a surfactant-induced dissolution/reprecipitation process [C.E. Fowler, et al., Chem. Phys. Lett. 398, 414 (2004)] to enhance the microshell surface area, without altering the microshell shape. The SiO 2 microshells were then converted into anatase TiO 2 replicas via reaction with TiF 4 gas and then humid oxygen. Hydrothermal reaction with a barium hydroxide-bearing solution then yielded three-dimensional nanocrystalline microshell replicas composed of BaTiO 3 . The enhanced surface area of the surfactant-treated microshells resulted in faster conversion into phase-pure BaTiO 3 at 100°C.The attractive electronic, optical, and chemical properties exhibited by barium titanate-based compositions have led to the use of these ceramics as capacitors, thermistors, actuators, sensors, phosphors, and other devices. 1-8 A variety of approaches (e.g., mixed oxide, mixed salt, sol-gel, polymeric precursor, hydrothermal, microemulsion, mechanochemical, and combustion syntheses) have been used to synthesize BaTiO 3 powders with fine particle and crystal sizes. 9-19 Nanocrystalline barium titanate-based ceramics have exhibited relatively high room-temperature dielectric constants that are temperature-and voltage-stable for integrated capacitors, 20,21 high sensitivity to water vapor and carbon dioxide for gas sensors, 22-24 and enhanced response of fluorescence to temperature changes for real-time temperature monitoring. 25 The worldwide interest in nanoscale ferroelectric devices has also led to the recent syntheses of BaTiO 3 nanowires, 26 nanorods, 27 nanoshell tubes, 28 and nanoshell spheres. 29,30 However, the scalable fabrication of complex three-dimensional (3D) BaTiO 3 -based nanostructures in a variety of wellcontrolled morphologies via synthetic methods has been a significant challenge. Nature, on the other hand, provides impressive examples of 3D microscale to nanoscale mineral assembly. 31-39 For example, coccolithophorids (Haptophyta) and diatoms (Bacillariophyta) are single-celled algae that assemble intricate nanostructured calcium carbonate and silica microshells, respectively. 35-40 A particularly wide variety of morphologies can be found among the microshells of the estimated 10 5 species of diatoms. 40,41 Each species of diatom assembles an amorphous silica-based microshell with a particular 3D shape and a specific pattern of nanoscale features (e.g., nanoscale pores, channels, ridges, tubules). [38][39][40] The sustained reproduction of a given diatom species can yield enormous numbers of diatom cells with the same 3D microshell shape. 42,43 Such intricate, genetically precise, and massively parallel 3D self-assembly under ambient conditions has no analog in man-made processing. Continued progress in the genetic modification of diatoms promises to yield microshells with shape...

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