Gas-Solid Displacement Reactions for Converting Silica Diatom Frustules into MgO and TiO2
- Iowa State Univ., Ames, IA (United States)
Technology for the microfabrication of freely moving parts began with a Bell Labs microgear spun by an air jet, and electrostatic silicon micro motors in the mid-1980s. It continued with development work on micropositioning of optics, miniature heat exchangers, small fluidic devices, and chemical reaction chambers. Recently, there has been a great deal of interest centered on the design and manufacture of devices of nanometer proportions and this speculation has spawned a new industry named, nanotechnology. Despite the technological and economic promise of this technology, current commercial micro/mesofabrication methods have largely been based upon two-dimensional processing principles which is not well suited to the low-cost mass production of three-dimensional micro devices with complex geometries and meso/nanoscale features. Diatoms are three dimensional (3D) microstructures from nature that provide a practical alternative for nanotechnology and microfabrication. Diatoms (Figure 1) are single-celled micro algae that form rigid cell walls (frustules) composed of amorphous silica. Their dimensions can range from less than 1 micron to several hundreds of microns. They are distributed throughout the world in aquatic, semi-aquatic and moist habitats, and extremely abundant in freshwater and marine ecosystems. Diatoms are thought to be responsible for up to 25% of the world's net primary production of organic carbon (by transforming of carbon dioxide and water into sugars by photosynthesis). Approximately 105 unique diatom frustule shapes have been claimed to exist in nature. The frustules are composed of two valves that fit together like a petri-dish, connected to each other by one or more girdle bands. The frustule wall consists of a nanoporous assembly of silica nanoparticles. They absorb soluble silica from water even at extremely low concentrations and metabolize and deposit it as an external skeleton. Continued reproduction of a single parent diatom can yield large numbers of descendant diatoms, each of which possesses a frustule with the same microshape and meso/nano features. Each mitotic division results in the formation of two differently sized daughter cells, one that is the same size as the parent and one that is slightly smaller. Therefore, over successive generations the mean cell size of a population decreases and standard deviation about this mean increases. It is believed that when a cell decreases in size to a diameter of less than about 30 to 40% of the maximum diameter for a given species, sexual reproduction initiates. This enables an entirely new frustule to be generated that is many times larger than either parent. Importantly, these newly formed large cells rapidly resume asexual reproduction and are essentially ''immune'' to sexual reproduction until an appropriate small cell size is obtained.
- Research Organization:
- Ames Lab., Ames, IA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- W-7405-Eng-82
- OSTI ID:
- 837272
- Report Number(s):
- IS-T 2488; TRN: US200506%%84
- Resource Relation:
- Other Information: TH: Thesis (M.S.); Submitted to Iowa State Univ., Ames, IA (US); PBD: 19 Dec 2004
- Country of Publication:
- United States
- Language:
- English
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