Nanosized Ceramic Powders

A recent example of the potential of nanosized ceramic powders in medicine is the demonstration that 5-nm cerium oxide (CeOi) nanoparticles can prolong the life of brain cells. Usually these cells live for around 25 days in the laboratory, but after a low dose of the nanoparticles they have been shown to survive and function normally for 6 months. The hope is that this approach might one day be used to treat age-related disorders such as Alzheimer s disease. It was also... 

Nanosized ceramic powders have grain sizes on the order of tens of nanometers or less conventional ceramic particles typically have grain sizes of several micrometers or more. 

Table 9.2 Oxygen content of nanosized AIN powders and ceramics samples, sintered without sintering additives.

It is proposed that advanced ceramic and nanosized ceramic powders will record a healthy AAGR of 8.9% between 2006 and 2011, boosting the market volume in the US from US 2.2 billion in 2006 to US 3.4 bUUon in 2011 (McWilliams, 2006). 

The synthesis of microsized to nanosized ceramic powders with a spherical geometry and a narrow grain size distribution, from aqueous solutions or colloidal suspensions. 

Novel nanoporous membranes have recently been developed by Peled and coauthors [156]. Such membranes consisted of PTFE as the backbone with a nanosized ceramic powder (Aerosil 200 or Aerosil 130) dispersed in it. An aqueous solution of sulfuric acid adsorbed inside the pores of such membranes acted as an ionic conductor. Thus prepared membranes consisted of 50-200 nm spherical particles with nanovoids between them. They have been found to be quite elastic. Preliminary tests conducted using FCs with 250 pm thick nanoporous membrane, with electrodes on which 4 mg Pt/cm was dispersed on both the anode and the cathode, and fueled by 1 M methanol (in 3 M aq. H2SO4) flowing at the rate of 180 ml/min, against 3 atm of dry air, yielded 50 and 130 mW/cm at 80 °C and at 130°C, respectively. The crossover of methanol in these relatively inexpensive membranes was 0.27 and 0.56 A/cm at 80 and 130°C, respectively. Its selectivity to methanol was estimated to be in the same range as PVDF-ceramic powder hybrid [157]. 

Contrary to the above mentioned technologies, which are based on arc plasma furnaces, a radiofrequency (RF) plasma system can process fine powders without granulation in a continuous operation. This possibility, together with the advantageous features of the thermal plasmas mentioned above, offer great perspectives for the synthesis of special ceramic powders such as spinel ferrites [5]. The RF plasma treatment produces nanosized metal and/or oxide powders depending on the parameters of processing. In this paper application of an RF thermal plasma system for the treat-... 

Yamanaka T, Fukumori Y (1995) Molecular aspects of the electron transfer system which participates in the oxidation of iron by Thiobacillus ferrooxidans. FEMS Microbiol Rev 17 401-413 Yanagisawa K, Ovenstone J (1999) Crystallization of anatase from amorphous titania using the hydrothermal technique Effects of starting material and temperature. J Phys Chem B 103 7781-87 Yang J, Mei S, Ferreira IMF (2000) Hydrothermal synthesis of nanosized titania powders lirfluence of peptization and peptizing agents on the crystalline phases and phase transition. J Am Ceram Soc 83 1361-1368... 

Yang, J., Mei, S., and Ferreira, J.M.R, Hydrothermal synthesis of nanosized titania powders Influence of tetraalkyl ammonium hydroxides on particle characteristics, J. Am. Ceram. Soc., 84, 1696, 2001. 

As compared to materials produced by traditional ceramic technologies using micrometer-sized powders, ceramics prepared from nanosized powders usually have different characteristics a dense ceramic with a submicron stracture is synthesized from nanopowders at relatively low temperatures (1100-1300 °C) and has a higher strength and a larger electroconductivity. 

Reactions of nanoscale materials are classified with respect to the surrounding media solid, liquid, and gas phases. In the solid phase, nanoscale crystals are usually connected with each other to form a powder particle (micron scale) or a pellet (milli scale) see Figure 14.1. Two or more materials (powder or pellet) are mixed and fired to form a new material. The nanosized structure is favored, due to the mixing efficiency and high reaction rate. Alloys (metals), ceramics (oxides), cement (oxides), catalysts (metals and oxide), cosmetics (oxides), plastics (polymers), and many functional materials are produced through solid reaction of nanoscale materials. One recent topic of interest is the production of superconductive mixed oxides, where control of the layered stracture during preparation is a key step. 

Ceramic powders SiC tor abrasives Nanosized TiQs tor sunscreen Bioactive glasses tor bone reconstruction Bayer process AI2Q3 tor the production of Al using Hall-H4roult cells... 

Nanotechnology is a hot research topic. The field is trendy, popular, and high-tech. Although silica and iron oxide nanoparticles have a commercial history spanning half a century or more it is really only within the plast 15-20 years that technologies have been developed for producing ultrapure nanosized powders of a range of ceramics. The... 

The market for nanosized powders is much smaller than for conventional ceramic powders, but the cost per kilogram is much higher. Despite progress in scaling up production and reducing costs, nanosized powders remain relatively expensive (often 100 times more than conventional ceramic powders). 

In the form of a table compare the cost of conventional (micrometer-sized) ceramic powders with the nanosized equivalents. 

Effects of the nature of the dopants, thermal pretreatment, and sintering temperature on SPS of transparent alumina have been systematically investigated [68]. A slurry of a-Al203 was doped with Mg, Zr, and La nitrates or chlorides, with concentrations of 150-500 weight ppm and then freeze-dried to produce nanosized doped powders ( 150 nm). The powders were sintered by SPS to yield transparent polycrystaUine alumina ceramics. Transparency of the nanosized AI2O3 ceramics was shown to depend mainly on the way the powder was prepared, as well as the nature of the dopants. RIT values at 640 nm of the samples doped with Zr02, MgO, and La203 were 40.1, 44.1, and 48.1 %, as compared to 30.5 % for pure alumina. 

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