ONLINE EXCLUSIVE: Nanoscale Ceramics: The Building Blocks of Nanotechnology

January 11, 2006
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Ceramic nanomaterials are beginning to offer a foundation for a wide range of innovative, value-added products.

Nanoscale materials are the building blocks of nanotechnology. In this picture, each sphere represents an atom.


Production plants capable of producing tons per month-and even tons per week-of nanoscale ceramic particles are already in operation. Shown here is NanoProducts' Longmont, Colo., facility.

Nanomaterials-powders that have been precision manufactured to sizes less than 100 nanometers (also known as nanoparticles, nanopowders, quantum dots, nanowires, nanoplatelets and nanocrystals)-are emerging as one of the fastest-growing segments of the ceramic industry. One nanometer equals 0.001 micron and corresponds to about four or five bonded atoms. In these size ranges, most compositions begin to show commercially useful novel properties and unusual performance, in part because of their size confinement effects-i.e., performance that is influenced by Newtonian and size-confined quantum physics.1

Nanomaterials are not new. The catalyst, carbon black, sol, fumed oxide and pigment industries have already commercialized several simple oxide nanopowders, nanoscale dispersion products and nanoparticle manufacturing processes that are an integral part of today's ceramic industry and the global economy.

What is new in the developing nanomaterials industry is the emergence of low-cost, high-volume, novel processes and processing innovations, which offer complex compositions with a level of precision and characteristics that were, in the past, either too difficult to achieve or too expensive to be commercially useful.

The continued development of processing technologies, the availability of better instruments to measure quality and features at ever-shrinking dimensions, the integration of computer-aided manufacturing, and a market demand for materials innovation is fueling the growth of nanomaterials and related nanotechnologies. Combined with the expertise that already resides in industries such as catalysts, pigments and fumed silica, nanomaterials are beginning to offer a foundation for innovative, value-added ceramic products.

Table 1.

Demand Drivers

Nanoscale materials are the building blocks of nanotechnology. Nanoelectronics need nanoclusters, nanowires, inks and materials for high-density interconnects and layers. Similarly, further increases in data storage density require novel magnetic compositions, and energy storage and batteries require innovations in materials at the nanometer scale. Ceramic parts that sinter faster or at lower temperatures, thereby enabling lower-cost manufacturing, require ceramic powders that are smaller and more reactive. Coatings, performance additives, catalysts, consumer goods such as toothpaste and ultraviolet protection products, bandages and fabrics that offer antimicrobial protection, drug delivery, dental implants, optics, and nanometer-scale precision polishing of silicon wafers, hard disks and micro-electro mechanical system (MEMS) surfaces all require the availability of high-quality, complex, nanoscale materials in high volume at an affordable price.

To be commercially useful, nanoscale materials must possess certain characteristics. Table 1 lists some of the key properties for nanomaterials used in value-added and technology-intensive applications, such as those in the ceramic industry, as well as electronics, displays, energy devices, magnetics, dielectrics, coatings, additives, catalysts, multilayered devices, pigments, security and plastics.

Manufacturing Methods

In addition to the nanomaterial production processes that have already been commercialized, numerous other routes to manufacturing nanomaterials are being explored and developed. While an exhaustive review of all of these techniques is beyond the scope of this article, some of the most common include attrition, solution and vapor methods.

Attrition methods attempt to break coarse, micron-sized particles into smaller particles by applying directed energy, such as milling. Some teams are exploring ways to perform the milling in a carefully controlled thermal, shear and chemical environment, and other teams are exploring the use of ultrasound energy. While appropriate for certain applications, these techniques have been reported to yield a product that is contaminated with the media or vessel that is used to break the coarse particles. Cost, yield and scalability are other issues that remain to be addressed with attrition methods.

Chart 1. (Click image for larger view)

Solution methods attempt to precipitate nanoparticles from liquid precursors. The attractive feature of these processes is their low temperature and capital costs. Some of the most uniform, transparent nanoparticle dispersions available commercially for single-metal oxides are those derived from solution methods. However, solution thermodynamics can sometimes limit the complexity of material compositions that can be cost-effectively manufactured through these processes. Solution methods such as sol-gel processing also often produce hydroxides, which need to be filtered and then calcined at higher temperatures to yield oxides. Both of these steps can be expensive and difficult to control while retaining the material's nanoscale features and yields in high volumes.

Vapor methods first create a vapor comprising atoms and atomic clusters, followed by condensation and quenching of nanoparticles. The benefit of these processes is the diverse range of compositions they can achieve. However, in some versions of this approach, the need for high temperatures can result in higher energy costs, and it can also cause agglomeration and purity issues with some materials. If the quench is accomplished by adding coolants, the raw material and separation costs become higher. In certain cases, vapor methods tend to produce higher particle sizes for compositions (such as titanium oxide) with a very high refractive index and emissivity. Additionally, certain methods of feeding precursors and achieving higher temperatures (e.g., electrical energy) can, in some cases, limit the flexibility and scalability of the process.

A Different Approach

An alternative, patented approach* to creating nanoscale materials has been developed that begins with a solid, liquid or gas mixture. The raw material can be derived from blending different raw materials, and in some cases a fuel can be added. The raw material mixture preferably corresponds to the ratio of the metals desired in the final powders. In the case of fluid precursors, the raw materials are atomized with a reactant gas, such as oxygen. The mix combusts into a product stream with temperatures in the 1600 K (2420ºF) or higher range.

The combustion product stream is further heated in a plasma to achieve peak temperatures greater than 3000 K (4940ºF) at supersonic velocities. The vapor is then cooled, which leads to nucleation of nanoscale powders. Thereafter, the powder-containing gas stream is quenched at near-sonic to supersonic velocities using a Joule-Thompson expansion step. The sonic quenching reduces collisions between the particles and produces free-flowing, non-agglomerated nanopowders, which are then continuously harvested.

If solid raw materials such as commercially available micron-sized ceramic powders are used, these are fed directly into a DC plasma to create a vapor comprising various metals. Thereafter, the nucleation and quench of nanoparticles is performed as explained previously.

Chart 2. (Click image for larger view)

The process has low energy costs because it is thermally integrated. In addition, by using Joule-Thompson expansion, the process avoids the need for coolants or cooling gases and the associated raw material and separation costs. And because the process is based on established combustion processes that have been used to produce carbon black, fumed silica and other nanoparticles, it is easily scalable to larger capacities. Production plants capable of producting tons per month-and even tons per week of-nanoscale ceramic particles are already in operation.

The process has been used to produce more than 200 compositions, including simple oxides, complex doped or multi-metal oxides, non-oxides, and metals in particle sizes as small as 2 to 10 nanometers, coarser 20 to 40 nanometers, 60 to 80 nanometers, and submicron particles. Nanoscale materials produced from this process have been dispersed successfully in water and solvents at high loadings. The process can be used to produce stoichiometric compositions, such as Al2O3, stabilized ZrO2, BaFe2O4 and SiO2, as well as non-stoichiometric compositions, such as BaFe1.5Ox and SiOxNy. The flexibility of the process has enabled systematic nanoscale material discovery and optimized material performance.

The Future

If less expensive micron-scale powders and specialty chemical building blocks suffice for an application, they will continue to be preferred and used. However, as the nanomaterials industry develops and matures, nanoscale materials will increasingly become more cost-competitive with conventional materials, while offering superior or novel performance.

The volume and pricing of nanomaterials is already in a range that makes a number of commercial applications economically compelling. With the increasing availability of nanomaterials and the associated processing know-how, a commercial world based on nanotechnology is beginning to emerge. c

About the Author

Tapesh Yadav is chairman and chief executive officer of NanoProducts Corp., which he founded in 1994. Yadav has a doctorate in chemical engineering from the Massachusetts Institute of Technology and a minor in finance from the Sloan School of Management. He has more than 12 years of experience with a wide range of nanomaterials and related nanotechnology applications, and has been awarded more than 45 U.S. patents on nanomaterials and related nanotechnology applications.

Fore More Information For more information about nanoscale materials, contact NanoProducts Corp., 14330 Longs Peak Court, Longmont, CO 80504; (970) 535-0629; fax (970) 535-9309; e-mail staff@nanoproducts.com; or visit www.nanoproducts.com.

FOOTNOTE: *The Joule-QuenchTM technology, a process patented by NanoProducts Corp.2 References

1. Gammon, D. Nature, Vol. 405, No. 899, 2000; Gleiter, H. Acta Mater., Vol. 48, No. 1, 2000; and Valiev, R. Nature, Vol. 419, No. 887, 2002.

2. U.S. Patent Nos. 6652967, 6641775, 6610355, 6344271, 6228904, 5984997, 5851507 and 5788738.

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