Advanced Ceramics / Raw and Processed Materials

Developing Ceramic Nanofibers

October 1, 2011
Ceramic nanofibers can offer a number of technical advantages in a variety of applications.

Figure 1. Uniform ceramic fibers feature fiber diameters in the range of 75-125 nm.


Technical ceramic products are traditionally made in a number of ways, including slip casting and injection molding. In these processes, tiny ceramic particles are mixed with water and other liquids as a critical step in the process. The ceramic industry has made significant advances in these methods to attain better specifications.

However, a very different method has been developed. The process begins with polymer chemistry, which is used to form ultrafine fibers that are treated and converted into ceramics. These ceramic materials feature characteristics that are useful in many industries and applications, including automotive, energy, pharmaceutical, and plastics and polymers.

Uniform ceramic fibers feature fiber diameters in the range of 75-125 nm. Studies of the ceramic fibers using scanning electron microscope (SEM) images (such as the one shown in Figure 1) have been inconclusive regarding fiber length due to the narrow range of imagery using this analytical method. However, SEM analysis confirms the narrow range of diameters. Some of the ceramic materials that can be made into fibers are listed in the sidebar.

Figure 2. A single ceramic fiber "holds" tiny catalyst particles in its surface.

Development Process

The University of Akron is globally respected for its polymer science and engineering programs, which have roots in the rubber and tire industry. Around 1990, Darrell Reneker, Ph.D., left a research position with The National Institute of Standards and Technology to join the faculty in the university's Polymer Science department. Reneker's interest focused on a 1930s process called electrospinning, which is used to make nano-scale polymeric fibers.

The concept behind electrospinning is that a liquid polymer, when charged positively, can be drawn to a negatively charged collection plate. The process requires very low power (measured in milli-amperes), but very high voltage (in the range of 20-75 kilovolts). Companies in the filtration industry have been making nano-scale fibers for decades to improve particle capture. Electrospinning is believed to be the most prevalent method for making nano-scale fibers.

In 1989, George Chase, Ph.D., joined The University of Akron's Chemical Engineering department. In the early 1990s, Chase's interest in filter media with fine fibers led him to collaborate with Reneker in making polymeric nanofibers. Interests in fibers for high-temperature applications led the two researchers to fabricate ceramic nanofibers made by a polymer fiber template that is calcined to produce a pure ceramic material.

Together, the two researchers discovered that electrospinning can be used to make ceramic fibers, beginning with a polymer mixture and finishing with a heat treating process. The results were significant because the ceramic fibers are well into the nano-scale range of diameters (100 nm ñ 25 nm). The University of Akron Research Foundation has secured patents on Chase and Reneker's inventions.

Later research by Chase and his students showed that ceramic fibers can be "functionalized" by adding materials to the polymer mixture. An example of this is the inclusion of catalysts, which results in "catalyzed ceramic nanofibers."

Figure 2 illustrates a single ceramic fiber that "holds" tiny catalyst particles in its surface. The black spots on the fiber are palladium particles embedded in the surface of the ceramic fiber. (Validation of the process to make catalyzed fibers was funded by the National Science Foundation.)

Commercialization

In 2008, MemPro Ceramics Corp. entered into an exclusive license with The University of Akron Research Foundation to use intellectual property developed by Chase, Reneker and others at the university. This license is supported by international patents, as well as unpatented knowhow protecting the fiber-making process.

In 2010, MemPro designed and built a pilot production system, called PreciseFiber™, which increased the laboratory-scale production rates 100-fold and allowed MemPro to begin supplying samples to customers. A PreciseFiber production system is in development that will scale up 100-fold from pilot scale and allow the company to eventually make metric ton quantities.

Applications

Ceramic nanofibers offer a number of technical advantages, including:
  • Large surface area, leading to high efficiency
  • Small diameter (nano-scale) and long length (macro-scale) keep these materials from being classified as nanoparticles
  • Fibers can be made in various forms (e.g., polymer with the ceramic precursor in the polymer, crosslinked polymer, ceramic fibers with no polymer content, catalyzed ceramic fibers)
  • Catalyzed fibers have catalyst particles "embedded" in the surface of fibers
In 2006, manufacturers in the automotive and chemical industries were invited to preview potential applications for ceramic nanofibers. Initial discussions focused on filtration, but they quickly moved on to additional possibilities. For example, the large surface area of nanofibers suggests that catalyzed fibers might require much less catalyst metal, such as the platinum, palladium and rhodium used in automotive catalytic converters, as well as other catalysts used in the production of chemicals and pharmaceuticals.

Development is ongoing for applications such as automotive exhaust systems, energy production, pharmaceuticals, specialty chemicals and the enhancement of polymers.

For more information, contact MemPro Ceramics Corp. at 585 Burbank St., Broomfield, CO 80020; call (888) 868-9222; email sales@mempro.com; or visit www.mempro.com.

SIDEBAR: Potential Nanofiber Materials

Aluminum oxide...(Al2O3)
Aluminum borate (2Al2O3-B2O3)
Alumina nitride (AlN)
Aluminum titanate (Al2TiO5)
Aluminum zirconate (Al2O3/ZrO2)
Boron carbide (B4C)
Barium titanate (BaTiO3)
Boron trioxide (B2O3)
Boron nitride (BN)
Cerium (IV) oxide (CeO2)
Ceria zirconia oxide (CexZr1-xO2)
Cobalt (II,III) oxide (Co3O4)
Chromic oxide (Cr2O3)
Indium oxide (In2O3)
Indium tin oxide (In2O3/SnO2 (90/10))
Lithium zirconate (Li2ZrO3)
Cordierite (Mg2Al4Si5O18)
Magnesium boride (MgB2)
Magnesium silicate (Mg3Si4O10)
Magnesia oxide (MgO)
Magnesium titanate (MgTiO3)
Manganese oxide (Mn3O4-Mn2O3)
Molybdenum disilicide (MoSi2)
Mullite (Al6Si2O13)
Nickel oxide (NiO)
Nickel ferrite (NiFe2O4)
Nickel titanate (NiTiO3)
Silicon carbide (SiC)
Silicon dioxide (SiO2)
Tin oxide (SnO)
Tin (IV) oxide (SnO2)
Tantalum nitride (TaN)
Titanium diboride (TiB2)
Titanium carbide (TiC)
Titanium carbonitride (TiCN)
Titanium nitride (TiN)
Titanium dioxide (TiO2)
Tungsten carbide (WC)
Tungsten trioxide (WO3)
Zinc oxide (ZnO)
Zinc peroxide (ZnO2)
Zirconium oxide (ZrO2)
Zirconium-yttrium oxide (ZrO2/Y2O3)


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