Ceramic Industry

INVESTING IN CERAMICS: The Perfect Microsphere

January 11, 2006
Technology available through a partnership between Harper International and Brace GmbH can be used to create perfectly round microspheres for a variety of ceramic applications. More than 50 people traveled to Lancaster, N.Y., in June 2005 to get a firsthand look at Harper International's new laboratory dedicated to microsphere and encapsulation technology from Brace GmbH.

A scanning electron microscope image of silica microspheres.

More than 50 people traveled to Lancaster, N.Y., in June 2005 to get a firsthand look at Harper International's new laboratory dedicated to microsphere and encapsulation technology from Brace GmbH. Attendees represented a wide range of industries, including pharmaceutical, agricultural, food processing and ceramics. But they all had one thing in common-a significant amount of interest in finding out how this technology might help them improve their product quality and production efficiency.

For that is precisely what the technology promises to do. First introduced in the 1990s to encapsulate uranium for nuclear energy applications, the process enables a variety of different materials to be formed into perfectly round microspheres or encapsulated with a host of shell materials. According to John Imhoff, marketing manager for Harper International, the process reduces manufacturing costs, produces a narrow particle size distribution and improves quality compared to conventional processes.

"The elimination of high-pressure systems and moving parts reduces operating and maintenance costs while maximizing running time. The process forms the feed into spheres of uniform size and perfect roundness, yielding a high-quality product," he says.

Figure 1. A schematic of the BRACE-Process.

Process Description

In the patented BRACE-Process, a liquid (typically a slurry or sol-gel for ceramics) is gently pumped through a vibrating nozzle system. As the fluid exits the nozzle, it is broken into uniform droplets. The surface tension of the droplets molds them into perfect spheres that are gelled during a short period of free fall. The droplets can be solidified in a gas or liquid medium through a cooling, drying or chemical reaction (see Figure 1).

The resulting spheres have a monodispersed grain size and a narrow size distribution (dmax/dmin œ 1.10, 1.05, 1.01). They are free flowing and roll with almost no friction or abrasion, thereby minimizing agglomeration and eliminating dust during material handling operations. The spheres can range in diameter from 50 to 6000 µm (6 mm), depending on the size requirements of the product, and can be modified through subsequent washing, additional chemical reactions, drying, calcining, sintering, coating or sorting processes.

"The technology's ability to produce small, uniform particles in smooth, perfectly round spheres is a significant benefit in many ceramic applications," says Imhoff. "Compared to conventional processes such as spray drying or dry pressing, the technology produces spheres with much higher densities and consumes significantly less energy, primarily because it's a much more efficient process. With spray drying, for instance, the material has to be first atomized and then dried at relatively high temperatures. It must then be screened, and much of the material typically has to be reprocessed to achieve the desired particle size. The BRACE-Process cuts out all of these extra steps. Additionally, spray drying produces small sized particles, there is often an accumulation of product in the drying chamber and ducts, and the density tends to be lower than what our process can achieve."

According to Imhoff, the technology can also eliminate the need for polishing steps that are sometimes required after dry pressing.

Ceramic Applications

In Harper International's laboratory, a pilot-scale unit capable of producing about 1 liter per hour is used to demonstrate the potential of the technology in various applications. Imhoff notes that the technology is easily scalable for production operations up to 1000+ liters per hour by increasing the number of nozzles and the size of the machine. "Production units have a minimal space requirement (15 to 40 square feet), consume a low amount of energy and are noiseless during operation. They operate at atmospheric pressure or slightly above, and they require practically no maintenance," he says.

Monodispersive alumina microspheres.

Few restrictions exist on the types of microspheres that can be produced using this process. The technology has been used to create dry metal oxide microspheres based on alumina, zirconia, hafnia, titania, ceria, silica and mixed oxides used as highly sinteractive press feed for the production of high-tech ceramics. Through calcining, the pore size and surface area of these microspheres can be tailored to the end user's exact specifications. The resulting microspheres can be used as catalyst carriers, homogeneous catalysts or filtering materials. Additionally, abrasion-resistant microspheres made from sintered aluminum, zirconium and hafnium oxides can be used as highly effective grinding media.

Nuclear metal oxides.

Other applications under development include nuclear-powered spacecraft and nuclear medicine, solar cells, bone fracture repair, cosmetic surgery, oil and gas recovery, and oil refining.

As users continue to experiment with the technology-both in Harper's laboratory and in their own pilot-plant installations-additional uses are likely to emerge.

"Ceramic materials are under-utilized in a number of areas because of the high expense and difficulty of getting a narrow particle size distribution and high yields of perfectly round spheres. The BRACE-Process can make these applications much more attractive and can help ceramic manufacturers gain a larger market share from metallic or other materials currently being used in these fields," Imhoff says. c

For More Information For more information about Harper's microsphere and encapsulation laboratory, or the BRACE-Process, contact Harper International Corp. at West Drullard Ave., Lancaster, NY 14086-1698; (716) 684-7400; fax (716) 684-7405; e-mail info@harperintl.com; or visit www.harperintl.com.