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Altair International realized when it first considered entering the TiO₂ business that entry into the US $9 billion pigment market would require assets and resources beyond its immediate reach, so it asked SRI Consulting (Menlo Park, CA) to identify other profitable niche markets. SRI recommended the ultra-fine TiO₂ nanoparticle technology as a stepping stone to other TiO₂ markets (3, 4). Precursors of the nanoparticles had been observed in intermediate products generated from the ilmenite (FeTiO₃) upgrading process, and Altair believed that it was possible to produce highly stable anatase nanoparticles. (Anatase and rutile are the most common naturally occurring polymorphs of TiO₂.)

Acting on the advice of the consultants, Altair purchased proprietary ilmenite processing technology from BHP Minerals (Melbourne, Australia) in November 1999. They found that simple modifications to the process produced significant quantities of nanoparticles. The ability to produce nanosized particles opened up several new marketing possibilities for TiO₂.

Unusual optical properties appear when the average particle size of TiO₂ is reduced to <100 nm, including high transparency to visible light and high UV absorption. Depending on the angle of incidence of light, nanoparticles of TiO₂ also cause some components of visible light to be reflected and refracted differentially, leading to the phenomenon of iridescence. Several market applications take advantage of these properties, including certain pearlescent or “metallic” paint formulations used in cosmetics, hard coatings, plastics, and self-cleaning additives for porcelain, ceramics, and specialty coatings. Reprographics applications are emerging, in which toners contain resin and hydrophobic TiO₂ particles, as well as TiO₂ particles surface-treated with alkyl polysiloxane. Other applications include industrial and residential filters that exhibit strong germicidal properties and remove odors.

Acquiring the technology
Prior to Altair’s 1999 acquisition of a proprietary ilmenite-processing technology from BHP Minerals, SRI Consulting had issued a very encouraging techno-economic feasibility study of the innovative process (2). Altair’s president and the board of directors agreed that the process had economic potential and synergies with existing projects. Altair acquired the technology and the physical demonstration plant, leased the BHP facility in Reno, NV, and secured the services of key BHP Ilmenite Upgrade Project personnel. The technology transfer included documents detailing 7 years of laboratory and pilot plant test work and several patent applications. The demonstration plant was sized to process 5 tons of ilmenite concentrate per day, and it was operational at the time of purchase. In addition, Altair acquired analytical instrumentation, the use of BHP’s scanning electron microscope, and the shop and fabrication equipment.

The demonstration plant was designed to produce TiO₂ pigments from ilmenite feedstock. Simple modifications of that process and some additional equipment have made it possible to produce significant quantities of nanoparticles economically and made Altair an immediate supplier to the growing nanoparticle market.

The proprietary technology was originally developed to make paint pigment at a cost forecast to be substantially lower than commercial technologies used today. This technology was subsequently modified to make nanocrystalline materials of superior quality, economically, and in large quantities. Shortly thereafter, in November 1999, a decision was made to defer work temporarily on the ilmenite upgrading process and pursue the nanoparticle and controlled crystal growth technology.

The company is currently developing special nanomaterials with potential applications in fuel cells, hard coatings, catalysts, cosmetics, paints, batteries, semiconductors, and telecommunications. The main focus has been to develop a range of TiO₂ nanomaterials with properties adapted to different applications.

Advantages and challenges

Figure 1. The new TiO2 process allows for tightly controlled and relatively large-scale production. A thin-film hydrolysis technique is coupled with a controlled thermal treatment and dispersing package.

The new pigment process (Figure 1) handles a variety of raw materials, ensuring good recovery from the ore. Waste streams are greatly decreased because HCl is regenerated and recycled as a concentrated solution. By separating the purification of the solution from the TiO₂ hydrolysis step, the process produces very pure TiO₂ and allows great flexibility in setting the particle size and other characteristics of the product. Further development of one step of the pigment process gave birth to the new method for making nanosized particles at very low cost compared with existing methods. This process presents the possibility to incorporate additives during the crystal growth process, which provides the ability to vary particle size, photocatalytic activity, and other characteristics.

The lixiviant acid (the HCl used to leach the ore) is recycled, leaving the metallic impurities—predominately iron—as innocuous metal oxides that are suitable for sale or use as landfill. These waste products are more benign than the waste discharges from the sulfate and chloride TiO₂ pigment processes, which include soluble iron compounds, dilute acids, and miscellaneous inorganic ore contaminants. Disposal of the waste products from the sulfate and chloride processes has become an international environmental issue, challenging the viability of existing plants. The costs of waste disposal have also been responsible for large increases in the manufacturing costs of TiO₂ pigments in areas where the iron salts produced by the traditional process can no longer be disposed of in deep wells.

Re-engineering the process
Existing equipment was used for the test work, and all energies were focused on developing the novel nanotechnology. Hundreds of combinations of experimental conditions were tested, and bench-scale experiments expedited the process development. In-house analytical laboratory capabilities provided the rapid product characterization required to develop the

Commercial products

Altair’s Altium TiNano 40 series of nanosized anatase-based materials covers a range of applications: VHP is produced without contamination and without the use of chemical controls. It exhibits high UV absorption, high photocatalytic activity, and high thermal stability. It is suitable for environmental purification, photocells, catalysts, and similar ceramic applications. USP qualifies as a U.S. Pharmacopeia-grade material. It has UV absorption characteristics that make it suitable for cosmetics and other applications requiring USP-grade material. HPC exhibits high UV absorption, high photocatalytic activity, and high thermal stability. Its uses and characteristics are similar to the VHP grade. LPC exhibits very high UV absorption, an important factor in cosmetics and coatings applications. It has the least photocatalytic activity of the TiNano 40 series without special coatings. Applications include pigments, cosmetics, and chemical modification of surface chemistry and physical characteristics. CNPC is a nonphotocatalytic product. Its very high UV absorption makes it suitable in cosmetics and coatings applications requiring USP-grade base material. A hydrous alumina and silica wet treatment totally eliminates photocatalytic activity.

nanotechnology quickly. When an acceptable combination of conditions was achieved, a production-scale run was made to demonstrate the feasibility of operating at a large scale under those conditions. More than 30 production-scale runs were made in a period of 3 months. Within a few months, the technical team successfully defined the conditions that enabled control of size and morphology, as well as the ability to control photocatalytic activity and the development of several anatase commercial products (see box, “Commercial products”).

The new proprietary process couples a dense-film crystal-growth technique with a controlled thermal treatment and dispersing package (Figure 1). This process allows for tightly controlled and relatively large-scale production.

External R&D affiliations
Altair has quickly established relationships with several renowned academic research organizations including Massachusetts Institute of Technology (MIT); the J. Heyrovsky´ Institute of Physical Chemistry and the Czech Republic Institute of Chemical Technology (both in Prague); and the University of Nevada, Reno. Altair has also contracted the services of BHP Steel Research in Port Kembla, Australia. Industrial collaborators include Nanopowder Enterprises Inc. (Piscataway, NJ) and Inframat Corp. (North Haven, CT).

MIT is working with Altair on the research and development of a novel fuel cell using micrometer-size rutile crystals, stabilized at 1150 °C, as a support substrate. The research program will focus on the synthesis and fabrication of a superior anode and cathode material. The integration of these structures with yttria-stabilized zirconia (YSZ) solid-film electrolytes produces a fuel cell that exhibits superior mechanical and thermal stability. The collaborative program will examine Altair’s stable porous structures as the support materials for cathode and anode catalysts.

The J. Heyrovsky´ Institute of Physical Chemistry is collaborating with Altair Technologies to enhance the understanding of nanomaterial photocatalytic activity (PCA) mechanisms (see box,“Photocatalytic TiO₂”). The PCA of TiO₂ semiconductor materials has been studied for several years (5). The photocatalytic mechanism using nanosized TiO₂ has been applied to the low-cost detoxification of organically polluted waters (5), destruction of bacteria and viruses (5, 6), and air purification (5). Several of these areas are now commercially successful.

The J. Heyrovsky´ Institute conducted photocatalytic activity experiments using a research standard test that measures the kinetics of disappearance of 4-chlorophenol. Their results indicate that Altair’s proprietary surface treatment process provides control over the PCA kinetics; that is, low-level treatments provide relatively high-PCA materials and vice versa (7). Preliminary experiments demonstrated that the PCA of TiNano 40 HPC was ~2.5 times that of the benchmarking material, Degussa’s P25 product.

The J. Heyrovsky´ Institute also studied the fundamental mechanisms of lithium insertion in Altair’s nanosized TiO₂ particles (8). It is believed that the mechanisms being defined will ultimately apply to a range of photoelectrochemical applications, including secondary lithium batteries, solar cells, and electrochromic devices. The results from these experiments indicate that Altair’s TiO₂ nanoparticle material behaves similarly to nanocrystalline anatase produced through exhaustive laboratory preparation from titanium isopropoxide. In addition, Altair’s TiNano 40 products exhibited unusually high thermal stability.

Photocatalytic TiO2

In general, the mechanism for the photocatalytic conversion is where Ebg is the band gap energy of the TiO2 semiconductor (5). Commercializing applications that use the unique capabilities of semiconducting TiO2 requires a material that is photoactive, able to use visible or near-UV light, biologically and chemically inert, photostable, and inexpensive. Altair’s TiNano 40 series products fulfill all of these criteria.

The Department of Chemical and Metallurgical Engineering at the University of Nevada, Reno, and the Institute of Chemical Technology are also collaborating with Altair in understanding the nanoparticle physical and chemical characterization by providing supplemental data and verifying previous analytical work. Analytical techniques include BET (Braunauer–Emmett–Teller method) surface area measurements, chemical analysis using inductively coupled plasma–mass spectroscopy (ICP–MS), and atomic force microscopy (AFM) imaging.

BHP Steel Research is studying PCA as it applies to paint pigments (9–11). Using their proprietary technique, the coatings group has performed numerous experiments on Altair’s nanoparticles. Electron spin resonance (ESR) is used to measure the rate of formation of hydroxy radicals to determine the degree of PCA. This technique is used to estimate the chalking (weathering oxidation) of the coated materials. Ordinarily, it requires years of testing to gain this PCA insight, but the ESR technique measures the formation of the extremely reactive hydroxyl radical (HO·) by “trapping” the free radicals using 5,5-dimethylpyrroline-N-oxide (DMPO). For the most part, the results of the BHP Research experiments were consistent with the ones carried out at the J. Heyrovsky´ Institute.

Nanopowder Enterprises Inc. (NEI) and Inframat Corp. have collaborated with Altair to develop a nanoparticle feed for ceramic hard-coating applications. Hard-metal and ceramic coatings are used in thermal spray applications to improve wear and corrosion resistance in machinery, heavy equipment, marine vessels, and similar applications. A significant part of the funding in these areas comes from the U.S. Office of Naval Research.

Altair is organizing a technical steering committee that currently includes executives from BHP and SRI Consulting to provide technical and commercial guidance in the pigment and the nanoparticle technology development markets. It was this committee that saw the potential in developing the emerging nanoparticle technology.

Putting the process to work
Currently, Altair has filed five patents in the U.S. and international patent offices. Ten additional invention conceptions have been recorded with emphasis on controlling particle size, morphology, and chemical and electrochemical activity. Research and experimental work is being carried out to define the scope of these innovative technologies.

While Altair pursues these research objectives, the primary focus has been to commercialize the TiNano 40 series products as quickly as possible. Altair hired Ken Lyon as operations manager and president of Altair Technologies Inc. in January 2000 to assist in moving from a research mode to a production mode of operating. He has developed a program for scaling up capacity to 200 t/year by the fall of 2000 then to 1500 t/year in 2001. Initial sales to customers have been scheduled for the fourth quarter of 2000.

Product characterization

Figure 2. SEM images are used to determine particle sizes and shapes, a critical factor in determining material properties. This photomicrograph shows a typical TiNano 40 nanosized TiO2 material before dispersion.

For many applications, it is critical to determine the median particle sizes and size distributions. These measurements are made directly using a laser scattering instrument. Individual particle sizes and shapes are determined using scanning electron microscope images. Figure 2 is a photomicrograph showing typical TiNano 40 nanosized TiO₂ before dispersion. The primary particles are ~40 nm in diameter.

X-ray diffraction is used to determine the degree of crystallization of the nanoparticles. The Scherrer formula (12) estimates particle size by measuring the crystal diffraction line broadening that is directly related to the crystal spacing and size. Crystalline TiO₂ exists predominately as the anatase polymorph in Altair’s TiNano 40 series products. The Scherrer formula is

where

t = characteristic crystal size (nm)

= wavelength of incident radiation (Cu K₁ = 0.1540562 nm)

= characteristic diffraction angle (0.221 radians for anatase)

B = angular width of the peak at half maximum height (radians)

A third approach to particle size estimation is applied by calculating a spherical diameter (d_BET ) from the BET surface area (SA) and specific gravity ().

Used together, laser scattering, X-ray diffraction, surface-area-derived diameters, and SEM images ensure a high degree of confidence in particle size estimates and distribution.

Altair’s chemical and physical characterization laboratory is also equipped with inductively coupled plasma–optical emission spectrometers (ICP–OES), differential thermal and thermal gravimetric analysis (DTA, TGA) instruments, colorimeters, and scanning UV spectrometers to determine impurities, thermal properties, whiteness, and UV absorption. This complement of equipment allows for thorough chemical and physical characterization. Development of the understanding of these characteristics is ongoing and is necessary to consistently produce a high quality nanoparticle product.

Building on success
Altair International has entered the field of nanosized materials by engineering, marketing, and producing the TiNano 40 series products. The proprietary technology possesses special attributes to control the purity of the product, select the size of the resulting particles within a very narrow range, and precisely define surface morphology.

Altair Technologies is participating in the acceleration of the development and commercialization of nanotechnology by broadening the range of materials available to meet the interests of different markets and industries. Development of the ilmenite upgrading and visible pigment processes will begin in earnest when appropriate development partners are selected.

References

1. Production and Stocks of Titanium Dioxide; Current Industrial Report M325AT(00)-09, U.S. Census Bureau, September 2000. (Available at www.census.gov/ftp/pub/cir/www/m28a.html; accessed Oct 24, 2000).
2. www.infac.com/inorganic.htm (accessed Oct 5, 2000).
3. Thiers, E. Technoeconomic Assessment of a Novel Process for Upgrading Titanium Dioxide; SRI Consulting: Menlo Park, CA, July 1999.
4. Thiers, E. SRI Consulting Report to Altair on Nano Technology Development and Market Strategy; SRI Consulting: Menlo Park, CA, 1999.
5. Mills, A.; Le Hunte, S. J. Photochem. Photobiol. 1997, 108, 1–35.
6. Matsunaga, T.; Tomoda, R.; Nakajima, T.; Nakamura, N.; Komine, T. Appl. Environ. Microbiol. 1998, 54, 1330.
7. Jirkovsky, J. Characterization of Photocatalytic Properties of the Titanium Dioxide Samples R45, R47, and R51; J. Heyrovsky´ Institute of Physical Chemistry: Prague, 2000.
8. Kavan, L. Lithium Insertion Electrochemistry of Altair Titanium Dioxide; J. Heyrovsky´ Institute of Physical Chemistry: Prague, 2000.
9. Barker, P. Preliminary Summary of Findings—Photocatalytic Activity of Altair Products by the DMPO Spin Trapping Technique; BHP Research, Port Kembla, NSW, Australia, 2000.
10. Barker, P. Evaluation of TiO₂ Pigments by ESR Spectroscopy Part 1: Principles of Spin Trapping and Feasibility Study; BHPR/N/1998/079; BHP Research: Port Kembla, NSW, Australia, 1998.
11. Barker, P. Evaluation of TiO₂ Pigments by ESR Spectroscopy Part 2: Scale-up, Method Development, and Correlation with Accelerated and Natural Exposure Data, BHPR/N/1998/080; BHP Research: Port Kembla, NSW, Australia, 1998.
12. Cullity, B. D. Elements of X-ray Diffraction, 2nd ed.; Addison-Wesley: London, 1978; pp 101–102.

Dirk Verhulst is a senior metallurgical engineer with BHP Minerals, Center for Minerals Technology. He received his undergraduate degree in chemical engineering from the Free University of Brussels and his Eng.Sc.D. in extractive metallurgy from Columbia University. He worked as an R&D engineer at ASARCO Inc. in South Plainfield, NJ, and at Union Minière, Hoboken, Belgium.

Timothy M. Spitler is a project engineer for BHP Minerals, Center for Minerals Technology. He received a B.S. degree in chemical engineering from Tri-State University, Angola, IN, where he received the AIChE Design Award. Before coming to work for BHP, he worked for Dupont White Pigment and Mineral Products Operations and Dupont Freon R&D at several locations.

Bruce J. Sabacky manages process development for BHP Minerals, Center for Minerals Technology. He received his B.S. and M.S. degrees in metallurgical engineering from South Dakota School of Mines and Technology, Rapid City, and his Ph.D. in materials science and mineral engineering from the University of California, Berkeley. He has worked as a metallurgical engineer at AMAX Extractive Research Laboratory, and he was the manager of engineering at Bandgap Technology Corp. He began work at BHP Minerals as a principal process engineer.