Department Faculty

Kenneth Sandhage

Professor

Ph. D., Massachusetts Institute of Technology, 1987

Tel. (614) 292-6731, Fax (614) 292-1537

Sandhage.1@osu.edu

  • Materials Science and Engineering at The Ohio State University
  • Fellow, The American Ceramic Society, 2002
  • Research Accomplishment Award, Ohio State University, 2001
  • Alexander von Humboldt Fellowship, 1998
  • Outstanding Materials Engineer Award, Purdue University, 1997
  • Lumley Research Award, The Ohio State University
  • Ross Coffin Purdy Award (best paper), ACerS, 1996
  • Co-director, Patrick K. Gallagher Thermal Analysis Center

Professor Sandhage and his group have invented and developed several near net-shape processing routes (BaSIC, DCP, VIMOX) to advanced ceramics and composites for biomedical, electronic, sensor, magnetic, structural, and refractory applications. Active research includes the near net-shape processing of:

  • chemically-tailored microcomponents with complex, three-dimensional (3D) shapes and nanoscale features (e.g., nanoporous capsules for drug delivery) from biological preforms via the BaSIC process
  • ultra-high-melting, carbide/refractory metal composites (e.g., for solid-fueled rocket nozzles) via the DCP route
  • creep resistant composites of oxide and intermetallic phases with matched thermal expansion coefficients (for applications involving extensive thermal cycling) via the DCP route
  • complex-shaped humidity sensors with controlled pore structures via the VIMOX process

Other active research includes: studying the basic mechanisms of fluid/solid reactions for synthesizing ceramic composites and superconductors; developing a combinatorial chemical/microcantilever method to study the role of segregants on interfacial fracture; and using novel gas/solid reactions to greatly enhance oxide surface areas.

Above: View of open end (other end is closed).

Below: Longitudinal view revealing fine (102 nm dia.) pores.
Figure 1. Secondary electron images of Aulacoseira diatom frustules after conversion into bioinert MgO microcapsules (BaSIC method). The shape and fine pores of the starting SiO2 frustules were retained upon conversion. Such mesoporous microcapsules can be attractive for biomedical applications.

The Bioclastic and Shape-Preserving Inorganic Conversion (BaSIC) Process (patent under review)

The BaSIC process is a novel hybrid (biological + synthetic chemical) route to large numbers of 3D microcomponents with complex shapes and tailored chemistries. Certain biological organisms generate mineralized ("bioclastic") structures with micro-, meso-, and nanoscale features. One such organism that is ubiquitous to marine and freshwater environments is the diatom.

Diatoms (Bacillariophyta) are single-celled microalgae that form intricate 3D microshells (frustules) assembled from nanoparticles of amorphous silica. The number of extant diatom species is on the order of 105, with each species forming a frustule of unique shape (i.e., approx. 105 shapes exist). The maximum dimensions of diatom frustules can range from less than one micron (e.g., for Chaetoceros Galvestonensis) to hundreds of microns (e.g., for Ethmodiscus Rex), whereas features on the frustule walls (pores, pore spacings, ridges, protuberances, etc.) can exhibit dimensions on the order of 102 to 101 nanometers. Furthermore, diatom reproduction rates can exceed several times per day. At a sustained replication rate of 3/day, 1.07 billion (230) similarly-shaped 3D frustules can be generated from a single parent diatom in 10 days! Such massively-parallel self-assembly of 3D nanoparticle structures under environmentally benign conditions is highly attractive for nanotechnological applications.

However, the range of potential applications for natural diatoms is limited by the properties of silica. The BaSIC process overcomes this limitation by using certain chemical reactions to convert bioclastic preforms into new compositions that retain the original preform shapes and surface features (Figure 1). Reactions leading to a wide variety of oxide and non-oxide nanoparticle structures have been identified for the BaSIC process. If future work reveals that diatoms and other organisms can be genetically engineered to produce microshells with non-naturally-occurring shapes, then this hybrid process could generate Genetically-Engineered Microdevices (GEMs) with tailored compositions and shapes (e.g., micronozzles, microbearings, microgears, microcapsules, microreactors) for numerous applications.

Links to further information on diatoms:

The Displacive Compensation of Porosity (DCP) Process (patent pending)

In this novel process, molten metal is infiltrated into, and reacted with, shaped, porous ceramic-bearing preforms to produce dense, near net-shaped ceramic/metal composites. Unlike other displacement-reaction-based methods, the DCP process utilizes reactions that generate more ceramic volume than is consumed, so that composites with high ceramic contents can be directly produced. Because the increase in internal ceramic volume is accommodated by the prior pore volume of the preform (reaction-induced densification without sintering), dense composites are produced that retain the external dimensions of the preforms (Figures 2a and b). The transformation time after infiltration is independent of the external dimensions of the preform, so that relatively large preforms can be converted at modest temperatures. DCP-derived composites formed to date at 900-1300°C include:

  1. oxide-rich (up to 86 vol%) MgO/Mg-Al alloy composites that are lightweight (2.9-3.3 g/cm3) and resistant to hydration,
  2. co-continuous (40-60 vol% oxide) MgAl2O4/Fe-Ni-Al alloy composites that are higher melting and relatively tough (up to 13 MPa.m1/2),
  3. creep-resistant, co-continuous MgO/FeAl composites, and
  4. ZrC/W-based (17-72 vol% carbide) composites that are ultra high melting (2800°C), hard, strong (bend strengths of 700+/-150 MPa), and creep resistant (Figure 2c).

The chemical, mechanical, and thermal properties of such net- shaped composites are attractive for a number of commercial (aerospace, automotive, manufacturing) and military applications. For example, functionally-graded, DCP-derived carbide/refractory metal composites can be attractive materials for solid-fueled rocket nozzles (Figure 2d).

a) b) c)
Figure 2. Optical images of: a) a porous WC preform, and b) the resulting dense, near net-shaped ZrC/W-bearing composite produced via reactive infiltration of a Zr-Cu liquid into the WC preform (DCP process; line = 1 cm). A secondary electron image of the dense ZrC/W-bearing microstructure (the grey phase = ZrC) is shown in c). Ultra-high-melting, graded ZrC/W composites could be used for nozzles in solid-fueled rockets, such as the one shown at left.

 

(Two of Dr. Sandhage's undergraduate students, Matthew Dickerson and Raymond Unocic, won the 2000 National Collegiate Inventors Award for demonstrating that the DCP process can be used to fabricate dense, near net-shaped ceramic/refractory metal composites with ultra-high melting points for applications such as rocket nozzles.)

The Volume Identical Metal Oxidation (VIMOX) Process (U.S. Patent #5,447,291)

Figure 3: (left) Machined Mg-Al2O3 precursor and (right) the resulting near net-shaped spinel (MgAl2O4) body after oxidative conversion (VIMOX process). The dimensional changes at the indicated positions were less than or equal to 0.6%. For this Mg-Al2O3 precursor, the volume decrease associated with the oxidation of magnesium was offset by the volume increase resulting from the reaction of magnesia and alumina to form spinel.

In this process, malleable metal-bearing precursors are formed and/or machined into desired shapes and then converted by oxidation into near net-shaped ceramics or ceramic composites. Unlike other reaction-bonding processes, the net-shape feature of the VIMOX process does not require the use of sintering shrinkage to counter volume expansion due to oxidation. As a result, dense, robust metal-bearing preforms can be converted into dense, near net-shaped ceramic products. For dense precursors containing an appropriate mixture of metallic phases (i.e., a mixture of alkaline earth and non-alkaline earth elements, such as Ba and Al), off-setting reaction-induced volume changes occur during oxidation and post-oxidation annealing so that the final ceramic body retains the shape and dimensions of the precursor. Alkaline-earth-metal-bearing precursors are quite reactive and can be converted into multicomponent ceramics at modest temperatures via novel reaction paths. A wide variety of ceramic components have been fabricated to date by the VIMOX process, including: aluminates (Figure 3b), silicates, aluminosilicates, and chromites for dielectric and refractory applications; superconducting cuprates for electromagnetic devices; ion-conducting cerates for fuel cells or gas sensors; magnetic ferrites for electric motors; biocompatible phosphates for implants; and dielectric or semiconducting titanates for electronic components (capacitors, thermistors) and sensors.

Prof. Sandhage's research has been funded by several government agencies (e.g., NSF, AFOSR, DOE, EMTEC) and companies (e.g., Babcock & Wilcox, Orton Ceramic Foundation, Lockheed). His work has led to 15 patents, with several more under review by the U.S. and European Patent Offices. He has been a Humboldt Fellow at the Technische Universitat Hamburg-Harburg, Germany, a Principal Editor of the Journal of Materials Research, a panel reviewer for the DOE Superconductivity Program for Electric Power Systems, a Technical Advisor on Superconducting Materials to the Journal of Metals, and a consultant for several companies (e.g., Alcoa, American Superconductor, Chase Brass, Erico, IAP, Preston Glass, and Johnson & Hatch). Prior to joining Ohio State University in 1991, Dr. Sandhage was a Senior Scientist at Corning, Inc. and at American Superconductor Corp., where he conducted applied R&D on optical waveguides and on superconducting oxides, respectively.

 

Selected Recent Publications

Patents

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