Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

One of the primary research components of the DOE2000 Materials Microcharacterization Collaboratory involves studies of catalyst materials for reduction of NOx emissions from diesel engine exhausts. A series of experimental catalysts is currently under investigation with colleagues from Ford Research Laboratory. The major thrust of this research is the study of catalyst reactions to determine the progressive changes in the structure and morphology of the catalytic materials with temperature and time under conditions simulating diesel exhaust exposures. Because the High Temperature Materials Laboratory (HTML) provides an ex-situ reactor system that permits TEM samples to be examined after sequential reactions without intermediate atmospheric exposures, the research was undertaken on a collaboratory basis, with microscopy sessions conducted remotely via telepresence. This permits Ford scientists to interact with HTML (and/or other collaboratory) scientists during the TEM sessions, but does not require their time and involvement during the actual reactor runs. The first of these telepresence sessions was held recently, as described below.

About 15 × 106 lbs of paint sludge, produced every year at Ford plants, is disposed of in landfills. An economical alternative to this disposal method, which reclaims or recycles components of paint sludge, is highly desirable to preserve valuable natural resources. Here, we describe an alternative to landfill disposal whereby paint sludge is converted into ceramic composites that can be used as reinforcing materials. The conversion of paint sludge to ceramic composite, I/N2/600, is achieved by pyrolysis under a nitrogen atmosphere. Two additional composites, labeled I/N2/1000 and I/NH3/1000, respectively, are prepared by sintering I/600 at 1000 °C under N2 and NH3. All three composites contain crystalline CaTiO3, BaTiO3, TiO2, amorphous alumina, and carbon. I/NH3/1000 contains an additional crystalline phase of titanium nitride. The application of these composites as reinforcing materials is demonstrated in the fabrication of representative metal matrix composites (MMC's) and reinforced plastic components.

The promise of new applications continues to drive research on ceramic precursor and sol-gel routes to materials preparation. These routes offer flexibility in the fabrication of materials in forms such as films, coatings, fibers, foams, and powders, etc. Our interest in ceramic precursors stems from their potential in the low cost fabrication of films. Such films can be employed in a variety of new automotive applications. In this article, we summarize our efforts to prepare soluble ceramic precursors and their conversion to group IV metal nitrides. A comparison of some properties of electrically conducting titanium nitride films prepared by dipcoat-fire cycle and low pressure CVD is presented. We also describe the fabrication of indium tin oxide films by a sol-gel process. These films are candidates in the low cost fabrication of electrically heatable catalyst devices.

The gels derived from mixtures of Pr(OiC3H7)3 and Zr(OiC3H7)4•iC3H7OH, upon hydrolysis and pyrolysis, furnish single-phase PrOy-ZrO2 materials crystallized in the fluorite structure. These materials can be coated onto high-surface-area γ-alumina powders or deposited onto dense α-alumina coupons in the form of thin films from a solution of parent alkoxides modified with 2,4-pentanedione in THF. The fluorite structure of the PrOy-ZrO2 in the films appears to be thermally stable in air up to 1200°C. Temperature-programmed-reduction (TPR) measurements show that the bulk PrOy-ZrO2 material with a Pr. Zr molar ratio of 1:1 can store and release oxygen while that with a molar ratio of 1:3 cannot.

The precursors play an important role in determining phase composition of the resulting PrOy-ZrO2 material. A mixture of monoclinic and cubic or tetragonal phases was found in PrOy-ZrO2 prepared from a new single-source heterometallic alkoxide, Pr2Zr6(μ4-O)2(μ-OAc)6(μ-OiPr)10(OiPr)10, whereas a mixture of cubic and tetragonal phases was present in PrOy-ZrO2 made previously by coprecipitation from aqueous solutions of the metal nitrates.

Exhaust gas heat is the primary source of warming in a conventional automotive exhaust catalyst. It typically becomes operational within minutes after the initial start-up of an engine, when it attains temperatures greater than approximately 350°C. However, around 70% of the total hydrocarbon and carbon monoxide (CO) emissions of a modern gasoline powered vehicle, under a normal driving cycle, are released during this period of cold-start. One of the strategies suggested to treat the pollutants during the first minute after initial start-up involves electrically heating the catalyst. However, devices developed for this purpose are power intensive, can require a second battery and can reduce fuel economy. The increased weight, in turn, results in increased pollution. Here we describe a low power consumption prototype which contains a conducting layer beneath the washcoat. The prototype [4 cm2] was tested at a gas flow rate of 100 seem and required less than 5 Watts to attain temperatures greater than 350°C in less than 10 seconds. The prototype was tested in a flow reactor and found to rapidly heat up to light-off temperatures where the conversion of the hydrocarbons and CO takes place. We also summarize progress made in our laboratory in the fabrication of a test device employing sol-gel processed metal oxide films.

The high cost of materials prepared by sol-gel processing and the loss of useful surface properties at elevated temperature has prevented the application of sol-gel processed materials in automotive exhaust reduction catalyst formulations. In this report, we briefly describe the important developments needed in the next generation automotive catalysts and the role of sol-gel processed materials. We will also discuss the application of heterometallic alkoxides as sol-gel precursors to achieve the molecular distribution of lanthanides and alkaline earths in alumina matrices needed for the stabilization of alumina based materials at elevated temperatures.

The application of sol-gel processed materials in a variety of sensors has been proposed. We describe microcalorimeter sensor devices employing sol-gel processed alumina based materials which can be used to monitor pollutants in automotive exhaust. These sensors operate by measuring changes in resistance upon catalysis and are economically acceptable for automotive applications. It is important to point out that automobiles will be required to have a means of monitoring exhaust gases by on-board sensors as mandated by the EPA and the California Air Resources Board (OBD-II).

There are very few demonstrated applications of ceramic precursor technology. Here, we describe two new applications of known ceramic precursors, thin film deposition and the fabrication of functionally gradient materials [FGM]. To demonstrate the thin film deposition, we prepared titanium nitride film on an alumina substrate using (CH3)3SiNHTiCl3 precursor by a single dipcoat-fire cycle. The fabrication of copper and aluminum based FGMs was demonstrated using Nicalon® fiber polycarbosilane and poly(methylsilane) precursors as binders and in situ sources of ceramics.

A common feature of reporting head and neck squamous cancer statistics in recent years has been to consider patients dying with no evident disease (NED) as successfully treated. We present two patients who died with no clinically evident squamous cancer and who could therefore have been reported as cured but for autopsy findings which showed significant distant spread. These findings are supported by several reports of distant metastases in squamous head and neck cancer and it is suggested that rates of post-mortem examinations be included in survival figures in the future.

Boron nitride has been prepared in the past from classical high temperature reactions and more recently by CVD methods. Few attempts have been made to prepare this important material from pyrolyses of preceramic oligomers or polymers. In the present study oligomerization reactions of substituted borazenes with silyamine crosslinking groups have been found to provide useful gel materials which upon pyrolysis form boron nitrogen materials. Selected aspects of this chemistry and some characterization of the materials is presented.