Project Title: DESIGN AND FABRICATION OF ADVANCED MATERIALS FROM ILLINOIS COAL RESIDUES

ICCI Project Number: 95-1/3.1A-5

Principal Investigator: Vivak M. Malhotra

Other Investigators: P. S. Valimbe, A. Radisic, X. Zhang, S. Kelley, and M. A. Wright, Southern Illinois University at Carbondale

Project Manager: Dan Banerjee, ICCI

The main goal of this project was to develop a bench-scale technology which converts coal combustion residues from Illinois sources into high-value, advanced composite materials, e.g., automotive brake pads and ultra-high strength composites fro automotive structures. In support of our goals, we systematically probed how: (a) the concentration of PCC fly ash and FBC spent bed ash controls the mechanical behavior of the composite, (b) heat controls the elastic properties of our composites, © the presence of coal combustion residues in brake materials affects materials' specific heat capacity and thermal conductivity, (d) our brake materials' wear characteristics compared to commercial automotive brakes, and (e) the fiction coefficient of our composite material matches the commercial automotive brakes. To answer these questions, we conducted SEM, DSC, DMA, three-point bending flexural, specific heat capacity, thermal conductivity, and wear and friction measurements on composites fabricated in our laboratory as well as on commercially bought automobile brake composites. The following was concluded: (1) The three point bending mechanical tests conducted on composites fabricated from FBC spent bed ash and coal char in which the PCC fly ash concentration was varied from 10 wt% to 50 wt% suggest that the fly ash concentration beyond 40 wt% dramatically affects the mechanical properties of the composite. (2) The thermomechanical tests on commercial brakes as well as on the brakes which were fabricated from coal combustion residues as a function of temperature indicate that our brakes are competitive with commercially available brakes. (3) The specific heat capacity and thermal diffusivity experiments suggest that the commercial brake materials are under cured. At lower temperatures (<160^oC), the commercial brakes had thermal conductivity which was higher than our brakes. However, this trend was reversed at temperatures greater than 200^oC. (4) The comparative wear and friction tests on our brake composites and on commercial automotive brakes indicate that our composites' wear characteristics are better than that of the commercial brake. In addition, our experiemtns show that our material has a higher coefficient of friction than the two commercial automotive brakes tested in our laboratory.

Objectives: The goals of our project were to develop and optimize a bench-scale procedure to design and fabricate advanced automotive materials from Illinois coal combustion residues and scrubber sludge. Two prototype materials were developed, i.e., (1) automotive brake materials and (2) lightweight, ultra-high strnegth composites fro automotive structures and body panels.

Fabrication of Composites: After our initial attempts to form structural composties, in the form of 1.25 inch disks, from PCC fly ash, FBC spent bed ash, scrubber sludge, coal char, and coal tar were successful, we upscaled teh size of our structural composites to 2.5 inch diamter disk size. We concluded the following from our measurements. (1) The SEM and Young's modulus analyses on the brake composites fabricated from PCC fly ash, FBC spent bed ash, scrubber sludge, coal char, and iron particles as a function of pressure showed that higher perssures lead to better particle pakcing and better mechanical performance. (2) When only FBC spent bed ash particles were used along with coal char to form brake composite materials, the hot pressed composite collapses. However, this is not the case for brake shoe disks formed from either scrubberr sludge particles or PCC fly ash particles. Therefore, it is concliuded that FBC spent bed ash by itself is not a good filler material for the brake shoe pad. On the other hand, when the irregularly shaped particles of FBC spent bed ash are combined with scrubber sludge particles or PCC fly ash particles, the resultant material is expectged to have better tribological behavior. (3) In contracst to the carbon fibers when we used mineral or slag fibers to form our brake shoe pads, excellent bonding occurred between the mineral or slag fibers and binder matrix. (4) Both DSC and FTIR results indicate that the binder material in the composite degrades on sintering the composite at 400^oC. Therefore, the barke shoe pad's mechanical strength should be enhanced by limiting the sintering temperature to 200^oC < T < 400^oC. This is reasonable since automotive brakes are exposed to temperatures up to 300^oC. (5) Fibers are incorporated in friction materials to provide mechanical strength to the material and to inhibit catastrophic failure of the composite. We studied how the concentration of the fibers in the composite affects such behavior. To achieve this we varied the concentration of the surface treated shot slag fibers from 0 wt% to 20 wt% in the composites fabricated under idential conditions. The composites were fabricated from PCC fly ash, FBC spent bed ash, coal char, and phosphorous modified 17a binder. Our data showed that the concentration of slag fibers has concderable beneficial effect on the cutting time of the composite. On the other hand, the Young's modulus of the composites remains unaffected byt he concentration of the fibers used. (6) Our flecural mechanical tests on composites, in which PCC fly ash concedntration was systematically varied, chowed the the brake materials had maximum strength for a concentration of 20 wt%. If the concentration of PCC fly ash was equal to or greater than 50 wt%, then the composites' flexural strength markedly deteriroated. Results are summarized in Fig. 1.

Effect of Heat on the Mechanical Properties: The temperatures to which a brake composite is exposed, especially under braking conditions, play a vital role in determining not only the friction of the material but also its wear properties. Generally, it is believed that under vigorous braking conditions brake pads' overall temperature may reach as high as 300^oC. At present, we do not understand how various bake ingredients contribute to the above-mentioned properties. We undertook SEM and DMA measurements on composites in which we systematically varied the fiber content. Our data suggested that chopped carbon fibers are not suitable for forming automobile brake composites. On the other hand, slag fibers cross-linked well with binder 97, and this was specially true for those slag fibers which were surface treated. Our mechanical tests on commercial brakes as well as on the brakes which were fabricated using slag fibers as a function of temperature indicate that our brakes are competitive with commercially avilable brakes. In fact, our brake composite's storage modulus was higher than the commercial brake tested in the termperature range of 50^oC to 300^oC.

Thermal and Wear Behavior of Composites: The specific heat capacity and thermal diffusivity measurements were conducted on our composites as well as on commercial automotive brakes. These measurements allowed us to calcualte the thermal conductivity, which is shown in Fig. 2. Both the specific heat capacity and thermal diffusivity experiments suggest that the commercial brake materials are under cured. Though under curing was also present in our materials, it was not as pronounced as in the commercial brakes. At lower temperatures (< 160^oC), the commercial brakes had thermal conductivity which was higher than our ALEX C01 brake. However, this trend was reversed at temperatures greater than 200^oC. The comparative wear and friction tests on our brake ocmposites and on commercial automotive brakes, shown in Figs. 3 and 4, respectively, indicate that our composites' wear characteristic are better than that of the commercial brake. In addition, our preliminary experiments show that our material has a higher coefficient of friction than the two commercial automotive brakes tested.

NOTE: The Figures referenced in this document are not available for viewing on the web. Please contact the ICCI as indicated below to receive a hard copy of this document containing the figures referenced.