Christopher H. Schilling

Mechanical properties of biodegradable soy-protein plastics

Experiments were performed to evaluate the room-temperature mechanical properties of soy-protein plastics that were compression-molded with varying concentrations of glycerin plasticizer. Specimens exhibited stiff and brittle behavior with good tensile strength reliability based on Weibull statistics analysis. Raising the glycerin concentration from 0 to 20% progressively increased the tensile strain-to-failure from 1.1 to 1.8% and reduced the tensile strength from 42.1 to 23.6 MPa, the tangent modulus from 4.56 to 1.79 GPa, and the Rockwell hardness from R118.4 to R75.7. Ultrasonic measurements indicated that raising the glycerin concentration from 0 to 20% increased Poisson`s ratio from 0.348 to 0.409 and reduced Young`s Modulus from 7.01 to 5.4 GPa and the shear modulus from 2.5 to 1.8 GPa. Significant increases in the tensile strength and the strength reliability resulted from eliminating Griffith`s flaws by sieving the press powder before compression molding. Rockwell hardness rapidly decreased upon immersing these plastics in water at 25 {degree}C, an effect which was pronounced for the glycerin-containing specimens.

Sedimentation in flocculating colloidal suspensions

A combined experimental and theoretical investigation of the sedimentation of unstable colloidal ceramic suspensions has been performed. Suspensions containing submicron-sized α-Al 2 O 3 particles were prepared at various pH values in order to modify suspension stability. Particle volume fraction during sedimentation was determined as a function of position and time by gamma-ray densitometry. A population balance model was developed to account for various coagulation and decoagulation mechanisms that affect sedimentation behavior in flocculating suspensions. Model predictions were then compared with experimental measurements, in order to establish the validity of the theoretical model.

Plastic shaping of aqueous alumina suspensions with sucrose and maltodextrin additives

Traditional methods for the shape-forming of engineering ceramics entail plastic deformation of powder slurries containing hazardous organic liquids as suspending media. Replacing these organic with aqueous media requires the development of environmentally benign, water-soluble additives which serve as plasticizers and binders. Fundamental studies were performed with aqueous suspensions of colloidalα-Al2O3 to evaluate the role of sucrose and maltodextrin on viscosity, sedimentation, and filtration characteristics, plastic flow behavior of filter cakes, and sinterability. Maltodextrin systems exhibited superior results, including filtration to high packing densities and clay-like plasticity with minimal cracking.

Processing Technical Ceramics with Maltodextrins: Crosslinking by Acetalation

Technical ceramics are made by a sequential process of: (i) mixing ceramic powder with an organic carrier liquid (e.g., organic solvents, polyethylene wax) to form a plastic slurry, (ii) molding the plastic slurry into a three-dimensional shape, (iii) thermal treatment to evaporate or pyrolyze the organic carrier, and (iv) kiln firing. In this paper, the use of aqueous polysaccharide solutions is examined as environmentally-friendly, economically-viable substitutes for organic carrier liquids in ceramic molding. The central focus of the present study is to examine optimum conditions for crosslinking model slurries of maltodextrin and colloidal aluminum oxide by acetalation of maltodextrin. Crosslinking is needed to prevent the common problem of cracks that form in ceramic shapes during thermal treatment (stage iii above). Experiments involving rheology and differential thermal analysis revealed that glyoxal and glutaraldehyde are effective crosslinkers, whereas formaldehyde and pyruvic acid did not exhibit measureable changes in slurry rheology over a wide range of concentrations. Glutaraldehyde reacted faster than glyoxal, however, glyoxal produced the strongest gels. Basic conditions catalyzed acetalation. The sequence of blending the slurry components had no significant effect on slurry rheology.

Protein plasticizers for aqueous suspensions of micrometric- and nanometric-alumina powder

Ovoalbumin and its hydrolysate were developed as economical and environmental friendly plasticizers for the production of engineering ceramics from micrometric- and nanometric-sized powders. These proteins are feasible as replacements for commonly used petrochemicals that suffer from problems of toxicity, volatility, flammability, and high cost. A key advantage to protein-based additives is that they are available from inexpensive plant and animal sources (e.g. waste products such as slaughterhouse blood, by-products from meat and plant production). Aqueous alumina suspensions and high-density aqueous alumina pastes were blended with such proteins to form green bodies that were easily moldable and could be sintered to full density without cracking. The application of proteins provides thermally induced gelation of aqueous alumina suspensions.

Ultrasonic velocity and reduction of surface area during solid-state sintering

Abstract We studied the relationships between the ultrasonic velocity and the reduction of specific surface area during solid-state sintering and addressed three questions: (1) What must be the correlation between ultrasonic velocity and specific surface area reduction during the solid-state sintering of monosize spheres? (2) How is this correlation affected by the particle-size distribution and/or changes in packing coordination? (3) How do the answers to these questions help us improve the use of ultrasonic measurements to monitor sintering kinetics and microstructure evolution? From both a theoretical and experimental basis, we found a general power law that describes the relationship between ultrasonic velocity and the reduction of specific surface area during solid-state sintering: V P / V B ∝(Δ S / S o ) x . The power-law exponent x depends on three possible scenarios: (1) x x =1 for random packing of monosize spheres where the average, particle coordination number changes upon sintering; and (3) x >1 for specimens containing a broad distribution of particle sizes. We also demonstrated that this power law could be used with ultrasonic velocity measurements to obtain reasonable values of the activation energy for solid-state sintering. The power-law relationship is useful to characterize microstructure evolution during solid-state sintering and is useful to classify different materials in a ceramic manufacturing setting. It is also a simple modeling tool that opens the way to optimize control of the sintering process.

Effects of polysaccharides on the particle packing and green strength of alumina slurries

The consolidation behaviors of alumina suspensions with polysaccharides having different concentrations and molecular weights were analyzed. The polysaccharide molecule absorbs to the surface of alumina powder in an aqueous suspension to give sorbate-mediated steric hindrance. Polysaccharides in aqueous suspension contributed to particle packing and green strength after drying. The tensile strength of alumina green body, and packing densities after slip casting changed in different style with the increase of polysaccharide molecular weight. Polysaccharide molecular weight played a major role in determining the green strength of alumina suspensions.

STRESS-DENSITY VARIATIONS IN ALUMINA SEDIMENTS: EFFECTS OF POLYMER CHEMISTRY

parameters with spatial variations of the packing density and the local effective stress. These correlations are difficult to achieve by traditional techniques (e.g., rheometry, sedimentation kinetics modeling, soil mechanics tests), especially for the low stresses (< 1000 Pa) that are typically encountered in sediments. Aside from being destructive to samples, these techniques also tend to measure volume-averaged properties, and as a result they usually fall short of describing localized consolidation phenomena. Significant variations in plasticity can arise through modification of interparticle forces by changing the chemistry of surface-adsorbed polymers or ions. In the present study, we address the question of how to design surface-adsorbed polysiloxanes to enhance particle rearrangement into densely packed structures. Polysiloxanes are excellent lubricants (e.g., silicon oil) due to the low rotational energy of the Si-O-Si bonds comprising the polymer backbone. These inorganic polymers are also available with a broad range of chemical structures that can pyrolyze to various inorganic silicon-based compounds under appropriate conditions. 2 This research is part of a larger program examining the use of polymeric additives that may form useful inorganic phases within the pores of a ceramic compact upon pyrolysis. 3

PbO Reduction and Crucible Reactions of 70 wt% PbO · 30 wt% B 2 O 3 Glass

Seventy wt% PbO · 30 wt% B 2 O 3 glass was melted in Pt and graphite crucibles; PbO reduction and subsequent crucible reactions were empirically investigated as a function of temperature and oxygen partial pressure. This research was conducted at NASA to determine optimum processing conditions for subcentimeter glass hollow spheres to be used as inertial confinement fusion targets for a particle beam fusion accelerator at Sandia National Laboratories. The research enables selection of appropriate crucible materials and oxygen partial pressure-temperature combinations necessary to avoid phase separation from PbO reduction and/or crucible reactions. Phase separation from PbO reduction was not detected in glass samples melted in Pt crucibles under oxidizing atmospheres. Under reducing atmospheres from mechanical and diffusion pump vacuum, oxygen gas emissions were detected along with Pb-Pt compounds forming on Pt crucibles. With graphite crucibles, glasses contained lead-rich phases and CO 2 gas bubbles. Experimental results were compared with the theoretical Pb-PbO stability boundary predicted on the basis of the standard free energy change of PbO reduction.