Michael P. Mallamaci

Faceting of the interface between Al2O3 and anorthite glass

The {l_brace}10{bar 1}0{r_brace} and {l_brace}11{bar 2}0{r_brace} Al{sub 2}O{sub 3} surfaces have been equilibrated in contact with anorthite liquid at 1,600 C. The structure of the resulting Al{sub 2}O{sub 3}/glass interfaces has been characterized using transmission electron microscopy. Both interfaces were unstable in the presence of the liquid and reconstructed to give regular arrays of facets. The (10{bar 1}0) interface developed (10{bar 1}1) and ({bar 1}012) facets while the (11{bar 2}0) interface developed {l_brace}hh{ovr 2h}3{r_brace} facets. It is proposed that the (10{bar 1}0) glass/crystal interface is thermodynamically stable, but that the (11{bar 2}0) interface facets due to interface-step migration. The microstructure thus shows that both the crystallography and the anisotropic interface energies are important in determining the wetting/dewetting behavior of glass on Al{sub 2}O{sub 3}.

New emulsion SBR technology : Part I. Raw polymer study

Emulsion styrene-butadiene rubber (ESBR) has been the workhorse of the tire industry since World War II. With the development of solution polymers, ESBR has seen a steady decrease in its use in tire applications. A novel ESBR has been developed which imparts some of the rheological behavior previously only observed in solution polymers. This new ESBR was prepared by blending a high molecular weight elastomer with a low molecular weight elastomer, each having a unique styrene-butadiene composition. A two-phase co-continuous morphology was observed by scanning probe microscopy when the bound styrene difference between the two components was greater than 18%, consistent with the two glass transition temperatures measured by thermal analysis. Blending also served to reduce the amount of very high molecular weight material (> 10 7 g/mol) readily observed in 1502- and 1712-type polymers by thermal field flow fractionation (ThFFF). ThFFF was found to be superior to size exclusion chromatography for fully characterizing the molecular weight and molecular weight distribution of the polymers. Time-temperature superposition was performed to characterize the viscoelastic behavior in the rubbery plateau and terminal zones. The ESBR blends showed a cross-over in the terminal flow region that was not observed in 1502- and 1712-type polymers.

Crystallization of calcium hexaluminate on basal alumina

Abstract The epitactic growth of calcium hexaluminate (CA6) on the basal plane of alumina was observed during an investigation of the interaction between silicate glass films deposited on single-crystal alumina (α-Al2O3). Two distinctly different orientation relationships occurred. The first can be described as perfect hexagon-on-hexagon epitaxy with (1120)CA6∥(1010)Al2O3 and (0001)Al2O3 ∥(0001)CA6. This relationship has 1.1% lattice misfit in the substrate plane; the misfit is accommodated at the interface by a hexagonal network of misfit dislocations. In the second relationship the CA6 grains are rotated about the substrate normal and can be explained by the coincident-site lattice model for phase boundaries. Both orientation relationships emphasize the influence of substrate crystallography on the crystallization process.

Multidisciplinary characterization of novel emulsion polymers

A series of novel emulsion styrene-butadiene copolymer blends were characterized using a multidisciplinary approach involving both analytical and rheological measurements. The blends were composed of 50/50 w/w high molecular weight (ca. 800,000 Da) ESBR and low molecular weight (ca. 200,000 Da) ESBR, each component having a different bound styrene level. When the difference in bound styrene between the two components was greater than 18%, a two phase co-continuous morphology was observed by scanning probe microscopy, consistent with two glass transitions measured by temperature modulated DSC. Molecular weight and molecular weight distributions were characterized by both size exclusion chromatography and thermal field flow fractionation with multiangle light scattering detection. ThFFF was unique in its ability to detect ultra-high molecular weight (> 107 Da) fractions suggesting that traditional SEC often under-estimates polymer molecular weight. Blending polymers of different molecular weights and styrene levels resulted in reduced molecular weight between entanglements which, based on rheological measurements, would be expected to improve processability.

In-situ tem crystallization of silicate-glass films on Al2O3

Abstract Silicate-glass films were grown by pulsed-laser deposition on single-crystal, basal-plane Al 2 O 3 substrates which had been pre-thinned to electron transparency. Experiments were then performed at high temperature in the TEM, which allowed direct observation and video-recording of the crystallization process. The epitactic growth of pseudo-orthorhombic anorthite (CaAl 2 Si 2 O 8 ) and grossular (Ca 3 Al 2 Si 3 O 12 ) on the basal Al 2 O 3 surface was observed, emphasizing the role of the substrate as a “seed” for glass devitrification. The grossular crystals nucleated and grew at random on the substrate surface. In contrast, the anorthite crystals showed preferential nucleation at defect sites in the as-deposited glass film. Nucleation was followed by lateral growth along the substrate surface radiating away from the defect sites. Rotational variants for the silicate crystals were found in both cases, owing to the three-fold symmetry of the substrate. The simultaneous growth of these rotational variants on the substrate surface caused the formation of high-symmetry grain boundaries within the silicate film. In the anorthite film, these grain boundaries were often faceted parallel to low-index planes in one or both grains.

Oil Distribution in iPP/EPDM Thermoplastic Vulcanizates

Scanning Probe Microscopy (SPM) was used to determine the volume fraction of oil-swollen particulate rubber and oil-swollen plastic in thermoplastic vulcanizates (TPVs) produced from iPP and EPDM rubber. Sample preparation and SPM imaging conditions allowed the ratio of the rubber and plastic area imaged for a TPV sample to be equated to the phase volume ratio. The hydrosilylation cured TPVs contained no filler or inorganic components (other than about 1 ppm of platinum catalyst, based on dry rubber) that would decrease the accuracy of the SPM analysis. The accuracy of the SPM method used for TPV phase volume determination was established by analysis of an oil-free TPV of known composition. The densities of the individual TPV components (rubber, oil, crystalline and amorphous plastic phase), which were assumed to be additive in the composite, were used to calculate the oil distribution between the TPV rubber and plastic phase, since the volumes of the individual components (the extent of plastic crystallinity was measured by differential scanning calorimetry) were known. Thus, the amount of oil in the oil-swollen TPV rubber and plastic phase could be quantified. This information, coupled with the Tg of the oil-swollen amorphous plastic phase, indicated that a substantial amount of oil was present as a separate oil phase that is surrounded by the oil-swollen amorphous plastic phase. To date, it has been assumed that the oil in a TPV partitions between the rubber and amorphous plastic phase, with the plastic crystallites being oil free. This work is the first demonstration of the presence of a separate oil phase in TPVs, and the first accurate determination of the oil content in the oil-swollen rubber, miscible oil in the oil-swollen amorphous plastic, and the free oil in TPVs.

In-Situ TEM Crystallization of Anorthite-Glass Films on α-Al2O3

Anorthite-glass films have been grown by pulsed-laser deposition on single-crystal α-Al 2 O 3 substrates which were pre-thinned to electron transparency. The glass films were crystallized in the transmission electron Microscope (TEM), which allowed direct observation and video-recording of the crystallization process. Crystallization of these films in the TEM resulted in the formation of hexagonal and orthorhombic anorthite. The orthorhombic phase was the predominant product of glass films grown at elevated substrate temperatures and displayed strong epitaxy with the underlying substrate. In contrast, the hexagonal phase was the major constituent of films grown at ambient substrate temperature and displayed no clear epitaxy with the substrate. The differences in degree of epitaxy and phase structure may be evidence of ordering at the original glass/oxide interface.

Initial stages of solid-liquid interactions in the MgO-CaMgSiO4 system

During liquid-phase sintering (LPS) a large number of transport mechanisms occur simultaneously. Most often the microstructure of the sintered product provides information on these mechanisms. Previous studies on the infiltration of dense, polycrystalline MgO by a silicate liquid were aimed at investigating microstructural development as a function of the volume-fraction of the liquid. In this paper results on the early stages of the liquid infiltrating the compact are presented. A unique experimental technique has been developed that permits microstructural comparison of the same grains before and only minutes after the start of infiltration. Qualitative results on microstructural developments such as grain-growth, grain-morphology and changes in the chemistry of the liquid are presented in this work. The choice of composition of the liquid was monticellite (CaMgSiO{sub 4}) which is in thermodynamic equilibrium with MgO at 1,700 C and is a commonly observed intergranular composition in LPS MgO.

Liquid Infiltration of MgO and Al 2 O 3 Thin Films

The deposition of glass films on thin ceramic substrates is a novel method for investigation of the initial stages of liquid infiltration into the grain boundaries of these materials. By maintaining electron transparency at all stages of the experiment, the transmission electron microscope (TEM) can be used to characterize individual grain boundaries before and after penetration by a liquid. The method has been tested for the MgO and AI2O3 systems, which have extensively studied experimental counterparts in which the corresponding bulk materials are infiltrated by a siliceous liquid.