Abstract-Density, electron microscopy, elastic modulus, and small-angle neutron scattering studies are used to characterize the microstructures of yttria-stabilized zirconia plasma-sprayed deposits as a function of both feedstock morphology and annealing. In particular, anisotropic multiple small-angle neutron scattering data are combined with anisotropic Porod scattering results to quantify each of the three main porous components in these thermal barrier coating materials: intrasplat cracks, intersplat lamellar pores and globular pores. An inverse correlation between the volume of porosity and its surface area is confirmed for the as-sprayed deposits, as is a preferential annealing of intrasplat cracks at elevated temperatures. The average elastic modulus is correlated with the total void surface area while the elastic anisotropy is related more closely to the intersplat porosity. However, depending on the feedstock morphology, globular pores are also shown to play a surprisingly significant role in post-anneal deposit microstructures and properties. 

This paper reports an experimental and theoretical investigation of the indentation of a layered elastic solid, with special reference to the surface force apparatus (SFA). The contacting surfaces of the SFA comprise a 3-layer material: a thin mica surface layer on a thicker epoxy layer supported by a thick silica substrate. An existing finite element analysis of the deformation of ideal mica/epoxy/silica surfaces used in the SFA is adapted to compare with the experimental measurements of the variation of contact size with load, both with and without adhesion at the interface. This is in marked difference to the Johnson, Kendall and Roberts (JKR) theory for homogeneous solids. Experiments and finite element calculations were also carried out on the elastic indentation of a thin (5.5 µm) layer of mica on a very thick layer of epoxy (>100 µm). As input data for the calculations, the elastic moduli of the mica and epoxy were measured in separate indentation experiments. The stiffness of a layered solid can be expressed by an ‘effective modulus’ , which has been deduced from the experimental measurements and compared with the theoretical values with fair success. The work of adhesion is commonly measured in the SFA by observing the ‘pull-off force’ to separate the surfaces. The theory shows that, for a layered solid, the pull-force can vary significantly from the JKR value for a homogeneous solid. In particular, it was found that the mica surface energy, γsv, measured by SFA experiments using crossed cylinders of mean radius R, where the materials are layered and the mica/mica adhesion is high, can vary with the pull-off force Fp according to Fp/4πR < γsv < Fp/2πR, and for this particular experiment was given as γsv = Fp/3.5 πR as compared with γsv = Fp/3πR for homogeneous materials.

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SynopsisThe enantioselective polymerization of bis(2,2,2-trichloroethyl) trans-3,4-epoxyadipate with 1,4-butanediol using the enzyme porcine pancreatic lipase as a catalyst is described. The polymerization was carried out at ambient temperature in anhydrous ethyl ether. End group analysis provided M , = 5,300 daltons, whereas GPC provided M , = 7,900 daltons for the polymer. The unchanged (+)-enantiomer of the diester was shown to have an enantiomeric purity of > 95% by proton NMR in the presence of the chiral shift reagent Eu(hfc),. The stereochemical purity of the (-)-polymer was estimated at > 96% by consideration of the amount of the slower reacting enantiomer that could have been incorporated and still attain the observed degree of polymerization (25) when the starting ratio of racemic diester to diol was 2 : 1. Direct determination of the stereochemical purity of the polymer using Eu(hfc), was unsuccessful. Similar studies on polymer having random stereochemical orientations of the epoxide showed that such polymers do not behave as if they are racemic in the presence of the shift reagent. The polymer required for the latter studies was prepared by epoxidation of the product from enzyme catalyzed polymerization of bis(2,2,2-trichloroethyl) trans-3-hexenedioate with 1,4-butanediol.

Using Brillouin scattering, we have determined the complete set of elastic constants of the technologically important β-Si3N4. Availability of single crystals has allowed us to measure all five independent cij, which (in units of GPa) are: c11=433(3), c33=574(3), c13=127(5), c44=108(2), c66=119(4), and c12=c11−2c66=195(8), giving a bulk modulus of 259. Our values are compared with existing calculations and cij determined from nano-indentation results combined with empirical relations and trends in related materials.

The mechanisms controlling normal and exaggerated grain growth in lead magnesium niobate-lead titanate (PMN-PT) ceramics have been investigated by varying the PbO-based liquid-phase volume fraction from 0.03 to 0.6 and sintering temperature from 900°to 1100°C. There is a transition in matrix grain growth rate and matrix grain shape with liquid fraction; samples with liquid volume fractions less than ϳ0.15 show relatively small equiaxed grains resulting from grain-tograin impingement. Samples with higher liquid fractions show significantly larger, facetted, cube-shaped grains, whose size is independent of liquid fraction, indicating that a surface nucleation rate mechanism controls growth in this regime. Exaggerated grains were found in the high liquid fraction samples. Electron backscatter diffraction showed that all of the exaggerated grains contained 60°͗111͘ twins but none of the normal matrix grains contained twins. The reentrant angles in the twinned grains give them a growth advantage over untwinned grains, resulting in a population of exaggerated grains.

SynopsisEnzyme-catalyzed preparation of polymers offers several potentially valuable advantages over the usual polymerization procedures. (1) Such polymerizations may allow the polymer to retain functionality that would be destroyed under normal polymerization conditions. (2) The selectivity provided by enzyme catalysts may permit polymers, including optically active polymers, to be prepared that are either not accessible or accessible only with difficulty by other methods. (3) The characteristics of the enzyme and the mild polymerization conditions may permit formation of polymers having highly regular sizes and backbone structures. This report describes the first successful use of an enzyme-catalyzed polycondensation to prepare a chiral (AA-BB), polyesters of more than a few repeat units. Polymerization of bis(2,2,2-trichloroethyl) alkanedioates (BB) with diols (AA) using the enzyme porcine pancreatic lipase (PPL) as a catalyst is detailed. The polycondensations were carried out at ambient temperature in anhydrous, low polarity organic solvents such as ether, THF, and methylene chloride. End group analysis by NMR provided M,, values of 1300-8200 daltons while GPC provided M , values of 2800-14900 daltons for the polymers. Based on proton NMR spectra obtained during the polymerization, relatively rapid formation of an AA-BB "dimer" and an AA-BB-AA " trimer," slower formation of a BB-AA-BB "trimer," and subsequent condensation of these to give higher polymers are suggested to be components of the polymerization mechanism.

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