Preceramic polymers were proposed over 30 years ago as precursors for the fabrication of mainly Si-based advanced ceramics, generally denoted as polymer-derived ceramics (PDCs). The polymer to ceramic transformation process enabled significant technological breakthroughs in ceramic science and technology, such as the development of ceramic fibers, coatings, or ceramics stable at ultrahigh temperatures (up to 2000°C) with respect to decomposition, crystallization, phase separation, and creep. In recent years, several important advances have been achieved such as the discovery of a variety of functional properties associated with PDCs. Moreover, novel insights into their structure at the nanoscale level have contributed to the fundamental understanding of the various useful and unique features of PDCs related to their high chemical durability or high creep resistance or semiconducting behavior. From the processing point of view, preceramic polymers have been used as reactive binders to produce technical ceramics, they have been manipulated to allow for the formation of ordered pores in the meso-range, they have been tested for joining advanced ceramic components, and have been processed into bulk or macroporous components. Consequently, possible fields of applications of PDCs have been extended significantly by the recent research and development activities. Several key engineering fields suitable for application of PDCs include high-temperature-resistant materials (energy materials, automotive, aerospace, etc.), hard materials, chemical engineering (catalyst support, food- and biotechnology, etc.), or functional materials in electrical engineering as well as in micro/nanoelectronics. The science and technological development of PDCs are highly interdisciplinary, at the forefront of micro- and nanoscience and technology, with expertise provided by chemists, physicists, mineralogists, and materials scientists, and engineers. Moreover, several specialized industries have already commercialized components based on PDCs, and the production and availability of the precursors used has dramatically increased over the past few years. In this feature article, we highlight the following scientific issues related to advanced PDCs research: (1) General synthesis procedures to produce silicon-based preceramic polymers.
(2) Special microstructural features of PDCs.
(3) Unusual materials properties of PDCs, that are related to their unique nanosized microstructure that makes preceramic polymers of great and topical interest to researchers across a wide spectrum of disciplines.
(4) Processing strategies to fabricate ceramic components from preceramic polymers.
(5) Discussion and presentation of several examples of possible real-life applications that take advantage of the special characteristics of preceramic polymers. Note: In the past, a wide range of specialized international symposia have been devoted to PDCs, in particular organized by the American Ceramic Society, the European Materials Society, and the Materials Research Society. Most of the reviews available on PDCs are either not up to date or deal with only a subset of preceramic polymers and ceramics (e.g., silazanes to produce SiCN-based ceramics). Thus, this review is focused on a large number of novel data and developments, and contains materials from the literature but also from sources that are not widely available.

Polymer-Derived Ceramics: 40 Years of Research and Innovation in Advanced Ceramics

The present invention is directed to secreted and transmembrane polypeptides and to nucleic acid molecules encoding those polypeptides. Also provided herein are vectors and host cells comprising those nucleic acid sequences, chimeric polypeptide molecules comprising the polypeptides of the present invention fused to heterologous polypeptide sequences, antibodies which bind to the polypeptides of the present invention and to methods for producing the polypeptides of the present invention.

Secreted and Transmembrane Polypeptides and Nucleic Acids Encoding the Same

A critical review of the physical and mechanical properties of NiAl is presented. The physical properties examined include electronic structure and bonding, crystal structure and phase stability, thermodynamic properties, elastic properties, and electrical, magnetic, and thermal properties. Discussion of crystal defects in NiAl include both constitutional and thermal point defects, the core structure and energy of line defects, and planar defects (shear faults, grain boundaries, and free surfaces). The mechanical properties, substructure, and mechanisms of ductility of NiAl single crystals and polycrystals are reviewed in detail, while alloying effects and the deformation of NiAl martensite are briefly described. The fracture toughness, modes of fracture, and cyclic properties reported in the literature are assessed. A critical analysis of diffusion data for NiAl is followed by a discussion of the activation energy and mechanisms of diffusion. This information is related to the creep properties of NiAl, and additional critical comments concerning the substructure and creep mechanisms of NiAl are provided. A review of the environmental resistance of NiAl is followed by a brief discussion of several current and potential applications of NiAl. Concluding remarks include suggestions for future research on NiAl.

Overview No. 104 The physical and mechanical properties of NiAl

Synthesis of nanoparticles in the gas phase for electronic, optical and magnetic applications—a review

Considerable work has been performed on NiAl over the last three decades, with an extremely rapid growth in research on this intermetallic occurring in the last few years due to recent interest in this material for electronic and high temperature structural applications. However, many physical properties and the controlling fracture and deformation mechanisms over certain temperature regimes are still in question. Part of this problem lies in the incomplete characterization of many of the alloys previously investigated. Fragmentary data on processing conditions, chemistry, microstructure and the apparent difficulty in accurately measuring composition has made direct comparison between individual studies sometimes tenuous. Therefore, the purpose of this review is to summarize all available mechanical and pertinent physical properties on NiAl, stressing the most recent investigations, in an attempt to understand the behavior of NiAl and its alloys over a broad temperature range.

Physical and mechanical properties of the B2 compound NiAl

Creep experiments have been made on a Ni-Ti-Al alloy, which has a microstructure consisting of a distribution of semi-coherent NiAl(β) precipitates with a Ni2AlTi(β′) Heusler phase matrix. The creep strength of this bcc type structure alloy is at least comparable with that of the nickel-base superailoy MARM-200 for values ofT/T
 m in the range 0.68 to 0.82. Quantitative electron microscope experiments show that both undissociated α0〈110〉 dislocations, and paired α0〈100〉 dislocations coupled by a sublattice A.P.B. exist within the β′ phase;α
 0 is the lattice parameter of a bcc cell of which the large Ni2AlTi unit-cell is composed. The sublattice A.P.B. is a crystallographic fault created by wrong bonds between atoms on the Al-Ti sublattice. Theoretically the energy γ of a sublattice A.P.B. is shown to be minimum on {100}, and the experimental value for γ on {100} is ~40 mJ/m2.

High temperature creep in a semi-coherent NiAl-Ni 2 AlTi alloy

A chemical synthetic route for nanostructured materials that is scalable to large volume production, comprising spray atomization of a reactant solution into a precursor solution to form a nanostructured oxide or hydroxide precipitate. The precipitate is then heat-treated followed by sonication, or sonicated followed by heat treatment. This route yields nanostructured doped and undoped nickel hydroxide, manganese dioxide, and ytrria-stabilized zirconia. Unusual morphological superstructures may be obtained, including well-defined cylinders or nanorods, as well as a novel structure in nickel hydroxide and manganese dioxide, comprising assemblies of nanostructured fibers, assemblies of nanostructured fibers and agglomerates of nanostructured particles, and assemblies of nanostructured fibers and nanostructured particles. These novel structures have high percolation rates and high densities of active sites, rendering them particularly suitable for catalytic applications.

Nanostructured oxides and hydroxides and methods of synthesis therefor

This invention relates to methods whereby reprocessed nanoparticle powder feeds, nanoparticle liquid suspensions, and metalorganic liquids are used in conventional thermal spray deposition for the fabrication of high-quality nanostructured coatings. In one embodiment of this invention, the nanostructured feeds consist of spherical agglomerates produced by reprocessing as-synthesized nanostructured powders. The method is applicable to as-synthesized nanostructured powders made by a variety of liquid chemical processing methods. In another embodiment of this invention, a fine dispersion of nanoparticles is directly injected into a combustion flame or plasma thermal spray device to form high-quality nanostructured coatings. In still another embodiment of this invention, liquid metalorganic chemical precursors are directly injected into the combustion flame of a plasma thermal spray device, whereby nanoparticle synthesis, nanoparticle melting, and nanoparticle quenching onto a substrate are performed in a single operation. In these various methods ultrasound is used for disintegration of the as-synthesized particle agglomerates, nanoparticle dispersion in liquid media, and liquid precursor atomization.

Method of manufacture of nanostructured feeds

A specific method for improving the high temperature creep strength of β-NiAl by a ternary addition giving rise to an additional degree of order is examined. The ternary alloy thus formed has theA
 2BC or Heusler type structure, and the present study is devoted to the creep behavior of polycrystalline Ni2AlTi of stoichiometric composition. Possible slip modes are predicted on the basis of the hard sphere model, and quantitative transmission electron microscopy is used to verify these predictions. All intracellular dislocations, and network dislocations have a α0〈110〉 type Burgers vector; α0 is the lattice parameter of a bcc cell of which the large Ni2AlTi unit cell is composed. The creep strength of this alloy is ∼ 3 times that of NiAl in its most creep resistant form, na mely [100] axis single crystals.

Peter R. Strutt

Papers

High temperature creep in a semi-coherent NiAl-Ni 2 AlTi alloy

Nanostructured oxides and hydroxides and methods of synthesis therefor

Method of manufacture of nanostructured feeds

Creep behavior of the heusler type structure alloy Ni 2 AlTi

Chemical processing and applications for nanostructured materials