Materials Literature
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Abstract This study reports a reactive extrusion process leading to very high levels of anhydride grafting (2.5–3 wt %) along polypropylene backbone without recovering grafted PP waxes at the die exit. Such high graftings are attainable without excessive degradation of the PP chain by using a brominated reagent. Simul…
Recent experiments show that external inplanar electric field can be employed to guide the molecular self-assembly in diblock copolymer (BCP) thin films to form lamellar nanostructures with potential applications in nanotechnology. We study this self-assembly process through a detailed coarse-grained phase-separation…
Lanthanum phosphate (LaPO4) is considered as a potential material for thermal insulation coating on Ni-based superalloys owing to its high-temperature stability, its high thermal expansion and low thermal conductivity (i.e., comparable to properties of dense zirconia). in addition, lanthanum phosphate is expected to h…
We present an ab initio study of the structural and electronic properties of the halogen-bridged MMX single polymer [Pt2(CH3CS2)4I]n and of various possible modifications of its sequence, in the framework of density functional theory. The computed band structure of the infinite regular polymer reveals a net metallic c…
A newly developed alumina-based ceramic coating consisting of La2O3 Al2O3 and MgO that possesses long term structural and thermochemical stability up to 1400°C is presented. This coating composition ages significantly slower than commercial zirconia based TBCs at these high temperatures. This is achieved through the f…
Abstract We utilized bulk‐synthesized nanowires (NWs) of germanium dioxide as nanoscale structures that can be coated with noble metals to allow the excitation of surface plasmons over a broad frequency range. The NWs were synthesized on substrates of silicon using gold‐catalyst‐assisted vapor–liquid–solid (VLS) growt…
Transformation of structural ceramics from the laboratory to production requires development of near net shape fabrication techniques which minimize finish grinding. One potential technique for producing large quantities of complex-shaped parts at a tance, and microstructure of sintered silicon nitride fabricated by i…
Submicron powders of boron carbide with composition near B4C show little tendency to densify via pressureless sintering. Coarsening of the pore-grain structure appears to be the responsible process. Addition of 4 to 12 wt% C retards the coarsening and allows sintering to densities >97% at temperatures ≥2220°C. Abnorma…
We have performed a detailed dielectric investigation of the relaxational dynamics of glass-forming benzophenone. Our measurements cover a broad frequency range of $0.1\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}120\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$ and te…
An alkene isostere of Gly-trans-Pro was synthesized and incorporated into a host Ac-(Gly-Pro-Hyp)8-Gly-Gly-Tyr-NH2 peptide to investigate the effect of locking a proline amide bond. Proline amide bond isomerization is the slow step in collagen folding. By locking the amide, we hypothesized an increase in stability of…
A new process of ceramic matrix composite production, named Nano-powder Infiltration and Transient Eutectoid (NITE) process, has been developed and unidirectional SiC/SiC composites were prepared, and the effects of densification conditions on the microstructural evolution and mechanical properties were investigated.…
Glass of stoichiometric celsian composition, BaO · Al2O3 · SiO2 has density of 3.39 g/cm3, thermal expansion coefficient of 6.6 × 106/°C, glass-transition temperature of 910°C, and dilatometric softening point of 925°C. On heat treatment, only hexacelsian crystallized out on the surface, but both celsian and hexacelsi…
Ceramic fiber-ceramic matrix composites are of interest because of their potentially higher strength and toughness. A vacuum-forming technique was used to fabricate low-density structures from SiC fibers. These fibrous structures were then infiltrated using chemical vapor deposition. Matrices of Si3N4 and SiC have bee…
A range of techniques available for the measurement of particle size and particle-size distribution of ceramic materials is described. Their fields of application and limits of applicability are considered. Dispersion procedures are outlined and their importance emphasized. A comparison is made, using a number of cera…
A recently developed alumina-zirconia ceramic fiber provides excellent mechanical properties and shows good retention of those properties after exposure to high-temperatures. The fiber, which is referred to as PRD-166, has a tensile strength of over 2100 MPa (300 kspi) at 380 GPa (55 mpsi) modulus. After exposure to 1…
Near-stoichiometric, high crystalline SiC fiber, Hi-Nicalon type S has been developed. This SiC fiber was obtained, as well as Hi-Nicalon, by curing of polycarbosilane fibers with electron beam irradiation and pyrolysis. In order to estimate capability for a reinforcement of CMCs, microstructure, thermal stability, ox…
Tensile strength, creep strength, and rupture strength properties were measured for the following types of polymer-derived stoichiometric SiC fibers: Hi-Nicalon Type S from Nippon Carbon, Tyranno SA from Ube, and Sylramic from Dow Corning. Also included in this study were an earlier version of the SA fiber plus two re…
A previous review of toughening mechanisms in ceramic matrix composites is updated. Evaluation of recent PSZ results indicates a single tetragonal phase (i.e., no precipitates) with a reversible transformation can give about 2/3 the toughening of that which occurs with irreversible transformation in normal two phase P…
A modified Bridgman-type crystal-growing technique was used to fabricate a directionally solidified eutectic composite of Al2O3 and Y3Al5O12 (YAG). The resulting composite did not have a truly directionally solidified microstructure, but the eutectic grains were large, elongated, and aligned with the continuous alumin…
Mechanisms of toughening of ceramic composites are reviewed from several perspectives, with the overall goal of providing guidance in composite development. Some theoretical concepts are used but are not the focus of the paper. The first perspective is an evaluation of why previous ceramic composites approaches were n…