Materials Literature
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To analyze the formation of bimodal particle size distributions during precipitation, the dynamic competition for supersaturation by growth of existing precipitates and nucleation of new particles was studied under continuous cooling conditions with constant cooling rates. The nucleation rate was calculated according…
In fiber reinforced ceramic composites, a critical need exists for the accurate measurement of interfacial properties such as the debond strength, sliding shear stress, and residual stress. The characterization of these properties frequently relies on the use of indentation techniques and their instrumentation which m…
Preparation and characterization of ceramic materials in the Ti-Si-C system are presented. Mixtures of titanium, silicon and carbon powders were ignited by microwave energy. Powders prepared by conventional SHS and microwave-initiated SHS were compared. Compositional characteristics of these powders were determined us…
Particulate sols and solutions were used to apply carbon-oxide multilayered coatings, mixed alumina-carbon coatings, and monazite (LaPO4) coatings to various SiC fiber tows and 3M Nextel 720™ fibers. These coatings can degrade fiber strength, sometimes to such an extent that the coated fibers cannot be spooled. Carbon…
The fracture strength as a function of temperature of single crystal alumina fibers oriented along the c-axis have been measured in air using three-point bending. The strength degradation observed in undoped sapphire at intermediate temperatures was removed by impurity doping with MgO, TiO2, and MgO+TiO2 co-doping. Si…
Red-emitting phosphor powders of SrIn2O4 activated with Eu3+ ions were fabricated by high pressure assisted combustion synthesis. X-ray diffraction analysis of these oxide phosphors revealed the formation of single-phase orthorhombic SrIn2O4 for concentrations up to 4 at% Eu. A detailed photoluminescence (PL) and cath…
Abstract The cerium modified sodium bismuth titanate (Na 0.5 Bi 4.5 Ti 4 O 15 , NBT) piezoelectric ceramics have been prepared by using the conventional mixed oxide method. X‐ray diffraction analysis revealed that the cerium modified NBT ceramics have a pure four‐layer Aurivillius phase structure. The piezoelectric ac…
3M Nextel 720 fibers were continuously coated with porous alumina and with dense lanthanum phosphate (monazite) using sol-gel and solution precursors. Porous alumina coatings were deposited as alumina-carbon mixtures. The carbon holds the pore space during processing under reducing conditions, and is burned out later.…
We propose a minimal model resolving a puzzle of enigmatic correlations observed in sodium-rich ${\text{Na}}_{x}{\text{CoO}}_{2}$ where one expects a simple, free motion of the dilute $S=1/2$ holes doped into a band insulator ${\text{NaCoO}}_{2}$. The model also predicts singlet superconductivity at experimentally obs…
Abstract A series of 10 poly(urethanes) were synthesized by solution polymerization from bis(chloroformates) and aromatic diamines, containing both silicon or germanium as central atom. So, the polymers prepared contain two silicon atoms or two germanium atoms exclusively or combinations of both. Me, Et, and Ph groups…
Ce(1-x-y)Ti(x)Pt(y)O(2-delta) (x=0.15; y=0.01) and Ce(1-x-y)Ti(x)Pd(y)O(2-delta) (x=0.25; y=0.02 and 0.05) are found to be good CO oxidation catalysts [T. Baidya et al., J. Phys. Chem. B 110, 5262 (2006); T. Baidya et al., J. Phys. Chem. C 111, 830 (2007)]. A detailed structural study of these compounds has been carri…
Unidirectionally solidified eutectic oxide fibers having lamellar or fibrous microstructures are potential reinforcements for ceramic composites. To achieve desired property levels, processing conditions must induce coupled growth between the two phases to produce structures having highly oriented interwoven single cr…
Sintered silicon nitride has many superior properties; however, for most applications these materials are too expensive to compete with metal parts. Sintered reaction-bonded silicon nitride (SRBSN) is more ecomonical, with raw material costs < 20% of those of comparable high-purity materials, making it competitive wit…
Economic and scientific aspects of ceramics processing for structural (including engine) components are presented. Estimated manufacturing costs and market penetration are given, followed by a discussion of the presintering science research at M.I.T. The fundamental principles which guide this research, and selected r…
Polycrystalline ceramic fibers now available from commercial sources include those of Al2O3, Al2O3-SiO2O3, Al2O3-B2O3-SiO2, and ZrO2-SiO2. Continuous filaments in roving, yarn, chopped, bulk, fabric or mat forms can be supplied. Properties and uses of these fibers are discussed.
The epoxidation reaction using heterogeneous solid catalysts with H 2 O 2 as oxidants are environmentally friendly routes to produce extensively useful epoxides which are traditionally obtained from capital-intensive or environmentally polluted processes. In this paper, various types of solid catalysts for the epoxida…
Near-stoichiometric, highly 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 potential capability for a reinforcement of CMCs, microstructure, thermomec…
Transmission electron microscopy observations of deformation after spherical indentation of polycrystalline monazite (LaPO4) and scheelite (CaWO4) are presented and discussed. Deformation mechanisms in monazite include extensive microcracking by cleavage, dislocation plasticity, and twinning. Similar mechanisms were o…
Interfacial properties were assessed for composites consisting of Sic fibers in a borosilicate glass matrix using single fiber pullout tests. Specimens were fabricated by melting the glass around the Sic fibers in graphite crucibles. The maximum debonding load and initial pullout load were determined as a function of…
Experimental studies by a number of researchers have shown that a carbon-rich interface is formed between Nicalon' Sic fibers and several different glass and glass-ceramic mahix materials. This carbon layer is believed to play an important role in the outstanding mechanical properties of these composites. A basic unde…