Materials Literature
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The transthickness tensile strength (TTS) of 2-D CVI-SiC/SiC composites reinforced with Tyranno SA fibers was evaluated by the diametral compression test. The effect of specimen size and specimen shape on the magnitude of the TTS were studied and the results were analyzed using Weibull statistics. Specimens failed alo…
Abstract Photo‐ and thermal stabilities of poly(propylene) (PP)/SiO 2 nanocomposites were studied by varying the particle size of the SiO 2 nanoparticles. It was found that smaller SiO 2 nanoparticles improved the stabilities of the nanocomposites by depressing the size of spherulites. The phenomenon was successfully…
The stress relaxation behavior of SN88, SN2S3, and NCX-5102 silicon nitride materials were experimentally determined in tension at 1300°C using buttonhead specimens. Specimens were held at constant strain after being loaded at 10 MPa/s to an initial stress of 276 MPa (40 ksi) or 414 MPa (60 ksi). The subsequent decay…
ZrC–based fibers and powders with –20 nm crystallite size were prepared by carbothermal reduction of zirconia/carbon mixtures. The reactant mixtures were prepared by solution-based processing in which zirconium 2, 4–pentanedionate (ZTP) was the zirconia-bearing precursor and phenol-formaldehyde resin was the carbon-be…
We report the magnetic and magnetotransport properties of Ca doped La1−xCaxCrO3 (x=0, 0.1, 0.2, and 0.3). Both the magnetic and transport properties are very sensitive to Ca substitution. The Néel temperature TN decreases substantially with increasing calcium doping concentration from 290to160K. A weak ferromagnetic s…
The adsorption, desorption, and reaction of CO on the (√5×√5)R27° surface oxide on Pd(100) grown by two methods was investigated with infrared reflection absorption spectroscopy. CO multilayer desorbs at ∼40 K, whereas monolayer desorption is complete at ∼210 K. The surface oxide formed at 575 K with a 600 Langmuir (L…
The increased interest in ceramic matrix composites requires the knowledge and models to manufacture them for their intended use. Prediction of the elastic moduli of composites requires estimates of the in situ properties of each of the phases of the material: fiber, matrix, and interface. Fiber tow testing was done t…
An environmental protection scheme is necessary to realize the full potential of SiC as a high temperature structural material. Mullite and mullite-yttria stabilized zirconia (YSZ) dual layer coatings have been developed to provide environmental protection for SiC. Preliminary tests show that mullite coatings are prom…
Carbon fiber/silicon carbide matrix composites (C/SiC) are promising materials for space applications such as nozzles, thrusters, and bladed disks. However the as-fabricated, cracked nature of the material makes it susceptible to environmental degradation due to fiber oxidation. Theoretical models can be used to gain…
Constant load, stressed oxidation testing was performed on T-300 C/SiC composites with a SiC seal coat. Test conditions included temperatures ranging from 350°C to 1500°C at stresses of 69 MPa and 172 MPa (10 and 25 ksi). The coupon subjected to stressed oxidation at 550°C/69 MPa for 25 hours had a room temperature re…
Temperature dependence of three-point bend strength of woven fabric boron nitride (BN)-coated Hi-Nicalon™ SiC fiber-reinforced SiC matrix composite has been studied. Amorphous BN was coated 0.4 m̈m on the surface of the fiber by CVD process and the composite was fabricated by repeated polymer infiltration-pyrolysis (P…
Experimental tests were conducted to determine the effect of temperature, sustained tensile load, and environment on the oxidation of continuous carbon fibers within a C/SiC composite. Stressed oxidation (stress rupture) tests were conducted in air and oxygen environments at temperatures of 800°C and 1200°C at sustain…
The mechanical properties of two SiC whisker/Al2O3 matrix composites were investigated as a function of whisker type. Composites were produced with both Silar-SC-9 and Tateho-SCW-1-S whiskers. The composites produced with the Silar-SC-9 whiskers exhibited a fracture strength of 641 MPa and a fracture toughness of 8.7…
Vinyl polymerization (in bulk and in solution) of a cyclic oligomer of vinyl-methylsilazane (i.e., 1,3,5-trimelhyl-1,3,5-trivinylcyclotrisilazane) was investigated as a method for preparing polymeric precursors to silicon carbide and silicon nitride. After synthesis, the polymers were characterized by size exclusion c…
Ceramic matrix composites were investigated for structural and thermal applications in high efficiency and environmental conscious fusion energy systems. In order to up-grade their low activation characteristics, thermal conductivity and high temperature properties, the crystallized Si-Al-C fiber (Tyranno-SA) and pyro…
Abstract Micron‐scale platelet (Na, K)NbO 3 particles were synthesized from the platelet precursor K 4 Nb 6 O 17 in a KCl medium using a topochemical method . The salt took part in the reaction and affected the composition of the products. Stoichiometric (Na 0.5 K 0.5 )NbO 3 could be accurately synthesized by controll…
It was described in the previous paper that fully dense TiB2-20 wt% (2 mol% Y2O3-ZrO-) sintered bodies were fabricated by glass encapsulation HIP (1600°C, 200 MPa, 2 h), and their 3-pt. bending strength was as high as 1200 MPa. In this material, grain growth occurred during sintering; the grain sizes of TiB2 and ZrO2i…
Abstract A new approach for determination of refractive index dispersion n(λ) (the real part of the complex refractive index) and thickness d of thin films of negligible absorption and weak dispersion is proposed. The calculation procedure is based on determination of the phase thickness of the film in the spectral re…
Armor-grade B4C and WC cylinders (25.4 mm × 25.4 mm) were impacted with WC-6Co (6 wt.% Co) spheres (6.35 mm diameter) at velocities between 100 m/s and 400 m/s. The recovered cylinders were subsequently sectioned and metallographically-prepared to reveal the dominant sub-surface damage types and change in damage sever…
Processing additives and conditions allow a wide variation in microstructures and mechanical properties for SiC-based ceramics prepared by hot pressing. Five experimental materials with a wide variety of microstructures and mechanical properties were fabricated and compared with SiC-N, a commercially available materia…