Janet Hurst

nasa grc · Materials Chemistry and Physics

Silicon carbide nanotube/nanowires (SiCNT/NWs) exhibit excellent mechanical properties in extreme thermal and oxidative environments. Here, we demonstrate an easily scalable process to synthesize millimeter-sized three-dimensional architectures using SiCNT/NW building blocks to create materials with excellent mechanical strength, stiffness, and res...

Exfoliated hexagonal boron nitride (hBN)/alumina composite can be fabricated by following the process of (1) heating a mixture of hBN, AlCl3, and NaF in nitrogen for intercalation; (2) heating the intercalated product in air for exfoliation and at the same time converting the intercalate (AlCl3) into Al2O3, (3) rinsing the oxidized product, (4) coa...

Two types of boron nitride nanotubes (BNNTs) were exfoliated into boron nitride nanoribbons (BNNR), which were identified using transmission electron microscopy: (1) commercial BNNTs with thin tube walls and small diameters. Tube unzipping was indicated by a large decrease of the sample’s surface area and volume for pores less than 2 nm in diameter...

The most recent and innovative silicon carbide (SiC) Fiber-SiC ceramic matrix composites, used for light-weight high-heat engine parts in aerospace applications, are woven, layered, then surrounded by a SiC ceramic matrix composite (CMC). To further improve both the mechanical properties and thermal and oxidative resistance abilities of this materi...

Hexagonal BN is an unusual material in that it is both highly thermally conductive as well as an electrical insulator. Additionally, hBN is also thermally stable in air. This unusual combination of properties makes hBN of significant interest for thermal management. Unfortunately, hBN is not easily consolidated into substrates without the addition...

Boron nitride nanotubes (BNNTs), an analogue of carbon nanotube (CNT) is one of the most used non-metallic materials in high technology applications related to thin film fabrications. Taking advantage of their unique properties such as electrically non-conductive, thermally conductive, and high hardness, it has been used in high-temperature electro...

A method of purifying a nanomaterial and the resultant purified nanomaterial in which a salt, such as ferric chloride, at or near its liquid phase temperature, is used to penetrate and wet the internal surfaces of a nanomaterial to dissolve impurities that may be present, for example, from processes used in the manufacture of the nanomaterial.

NaF was used as an activation agent to successfully intercalate FeCl3 into hexagonal boron nitride (hBN). This reaction caused the hBN mass to increase by ~100 percent, the lattice parameter c to decrease from 6.6585 to between 6.6565 and 6.6569 Ǻ, the x-ray diffraction (XRD) (002) peak to widen from 0.01° to 0.05° of the full width half maximum va...

This chapter describes the development of noncarbon nanotubes and compares the features of carbon and noncarbon nanotubes. Carbon nanotubes are the most widely available nanotube material and are typically used for reinforcement of polymeric and glass materials, electronic applications, etc. Noncarbon nanotubes such as boron nitride and silicon car...

Continuous fiber-reinforced ceramic composites (CFCCs) have been considered for a variety of high temperature structural applications including within hot sections of gas turbine engines. SiCf/SiCm compositions are of particular interest for these turbomachinery applications. Boron Nitride Nanotubes (BNNT) are of interest as reinforcement for high...

In an era of both declining NASA budgets and demanding space goals, the NASA Aeronautics Research Mission Directorate has elected to address foundational research problems for aeronautics. To this end, the Subsonic Fixed Wing (SFW) Project, within the Fundamental Aeronautics Program, has selected challenging goals which anticipate an increasing emp...

Boron nitride nanotubes (BNNT) are of significant interest to the scientific and technical communities for many of the same reasons that carbon nanotubes (CNT) have attracted wide attention. Both materials have potentially unique and important properties for structural and electronic applications. However of even more consequence than their similar...

Tensile static stress and static strain experiments were performed on woven Sylramic™ (Dow Coming, Midland, MI) and Hi-NicalonTM (Nippon Carbon, Japan) fiber reinforced, BN interphase, melt-infiltrated SiC matrix composites at 815°C. Acoustic emission was used to monitor the damage accumulation during the test. The stress-rupture properties of Sylr...

Barium calcium aluminosilicate glass composites reinforced with about 4 weight percent of BN nanaotubes (BNNTs) were fabricated by hot pressing. Flexure strength and fracture toughness of the glass-BNNT composites were determined at ambient temperature. The strength of the composite was higher by as much as 90% and fracture toughness by as much as...

Silicon effects on tensile and creep properties, and thermal conductivity of Hi-Nicalon SiC/SiC composites have been investigated. The composites consist of 8 layers of 5HS 2-D woven preforms of BN/SiC coated Hi-Nicalon fiber mats and a silicon matrix, or a mixture of silicon matrix and SiC particles. The Hi-Nicalon SiC/silicon and Hi-Nicalon SiC/S...

Boron nitride nanotubes of significant lengths were synthesized by reaction of boron with nitrogen. Barium calcium aluminosilicate glass composites reinforced with ~4 weight percent of BN nanotubes were fabricated by hot pressing. Ambient-temperature flexure strength and fracture toughness of the glass-BN nanotube composites were determined. The st...

Woven Hi-Nicalon™-reinforced melt-infiltrated SiC-matrix composites were tested under tensile stress-rupture conditions in air at intermediate temperatures. A comprehensive examination of the damage state and the fiber properties at failure was performed. Modal acoustic emission analysis was used to monitor damage during the experiment. Extensive m...

Silicon effects on tensile and creep properties, and thermal conductivity of Hi-Nicalon SiC/SiC composites have been investigated. The composites consist of 8 layers of 5HS 2-D woven preforms of BN/SiC coated Hi-Nicalon fiber mats and a silicon matrix, or a mixture of silicon matrix and SiC particles. The Hi-Nicalon SiC/silicon and Hi-Nicalon SiC/S...

Development of an updated single filament test standard for tensile strength determination has been undertaken by a joint government-industry task group under the auspices of the Subcommittee C28.07 of the American Society for Testing and Materials (ASTM). This update was initiated in response to a need expressed by people involved with fiber testi...

The fracture surfaces of several SiC/SiC composite specimens were examined after both room and elevated temperature tensile testing. The composites were manufactured with M-Nicalon, Sylramic, or a modified Sylramic fiber as the reinforcing phase. A distribution in BN interphase thickness was noted for some samples, particularly those containing the...

Three efforts aimed at investigating the process of self-propagating high temperature synthesis (SHS) for the fabrication of structural ceramics and intermetallics are summarized. Of special interest was the influence of processing variables such as exothermic dopants, gravity, and green state morphology in materials produced by SHS. In the first e...

Silicon carbide test bars were made by a simple wet-processing technique. The pressure casting method used the same equipment as conventional dry-pressing, but with a modified die. This casting technique was employed in order to produce test bars with improved strength and smaller fracture flaws than produced by dry-pressing. This was accomplished...

The effect of time and temperature on the density and strength of alpha-SiC was studied and mathematically modeled using a central composite experimental design. A sintering temperature of 2150 C for 1.7 h maximized the flexural strength and densification values. However, temperatures above 2200 C promoted abnormal grain growth, with resulting appr...