Dennis S. Tucker

Ultrastrong, Stiff and Multifunctional Carbon Nanotube Composites

Carbon nanotubes (CNTs) are an order of magnitude stronger than any other current engineering fiber. However, for the past two decades, it has been a challenge to utilize their reinforcement potential in composites. Here, we report CNT composites with unprecedented multifunctionalities, including record high strength (3.8 GPa), high Youngs modulus (293 GPa), electrical conductivity (1230 S·cm −1), and thermal conductivity (41 W m −1 K −1). These superior properties are derived from the long length, high volume fraction, good alignment and reduced waviness of the CNTs, which were produced by a novel-processing approach that can be easily scaled up for industrial production.

Effects of Gravity on Processing Heavy Metal Fluoride Fibers

The effects of gravity on the crystal nucleation of heavy metal fluoride fibers have been studied in preliminary experiments utilizing NASAs KC-135 reduced gravity aircraft and a microgravity sounding rocket flight. Commercially produced fibers were heated to the crystallization temperature in normal and reduced gravity. The fibers processed in normal gravity showed complete crystallization while the fibers processed in reduced gravity did not show signs of crystallization.

Effects of Gravity on ZBLAN Glass Crystallization

Abstract: The effects of gravity on the crystallization of ZrF4‐BaF2‐LaF3‐AlF3‐NaF glasses have been studied using the NASA KC‐135 and a sounding rocket. Fibers and cylinders of ZBLAN glass were heated to the crystallization temperature in unit and reduced gravity. When processed in unit gravity the glass crystallized, but when processed in reduced gravity, crystallization was suppressed. A possible explanation involving shear thinning is presented to explain these results.

Processing Glass Fiber from Moon/Mars Resources

Processing of Lunar/Mars raw materials into usable structural and thermal components for use on a Lunar/Mars base will be essential for human habitation. One such component will be glass fiber which can be used in a number of applications. Glass fiber has been produced from two lunar soil simulants. These two materials simulate lunar mare and lunar highlands soil compositions. Short fibers containing recrystallized areas were produced from the as-received simulants. Doping the highland simulant with 8 weight percent boria yielded a material which could be spun continuously. The effects of lunar gravity on glass fiber formation were studied utilizing NASAs KC 135 aircraft. Gravity was found to play a role in crystallization and final fiber diameter.

Increasing the working temperature range of ZrF4-BaF2-LaF3-AlF3-NaF glass through microgravity processing

Abstract. Fluorozirconate glasses, such as ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), have the potential for optical transmission from 0.3 μm in the ultraviolet to 7 μm in the infrared regions. However, crystallites formed during the fiber-drawing process prevent this glass from achieving its desired transmission range. The temperature at which the glass can be drawn into a fiber is known as the working range, defined as (Tx-Tg), bounded by the glass transition temperature (Tg) and the crystallization temperature (Tx). In contrast to silica glasses, the working temperature range for ZBLAN glass is extremely narrow. Multiple ZBLAN samples were subjected to a heating and quenching test apparatus on the parabolic aircraft under a controlled μ-g and hyper-g environments and compared with 1-g ground tests. Optical microscopy examination elucidates that crystal growth in ZBLAN is suppressed and initiates at a later temperature when processed in a microgravity environment. Thus, the crystallization temperature, Tx, at which the crystals form has increased. The glass transition temperature, Tg, remains constant, as crystallization does not occur until approximately 360°C for this composition of ZBLAN. Therefore, the working temperature range for ZBLAN has been broadened.

Effects of microgravity on ZBLAN optical fibers utilizing a sounding rocket

Samples of ZBLAN optical fiber were heated to the pulling and crystallization temperature in microgravity aboard a sounding rocket and on the ground at 1g. This was done in order to better understand the effects of gravity on the crystallization behavior of ZBLAN fibers. Samples heated in 1g at both temperatures crystallized. Samples heated to the crystallization temperature in microgravity were contaminated with water upon re-entry. Samples heated to the pulling temperature showed no evidence of crystallization in microgravity.

The Effects of a Magnetic Field on the Crystallization of a Fluorozirconate Glass

An axial magnetic field of 0.1T was applied to ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fibers during heating to the glass crystallization temperature. Scanning electron microscopy and x-ray diffraction were used to identify crystal phases. It was shown that fibers exposed to the magnetic field did not crystallize while fibers not exposed to the field did crystallize. A hypothesis based on magnetic work was proposed to explain the results and tested by measuring the magnetic susceptibilities of the glass and crystal.

Effects of Microgravity on Crystallization of ZBLAN Optical Fibers

ZrF4-BaF2-LaF3-ALF3-NaF (ZBLAN) optical fiber was flown on board NASAs KC-135 aircraft to determine the effects of microgravity on crystal growth in this material. Fiber samples were placed in evacuated quartz ampoules and heated to the crystallization temperature in 0-g and on the ground in 1-9. The 1 -g samples had many regions of crystallites, while the 0-g samples showed no evidence of crystallization.

Eliminating crystals in non-oxide optical fiber preforms and optical fibers

A method is provided for eliminating crystals in non-oxide optical fiber preforms as well as optical fibers drawn therefrom. The optical-fiber-drawing axis of the preform is aligned with the force of gravity. A magnetic field is applied to the preform as it is heated to at least a melting temperature thereof. The magnetic field is applied in a direction that is parallel to the preforms optical-fiber-drawing axis. The preform is then cooled to a temperature that is less than a glass transition temperature of the preform while the preform is maintained in the magnetic field. When the processed preform is to have an optical fiber drawn therefrom, the preforms optical-fiber-drawing axis is again aligned with the force of gravity and a magnetic field is again applied along the axis as the optical fiber is drawn from the preform.

ZBLAN Fibers: From Zero Gravity Tests to Orbital Manufacturing

The experimental findings of low loss ZBLAN optical fibers fabrication in zero gravity are presented. The mechanisms of the observed phenomena are discussed. The potential challenges of the orbital manufacturing are reviewed in detail.