The fabrication of high-density carbon–carbon composite by integrating mesophase injection and in situ transformation methods in different processing cycles was examined. Non-rigidized preform disks 30 mm thick and 68 mm in diameter were rigidized by an initial in situ transformation cycle to an average density of 0.92 g/cm3 after carbonization. The rigidized preforms were subsequently densified by 1–3 cycles of injection with the AR mesophase pitch. After each injection cycle, the flow-oriented mesophase matrix was stabilized and carbonized to 1150 °C. The composites from each injection cycle were further densified by a final in situ cycle. A final density of nearly 2 g/cm3 was attained after three injection cycles and a final in situ cycle. All the cycles except the third injection required only ambient or very moderate pressures.

In this work, we examined the microstructures formed during the pyrolysis of naphthalene mixed with AlCl3 catalyst, in the critical temperature range of 300–500°C and at varying pressures. In addition, non-rigidized preforms were densified by multiple cycle in situ transformation and compared the process with impregnation using fully transformed AR mesophase pitch under similar conditions. The process of mesophase formation in the bulk phase and within tightly packed fiber bundles was observed to be similar: spherule nucleation from the isotropic phase, coalescence of spherules forming bulk mesophase, and mesophase flow before hardening. The hardened mesophase displays the coarse, fibrous, and lamellar microstructure observed in needle cokes. The molten naphthalene was observed to evenly penetrate in-depth the large void spaces and fiber bundles. After two in situ cycles, the fiber bundles and the inter-fiber bundle regions were well filled with transformed mesophase. The incremental filling of the larger void spaces reduced the calculated filling efficiencies from 47% in the first cycle to below 15% in the third through fifth cycle. An 8% improvement in densification efficiencies was achieved by applying modest pressures during the pyrolysis. The extent of mesophase penetration with AR mesophase was observed to decrease from the outer to the inner regions of the preform. The results suggest impregnation with naphthalene catalyst mixture is efficient in filling tightly packed fiber bundles but not large void spaces. Multiple cycles are required in order to fill the large void spaces.

Dense, near net-shaped ZrC/W-based composites have been fabricated at modest temperatures and at ambient pressure by a reactive infiltration process known as the Displacive Compensation of Porosity (DCP) method. Porous WC preforms with hourglass shapes (for rocket nozzle liners) were produced by gel casting, whereas simple bar-shaped preforms were produced by uniaxial pressing. The porous preforms were exposed to molten Zr2Cu at 1200–1300°C and ambient pressure. The Zr2Cu liquid rapidly infiltrated into the preforms and underwent a displacement reaction with the WC to yield a more voluminous mixture of solid products, ZrC and W. This displacement reaction-induced increase in internal solid volume filled the prior pore spaces of the preforms (“displacive compensation of porosity”) to yield dense, ZrC/W-based composites. Because the preforms remained rigid during reactive infiltration, the final composites retained the external shapes and dimensions of the starting preforms. A DCP-derived, ZrC/W-based nozzle insert was found to be resistant to the severe thermal shock and erosive conditions of a Pi-K rocket motor test. The DCP process enables dense, ceramic/refractory metal composites to be fabricated in complex and near net shapes without the need for high-temperature or high-pressure densification or for extensive machining (i.e., relatively expensive processing steps are avoided).

: Carbon-carbon composites are ideal materials for high temperature structural uses, such as in rocket propulsion components, hypersonic vehicles, and aircraft brakes. In spite of their excellent properties, the use of carbon-carbon composites has been limited because of their high cost and rapid oxidation at elevated temperatures. Two novel approaches to solving these problems are described and these approaches are employed along with a ZrC/W-based nozzle insert to fabricate and test a recession-resistant carbon-carbon rocket nozzle as a potential replacement for solid tungsten nozzles.

Surface tension and wettability are important phenomena in many diverse areas of science and technology, such as adhesion, adsorption, lubrication, catalysis, solid-liquid reaction kinetics, and microelectromechanical systems. However, when the solid surface is not perfectly planar, liquid contact with that surface is poorly understood and the subject of considerable misconception. Here, we report that under static or near-static conditions wettability is dependent not only upon the contact angle between the liquid and the solid but also on the geometry of the surface that the liquid contacts. It is shown that the artificial dividing line of 90degrees between wetting and nonwetting behavior only holds on a planar surface or in a straight channel. The conditions controlling whether filling of an interstice takes place or not are demonstrated to be a function of both the liquid-solid contact angle and the included angle within the interstice. This behavior is both reversible and reproducible. A simple relationship is developed to express the transitional included angle of the interstice as a function of contact angle.

The behavior of non-wetting fluids in micro-channels can be utilized to create an unusual form of micro-hydraulic technology that enables fabrication of various kinds of micro-actuators and micro-bearings. In addition, this same technology can be used to construct micro-pumps capable of generating flows of wetting fluids in micro-channels and to manipulate and control these flows.

Hollow fibers spun from synthetic fiber forming polymers have been of interest, especially for producing high-bulk, low-density fabrics. Such fibers produced from a high temperature resistant polymer provide a number of advantages in certain applications. Ultem, a polyetherimide resin marketed by General Electric company, is a copolymer with ether molecules between imide groups and is thermoplastic. Being an amorphous thermoplastic polyimide, the Ultem resin combines the high performance associated with exotic specialty polymers and the good processability of typical engineering plastics. Equipment was built at the Air Force Research Laboratory of Edwards AFB, CA to spin hollow fibers. The spinneret designed has a hollow tube supported in the center of the orifice, and an inert gas is injected through the needle to maintain the tubular shape until the solidification of the fiber. Using that set-up, fibers were spun from Ultem under several different conditions. Effect of some of the processing conditions on the evolution of structure and properties during hollow fiber formation is discussed.

The behavior of fluid droplets contained within shaped capillaries and voids can be utilized to convert forces acting upon the droplets to observable displacements which accurately and reproducibly quantify these forces. The position of droplets within such micro-sensors is governed by surface tension, wettability, and the geometric configuration of the confining walls. These micro-sensors have no mechanical moving parts to wear out and are inherently immune to many orders-of-magnitude over-actuation. If non-wetting fluids are employed, the micro-sensors can also be made to operate as micro-valves, micro-switches, optical micro-shutters and irises, as well as other devices. Both circular and non-circular confining structures can be employed.

Hollow fibers spun from synthetic polymers have been investigated for a long time, especially for producing high-bulk, low-density fabrics. Such fibers produced from a high temperature resistant polymer have some advantages in certain applications. Ultem, a polyetherimide resin marketed by General Electric Company, is a copolymer with ether molecules between imide groups. The fully reacted polyimide with the imide group being part of the linear polymer chain makes this polymer thermoplastic and easily dissolvable. Being an amorphous thermoplastic polyimide, the Ultem resin combines the high performance associated with exotic specialty polymers and the good processability of typical engineering plastics. In addition to high strength, high modulus, and heat resistance, the polymer has high dielectric strength, broad chemical resistance, transparency, and good processability. Equipment was built at the Air Force Research Laboratory of Edwards AFB, CA to spin hollow fibers. The spinneret designed has a hollow tube supported in the center of the orifrce, and an inert gas is injected through the needle to maintain the tubular shape until the solidification of the fiber. Using that set-up, fibers were spun from Ultem under several different conditions. Effect of these processing conditions on the structure and properties of the formed hollow fibers are discussed.