Oxide fibers development

Under these conditions, many types of continuous oxide fiber were developed. The physical properties of these oxide fibers are shown in Table 2 [11]. Methods for preparation of these oxide fibers include spinning of a sol, a solution, or slurry, usually containing fugitive organics as part of a precursor. 

REGEN A process for removing mercaptans from hydrocarbon fractions by catalytic oxidation and extraction with aqueous alkali, using a bundle of hollow fibers. Developed by the Merichem Company, Houston, TX, and used in 34 plants as of 1991. 

More recently, mngsten oxide fibers have been detected in a hard metal production plant. Subsequent in vitro experiments showed that the tungsten oxide fibers were cytotoxic to human lung cells. The role of tungsten in the development of hard metal dust pulmonary fibrosis remains unclear. 

For nse in a detergent an enzyme mnst suffice the following criteria. In the first place it mnst have an adeqnate activity and stability at alkaline pH. It must also remain active and stable in a broad temperatme interval (e.g. 10-60°C). For domestic use the trend is to low temperatures (see 3.3.7 In-depth intermezzo). Additionally an enzyme should be resistant to hydrolysis and oxidation by other snbstances in the detergent, e.g. proteases. For enzymes with lanndry-softeiung properties two additional criteria apply, i.e. the enzyme must show a high fiber separation and at the same time not impair the fibers. Developments aim to further satisfy these criteria. 

Aluminum Oxide-Silicon Carbide Fiber, developed by the Carborundum Co at Niagara Falls, NY, will withstand temps of 2300°F. 

The need to develop fibers with better microstructural stability at elevated temperatures and ability to retain their properties between 1000-2000°C. The requirements of fiber properties for strong and tough ceramic composites have been discussed by DiCarlo.83 A small diameter, stoichiometric SiC fiber fabricated by either CVD or polymer pyrolysis, and a microstructur-ally stable, creep-resistant oxide fiber appear to be the most promising reinforcements. 

Several oxide fibers on the basis of Zr02, Pb(Zr,Ti)03 (PZT), Y3AI5O12 (YAG) and YBa2Cu30x, which exhibit e.g. catalytic, magnetic, dielectric or superconducting properties, are currently under development or in evaluation for special applications. 

J.E. Sheehan, J.T. Porter, C.H. Meyers, R.J. Price, R. Bacon, Coated Carbon Fiber Development for Oxidation Protection of Carbon-Carbon Composites, Interim Progress Report No. 10, Contract No. F33615-88-C-5449, MSNW, Inc., San Marcos, CA, 1990. 

Muscle fibers can be classified as either fast-twitch or slow-twitch. The slow-twitch fibers, or type 1 fibers (also called slow-oxidative), contain large amounts of mitochondria and myoglobin (giving them a red color), utilize respiration and oxidative phosphorylation for energy, and are relatively resistant to fatigue. Compared with fast-twitch fibers, their glycogen content is low. The slow-twitch fibers develop force slowly but maintain contractions longer than fast-twitch muscle. 

In spite of the fact that research on permanent waving has decreased over the past several decades, significant findings have been made within the past 10 years. For example, Wortmann and Kure [1,2] have developed a model and recently extended it to show that the bending stiffness of reduced and oxidized fibers controls the permanent waving behavior of human hair and that the cuticle plays a role in permanent waving. Further, they have shown not only that the cuticle functions as a barrier to reduction but also that its stiffness may contribute to fiber set. 

The synthesized oxide fibers have high porosity, developed surface, elevated reactivity when they interact with liquids because of their specific... 

Impact. Oxide fibers with improved creep resistance will allow higher temperature applications (e.g., combustors and heat exchangers) provided that suitable oxide fiber coatings are developed in parallel. 

The CMC market is divided into two classes, oxide and non-oxide materials. Oxide composites consist of oxide fibers (e.g., alumina [AI2O3]), interfacial coatings, and matrices. If any one of these three components consists of a non-oxide material (e.g., silicon carbide [SiC]), the composite is classified as a non-oxide composite. These classes have different properties, different levels of development, and different potential applications. 

Domier of Germany developed oxide fiber-reinforced mullite matrix composite systems in the 1980s. The system was based on SMs Nextel 312 fibers and slurry impregnation of a mullite matrix. This composite demonstrated modest levels of strength (120 MPa [17.4 ksi]) and low failure strain (0.2 to 0.3 percent). Several hot gas exhaust nozzles for Dormer s turboprop airerafl were successfully deployed and continue to be used in regular service. 

This means that until more oxidation tolerant matrix-interface-fiber systems are developed, service conditions will be rather limited for non-oxide fiber-reinforced CMCs. CMCs do have a large weight advantage over superalloys, however, as well as low observability to radar. 

In the last decade, many new oxide fibers with improved high-temperature performance have been commercialized. The keys to these improvements has been (1) the design of fiber microstructures to reduce the volume of amorphous phases and (2) the development of multiphase polycrystalline fibers. Eliminating amorphous phases prevents rapid, viscous deformation under load at high temperatures. Multiphase polycrystalline microstructures appear to inhibit creep, particularly at elevated temperatures. Examples of developmental fibers with improved high-temperature properties include polycrystalline AI2O3, YAG, and mullite filjers. 

New ceramic compositions and microstructures with thermomechanical and thermochemical properties beyond the capability of SiC will be required for the next generation of high-temperature materials. Developing and commercializing new non-oxide fibers that cost less and/or have improved properties are likely to be lengthy and expensive processes. Because non-oxide ceramic fibers have not been profitable so far, industry alone is unlikely to support further development. 

Oxide fibers (which are inherently resistant to oxidation) with improved creep resistance will, with the concurrent development of suitable fiber-matrix interfaces, enable CMCs to be used in higher-temperature applications in oxidative environments (e.g., gas turbine engine exhaust nozzles and heat exchangers for externally-fired combined-cycle power systems). Therefore, the committee recommends that the following research be supported ... 

---