Randall S. Hay

Effect of coating deposition temperature on monazite coated fiber

Abstract Monazite (LaPO 4 ) was continuously coated on 3M Nextel ™ 720 fiber tows with an ethanolic precursor using hexadecane for immiscible liquid displacement. Coating deposition temperatures were varied from 900 to 1300°C. Fibers coated at 900°C were heat-treated up to 100 h at 1200°C. Coated fibers were characterized by analytical TEM, and tensile strengths were measured by single filament tensile tests. The monazite precursor was characterized by X-ray, DTA/TGA, and mass spectrometry. Microstructure evolution was complex and may have involved recrystallization of large defective grains into smaller grains and then subsequent growth of these grains, along with coarsening of porosity. After 100 h at 1200°C there was significant roughening of the coating–fiber interface, with facetting of alumina grains in the fiber and some lanthanum segregation to these facetted boundaries. Spheroidization of thin coatings was also observed. Tensile strength of coated fiber decreased with increasing deposition temperature and with time at temperature after deposition. Possible reasons for the strength decrease are discussed.

TEM specimen preparation and characterization of ceramic coatings on fiber tows

Abstract A method for making transmission electron microscopy (TEM) specimens of ceramic fibers is described. The specimens are particularly well suited for observation of ceramic coatings on a large number of filaments. The technique is also useful for preparation of extremely flat SEM specimens with good edge retention.

Predicted performance limits of yttrium aluminum garnet fiber lasers

The effect of various parameters that limit the performance of fiber lasers are calculated for yttrium aluminum garnet (YAG) as the fiber core. The optimum core diameter, the optimum fiber length, and the corresponding output power capability are determined for a variety of optical and structural parameters of YAG, based on available data in the literature to date. It is shown that a conservative limit for YAG fiber laser is 6 kW per fiber in multimode operation, compared to 1.8 kW for a silica-based fiber laser. Furthermore, it is shown that if stimulated brillouin scattering gain, a key limiting parameter, is <10−12 m/W in YAG, as a recent publication suggests, the maximum output power is 30 kW per fiber without a significant increase in fiber core diameter. Similar gains are predicted for single-mode operation, although with much lower output power limits. A parametric study shows the relative merits of improving on various optical parameters.

Carbon and oxide coatings on continuous ceramic fibers

Oxide-carbon multilayer coatings were continuously applied to various fibers of nominal SiC composition. A liquid-phase coating system that allows application of the coatings in a controlled atmosphere at relatively rapid rates was employed. Sugar-ammonium hydroxide solutions were used for carbon coatings, and aqueous sols were used for the oxides. Carbon was also deposited simultaneously with alumina by chemical vapor deposition of a hydrocarbon in the coating furnace. The coatings were extensively characterized by optical microscopy and TEM. Problems with embrittlement by oxide coatings and poor adherence of oxide coatings on carbon, and some possible solutions to these problems, are discussed.

Mixed Carbon-Aluminum Oxide Coatings from Aqueous Sols and Solutions

3M Nextel 720 fiber tows were continuously coated with carbon-alumina mixtures. Water soluble hydrocarbons such as sucrose and ammonium polymethacrylate (Darvan C) were used as carbon sources. Bridging of coating between filaments was reduced by displacing excess sol in the fiber tow with 1 -octanol. The effect of carbon-alumina association (sucrose or polyelectrolyte and alumina interaction) on the homogeneity of the alumina/oxide coatings are presented and discussed.