A Method for Coating Fibers in Oxide Composites

Abstract

A method for applying monazite coatings onto oxide fibers after matrix infiltration and sintering is devised and demonstrated. It uses an intermediate fugitive coating, followed by impregnation and pyrolysis of a monazite precursor solution. Composites with monazite coatings produced in this manner as well as those with only a fugitive coating exhibit superior mechanical performance to composites without any coating, as manifested in higher notched strength and fracture energy as well as significantly greater amounts of fiber pullout.

Precipitation Coating of Rare‐Earth Orthophosphates on Woven Ceramic Fibers—Effect of Rare‐Earth Cation on Coating Morphology and Coated Fiber Strength

“…These coated fibers often have to be woven into fiber preforms, 22 and the coating may debond during weaving. Recently, methods to coat woven ceramic fibers with La‐monazite using heterogeneous precipitation from solution precursors have been developed 23–25 . One method uses the temperature dependence of the reaction between La‐citrate and phosphoric acid to coat woven fibers by first saturating the woven fibers with the solution precursors and then submerging the saturated fibers in warm water to cause rapid precipitation of rhabdophane, LaPO 4 · x H 2 O 25 .…”

Fully Organic Nanocomposites with High Thermoelectric Power Factors by using a Dual‐Stabilizer Preparation

“…As the DWNT concentration is increased to 40 wt % (Sample F4, Figure 3 b), the porosity dramatically increases and becomes a factor in the degradation of the mechanical properties, which are linked to the critical pigment volume concentration (CPVC) phenomenon commonly seen in this type of polymer nanocomposite. [23,30,[56][57][58][59] The CPVC describes the maximum amount of filler that can be added to the matrix and still maintain sufficient wetting of the filler by the polymer. Above the CPVC, the mechanical properties can deteriorate to such a degree that it will affect the transport properties.…”

Developments in Oxide Fiber Composites

“…The retention in properties following high‐temperature exposure was also improved. A more recent investigation has also shown the benefits of combining fugitive coatings with porous matrices 34 . For this purpose, composites were fabricated by infiltration of a mullite–20% alumina slurry into a carbon‐coated Nextel™ 720 preform, repeated impregnation and pyrolysis of an alumina precursor, followed by oxidation of the carbon 34 .…”

“…In addition to the combined porous‐matrix/coated fiber scheme, a second hybrid approach has emerged, using (in some sense) all three principal toughening schemes: porous matrices, fugitive coatings, and monazite coatings 34 . The initial processing steps are identical to those used to produce porous‐matrix CFCCs with an interfacial gap (described above).…”

“…29,35 In addition to the combined porous-matrix/coated fiber scheme, a second hybrid approach has emerged, using (in some sense) all three principal toughening schemes: porous matrices, fugitive coatings, and monazite coatings. 34 The initial processing steps are identical to those used to produce porous-matrix CFCCs with an interfacial gap (described above). Following oxidation of the carbon, a monazite precursor is repeatedly impregnated and pyrolyzed, thereby filling the interface gaps formerly occupied by carbon as well as between the matrix particles ( Fig.…”