Corundum fibers

This concept has been transferred to corundum fibers. The experimental fiber, PRD-166, is an example of a zirconia-corundum fiber. PRD-166 is polycrystalline and contains 80 wt.% a-alumina and 20 wt.% yttria-stabilized zirconia and it is slurry spun, like Fiber FP [19] [61]. Zirconia-corundum fibers can be prepared by the slurry route, the slurry being an aqueous suspension of fine alumina particles, to which are added a basic aluminum salt (such as aluminum chlorohydroxide), zirconyl acetate and yttrium chloride hexahydrate. After... 

In contrast, the fibers which have (in terms of phases) reached their equilibrium state during processing, e.g., mullite or corundum fibers, simply undergo grain grovrth when annealed at a sufficiently high temperature and their room temperature tensile strength decreases [18-19] [45] [54-55] [71],... 

Cortexes, in wool fibers, 11 173 Cortisone, production of, 11 10 Corundum, 1 1 2 345t color, 7 328... 

The dope is concentrated by heating under vacuum and is then dry spun through a spinneret. The green fibers are partially dehydrated in a drying column and are taken up on a collapsible reel [23-24] or further processed continuously on line [25]. They are prefired at 600-800°C and subsequently sintered at 1350 - 1500°C in a furnace or/and a propane/oxygen flame. Fiber FP is 18-20 pm in diameter whereas the Almax fiber obtained from ultrafine y-alumina powder displays a smaller diameter ( 10 pm). In both fibers, alumina is present as corundum. 

The precursor of a similar fiber was prepared by polycondensation of an organoaluminum compound, such as monoisopropoxydiethyl aluminum, dissolved in ethylether [60]. Some isopropoxy groups were presumably replaced by a phenoxy group, such as ethyl 0-hydroxybenzoate, in order to improve the spinnability of the final dope. The polyaluminoxane was dissolved in benzene, the ether was distilled off and ethyl silicate was added. After concentration, the dope was dry spun and the green fibers were aged in a humid atmosphere and calcined. The fibers (Table II) had a glassy appearance and were composed of a nanocrystalline Al-Si spinel phase (or r /y-transition alumina) in an amorphous silica based matrix [33] [53]. After mullitization that starts at 1150 C and is complete after 2 min at 1400 C, the fibers were composed of mullite and corundum [33]. 

Fibers with a large excess of alumina with respect to the nominal mullite composition exhibit similar features. When fired below the mullitization temperature, they consist of a mixture of transition alumina and amorphous silica with (pre-crystallized Nextel 720 fiber) or without (Altex fiber) corundum. Conversely, after mullitization in the 1100-1200"C temperature range (Figure 2a), the crystalline phases present in the fibers are mullite and corundum [18] [33]. 

Alumina 9- lu-m9-n9 [NL, fr. L alumin-. alumen alum] (1801) (corundum) n. The oxide of aluminum, AI2O3, very refractory and next to diamond and boron nitride in hardness, obtained by the calcinations of bauxite. Alumina powder is used as a fire-retardant filler in plastics and, over the past two decades, alumina fibers have enjoyed increasing use as reinforcements for plastics, metals, and even ceramics. Its density is 3.965 g/cm. ... 

Aluminum oxides and related compounds have long been technologically important as abrasives (corundum) and in refractories and ceramics in the a-crystalline modification. In the y modification, a more open, defect structure, aluminum oxide becomes activated alumina and is useful in chromatography and in catalysis. A third modification occurs on the surface of the metal on exposure to air and serves as the well-known protective oxide. A more recent technological achievement is the production of remarkably uniform cylindrical fibers of AI2O3. These fibers can be incorporated in a variety of fabrics, papers, ropes, and so on, which gain the advantage of stability to very... 

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