Alumina fibers Saffil fiber

A sol-gel method is used to produce silica-stabilized alumina (Saffil) and calda-stabilized zirconia fibers. The flow diagram for Saffil fiber is shown in Fig. 

For Saffil alumina fiber, aluminum oxychloride [Al2(OH)jCI] is mixed with a medium molecular weight polymer such as 2wt% polyvinyl alcohol. The aqueous phase contains an oxide sol and an organic polymer. The sol is extruded as filaments into a coagulating (or precipitating) bath in which the extruded shape gels. The gelled fiber is then dried and calcined to produce the final oxide fiber. This solution is slowly evaporated in a rotary evaporator imtil a viscosity... 

The Saffil fiber which contains 4% of silica is produced by the blow extrusion of partially hydrolyzed solutions of some aluminum salts with a small amount of silica, in which the liquid is extruded through apertures into a high velocity gas stream. The fiber contains mainly small 8-alumina grains of around 50 run but also some a-alumina grains of 100 run. The widest use of the Saffil type fiber in composites is in the form of a mat which can be shaped to the form desired and then infiltrated with molten metal, usually aluminium alloy. It is the most successful fiber reinforcement for metal matrix composite. 

The alumina based fibers discussed in section 3.2 possess a range of compositions. They can be short, as with the S affil fibers or continuous, as with the others described. Their properties at room temperature depend on the ct-alumina content and at high temperature, the presence of any second phase (31). The Saffil fiber contains a few percent of silica with the remainder of the composition being alumina in one of its transition phases or as a mixture of transition phases and a-alumina. Table 7 shows the changes in processing of fibers of this type (32).The properties of alumina based fibers areshown in Table 8. Figure 3 shows the tensile curves of a pure a-alumina fiber, the Fiber FP, which had a grain size of 0.5 p,m (23). 

Alumina silica based fibers Saffil Saffil 95% AI2O3 5% Si02 1-5 3.2 2 0.67 300 6... 

The formation of S-alumina at --1070°C (Figure 2b) is accompanied by a decrease in porosity and an increase in grain size (Table III), but the fiber retains high strength. Saffil fibers consist of 8-alumina nanocrystals (10-50 nm in size) whose structure is related to spinel [10], small amounts of y (and y ) phase and a-alumina platelets [63]. As temperature is further increased, the amount of a-alumina increases, the porosity decreases, grain growth continues, and fiber strength decreases. 

J. Dinwoodie, Saffil alumina fiber, manufacture, properties and application in high temperature furnaces, Canadian Ceramics Quarterly, 23-29, Feb. 1996. 

Saffil. TM for a group of synthetic inorganic fibers made from alumina and zirconia. 

Saffil alumina-silica fibers have excellent thermal insulation behavior and resilience up to 1600°C. Their diameter is small, about 3 p.m. 

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