Calcium aluminate fibers

This calcium aluminate fiber was evaluated in structural applications but it was not suitable for the evaluation of infrared optical properties because it contained bound water as evidenced by a strong hydroxyl band at 29 jjm in the IR transmission spectra. Hydroxyl-free compositions were made in carbon crucibles [17] by the Davy process [39], i.e., by a procedure [40] by which disposable optical calcium aluminate bulk glasses are prepared for commercial applications in optical windows. 

Table VII. Modulus of updrawn calcium aluminate fibers [4, 6-8,31]...

Figure 15. SNMS depth profile of a translucent calcium aluminate fiber. Redrawn from F. T. Wallenberger and S. D. Brown, High modulus glass fibers for new transportation and infrastructure composites and for new infrared uses, Composites Science and Technology, 51,243-263 (1994).

Inviscid melt spun calcium aluminate glass fibers have low strength (0.5-1.1 GPa) and moduli (46-58 GPa). Low strength and low stiffness can be attributed to the random structure frozen into the fibers during rapid solidification. As a result, they are not likely to become composite reinforcing fibers, despite their excellent alkali resistance which they share with quaternary calcium-aluminate fibers [9]. 

Calcium aluminate glasses can be made quite easily by air quenching liquids of 61 39 composition, which is the composition most extensively used for glass fiber production [20, 44], The glass-forming ability is considerably enhanced by adding components such as BaO, SrO, and NaO [21] without affecting the optical performance. 

Calcium aluminate cements are examples of conventional refractory castables. Development of low, ultralow cement, no-cement pumpables, and self-flow castables has increased the applications of monolithics [42], Steel-reinforced refractories (SFRR) are used in applications that include ferrous and nonferrous metal production and processing, petroleum refining, cement rotary kilns, boilers, and incinerators. Steel fibers are added to refractory concretes to improve resistance to cracking and spalling in applications of heavy thermal cycling and thermal shock loads. 

Due to the absence of Ca(OH)2 in the calcium aluminate cement paste a higher durabiUty of glass fibers was expected in fiber reinforced composites. Majumdar [26] proved that the calcium aluminate cement composites had much better mechanical properties, but only the case of alkali resistant glass. 

Glass fiber reinforced systems made with calcium aluminate cements... 

Quaternary calcium aluminate glass fibers were also downdrawn from preforms on a laboratory [9] and a development unit [41], Downdrawing is a valid, but costly, method for fiberizing fragile melts. In addition, only one of >500 compositions could be fiberized on a conventional melt fiberizing unit [17], This process is not suitable for fragile melts. 

Quaternary calcium aluminate glass fibers made by updrawing from a supercooled fragile melt offer superior mechanical properties and sapphire-like infrared transmission spectra. 

Their resistance to aikaline media exceeds that of commercially available AR silicate glass fibers (Chapter 6) having a zirconia content of up to 15% [20]. Hydroxyl-free quaternary calcium aluminate glass fibers (Figure 9), e.g., non-silica fibers containing 46.2% AI2O3 -36.0% CaO - 4.0% MgO -13.8% BaO, afford sapphire-like infrared transmission properties. 

Continuous binary calcium aluminate glass fibers can also be formed by inviscid melt spinning. In this case, carbon particles which are formed by the decomposition of propane enter into the surface of the molten jet and raise its surface viscosity, a process that lengthens the lifetime of the jet and prevents its breakup. 

Table Vm. Properties of inviscid melt spun calcium aluminate glass fibers [11]...

A special type of this material is called SIFCA slurry infiltrated fiber-reinforced castable. This is a composite material of ceramic matrix with calcium aluminate cement and with aggregate made of aluminum oxide, mullite, zircon and calcined fireclay. The matrix is reinforced with stainless-steel fibres. SIFCA is used to made pre-cast elements for refractory structures, where temperature can rise up to 1100°C. Heat curing is often used during the pre-casting. Another kind of similar material is called SIMCON slurry infiltrated mat concrete in which arrays of single fibres are replaced by a system of steel mats for better and easier distribution of reinforcement (Murakami and Zeng 1998). 

Calciiun aluminate cement has been suggested as a binder for glass fiber reinforced composites. (Majumdar et al, 1981). This cement appears to be more siritable for this purpose than Portland cement, as the pH of its pore solution is distinctly lower. Also, it does not liberate calcium hydroxide in its hydration, which is resportsible for the embrittlement seen in such materials after prolonged times of ciuing. 

The commercial potential of updrawn quaternary calcium aiuminate giass fibers was tested in two stages. In the early 1960s, they were evaluated because they yielded higher moduli than those which couid then be achieved with siiicate glass fibers [36-37]. Timing for this development coincided with the onset of the commercial development of carbon fibers and no new aluminate or silicate glass fiber was commercialized until 1995. 

The manufacture of paper and allied products involves the preparation of wood and other raw materials, separation and recovery of cellulose fibers, and blending of the fibers with proper additives to produce furnish , which is formed into paper. The additives include sizing materials such as alum and resins, sodium aluminate, and wax emulsions synthetics, such as acrylics, isocyanates, and fiuocarbons and fillers such as clays, calcium carbonate and sulfate, talc, barium sulfate, aluminum compounds, and titanium oxide. When fillers are used, retention aids (starches or synthetic resins) are added to increase the retention of the filler. 

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