Friable

Low Temperature Carbonization. The Lurgi Sptlgas process was developed to carbonize brown coal at relatively low temperatures to produce tars and oils (Fig. 5). A shaft furnace internally heated by process-derived fuel gas (Spblgas) is used. The product can range from a friable coke breeze to hard lump coal depending on the quality of the briquettes used in the feed. The briquettes, made in normal extmsion presses, break down into smaller sizes during carbonization. 

The reaction of finely ground ores and an excess of carbon at high temperatures produces a mixture of metal carbides. The reaction of pyrochlore and carbon starts at 950°C and proceeds vigorously. After being heated to 1800—2000°C, the cooled friable mixture is acid-leached leaving an insoluble residue of carbides of niobium, tantalum, and titanium. These may be dissolved in HF or may be chlorinated or burned to oxides for further processing. 

Belt Feeders. Belts ate used to feed overlong slotted openings. Typically, belt feeders are used to handle friable, coarse, fibrous, elastic, sticky, or very cohesive soHds. Because belts are available in widths up to 2.74 m and unrestricted lengths, such feeders can be designed for very large outlets. 

Xanthates have been synthesized from C -Cg oxo alcohols ia a reactor with iatensive stirring at 25°C. The water and unreacted alcohol are removed from the product at 40—50°C under vacuum to give a friable powder of 80% purity ia 77% yield (79) (see Oxo process Alcohols, higher aliphatic). 

Above 40 wt % hydrogen content at room temperature, zirconium hydride is brittle, ie, has no tensile ductiHty, and it becomes more friable with increasing hydrogen content. This behavior and the reversibiHty of the hydride reaction are utilized ki preparing zirconium alloy powders for powder metallurgy purposes by the hydride—dehydride process. The mechanical and physical properties of zirconium hydride, and thek variation with hydrogen content of the hydride, are reviewed in Reference 127. 

Material Characteristics InnuencingDesign. Materials ranging from fine powders to large lumpy materials, nonabrasive to very abrasive, free-flowing to cohesive, and nonfriable to friable can be handled on properly designed belt conveyors. Very sticky materials can be a problem, however, if these cannot be continuously cleaned from the belt surface. 

After the molten glass has become a homogeneous Hquid, it is poured in a thin stream into water or between closely spaced, water-cooled rotating metal rollers. This quenched glass, termed frit, is a friable material easily reduced to small-sized particles by a ball-milling operation. Ball-milling the glass frit into small-sized particles can be carried out whether the frit is to be used wet or dry (see Size reduction). 

Description of class Wet feed is granular and damp but not sticky or muddy and dries to granular meal Wet feed is pasty, muddy, or sloppy product is mostly hard pellets Wet feed is crumbly and friable product is powder with very few lumps... 

The plate dryer is limited in its scope of apphcations only in the consistency of the feed material (the products must be friable, free flowing, and not undergo phase changes) and diying temperatures up to 320°C. Applications include speci ty chemicals, pharmaceuticals, foods, polymers, pigments, etc. Initial moisture or volatile level can be as high as 65 percent and the unit is often used as a final dryer to take materials to a bone-dry state, if necessary. The plate dryer can also be used for heat treatment, removal of waters of hydration (bound moisture), solvent removal, and as a product cooler. 

Cowan reported that significant size reduction of sohds occurred when cellulose acetate was dried in a spouted bed, indicating its possible hmitations for handling other friable particles. 

---