Aluminizing process availability

There are several processes available for the manufacture of cryoHte. The choice is mainly dictated by the cost and quaUty of the available sources of soda, alumina, and fluoriae. Starting materials iaclude sodium aluminate from Bayer s alumina process hydrogen fluoride from kiln gases or aqueous hydrofluoric acid sodium fluoride ammonium bifluoride, fluorosiUcic acid, fluoroboric acid, sodium fluosiUcate, and aluminum fluorosiUcate aluminum oxide, aluminum sulfate, aluminum chloride, alumina hydrate and sodium hydroxide, sodium carbonate, sodium chloride, and sodium aluminate. 

More than one boride phase can be formed with most metals, and in many cases a continuous series of solid solutions may be formed. Several methods have been used for the relatively large-scale preparation of metal borides. One that is commonly used is carbon reduction of boric oxide and the appropriate metal oxide at temperatures up to 2000 °C. Fused salt electrolysis of borax or boric oxide and a metal oxide at 700 1000 °C have also been used. Small-scale methods available include direct reaction of the elements at temperatures above 1000 °C and the reaction of elemental boron with metal oxides at temperatures approaching 2000 °C. One commercial use of borides is in titanium boride-aluminum nitride crucibles or boats for evaporation of aluminum by resistance heating in the aluminizing process, and for rare earth hexaborides as electronic cathodes. Borides have also been used in sliding electrical contacts and as cathodes in HaU cells for aluminum processing. 

Globar LL—made by a process similar to Hot Rod, but in three sections with the low resistance cold ends jointed, bonded and then aluminized and available with a hot zone length up to 2.5 m. Silit ED—made in one piece with the outer extremities of cold ends aluminized and available with a hot zone length up to 2.5 m. 

The majority of metals and alloys available depend for their resistance to corrosion on the properties of an oxide film or corrosion product which is formed initially by the corrosion process. In many cases the protectiveness of the oxide film is determined by its stability in aqueous solutions in a specific pH range, either chemically dissolving to form aquocations at lower pH values or complex anions (aluminate, ferroate, plumbate, zincate, etc.) at higher pH values (Fig. 2.22). An important property of the chemical is therefore the pH value that it develops when dissolved in water. For many materials and many chemicals this is the overriding factor and in many cases... 

As noted in the earlier section Basics of Electrophilic Substitution Reactions, the loss of the hydrogen ion (H ) requires the presence of a strong base. The chloride ion (CL) is a base, but it isn t strong enough to accomplish this task. However, as shown in the mechanism, the tetrachloro-aluminate ion (A1C1 ) is a sufficiently strong base. This process also regenerates the catalyst so that it s available to continue the process. 

WWII. Development of hydroforming 45 processes for petroleum naphthas insured availability of unlimited quantities of toluene. Improved purification procedures for toluene were also developed. US capacity for producing TNT reached 3.6 billion lbs per year. Widespread use of binary expls (TNT with PETN, RDX, Tetryl, Ammonium Picrate, etc), and of aluminized TNT compns... 

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