High-Chrome-Molybdenum Alloys

Chrome—nickel alloy heating elements that commonly ate used in low temperature furnaces are not suitable above the very low end of the range. Elements commonly used as resistors are either silicon carbide, carbon, or high temperature metals, eg, molybdenum and tungsten. The latter impose stringent limitations on the atmosphere that must be maintained around the heating elements to prevent rapid element failure (3), or the furnace should be designed to allow easy, periodic replacement. 

Common metals are suitable as materials of construction. These include the following metals and metal alloys chrome-molybdenum steel, IVpe 300 stainless steel, brass, lead. Monel, K-Monel, and nickel. Piping and appurtenances for undiluted diborane must be designed by experienced engineers and safety and fire protection specialists. Sa-ran, polyethylene, Kel-F, Teflon, graphite, and high-vacuum silicone grease are satisfactory for use with diborane. 

Which Alloy to Use. Unalloyed mild steel parts have been known to corrode at rates as high as 800 mils per year. The low-chrome steels, through 9-Cr, are sometimes much more resistant than mild steel. No corrosion has been reported, with both 2%-Cr and 5-Cr furnace tubes, whereas carbon steel tubes in the same service suffered severe coiTosion. The 12-Cr stainless steels are scarcely, if any, better than the low-chromes. But the 18-8 Cr-Ni steels, without molybdenum, are often quite resistant under conditions of low velocity although they are sometimes subject to severe pitting. 

Metals are utilized for applications requiring high strength and/or endurance, such as structural components of heart valves, endovascular stents, and stent-graft combinations. Commonly used alloys include austenitic stainless steels (SS), cobalt-chrome (Co-Cr) alloys including molybdenum-based alloys, tantalum (Ta), and titanium (Ti) and its alloys. Elgiloy, a cobalt-nickel-chrome-iron... 

The major fermentation method used to produce lactic acid on an industrial scale is the batch fermentation process. The factors affecting the batch process have been reviewed (Litchfield 1996 Vick Roy 1985). Because of the very corrosive properties of lactic acid, construction materials used for the fermenter and downstream processing equipment are a major cost item. Copper, copper alloys, steel, chrome steel, and high-nickel steels are all unsatisfactory. High-molybdenum stainless steel like SS316 is satisfactory. Plastic linings of fermentation tanks have been used successfiilly, and new developments in ceramics and plastics may provide future choices (Vick Roy 1985). 

---