5.2.1 Nickel-copper alloys
Nickel and copper can be intermixed in any proportion to form solid solution alloys. Nickel-copper alloys are more resistant to corrosion in reducing media than pure nickel and more resistant to corrosion in oxidizing media than pure copper. Nickel-copper alloy is usually between 10% ~ 30%. Commonly used nickel-copper corrosion-resistant copper about 28%, in the reducing medium has good corrosion resistance.
5.2.1.1 Corrosion resistance of nickel-copper alloys
Ni68Cu28Fc and Ni68Cu28Al are two commonly used Ni-Cu-type corrosion-resistant alloys, have the same corrosion resistance, the chemical composition is listed in this chapter of Schedule 2. Ni68Cu28Al alloy containing the appropriate amount of Al, Ti, because Ni3(Al), Ni3(Cu), Ni3(Cu), Ni3(Cu), Ni3(Cu), Ni3(Cu).
Ni68Cu28Al alloy containing moderate amounts of Al, Ti, Ni68Cu28Al alloy due to Ni3 (Al, Ti) intermetallic phase dispersion strengthened Ni68Cu28Fe have higher strength and hardness. Ni68Cu28Fe and Ni68Cu28Al alloys in the high-temperature hydrogen fluoride gas and hydrofluoric acid solution, in the molten caustic soda and alkaline and alkaline salts and their solutions, have good corrosion resistance. Ni68Cu28Fe alloy due to the absence of chromium in the air-filled (oxygen) or Containing oxidizing agents in the medium of poor corrosion resistance.
(1) Ni68Cu28Fe (or Ni68Cu28A1) alloy is not filled with air in the hydrofluoric acid solution has excellent corrosion resistance, can withstand any concentration of hydrofluoric acid corrosion, in the presence of oxygen (air-filled) conditions will accelerate its corrosion, affecting the corrosion resistance (Figure 5-16).
Ni68Cu28Fe and other alloys in the confined airless hydrofluoric acid has the best corrosion resistance; in the confined saturated air hydrofluoric acid has the maximum corrosion rate. Oxygen-containing nitrogen purification of hydrofluoric acid gas phase, nitrogen in the oxygen content of more than 1,000mg/kg, whether the hydrofluoric acid gas phase or liquid phase accelerated the corrosion of Ni68Cu28Fe alloy
(3)The Ni68Cu28Fe alloy containing 68% Ni is corroded in caustic alkali (e.g. NaOH- etc.), neutral salt (e.g. NaCI etc.) and alkaline salt (Na2CO2). and alkaline salts (Na2CO3, etc.) have the same good corrosion resistance as pure nickel in solutions of caustic (e.g., NaOH-, etc.), neutral salts (e.g., NaCI, etc.), and alkaline salts (e.g., Na2CO3, etc.), as shown in Tables 5-25 and 5-26; in Aluminum sulfate, ammonium sulfate, ammonium chloride, zinc chloride and other acidic salt solutions are also corrosion resistant.
(4) Ni68Cu28Fe alloy can resist 550 ~ 650 ℃ high temperature hydrogen fluoride gas, 550 ℃ fluorine gas, and ≤ 485 ℃ high temperature steam corrosion. Steam corrosion; in the flow of seawater corrosion resistance is also very good.
(5) Ni68Cu28Fe alloy in air-filled or oxidizing agent in the presence of hydrofluoric acid in the liquid phase and gas phase, in the Cu2+-containing hydrogen Fluoric acid, in fluosilicic acid (H2SiF.) solution, in sulfuric acid containing MF acid, fluosilicic acid and HgCl2, in liquid metallic mercury at 100 ℃ and in molten metal. Stress corrosion rupture occurs in liquid metallic mercury and in molten or high-temperature, highly concentrated caustic soda (potassium). Stress corrosion ruptures can occur in molten or high-temperature, highly concentrated sodium (potassium) caustic. Ni68Cu28Fe alloys annealed at 850°C or 950°C do not produce stress corrosion rupture in NaOH (or KOH) at 300°C.
5.2.1.2 Application of Nickel-Copper Alloys
Ni68Cu28Fe alloy is mainly used as heat exchangers, boiler feedwater heaters, piping, vessels, towers, and other equipment in chemical, petrochemical, and marine development. Ni68Cu28Al has higher strength and hardness than Ni68Cu28Fe alloy, mainly used for pumps. Ni68Cu28Al has higher strength and hardness than Ni68Cu28Fe alloy, and is mainly used as pump shafts, impellers, oil well drilling rings, conveyor scrapers and elastic parts.
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