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Inconel

An Economical Substitute for Platinum in many High Temperature Environments

Inconel® nickel-chromium-iron alloy 601 is a general purpose engineering for applications that require resistance to heat and corrosion. Inconel® alloy 601 has excellent resistance to oxidation in the 1000° to 1200° C temperature range and also has good corrosion resistance to many acid and aqueous salt solutions. The limiting chemical composition of the alloy is shown in TABLE 1

The properties of Inconel® alloy 601 make it a material of broad utility in such fields as thermal processing, chemical processing, pollution control, aerospace, and power generation. It has been used for crucibles, baskets, trays and fixtures for annealing, carburizing, carbonitriding, nitriding and other heat-treating operations. Industrial furnace applications include radiant tubes, mufflers, retorts, flame shields, burner nozzles and electrical resistance heating elements. In the pollution-control industry it is used for combustion chambers in solid waste incinerators. The alloy is also used for jet engine igniters and containment rings in gas turbines for aircraft.

Some physical constants of the alloy are listed in the Resistance Table below.
Inconel® alloy 601 Laboratory Ware
Metal Technology now offers Inconel® alloy 601 laboratory ware in a wide variety of standard shapes and sizes. See our price list. Quotations for specialized items supplied upon request.

Inconel® alloy 601 may be your answer to high-temperature applications requiring resistance to oxidation and spalling where platinum has traditionally been relied upon. In addition to its resistance to corrosive oxidation, the alloy is also unaffected by rapid changes from hot to cold and retains its mechanical strength at elevated temperatures. The high resistance of Inconel® alloy 601 to oxidation, carburization or sulfidation make it well suited for vessels used in determining moisture, volatiles, fixed-carbon and ash in most coal and coke products, or wood pulp or fiber.

It has also been recommended for use in drying and ashing biological materials whose residues are soluble in dilute acid or alkali for subsequent analysis. Race-level determinations of principal constituent elements are excluded.

Smoothing and reshaping after use is not necessary. Uniform heating is assured since the inherent strength of Inconel® alloy 601 laboratory ware precludes the necessity of reinforced rims and thicker bottoms as is the case with platinum in some instances. The vessels can be cleaned simply by scouring with sea-sand or some other mild abrasive. NOTE: Strong alkaline or oxidizing fusions are not recommended with Inconel® alloy 601 laboratory ware.

Inconel® alloy 601 crucibles may replace platinum for many high-temperature ashing applications.
Oxidation
Inconel® alloy 601 has exceptional resistance to oxidation at high temperatures. The alloy forms a protective oxide coating that resists scaling even under the severe conditions of cyclic exposure to temperature. FIGURE 1 compares performance of Inconel® alloy 601 with the behavior of other oxidation resistant materials in a cyclic oxidation test at 2000º F (1095º C) for 15 minutes. and rapid cooling in air for 5 min. Weight change was determined periodically throughout the test.



The resistance of alloy 601 to oxidation at temperatures of 2100º F (1150º C) is illustrated by FIGURE 2, FIGURE 3 and FIGURE 4. The data were derived from tests in which the specimens were exposed to temperatures for ten consecutive 50-hr. periods. After each exposure period, the specimens were cooled to room temperature, brushed lightly to remove loose oxide, and then weighed to determine weight change.

The superior oxidation resistance of Inconel® alloy 601 is related to the amounts of nickel, chromium and aluminum in the alloy. During high temperature exposure, those elements form an extremely protective and adherent oxide film on the surface of the material. In addition, a slight amount of internal oxidation occurs and provides a higher chromium content in the surface oxide. The protective oxide layer is illustrated in FIGURE 5, FIGURE 6 and FIGURE 7, which are unetched photomicrographs of the cross-section of specimens exposed to high temperatures.
Carburization
Inconel® alloy 601 has good resistance to carburization. TABLE 2 and TABLE 3 give the results of gas carburization tests performed at three different temperatures. The weight-gain measurements indicate the amount of carbon absorbed by the specimens during the exposure periods.

Alloy 601 also has good resistance to carbonitriding environments. TABLE 4 gives the results of tests performed in a gas mixture of 5% ammonia, 2% methane, and 92% hydrogen at 2000º F (1095º C).
Sulfidation
The resistance of Inconel® alloy 601 to sulfidation in an atmosphere of 1.5% hydrogen sulfide and 98.5% hydrogen at temperatures from 1200 to 1400°F (650-760ºC) is shown in FIGURE 8. The weight-loss measurments are for completely de-scaled specimens after 100 hours of exposure to the environment.
General Corrosion
Inconel® alloy 601 has good resistance to nitric acid. TABLE 5 gives corrosion rates for the alloy in 5% to 70% nitric acid at boiling temperature. The rates were determined for specimens of annealed sheet.

Alloy 601 has good resistance to low concentrations of phosphoric acid. Tests of 48-hr. duration in 10% phosphoric acid yielded corrosion rates of 0.3% mpy (0.008 mm/yr) at 176º F (80º C) and 0.1% mpy (0.002 mm/yr) at boiling temperature. The alloy has poor resistance to higher concentrations of phosphoric acid.

Inconel® alloy 601 has excellent resistance to general corrosion in sodium hydroxide solutions. TABLE 6 gives corrosion rates for specimens of annealed sheet in sodium hydroxide at up to 98% concentration. As shown in TABLE 7, Inconel alloy 601 has good resistance to many other corrosive solutions. The alloy's high nickel content provides resistance to reducing environments, and its substantial chromium content provides resistance to oxidizing conditions.

The alloy is not resistant to sulfuric, hydrochloric and hydrofluoric acids.

Inconel is a registered trademark of Special Metals Company.

Corrosion Resistance Table

Laboratory Tests at 176F° (80C°)
Corrosion Rate
Environment
Test Duration, days
mpy*
mm/yr

Acetic Acid (10%) 7 <0.1
<0.002
Acetic Acid (10%)+
-Sodium Chloride (0.5%) 30 2.18**
0.554
Acetic Acid (10%)+
-Sulfuric Acid (0.5%) 7 45.7**
1.161
Alum (5%) 7 28.6**
0.726
Aluminum Sulfate (5%) 7 <0.1
<0.002
Ammonium Chloride (5%)*** 30 0.1
0.002
Ammonium Hydroxide (5%) 7 Nil
Nil
Ammonium Hydroxide (10%) 7 Nil
Nil
Ammonium Sulfate (5%) 7 0.1
0.002
Barium Chloride (10%)*** 30 0.1
0.002
Calcium Chloride (5%)*** 30 0.1
0.002
Chromic Acid (5%) 7 3.6**
0.091
Citric Acid (10%) 7 <0.1
<0.002
Copper Sulfate (10%) 7 Nil
Nil
Ferric Chloride (5%)*** 7 354**
8.99
Ferrous Ammonium
-Sulfate (5%) 7 Nil
Nil
Lactic Acid (10%) 7 36.4
0.925
Methanol 7 Nil
Nil
Oxalic Acid (5%) 7 23.8**
0.605
Oxalic Acid (10%) 7 52.2**
1.326
Potassium Ferricyanide (5%) 7 Nil
Nil
Sodium Bisulfite (5%) 7 <0.1
<0.002
Sodium Carbonate (5%) 7 Nil
Nil
Sodium Chloride (10%)*** 30 0.2
0.005
Sodium Chloride (20%)*** 30 0.3
0.008
Sodium Hypochlorite (1%)*** 7 3.5**
0.089
Sodium Hypochlorite (5%)*** 7 <6.9**
0.175
Sodium Sulfate (5%) 7 Nil
Nil
Sodium Sulfate (10%) 7 <0.1
<0.002
Sulfurous Acid (6%)*** 7 56.2**
1.427
Tartaric Acid (20%) 7 21.8
0.554
Zinc Chloride (10%) 7 0.1
0.002

*Mils penetration per year **Average of two tests ***Environment caused pitting attack