• journal_title：American Mineralogist
• Contributor：Haipeng Wang ; Allan Pring ; Yung Ngothai ; Brian O’Neill
• Publisher：Mineralogical Society of America
• Date：2006-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2006.1985
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：91
• issue：4
• firstpage：537
• section：Articles

The oxidation behavior of synthetic α-NiS in air has been investigated over the temperature range 670–700 °C. The α-NiS was ground and sieved to give a particle size ranging from 53 to 90 μm. Three oxidation paths were observed:

No Ni₃S₂ (heazlewoodite) was observed over the course of α-NiS oxidation at 670 and 680 °C. The dominant oxidation path at this temperature is path i. At 700 °C, however, all three oxidation paths were observed. As an intermediate oxidation product, Ni₃S₂ steadily exsolved from α-NiS, reaching a maximum quantity after about 80 min of oxidation, declining afterward, and approaching annihilation at 160 min of oxidation. Experimental results show that the exsolution of Ni₃S₂ is likely triggered by the loss of one third of S in the α-NiS structure with the release of SO₂ rather than by an intrinsic thermal decomposition of α-NiS to α-Ni_1−xS + Ni₃S₂. The eventual annihilation of Ni₃S₂ was caused by a further oxidation of Ni₃S₂ to NiO. Oxidation paths 2 and 3 form a typical single chain reaction:

The approximate values of k₁ are k₂ are 3 × 10⁻⁴s⁻¹ and 5 × 10⁻⁴s⁻¹ respectively.

Oxidation temperature was found to play important roles both in the oxidation kinetics and the oxidation mechanism. By decreasing 10 °C from 680 to 670 °C, the average reaction rate (dy/dt, where y is the reaction extent) over the experiment time scale almost decreased to one third of its original rate (from 3.3 × 10⁻⁵s⁻¹ to 1.2 × 10⁻⁵s⁻¹). The reaction mechanism in the temperature range 670 to 680 °C is constant with E_a = 868.2 kJ/mol.