Methods of making manganese sulfide

#This invention relates to methods of making manganese sulfide. In particular, the present invention relates to methods of making manganese sulfide using iron pyrite as a reaction moderating material.

#Manganese sulfides occur routinely when making steel. Sulfur is present in many of the raw materials to make steel and manganese has long been one of the most common and inexpensive alloying elements used in steelmaking. During melting and refining, the sulfur present in the molten raw materials selectively combines with manganese to form manganese sulfides (MnS). In addition to preventing sulfur from causing a hot short condition in the iron matrix during hot working, the discrete manganese sulfide particles (commonly referred to as inclusions) also serve as chip breakers during subsequent machining operations. These natural breaks in the chips generated during a machining operation reduce tool wear, and allow better control of the machining and a better surface finish on the final part.

#Many metallurgical powders used to fabricate powder metal parts are made from pure elemental powders, such as iron, manganese and chrome. When using powders that do not contain sulfur, no inclusions are formed. Therefore, machining the metal parts made from powders without sulfur is difficult and expensive. The addition of pure sulfur powder is not a solution to this difficulty because sulfur powders are potentially both safety and environmental hazards. In addition, sulfur powder may not react, or completely react, to form MnS.

#The numerous features and advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying detailed description and the following drawings, in which:

#FIG. 1 is a graph of weight percent carbon in a manganese sulfide product verses the total weight of initial reactants.

#FIG. 2 is a graph of weight percent oxygen in a manganese sulfide product verses the total weight of initial reactants.

#The present invention provides methods for making manganese sulfide compounds without the need for recycling a significant amount of manganese sulfide back to the reaction chamber from an earlier reaction. The methods are performed by reacting substantially pure manganese with substantially pure sulfur in the presence of iron pyrite. First, the substantially pure manganese, substantially pure sulfur, and iron pyrite are admixed. Then the admixture is reacted in a reaction chamber. After the reaction is complete, the manganese sulfide compound is recovered. In some embodiments, carbon is added to the reaction chamber to control the oxygen content of the final manganese sulfide compound.

#The term manganese sulfide compound as used in the specification and claims herein means compounds composed substantially of manganese monosulfide (MnS). Manganese sulfide compounds may also include carbon, oxygen, or impurities. The term substantially pure as used in the specification and claims is defined as used in the metallurgical industry. The term impurity refers to impurities commonly found in the formation of manganese sulfide or those impurities found in the materials added to the reaction chamber.

#Thermodynamic calculations show that the direct combination of equimolar quantities of manganese and sulfur to produce manganese sulfide is an extremely exothermic reaction. Starting at room temperature the adiabatic reaction temperature is greater than 2500° Centigrade. Once initiated, the reaction is self-sustaining and can be quite violent until the reactants are depleted. Sulfur can vaporize during this process.