The present study focuses on the physical and chemical mechanisms of lubricant removal during the first step of the sintering process during powder metallurgy (P/M) processing of ferrous systems. Previous works on the kinetics of delubrication made it possible to develop an empirical model which accounts for the typical weight loss profile observed upon heating of green compacts. It has been established that the rate at which the parts are heated dictates the overall process kinetics, and fitting curve methods yield two parameters which contain the corresponding information: (i) TMAX is the temperature of 50% lubricant removal, and (ii) b is representative of the slope of the curve during weight loss stage. Phase I of this study aims at determining the dependencies of these two parameters with respect to a series of physical variables: green density of the compacts; presence of an alloying element potentially catalytic for the reaction of lubricant pyrolysis; and procedure of compaction and geometry of the compacts. Also, it is suggested that the two parameters obtained from the fitting curve methods can be related to the main two mechanisms of delubrication: evaporation of the lubricant and conversion of the lubricant molecules into smaller hydrocarbons, assuming that these two mechanisms are the kinetically limiting mechanisms. Furthermore, recent studies of the delubrication process have been opening the way to the potential development of gas sensors, which could eventually allow the direct monitoring of the emissions of gaseous species. Several key features have been reported in the literature, including a peak emission of hydrocarbons at the delubrication temperature, as well as strong emissions of CO and CO2 at temperatures above 700°C. The scope of Phase II of this project was thus to verify that these features were retained under various processing conditions, so that the development of a sensor suitable for various sintering environments is viable. Variations in the emission profiles of gaseous species were observed as the processing conditions were changed, and when possible, potential justifications for these changes have been proposed.

"De-lubrication is the first stage in a sintering operation, where the lubricants (higher weight hydrocarbons) are removed from the parts by controlled heating. Improper de-lubrication leads to defects such as blistering, sooting, micro-porosity etc in a sintered part. Most of these problems arise, as there exists a gap in the present understanding of de-lubrication. The primary motive of this work is to direct research towards the development of sensors and controls and thus, mitigate the various problems due to improper de-lubrication. Currently, there exists a myriad of lubricants being used during the process of compaction. They include metallic based lubricants, polymers and non-metallic lubricants. In this work, research was limited in understanding the de-lubrication of EBS (Ethylene Bisstearimide), as, it the most commonly used lubricant in the industry. It has replaced commonly used lubricant due to cleaner burnouts, absence of metallic residue and, cost effectiveness. The entire work is divided into three phases: • Phase 1: Ascertained the most important parameters that affect the kinetics of de-lubrication. • Phase 2: Investigated the type of gases released during the decomposition of EBS. • Phase 3: Recommended a control strategy. TGA (Thermo-gravimetric analysis) was used in the phase I, the results clearly show that the rate of heating is the most important parameter during de-lubrication. Identification of gases was performed using the FTIR (Fourier transform infrared spectroscopy) and DUV (Deep ultraviolet spectroscopy). This constituted the second phase of our experiments. The primary gases identified in Phase II were carbon dioxide and a hydrocarbon (hepta-decane). Finally, an empirical model for de-lubrication has been proposed in Phase III. The model was verified in an industrial furnace. It has been observed that there exists a very good correlation between the proposed empirical model and the experiments performed in Phase II of this study. This study lays down the following guidelines for the development of future sensors and controls: • The development of future sensors should focus in the detection of CO2 and hepta-decane. • Rate of heating determines how fast or slow the lubricant decomposes and finally escapes form the compacted part. • The empirical model may be used, as a means to determine the time a part should reside in a furnace for complete lubricant burnout at a given heating rate."