JOURNAL OF MATERIALS SCIENCE 39 (2 0 0 4 ) 3397 – 3402 Effect of solvent debinding variables on the shape maintenance of green molded bodies M. T. ZAKY Petroleum Refining Division, Egyptian Petroleum Research Institute (EPRI), Nasr City, P.O. Box 11727, Cairo, Egypt E-mail: magdytadrous@hotmail.com In order to study the effect of solvent extraction debinding variables on the shape maintenance of green molded bodies, powder compression molded bodies (the feed) were debound in various organic solvents such as n-hexane, n-heptane and isooctane at various extraction temperatures ranging from 30 to 60 ◦ C. The solvent to feed ratio of dilution was studied in the range of 7:1 to 15:1 by weight. Finally the effect of extraction time on the amount of binder extracted and diffusion coefficient of paraffin wax was studied in the range of 1 to 5 h. Thermo gravimetric analysis (TGA) was used to confirm the extraction of the major binder and stearic acid constituents completely from the binder mixture. Scanning electron microscopy (SEM) was used to see the pores in the green bodies created after solvent extraction process which allowing the degraded products (minor binder) to diffuse to the surface easily. C  2004 Kluwer Academic Publishers 1. Introduction The powder injection molding (PIM) process is used widely for the production of metal parts with complex shapes [1]. It consists of the preparation of a feedstock by mixing of a binder and metal powders, injection molding of the feedstock into a mold, removal of the binder from the feedstock (solvent and thermal debind- ing), and sintering of the metal or ceramic powders [2]. The removal of organic binder is a procedure (usu- ally termed debinding) that is known to be critical in obtaining a green compact with desired microstructure [3]. Debinding is a key problem with PIM because the time for binder removal depends on the section thick- ness. Consequently, various manufactures have set up- per limits on section thickness ranging from 10 to 50 mm. Thus, the goal in debinding is to remove the binder in the shortest time with the least impact on the compact [4]. There are several debinding techniques consisting of solvent and thermal methods in PIM process. Sol- vent debinding takes advantage of the high solubility of low molecular weight constituents (major binder) in organic solvents. The leaching or extraction of one binder component creates porosity in green bodies. A large amount of open porosity, after solvent debinding, allows the degraded products (minor binder) to diffuse to the surface easily. Therefore, the thermal removal of insoluble binder components will be finished in a much shorter period without endangering the integrity of the green piece. Consequently the combination of solvent debinding and thermal debinding can be time saving [5, 6]. Many authors studied different variables affecting the solvent debinding process but they keep the solvent to feed ratio constant. White and German [6] found that a high powder loading needed a long solvent debinding time to remove the wax from the binder. They attributed the long debinding time to the difficulties of diffusion through smaller pores. Lin and German [7] studied the debinding of PIM parts by the condensed C7 solvent at 95 ◦ C and used a diffusion model to describe the wax removal process. Nanjo et al. [5] reported the rate con- trolling step in the solvent debinding process by using different organic solvent vapors when using two kinds of binders. They stated that, selection of organic sol- vents of lower viscosity such as hexane is most im- portant to enhance the debinding rate. In addition, they investigated whether a liquid component involved in binders such as dispersant can enhance the debinding rate in order to shorten the debinding times. Tsai and Chen [6] studied the effect of C 6 ,C 7 and C 8 leach- ing solvents at different high temperatures (50, 60 and 80 ◦ C) on the kinetics of solvent immersion debinding process. They used very large amounts of solvents in the leaching operations. Thus, the objective of the present study is to investi- gate the effects of different organic solvents at different extraction temperatures (30, 40, 50 and 60 ◦ C) by vary- ing the solvent to feed ratios ( S/ F ) and extraction times on the amount of binder extracted, diffusion coefficient of paraffin wax and the shape maintenance of green molded bodies. 2. Experimental 2.1. Materials and preparation of green molded bodies The metallic powder used in this study was water- atomized 17-4PH stainless steel (STS, Mitsubishi Steel 0022–2461 C  2004 Kluwer Academic Publishers 3397