【正文】 irstly, ZrO2 and MgHC powders were mechanically blended at room temperature for 30 min and then the powder blend was dried to remove humidity in an electrical furnace at 200_C for 30 min. At the same time, paraffin wax was melted in a sigma blender (Santos Inc., Spain) at 80_C and oleic acid was added. The powder mixture was gradually added to the polymer melt and mixed for 60 min to form a homogeneous mix. After deairing with a vacuum, the powder plus polymer mixture was solidified and finally granulated into small pieces, as shown in Figure 2.MouldingTypical feedstocks contained 40 vol. % ceramic powder and 60 vol. % binder phase. These feedstocks were injection moulded using a 50 ton plungertype plastic injection moulding machine (Florin Inc.,316 England) to form them in the shape of ZrO2 tubes with one closed end. Tubes were 6 mm in outer diameter, 4 mm in inner diameter and 50 mm in length.Figure 2. Feedstock pellets of the powder plus polymer mixtureDensity and weight loss measurementsIn general, indices that can be used to quantify the extent of mixing are based on the standard deviation or the variance of the positions of spot samples taken in intervals from the mixture. For this purpose, densities and weight losses of the samples were measured. An Hgdisplacement method based on Archimedes39。 Principle was used for density measurements and the results were pared with the calculated values. The consistency in the density was used to measure the homogeneity of the feedstock. The feedstock homogeneity on a macroscopic scale was also assessed from the sample weight loss measurements after partial debinding. For this test, the samples were embedded into ZrO2 powder in a copper box and were put into a furnace at 130_C for 5 hours. In this process, partial debinding occurred with a wicking mechanism by capillary action. At the end of this test, the samples were reweighed to determine the amount of binder that had been present in each. The deviation from the original amount of the binder in the feedstock mixture was calculated to determine the level of homogeneity.Results and DiscussionWith SEM studies, it was found that ZrO2 particles were spherical in shape and MgHC particles were flaketype, as shown in Figure 3. The results of the article size distributions are shown in Figure 4. ZrO2 had a mean particle size of m and did not contain any agglomerates. MgHC contained weak agglomerates (1017 m) and its mean particle size was around m. According to the results, these powders are suitable for injection moulding process.Figure 3. Scanning electron micrographs of the powders, a) ZrO2 and b)MgHCGreen density resultsThe feedstock prepared with this method was injected easily at around 120_C using a cold mold. The viscosity of the feedstock was sufficient at moulding temperature. A setting time of 20 seconds was sufficient for the ejecting of the tubes from the mould without distortion and sticking. The green densities obtained from different batches are shown in Table values were very similar in all batches as a result of the wellmixed feedstock. The maximum difference between theoretical and measured sample densities was less than 3%. This shows that the binder and the ceramic particles were essentially uniformlymixed.Weight loss resultsThe results of partial debinding are given in Table 3. The values for all the batches showed a uniform binder distribution on the scale of size examined,., tubes of 2 grams. The debinding rate as weight loss divided by the initial binder content of sample changed in a limited range for three batches. The maximum difference in the debinding rates for all the batches was less than 1% and the values obtained from different samples for batches were close to each other. This is a result of mixture homogeneity.Microstructure evaluationA scanning electron micrograph of a specimen from which the binder had been removed pletely and which was sintered at 1750_C for 5 hours is shown in Figure 5. This micrograph reveals uniform packing of the ceramic particles in terms of grainstructure and grain size.Figure 5. Scanning electron micrograph of a specimen,showing uniformgrain size due to homogeneous packing of the ceramic particlesConclusionsThis study was carried out on products in the shape of small tubes. The results of this study indicate that the proposed feedstock preparation can be used for largescale industrial applications. The use of vacuum in the feedstock during preparation eliminated air from the final mixture. This makes the moulding step very easy. Using this method, feedstocks without any segregation of the binder can be prepared and injected.AcknowledgementThe authors gratefully acknowledge the TUBITAKMunir Birsel Foundation for financial support.ReferencesDow, ., Sacks, ., Shenoy, ., “Dispersion of Ceramic Particles in Polymer Melts, Ceramic Transactions, Vol. 1A, Ceramic Powder Science, TheAme. Cer. Soc., Ohio, 380388, 1988.Evans, , \Injection Moulding, Materials Science and Technology: A Comprehensive Treatment, Vol. 17A, Processing of Ceramics, VCH, Weinheim, 267311, 1996.German, ., “Powder Injection Moulding,MPIF, New Jersey, 1990.German, ., Hens, ., Lin, ., “Key Issues in Powder Injection Moulding”,Cer. Bull., 70, 8, 12941302, 1991.Mutsuddy, ., Ford, ., “Ceramic Injection Mgoulding, Chapman amp。 Hall, London, 1995.Waugh, A., “Process for Forming Sintered Leachable Objects for Various Shapes, Patent , 1970