Layered manufacturing methods for fabricating ceramic components can involve selective deposition of binder using ink-jet printing. Selection of a proper binder plays a critical role in fabricating parts with good surface finish, dimensional accuracy, and high resolution. Several polymeric solution-phase binders were investigated in terms of their physical properties, printing performance, and binder-powder bed interaction. It was observed that the molecular weight should be <15 000 for the binder to be penetrated into dense powder compacts. Binder infiltration kinetics and printed line width were also significantly influenced by powder-bed characteristics, such as surface roughness and pore size, as well as the physical properties of the binder, such as viscosity and surface tension.
Additions of urea were found to increase the yield of nickel sulfides. Reaction rates for the hydrolysis reaction 12 are of the sulfide formation from acidic solutions of thioacetamide.formFor this type of reaction, the Two precipitation mechanisms were identified: hydrolysis rate of precipitation is directly proportional to decomposition and direct reaction between nickel and thioacetamide.of thioacetamide, which is dependent on the concentrations of Hydrolysis-controlled precipitation is evident with low inithioacetamide and hydrogen ion. Therefore, the precipitation tial pH. The direct reaction is dominant at high initial pH.rate increases with decreasing pH.
Nucleation proceeds by a direct reaction between nickel andIn the direct reaction mechanism, metal cations directly react thioacetamide. The role of urea in precipitation of nickel with thioacetamide to form the metal sulfide. The actual reacwas found to be twofold. Urea increases the rate of thioacettion mechanism and the intermediate species involved in the amide decomposition, thus increasing the concentration of reaction were not reported by Swift and co-workers. H 2 S form. Secondly, decomposition increases the pH of the Bowersox et al. 13 reported the precipitation of nickel sulfide solution, which in turn increases the relative concentration by direct reaction. Rate expressions for the direct reaction are of S ؍ ions. Agglomeration of particles was more evident in of the form the powders obtained in the presence of urea.Ϫd[M]/dt ϭ k[M][TAA][H ϩ ] Ϫ1/2
Nickel sulflde powders were precipitated by utilizing the thermal decomposition of thioacetamide in acidic aqueous solutions. Precipitation was induced by a direct reaction between thioacetamide and nickel at 70° and 80°C with thioacetamide concentrations of 0.80M. Precipitation was induced by reaction of sulfide ions with nickel at 90°C and at low pH. Direct reaction products were amorphous and contained significant amounts of carbon, excess sulfur, and hydrogen. Hydrolysis‐controlled precipitation yielded faceted crystalline particles 2 to 4 μm in size. Crystalline, spherical particles with compositions near stoichiometric NiS were precipitated with high yields.
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