Structure Formation and Mechanical Behavior of Two-phase Nanostructured Materials

Phase Homogeneity in Y2O3–MgO Nanocomposites Synthesized by Thermal Decomposition of Nitrate Precursors with Ammonium Acetate Additions

“…(1) Making the Precursor Solutions A stock oxide precursor solution was made by mixing 37.5 g of yttrium nitrate hexahydrate (Y(NO 3 ) 3 ·6H 2 O, 99.9%), and 56.9 g of magnesium nitrate hexahydrate (Mg(NO 3 ) 2 ·6H 2 O, 98%-102%) and then dissolving the salts in 120 ml of de-ionized water. Ammonium acetate (CH 3 COONH 4 , 97.0%)-which is designated, hereafter, as NH 4 [a]-was then added to the stock solution and the mixture was stirred gently until a clear solution was obtained; all these salts were purchased from Alfa Aesar (Ward Hill, MA). The proportions of the yttrium and magnesium salts in the stock solution were selected such that the conversion of all the cations to the corresponding oxides with the usual crystal structures would give a 50-50 vol% Y 2 O 3 -MgO composite, and this corresponds to a 20-80 mol% oxide mixture.…”

“…The proportions of the yttrium and magnesium salts in the stock solution were selected such that the conversion of all the cations to the corresponding oxides with the usual crystal structures would give a 50-50 vol% Y 2 O 3 -MgO composite, and this corresponds to a 20-80 mol% oxide mixture. A series of precursor solution mixtures was obtained by varying the quantity of NH 4 [a] added to the stock solution. A thermochemical calculation, based on the ratio of oxidizing to reducing elements (Q e ) in the salts, 37,38 was used to obtain the amount of NH 4 [a] (reducer/fuel) required for a stoichiometric redox reaction with the nitrates (oxidizers).…”

“…M ETAL oxide materials, with microstructural features in the nanometer range (i.e., particle or grain sizes, domain sizes, or layer thickness) can exhibit enhanced properties over their coarse-grained counterparts. [1][2][3][4] For example, nanostructured oxides may exhibit enhanced diffusivity, superior magnetic properties, enhanced catalytic activity, ultrahigh strength, improved ductility and toughness, unique optical properties, and the ability to densify by sintering at relatively low temperatures. 4,5 However, it is difficult to obtain nanostructured consolidated bulk ceramics using nanograined oxide powders as starting materials.…”

“…[1][2][3][4] For example, nanostructured oxides may exhibit enhanced diffusivity, superior magnetic properties, enhanced catalytic activity, ultrahigh strength, improved ductility and toughness, unique optical properties, and the ability to densify by sintering at relatively low temperatures. 4,5 However, it is difficult to obtain nanostructured consolidated bulk ceramics using nanograined oxide powders as starting materials. 4 The processing conditions necessary for the consolidation of these oxide particles promote excessive grain coarsening, which leads to a deterioration of the property enhancements.…”

“…4,5 However, it is difficult to obtain nanostructured consolidated bulk ceramics using nanograined oxide powders as starting materials. 4 The processing conditions necessary for the consolidation of these oxide particles promote excessive grain coarsening, which leads to a deterioration of the property enhancements. One way to alleviate the grain growth problem during the consolidation of oxide powders is to incorporate a second oxide phase to form a composite ceramic system.…”