Yttria Hydroxy‐Salt Binders

Binder phase (primarily chloride or nitrate) formation was examined in YX 3 ‐NaOH‐H 2 O, Y 2 O 3 ‐acid‐H 2 O, and Y 2 O 3 ‐salt‐H 2 ‐O systems. The cementitious phase consisted mostly of plate‐ (or needle‐) shaped hydroxy salts of the general formula Y 2 (OH) 6‐m X m n H 2 O, where m and n normally equal one. These binders were examined by X‐ray diffraction and thermal analysis techniques. Nitrate binders decompose to Y 2 O 3 by 600°C, whereas chloride binders form oxychlorides that sublime or convert to Y 2 O 3 after oxygen replacement of chlorine (in air) at >1000°C. Although nitric and hydrochloric acid solutions form porous (< 50% dense) plasterlike bodies in 2 to 10 min of reaction with Y 2 O 3 powder, salt solutions (i.e. NH 4 NO 3 Mg(NO 3 ) 2 , NH 4 Cl, and YCl 3 ‐ ∼6H 2 O) slow the reaction considerably (48 h to 4 weeks), allowing 70‐ to 80%‐dense cements to form. The effects of formation conditions on physical properties of binders were studied. Examination of scandium and lanthanide oxides showed that several behave in the same way as yttria.