Alkaline Earth Effects on the Reaction of Sodium with Aluminum Oxide

Abstract

The growth of beta alumina in high pressure sodium lamps is often associated with the presence of alkaline earths, such as calcium and magnesium.Studies of the reaction kinetics and phase equilibria in these systems indicate that while the thermodynamic stabilization of beta alumina by magnesium may be important in some instances, the primary effect of these alkaline earths is to aid in the nucleation of beta alumina.

Translucent Polycrystalline Alumina with Improved Resistance to Sodium Attack

“…9 The "spinel block" refers to the closed-packed oxygen layers and aluminum ions in ␤-Al 2 O 3 . These "blocks" are similar in structure to MgAl 2 O 4 spinel if we consider the magnesium and aluminum in the spinel are equivalent.…”

“…It is thus argued that spinel accelerates sodium attack in PCA. 9 As has been discussed in Section III(6)(A), spinel reacts with sodium plus Al 2 O 3 to form ␤ٞ-Al 2 O 3 : 6Na ϩ 12MgAl 2 O 4 ϩ 34Al 2 O 3 3 3͑Na 2 O⅐4MgO⅐15Al 2 O 3 ͒ ϩ 2Al (2) Usually there are many spinel particles in as-sintered MgO-doped PCA, 13 although in some cases there are few to none. The distribution of the spinel in PCA depends on the MgO level of the starting powder as well as the sintering temperature, time, atmosphere, and gas flow rate.…”

“…The spinel phase in PCA provides ideal sites for nucleation of ␤-Al 2 O 3 , because of the similarity of the spinel crystal structure and the structure of the "spinel blocks" in ␤-Al 2 O 3 . 9 The "spinel block" refers to the closed-packed oxygen layers and aluminum ions in ␤-Al 2 O 3 . These "blocks" are similar in structure to MgAl 2 O 4 spinel if we consider the magnesium and aluminum in the spinel are equivalent.…”

Experimental Establishment of the CaAl2O4–MgO and CaAl4O7–MgO Isoplethal Sections within the Al2O3–MgO–CaO Ternary System

“…Making use of the thermodynamic information provided by this system, different kind of materials can be designed. Besides materials for nuclear waste storage 4 or catalysis applications, 5 there are a wide range of refractory materials that can be developed. Some outstanding examples are: synthetic slags for secondary steel refining, 6 different types of new refractory cements, as spinel‐containing cements, 7 and improved refractory concretes 8,9 .…”