The oxidative transformation of solid, barium-metal-bearing precursors into monolithic celsian with a retention of shape, dimensions, and relative density

Abstract

precursors into monolithic, monoclinic celsian has been examined. The relative amounts of metal and oxide in each type of precursor were adjusted so that the overall stoichiometry and molar volume were similar to those of the desired product, celsian. Metal 1 oxide mixtures were mechanically alloyed and then uniaxially pressed to yield 84-92% dense precursor disks. The precursors were converted into celsian by exposure to a series of heat treatments from 300-1500 ± C in oxygen-bearing gases. Differences and similarities in the phase evolution of the various precursors are discussed. Celsian disks were produced that retained the precursor shape, dimensions, and relative (% theoretical) density. et al.: The oxidative transformation of solid, barium-metal-bearing precursors into monolithic celsian

Synthesis of Celsian (BaAl2Si2O8) from Solid Ba‐Al‐Al2O3‐SiO2 Precursors: I, XRD and SEM/EDX Analyses of Phase Evolution

“…Prior work has revealed that, with proper adjustment of phase content, alkaline-earth-metal-bearing precursors can be transformed to ceramic bodies that retain the precursor shape. 19,71,87 Finally, to be able to compact and form the precursor to a shaped green body, the precursor should contain an appreciable amount of ductile metal. The amount of ductile metal (Ba + Al) in a Ba-Al-Al 2 O 3 -SiO 2 precursor with x ‫ס‬ 0.84 (i.e., Al:Al 2 O 3 ‫ס‬ 10.5) is ∼49.7 vol%.…”

“…A precursor with a Ba:Al:Al 2 O 3 :SiO 2 molar ratio of 1.0:1.68:0.16:2.0 has been transformed to monoclinic celsian with dimensional changes <0.5%. 87 The phase evolution during transformation of such a Ba-Al-Al 2 O 3 -SiO 2 precursor is the subject of the present paper.…”

Tailor-made ceramic-based components—Advantages by reactive processing and advanced shaping techniques

“…[47][48][49][50][51][52] The resulting materials can be spinel (MgAl 2 O 4 ), strontium-doped celsian ((Ba,Sr)Si 2 O 8 , hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ), or others. 47,48 The process uses the shrinkage occurring during oxidation of most alkaline-earth metals to compensate for the expansion associated with other reactions, such as aluminum oxidation, spinel or celsian formation, hence dimensional changes are very small.…”

“…47,48 The process uses the shrinkage occurring during oxidation of most alkaline-earth metals to compensate for the expansion associated with other reactions, such as aluminum oxidation, spinel or celsian formation, hence dimensional changes are very small. 49,50 . Due to the content of a soft, malleable metal, the precursor compacts can be green-machined using conventional equipment.…”

Reactive Hot Pressing of Alumina‐Molybdenum Disilicide Composites

“…Several of these methods are listed in Table I. [5][6][7][8][9][10][11][12][13][14][15] The advantages of reactive processing include significantly lower processing temperatures and improved purity of final products. Moreover, reactive processes often produce desirable interpenetrating microstructures.…”