Transparent ceramic lamp envelope materials

Abstract

Transparent ceramic materials with optical qualities comparable to single crystals of similar compositions have been developed in recent years, as a result of the improved understanding of powder-processing-fabrication- sintering-property inter-relationships. These high-temperature materials with a range of thermal and mechanical properties are candidate envelopes for focused-beam, short-arc lamps containing various fills operating at temperatures higher than quartz. This paper reviews the composition, structure and properties of transparent ceramic lamp envelope materials including sapphire, small-grained polycrystalline alumina, aluminium oxynitride, yttrium aluminate garnet, magnesium aluminate spinel and yttria–lanthana. A satisfactory thermal shock resistance is required for the ceramic tube to withstand the rapid heating and cooling cycles encountered in lamps. Thermophysical properties, along with the geometry, size and thickness of a transparent ceramic tube, are important parameters in the assessment of its resistance to fracture arising from thermal stresses in lamps during service. The corrosive nature of lamp-fill liquid and vapour at high temperatures requires that all lamp components be carefully chosen to meet the target life. The wide range of new transparent ceramics represents flexibility in pushing the limit of envelope materials for improved beamer lamps.

Transparent ZnAl₂O₄ ceramics fabricated by spark plasma sintering

“…For the wavelengths of >5¯m, the transmission is slightly higher than that of MgAl 2 O 4 spinel. 19) The absorption peak at 4.27¯m is attributed to CO 2 . 20) We consider that the carbon diffused into the ZA from both carbon paper and mold during SPS reacted with oxygen during annealing in air, to form CO 2 gases.…”

Transparent polycrystalline alumina using spark plasma sintering: Effect of Mg, Y and La doping

“…Over recent years, attempts have been made to replace sapphire by transparent polycrystalline alumina (PCA) [1][2][3][4][5][6] for both economic and ecological reasons.…”

Freeze granulation: Powder processing for transparent alumina applications

“…3 In recent years, many advances have been made in production of transparent ceramics by various processing and sintering strategies. 1,[6][7][8][9][10][11][12][13][14] Mainstream ceramic processing techniques rely either on dry 11,14,15 or wet powder processing [1,6,9,13,16]-both allowing production of highly dense green bodies (GBs), one key factor for transparent ceramics-as well as on classic sintering followed by hot isostatic pressing (post-HIP) or novel fast sintering techniques. Among the latter, the most popular for transparent ceramics is pulsed electric current sintering (PECS), also known as spark plasma sintering (SPS).…”