Calcium phosphate ceramics have high potential in use as bio-substituent materials such as artificial bones or dental crowns [l] because their chemical composition is close to that of hard human tissues. We have developed a new calcium phosphate glass-ceramic [2] by unidirectional crystallization and have reported in detail the preparation procedures and some mechanical properties [3]. This glass-ceramic has a composite structure. Numerous fl-Ca(PO3) 2 crystalline fibres with ~ 1 #m diameter are aligned along a direction, forming a fibre bundle as a whole. Ultraphosphate glass and crystals such as 2CaO • 3P205 lie as matrix phases between the crystalline fibres. This composite structure gives the glass-ceramic unique mechanical properties [2]: the bending strength (a) is extremely high (up to 500 to 7 0 0 M N m -2) and the Young's modulus (E) is relatively low (~ 85 GN m -2 average). Furthermore, it shows stable fracture, i.e. fracture proceeds step by step, not catastrophically, even beyond o .... which is entirely different from that for conventional sintered ceramics or glass-ceramics. It is, therefore, essential for controlling the mechanical properties of this glass-ceramic to control the orientation degree of the crystalline fibres of fl-Ca (PO3) 2.In this letter, the effect of crystallization temperature and a third additive component is reported on the degree of orientation for unidirectionally crystallized (UDC) glass-ceramic.First, the relation is clarified between the growing axis of the fibre and crystallographic axes of fl-Ca (PO3)2 (monoclinic, a = 1.699nm, b = 0.7710nm, c = 0.6994nm, fl = 90.34 [4]). The X-ray rotation camera method was applied. The specimen employed was a bundle (~0 . 1 m m diameter) of fl-Ca(PO3) 2 fibre which was taken out of the U D C glass-ceramic, having almost complete orientation because its image was extinguished simultaneously at a certain position under polarized microscopic observation. The photograph of the rotation around the fibre axis shows the presence of a 0.70 nm period along the axis. This value agrees well with that of the crystallographic c-axis (0.6994 nm) of fl-Ca(PO3)> It is, therefore, concluded that the growing axis of the fibre is parallel to that of the c-axis of fl-Ca(PO3)2. The previous suggestion [2] concerning orientation that all fibrous elements do n o t grow in a specific crystallographic direction must be corrected according to the present results. Although no detailed atomic arrangement of fl-Ca(PO3)2 has been reported, it is obvious that its skeletal structure is composed of a long chain, not a ring, of condensed phosphate [5]. Maries and Rogers [6] reported that fl-CaSiO3 (wollastonite) crystalline fibres produced unidirectionally from the melt grow along the direction of the crystallographic b-axis, which corresponds to the chain direction of the (SiO4) 3 tetrahedra. From the analogy of skeletal topology, a similar orientation relation is suggested for fl-Ca(PO3) 2 fibres in the direction of the axis between the fibre and the condensed phos...
The large negative temperature coefficient of resonant frequency ( τ f ) of Al2O3 is a problem for applicable microwave/millimeter wave dielectrics. A Previous study reported that the τ f was improved by sintering with TiO2 and then annealing, where the annealing decompose the secondary phase of Al2TiO5. This study investigated the hold time of annealing. The Quality factor (Qf ) value decreased when the sample was annealed at 1100°C for 2hrs. While Al2TiO5 was not detected by X-ray powder diffraction, it was located around TiO2 by scanning transmission electron microscopy equipped with energy dispersive X-ray spectroscopy. It should be considered that the degradation of the Qf was caused by the existence of noncrystalline Al2TiO5 and new boundaries between noncrystalline Al2TiO5 and TiO2.
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