The system beryllia-alumina-titania: phase relations and general physical properties of three-component porcelains

Abstract

.Th e da ta obtain ed in the in vestigation of t he phase equilibria in the systems ber~' llia a lumina, ber yllia-titania, and a lumina-titan ia suggest that the published equilibrium diagrams of these systems n eed to be revised : the system BeO-Ti02 shows no compounds, an eutectic at about 85 weight per cent of Ti02 and 1,670° ± 3° C, and an area of Ti02 solid-solu tion . The system BeO-A120 3 has three eu tectics: (1) at 1,890° ± 10° C a nd abo u t mole r atio 1BeO: 4Ah03 (94. 2% AI,03); (2) at 1,850° ± 10° C a nd abou t mol e ratio 2BcO : 3AI,03 (85.9% Ah03); and (3) at 1,835° ± 10° C and about 75 weight percen t of A1,03, an d t wo co ngru ently melt ing co mpounds, Be O.3 A1,03 (92.4% A1,03) at 1,9 10° ± 10° C and chr,vsobery l (B eO.-AI,03-80. 3% A1,03) at 1,870° ± 10° C. The system Al, 0 3-TiOz has two eutect ics: ( 1) at 1,705° ± 5° C and about 20 weight percen t of A1,03; a nd (2) at 1,840° ± 10 0 C and about mo le rat io 5AJ,03:4TiO, (6 1.5% AI,03), and a hig h-and low-temperat ure form (a lpha a nd beta) of aluminum t itanate (AIz03.TiOz-56. 1% AI,03); t he a lpha form is stable from t he alpha-beta inversion te mperat ure of 1,820° ± 10° C and melts co ngruently at 1,860° ± 10° C, and t he beta form seems to be stable for p eriods up to 100 hours from room temperature to abo ut 750° C and from abo u t 1,300° C to its inversion te mperature. The eq uilibria for t he system BeO-AL,03-Ti02 was found to contain four invarient points : (1) at 1,572° ± 5° C and abou t mole ratio ZBeO: 1A120 3: 2Ti02 (16.1% BeO, 32.7% A1,03, 51.2 % TiO,); (2) at 1,577° ± 5° C and abou t mole ratio 2BeO: l A1,03: 4Ti02 (10.6% Be O, 21.6 % A.120 3, 67.8% TiO,); (3) a t 1,580° ± 5° C and about mole ratio IBeO:lAI20 3 :1Ti02 (12.1% B eO, 49.3% A1,03 38.6 % TiO,); and (4) probabl y at abo ut 1,755° ± 10° C and abo ut mole mlio 2Beo': 5AI,03: 2Ti02 (7.0 % B eO, 79. 8% AI, 0 3, 22.2 % TiO,). No ternary co mpounds were foun d in t his system.The genera l physical propert ies of practically imper vious porcelai ns of t hi s syste m were found to be : maturing range, usua lly 1,525° to 1,575° C, bu t with some of t he higha lumina-con tain ing bodies maturing between 1,600° and 1,700° C ; apparent d ensity. 3.3 to 3.7 g/ cm3 ; shrinkage, 11 to 19 percent ; Toom-temperature co mpressive strength , 187,000 to 280000 Ib/in.2; room-te mpera t ure transverse strengt h, 13,700 t o 25,000 Ib/ in . 2 ; Young's modulus at room temperature, 42,000,000 to 47,000,000 Ib/in .2; tran sverse strength a t 1,800° F (982° C), 10,500 to 17,000 Ib/ in.2; approximate Young's modulus at 1,800° F , 22,000,000 to 41 ,000,000 Ib/ in.2; relative the rmal-shock Tesistance, pOol' ; and the lin ear t her mal expansion of a few selected bodies, in t he range 25° to 950° C, usua lly was regular and ranged from 0 .81 to 0. 89 per cent.

Morphology Control of Pseudobrookite-Type MgTi₂O₅ Powders by LiF Doping

“…Among the pseudobrookite-type ceramics, aluminum titanate, Al 2 TiO 5 , is applied for next-generation diesel particulate filters (DPF) and so on due to its low bulk thermal expansion [2]. However, Al 2 TiO 5 is thermodynamically metastable under 1200 °C and it gradually decomposes into Al 2 O 3 and TiO 2 [3][4][5]. Furthermore, due to the strong anisotropy of thermal expansion, Al 2 TiO 5 ceramics have poor mechanical properties caused by microcrack formation.…”

Thermal Sprayed Nanostructured Hard Coatings

“…At 1000°C, the first such intermediate phase to appear has an unknown structure, with no known structural analogue. At 1200 °C, a tetragonal phase appears, which is similar to the (Ta, Ti)AI 2 0 6 crystal structure described in Powder Diffraction File #32-0028 [15]. This phase is also metastable, and further decomposes at 1400 °C into the equilibrium two-phase structure, consisting of …”

Reactive Sintering of Aluminum Titanate

“…This phenomenon has been confirmed by subsequent research (Fonseca & Baptista 2003). Lang et al, (1952) concluded that opposing formation and decomposition processes occurred in dynamic equilibrium, promoting decomposition at a certain temperature range, i.e. the β-Al 2 TiO 5 phase is stable above 1300°C, below this temperature aluminum titanate undergoes an eutectoid transformation according to the reaction:…”

“…Density (g/cm 3 ) 3.702 Holcombe (1973) Thermal Expansion Coefficient Average (x10 -6 ºC -1 ) α a20-520 -α a20-1000 α b20-520 -α b20-1000 α c20-520 -α c20-1000 -2.9 --3 10.3 -11.8 20.1 -21.8 Wohlfromm (1990) Milosevski (1997) Hardness, Hv (GPa) 5 Wohlfromm (1990) Bending Strenght, σ (MPa) 4 -20 25 -40 Milosevski (1995) Thermal shock resistance (Wm -1 ) 500 Stingl (1986) Thermal Conductivity, k(W/mK) 1.5 -2.5 Stingl (1986) Milosevski (1997 Lang et al (1952) studied the Al 2 O 3 -TiO 2 equilibrium diagram ( Fig. 1) Lang (1952).…”