Water vapour corrosion resistance of five rare earth monosilicates Y 2 SiO 5 , Gd 2 SiO 5 , Er 2 SiO 5 , Yb 2 SiO 5 , and Lu 2 SiO 5 was investigated during testing at 1350 ˚C for up to 166 h in static air with 90% water vapour. Four of the RE-silicates showed little weight gain (0.859 mg cm -2 ) after 166 h of exposure. Prior to testing the microstrucre consists of equiaxed grains of 4-7 ± 0.4 µm. XRD analysis showed that after 50 h exposure to water vapour corrosion Y, Er, Yb and Lu-silicates had both mono and disilicates present on their surfaces as a result of the reaction between monosilicate and water vapour to form disilicate, while Gd-silicate has converted completely to G 4.67 Si 3 O 13 making it less stable for environmental barrier coatings application. The microstructures of corroded Y, Er, Yb and Lu-silicates contain ridges and cracks, while that of Gd-silicate contains rounded grains suggesting melting along with striped contract grains.Keywords: Rare earth monosilicates, environmental barrier coating, water vapour resistance. IntroductionSilicon carbide fibre-reinforced ceramic matrix composites (CMCs) possess high temperature (Abcr, Germany, 4 ± 0.2 µm particle size) and SiO 2 (Abcr, Germany, 4 ± 0.1 µm particle size). All RE-oxides powders were 99.9% pure, while the SiO 2 powder was 99.0% pure.Particle size measurements were conducted using Malvern hydro equipment (2000SM, UK) and the average value was obtained based on three measurements for each powder. The exact weight per gram of each powder was homogeneously mixed in a ball mill using silicon carbide media (Union process, USA, 5 mm diameter) in ethanol for 24 h. The slurries were dried for 24h at 110 ˚C. 13 mm diameter and 3 mm thick pellets were obtained using uniaxial cold pressing (50 MPa) at room temperature. Y, Gd, Yb and Lu monosilicates were sintered for 3 hours at 1580˚C at a heating rate of 10˚C min -1 in a box furnace in air. However, to produce Er 2 SiO 5 , 12h sintering was necessary to obtain dense samples [18].Water vapour corrosion tests were conducted at 1350 ˚C for 50, 100 and 166 h in 90% water:10% air ratio with flow rate of 40 ml/min in an alumina tube (50 mm diameter and 1200 mm length) furnace ((Lenton, Hope, UK) at a heating and cooling rate of 10 ˚C min -1 and 20 ˚C min -1 respectively. Sample dimensions were 10 mm diameter and 3 mm thick. Samples were placed on high purity alumina boats (Almath crucibles, Newmarket, UK) and their weight was recorded before and after the corrosion tests with an accuracy of ± 0.001 g to determine the weight change. To exclude the water vapour corrosion taking place at low temperature, the water vapour was introduced when the temperature reached 1350 ˚C and the flow was stopped after the desired testing period.Phases were identified by XRD (Bruker D2 Phaser, Germany) on sample's surface which was not in contact with the alumina boat during corrosion test using CuKα radiation with spectra recorded from 10-70˚. Crystalline phases were determined using Xpert High Score Plus softwa...

Microstructural evolution on sintering of porcelain powder compacts using microwave radiation was compared with that in conventionally sintered samples. Using microwaves sintering temperature was reduced by ~ 75 °C and dwell time from 15 min to 5 min while retaining comparable physical properties i.e. apparent bulk density, water absorption to conventionally sintered porcelain. Porcelain powder absorbed microwave energy above 600 °C due to a rapid increase in its loss tangent. Mullite and glass were used as indicators of the microwave effect: mullite produced using microwaves had a nanofibre morphology with high aspect ratio (~32±3:1) believed associated with a vapour-liquid-solid (VLS) formation mechanism not previously reported. Microwaves also produced mullite with different chemistry having ~63 mol% alumina content compared to ~60 mol% alumina in conventional sintered porcelain. This was likely due to accelerated Al +3 diffusion in mullite under microwave radiation. Liquid glass was observed to form at relatively low temperature (~900-1000°C) using microwaves when compared to conventional sintering which promoted the porcelains ability to absorb them.

The effect of the spark plasma sintering (SPS) process on mullite formation in porcelains was studied using X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. SPS affected the kinetics and morphology of formed mullite. After sintering at 1100°C, unlike conventional sintering, SPS promoted the formation of mullite due to the combination of vacuum and applied pressure. Mullite crystal growth was altered by the atmosphere (vacuum), dwell time (0‐15 minutes), and temperature (1000‐1200°C). The applied pressure caused the mullite needles to orient perpendicular to the direction of the applied load. Depending on SPS dwell time, the mullite formed after sintering at 1100°C also had different crystal structure (tetragonal for short dwell time of 0‐5 minutes and orthorhombic for a long dwell time of 10‐15 minutes). Dissolution of mullite was observed at 1100°C by extending the dwell time by up to 15 minutes and the dissolved mullite reprecipitated on the small needles (~40 nm) and coarsened via Oswald ripening resulting in larger mullite needles (~60 nm).

27Porcelain powder was consolidated using spark plasma sintering (SPS) at a constant 28 heating rate of 100°C/min to peak temperatures ranging from 1000-1200°C and was Vickers hardness from 2-4 to 6-7 GPa, and improved fracture toughness from 2

No abstract

No abstract

High emissivity coatings which aim to help the cement industry reduce heat loss in its production process have been developed with different CeO 2 and AlH 6 O 12 P 3 ratios (1:3, 1:5, and 1:12 by volume). The coating slurries were shear thinning and after heat treatment in air at 1300°C, 1°C/min, dwell 3 hours, XRD revealed that CePO 4 forms more easily as the Ce/P ratio decreases. The composition with a 1:5 ratio of CeO 2 :AlH 6 O 12 P 3 was gun sprayed on basic refractory bricks, then heat treated under the same conditions as the slurries. SEM, (S)TEM and EDX were used to study thickness, microstructure, and chemical composition of the coatings which revealed that the coating was composed of pores, CeO 2 grains, CePO 4 grains, and M-P-O glass. SEM images show that CePO 4 was nucleated from a reaction between CeO 2 and AlH 6 O 12 P 3 . Consequently, CePO 4 grains (~2 µm diameter) were smaller than CeO 2 (~10 µm diameter). The emissivities of un-coated and coated basic refractory bricks were measured at 1100 and 1300°C over the wave number range of 700-12 000 cm −1 . At both temperatures, the emissivity of the coated bricks was higher than the uncoated bricks and the emissivity was measured to be higher at a higher temperature for both samples. The coated bricks gave the highest emissivity of 0.81 from 1050 to 11 000 cm −1 which is about twice the un-coated bricks for the same conditions. This demonstrates that the developed high emissivity coating has potential to be used with basic refractory brick. K E Y W O R D Scements, cerium/cerium compounds, coatings, refractories How to cite this article: Juthapakdeeprasert J, Gavalda Diaz O, Lerdprom W, De Sousa Meneses D, Jayaseelan DD, Lee WE. Reactions and emissivity of cerium oxide with phosphate binder coating on basic refractory brick. Int J Appl Ceram Technol.

No abstract