			Home About us Contact

Alumina Coatings (alumina + coating)

Distribution by Scientific Domains

Polymers and Materials Science	75%

Selected Abstracts

Deformation Mechanisms in Compression-Loaded, Stand-Alone Plasma-Sprayed Alumina Coatings

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2000
Rodney W. Trice
Cylindrical, stand-alone tubes of plasma-sprayed alumina were tested in compression in the axial direction at room temperature, using strain gauges to monitor axial and circumferential strains. The primary compression-loading profile used was cyclic loading, with monotonically increased peak stresses. Hysteresis was observed in the stress,strain response on unloading, beginning at a peak stress of 50 MPa. The modulus decreased as the maximum applied stress increased. The stress,strain response was only linear at low stresses; the degree of nonlinearity at high stresses scaled with the stress applied. One-hour dwells at constant stress at room temperature revealed a time-dependent strain response. Using transmission electron microscopy and acoustic emission to investigate deformation mechanisms, the stress,strain response was correlated with crack pop-in, growth, and arrest. It is proposed that the numerous defects in plasma-sprayed coatings, including porosity and microcracks, serve as sites for crack nucleation and/or propagation. As these small, nucleated cracks extend under the applied stress, they propagate nearly parallel to the loading direction along interlamellae boundaries. With increasing stress, these cracks ultimately link, resulting in catastrophic failure. [source]

Deposition of Compositionally Graded Mullite/Alumina Coatings from Mixtures of SiCl4, AlCl3, CO2 and H2,

CHEMICAL VAPOR DEPOSITION, Issue 2 2003
S.F. Nitodas
Abstract Using CVD, compositionally graded coatings of mullite (3,Al2O3·2,SiO2) and alumina (Al2O3) were deposited on Si-coated substrates from mixtures of silicon tetrachloride, aluminum trichloride, carbon dioxide, and hydrogen. The coatings were compositionally graded, with the Al/Si ratio increasing towards the outer layer of the coatings. The preparation of the coatings was carried out in a vertical, hot-wall CVD reactor. The results of previous experimental studies on the deposition of aluminosilicate species have been used to identify operating conditions where deposition of coatings with alumina content equal to, or greater than, that corresponding to stoichiometric mullite was possible. The scheme for the preparation of the graded mullite/alumina coatings was based on utilizing the positive effect of decreasing the residence time of the reactive mixture in the reactor, and of increasing the Al/Si ratio in the feed on the incorporation of Al2O3 in the deposit. [source]

Influence of contamination on resin bond strength to nano-structured alumina-coated zirconia ceramic

EUROPEAN JOURNAL OF ORAL SCIENCES, Issue 4 2010
Shanchuan Zhang
Zhang S, Kocjan A, Lehmann F, Kosma, T, Kern M. Influence of contamination on resin bond strength to nano-structured alumina-coated zirconia ceramic. Eur J Oral Sci 2010; 118: 396,403. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci The purpose of this study was to evaluate the influence of contamination and subsequent cleaning on the bond strength and durability of an adhesive resin to nano-structured alumina-coated zirconia ceramic. Zirconia ceramic disks were coated with nano-structured alumina, utilizing the hydrolysis of aluminum nitride powder. After immersion in saliva or the use of a silicone disclosing agent, specimens were cleaned with phosphoric acid etching or with tap water rinsing only. Uncontaminated specimens served as controls. Plexiglas tubes filled with composite resin were bonded with a phosphate monomer [10-methacryloxydecyl-dihydrogenphosphate (MDP)]-containing resin (Panavia 21). Subgroups of eight specimens each were stored in distilled water at 37°C, either for 3 d without thermal cycling (TC) or for 150 d with 37,500 thermal cycles from 5 to 55°C. The tensile bond strength (TBS) was determined using a universal testing machine at a crosshead speed of 2 mm min,1. The topography of the debonded surface was scrutinized for fractographic features, utilizing both optical and scanning electron microscopy. The TBS to uncontaminated nano-structured alumina-coated zirconia ceramic was durable, while contamination significantly reduced the TBS. Phosphoric acid cleaning was effective in removal of saliva contamination from the coated bonding surface but was not effective in removal of the silicone disclosing agent. Nano-structured alumina coating improves resin bonding to zirconia ceramic and eliminates the need for air-abrasion before bonding. [source]