Deposition Of Alumina Research Articles

Influence of Spray Angle on the Pore and Crack Microstructure of Plasma‐Sprayed Deposits

To understand the influence of processing parameters on the microstructure of plasma‐sprayed deposits, smallangle neutron scattering measurements were made of the processing‐parameter‐dependent specific surface area of the voids in gray alumina deposits. These studies indicate that the voids are in the form of pores between the splats and around inclusions or unmelted particles, and are also in the form of cracks within the splats which may develop during cooling. The porous volume increases as the angle between the spray gun and the substrate (the “spray angle”) decreases. This study also indicates that the cracks are preferentially oriented, and that the crack orientation also depends on the spray angle. The interlamellar pores, however, are preferentially oriented parallel to the substrate surface, and the orientation of the pore is independent of the spray angle.

Electrophoretic deposition of aqueous alumina slips

Electrophoretic deposition (EPD) of aqueous alumina slips on a graphite electrode is studied. The suspension is characterized in terms of viscosity, zeta potential and conductivity. The conductivity has proved to be a determining parameter for obtaining deposits. Well-dispersed slips having an adequate value of conductivity are used for constant current density experiments. Current densities of 1.6 to 12.8 mA cm −2 are applied for 10 min. After defining the optimal slip properties for the deposition, both the process development and the final properties of the materials obtained depend on the current/time relationship. Alumina deposits obtained at different current densities are characterized. The best conditions for obtaining uniform and dense coatings are 6.4 mA cm −2 for up to 10 min. The applied current allows not only to modify the properties and microstructure of the deposit, but also to increase the margin of slip conductivity assuring the success of the EPD process, that is, the working conditions.

Preparation of MFI-Type Zeolite Membranes and Their Use in Separating n-Butane and i-Butane.

MFI-type zeolite membranes were synthesized by hydrothermal reaction on the surface of porous α-alumina support tubes with different pore sizes. The zeolite membranes consisted of three zones: The top zone was a polycrystalline zeolite layer and the inner zone was a layer of α-alumina macropores, partially filled with deposits. The intermediate zone was a mixture of alumina particles and deposits. The morphology of the zeolite membranes was dependent on the substrates. The permeance of zeolite membranes formed on the substrate possessing pores of 150–170 nm under identical conditions ranged over two orders of magnitude. There was no definite relationship between n-butane/i-butane (n-C4H10/i-C4H10) permselectivity and permeance, although permeance was affected by the substrates. The n-C4H10/i-C4H10 permselectivity calculated from single-component permeances was in the range of 1.5~12 at 100°C, and the activation energy for the permeances was 11 kJ·mol-1. The selectivity increased in the case of n-C14H10 separation from a mixture containing a small amount of i-C4H10. The zeolite membranes thus served as molecular-sieving for C4 isomers.

The deposition of hard crystalline Al 2O 3 layers by means of bipolar pulsed magnetron sputtering

Crystalline Al 2O 3 layers with hardness values up to those of pure corundum (22 GPa) were produced by reactive pulsed magnetron sputtering of aluminum. Used for the purpose was a dual magnetron system with a bipolar pulsed square-wave power supply in the MF range. Via a variation of pulse parameters it was possible to exert an influence on the plasma density and therefore on the layer properties obtained. It is shown that the pulsed power supply substantially reduces the temperature needed for the deposition of crystalline alumina, i.e., especially of α-Al 2O 3. Irrespective of the chosen working point, the coating process can be performed in a stable long-term manner without the occurrence of hysteresis effects. Both plant and process are upscaled to the conditions of industrial application with respect to productivity and three-dimensional substrates. In addition, an adhesion-improving sublayer of another material can be applied; e.g., (Ti,Al)N, etc. Hence, facility is provided to coat not only hard metal components (e.g., cemented carbide inserts) with a hard layer of alumina but also temperature-sensitive materials such as tool steel.

Morphology and gas permeance of ZSM-5-type zeolite membrane formed on a porous α-alumina support tube

ZSM-5-type zeolite membranes were synthesized by hydrothermal reaction on the surface of a porous α-alumina support tube of 2.8 mm o.d. and 1.9 mm i.d. The average pore size of the tube was about 150 nm and the void fraction was 0.45. The silicon source was a fine silica powder and the template was a mixture of tetrapropylammoniumhydroxide and bromide. Three zones were observed in the film formed on the support tube. The top zone was a polycrystalline zeolite layer and the inner zone was a layer of α-alumina macropores partially filled with deposits. The intermediate zone was a mixture of alumina particles and deposits. The permeance of the zeolite membranes increased with decreasing thickness of zeolite layer, but permselectivity was not connected with membrane morphology. The permselectivity of n-butane to i-butane was 10–50 in the range of 30–100°C, which showed practical molecular sieving ability of the formed membranes.

Deposition of alumina by pyrolysis of aluminium acetylacetonate in argon: M. Danzinger et al. (Technical University of Vienna, Vienna, Austria). Int. J. Refractory Metals Hard Mater., vol 14, no 1/3, 1995, 59–67

Deposition of alumina by pyrolysis of aluminium acetylacetonate in argon: M. Danzinger et al. (Technical University of Vienna, Vienna, Austria). Int. J. Refractory Metals Hard Mater., vol 14, no 1/3, 1995, 59–67

Effect of addition of aluminium acetylacetonate on chemical vapour deposition of alumina: M. Danzinger et al. (Technical University of Vienna, Vienna, Austria). Int. J. Refractory Metals Hard Mater., vol 14, no 1/3, 1995, 69–77

Effect of addition of aluminium acetylacetonate on chemical vapour deposition of alumina: M. Danzinger et al. (Technical University of Vienna, Vienna, Austria). Int. J. Refractory Metals Hard Mater., vol 14, no 1/3, 1995, 69–77

Ion beam mixing at copper/alumina interfaces using marker geometry

In the present paper results on ion beam effects such as ion beam mixing, radiation enhanced diffusion (RED) and phase stability in Cu Al 2O 3 marker interfaces are presented. Cu/Al 2O 3/Cu samples with marker geometry were prepared by vapor deposition of copper and alumina on polished glassy carbon and single crystal silicon substrates. The top Cu layer had a thickness of 70 nm and the marker thickness was 2.5 nm. In case of the Al 2O 3/Cu/Al 2O 3 samples a 2.5 nm Cu marker followed by an amorphous alumina layer with a thickness of 110 nm and a density of 2.9 g/cm 3 were deposited on single crystal alumina substrates. The marker samples were irradiated with 150 keV Ar + ions. Ion doses were in the range of 1.1 × 10 16 to 5.4 × 10 16 Ar +/cm 2. The sample temperature was varied between room temperature and 673 K. The mixing of the marker layers with the matrix was analyzed by depth profiling using Rutherford backscattering spectroscopy (RBS). Additionally, in case of the alumina marker system, to measure the aluminium depth distribution, nuclear reaction analysis (NRA) was applied using the 27Al(p, γ) 28Si reaction with a resonance energy of 992 keV. Film stability was checked by scanning electron microscopy (SEM)

Surface modification of chemically vapor deposited diamond for producing adherent thick and thin film metallizations for electronic packaging

In order to make chemically vapor deposited diamond (CVDD) substrates amenable to surface metallization without significant reduction in thermal conductivity, very thin alumina films were grown on diamond by vapor deposition of Al in oxygen atmosphere, followed by very low-temperature annealing in oxygen. A Cr interlayer initially deposited on CVDD prior to alumina deposition was found to lead to excellent adhesion between the substrate and the deposit. The alumina films were characterized by scanning and transmission electron microscopy as well as Auger electron spectroscopy.

Study of Al 2O 3 condensation on Si(100) and InP(100) substrates

AES (Auger electron spectroscopy) and EELS (electron energy loss spectroscopy) have been used to study the first stages of the Al 2 O 3 Si and Al 2 O 3 InP interfaces formations. Alumina was condensed using an evaporation cell heated by an electronic bombardment. InP is one of the most promising materials for applications in high speed and optoelectronic devices, but surface and interface properties have an important influence on the performance of components. This paper is divided in two parts: (1) Test of alumina deposition on Si(100) substrates and comparison with published results. (2) Condensation on InP(100) substrates (cleaned with a Ar + bombardment)

Conversion coating on stainless steel as a support for electrochemically induced alumina deposit

Conversion coatings on stainless steel were used as a support for alumina coatings deposited by electrolytic treatment from an aqueous solution of aluminium sulphate. The conductive conversion coating with its particular morphology facilitates the reduction reactions responsible for the increase of the pH at the surface and acts as a porous electrode allowing favourable local pH conditions for aluminium oxyhydroxide deposition. The effects of potential, current density, time, temperature and stirring on coating weight were studied.

Characterization and adhesion study of thin alumina coatings sputtered on PET

Thin amorphous alumina coatings have been deposited on polyethylene terephthalate (PET) by rf magnetron sputtering in a pure argon plasma. Their microstructure, composition, stresses and adhesion to the PET films have been studied. SEM microstructure study showed a good agreement with Thornton's structure zone model, i.e. a progression from a dense structure to a columnar structure was observed as the pressure was increased. The composition of deposits, determined by RBS, showed that oxygen-rich alumina was obtained when high plasma pressures (more than 1 Pa) were used. FTIR spectra of alumina indicate that the excess oxygen was essentially due to the presence of hydroxyl groups in the coatings. The stress evolution in alumina deposits, determined by the bending beam method, was correlated with the microstructural change. Adhesion of alumina on PET has been studied by a peel test. Best results were obtained when sputtering parameters combined moderate power (1 W cm −2) and pressure of about 1 Pa. XPS analysis of the alumina PET interface showed that bonding between the ceramic and the polymer occurred primarily via Al-O-C bonds.

The influence of the nucleation surface on the growth of CVD α-Al 2O 3 and κ-Al 2O 3

In this work, in order to increase the understanding of the nucleation and growth of CVD alumina, three different types of specimen have been investigated by cross-section TEM. The alumina layers were deposited onto Ti(C,N) (i) with and (ii) without an intermediate α-bonding layer, and (iii) onto an intermediate Ti 2O 3 layer. It was found that pure κ-Al 2O 3 was obtained on the Ti(C,N) layer, while pure α-Al 2O 3 was obtained on the α-bonding and Ti 2O 3 layers. As the process parameters of the alumina deposition were the same in all cases, this demonstrates that the resulting alumina polymorph is governed by its nucleation on the intermediate layers. Pores could frequently be observed at the Ti(C,N)-Ti 2O 3 layer interfaces, while no pores could be detected at the Ti 2O 3- α-Al 2O 3, Ti(C,N)- α-Al 2O 3 or α-bonding- α-Al 2O 3 interfaces. No orientation relationships between the grains in the α- bonding and the α-Al 2O 3 layer could be found, while epitaxial growths of κ-Al 2O 3 on Ti(C,N) and α-Al 2O 3 on Ti 2O 3 were frequently observed and are described as: [Display omitted] Both orientation relationships describe close-packed planes growing on close-packed planes, with close-packed directions being parallel.

Properties of alumina films prepared by metal-organic chemical vapour deposition at atmospheric pressure in the presence of small amounts of water

Thin alumina films were deposited on stainless steel, type AISI 304. The deposition process was carried out in nitrogen with low partial pressures of water (0–2.6 × 10 −2 kPa (0−0.20 mmHg)) by metal-organic chemical vapour deposition (MOCVD) with aluminium-tri- sec-butoxide (ATSB) as the precursor. Also results are presented regarding the alumina deposition in the presence of small amounts of 2-butanol. The film properties, including the protection of the underlying substrate against aggressive gas compounds such as sulphur at high temperatures, the chemical composition, the microstructure, and the refractive index were investigated as a function of the water vapour pressure. In contrast with the results of stress reduction in silica films by the addition of small amounts of water to the deposition process, no significant effect on the internal stress in alumina films was found. TEM analysis showed that extremely fine grains of γ- Al 2O 3 AlO(OH) were formed, in agreement with the refractive index. Only an increase of the OH groups was found if water was added to the process, which also was the only impurity in the oxide film. Carbon was not detected.

Can Thermal Barrier Coatings be Sealed by Metal-Organic Chemical Vapour Deposition of Silica and Alumina?

Thin Al 2 0 3 and SiO 2 films were deposited on thermal barrier coatings (TBC) by means of metal-organic chemical vapour deposition (MOCVD). The thermal barrier coatings consist of ZrC 2 , partially stabilised by MgO (Magnesium Zirconate Amdry 333) and a bond coat of NiAl (Amdry 956). Alumina films were deposited at low temperatures by low pressure MOCVD, carried out in nitrogen gas using aluminium-tri-sec-butoxide (ATSB) as the precursor. Silica films were deposited on the thermal barrier coatings by atmospheric pressure MOCVD with di-acetoxy-di-t-butoxy-silane (DADBS) as the precursor. Besides the deposition of thin oxide films on TBC, pre-oxidation experiments were performed at 600, 800 and 1000°C for 175 h. In order to evaluate the effectiveness of sealing and pre-oxidation, sulphidation experiments were carried out at 600°C for 200 h. Low pressure deposited alumina films did not show any increased protective power. Pre-oxidation of the TBC to form a dense and continuous alumina layer on the top of the bond coat also did not show any significant improvement of the protection against sulphide containing gases.

Quenching stress in plasma sprayed coatings and its correlation with the deposit microstructure

Quenching stress arises within a thermally sprayed splat as its thermal contraction after solidification is constrained by the underlying solid. Dependence of the quenching stress in plasma-sprayed deposits of Ni-20Cr alloy and alumina on the substrate temperature during spraying was discussed in conjunction with the change in the nature of the interlamellar contact between splats. It was found by mercury intrusion porosimetry and observation of cross sections of impregnated deposits that the interlamellar contact is improved significantly by raising the substrate temperature during deposition from 200 to 600 °C. The positive dependence of the quenching stress on the substrate temperature in this temperature range was attributed to a stronger constraint against thermal contraction of sprayed splats after solidification due to the improved contact.

Ion beam deposition of alumina for recording head applications

In this work, aluminum oxide films were prepared by Ion Beam Deposition (IBD) in a dual-gun system. Films prepared from alumina target at high deposition beam parameters and low assist parameters resulted in lower compressive stress and better etch resistance than sputtered alumina films. Excellent thickness uniformity and topological step coverage were also achieved. Nano-crystalline alumina films with superior etch resistance were grown by reactive sputtering from an aluminum target at low deposition rate. Appropriate balance between the deposition beam and assist beam was important in order to get such high etch resistance. Discussions of both IBD and sputtering methods, the effect of beam parameters on the alumina properties, and structural analysis were presented in this paper.

Preparation and ESCA analysis of the germanium surface: electrical characterization of the [formula omitted] and [formula omitted] structures

The preparation of the (100) structure of germanium is a crucial step in the realization of electronic components. Chemical and thermal treatments were used in order to obtain samples with reproducible physical properties. Thin films of GeO x were obtained by thermal oxidation. Surface analysis was performed using electron spectroscopy for chemical analysis (ESCA). Results show the growth of oxide film (thickness 30 Å) with a GeO 2-like composition. It is also possible to remove the native germanium oxide with a chemically controlled process. In addition, two kinds of structures, Al 2O 3 Ge and Al 2O 2:GeO 2 Ge , were prepared and characterized electrically. It was found that the germanium oxide layer can protect the surface during the deposition of alumina using an electron gun evaporation set. In this case, the density of defects was greatly reduced.

Alumina coatings on PMMA: optimization of adherence

Alumina is deposited on polymethyl methacrylate (PMMA) using the RF magnetron sputtering method. The adhesion is characterized by means of a 180° peeling test and a fragmentation test. The surface energy of the materials is determined by measuring the contact angles using the two liquids method. The plasma surface treatment of the polymer help to smooth it and increase its surface energy. The modifications of the dispersive and polar components of this energy depend on the type of the plasma-gas used. Oxygen rich plasmas, such as air or carbon dioxide, allow the surface polarity of the polymer to be increased by a superficial oxidation whilst limiting the reticulation. They give better adhesion values. The analysis by ATR-FTIR displays the reticulation phenomenon for the extended application of argon plasma at low power. The RBS analysis shows that the quantity of argon incorporated into the alumina deposit is dependent on the operating conditions, particularly the pressure in the sputtering chamber. Different values of surface energy are due to the variations in composition. The alumina films with the lowest percentage of argon have the highest polar component. Their adhesion to the PMMA is also the highest. The best adhesion of alumina on PMMA is obtained for a polymer activation during a short time (10 s), by means of an oxygen rich plasma (CO 2) and for alumina coatings which have the lowest argon content ( p = 1 Pa).

Laser-induced deposition of alumina from condensed layers of organoaluminum compounds and water

The photoassisted deposition of thin aluminum oxide films from layers of trimethylaluminum (TMA), dimethylaluminum hydride, and aluminum hexafluoroacetylacetonate condensed with water on a cold substrate has been investigated. Laser energies of 4.6 or 2.3 eV were used to drive the reactions which led to film growth. Experiments show that clean aluminum oxide films can be synthesized at 80 K by irradiating co-condensed TMA and H2O with 4.6 eV light. Techniques used to characterize the films include Auger electron spectroscopy and scanning electron microscopy.