Ein Beitrag zur Kenntnis der Struktur des elektrolytisch erzeugten Aluminiumoxyds

Roth, Albert

doi:10.1002/zaac.19402440105

Cited by 12 publications

(2 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…α-Al2O3 can be formed only when γ-alumina is heated at more than 1000°C and the films anodically formed in aqueous solutions are amorphous or of very fine grain γ-alumina or of its deformed type (12,13). The α-alumina (Corundum) film can be developed when aluminum is anodically oxidized in the low temperature melts of bisulphates or their mixed systems (12), which occurred between 100 and 250°C.…”

Section: Methodsmentioning

confidence: 99%

Porous Dielectric Structure and Response Speed of Moisture Sensors

Ali,

Swartz,

Badhan

et al. 2024

ECS Trans.

View full text Add to dashboard Cite

We made moisture sensors using α-Al2O3 films as porous dielectric materials deposited through the anodic spark deposition (ASD). In this study, a variety number of small pores has been studied to investigate the response speed of moisture sensors. Three different surface morphologies have been studied using scanning electron microscopy (SEM). Sample DM23 has the maximum number of small pores. Small pores are defined as pore size ranging from 40 nm to several hundred nm. Sample TA40 has the minimum number of small pores. Sample FW06 has the medium number of small pores. We found that the sensor made from dielectric material with the maximum number of small pores has the fastest response speed, and that from the minimum number of small pores has the slowest response speed either from high humidity to low humidity or from low humidity to high humidity.

show abstract

Section: Methodsmentioning

confidence: 99%

Porous Dielectric Structure and Response Speed of Moisture Sensors

Ali,

Swartz,

Badhan

et al. 2024

ECS Trans.

View full text Add to dashboard Cite

show abstract

“…1989, No 7. At smaller Q, however, SN is different from Sx where the most drastic difference is the appearance of a large sharp peak in SN at Q = 2.8 k' which in Sx shows up only as a small hump.…”

mentioning

confidence: 90%

Structure of Anodic Oxide Coatings on Aluminum

1989

View full text Add to dashboard Cite

show abstract

Structure of anodic oxide coatings on aluminum

1989

View full text Add to dashboard Cite

Porous surface coatings on aluminum are produced by anodic oxidation in acid electrolytes.[" Pore sizes (10-250 nm) as well as pore densities (10'2-1015 m-') are mainly controlled by the anodizing voltage; the thickness of the layers may reach more than 100 pm and is determined by the amount of charge transferred. The remarkably uniform array of the pores in the centers of the almost hexagonally shaped cells makes the films of interest for application in the field of synthetic membranes and as supports for active materials. [" s] Furthermore, the coatings are widely used as protective layers which can also be colored by impregnation of the pores with organic dyes or by precipitation of inorganic pigments in the pores.[43 After coloring, the pores are closed by treatment with water or steam. This "sealing" process causes the formation of gelatinous boehmite and amorphous oxide hydroxide by reaction of the pore wall material with water.l61The structure of the (amorphous) porous coatings is not clear at present. It is assumed that they are structurally related to the non-porous "barrier-layer" (in direct contact with the metal; thickness 0.1 -0.2 Fm) which consists of almost pure A1,0, and contains the q-and y-phases of alumina (spinel-type structures). This assumption is supported by the primary products of crystallization which are formed by thermal treatment of the porous coatings and which were identified as the y-and y'-phases of alumina.[71 A recent IR-investigation of dried porous layers ['] is consistent with coordination numbers of four and six (tetrahedral and octahedral) for the aluminum atoms.In the present work freshly prepared porous coatings were investigated with X-ray and neutron diffraction methods. The aluminum atoms were found mostly to be surrounded tetrahedrally by four oxygen atoms. The close similarities of the radial distribution function (RDF) of the porous layers to that of vitreous silica suggest that the same structural model should be applied for both materials.Samples for the diffraction experiments were prepared by anodic oxidation of aluminum foils applying the following parameters: bath temperature 12 "C; natural bath convection; current 1. with deviations less than one wt-% for the distinct components. The amount of water given inside the brackets of the formula is regarded as the water of constitution (OH-groups) which is released only at temperatures above 470°C; the amount of water given outside the brackets is regarded as H,O-molecules (structural water and/or adsorbed water at the pore walls) which is already released between 80 "C and 250 "C. Figure 1 (a) shows the X-ray structure factors S" (Q) from angular dispersive X-ray diffraction (ADXD) and from en- ergy dispersive X-ray diffraction (EDXD). Both curves have the same overall shape without sharp reflexes, giving evidence that the anodic oxide coating material is amorphous.In the region of the first peak near Q = 2 A-' the EDXD reflects lower resolution, whereas the high Q-tail of the ADXD curve near Q = 12 k' we judge ...

show abstract

Ein Beitrag zur Kenntnis der Struktur des elektrolytisch erzeugten Aluminiumoxyds

Cited by 12 publications

References 5 publications

Porous Dielectric Structure and Response Speed of Moisture Sensors

Porous Dielectric Structure and Response Speed of Moisture Sensors

Structure of Anodic Oxide Coatings on Aluminum

Structure of anodic oxide coatings on aluminum

Contact Info

Product

Resources

About