After finish class v glass ionomer cement we do finishing with:
1- Pumice slurry.
2- Aluminum-oxide disc.***
Micron finishing diamonds used with a petroleum lubricant to prevent desiccation are ideal for contouring and finishing conventional glass ionomers.
Also, flexible abrasive discs used with a lubricant can be very effective. A fine grit aluminum oxide polishing paste applied with a prophy cup is used to impart a smooth surface.
-----------------------------
Aluminum oxide:
modifications:
The most important modifications of the alumina are:
the cubic γ-Al2O3 (clay, starting material for ceramic and aluminum production)
the rhombohedral (trigonal) α-Al2O3 (known as mineral corundum, sapphire or - for chromium doping - ruby, as abrasive and alumina ceramic)
Extraction and presentation:
Aluminum hydroxide (ATH) is obtained from bauxite by digestion in sodium hydroxide solution (Bayer process). By removing the water, z. B. by firing, sintering or calcination is obtained aluminum oxide.
The preparation of aluminum oxide can also be done by careful dehydration of gibbsite (hydrargillite) or boehmite.
Aluminum oxide can also be produced by electrolytic oxidation on aluminum surfaces, see anodizing and electrolytic capacitor.
The pure metal aluminum has a thin spontaneous aluminum oxide layer (self-passivation) after storage in air, which protects it from corrosion.
Aluminum oxide is also produced by the combustion of aluminum powder with ammonium perchlorate in solid rockets.
Properties:
The γ-Al2O3 is a hygroscopic, white, loose powder that is not soluble in water, but in strong acids and bases.
Already at 800 ° C, the γ-Al2O3 goes into the α-Al2O3, which is generally insoluble in acids such as bases.
Aluminum oxide forms aluminates with various metal oxides.
γ-Al2O3 is a porous material whose surface structure can be strongly influenced by the manufacturing process, or its temperature. In chromatography, it is used as an adsorbent.
Use:
The α-Al2O3 has a Mohs' hardness of 9 to 9.5 and is used among other things to bearing stones of measuring instruments and watches, as well as to abrasives. The basis for this is often the by-product of aluminothermy accumulating Alundum.
Calcined aluminas are used in ceramics (eg, in spark plugs, sinks, hotel ware, bulletproof clothing) or in the broadest sense as polishing agents (e.g., in glass ceramic cleaners, car care products, brake pads, toothpastes). Furthermore, sintered α-Al2O3 (sintered corundum) serves as a refractory material in furnace linings or laboratory equipment.
Contaminated by small amounts of Cr2O3 or TiO2, the corundum forms the gems ruby and sapphire.
Ti2O3-doped Al2O3 single crystals form the heart of the Titan: sapphire laser.
γ-Al2O3 serves as adsorbent and as catalyst support, as well as catalyst itself.
In electrical engineering aluminum oxide is used because of its high relative dielectric constant as a dielectric. The main field of application is the realization of strip lines and capacitors in high-frequency technology.
Latest sintering methods make it possible to use alumina for the production of extremely strong and unbreakable glasses, for. As wrist watches glasses (Nature, Vol 430, p 761, 2004).
Recently, Al2O3 ceramics have also been used in armor of vehicles. The ceramic tiles are glued to an aramid or dyneema fabric. This type of armor achieves, with the same basis weight, the double protective effect of armor steel. The ceramic fragments the projectile, and the aramid fibers then catch the fragments.
1- Pumice slurry.
2- Aluminum-oxide disc.***
Micron finishing diamonds used with a petroleum lubricant to prevent desiccation are ideal for contouring and finishing conventional glass ionomers.
Also, flexible abrasive discs used with a lubricant can be very effective. A fine grit aluminum oxide polishing paste applied with a prophy cup is used to impart a smooth surface.
-----------------------------
Aluminum oxide:
modifications:
The most important modifications of the alumina are:
the cubic γ-Al2O3 (clay, starting material for ceramic and aluminum production)
the rhombohedral (trigonal) α-Al2O3 (known as mineral corundum, sapphire or - for chromium doping - ruby, as abrasive and alumina ceramic)
Extraction and presentation:
Aluminum hydroxide (ATH) is obtained from bauxite by digestion in sodium hydroxide solution (Bayer process). By removing the water, z. B. by firing, sintering or calcination is obtained aluminum oxide.
The preparation of aluminum oxide can also be done by careful dehydration of gibbsite (hydrargillite) or boehmite.
Aluminum oxide can also be produced by electrolytic oxidation on aluminum surfaces, see anodizing and electrolytic capacitor.
The pure metal aluminum has a thin spontaneous aluminum oxide layer (self-passivation) after storage in air, which protects it from corrosion.
Aluminum oxide is also produced by the combustion of aluminum powder with ammonium perchlorate in solid rockets.
Properties:
The γ-Al2O3 is a hygroscopic, white, loose powder that is not soluble in water, but in strong acids and bases.
Already at 800 ° C, the γ-Al2O3 goes into the α-Al2O3, which is generally insoluble in acids such as bases.
Aluminum oxide forms aluminates with various metal oxides.
γ-Al2O3 is a porous material whose surface structure can be strongly influenced by the manufacturing process, or its temperature. In chromatography, it is used as an adsorbent.
Use:
The α-Al2O3 has a Mohs' hardness of 9 to 9.5 and is used among other things to bearing stones of measuring instruments and watches, as well as to abrasives. The basis for this is often the by-product of aluminothermy accumulating Alundum.
Calcined aluminas are used in ceramics (eg, in spark plugs, sinks, hotel ware, bulletproof clothing) or in the broadest sense as polishing agents (e.g., in glass ceramic cleaners, car care products, brake pads, toothpastes). Furthermore, sintered α-Al2O3 (sintered corundum) serves as a refractory material in furnace linings or laboratory equipment.
Contaminated by small amounts of Cr2O3 or TiO2, the corundum forms the gems ruby and sapphire.
Ti2O3-doped Al2O3 single crystals form the heart of the Titan: sapphire laser.
γ-Al2O3 serves as adsorbent and as catalyst support, as well as catalyst itself.
In electrical engineering aluminum oxide is used because of its high relative dielectric constant as a dielectric. The main field of application is the realization of strip lines and capacitors in high-frequency technology.
Latest sintering methods make it possible to use alumina for the production of extremely strong and unbreakable glasses, for. As wrist watches glasses (Nature, Vol 430, p 761, 2004).
Recently, Al2O3 ceramics have also been used in armor of vehicles. The ceramic tiles are glued to an aramid or dyneema fabric. This type of armor achieves, with the same basis weight, the double protective effect of armor steel. The ceramic fragments the projectile, and the aramid fibers then catch the fragments.
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