Method of producing aluminum oxides and products obtained on the basis thereof

A process for producing redispersible nanocorundum with an average particle size D50<100 nm with addition of nuclei that promote transformation to corundum in subsequent annealing, comprising:

• (a) dissolving in a liquid medium or processing in a liquid medium to a sol, as starting materials, organic precursors;
• (b) hydrolyzing either (i) with excess water through addition of the precursor solution or the precursor sol of (a) to water at a mole ratio of water:precursor>3, and with addition of an acid that leads to pH=3-5, or (ii) through addition of an amount of water restricted to a mole ratio of water:precursor≦3 to the precursor solution or precursor sol of (a) that are to be mixed with complex-forming ligands;
• (c) aging the hydrolyzed solution or sol of (b) at temperatures of ≦50° C. within 5 hours, and subsequently aging at temperatures of 80 to 98° C. within 1 to 24 hours;
• (d) subsequently drying the aged solution or sol of (c) followed by calcination at temperatures between 350 and 650° C. for converting the hydrolyzed precursor into a semiamorphous intermediate phase and then to transitional aluminum oxides;
• and
• (e) performing annealing by increasing temperature to ≦950° C. for converting product of (d) into corundum phase.

A process for the production of sintered porous or dense corundum layers on a substrate by a process for producing redispersible nanocorundum with an average particle size D50<100 nm with addition of nuclei that promote transformation to corundum in subsequent annealing, comprising:

• (a) dissolving in a liquid medium or processing in a liquid medium to a sol, as starting materials, chlorine-free inorganic precursors;
• (b) hydrolyzing the solution or the sol of (a) through the addition of a base in a mole ratio of base:precursor of 1 to 3;
• (c) aging the hydrolyzed solution or sol of (b) at temperatures between 60 and 98° C. for 1 to 72 hours;
• (d) applying the aged hydrolyzed solution or sol of (c);
• (e) subsequently drying the applied aged solution or sol of (d) followed by calcination at temperatures between 350 and 650° C. for converting hydrolyzed precursor into a semiamorphous intermediate phase and ultimately into transitional aluminum oxides;
• and
• (f) performing annealing by increasing temperature to ≦950° C. for converting product of (e) into corundum phase.

A process for the production of sintered porous or dense corundum layers on a substrate by a process for producing redispersible nanocorundum with an average particle size D50<100 nm with addition of nuclei that promote transformation to corundum in subsequent annealing, comprising:

• (a) dissolving in a liquid medium or processing in a liquid medium to a sol, as starting materials, organic precursors;
• (b) hydrolyzing either (i) with excess water through addition of the precursor solution or the precursor sol of (a) to water at a mole ratio of water:precursor>3, and with addition of an acid that leads to pH=3-5, or (ii) through addition of an amount of water restricted to a mole ratio of water:precursor≦3 to the precursor solution or precursor sol of (a) that are to be mixed with complex-forming ligands;
• (c) aging the hydrolyzed solution or sol of (b) at temperatures of ≦50° C. within 5 hours, and subsequently aging at temperatures of 80 to 98° C. within 1 to 24 hours;
• (d) applying the aged hydrolyzed solution or sol of (c);
• (e) subsequently drying the applied aged solution or sol of (d) followed by calcination at temperatures between 350 and 650° C. for converting the hydrolyzed precursor into a semiamorphous intermediate phase and then to transitional aluminum oxides;
• and
• (f) performing annealing by increasing temperature to ≦950° C. for converting product of (e) into corundum phase.

Dense sinter corundum layers consisting essentially of Al2O3 on a substrate produced by a process for producing redispersible nanocorundum with an average particle size D50<100 nm with addition of nuclei that promote transformation to corundum in subsequent annealing, which process comprises:

• (a) dissolving in a liquid medium or processing in a liquid medium to a sol, as starting materials, chlorine-free inorganic precursors;
• (b) hydrolyzing the solution or the sol of (a) through the addition of a base in a mole ratio of base:precursor of 1 to 3;
• (c) aging the hydrolyzed solution or sol of (b) at temperatures between 60 and 98° C. for 1 to 72 hours;
• (d) applying the aged hydrolyzed solution or sol of (c) to a substrates;
• (e) subsequently drying the applied aged solution or sol of (d) followed by calcination at temperatures between 350 and 650° C. for converting hydrolyzed precursor into a semiamorphous intermediate phase and ultimately into transitional aluminum oxides;
• and
• (f) performing annealing by increasing temperature to ≦950° C. for converting product of (e) into corundum phase,
• wherein the substrate is composed of a different material from the corundum layers, and in which through sintering at a temperature of ≦1250° C. there is an average grain size of ≦0.5 μm.

Dense sinter corundum layers consisting essentially of Al2O3 on a substrate produced by a process for the production of sintered porous or dense corundum layers on a substrate by a process for producing redispersible nanocorundum with an average particle size D50<100 nm with addition of nuclei that promote transformation to corundum in subsequent annealing, which process comprises:

• (a) dissolving in a liquid medium or processing in a liquid medium to a sol, as starting materials, organic precursors;
• (b) hydrolyzing either (i) with excess water through addition of the precursor solution or the precursor sol of (a) to water at a mole ratio of water:precursor>3, and with addition of an acid that leads to pH=3-5, or (ii) through addition of an amount of water restricted to a mole ratio of water:precursor≦3 to the precursor solution or precursor sol of (a) that are to be mixed with complex-forming ligands;
• (c) aging the hydrolyzed solution or sol of (b) at temperatures of≦50° C. within 5 hours, and subsequently aging at temperatures of 80 to 98° C. within 1 to 24 hours;
• (d) applying the aged hydrolyzed solution or sol of (c) to a substrate;
• (e) subsequently drying the applied aged solution or sol of (d) followed by calcination at temperatures between 350 and 650° C. for converting the hydrolyzed precursor into a semiamorphous intermediate phase and then to transitional aluminum oxides;
• and
• (f) performing annealing by increasing temperature to ≦950° C. for converting product of (e) into corundum phase,
• wherein the substrate is composed of a different material from the corundum layers, and in which through sintering at a temperature of ≦1250° C. there is an average grain size of ≦0.5 μm.

A process for producing nanoporous Al2O3 sintered products comprising:

• (a) dissolving in a liquid medium or processing in a liquid medium to a sol, as starting materials, chlorine-free inorganic precursors;
• (b) hydrolyzing the solution or the sol of (a) through the addition of a base in a mole ratio of base:precursor of 1 to 3;
• (c) aging the hydrolyzed solution or sol of (b) at temperatures between 60 and 98° C. for 1 to 72 hours;
• and
• (d) subsequently drying followed by calcination at temperatures between 350 and 750° C. for converting hydrolyzed precursors into aluminum oxide.

A process for production of nanoporous layers comprising:

• (a) dissolving in a liquid medium or processing in a liquid medium to a sol, as starting materials, chlorine-free inorganic precursors;
• (b) hydrolyzing the solution or the sol of (a) through the addition of a base in a mole ratio of base:precursor of 1 to 3;
• (c) aging the hydrolyzed solution or sol of (b) at temperatures between 60 and 98° C. for 1 to 72 hours;
• (d) applying the aged solution or the sol of (c) to a substrate;
• and
• (e) subsequently drying followed by calcination at temperatures between 350 and 750° C. for converting hydrolyzed precursors into aluminum oxide.

A process for coating a porous or dense metallic substrate comprising:

• (a) dissolving in a liquid medium or processing in a liquid medium to a sol, as starting materials, chlorine-free inorganic precursors;
• (b) hydrolyzing the solution or the sol of (a) through the addition of a base in a mole ratio of base:precursor of 1 to 3;
• (c) aging the hydrolyzed solution or sol of (b) at temperatures between 60 and 98° C. for 1 to 72 hours;
• (d) electrophoretically depositing on the metallic substrate particles of the aged hydrolyzed sol or particles of a suspension of nanoporous aluminum oxide of (c);
• and
• (e) subsequently drying followed by calcination at temperatures between 350 and 750° C. for converting hydrolyzed precursors into aluminum oxide.

A process for producing nanoporous Al2O3 sintered products, comprising:

• (a) dissolving in a liquid medium or processing in a liquid medium to a sol, as starting materials, organic precursors;
• (b) hydrolyzing either (i) with excess water through addition of the precursor solution or the precursor sol of (a) to water at a mole ratio of water:precursor >3, and with addition of an acid that leads to pH=3-5, or (ii) through addition of an amount of water restricted to a mole ratio of water:precursor ≦3 to the precursor solution or precursor sol of (a) that are to be mixed with complex-forming ligands;
• (c) aging the hydrolyzed solution or sol of (b) at temperatures of ≦50° C. within 5 hours, and subsequently aging at temperatures of 80 to 98° C. within 1 to 24 hours;
• and
• (d) subsequently drying the aged solution or sol of (c) followed by calcination at temperatures between 350 and 750° C. for converting hydrolyzed precursors into aluminum oxide.

A process for production of nanoporous layers comprising:

• (a) dissolving in a liquid medium or processing in a liquid medium to a sol, as starting materials, organic precursors;
• (b) hydrolyzing either (i) with excess water through addition of the precursor solution or the precursor sol of (a) to water at a mole ratio of water:precursor>3, and with addition of an acid that leads to pH=3-5, or (ii) through addition of an amount of water restricted to a mole ratio of water:precursor≦3 to the precursor solution or precursor sol of (a) that are to be mixed with complex-forming ligands;
• (c) aging the hydrolyzed solution or sol of (b) at temperatures of ≦50° C. within 5 hours, and subsequently aging at temperatures of 80 to 98° C. within 1 to 24 hours;
• (d) applying the aged solution or the sol of (c) a substrate;
• and
• (e) subsequently drying the aged solution or sol of (d) followed by calcination at temperatures between 350 and 750° C. for converting hydrolyzed precursors into aluminum oxide.

A process for coating a porous or dense metallic substrate comprising:

• (a) dissolving in a liquid medium or processing in a liquid medium to a sol, as starting materials, organic precursors;
• (b) hydrolyzing either (i) with excess water through addition of the precursor solution or the precursor sol of (a) to water at a mole ratio of water:precursor>3, and with addition of an acid that leads to pH=3-5, or (ii) through addition of an amount of water restricted to a mole ratio of water:precursor≦3 to the precursor solution or precursor sol of (a) that are to be mixed with complex-forming ligands;
• (c) aging the hydrolyzed solution or sol of (b) at temperatures of ≦50° C. within 5 hours, and subsequently aging at temperatures of 80 to 98° C. within 1 to 24 hours;
• (d) electrophoretically depositing on the metallic substrate particles of hydrolyzed sol or particles of a suspension of nanoporous aluminum oxide of (c);
• and
• (e) subsequently drying the aged solution or sol of (d) followed by calcination at temperatures between 350 and 750° C. for converting hydrolyzed precursors into aluminum oxide.