WO2007029237A2 - Improved alumina based ceramic objects - Google Patents

Improved alumina based ceramic objects Download PDF

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Publication number
WO2007029237A2
WO2007029237A2 PCT/IL2006/001014 IL2006001014W WO2007029237A2 WO 2007029237 A2 WO2007029237 A2 WO 2007029237A2 IL 2006001014 W IL2006001014 W IL 2006001014W WO 2007029237 A2 WO2007029237 A2 WO 2007029237A2
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Prior art keywords
liquid medium
alumina
ceramic objects
objects
ceramic
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PCT/IL2006/001014
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French (fr)
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WO2007029237A3 (en
Inventor
Gideon Shikolski
Eyal Yehiel Vultz
Rima Kodakovskaya
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Imi Tami Institute For Research And Development Ltd.
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Publication of WO2007029237A2 publication Critical patent/WO2007029237A2/en
Publication of WO2007029237A3 publication Critical patent/WO2007029237A3/en

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    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
    • C04B35/111—Fine ceramics
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    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
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    • C04B35/62645—Thermal treatment of powders or mixtures thereof other than sintering
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    • C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
    • C04B35/638—Removal thereof
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F41—WEAPONS
    • F41H—ARMOUR; ARMOURED TURRETS; ARMOURED OR ARMED VEHICLES; MEANS OF ATTACK OR DEFENCE, e.g. CAMOUFLAGE, IN GENERAL
    • F41H5/00—Armour; Armour plates
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    • F41H5/04—Plate construction composed of more than one layer
    • F41H5/0414—Layered armour containing ceramic material
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F41—WEAPONS
    • F41H—ARMOUR; ARMOURED TURRETS; ARMOURED OR ARMED VEHICLES; MEANS OF ATTACK OR DEFENCE, e.g. CAMOUFLAGE, IN GENERAL
    • F41H5/00—Armour; Armour plates
    • F41H5/02—Plate construction
    • F41H5/04—Plate construction composed of more than one layer
    • F41H5/0492—Layered armour containing hard elements, e.g. plates, spheres, rods, separated from each other, the elements being connected to a further flexible layer or being embedded in a plastics or an elastomer matrix
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    • C04B2235/3205—Alkaline earth oxides or oxide forming salts thereof, e.g. beryllium oxide
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    • C04B2235/3217—Aluminum oxide or oxide forming salts thereof, e.g. bauxite, alpha-alumina
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    • C04B2235/5418—Particle size related information expressed by the size of the particles or aggregates thereof
    • C04B2235/5445—Particle size related information expressed by the size of the particles or aggregates thereof submicron sized, i.e. from 0,1 to 1 micron
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    • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
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    • C04B2235/725—Metal content
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Definitions

  • the present invention relates to ceramic objects. More particularly, the present invention relates to alumina-based ceramic objects with improved properties for various applications, particularly for ballistic protection.
  • Ceramics are materials, which are made of nonmetallic minerals, usually in the form of metallic oxides that have been permanently hardened by firing at a high temperature, or objects made of such materials.
  • Traditional ceramics are made of alumina, magnesia, clay and other naturally occurring materials, while modern high-tech ceramics use silicon carbide, zirconia boron nitride and other specially purified or synthetic raw materials.
  • Processing of ceramic materials, particularly crystalline ceramics, into a desired shape is made viable, inter alia, by pressing a ceramic powder into a "Green Body” (hereinafter Green Body) and sintering (firing) below the melting temperature of the ceramic.
  • Green Body Green Body
  • This method is subject to various modifications, including adding glue and pressing wax material to the raw materials mixture prior to pressing it into a Green Body, in order to increase the powder lubrication, and then burning the glue and pressing wax material at elevated temperatures prior to or during the sintering stage.
  • Ceramic Objects are applied in various applications for example in grinding media, heat resistant bricks, ballistic protection, and in various other uses. It is an object of the present invention to provide an advantageous Ceramic Objects, having qualities as high hardness, high density combined with low- porosity, which makes it a superior candidate material for various applications, particularly for ballistic protection for people, vehicles and equipment, hereinafter "Ballistic Ceramics”.
  • Still another object of the present invention is to provide a process for preparing an advantageous Ceramic Objects.
  • the present invention provides use of an advantageous Ceramic Objects for preparing in particular Ballistic Ceramics.
  • Ballistic Ceramics may be formed in various shapes, particularly as tiles, monolithic bodies, cylinders (with and without dome or domes), balls, as well as other forms, hereinafter "Ballistic Ceramic Objects”.
  • the present invention provides use of the advantageous Ceramic Objects for preparing other equipment items, such as manufacturing tools, ceramic valves, as well as grinding media.
  • the present invention provides advantageous Ceramic Objects, which have improved qualities of high hardness and high density combined with low porosity, that make them superior candidate materials for various applications, particularly for ballistic protection.
  • the Ceramic Objects of the present invention are provided in their primary stages as a powder, also known as Ready To Press Powder (hereinafter "RTP Powder”).
  • the unique improved qualities of the advantageous Ceramic Objects made from the RTP Powder of the present invention are due, inter alia, to the raw materials used in its preparation.
  • the RTP Powder composition described hereinafter is not only without precedent in the art, but furthermore enables the improved qualities and hence better performances of the advantageous Ceramic Objects.
  • the above mentioned RTP Powder comprises, in addition to alumina, residual liquid medium, glue and pressing wax material, also small quantities of a grain growth-inhibiting material that controls the size of the alumina grains, where said growth-inhibiting material is soluble in the Liquid Medium (as defined below) and may be in the form of a soluble magnesium salt such as magnesium halides (e.g. magnesium chloride, magnesium bromide, etc.) or magnesium organic compounds (e.g. magnesium formate, magnesium acetate, etc.).
  • magnesium halides e.g. magnesium chloride, magnesium bromide, etc.
  • magnesium organic compounds e.g. magnesium formate, magnesium acetate, etc.
  • magnesium chloride (MgCb), and/or its hydrates may be introduced into the RTP Powder of the present invention for inhibiting the growth of the alumina grains, instead of metallic oxides such as magnesia (MgO), zirconia (Zr ⁇ 2), ceria (Ce ⁇ 2), ytrria (Y2O3) etc., which are known in the art.
  • metallic oxides such as magnesia (MgO), zirconia (Zr ⁇ 2), ceria (Ce ⁇ 2), ytrria (Y2O3) etc.
  • the advantage of using soluble magnesium compounds such as magnesium chloride, including its hydrates, rather than, for example, magnesium oxide lies in the fact that magnesium chloride is soluble in the Liquid Medium (as defined below), while magnesia and other metallic oxides are not, and thereby a more uniform coating of the alumina particles by the dissolved magnesium chloride is facilitated when mixed together.
  • This fact is advantageously exploited in the manufacturing process of the RTP Powder of the present invention, by mixing the raw materials, which form the RTP Powder in the Liquid Medium (as defined below), and not by mixing solid raw materials as in the case of mixing alumina and magnesia powders, which inherently produces less uniformly coated alumina particles.
  • Finished advantageous Ceramic Objects of the present invention therefore, acquire the desired mechanical properties, especially high hardness and high density combined with low porosity.
  • the raw materials used in the RTP Powder of the present invention include: a) alumina powder, b) grain growth inhibiting material, particularly magnesium chloride, including its hydrates, c) a glue and pressing wax material, and d) a Liquid Medium.
  • the alumina powder is selected such that it meets the specifications summarized in Table I below:
  • the first stage of the process includes the preparation of the raw materials mixture in a liquid medium.
  • the raw materials ingredient mixture includes alumina, grain growth inhibiting material, and glue and pressing wax material.
  • the liquid medium may be an organic liquid, an inorganic liquid, or a mixture thereof, which is able to dissolve the grain growth inhibiting material, and said glue and pressing wax material, but not the alumina (hereinafter "Liquid Medium”).
  • the next stage of the process includes the removal of most of the Liquid Medium, and then pressing it to obtain Green Bodies of the desired dimensions. After this step, essentially all of the glue and pressing wax material, and the Liquid Medium residues, are removed from the Green Bodies by heating.
  • the last stage is the sintering stage, in which the desired advantageous Ceramic Objects are obtained. Such a process produces advantageous Ceramic Objects having the desired properties, especially the hardness and grain size.
  • the ratio between the overall surface area of the alumina and the weight of the rest of the dissolved materials in the Liquid Medium is maintained at the stage of preparing the initial raw materials mixture in order to ensure optimal coating of the alumina particles.
  • the above process comprises the following main five stages: i. Preparation of the raw materials mixture stage; ii. Removal of the Liquid Medium stage; iii. Pressing stage; iv. De-waxing stage, and v. Sintering stage.
  • Preparation of the raw materials mixture stage In this stage homogeneous liquid slurry is prepared which comprises, besides alumina, a Liquid Medium, grain growth inhibiting material, and glue and pressing wax material.
  • a method for achieving the slurry uses a ball mill and is carried out according to the following steps: a) adding the Liquid Medium to the ball mill; b) adding the grain growth inhibiting material; c) operating the ball mill; d) adding the glue and pressing wax material; e) operating the ball mill; f) adding alumina; and g) operating the ball mill.
  • Removal of the Liquid Medium stage Removing most or all of the Liquid Medium and obtaining a free flowing RTP Powder, for example by using a spray drier, and as described in Example 2.
  • iii. Pressing stage In this stage, Green Bodies are formed by placing the RTP Powder into a suitable mold with the desired dimensions and then applying the required pressure by using a suitable press.
  • De-waxing stage Removing essentially all or all of the glue and pressing wax material and Liquid Medium residues in the Green Bodies by heating in an appropriate furnace at 600 0 C-IlOO 0 C.
  • MgCk is converted to magnesia during this stage, and HCl is released according to equation 1:
  • magnesia then reacts with the alumina at the alumina grain boundaries, resulting in the formation of spinel, according to equation 2:
  • v. Sintering stage Obtaining the finished advantageous Ceramic Objects of the desired grain size and mechanical properties at an elevated temperature, maintained below the alumina melting temperature.
  • the grain growth inhibiting material is magnesium chloride.
  • magnesium chloride is provided in its hydrated form as magnesium chloride hexahydrate, MgCl 2 *6H 2 O.
  • the RTP Powder obtained in the above stage ii) contains no more than about 0.5% of water, as determined according to the LOD (Loss On Drying) method. In still another preferred embodiment, when the Liquid Medium is water, then the RTP Powder obtained in the above stage ii) contains no more than about 2% of organic material and water, as determined according to the LOI (Loss On Ignition) method heating to a temperature of a 1000°C for 2 hours.
  • the LOD Liquid On Drying
  • the advantageous Ceramic Objects contain spinel (MgAbO 4 ), which is essentially formed by heating a Green Body made from a Ready To Press (RTP) alumina-base powder and magnesia, where the magnesia originates from a grain growth-inhibiting material, which is soluble in the Liquid Medium.
  • MgAbO 4 spinel
  • RTP Ready To Press
  • MgCl2 grain growth inhibiting material
  • hydrates of MgCk hydrates of MgCk.
  • the advantageous Ceramic Objects are suitable for use in ballistic protection, as grinding balls for grinding media, heat resistant bricks, manufacturing tools, wire guides and in other uses.
  • the advantageous Ceramic Objects are formed into various items, preferably into ceramic balls, suitable for use as grinding media, and also into wire guides, manufacturing tools, valves, and tap machines.
  • the advantageous Ceramic Objects are formed into various types of Ballistic Ceramic Objects, intended for use in ballistic protection systems.
  • the Ballistic Ceramic Objects are shaped into any form, preferably into the form of a tile, a monolithic body, and a cylinder with or without a dome or domes. Measurement and Test Methods
  • Table II details particular features of both the LOD method for measuring water content in powders, when water is used as the Liquid Medium and the LOI method as an indication for the RTP Powder composition.
  • Ballistic Ceramics Objects such as armor ceramic tiles
  • the ballistic test which is a destructive test
  • the chemical/physical test which is a non-destructive test. Both methods are detailed below for ballistic tiles.
  • the non-destructive method includes tests of the following properties: density, porosity (determined by the subtraction of the measured density from the theoretical density, as can be found in the relevant literature), hardness, grain size and presence of cracks, the latter being detected by a colored ink penetration test.
  • density density
  • porosity determined by the subtraction of the measured density from the theoretical density, as can be found in the relevant literature
  • the ballistic tiles were found to be 50% harder, according to the hardness test which is listed in Table III, in comparison with commercial alumina-based ballistic tiles which were tested according to the same method.
  • Another preferred embodiment of the present invention provides advantageous Ceramic Objects having the properties of hardness of not less than about 1850 HV (according to the Vickers method) upon application of a load of about 10 kilograms, a density of not less than about 3.9 g/cm 3 or greater (according to the Archimedes method or the Gas pycnometer method), and a grain size smaller than about 5 ⁇ m, preferably smaller than about 2 ⁇ m (according to the Scanning Electron Microscope method).
  • the density is 3.9 g/cm 3 .
  • the destructive test is a ballistic test, carried out by a controlled gunfire test in which the type of gun, type of projectile, muzzle velocity, distance from the target and target set-up are controlled.
  • the results of the ballistic tests on the ballistic tiles produced according to the process of this invention were better than those for other commercial alumina-based ballistic tiles that were tested:
  • Water and magnesium chloride hexahydrate are introduced into a ball mill having zirconia milling balls and the ball mill is operated for several minutes. Then, the glue and pressing wax material is introduced and the ball mill is operated again for several minutes more. Finally, the alumina is introduced and the mill is operated in order to deagglomerate the alumina powder until a homogeneous slurry is formed.
  • the preparation of the raw materials mixture is performed under normal room conditions (temperature of ca. 25 0 C and 1 atm. pressure).
  • An example for the removal of the Liquid Medium stage is the removal of most of the Liquid Medium by means of a spray drier, when water is the Liquid Medium as follows:
  • the raw materials mixture (formed in stage i.) and air, hereinafter “Feed Air” are fed simultaneously to the spray drier via an atomizing nozzle, so for example a ratio of 0.57 m 3 of Feed Air to one liter of the raw materials mixture is kept and the Feed Air pressure is 0.5 bar.
  • the nozzle sprays the raw material mixture and the Feed Air through the opening in the base of the drying chamber of the spray drier in the direction of the upper part of the chamber, in the form of a fountain and in a counter current direction to a stream of heated air which enters the spray dryer at the top of the drying chamber, hereinafter "Drying Air”.
  • the Drying Air temperature can be 25O 0 C. This method promotes the formation of the desired free flowing RTP Powder.

Abstract

Sintered alumina-based ceramic objects exhibiting high hardness and density combined with low porosity, and a process for making them are provided. The process includes mixing alumina with a grain growth-inhibiting material, and with a glue and pressing wax material, in a liquid medium in which the last two materials are soluble while the alumina is not, sequentially removing essentially all of the liquid medium in order to form a ready to press (RTP) free flowing powder, pressing the RTP powder to a 'green body', de-waxing and sintering the green body. The so obtained sintered objects are suitable for ballistic protection, as well as for other uses.

Description

IMPROVEDALUMINA BASED CERAMIC OBJECTS
Field of the Invention
The present invention relates to ceramic objects. More particularly, the present invention relates to alumina-based ceramic objects with improved properties for various applications, particularly for ballistic protection.
Background
Ceramics are materials, which are made of nonmetallic minerals, usually in the form of metallic oxides that have been permanently hardened by firing at a high temperature, or objects made of such materials. Traditional ceramics are made of alumina, magnesia, clay and other naturally occurring materials, while modern high-tech ceramics use silicon carbide, zirconia boron nitride and other specially purified or synthetic raw materials.
Processing of ceramic materials, particularly crystalline ceramics, into a desired shape, is made viable, inter alia, by pressing a ceramic powder into a "Green Body" (hereinafter Green Body) and sintering (firing) below the melting temperature of the ceramic. This method is subject to various modifications, including adding glue and pressing wax material to the raw materials mixture prior to pressing it into a Green Body, in order to increase the powder lubrication, and then burning the glue and pressing wax material at elevated temperatures prior to or during the sintering stage.
Among the most known materials in the field of ceramics, particularly of sintered ceramics, is alumina, AI2O3, due to its relatively high hardness and its relatively low cost. Sintered alumina-based ceramic objects, referred to hereinafter as "Ceramic Objects", are applied in various applications for example in grinding media, heat resistant bricks, ballistic protection, and in various other uses. It is an object of the present invention to provide an advantageous Ceramic Objects, having qualities as high hardness, high density combined with low- porosity, which makes it a superior candidate material for various applications, particularly for ballistic protection for people, vehicles and equipment, hereinafter "Ballistic Ceramics".
Still another object of the present invention is to provide a process for preparing an advantageous Ceramic Objects.
In still another object, the present invention provides use of an advantageous Ceramic Objects for preparing in particular Ballistic Ceramics.
In still another object of the present invention, Ballistic Ceramics may be formed in various shapes, particularly as tiles, monolithic bodies, cylinders (with and without dome or domes), balls, as well as other forms, hereinafter "Ballistic Ceramic Objects".
In still another object of the present invention to prepare a Ballistic Ceramic Objects of high density combined with low porosity.
In yet another object, the present invention provides use of the advantageous Ceramic Objects for preparing other equipment items, such as manufacturing tools, ceramic valves, as well as grinding media.
This and other objects of the present invention shall become clear as the description proceeds.
Summary of the Invention
The present invention provides advantageous Ceramic Objects, which have improved qualities of high hardness and high density combined with low porosity, that make them superior candidate materials for various applications, particularly for ballistic protection. The Ceramic Objects of the present invention are provided in their primary stages as a powder, also known as Ready To Press Powder (hereinafter "RTP Powder").
The unique improved qualities of the advantageous Ceramic Objects made from the RTP Powder of the present invention are due, inter alia, to the raw materials used in its preparation. The RTP Powder composition described hereinafter is not only without precedent in the art, but furthermore enables the improved qualities and hence better performances of the advantageous Ceramic Objects.
The above mentioned RTP Powder comprises, in addition to alumina, residual liquid medium, glue and pressing wax material, also small quantities of a grain growth-inhibiting material that controls the size of the alumina grains, where said growth-inhibiting material is soluble in the Liquid Medium (as defined below) and may be in the form of a soluble magnesium salt such as magnesium halides (e.g. magnesium chloride, magnesium bromide, etc.) or magnesium organic compounds (e.g. magnesium formate, magnesium acetate, etc.). Particularly, magnesium chloride (MgCb), and/or its hydrates may be introduced into the RTP Powder of the present invention for inhibiting the growth of the alumina grains, instead of metallic oxides such as magnesia (MgO), zirconia (Zrθ2), ceria (Ceθ2), ytrria (Y2O3) etc., which are known in the art.
It is worth noting that all said soluble magnesium compounds present in the RTP Powder and in the Green Body are converted, under the temperature conditions prevailing during the de-waxing stage (as described below), to magnesia, which in turn starts reacting with the alumina during the de- waxing stage and completes the reaction during the sintering stage (as described below), to form spinel (AIgMgO4). The advantage of using soluble magnesium compounds such as magnesium chloride, including its hydrates, rather than, for example, magnesium oxide lies in the fact that magnesium chloride is soluble in the Liquid Medium (as defined below), while magnesia and other metallic oxides are not, and thereby a more uniform coating of the alumina particles by the dissolved magnesium chloride is facilitated when mixed together. This fact is advantageously exploited in the manufacturing process of the RTP Powder of the present invention, by mixing the raw materials, which form the RTP Powder in the Liquid Medium (as defined below), and not by mixing solid raw materials as in the case of mixing alumina and magnesia powders, which inherently produces less uniformly coated alumina particles.
Finished advantageous Ceramic Objects of the present invention, therefore, acquire the desired mechanical properties, especially high hardness and high density combined with low porosity.
The raw materials used in the RTP Powder of the present invention include: a) alumina powder, b) grain growth inhibiting material, particularly magnesium chloride, including its hydrates, c) a glue and pressing wax material, and d) a Liquid Medium. Preferably, the alumina powder is selected such that it meets the specifications summarized in Table I below:
Table I Alumina preferred properties
Figure imgf000005_0001
Figure imgf000006_0001
General Description of the Process
The following describes in general the principles of the process for preparing advantageous Ceramic Objects in accordance with the present invention, starting from the preparation of the raw materials mixture and until the sintering of the dewaxed objects:
The first stage of the process includes the preparation of the raw materials mixture in a liquid medium. The raw materials ingredient mixture includes alumina, grain growth inhibiting material, and glue and pressing wax material. The liquid medium may be an organic liquid, an inorganic liquid, or a mixture thereof, which is able to dissolve the grain growth inhibiting material, and said glue and pressing wax material, but not the alumina (hereinafter "Liquid Medium"). The next stage of the process includes the removal of most of the Liquid Medium, and then pressing it to obtain Green Bodies of the desired dimensions. After this step, essentially all of the glue and pressing wax material, and the Liquid Medium residues, are removed from the Green Bodies by heating. The last stage is the sintering stage, in which the desired advantageous Ceramic Objects are obtained. Such a process produces advantageous Ceramic Objects having the desired properties, especially the hardness and grain size.
It is important to note with regard to the above-described process, that the ratio between the overall surface area of the alumina and the weight of the rest of the dissolved materials in the Liquid Medium is maintained at the stage of preparing the initial raw materials mixture in order to ensure optimal coating of the alumina particles.
In summary, the above process comprises the following main five stages: i. Preparation of the raw materials mixture stage; ii. Removal of the Liquid Medium stage; iii. Pressing stage; iv. De-waxing stage, and v. Sintering stage.
These stages will now be described in further detail with reference to a preferred embodiment of the invention.
Detailed Description of the Process i. Preparation of the raw materials mixture stage: In this stage homogeneous liquid slurry is prepared which comprises, besides alumina, a Liquid Medium, grain growth inhibiting material, and glue and pressing wax material. A method for achieving the slurry uses a ball mill and is carried out according to the following steps: a) adding the Liquid Medium to the ball mill; b) adding the grain growth inhibiting material; c) operating the ball mill; d) adding the glue and pressing wax material; e) operating the ball mill; f) adding alumina; and g) operating the ball mill.
. Removal of the Liquid Medium stage: Removing most or all of the Liquid Medium and obtaining a free flowing RTP Powder, for example by using a spray drier, and as described in Example 2.
iii. Pressing stage: In this stage, Green Bodies are formed by placing the RTP Powder into a suitable mold with the desired dimensions and then applying the required pressure by using a suitable press. iv. De-waxing stage: Removing essentially all or all of the glue and pressing wax material and Liquid Medium residues in the Green Bodies by heating in an appropriate furnace at 6000C-IlOO0C. When magnesium chloride or its hydrates are used as the grain growth inhibiting material in the above stage L), the MgCk is converted to magnesia during this stage, and HCl is released according to equation 1:
(1) MgCl2 + H2O → MgO + 2HCl t
The so formed magnesia then reacts with the alumina at the alumina grain boundaries, resulting in the formation of spinel, according to equation 2:
(2) MgO + Al2O3 → MgAl2O4
v. Sintering stage: Obtaining the finished advantageous Ceramic Objects of the desired grain size and mechanical properties at an elevated temperature, maintained below the alumina melting temperature.
According to one preferred embodiment of the invention the grain growth inhibiting material is magnesium chloride.
In another preferred embodiment of the invention the magnesium chloride is provided in its hydrated form as magnesium chloride hexahydrate, MgCl2*6H2O.
In still another preferred embodiment, when the Liquid Medium is water, then the RTP Powder obtained in the above stage ii) contains no more than about 0.5% of water, as determined according to the LOD (Loss On Drying) method. In still another preferred embodiment, when the Liquid Medium is water, then the RTP Powder obtained in the above stage ii) contains no more than about 2% of organic material and water, as determined according to the LOI (Loss On Ignition) method heating to a temperature of a 1000°C for 2 hours.
In still another preferred embodiment of the present invention, the advantageous Ceramic Objects contain spinel (MgAbO4), which is essentially formed by heating a Green Body made from a Ready To Press (RTP) alumina-base powder and magnesia, where the magnesia originates from a grain growth-inhibiting material, which is soluble in the Liquid Medium. Preferably but not limited to the grain growth inhibiting material is MgCl2 or hydrates of MgCk.
In still another preferred embodiment of the present invention, the advantageous Ceramic Objects are suitable for use in ballistic protection, as grinding balls for grinding media, heat resistant bricks, manufacturing tools, wire guides and in other uses.
In still another preferred embodiment of the present invention, the advantageous Ceramic Objects are formed into various items, preferably into ceramic balls, suitable for use as grinding media, and also into wire guides, manufacturing tools, valves, and tap machines.
In still another preferred embodiment of the present invention, the advantageous Ceramic Objects are formed into various types of Ballistic Ceramic Objects, intended for use in ballistic protection systems.
In yet another preferred embodiment of the present invention, the Ballistic Ceramic Objects are shaped into any form, preferably into the form of a tile, a monolithic body, and a cylinder with or without a dome or domes. Measurement and Test Methods
I. RTP Powder analytical tests:
Table II below details particular features of both the LOD method for measuring water content in powders, when water is used as the Liquid Medium and the LOI method as an indication for the RTP Powder composition.
Table II RTP Powder analysis test methods
Figure imgf000010_0001
II. Ballistic Ceramics Objects quality tests:
There are two methods for testing Ballistic Ceramics Objects such as armor ceramic tiles; the ballistic test, which is a destructive test, and the chemical/physical test, which is a non-destructive test. Both methods are detailed below for ballistic tiles.
a. Non-destructive method:
The non-destructive method includes tests of the following properties: density, porosity (determined by the subtraction of the measured density from the theoretical density, as can be found in the relevant literature), hardness, grain size and presence of cracks, the latter being detected by a colored ink penetration test. The specification for the Ballistic Ceramics Objects relating to the invention, including a short description of the methods upon which it is based, is summarized in the following Table III:
Table HI Ballistic Ceramics Objects non- destructive quality test methods
Figure imgf000011_0001
Spread of coloring ink on the Ballistic Ceramic < 5% of the Object surface, followed by visual scanning for Ballistic
Presence of Penetrating the existence of cracks. Ceramic cracks coloring ink Objects have cracks
* D. Alon, D. G. Brandon, S. Nadiv and A. Rosen, "Introduction to materials engineering", PP. 200 - 201, Michlol - Publishing house, Technion Haifa, 1974.
In one preferred embodiment of the present invention, the ballistic tiles were found to be 50% harder, according to the hardness test which is listed in Table III, in comparison with commercial alumina-based ballistic tiles which were tested according to the same method.
Another preferred embodiment of the present invention provides advantageous Ceramic Objects having the properties of hardness of not less than about 1850 HV (according to the Vickers method) upon application of a load of about 10 kilograms, a density of not less than about 3.9 g/cm3 or greater (according to the Archimedes method or the Gas pycnometer method), and a grain size smaller than about 5 μm, preferably smaller than about 2 μm (according to the Scanning Electron Microscope method).
In still another embodiment of the present invention the density is 3.9 g/cm3.
b. Destructive method:
The destructive test is a ballistic test, carried out by a controlled gunfire test in which the type of gun, type of projectile, muzzle velocity, distance from the target and target set-up are controlled.
The results of the ballistic tests on the ballistic tiles produced according to the process of this invention were better than those for other commercial alumina-based ballistic tiles that were tested: The average residual penetration depth, obtained according to the present invention, and which resulted by firing armor piercing 7.62 mm projectiles, with a muzzle velocity of 800 m/sec, from a FNB semi-automatic rifle, shot 15 meter away from the target, was 0.54 mm, with a standard deviation of 0.22 mm, while the results of the same ballistic test, carried out under the same conditions on commercial alumina ballistic tiles, gave an average penetration depth of 3 mm.
Examples
The following exemplifies, without limiting the scope of the invention, illustrate some aspects of the present invention:
Example 1 - Preparation of the raw materials mixture
Water and magnesium chloride hexahydrate are introduced into a ball mill having zirconia milling balls and the ball mill is operated for several minutes. Then, the glue and pressing wax material is introduced and the ball mill is operated again for several minutes more. Finally, the alumina is introduced and the mill is operated in order to deagglomerate the alumina powder until a homogeneous slurry is formed. The preparation of the raw materials mixture is performed under normal room conditions (temperature of ca. 25 0C and 1 atm. pressure).
Example 2 - Removing the Liquid Medium by spray drying
An example for the removal of the Liquid Medium stage is the removal of most of the Liquid Medium by means of a spray drier, when water is the Liquid Medium as follows:
The raw materials mixture (formed in stage i.) and air, hereinafter "Feed Air" are fed simultaneously to the spray drier via an atomizing nozzle, so for example a ratio of 0.57 m3 of Feed Air to one liter of the raw materials mixture is kept and the Feed Air pressure is 0.5 bar. The nozzle sprays the raw material mixture and the Feed Air through the opening in the base of the drying chamber of the spray drier in the direction of the upper part of the chamber, in the form of a fountain and in a counter current direction to a stream of heated air which enters the spray dryer at the top of the drying chamber, hereinafter "Drying Air". The Drying Air temperature can be 25O0C. This method promotes the formation of the desired free flowing RTP Powder.
While examples of the invention have been described for purposes of illustration, it will be apparent that many modifications, variations and adaptations can be carried out by persons skilled in the art, without exceeding the scope of the claims.

Claims

1. Sintered alumina-based Ceramic Objects, wherein said Ceramic Objects are generated using a grain growth-inhibiting material, and a glue and pressing wax material, which are both soluble in a Liquid Medium, said Liquid Medium being selected from organic liquids, inorganic liquids, and a mixture thereof, and said grain growth-inhibiting material being a magnesium salt soluble in said Liquid Medium.
2. Ceramic Objects according to claim 1, wherein said magnesium salt is selected from the group consisting of magnesium halides, magnesium halide hydrates, and magnesium organic salts.
3. Ceramic Objects according to claim 1 having a hardness of not less than about 1850 HV (according to the Vickers method) upon application of a load of about 10 kilograms, a density of not less than about 3.9 g/cm3 or greater (according to the Archimedes method or the Gas pycnometer method), a grain size smaller than about 5 μm (according to the Scanning Electron Microscope method).
4. Ceramic Objects according to claim 3 having a grain size smaller than about 2 μm.
5. Ceramic Objects according to claim 1, wherein the Objects contain spinel (MgAbO4) essentially formed by heating a Green Body made from a Ready To Press (ETP) alumina-based powder which contains a grain growth-inhibiting material which is soluble in the Liquid Medium.
6. Ceramic Objects according to claim 5, wherein said grain growth- inhibiting material is MgCk or hydrates of MgCl2.
7. A Green Body made as described in claim 5, further comprising a glue and pressing wax material, and residual Liquid Medium.
8. Ceramic Objects according to claim 1, wherein the Objects are formed into various types of ceramic objects, preferably into ceramic ball mill objects intended for use as a grinding medium.
9. Ceramic Objects according to claim 1, wherein the Objects are intended for use in wire guides, manufacturing tools, valves, and tap mechanisms.
10. Ceramic Objects according to claim 1, wherein the Objects are formed into various forms of Ballistic Ceramic Objects intended for use in ballistic protection systems.
11. Ceramic Objects according to claim 10, wherein said Ballistic Ceramic Objects are shaped into any form, preferably selected from the form of a tile, the form of a monolithic body, and the form of a cylinder with or without a dome or domes.
12. Ceramic Objects comprising a sintered ceramic composition, said Ceramic Objects being generated using magnesium chloride or magnesium chloride hexahydrate, having a hardness of about 1850 HV or greater (according to the Vickers method) upon application of a load of about 10 kilograms, a density of 3.9 gr/cm3 (according to the Archimedes method or the Gas pycnometer method), and a grain size of about 5 μm or smaller (according to the Scanning Electron Microscope method) for use in ballistic protection, as grinding balls for grinding media, heat resistance bricks, manufacturing tools, wire guides and the like uses.
13. A Ready To Press Powder comprising alumina, a grain growth inhibiting material, a glue and pressing wax material, and a residue of Liquid Medium selected from organic liquids, inorganic liquids, and a mixture thereof, wherein said inhibiting material and said glue and pressing wax material are soluble in said Liquid Medium while the alumina is not soluble.
14. A Ready To Press Powder according to claim 13, wherein the grain growth-inhibiting material is MgCl2 or hydrates thereof.
15. A process for the preparation of Ceramic Objects wherein said Objects have a hardness of about 1850 HV or greater (according to the Vickers method) upon application of a load of about 10 kilograms, a density of about 3.9 g/cm3 or greater (according to the Archimedes method or the Gas pycnometer method) and grain size smaller than about 5 μm, (according to the Scanning Electron Microscope method), said process comprising the stages of: i. preparing the raw materials mixture, wherein the raw materials comprise alumina, a grain growth-inhibiting material, a glue and pressing wax material, and a Liquid Medium selected from organic liquids, inorganic liquids, and mixtures thereof, said grain growth- inhibiting material, and said glue and pressing wax material being soluble in said Liquid Medium while the alumina is not; ϋ. removing essentially all Liquid Medium, wherein said removal forms a Ready To Press (RTP) Powder, which is essentially a free flowing powder; iϋ. forming Green Bodies by placing the RTP Powder into a suitable mold, or molds with the desired dimensions and then applying the required pressure by using a suitable press; iv. removing essentially all of said glue and pressing wax material, and residues of said Liquid Medium in the Green Bodies, by heating in an appropriate furnace at 6000C - HOO0C, and v. sintering the resulting material to obtain the final Ceramic Objects of the desired grain size and mechanical properties, at an elevated temperature, maintaining it below the melting temperature of the alumina.
16. The process of claim 15, wherein said Liquid Medium is selected from organic liquids, inorganic liquids, and a mixture thereof in which the grain growth-inhibiting material and the glue and pressing wax material are soluble while the alumina is not.
17. The process of claim 15, wherein the preparation of the raw materials mixture stage comprises the steps of: a) adding to a homogenizing device the Liquid Medium; b) adding the grain growth-inhibiting material; c) operating the homogenizing device; d) adding the glue and pressing wax material; e) operating the homogenizing device; f) adding the alumina; and g) operating the homogenizing device.
18. The process of claim 15, wherein said grain growth-inhibiting material is magnesium chloride or magnesium chloride hydrate.
19. The sintered alumina-based Ceramic Objects according to any one of claims 1 to 6 for use in ballistic protection of people, vehicles, and equipment.
PCT/IL2006/001014 2005-09-08 2006-08-31 Improved alumina based ceramic objects WO2007029237A2 (en)

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CN106747351A (en) * 2016-11-29 2017-05-31 伍志文 The manufacturing process of aluminum oxide toughening ceramic tap main body and accessory
DE102017102975B4 (en) 2016-02-17 2022-03-10 BLüCHER GMBH Ballistic protective outerwear and ballistic protective clothing unit
CN115073145A (en) * 2021-03-15 2022-09-20 上海召明实业有限公司 Aluminum oxide bulletproof ceramic and preparation method thereof
CN117164340A (en) * 2023-11-02 2023-12-05 北京利尔高温材料股份有限公司 AlON and Al 2 O 3 -ZrO 2 Composite toughening phase, low-carbon magnesia carbon brick and preparation method thereof

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WO2012176196A1 (en) * 2011-06-23 2012-12-27 Dead Sea Bromine Company Ltd. Method of manufacturing improved alumina objects for various applications
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CN106747351A (en) * 2016-11-29 2017-05-31 伍志文 The manufacturing process of aluminum oxide toughening ceramic tap main body and accessory
CN115073145A (en) * 2021-03-15 2022-09-20 上海召明实业有限公司 Aluminum oxide bulletproof ceramic and preparation method thereof
CN117164340A (en) * 2023-11-02 2023-12-05 北京利尔高温材料股份有限公司 AlON and Al 2 O 3 -ZrO 2 Composite toughening phase, low-carbon magnesia carbon brick and preparation method thereof
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