IL176662A - Protection from kinetic threats using glass-ceramic material - Google Patents

Description

¾r DVN ·»39» rmn"? ircnj? -η^^τ PROTECTION FROM KINETIC THREATS USING GLASS-CERAMIC MATERIAL FIELD AND BACKGROUND OF THE INVENTION The present invention relates to the field of ballistic protection and specifically to methods and articles for protecting an object from kinetic threats using an article including a glass-ceramic component and methods for manufacturing such an article. The present invention also relates to the use of coal ash for the manufacture of an armor component. The present invention also relates to the field of materials and specifically to an improved method for manufacturing a crystalline material such as glass-ceramics.

A sensitive object is often protected by armor interposed between the sensitive object and an approaching kinetic threat and as a result the kinetic threat impacts with the armor instead of with the sensitive object. The armor is configured to neutralize the kinetic threat by one or more methods such as deflection of the kinetic threat, destruction/deformation of the kinetic threat and dissipation of the kinetic energy of the kinetic threat. In the art, known mechanisms for dissipating the kinetic energy of the kinetic threat include deformation of the kinetic threat, deformation of the armor, absorption of the kinetic energy of the kinetic threat and distribution of the kinetic energy over a large area.

Sensitive objects in many fields are increasingly subject to increasingly dangerous kinetic threats.

In the past, kinetic threats in the field of sports were rare. The speed of sports such as motorcycling, automobile racing, skiing and bobsledding has increased to the point where the danger from kinetic threats resulting from collision with static objects has increased significantly. Since sport performance is adversely affected by increased weight, the use of massive armor and shielding devices is impossible, necessitating the use of lightweight but not necessarily effective protection devices. There is a need to provide lightweight but effective protection from kinetic threats for individuals involved in sports.

Modern automobiles are constructed from thin metal or plastic panels designed to minimize vehicular weight and thus increase performance and economy of fuel use. At the same time, the cruising velocity of automobiles has continuously increased. Both factors together have led to an increase in traffic casualties. Although the effects of sudden deceleration cause most traffic casualties, a significant percentage of traffic casualties result from the penetration of objects into the passenger volume of an automobile through the thin panels. In the field of personal transport, there is a need to provide lightweight protection from objects penetrating the passenger volume of personal transport vehicles such as automobiles.

Satellites and space exploration vehicles are generally not protected from kinetic threats due to the prohibitive unit weight cost of launching an object with sufficient armor into orbit and due to the fact that the risk of catastrophic failure, for example resulting from impact with a meteorite, has been judged to be very low. However, the increasing density of debris at desired orbit altitudes ("space junk") increases the chance of such an impact occurring. In the field of aerospace, there is a need to protect satellites and other space vehicles from kinetic threats such as the impact of "space junk" with armor that weighs as little as possible so as to make launch financially feasible. Since satellites are generally not reparable, it is preferred that such protection be useful for protecting against multiple kinetic threats.

In the past, non-military vehicles and installations were not targets for attacks from kinetic threats. Fragment-projecting explosive devices, high-velocity firearms, especially automatic firearms, and large caliber firearms have become increasingly available and at the same time, the will to use these devices and firearms by both criminal and terrorist organizations against civilian and other non-military targets has increased. As a result traditionally "soft" vehicles such as civilian buses and trains, limousines, fuel transport vehicles, police vehicles, logistical vehicles such as trucks and light utility vehicles are increasingly hardened. Traditional armors are heavy. The increase in weight caused by the addition of sufficient armor reduces vehicle mobility, maneuverability and stability, requires a massive and expensive frame, and leads to greater wear and consequent increased acquisition and operating costs. In the field of civil defense and crime fighting there is a need for lightweight, simple to produce and cheap armor to neutralize kinetic threats to military, non-military and civilian vehicles.

Metal armor is generally chosen for protecting combat vehicles and military aircraft from kinetic threats. Increasingly, requirements for air transport and amphibious operation requires that lighter weight armor solutions be found. Prior-art ceramic armors are effective against single kinetic threat impacts but are significantly less effective against the increasingly common multiple and serial kinetic threats posed by fragment-projecting devices, cluster weapons and automatic weapons. There is a need for high-performance, lightweight materials for use in military armor applications with multiple-threat neutralization capabilities.

Individual armor became outmoded with the introduction of firearms. For the first half of the twentieth century it was believed that the small size and mobility of an individual person conferred sufficient defense from kinetic threats and was preferable to weighing down the individual with massive armor. With the increased availability and use of fragment-projecting explosive devices and high-velocity automatic firearms, the survivability of an individual subjected to standard kinetic threats is significantly reduced. As a result individual body armor is becoming standard equipment for high-risk individuals, police and infantry soldiers. However, current body armor materials are either too bulky, reducing the efficacy of the individual in performing standard tasks when worn, or provide insufficient protection from increasingly effective kinetic threats. Further, both fragment-projecting devices and automatic weapons produce multiple kinetic threats for which the protection afforded by currently available body armor is insufficient. In the field of personal defense, there is a need for lightweight body armor protection capable of protecting an individual from multiple kinetic threats such as produced by fragment-projecting explosive devices and high-velocity automatic firearms.

Materials used in currently available armors can be divided into three types: textiles, metals and ceramics.

Textile armors are considered lightweight, easy to produce, simple to install and relatively comfortable to wear as body armor. When a kinetic threat impacts textile armor, the kinetic threat is caught in a web of fibers. The fibers absorb and disperse the energy of the impact to other fibers. Specific textile armors include textiles woven from aramid fibers, e.g. Kevlar® (E.I. du Pont de Nemours and Company) and Twaron® (Teijin Twaron B.V., Arnhem, The Netherlands) and textiles based on polyethylene fibers, e.g. Dyneema® (Koninklijke DSM N.V., Heerlen, The Netherlands). Generally, textile armors are suitable for protecting against low energy threats such as shrapnel small caliber bullets having impact velocities up to about 450 m sec"1 but provide little protection against specially designed armor-piercing rounds and bullets from high-velocity firearms having typical impact velocities of 900 m sec" 1 unless used in conjunction with a metal or ceramic strike face.

Metal armor provide excellent protection from kinetic threats, are cheap and relatively easy to produce from alloys, usually including aluminum, cobalt, titanium and iron. A kinetic threat impacting metal armor is deflected or deformed and the kinetic energy dissipated by inelastic and elastic deformation of the armor. Metal armor is effective against multiple kinetic threats since damage to the armor caused by the kinetic threat is generally local to the area of impact. However, the weight of metal armor is such that providing sufficient protection against increasingly common kinetic threats is often impractical.

Although expensive, armor made of ceramic plates provides a high level of protection from kinetic threats and is light in weight in comparison to equivalent metal armor. Ceramics most often used for protection of objects from kinetic threats are monolithic ceramics such as A1203, B4C, SiC and A1N.

A kinetic threat impacting ceramic armor is deformed and the kinetic energy dissipated by inelastic deformation of the armor through a combination of a pulverization energy mechanism and a fracture energy mechanism. In the pulverization energy mechanism, a comminution zone of pulverized ceramic in the shape of a conoid emerging from the impact point is produced. In the fracture energy mechanism, kinetic energy is absorbed by the ceramic plate, distributed throughout the plate and subsequently expended by the shattering of the ceramic plate itself along many radial and circumferential cracks. A liner, usually of textile or metal armor located behind the ceramic, absorbs and dissipates any residual kinetic energy of fragments of the ceramic armor and of the kinetic threat. The use of ceramic materials for protecting objects from kinetic threats is discussed in, for example, Medvedovski, American Ceramic Society Bulletin (2002), 81 (3), 27-32 and U.S. Patent No. 3,765,600, U.S. Patent No. 4,953,442, U.S. Patent No. 4,91 1,061, U.S. Patent No. 4,138,456, U.S. Patent No. 5,456,156, U.S. Patent No. 5,469,773, U.S. Patent No. 5,705,764, U.S. Patent No. 6,112,635 and U.S. Patent No. 6,408,733.

In the art it is known that energy dissipation through the fracture energy mechanism is most efficient in ceramic materials that are hard, stiff and have a high sonic velocity. A high stiffness leads to maximal post-impact stress in the ceramic with very little elastic deformation whereas a high sonic velocity spreads the stress throughout the ceramic plate before actual shattering occurs. Ultimately, the impact energy of the kinetic threat is dissipated by the cleavage of many chemical bonds of the ceramic plate, thereby shattering the entire ceramic plate, see for example U.S. patent No. 5,469,773. Very hard ceramics are preferred so as to dissipate some kinetic energy by deformation of the kinetic threat and to reduce the chance of follow-through penetration subsequent to ceramic plate shattering.

Ceramic-matrix composites are increasingly used instead of monolithic ceramics for protecting objects from kinetic threats. The primary advantage of ceramic-matrix composites compared to monolithic ceramics is improved mechanical properties. Suitable ceramic-matrix composites include fiber-reinforced materials such as A i SiC and A1203/C, ceramic/particulates such as TiB2/B4C and TiB2/SiC and cermets such as SiC/Al, TiC/N and B4C/A1. Ceramic-matrix composites are generally prohibitively expensive to manufacture and process.

Since the kinetic energy of an impacting kinetic threat is dissipated by shattering of the ceramic plate, armor including a ceramic plate as a component is generally useful for protecting an object only against impact from a single kinetic threat. Due to the extensive shattering of the ceramic plate, subsequent impacts have a statistically significant chance to impact on a crack and penetrate with little or no resistance. Further, the shards of the ceramic plate are relatively small and have little mass: the small size means that there only a few bonds are available for dissipation of energy from subsequent kinetic threat impacting on such a shard and that such a shard may be pushed through by an impacting kinetic threat into the sensitive object being protected.

One method to provide multiple kinetic threat protection involves using many small ceramic scales to cover the surface of a protected object. When an individual small ceramic scale shatters, the protected object is still substantially protected from subsequent threats. Such solutions have many disadvantages, including the high price, added manufacturing complexity and the existence of chinks between any two ceramic scales. Multiple kinetic threats such as those projected by automatic weapons or cluster weapons can incidentally impact at the chinks in the armor or areas where ceramic scales were destroyed by previously impacting kinetic threats. As with shards, the small size of each individual scale means that the amount of energy potentially dissipated is relatively small.

A class of material not often used for protecting against kinetic threats is that of glass-ceramics.

In U.S. Patent No. 4,476,653 is taught the use of a glass-ceramic material as armor. A composition of U.S. Patent No. 4,476,653 includes Li20 (9.5% - 15% by weight), A1203 (1.0% - 6.0% by weight), Si02 (78.5% - 84.5% by weight) and K20 ,(1.0% - 4.0% by weight) as lithium disilicate, cristobalite and spinel crystals in a glassy matrix, where the essential nucleation agent is a combination of Ti02, Zr02 and Sn02 in a ratio of 3:2:1. A preferred glass-ceramic of U.S. Patent No. 4,473,653 is reported to have a hardness of between 4.95 and 6.23 GPa, a density of 2.4-2.5 g cm"3 and a coefficient of thermal expansion (TCLE) of greater than lOOxlO"7 °C_1. The maximal Ti02 content in a composition of U.S. Patent No. 4,473,653 is 3%. The impact of a single kinetic threat (7.62 mm copper jacketed bullet at 152 cm with a muzzle velocity of 777 m sec"1) on a 21.7 mm thick glass-ceramic plate of U.S. Patent 4,476,653 leads to shattering of the plate.

In U.S. Patent No. 5,060,553 is taught the use of monolithic, sintered or hot-pressed glass-ceramic plates for use as armor. Suitable glass-ceramics according to the teachings of U.S. Patent No. 5,060,553 are silicates of lithium zinc, lithium aluminum, lithium zinc aluminum, lithium magnesium, lithium magnesium aluminum, magnesium aluminum, calcium magnesium aluminum, magnesium zinc, calcium magnesium zinc, zinc aluminum, barium silicate and both calcium phosphates and calcium silico phosphates. In a first embodiment of the teachings of U.S. Patent No. 5,060,553 is disclosed a composition that includes, in addition to other components, 7% by weight A1203 and 72% by weight Si02 having a density of 2.45 g cm"3, a hardness of 5.7 GPa, and an elastic modulus of 104 GPa. In a second embodiment of the teachings of U.S. Patent No. 5,060,553 is disclosed a composition that includes, in addition to other components, 13% by weight A1203 and 71% by weight Si02 having a density of 2.4 g cm" , a hardness of 5.25 GPa, and an elastic modulus of 88 GPa. In a third embodiment of the teachings of U.S. Patent No. 5,060,553 is disclosed a composition that includes, in addition to other components, 33% by weight A1203 and 36% by weight Si02 having a density of 3.1 g cm"3, a hardness of 10.8 GPa, and an elastic modulus of 150 GPa. In a fourth embodiment of the teachings of U.S. Patent No. 5,060,553 is disclosed a composition that includes, in addition to other components, 26% by weight A1203 and 50% by weight Si02 having a density of 2.7 g cm" , a hardness of 6.0 GPa and an elastic modulus of 105 GPa. Although a mechanism for energy dissipation of an impacting kinetic threat is discussed, no report as to the actual ability of the compositions in neutralizing kinetic threats is presented.

In U.S. Patent No. 5,045,371 is taught armor including ceramic particles dispersed in a glass matrix. In U.S. Patent No. 5,469,773 is taught armor made of a composition including 92% MgO ceramic powder hot pressed with glass. These materials are not glass-ceramics.

It would be advantageous to have a material that provides protection from a kinetic threat on par with that of ceramics known in the art yet is lighter, is cheaper to manufacture and is more effective against multiple kinetic threats.

SUMMARY OF THE INVENTION At least some of the objectives above are achieved by the teachings of the present invention.

The teachings of the present invention provide for the use of glass-ceramics for protecting objects against kinetic threats. Although efforts have been made to provide glass-ceramics for protection against kinetic threats, notably U.S. Patent No. 4,473,653 and U.S. Patent No. 5,060,553, these efforts have not met with success.

Some embodiments of the present invention provide a method of protecting an object from a kinetic threat by providing a shield, armor or such-like item including a glass-ceramic component. It has been found, for example in the case of the ovel glass-ceramic composition including an Anorthite phase of the present invention, that some glass-ceramics neutralize an impacting kinetic threat primarily through a pulverization energy mechanism as opposed to primarily a fracture energy mechanism as occurs with monolithic ceramics or ceramic-matrix composites. Thus a glass-ceramic component used in implementing the teachings of the present invention preferably dissipates the energy of impact of a kinetic threat by a pulverization energy mechanism. In the pulverization energy mechanism, the glass-ceramic component is pulverized in the immediate vicinity of the impact of a kinetic threat. As pulverization necessarily requires destruction of many bonds, much kinetic energy is dissipated by destruction of only a small part of the glass-ceramic component. Since damage caused by an impacting kinetic threat is localized and since the glass-ceramic component does not significantly crack or shatter, the overall structural integrity of the shield, armor or item is retained, providing protection from multiple kinetic threats.

According to the teachings of the present invention there is provided a method of protecting an object from kinetic threats comprising providing the object with armor including a glass-ceramic component, the glass-ceramic component including an Anorthite phase.

According to the teachings of the present invention there is provided an article for protecting an object from a kinetic threat including a glass-ceramic component (for example, is part of or is integrated into the article), the glass-ceramic component comprising an Anorthite phase. In embodiments of the present invention, the article further comprises a textile component (e.g., a backing or spall layer), for example including aramid and/or polyethylene fibers. In embodiments of the present invention, the article further comprises a metal component (e.g., an aluminum or steel backing plate or mesh). In embodiments of the present invention, the article has the shape of a component of or of an entire armor plate, armor sheet, armor scale, armor panel, bullet-proof vest, body armor, panel, door panel, floor panel, wall panel, helmet, seat, aircraft, rotary wing aircraft, fixed wing aircraft, armored fighting vehicle, limousine or other motor vehicle.

In embodiments of the present invention, a glass-ceramic component includes an Anorthite phase that is at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80% and even at least about 90% by weight of the glass-ceramic component.

In an embodiment of the present invention, the glass-ceramic component comprises at least about 5.0% by weight CaO.

In an embodiment of the present invention, the glass-ceramic component comprises, both CaO and AI2O3, the weight ratio of CaO to A1203 preferably being between about 1 : 1.3 and about 1 : 2.5, between about 1 : 1.4 and about 1 : 2.3, between about 1 : 1.6 and about 1 : 2.1, between about 1 : 1.7 and about 1 : 1.95 or between about 1 : 1.75 and about 1 : 1.89.

In an embodiment of the present invention, the glass-ceramic component comprises both CaO and Si02, the weight ratio of CaO to Si02 preferably being between about 1 : 1.5 and about 1 : 3.0, between about 1 : 1.6 and about 1 : 2.8, between about 1 : 1.9 and about 1 : 2.4, between about 1 : 2.0 and about 1 : 2.3 or between about 1 : 2.1 and about 1 : 2.2.

In an embodiment of the present invention, the glass-ceramic component comprises between about 15% and 23% by weight Si02, between about 13% and 20% by weight A1203 and between about 7% and 11% by weight CaO.

In an embodiment of the present invention, the glass-ceramic component comprises between about 17% and 26% by weight Si02, between about 15% and 22% by weight A1203 and between about 8% and 12% by weight CaO.

In an embodiment of the present invention, the glass-ceramic component comprises between about 19% and 28% by weight Si02, between about 16% and 24% by weight A1203 and between about 9% and 13% by weight CaO.

In an embodiment of the present invention, the glass-ceramic component comprises between about 21 % and 31 % by weight Si02, between about 18% and 27% by weight A1203 and between about 10% and 14% by weight CaO.

In an embodiment of the present invention, the glass-ceramic component comprises between about 22% and 34% by weight Si02, between about 19% and 29% by weight A1203 and between about 10% and 16% by weight CaO.

In an embodiment of the present invention, the glass-ceramic component comprises between about 24% and 36% by weight Si02, between about 21% and 31% by weight A1203 and between about 11% and 17% by weight CaO.

In an embodiment of the present invention, the glass-ceramic component comprises between about 26% and 39% by weight Si02, between about 22% and 33% by weight A1203 and between about 12% and 18% by weight CaO.

In an embodiment of the present invention, the glass-ceramic component comprises between about 28% and 41% by weight Si02, between about 24% and 36% by weight A1203 and between about 13% and 19% by weight CaO.

In an embodiment of the present invention, the glass-ceramic component comprises between about 29% and 44% by weight Si02, between about 25% and 38% by weight A1203 and between about 14% and 20% by weight CaO.

In an embodiment of the present invention, the glass-ceramic component comprises between about 31% and 46% by weight Si02, between about 26% and 40% by weight A1203 and between about 14% and 22% by weight CaO.

In an embodiment of the present invention, the glass-ceramic component comprises at least one crystalline phase in addition to the Anorthite phase. Preferably at least one of the at least one additional crystalline phases has a TCLE (thermal coefficient of linear expansion) similar to that of Anorthite, that is between about 5 x 10"7 °σ' and about 250 x 10"7 °C"1, preferably between about 10 x 10"7 °C"' and about 160 x 10"' °C"1 and even more preferably between about 20 x 10" °C" and about 80 x 7 1 10" °C" . In a preferred embodiment of the present invention, at least one of the at least one additional crystalline phases is crystalline Ti02, especially Rutile. In an embodiment of the present invention, the glass-ceramic component includes at least 0.3%, at least 1%, at least 2%, at least 4% or even at least 6% by weight Ti02. Preferably, the glass-ceramic of the present invention includes between about 0.3% and 5% or between about 5% and 10% by weight Ti02.

According to the teachings of the present invention there is also provided a method of manufacturing an article for protecting an object from a kinetic threat comprising: a. providing a molten glass composition at a first temperature Tl including more than about 5% by weight CaO; b. devitrifying the glass composition; and c. (simultaneously or subsequently) fashioning the glass composition into a glass-ceramic structure. According to embodiments of the present invention, the glass-ceramic structure is combined with additional components (e.g., metal or fabric components) so as to yield the item for protecting an object from a kinetic threat.

In an embodiment of the present invention, the molten glass composition comprises molten coal ash.

To fashion a glass-ceramic component from the molten glass composition, devitrification is preferably performed while press molding.

In embodiments of the present invention, devitrification is performed under a one-stage or a two-stage crystallization regime (vide infra). Preferably, devitrification is performed in accordance with the crystallization regime of the present invention.

Generally, devitrification involves maintaining a molten glass composition within an appropriate temperature range for a period of time sufficient to allow crystallization of at least some of the molten glass composition.

In embodiments of the present invention, the devitrification includes maintaining the glass composition within a relatively narrow temperature range for a period of time sufficient to allow crystallization of at least some of the glass composition, that is, a one-stage crystallization regime.

In embodiments of the present invention, the molten glass composition is contained in a mold inside a chamber of a furnace provided with a heating controller that is configured to control the rate of heating of the chamber and the devitrification of the molten glass composition includes the steps of: i) using the heating controller to reduce the temperature of the chamber to a second temperature T2 so as to allow formation of nucleation centers in the molten glass composition; ii) using the heating controller to increase the chamber temperature from the second temperature T2 to a third temperature T3 at a first rate; iii) using the heating controller to increase the chamber temperature from the third temperature T3 to a fourth temperature T4 at a second rate; and iv) allowing the glass composition to crystallize, yielding the crystalline object.

In embodiments of the present invention, the second temperature T2 is between about 650°C and about 750°C. In embodiments of the present invention the fourth temperature T4 is between about 900°C and about 1000°C.

In embodiments of the present invention, subsequent to (i) the heating controller is used to maintain the chamber temperature at the temperature T2 for a period of time sufficient to allow the formation of more nucleation centers in the molten glass composition. The formation of more or less nucleation centers often influences physical properties of glass-ceramic structures fashioned according to the teachings of the present invention.

In embodiments of the present invention, the chamber temperature is increased beyond the fourth temperature T4 for crystallization. In embodiments of the present invention, once the fourth temperature T4 is attained the chamber temperature is allowed to cool either because a sufficient degree of crystallization has been attained or because sufficient crystallization occurs during the cooling process. In embodiments of the present invention, subsequent to (iii) the heating controller is used to maintain the chamber temperature at least at the fourth temperature T4 for a period of time sufficient to allow the crystallization of the glass composition. A greater or lesser extent of crystallization often influences physical properties of glass-ceramic structures fashioned according to the teachings of the present invention.

In embodiments of the present invention, the increase from the second temperature T2 to the third temperature T3 is monotonic, that is the heating controller is set to increase the temperature between T2 and T3 at a constant first rate.

In embodiments of the present invention, the increase from the second temperature T3 to the third temperature T4 is monotonic, that is the heating controller is set to increase the temperature between T3 and T4 at a constant second rate.

In embodiments of the present invention, the first rate and the second rate of temperature increase are substantially equal, that is a two-stage crystallization regime.

In embodiments of the present invention, the second rate is substantially lower than the first rate, that is the crystallization regime of the present invention.

In embodiments of the present invention, the first rate is between about 10°C h"1 and about 60°C h"\ or between about 20°C h"1 and about 40°C h"1.

In embodiments of the present invention, the second rate is between about 2°C h"1 and about 15°C h"1, or between about 3°C h"1 and about 10°C h"1.

In embodiments of the present invention, the first rate is at least twice the second rate, at least three times greater than the second rate and even at least four times greater than the second rate.

In an embodiment of the present invention, the molten glass composition comprises, amongst other components, both CaO and AI2O3, the weight ratio of CaO to A1203 preferably being between about 1 : 1.3 and about 1 : 2.5, between about 1 : 1.4 and about 1 : 2.3, between about 1 : 1.6 and about 1 : 2.1, between about 1 : 1.7 and about 1 : 1.95 or between about 1 : 1.75 and about 1 : 1.89.

In an embodiment of the present invention, the molten glass composition comprises, amongst other components, both CaO and Si02, the weight ratio of CaO to Si02 preferably being between about 1 : 1.5 and about 1 : 3.0, between about 1 : 1.6 and about 1 : 2.8, between about 1 : 1.9 and about 1 : 2.4, between about 1 : 2.0 and about 1 : 2.3 or between about 1 : 2.1 and about 1 : 2.2.

In an embodiment of the present invention, the molten glass composition comprises between about 15% and 23% by weight Si02, between about 13% and 20% by weight A1203 and between about 7% and 11% by weight CaO.

In an embodiment of the present invention, the molten glass composition comprises between about 17% and 26% by weight Si02, between about 15% and 22% by weight A1203 and between about 8% and 12% by weight CaO.

In an embodiment of the present invention, the molten glass composition comprises between about 19% and 28% by weight Si02, between about 16% and 24% by weight A1203 and between about 9% and 13% by weight CaO.

In an embodiment of the present invention, the molten glass composition comprises between about 21% and 31% by weight Si02, between about 18% and 27% by weight A12Q3 and between about 10%» and 14% by weight CaO.

In an embodiment of the present invention, the molten glass composition comprises between about 22% and 34% by weight Si02, between about 19% and 29% by weight A1203 and between about 10% and 16% by weight CaO.

In an embodiment of the present invention, the molten glass composition comprises between about 24% and 36% by weight Si02, between about 21% and 31% by weight A1203 and between about 11% and 17% by weight CaO.

In an embodiment of the present invention, the molten glass composition comprises between about 26% and 39% by weight Si02, between about 22% and 33% by weight A1203 and between about 12% and 18% by weight CaO.

In an embodiment of the present invention, the molten glass composition comprises between about 28% and 41% by weight Si02, between about 24% and 36% by weight A1203 and between about 13% and 19% by weight CaO.

In an embodiment of the present invention, the molten glass composition comprises between about 29% and 44% by weight Si02, between about 25% and 38% by weight A1203 and between about 14% and 20% by weight CaO.

In an embodiment of the present invention, the molten glass composition comprises between about 31% and 46% by weight Si02, between about 26% and 40% by weight A1203 and between about 14% and 22% by weight CaO.

In an embodiment of the present invention, the molten glass composition comprises Ti02. In an embodiment of the present invention, the molten glass composition comprises a nucleating agent, preferably Ti02. In an embodiment of the present invention, the molten glass composition includes at least 0.3%, at least 1%, at least 2%, at least 4% or even at least 6% by weight Ti02. In an embodiment of the present invention, the molten glass composition includes between about 0.3% and 5% by weight Ti02 or between about 5% and 10% by weight Ti02.

According to the teachings of the present invention there is also provided a method for the manufacture of a crystalline object, comprising: a) providing a furnace (e.g., a gas-fired furnace) comprising at least one chamber, within the chamber a mold containing a substrate (e.g., a glass composition), and a heating controller configured to control the rate of heating the chamber; b) using the heating controller to raise the temperature of the chamber to a first temperature Tl so as to melt the substrate (forming a molten substrate); c) using the heating controller to reduce the temperature of the chamber to a second temperature T2 so as to allow formation of nucleation centers in the molten substrate; d) using the heating controller to increase the chamber temperature from the second temperature T2 to a third temperature T3 at a first rate; e) using the heating controller to increase the chamber temperature from the third temperature T3 to a fourth temperature T4 at a second rate; and f) allowing the substrate to crystallize, yielding the crystalline object wherein the second rate is substantially lower than the first rate.

In embodiments of the present invention, subsequent to (c) the heating controller is used to maintain the chamber temperature at the temperature T2 for a period of time sufficient to allow the formation of more nucleation centers in the substrate. The formation of more or less nucleation centers often influences physical properties of a crystalline object manufactured according to the teachings of the present invention.

In embodiments of the present invention, the chamber temperature is increased beyond the fourth temperature T4 for crystallization. In embodiments of the present invention, once the fourth temperature T4 is attained the chamber temperature is allowed to cool either because a sufficient degree of crystallization has been attained or because sufficient crystallization occurs during the cooling process. In embodiments of the present invention, subsequent to (e) the heating controller is used to maintain the chamber temperature at least at the fourth temperature T4 for a period of time sufficient to allow the crystallization of the substrate. A greater or lesser extent of crystallization often influences physical properties of crystalline objects manufactured according to the teachings of the present invention.

In embodiments of the present invention, the increase from the second temperature T2 to the third temperature T3 is monotonic, that is the heating controller is set to increase the temperature between T2 and T3 at a constant first rate.

In embodiments of the present invention, the increase from the second temperature T3 to the third temperature T4 is monotonic, that is the heating controller is set to increase the temperature between T3 and T4 at a constant second rate.

In embodiments of the present invention, the first rate is between about 10°C h"1 and about 60°C h'1, or between about 20°C h"1 and about 40°C h"1.

In embodiments of the present invention, the second rate is between about 2°C h"1 and about 15°C h"1, or between about 3°C h"1 and about 10°C h"1.

In embodiments of the present invention, the first rate is at least twice the second rate, at least three times greater than the second rate and even at least four The teachings of the present invention provide glass-ceramics material that may be produced from cheap raw materials, especially coal ash, and yet has good material properties, allowing the production of high-added value products such as the armor and such articles as discussed herein. Thus, according to the teachings of the present invention there is also provided the use of coal ash for the manufacture of an armor component (e.g., armor plates, armor scales and armor panels). In embodiments of the present invention the armor component comprises or is a glass-ceramic.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings: FIG. 1 (prior art) is a graph showing the relationship between temperature and the nucleation center formation rate (dashed) and the crystallization rate (solid); FIG. 2 depicts a furnace useful in implementing the crystallization regime of the present invention; FIG. 3 is a graph showing the temperature setting (in degrees Celsius) as a function of time (in hours) of a temperature controller implementing the crystallization regime of the present invention; FIG. 4 is a reproduction of an image of the damage caused to a plate of the composition of the present invention by impact of multiple bullets; and FIG. 5 is a reproduction of an electron microscope image of the surface of a composition of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is of a method and of an article of manufacture for protecting an object from kinetic threats. The present invention is also of a method of manufacturing an article for protecting an object from a kinetic threat. The present invention is also of a method for the manufacture of a crystalline object. The present invention is also of the use of coal ash for the manufacture of an armor component.

As used herein, the terms "comprising" and "including" or grammatical variants thereof are to be taken as specifying the stated features, integers, steps or components but do not preclude the addition of one or more additional features, integers, steps, components or groups thereof. This term encompasses the terms "consisting of and "consisting essentially of.

The phrase "consisting essentially of or grammatical variants thereof when used herein are to be taken as specifying the stated features, integers, steps or components but do not preclude the addition of one or more additional features, integers, steps, components or groups thereof but only if the additional features, integers, steps, components or groups thereof do not materially alter the basic and novel characteristics of the claimed composition, device or method. 17 \Ί '6662/2 As used herein, the term "process" and the term "method" refers to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the chemical, material, defense and ceramic arts.

The principles and uses of the processes, compositions and methods of the present invention may be better understood with reference to the description, figures and examples herein.

Before explaining at least one embodiment of the present invention in detail, it is to be understood that the present invention is not limited in its application to the details set forth in the following description or exemplified by the Examples. The present invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

In the present invention it has been found that glass-ceramics are a class of materials useful for protecting objects from kinetic threats. Glass-ceramics are compositions containing one or more crystalline phases uniformly distributed in a glassy (amorphous) phase. Glass-ceramics are formed by devitrification of molten glass, usually in the presence of a nucleating agent, the crystalline phase or phases produced by cooling a molten glass composition so that a portion of the composition crystallizes while the remainder of the composition (the matrix) solidifies in a glassy state. The crystalline phase or phases are typically uniformly dispersed throughout the glassy phase and generally constitute at least 50 percent by weight of the total composition. Glass-ceramics generally have high strength, high thermal conductivity, low thermal expansion, are resistant to thermal shock and are cheaply and easily fabricated.

Generally, the physical properties of a glass-ceramic material are dependent on number of material properties. The first property is the identity and relative abundance of the crystal phase or phases. The second property is the ratio of crystalline phase to amorphous phase. Generally, the higher the proportion of the amorphous phase the softer and more frangible the glass-ceramic. The third property is crystal size. The smaller the crystals, the more difficult it is for cracks to spread throughout a glass- ceramic structure, making such a structure more robust. Generally, when the crystals are smaller than 1 micron in diameter the structure is sufficiently robust for most implementations.

The crystal size and crystal content in a glass-ceramic material is dependent on at least two production parameters: the rate of formation of nucleation centers (which occurs at a maximal rate at some temperature Tmaxl) and the rate of crystal growth (which occurs at a maximal rate at some temperature Tmax2, where Tmax2 > Tmaxi), see Figure 1. Ideally, once Tmaxl and Tmax2 are known, a crystallization regime can be formulated. The problem is that Tmaxl and TmaX2 are dependent on many factors, are not predictable and fluctuate depending on many conditions.

Generally, when a new glass-ceramic composition is formulated, preferred furnace conditions such as temperatures Tmaxl and Tmax2, rates of heating are determined using a small-scale furnace holding a single or a few workpieces at any one time. In subsequent scale-up to a furnace used for simultaneously manufacturing many glass-ceramic workpieces, under conditions which are identical or similar to those optimized using the small-scale furnaces, a very high percentage of workpieces are rejected. These include workpieces that are cracked or have improperly crystallized, such that the physical properties are unsuitable for the intended use. This is a result of the fact that temperature, heat transfer and heating rate in a furnace chamber are spatially inhomogeneous, especially for large-volume production furnaces chambers filled with many workpieces.

As a compromise, in the art it is known to use either a one-stage crystallization regime or a two-stage crystallization regime.

In a one-stage crystallization regime, a molten substrate is maintained at a single temperature midway between Tmaxi and Tmax2, the single temperature giving an acceptable compromise of properties.

In a two-stage crystallization regime, a molten substrate is maintained at a first temperature, the first temperature being roughly Tmaxi . After a certain amount of time deemed sufficient for formation of enough nucleation centers, the temperature of the substrate is raised to a second higher temperature, the second temperature being roughly Tmax2.

The one-stage and two-stage crystallization regimes generally provide a reasonable percentage of rejected workpieces. That said, it is generally preferable to reduce the percentage of rejected workpieces even further. Further, the batch to batch reproducibility of one-stage and two-stage crystallization regimes is low, with the percentage of rejected workpieces varying greatly as a result of varying ambient temperature, pressure and humidity. Further, for certain glass-ceramic substrates it is very difficult if not impossible to find parameters for either the one-stage or two-stage crystallization regimes giving a reasonable percentage of rejected workpieces.

It has been found that it is possible to achieve a very low percentage of rejected workpieces with a very high batch-to-batch reproducibility when using the crystallization regime of the present invention. It is believed that the applicability of the crystallization regime is not limited to the devitrification of glass compositions to yield glass-ceramics but is generally applicable to the manufacture of crystalline objects from molten substrates.

The crystallization regime of the present invention can be understood with reference to Figure 2 and Figure 3. In Figure 2 a furnace 10 is provided with a heating controller 12 in communication with temperature sensors 14 and a heating device 16 (in Figure 2, a gas heating system). Inside a chamber 18 of furnace 10 are three racks 20. On each rack 20 are found three molds 22 containing a molten substrate 24. In Figure 3, an example of the temperature setting of heating controller 12 as a function of time is graphically depicted.

Heating controller 12 is used to raise the temperature inside chamber 18 to a first temperature Tl high enough so as to melt substrate 24.

Heating controller 12 is then used to reduce the temperature in chamber 18 to a second temperature T2 so as to allow formation of nucleation centers in molten substrate 24. Generally, but not necessarily, T2 is roughly equal to or somewhat lower than Tmaxi of substrate 24. In Figure 3, it is seen that from hour 1 to hour 2 heating controller 12 is set to maintain the temperature of chamber 18 at 725 °C.

Heating controller 12 is then used to increase the chamber temperature from the second temperature T2 to a third temperature T3 at a first rate and subsequently from the third temperature T3 to a fourth temperature T4 at a second rate where the second rate is substantially slower than the first rate during which time the rate of nucleation center formation gradually decreases but the rate of crystallization increases. In embodiments of the present invention, the first rate is at least twice the second rate, at least three times greater than the second rate and even at least four n times greater than the second rate. Generally, but not necessarily, T4 is roughly equal to or somewhat higher than Tmax2 of substrate 24. In Figure 3 it is seen that from hour 2 to hour 8 heating controller is set to increase the chamber temperature from the second temperature T2 (725 °C) to a third temperature T3 (900 °C) at a first rate (29 °C hour"1) and from hour 8 to hour 18 to increase the chamber temperature from third 5 temperature T3 to fourth temperature T4 (950 °C) at second rate (6.25 °C hour"1).

Although not necessary, it is often advantageous to maintain chamber 18 at approximately second temperature T2 for a period of time as depicted in Figure 3 (hour 1 to hour 2) to allow the formation of more nucleation centers in substrate 24.

The formation of more or less nucleation centers often influences physical properties 10 of a crystalline object manufactured according to the teachings of the present invention.

In embodiments of the present invention, the chamber temperature is increased beyond the fourth temperature T4 allowing further crystallization. In embodiments of the present invention, once the fourth temperature T4 is attained the chamber 15 temperature is allowed to cool as depicted in Figure 3, either because a sufficient degree of crystallization has been attained or because sufficient crystallization occurs during the cooling. In embodiments of the present invention, it is often advantageous to maintain chamber 18 about at fourth temperature T4 to allow crystallization of substrate 24. A greater or lesser extent of crystallization often influences physical 20 properties of crystalline objects manufactured according to the teachings of the present invention.

Preferably but not necessarily, the increase from the second temperature T2 to the third temperature T3 is monotonic, that is heating controller 12 is set to increase the temperature between T2 and T3 at a constant first rate as depicted in Figure 3. 25 Preferably but not necessarily, the increase from the third temperature T3 to the fourth temperature T4 is monotonic, that is heating controller 12 is set to increase the temperature between T3 and T4 at a constant second rate as depicted in Figure 3.

In embodiments of the present invention, the first rate is between about 10°C h"1 and about 60°C h"1, or between about 20°C h"1 and about 40°C h"1. In embodiments of the 30 present invention, the second rate is between about 2°C h"1 and about 15°C h"1, or ,r between about 3°C h"1 and about 10°C h"1. Such rates have been found useful for manufacturing glass-ceramics, especially Anorthite containing glass-ceramics described herein.

It is important to note that although the crystallization regime of the present invention described above and in Figure 3 includes only two rates of temperature increase between T2 and T4, embodiments of the present invention are countenanced having three rates, four rates and even more rates, including a continuously varying rate. Thus, the crystallization regime of the present invention is characterized amongst other characteristics, that during a stage of the crystallization where the furnace temperature is increases, the rate of temperature increase is reduced at least once.

An important advantage of glass-ceramics over other ceramics used in armor applications is the low cost of production. Glass-ceramics are made by heating a substrate to a temperature that is low in comparison to temperatures required for producing monolithic ceramics. Thus, the cost of energy and the cost of vessels necessary for producing glass-ceramics are relatively low in comparison to those of monolithic ceramics. Since glass-ceramics are well defined crystalline phases found within an amorphous glassy matrix, the requirements for composition of a substrate from which a glass-ceramic are made are lenient. Thus, an additional reason for the low cost of glass-ceramics is that in contrast with ceramics used in armor applications made from highly pure components in exact proportions, glass-ceramics are often fabricated from cheap impure starting materials such as ores and sand or industrial slag and ash, see for example, Russian Patent RU 2052400, English Patent GB 1,459,178, as well as U.S. Patent No. 4,191,546, U.S. Patent No. 5,521,132 and U.S. Patent No. 5,935,885.

As discussed above, the fracture energy mechanism by which monolithic ceramic armors dissipate energy is not an optimum way for dissipating the energy of kinetic threat. The fracture energy mechanism produces many potentially dangerous ceramic shards and renders a shield device useful against only a single kinetic threat. It has been found that at least some glass-ceramics dissipate the energy of impact of a kinetic threat primarily by a pulverization energy mechanism instead of by primarily a fracture energy mechanism.

Thus, an aim of the present invention is to provide a method for protecting an object from kinetic threats by dissipating energy according to three concepts. The first concept is that damage to a shielding device caused by a kinetic threat is localized to the vicinity of impact. The second concept is that energy dissipation through breaking of chemical bonds is maximized by a pulverization energy mechanism rather than a fracture energy mechanism. The third concept is that the formation of harmful shards, ricochets, spatters and spalls that may damage the protected object or other objects in the vicinity is preferably reduced if not eliminated.

A material for implementing the method of the present invention is preferably, but not necessarily, harder than the kinetic threat. When a kinetic threat impacts a harder shield material, the kinetic threat itself deforms and fragments, a process that dissipates kinetic energy. Further, fragmentation of an impacting kinetic threat reduces the chance of ricochet or follow-through penetration.

In the art, ceramics used in protecting against kinetic threats are chosen to be brittle and as hard as possible. These properties enhance the extensive shattering of the ceramic material so as to maximize the amount of kinetic energy used for breaking chemical bonds of the ceramic material. In contrast, a material used in protecting ah object according to the teachings of the present invention is preferably hard enough so as to deform and fragment the kinetic threat, but not be brittle. Thus, in contrast to the prior art where ceramic materials used for protection against kinetic threats have a hardness of greater than 12 GPa [HV] (see, for example U.S. Patent No. 5,443,917), materials useful in implementing the teachings of the present invention optionally, but not necessarily, have a hardness of less than about 12 GPa [HV], less than about 11 GPa [HV], less than about 10 GPa [HV] and even less than about 9 GPa [HV].

In order to prevent shattering, a material used in implementing the method of the present invention preferably has a relatively high bending strength.

Further, materials used in implementing the teachings of the present invention preferably, but not necessarily, have a relatively low sonic velocity and low stiffness so as to localize damage caused by impact of a kinetic threat. Thus, in contrast to the prior art where ceramic materials used for protection against kinetic threats have a sonic velocity of greater than about 10 km sec-1, materials useful in implementing the teachings of the present optionally have, depending on the exact embodiment, a sonic velocity of less than about 9 km sec-1, less than about 8 km sec"1, less than about 7 km sec-1 and even less than about 6 km sec-1.

Proof of Concept To reduce the innovative hypothesis of the present invention to practice, a novel glass-ceramic was designed, produced and tested.

Glass-ceramics are characterized by the presence of one or more different crystalline phases, each crystalline phase having a characteristic stochiometry. It is known in the art that it is possible to produce glass-ceramics having specific crystalline phases by choosing glass compositions having appropriate ratios of compounds, proper crystallization conditions and appropriate nucleating agents. Many different crystalline phases are useful in implementing the teachings of the present invention using a glass-ceramic. One suitable crystalline phase is Anorthite.

Anorthite (stochiometric ratio 1 CaO : 1 A1203 : 2 Si02 and weight ratio 1 CaO : 1.82 A1203 : 2.14 Si02) is a triclinic feldspar having a density of about 2.75 g cm" , a melting temperature of about 1550°C, a thermal coefficient of linear expansion (TCLE) of about 40 x 10"7 °C_1, a dielectric constant of 6.9, and a hardness of about 10 HV [GPa]. By weight, Anorthite is 20% CaO, 37% A1203 and 43% Si02. Due to the relatively low density, sufficient hardness (harder than the about 8 HV [GPa] of the hardest steel) and relatively low melting temperature (to reduce production costs) Anorthite was selected to be the predominant crystalline phase of a glass-ceramic for implementing the teachings of the present invention.

Preferred embodiments of glass-ceramics used in implementing the teachings of the present invention include more than about 40% by weight Anorthite, more than about 50% by weight Anorthite, more than about 60% by weight Anorthite, more than about 70% by weight Anorthite, more than about 80% by weight Anorthite, and even more than about 90% by weight Anorthite.

Further, when considering that in Anorthite the weight ratio of CaO to Al2O3 is 1 : 1.82, in a preferred embodiment of a glass-ceramic of the present invention and in a composition of the present invention used for making a glass-ceramic the weight ratio of CaO to Al2O3 is between about 1 : 1.3 and about 1 : 2.5, between about 1 : 1.4 and 1 : 2.3, between about 1 : 1.6 and 1 : 2.1, between about 1 : 1.7 and 1 : 1.95 and between about 1 : 1.75 and 1 : 1.89. At the same time, when considering that in Anorthite the weight ratio of CaO to Si02 is 1 : 2.14, in a preferred embodiment of a glass-ceramic of the present invention and in a composition of the present invention used for making the glass-ceramic the weight ratio of CaO to Si02 is between about 1 : 1.5 and about 1 : 3.0, between about 1 : 1.6 and 1 : 2.8, between about 1 : 1.9 and 1 : 2.4, between about 1 : 2.0 and 1 : 2.3 and between about 1 : 2.1 and 1 : 2.2.

Compositions of some suitable glass-ceramic of the present invention having a predominant Anorthite crystalline phase are listed in Table 1.

Table 1: Suitable glass-ceramics of the present invention W Tlhen producing a glass-ceramic, it is important to select a suitable nucleating agent. Many nucleating agents are known, including but not limited to Ce02, Cr203 (provided, for example, as Cr203 · FeO), F" (provided, for example, as Na3AlF6), Fe203, Mn02, P205 (provided, for example, as phosphate), Sn02 (provided, for example, as Cassiterite, Sn204), S042", S2", Ti02 (provided, for example, as Rutile or Ilmenite FeTi03), V205, ZnO and Zr02 (provided, for example, as Zircon ZrSi04).

Often it is desirable, to provide a glass-ceramic having more than one crystalline phase. When more than one crystalline phase is present in a glass-ceramic, it is important that the different crystalline phases have matching physical properties. For example, to reduce internal stress during dissipation of thermal energy in a glass-ceramic it is preferred that the component crystalline phases have a similar TCLE.

Ti02 is a well-known nucleating agent for producing glass-ceramics. Rutile (a-Ti02) is a tetragonal oxide, having a density of about 4.2 g cm" , a melting temperature of 1825°C, a TCLE of about 78 x lO"7 °C_1, a dielectric constant of between 89 and 173, and a hardness of about 10 HV [GPa]. Since Rutile has a TCLE similar to that of Rutile and since Ti02 is an effective nucleating agent, a glass-ceramic produced using Ti02 as a nucleating agent and Rutile as a secondary crystalline phase is a preferred glass-ceramic for implementing the teachings of the present invention.

In summary, although many different glass-ceramics are suitable for implementing the teachings of the present invention, a glass-ceramic having Anorthite as a predominant crystalline phase is preferred due to advantageous physical properties and low cost of production resulting from a low melting point. Although many nucleating agents are suitable for implementing the teachings of the present invention, when Anorthite is a predominant crystal phase it is preferred to use Ti02 as a nucleating agent. Ti02 is not only an effective nucleating agent, but Rutile is an exceptionally suitable secondary crystalline phase for an Anorthite-containing glass-ceramic. Therefore, a preferred glass-ceramic for implementing the teachings of the present invention is an Anorthite or an Anorthite / Rutile glass-ceramic.

When an Anorthite glass-ceramic of the present invention includes Ti02 as a nucleating agent, preferred embodiments include more than about 0.3% by weight Ti02, more than about 1% by weight Ti02, more than about 2% by weight Ti02, more than about 4% by weight Ti02, and even more than about 6% by weight Ti02.

The composition of some suitable glass-ceramic of the present invention, predicted to have a predominant Anorthite crystalline phase and Ti02 as a nucleating agent are listed in Table 2.

Table 2: Suitable glass-ceramics of the present invention A specific glass-ceramic of the present invention having a predominant Anorthite phase and using Ti02 as a nucleating agent was prepared (see below) and shown to have mechanical characteristics predicted to be suitable for implementing the teachings of the present invention. It is important to note that the glass-ceramic of the present invention has a high Ti02 content so it is expected that the Ti02 crystallized to form Rutile as a secondary crystalline phase. Although not confirmed, it is assumed that the Ti02 crystallized into Rutile as the glass-ceramic was allowed to crystallize at 1500 °C, and due to the fact that both alternate Ti02 crystalline forms, Brookite and Anatase, convert to Rutile at low temperatures (750 °C and 915 °C, respectively).

In Russian patent RU 2052400 is taught a glass composition made from an ash-slag waste substrate, where the ash-slag substrate contains 9%-54% by weight CaO, 13%-75% by weight Si02, 5%-26% by weight A1203 and 0.2% by weight Ti02. Between 3% and 8% graphite by weight is added to the molten substrate to reduce oxides to carbides, especially Si02 to carborundum. Devitrification of the glass to produce a glass-ceramic is discussed in one embodiment of RU 2052400. The relatively high CaO content coupled with the relatively low A1203 content and the relatively low Si02 content (especially after reduction to carborundum) precludes the formation of a significant Anorthite phase. Further, the low Ti02 content precludes the formation of a crystalline Ti02 phase.

In French patent application FR 7,436,270 (published as FR 2,367,027) are taught glass-ceramics produced from ash and other industrial waste. The composition most rich in A1203 taught therein comprises 15% A1203 to which is added 40% by weight phonolite. As phonolite comprises 21% A1203, the final composition includes only 23.4% A1203. Further, the low A1203 content together with the relatively high CaO and Si02 content preclude the formation of a significant Anorthite phase.

In English patent GB 1,459,178 are taught glass-ceramics produced from ash and other industrial waste. The formation of Anorthite is neither taught nor disclosed and not recognized as being of any significance. Since formation of Anorthite is dependent on a proper ratio of Si02, A1203 and CaO, Anorthite formed in a glass-ceramic of GB 1,459,178 is formed, if at all, incidentally and not in any significant proportion. In the two examples described a dearth of CaO makes the formation of Anorthite at best insignificant. Further, GB 1,459,178 teaches that BaO and/or ZnO are critical components of a glass-ceramic. Whereas some embodiments of a glass-ceramic of the present invention may include some BaO and/or ZnO, most embodiments of the present invention are devoid of these two components. In some embodiments of the present invention, BaO and/or ZnO may be incidentally present.

The mechanical properties of a glass-ceramic of the present invention are compared to the mechanical properties of monolithic ceramics known in the art as useful for protecting objects from kinetic threats in Table 3.

Table 3: Comparison of mechanical properties of ballistic monolithic ceramics with mechanical properties of a glass-ceramic of the present invention (from Medvedovski American Ceramic Societ Bulletin (2002), 81 (3), 27-32 and from U.S. Patent 5,443,917.) It is seen that the bending strength of the Anorthite / Ti02 glass-ceramic of the present invention is comparable to that of known monolithic ballistic ceramics. It is also seen that, as predicted, the hardness of the glass-ceramic is significantly lower than that of the prior art monolithic ceramics used in armor applications. At the same time, it is seen that both the sonic velocity and the stiffness of the glass-ceramic (as described by Young's modulus) are significantly less than that of the prior art monolithic ceramics used in armor applications.

Twelve 1 cm thick fabric-lined plates made of the Anorthite / Ti02 glass- ceramic of the present invention were tested in accordance with the NIJ 0101.03 (formulated and published by the National Institute of Justice of the United States Department of Justice) and shown to effectively neutralize kinetic threats at the III and III-A levels. The results of the ballistic tests are summarized in Table 4.

Table 4: Ballistic tests of glass-ceramic plates As is seen from Table 4, plates made from the Anorthite/Ti02 glass-ceramic of the present invention neutralized serious kinetic threats. Under the test conditions, neither penetration nor follow-through occurred. The backface deformation of all plates, the trauma effect, did not exceed acceptable standard values.

In Figure 2, an image of plate XII after the impact of three SSI 09 bullets at an impact velocity of between 943 and 951 m sec"1 is shown. It is seen that the plate did not shatter and damage caused by each bullet is localized to a respective impact site. The damage to the plate was localized pulverization producing a fine powder.

A 1 cm thick plate made of the Anorthite / Ti02 glass-ceramic of the present invention was tested for resistance against consecutive impact of six M-80 bullets using the plasticine test. The result of the plasticine test is summarized in Table 5.

Table 5: Plasticine test of glass-ceramic plate of the present invention As is seen from Table 5, a plate made from the Anorthite/Ti02 glass-ceramic of the present invention neutralized consecutive impact of six M-80 bullets. The measured trauma effect did not exceed acceptable values.

In conclusion, it has been demonstrated that glass-ceramics of the present invention are exceptionally useful in protecting objects from kinetic threats. Further, it has been demonstrated that the pulverization energy mechanism of energy dissipation is superior to the fracture energy mechanism as it produces localized damage to the shielding device, giving multiple threat protection capability, and avoids production of dangerous fragments and shards. Further, it has been confirmed that a material having certain physical properties dissipates energy through the pulverization energy mechanism.

EXAMPLES Reference is now made to the following example that, together with the above description, illustrate the invention in a non-limiting fashion MATERIALS, INSTRUMENTS AND EXPERIMENTAL METHODS Materials: Coal ash was obtained from the Rutenberg Power Plant (Ashkelon, Israel), the plant burning coal supplied by TotalFinaElf S.A., South Africa. The composition of the coal ash was Si02 (46.5 % by weight), Fe203 (3.7 % by weight), A1203 (30.1% by weight), Ti02 (1.6 % by weight), CaO (10 % by weight), MgO (1.9 % by weight), S03 (2.3 % by weight), Na20 (0.2 by weight), P205 (2.2 by weight), and K20 (0.4 % by weight).

Rutile sand was obtained from Richards Bay Iron and Titanium (ΡΤΎ) Ltd. (Richards Bay, Republic of South Africa). The composition of the Rutile sand was Ti02 (89 % by weight), Fe203 (2.5 % by weight), Zr02 (2 % by weight), P (0.04% by weight), S (0.008% by weight), Si02 (3% by weight), A1203 (0.88% by weight), CaO (0.25 % by weight), MgO (0.08 % by weight), Cr203 (0.14 % by weight), V205 (0.45 % by weight), MnO (0.03 % by weight) and Ν¾05 (0.35 % by weight).

CaC03 was obtained from Negev Industrial Minerals, Ltd. (Omer, Israel).

Instruments: X-ray crystallographic analysis was performed on a Phillips PW 11000 diffractometer in the co/20 mode using a graphite monochromator and MoK radiation.

Electron microscopy was performed using a XVP HV SEM electron microscope by Carl Zeiss SMT AG (Oberkochen, Germany).

Thermal coefficients of linear expansion (TCLE) were determined using a Chevenard Differential Dilatometer Model 5.

Preparation of Anorthite/Ti02 glass-ceramic 79 kg coal ash, 8 kg Rutile sand and 13 kg CaC03 were comminuted and mixed together to make an oxide mixture. 100 kg of the oxide mixture was placed in a MG-300 gas-fired glass-melting furnace (Falorni Glass Furnaces, Empoli, Italy) and heated to and maintained at 900 °C with continuous mixing and the introduction of air for a period of 1 hour to convert residual elemental carbon to volatile C02.

After all elemental carbon was volatilized, the oxide mixture was heated to 1350 °C and thereafter from 1350 °C to 1520 °C at a rate of between 50 °C hour"1 and 100 °C hour"1 in a. The melt was maintained at 1520 °C for 120 minutes to ensure thorough melting, convective mixing and the conversion of CaC03 to CaO.

The mixture was cooled to 1450 °C at a rate of 100 °C hour"1 and poured into a plurality of press molds to form 10 mm thick curved plates of 300mm x 250 mm and a curvature equivalent to that of a 400mm cylinder. The molten glass was allowed to crystallize for four hours during cooling from 1020 °C to 950 °C at a rate of 30 °C hour" 1 The density of the glass-ceramic plates thus produced was roughly 2.7 g cm" . It is clear to one skilled in the art that the glass-ceramic contained 8.9% by weight Ti02, 39.2% by weight Si02, 25.3% by weight A1203 and 16.2% by weight CaO. The weight ratio CaO to Si02 was 2.43 and the weight ratio CaO to A1203 was 1.57. The ratio Si02 / A1203 / CaO was 49 : 31 : 20, close to the desired 43 : 37 : 20 ratio of Anorthite. The glass-ceramic plates were resistant to water, acids and alkalines. It was possible to slowly etch the glass-ceramic plates using a concentrated HF solution.

It was possible to increase the strength of the glass-ceramic plates using both thermal tempering method and by chemical hardening. For chemical hardening, the surface of the glass-ceramic was etched with a 40% (v/v) HF solution to a depth of between about 100 and 200 microns. Subsequently, ion exchange was performed in the usual way using a 80% KN03 / 20% K2S04 mixture (w/w) at between 500 °C and 600 °C for four hours.

Using an X-ray diffractometer, it was confirmed that the predominant crystal phase in the produced glass-ceramic plates was Anorthite.

The surface of a produced glass-ceramic plate was examined using an electron microscope and shown to have a dense glass-ceramic structure with crystals of the order of 0.1 micron diameter, Figure 3.

A swatch of woven aramid fabric (Twaron® CT microfilament 930 dtex, Teijin Twaron B.V., Arnhem, The Netherlands) was glued to the concave side of each plate using an adhesive sheet (ADP-422-X produced by Polyon-Barkai Industries Ltd., Kibbutz Barkai, Israel) in a vacuum chamber at between 150 °C and 170 °C for 1 hour.

Twelve glass-ceramic plates were tested in accordance with the NIJ 0101.03 and shown to effectively neutralize ballistic threats at the III and III- A levels. The results of the ballistic tests are summarized in Table 4, above.

A glass-ceramic plate was tested in accordance with the NIJ plasticine test. The result of the plasticine test is summarized in Table 5, above.

Preparation of Anorthite/Ti02 glass-ceramic using the crystallization regime of the present invention The method of production discussed above was deemed unsatisfactory for industrial purposes due to the high percentage of rejected glass-ceramic plates that were cracked or had inferior physical properties, reaching up to about 80% in some batches.

To reduce the number of rejected glass-ceramic plates, a batch of glass-ceramic plates was manufactured using the crystallization regime of the present invention as depicted in Figure 3.

A molten and decarbonized glass composition prepared as above was cooled to 1450 °C at a rate of 100 °C hour"1 and poured into a plurality of press molds to form 10 mm thick curved plates of 300mm x 250 mm and a curvature equivalent to that of a 400mm cylinder. The molten glass was cooled to 725 °C at a rate of 100 °C hour"1 and maintained at 725 °C for one hour. The temperature was then increased at a monotonic rate from 725 °C to 900 °C over a period of 6 hours (a rate of 29 °C hour"1). After the 6 hours, the temperature was then increased at a monotonic rate from 900 °C to 950 °C over a period of 8 hours (a rate of 6.25 °C hour"1). After the 8 hours, the thus-produced glass-ceramic was allowed to cool from 950 °C to 600 °C over a period of 12 hours (a rate of -29 °C hour"1) before removal from the furnace.

Claims (4)

35 176662/2 WHAT IS CLAIMED IS:

1. A method of manufacturing an article for protecting an object from a kinetic threat comprising: a. providing a molten glass composition at a first temperature Tl including more than about 5% by weight CaO; b. devitrifying said glass composition; c. fashioning said glass composition into a glass-ceramic structure; and d. combining said glass-ceramic structure with additional components so as to yield the item for protecting an object from a kinetic threat.

2. The method of claim 1, wherein said molten glass composition comprises molten coal ash.

3. The method of claim 1 wherein said devitrifying includes maintaining said glass composition within a temperature range for a period of time sufficient to allow crystallization of at least some of said glass composition.

4. The method of claim 1 , wherein said molten glass composition is contained in a mold inside a chamber of a furnace provided with a heating controller configured to control the rate of heating of said chamber and said devitrifying said molten glass composition includes the steps of: i) using said heating controller to reduce the temperature of said chamber to a second temperature T2 so as to allow formation of nucleation centers in said molten glass composition; ii) using said heating controller to increase said chamber temperature from said second temperature T2 to a third temperature T3 at a first rate; iii) using said heating controller to increase said chamber temperature from said third temperature T3 to a fourth temperature T4 at a second rate; and iv) allowing said glass composition to crystallize, yielding the crystalline object. 37 176662/2