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Definitions

• This invention is directed to novel and useful process for the preparation of boron carbide, boron nitride and silicon carbide comprising carbidization or nitrization step of boron oxides or silicon oxides, using nanoparticles substrates.
• Ceramic materials including boron carbide (B 4 C), silicon carbide (SiC) and boron nitride (BN) have useful properties including high melting temperature, low density, high strength, stiffness, hardness, wear resistance, and corrosion resistance. Many ceramics are good electrical and thermal insulators.
• Boron Carbide (B 4 C) is a black crystalline material and is one of the hardest materials known, ranking third behind diamond and cubic boron nitride. Boron Carbide powder is mainly produced by reacting carbon with boric oxide in an electric arc furnace, through carbothermal reduction or by gas phase reactions. For commercial use, boron carbide powders usually need to be milled, and purified to remove metallic impurities.
• Boron carbide may be used in several applications, for example as an abrasive, where due to its high hardness; boron carbide powder is useful in polishing and lapping applications. [006] Boron carbide may also find application in the preparation of nozzles or ballistic armors where the extreme hardness of boron carbide gives it excellent wear and abrasion resistance and as a consequence it finds application in nozzles used in slurry pumping, grit blasting and in water jet cutters. [007] Boron carbide may also be useful in nuclear applications, for its ability to absorb neutrons without forming long lived radio-nuclides which makes the material attractive as an absorbent for neutron radiation.
• Silicon carbide is man-made for use as an abrasive or more recently as a semiconductor and moissanite gemstones. Silicon carbide is known as a wide bandgap semiconductor existing in many different polytypes. All polytypes have a hexagonal frame with a carbon atom situated above the center of a triangle of Si atoms and underneath a Si atom belonging to the next layer, this affects all electronic and optical properties of the crystal.
• SiC silicon carbide
• All polytypes are extremely hard, very inert and have a high thermal conductivity. Properties such as the breakdown electric field strength, the saturated drift velocity and the impurity ionization energies are all specific for the different polytypes.
• the simplest manufacturing process of SiC is to combine silica sand and carbon at a high temperature in electric furnaces, between 2000 0 C and 2500 0 C.
• Carbidization in general and carbidization of silicon or boron comprise formation of SiC or B 4 C on a surface of carbon particles, wherein such carbon particles are large, and a layer of carbides is formed on the carbon outer layer and requires elevated temperature to form carbides on the inner layer of said carbon particles.
• Boron nitride is a white powder with high chemical and thermal stability and high electrical resistance. Boron nitride possesses three polymorphic forms; one analogous to diamond, one analogous to graphite and one analogous to fullerenes. Boron nitride can be used to make crystals that are extremely hard, second in hardness only to diamond, and the similarity of this compound to diamond extends to other applications. Like diamond, boron nitride acts as an electrical insulator but is an excellent conductor of heat.
• Boron nitride has ability to lubricate (qualities similar to graphite) in extreme cold or heat, is suited to extreme pressure applications, environmentally friendly and inert to most chemicals powders
• BN is used in electronics e.g. as a substrate for semiconductors, microwave-transparent windows, structural material for seals, electrodes and catalyst carriers in fuel cells and batteries.
• electronics e.g. as a substrate for semiconductors, microwave-transparent windows, structural material for seals, electrodes and catalyst carriers in fuel cells and batteries.
• the synthesis of hexagonal boron nitride powder is achieved by nitrization or ammonalysis of boric oxide at elevated temperature. Cubic boron nitride is formed by high pressure, high temperature treatment of hexagonal BN.
• Single crystal fibers are crystal whiskers, filamentary crystals or acicular crystals which are small, needle-shaped single crystal fibers of refractory elements (i.e., oxides, carbides, nitrides and borides) that exhibit . exceptional mechanical properties in addition to other useful features.
• Single crystal fibers are used for reinforcements for various matrices. When added to castable metals, the single crystal fibers stiffen and harden the alloy. The addition of single crystal fibers to ceramic matrices provides ceramics that possess improved properties of high mechanical strength and toughness at both room temperature and elevated temperatures. Other applications include field emitters, microfabrication tools, planar light traps, etc.
• the diameter of the single crystal fibers can sometimes be as small as 0.3 microns and the length is frequently within the 10 to 30 micron range.
• this invention provides a process for the preparation of ceramics comprising carbides, wherein said process comprising the step of carbidizing a metal oxide or metalloid oxide, whereby: a. said carbidizing comprises heating said metal oxide or metalloid oxide in an inert atmosphere together with carbon particles, at a temperature not to exceed 1900 0C ; and b. said carbon particles have a diameter which does not exceed 50 nm.
• this invention provides a process for the preparation of boron carbide (B 4 C) comprising the step of carbidizing boron oxide, whereby: a. said carbidizing comprises heating boron oxide and carbon particles in an inert atmosphere, at a temperature not to exceed 1900 0 C; and b. said carbon particles have a diameter which does not exceed 50 nm.
• this invention provides a process for the preparation of boron carbide (B 4 C) comprising the following steps: a. dehydrating an aqueous solution of boric acid or boron salt and a carbohydrate to obtain boron oxide and carbon particles; b. carbidizing boron by heating boron oxide and carbon particles of step (a) in an inert atmosphere, wherein -said carbidizing is conducted at a temperature not to exceed 1900 0 C; and -said carbon particles have a diameter which does not exceed 50 nm.
• this invention provides a process for the preparation of silicon carbide (SiC) comprising the step of carbidizing silicon oxide, whereby: a. said carbidizing comprises heating silicon oxide and carbon particles in an inert atmosphere, at a temperature not to exceed 1900 0 C; and b. said carbon particles have a diameter which does not exceed 50 nm.
• SiC silicon carbide
• this invention provides a process for the preparation of silicon carbide (SiC) comprising the following steps: a. dehydrating an aqueous solution of silicic acid or silicon salt and a carbohydrate to obtain silicon oxide and carbon particles; b. carbidizing silicon oxide by heating silicon oxide and carbon particles of step (a) in an inert atmosphere, wherein
• -said carbidizing is conducted at a temperature not to exceed 1900 0 C; and -said carbon particles have a diameter which does not exceed 50 nm.
• this invention provides a process for the preparation of boron nitride (BN) comprising the following steps: a. interaction of boric acid or boron salt, carbamide and a carbohydrate at a temperature between 250-350 0 C to obtain poly-amoniumborate, and carbon nano-particles; b. heating said poly-amoniumborate and carbon particles of a step (a) under N 2 to obtain boron nitride, wherein said heating is conducted at a temperature of between 1300-1500 0 C.
• Fig. Ia - Fig. Ib depicts a Scanning Electron Micrographs of different Forms of single crystal fibers B 4 C.
• Fig.2 depicts a Scanning Electron Micrographs of Isometeric rombohedral and platelet like crystals of B 4 C.
• Fig.3 depicts a Scanning Electron Micrographs of single icosahedral crystal of B 4 C.
• Fig.4 depicts a Scanning Electron Micrographs of isometric nanocrystals of B 4 C.
• Fig. 5 depicts a Scanning Electron Micrographs of isometric nanocrystals after grinding of B 4 C.
• Fig. 6 depicts a Scanning Electron Micrographs of B 4 C wherein up to 50% of the particles are single crystal fibers and platelet like crystals.
• Fig. 7 depicts a Scanning Electron Micrographs of SiC powder enlarged by A) 10,000; B) 40,000; C)60, 000 and D) 200,000
• Fig. 8 depicts a Scanning Electron Micrographs of BN nanoparticles powder.
• this invention provides a process for the preparation of ceramics comprising carbides or nitrides.
• said ceramics are boron carbide (B 4 C), silicon carbide (SiC) or boron nitride (BN).
• this invention provides a process for the preparation of ceramics, wherein said process yields ceramic particles in controlled size manner. In another embodiment, said process yields ceramic particles in the range of between 1-100 microns. In another embodiment, the ceramic particles in the range of 25 nm to 10 ⁇ m. [0035] In one embodiment, this invention provides a process for the preparation of ceramics, wherein said process yields ceramic particles in controlled crystalline structure manner. In one embodiment said ceramics are in single crystal fiber structure. In another embodiment said ceramics are in platelet crystal structures. In another embodiment said ceramics are in an isometric rombohedral crystal structures. In another embodiment said ceramics are in an isometric crystal structures.
• this invention provides a process for the preparation of ceramics, wherein said process yields ceramic particles in high purity level.
• the purity of the ceramics of this invention is above 97%.
• the purity of the ceramics of this invention is in the range of between about 98-100%.
• the purity of the ceramics of this invention is in the range of between about 97-100%.
• the purity of the ceramics of this invention is in the range of between about 99-100%.
• this invention provides a process for the preparation of ceramic materials comprising carbides or nitrides, wherein said process comprising the step of carbidizing or nitridizing a metal oxide or metalloid oxide, whereby: a. said carbidizing or nitridizing comprises heating said metal oxide or metalloid oxide in an inert atmosphere together with nanoparticles substrates, wherein said carbidizing at a temperature not to exceed 1900. 0 C, and said nitridizing at a temperature not to exceed 1500 0 C ; and b. said nanoparticles substrates have a diameter which does not exceed 50 nm.
• this invention provides a process for the preparation of ceramics comprising carbides, wherein said process comprising the step of carbidizing a metal oxide or metalloid oxide, whereby: a. said carbidizing comprises heating said metal oxide or metalloid oxide in an inert atmosphere together with carbon particles, at a temperature not to exceed 1900 0C ; and b. said carbon particles have a diameter which does not exceed 50 nm.
• the processes of this invention provides a carbidization or nitridizing step of metal oxide or metalloid oxide.
• said metal oxide is tungsten oxide, or calcium oxide.
• the term metalloid refers to chemical elements having both metals and nonmetals properties.
• the metalloid oxide is silicon oxide, boron oxide, germanium oxide, arsenic oxide, antimony oxide, tellurium oxide or any combination thereof.
• this invention provides a process for the preparation of boron carbide (B 4 C) comprising the step of carbidizing boron oxide, whereby: a. said carbidizing comprises heating boron oxide and carbon particles in an inert atmosphere, at a temperature not to exceed 1900 0 C; and .b. said carbon particles have a diameter which does not exceed 50 nm.
• this invention provides a process for the preparation of boron carbide (B 4 C) comprising the following steps: a. dehydrating an aqueous solution of boric acid or boron salt and a carbohydrate to obtain boron oxide and carbon particles; b. carbidizing boron by heating boron oxide and carbon particles of step (a) in an inert atmosphere, wherein -said carbidizing is conducted at a temperature not to exceed 1900 0 C; and
• -said carbon particles have a diameter which does not exceed 50 nm.
• dehydrating comprises the steps of: a. drying aqueous solution of boric acid or boron salt and a carbohydrate at a temperature not to exceed 150 0 C; b. caramelizing of boric acid or boron salt and a carbohydrate of step (a) at a temperature between 250-350 0 C; and c. carbonizing of the product of (b), in an inert atmosphere, at a temperature ranging from about 400-600 0 C.
• this invention provides a process for the preparation of silicon carbide (SiC) comprising the step of carbidizing silicon oxide, whereby: a. said carbidizing comprises heating silicon oxide and carbon particles in an inert atmosphere, at a temperature not to exceed 1900 0 C; and b. said carbon particles have a diameter which does not exceed 50 nm.
• SiC silicon carbide
• this invention provides a process for the preparation of silicon carbide (SiC) comprising the following steps: a. dehydrating an aqueous solution of silicic acid or silicon salt and a carbohydrate to obtain silicon oxide and carbon particles; b. carbidizing silicon oxide by heating silicon oxide and carbon particles of step (a) in an inert atmosphere, wherein
• -said carbidizing is conducted at a temperature not to exceed 1900 0 C; and , -said carbon particles have a diameter which does not exceed 50 nm.
• dehydrating comprises the steps of: a. drying aqueous solution of silicic acid or silicon salt and a carbohydrate at a temperature not to exceed 150 0 C; b. caramelizing of said silicic acid or silicon salt and carbohydrate of step (a) at a temperature not to exceed 250-350 0 C; and c. carbonizing of the product of (b), in an inert atmosphere, at a temperature ranging from about 400-600 0 C.
• the carbohydrate is saccharide.
• the saccharide used is a polysaccharide.
• the saccharide is glucose.
• the saccharide is dextrose.
• the saccharide is lactose.
• the boron salt is any salt or alloy comprising boron.
• the silicon salt is any salt or alloy comprising silicon.
• a boron salt is a salt of boric acid.
• a silicon salt is a salt of silicic acid.
• the salts of boric acid or silicic acid include metallic salts made from alkaline metals, or alkaline earth metals, or transition metals.
• the salts of boric acid or silicic acid include organic salts such as N,N'- dibenzylethyleneldiamine, choline, chloroprocaine, diethanolamine, ethylenediamine, meglumine (N-methylglucamine) and procain.
• the salts may be formed by conventional means, such as by reacting the free base or free acid form of the product with one or more equivalents of the appropriate acid or base.
• the boric acid is selected from H 3 BO 3 , H 2 B 4 O 7 OrHBO 2 .
• the silicic acid is selected from H 2 SiOS 1 H 4 SiO 41 H 2 Si 2 O 5 or H 6 Si 2 O 7 .
• silicon oxide is silicon containing at least one oxygen atom. In another embodiment silicon oxide is silicon dioxide (SiO 2 ).
• boron oxide is boron containing at least one oxygen atom. In another embodiment boron oxide is boron trioxide (B 2 O 3 ).
• the dehydration step comprises a drying step at a temperature not to exceed 200 0 C. In one embodiment of this invention, according to any process of this invention, the drying step is at a temperature not to exceed 150 0 C.
• the drying step is ranging from about 100-150 0 C. In another embodiment, the drying step is ranging from about 100-120 0 C. In another embodiment, the drying step is ranging from about 120-150 0 C. In another embodiment, the drying step is ranging from about 135-150 0 C. In another embodiment, the drying step is ranging from about 150-200 0 C. In another embodiment, the drying step is ranging from about 150-200 0 C. In another embodiment, the drying step is at a temperature ranging from about 160-200 0 C. In another embodiment, the drying step is at a temperature ranging from about 150-160 0 C. In another embodiment, the drying step is at a temperature ranging from about 160-170 0 C.
• the drying step is at a temperature ranging from about 170-180 0 C. In another embodiment, the drying step is at a temperature ranging from about 180-200 0 C.
• the aqueous solution may be prepared with the use of an ultrasonic dispenser. In another embodiment, the drying step may be conducted using an atomizing dryer.
• caramelizing refers to the preparation of a non-crystallizable substance obtained by pyrogenation of sugars or from molasses.
• caramelization is at a temperature not to exceed 400 0 C. In another embodiment, the caramelization is at temperature ranging from about 350-400 0 C. In another embodiment, the caramelization is at temperature ranging from about 250-350 0 C. In another embodiment, the caramelization is at temperature ranging from about 300-350 0 C. In another embodiment, the caramelization is at temperature ranging from about 250-300 0 C. In another embodiment, the caramelization is at temperature ranging from about 320-350 0 C.
• carbonization is at a temperature ranging from about 350-360 0 C. In another embodiment, carbonization is at a temperature ranging from about 360-370 0 C. In another embodiment, carbonization is at a temperature ranging from about 370-380 0 C. In another embodiment, carbonization is at a temperature ranging from about 380-390 0 C. In another embodiment, carbonization is at a temperature ranging from about 390-400 0 C. [0057] In one embodiment, carbonizing refers to the decomposition of organic substances by heat with a limited supply of air, whereby carbon is formed.
• carbonization is at a temperature ranging from about 400-600 0 C. In another embodiment, carbonization is at a temperature ranging from about 450-550 0 C. In another embodiment, carbonization is at a temperature ranging from about 450-460 0 C. In another embodiment, carbonization is at a temperature ranging from about 460-470 0 C. In another embodiment, carbonization is at a temperature ranging from about 470-480 0 C. In another embodiment, carbonization is at a temperature ranging from about 480-490 0 C. In another embodiment, carbonization is at a temperature ranging from about 490-500 0 C.
• carbonization is at a temperature ranging from about 500-510 0 C. In another embodiment, carbonization is at a temperature ranging from about 510-520 0 C. In another embodiment, carbonization is at a temperature ranging from about 520-530 0 C. In another embodiment, carbonization is at a temperature ranging from about 530-540 0 C. In another embodiment, carbonization is at a_temperature ranging from about 540-550 0 C. In another embodiment, carbonization is at a temperature ranging from about 500-600 0 C. In another embodiment, carbonization is at a temperature ranging from about 550-600 0 C. In another embodiment, carbonization is at a temperature ranging from about 500-550 0 C. [0059] In one embodiment, carbidizing refers to reaction between a carbon atom and one or more metalloid or metal elements.
• the B 4 C powder obtained having chemical properties as described in Example 1.
• B 4 C powder obtained having chemical properties as described in Example 2 and presented in Figures 1-6.
• preparation of B 4 C via a process as described herein, B 4 C following hot pressing of the powder includes anti-ballistic properties as presented in Example 4.
• hot pressing refers to applying pressure at high temperature to enhance densification.
• hot pressing is conducted by placing a powder and applying uniaxial pressure while the entire system is held at an elevated temperature.
• B 4 C particles after hot pressing include an average grain size of between 3.5-7.5 ⁇ m, hardness of between 2630-3800 kg/mm 2 , and minimum bulk density of 2.5 g/cm 3 .
• carbidization may be performed at a temperature which does not exceed 1900 0 C.
• the temperature may be at a range of between 1600-1850 0 C. In another embodiment of this invention, the temperature of carbidization is between 1700-1800 0 C. In another embodiment, the temperature of carbidization is between 1650-1700 0 C. In another embodiment, the temperature of carbidization is between 1700-1750 0 C. In another embodiment, the temperature of carbidization is between 1750-1800 0 C. In another embodiment, the temperature of carbidization is between 1800-1850 0 C.
• carbidization comprises reacting boron oxide or silicon oxide and carbon particles with a heating rate of between 80- 180 o C/min.
• the heating rate is between 80- 90 °C/min.
• the heating rate is between 90-100 °C/min.
• the heating rate is between 100-110 °C/min.
• the heating rate is between 110-120 o C/min.
• the heating rate is between 120-130 °C/min.
• the heating rate is between 130-140 o C/min.
• the heating rate is between 140-150 °C/min.
• the heating rate is between 150-160 o C/min.
• the heating rate is between 160-170 °C/min.
• the heating rate is between 170-180 °C/min.
• the w/w ratio of boron trioxide or silicon dioxide and carbon particles is in between about 1.78-1.86: 1. In another embodiment, the ratio is between about 1.78-1.79: 1. In another embodiment, the ratio is between about 1.79-1.8: 1. In another embodiment, the ratio is between about 1.8-1.81: 1. In another embodiment, the ratio is between about 1.81-1.82: 1. In another embodiment, the ratio is between about 1.82-1.83: 1. In another embodiment, the ratio is between about 1.83- 1.84: 1. In another embodiment, the ratio is between about 1.84-1.85: 1. In another embodiment, the ratio is between 1.85-1.86: 1.
• the w/w ratio of silicon dioxide and carbon particles is in between about 1.69-1.71: 1. In another embodiment the w/w ratio of silicon dioxide and carbon particles is in between about 1.65- 1.75: 1. In another embodiment the w/w ratio of silicon dioxide and carbon particles is in between about 1.65-1.70: 1. In another embodiment the w/w ratio of silicon dioxide and carbon particles is in between about 1.68-1.72: 1. In another embodiment the w/w ratio of silicon dioxide and carbon particles is in between about 1.66-1.73: 1.
• the w/w ratio of silicon dioxide and carbon particles is in between about 1.6-1.8: 1 [0068]
• the carbon particles used are nano particles.
• the nano particles are nanotubes, nanofibers or a combination thereof.
• .the diameter of the nanotubes or the nanofibers carbon particles ranges from about 5 - 20 nm.
• the diameter of the nanotubes, nanofibers, or any combination thereof is about between 10-20 nm.
• the diameter of the nanotubes, nanofibers, or any combination thereof is about between 15-30 nm.
• the diameter of the nanotubes, nanofibers, or any combination thereof is about between 30-50 nm.
• the particles of boron carbide obtained by any process of this invention are single crystal fibers with dimensions of between of 0.2x2 ⁇ m to 30x200 ⁇ m.
• the particles of boron carbide obtained by any process of this invention are in a platelet crystaline form with dimensions of between of 2x2x0.3 ⁇ m to 100xl00x3 ⁇ m.
• the particles of boron carbide obtained by any process of this invention are isometric nanocrystals with dimensions of between of 25nm to 10 ⁇ m.
• the particles of boron carbide obtained by any process of this invention are isometric nanocrystals with dimensions of between of 25nm to 10 ⁇ m or any combination thereof.
• a mixture of isometric and platelet crystals are obtained as presented in Figure 2.
• the particles of silicon carbide obtained by any process of this invention are single crystal fibers with dimensions of between of 0.2x2 ⁇ m to 30x200 ⁇ m.
• the particles of silicon carbide obtained by any process of this invention are in a platelet crystaline form with dimensions of between of 2x2x0.3 ⁇ m to 100xl00x3 ⁇ m.
• the particles of silicon carbide obtained by any process of this invention are isometric nanocrystals with dimensions of between of 25nm to 10 ⁇ m or any combination thereof.
• SiC particles are obtained as presented in Figure 7.
• this invention provides a process for the preparation of boron carbide (B 4 C) enriched with single crystal fibers comprising the step of carbidizing boron, comprising the steps of: a. dehydrating an aqueous solution of boric acid or boron salt and a carbohydrate to obtain boron oxide and carbon particles; b. carbidizing silicon by heating boron oxide and carbon particles of step (a) in an inert atmosphere, wherein
• -said carbidizing is conducted at a temperature not to exceed 1900 0 C; and -said carbon particles have a diameter which does not exceed 50 nm.
• this invention provides a process for the preparation of silicon carbide (SiC) enriched with single crystal fibers comprising the step of carbidizing boron, comprising the steps of: a. dehydrating an aqueous solution of silicic acid or silicon salt and a carbohydrate to obtain silicon oxide and carbon particles; b. carbidizing silicon by heating silicon oxide and carbon particles of step (a) in an inert atmosphere, wherein
• -said carbidizing is conducted at a temperature not to exceed 1900 °C; and -said carbon particles have a diameter which does not exceed 50 nm.
• the process for the preparation of boron carbide (B 4 C) or silicon carbide (SiC) enriched with single crystal fibers further comprises the step of isolating the single crystal fibers.
• the single crystal fibers are sized such that the ratio of the length of said fiber axis versus the diameter of said fiber is at least 10.
• this invention provides a process for the preparation of boron nitride (BN) comprising the step of nitrization of boron, whereby said nitrization comprises heating carbamide, carbohydrate and boric acid in an inert atmosphere, at a temperature not to exceed 1600 0 C.
• this invention provides a process for the preparation of boron nitride (BN) comprising the following steps: a. interaction of boric acid or boron salt, carbamide and a carbohydrate at a temperature between 250-350 0 C to obtain poly-amoniumborate, and carbon nano-particles; b. heating said poly-amoniumborate and carbon particles of a step (a) under N 2 to obtain boron nitride, wherein said heating is conducted at a temperature of between 1300-1500 0 C.
• the process for the preparation of boron nitride comprises a carbamide, boric acid and carbohydrate.
• said carbamide is urea.
• said carbohydrate is sacharide.
• the BN powder obtained has chemical and physical properties as described in Example 3 and-presented in Figure 8.
• the temperature of nitization is between 1450-1500 0 C.
• nitrization comprises reacting carbamide, carbohydrate and boric acid with a heating rate of between 80- 180 °C/min. In another embodiment the heating rate is between 80-90 °C/min. In another embodiment, the heating rate is between 90-100 °C/min. In another embodiment, the heating rate is between 100-110 °C/min. In another embodiment, the heating rate is between 110-120 °C/min. In another embodiment, the heating rate is between 120-130 °C/min. In another embodiment, the heating rate is between 130-140 °C/min.
• the heating rate is between 140-150 °C/min. In another embodiment, the heating rate is between 150-160 °C/min. In another embodiment, the heating rate is between 160-170 °C/min. In another embodiment, the heating rate is between 170-180 °C/min. [0080] In another embqdiment of this invention, for any process of this invention, the ratio (w/w) between the boric acid (H 3 BO 3 ), urea (NH 2 ) 2 CO and saccharide (C 12 H 22 O n ) is (11:26:1) up to 13:23:1 , respectively. In another embodiment, the ratio (w/w) between the boric acid and sacharide is in the range of 11.5-12.5: 1, respectively.
• the ratio (w/w) between the boric acid and sacharide is in the range of 11-12: 1, respectively. In another embodiment, the ratio (w/w) between the boric acid and sacharide is in the range of 12-13:1 respectively.
• the particles of boron nitride obtained by any process of this invention are crystal whiskers with dimensions of between of 0.2x2 ⁇ m to 30x200 ⁇ m. In another embodiment of this invention, the particles of boron nitride obtained by any process of this invention are in a platelet crystaline form with dimensions of between of 2x2x0.3 ⁇ m to 100xl00x3 ⁇ m. In another embodiment of this invention, the particles of boron nitride obtained by any process of this invention are isometric nanocrystals with dimensions of between of 25nm to 10 ⁇ m, or any combination thereof.
• the process further includes separation of the different crystalline forms of the B 4 C of this invention.
• the single crystal fiber Form of B 4 C can be isolated from other crystalline or amorphous B 4 C Forms by means known in the art such as sedimentation.
• the isometric crystal Forms of B 4 C can be isolated from other crystalline or amorphous B 4 C Forms by means known in the art such as sedimentation.
• the platelet crystal Forms of B 4 C can be isolated from other crystalline or amorphous B 4 C Forms by means known in the art such as sedimentation.
• the process further includes separation of the different crystalline forms of the SiC of this invention.
• the crystal whiskers Form of SiC can be isolated from other crystalline or amorphous SiC Forms by means known in the art such as sedimentation.
• the isometric crystal Forms of SiC can be isolated from other crystalline or amorphous SiC Forms by means known in the art such as sedimentation.
• the platelet crystal Forms of SiC can be isolated from other crystalline or ( amorphous SiC Forms by means known in the art such as sedimentation.
• the process further includes separation of the different crystalline forms of the BN of this invention.
• the crystal whiskers Form of BN can be isolated from other crystalline or amorphous BN Forms by means known in the art such as sedimentation.
• the isometric crystal Forms of BN can be isolated from other crystalline or amorphous BN Forms by means known in the art such as sedimentation.
• the platelet crystal Forms of BN can be isolated from other crystalline or amorphous BN Forms by means known in the art such as sedimentation.
• the process further includes grinding the ceramics.
• the boron carbide, silicon carbide or boron nitride particles following grinding range in size from about 15-100 run.
• the boron carbide, silicon carbide or boron nitride particles following grinding range in size from about 70-80 nm.
• the boron carbide, silicon carbide or boron nitride particles following grinding range in size from about 80-100 nm.
• the boron carbide, silicon carbide or boron nitride particles are obtained after a short grinding period, and are between about 50-80 nm in diameter characterized by granulometric analysis.
• the granulation analysis is performed by ball milling.
• grinding refers to any means by which the B 4 C undergoes size reduction into fine particles.
• this invention provides a boron carbide, silicon carbide or boron nitride preparation obtained by a process of this invention comprises at least 5 % single crystal fibers.
• a boron carbide, silicon carbide or boron nitride preparation obtained by a process of this invention comprises at least 10% single crystal fibers, or in another embodiment, at least 11 % single crystal fibers of boron carbide, silicon carbide or boron nitride, or in another embodiment, at least 12 % single crystal fibers of boron carbide, silicon carbide or boron nitride, or in another embodiment, at least 15 % single crystal fibers boron carbide, silicon carbide or boron nitride, or in another embodiment, at least 17 % sinsle crystal fibers boron carbide, silicon carbide or boron nitride, or in another embodiment, at least
• boron carbide, silicon carbide or boron nitride preparation obtained by a process of this invention comprises from about 10% to about 30 % single crystal fibers.
• 80% of the isolated single crystal fibers comprise a ratio of the length of the crystals versus their cross section as being not less than 10. In another embodiment, 80% of the isolated single crystal fibers comprise a ratio of the length of the crystals versus their cross section, as being not less than 20.
• the single crystal fibers obtained by a process of this invention are filamentary crystals. In another embodiment the single crystal fibers are acicular crystals. In another embodiment the single crystal fibers are in a lamellar form. In another embodiment the single crystal fibers are in a platelet form. In one embodiment the single crystal fibers obtained by a process of this invention are crystal whiskers.
• the inert gas in the processes of this invention may be argon or helium.
• B 4 C powders Chemical Formula - B 4 C; Density - 2, 52 g/cm 3 Grade Available - high purity B 4 C powder for hot pressing, filling, etc. Chemical Characteristics (% mass.):
• a ballistic test was performed using a bullet with the steel thermally -strengthened core in the steel core of the caliber of 7.62 mm (B-32), a mass of 1.5 g.
• the distance between the caliber and the B 4 C (monoblock- 10x12 inch, thickness of B 4 C - 8 mm, prepared by hot pressing) was 10 m, angle of traverse -0 ° with respect to the standard. Shots were produced into the apexes of equilateral triangle with the side 100 mm. The results of the test are:

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