PROCESS FOR MANUFACTURING HIGH DENSITY BORON CARBIDE Field of the Invention The present invention relates to a process for manufacturing high density boron carbide by pressureless high temperature sintering. Background of the Invention The fast growing demand for extremely hard materials results from their numerous applications. Boron carbide, a typical representative of such materials, can be used in armor plates, and as an abrasion resisting material. Most applications of boron carbide require that its density be as high as possible - in other words, the density should be close to the theoretical density (TD). The manufacturing of high density boron carbide is a multistage process, whose final stage is sintering which can be conducted under high pressure or without applying a pressure. Pressureless sintering of materials is more advantageous compared to hot pressing with respect to process cost and ability to organize it in a continuous mode. In the case of a batch mode, pressureless sintering permits a larger scale production. The common practice to achieve high density of materials (more than 90% TD) is a use of sintering additives. In the case of boron carbide, carbon is used as a sintering aid. The source of carbon may be amorphous carbon (in a form of carbon black, for example) or carbon precursors. In both cases, the boron carbide powder is blended with an additive, then press compacted and sintered. If a carbon precursor is used as an additive, the compacted "green" body should be further heat-treated by pyrolysis or carbonization (prior to sintering) in order to transform the precursor to carbon. US 4,195,066 discloses a process which requires very fine raw boron carbide powder (grain size o—5.8um, DgcFlOum and specific area (B.E.T.) 2.2 m2/gr was gradually added to the resin solution. Haw resin/powder ratio was 15:100 (mass). The blend was mixed for 24 hrs, oven dried at 70°C and the dried cake was granulated using a 20 mesh size sieve. A finer sieve can also be used. The granulated powder was cold pressed (SOMPa) in a 59x59 mm mold to form flat green square-shaped objects having density of 1.36 to 1.60 g/cc. Further these objects were carbonized in a stream of nitrogen (1 lit/min). The heating schedule was as follows: heating at the rate 25°C/hr up to 550"C, further heating at the rate 100°C/hr up to 1000°C, soaking for 5 hrs., furnace cooling to room temperature. When this stage completed the carhoni/cd green objects contained 5.4% of amorphous carbon. At the next stage the carbonized green objects were sintered in the stream of argon, utili/ing the electrical resistance furnace having graphite elements and insulation. The heating schedule was as follows: double vacuum purge prior to heating in order to eliminate oxygen residues, Argon flow, heating to 1800 "C at the rate 900°C/hr, heating up to 2100 °C at the rate 300°C/hr, heating up to 233()<>C at the rate 15()"C/hr, soaking for 30 mins., cooling at the rate 600"C/hr to approximately 1000°C and then furnace cooling to room temperature. The sintered objects has undergone 18% linear shrinkage upon sintering, and had a density of 2.3 g/cc, corresponding to 92.9% TD. ExampleJ! Operating similarly to the procedure of Example 1, but with the difference that the stage of pre-washing was conducted in the following way: the boron carbide powder was mixed with IPA for 24 hours (mixing ratio 0.75 Kg powder/1 liter IPA). Then the mixture was dried in the oven at 7()"C and further processed according to Example 1 to form sintered boron carbide objects. The final product had a density of 2.38 g/cc, corresponding to 94.4% Tl). Example 3 Operating similarly to Example 2, but with the difference that the pre-washing was carried out in methanol, the boron carbide powder was mixed with methanol for 24 hours (mixing ratio 0.75 Kg powder/1 liter methanol). Then the mixture was dried in the oven at 70°C and further processed according to Example 1 to form sintered boron carbide objects. The final product had a density of 2.376 g/cc, corresponding to 94.3 % Tl). Example 4 (Comparative) Operating similarly to Example 1, but with the difference that boron carbide powder had a smaller particle size, namely D5o=4.6?m, D9o=9.2?m and specific area (B.E.T.) 2.49 m2/gr. The final product had a density of 2.38 gr/cc, corresponding to 94.4% TD. Example 5 Operating similarly to Example 4, but with the difference that pre-washed boron carbide powder was mixed with IPA as described in Example 2. The heating rate during the carbonization stage was 100°C/hr. The final product had a density of 2.42 gr/cc, corresponding to 96% TD. Example 6 (Comparative) Operating similarly to Example 4, but with the difference that compaction process was carried out while the mold was heated to 160°C. The granulated powder was poured into the mold cavity, and then the pressure was applied for 10 minutes. The final product had a density of 2.40 gr/cc, corresponding to 95.2% TD. Example 7 Operating similarly to Example 6, but with the difference that pre-washed boron carbide powder was mixed with IPA as described in Example 2. The final product had a density of 2.43 glee, corresponding to 96.4% TD. Example 8 (Comparative) Operating similarly to Example 6, but with the difference that compaction process was conducted in a spherical dome shaped mold. The dome inner spherical radius was 242 mm, the dome outer spherical radius was 247.5 mm, and basal diameter of the dome was 105 mm. The granulated powder was poured into the mold cavity and pressure was applied while the powder was not leveled. The phenolic resin has undergone a viscous flow along with the ceramic particles to fill the mold cavity between the dies and to form a uniform green compact. The domes were sintered between top and bottom graphite dies, each one machined to match the outer and inner sphere radius, respectively. While sintering without the shaped graphite dies the domes have undergone a severe geometrical distortion, due to free sagging while being at the high sintering temperature. The sintered domes had a density of 2.395 g/cc, corresponding to 95% TD. While the spherical radii remained unchanged, both the dome basal diameter and the thickness have undergone 18% shrinkage. Example 9 Operating similarly to Example 8, but with the difference that pre-washed boron carbide powder was mixed with IPA as described in Example 2. The sintered domes had a density of 2.434 g/cc, corresponding to 96.6% TD. Example 10 (Comparative) An aqueous solution of 230 gr maltodextrin (dextrose equivalent, DE=15), 10 gr PVA (polyvinyl alcohol) and 1000 gr water were mixed with 1000 gr boron carbide powder having the same properties as in Example 4. After that the slurry was spray-dried. A free flowing spherical granulated powder was obtained. The powder was then hot compacted in a 59x59mm mold, while the mold was heated to 130°C. The compacting pressure SOMPa, was applied for 10 minutes. Uniform high strength green objects were obtained. The green objects were pyrolyzed in a nitrogen stream in order to convert the maltodextrin to carbon. The heating schedule was as follows: heating at the rate 25°C/hr to 650°C, soaking for 5 hours, furnace cooling to room temperature. Sintering was carried out according to Example 1. The final product density was 2.395 g/cc, corresponding to 95.1% TO. Example 11 Operating similarly to Example 10, but with the difference that a pro-washed boron carbide powder had the same properties as in Example 1. The final product density was 2.425 g/cc, corresponding to 96.2% TI). Example 12 Operating similarly to Example 11, but with the difference that, the objects had a shape of a spherical dome as described in Examples 8 and 9. During pressing, maltodcxtrin has undergone a viscous flow along with the ceramic particles to fill the mold cavity between the dies and to form a uniform, high strength green compact object. Carbonizing and sintering were conducted in the same mode as in Example 10. The final product had a density of 2.43 g/cc, corresponding to 96.4% TI). We claim: 1. A process for manufacturing boron carbide objects comprising the steps of: (a) pre-washing a raw boron carbide powder with an organic solvent selected from the group consisting of isopropyl alcohol, ethyl alcohol, methyl alcohol, acetone, and a combination thereof, said pre-washing including mixing for about 24 hours, followed by drying the washed boron carbide; (b) mixing the washed boron carbide powder with a carbon precursor selected from the group consisting of phenolic resin, aqueous solution of a polysaccharide, and a mixture of two or more saccharides; (c) drying the mixture; (d) granulating the dried mixture; (e) compacting the granulated dried mixture to form a shaped object by applying a pressure thereto; (f) carbonizing the shaped body in an inert atmosphere, by dwelling at a high temperature for a predetermined period of time; and (g) sintering the carbonized shaped body at a temperature between about 2300°C and about 2350°C in an inert atmosphere for a time period of not less than about 30 min. 2. The process as claimed in 1, wherein the carbon precursor which is mixed with the boron carbide powder includes a phenolic resin. 3. The process as claimed in 1, wherein the carbon precursor which is mixed with the boron carbide powder includes an aqueous solution of a polysaccharide or a mixture of two or more saccharides. 4. The process as claimed in claim 4, wherein the polysaccharide is maltodextrin. 5. The process as claimed in claim 4, wherein the drying is carried out by spray drying. 6. The process as claimed in 1, wherein the pressure is applied uniaxially. 7. The process as claimed in 1, wherein the pressure is applied isostatically. 8. The process as claimed in 1, wherein the compacting is carried out with heating. 9. The process as claimed in 9, wherein the compaction is carried out at a temperature of between about 130°C and about 170°C. 10. The process as claimed in 1, wherein compaction is carried out until the density of the compacted shaped body reaches between about 1.36 to about 1.60 g/cc. 11. The process as claimed in 1, wherein the carbonization step is carried out in a nitrogen atmosphere. 12. The process as claimed in 1, wherein the carbonization step is carried out in an argon atmosphere. 13. The process as claimed in 1 wherein the carbonization step is carried out at a controlled heating rate, which is between about 25°C/hr to about 100°C/hr. 14. The process as claimed in 1, wherein the sintering is carried out in an argon atmosphere. 15. The process as claimed in 1, wherein the sintering is carried out for a time period of about 120 minutes. 16. The process as claimed in 1, wherein the sintering is performed while the shaped body is constrained between shaped graphite dies having essentially a geometry to match a desired final geometry of said shaped body. 17. The process as claimed in 17, wherein the graphite dies have a non-flat, multi-curved shape.