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The synthesis of boron carbide powder from polymeric precursors prepared via different chemical reaction processes was investigated.The low-cost of production of B4C has been attained by using cheap starting materials,mainly poly（vinyl alcohol）PVA and boric acid（BA）.The condensation reaction（CR）was used to prepare poly（vinyl borate）（PVBO）precursor from PVA and BA.The reaction was controlled by extracting of a white PVBO-gel which formed on the surface of the reaction mixture.Consequently,the solution viscosity and the concentration of the reacting species was decreased,and the interface between the reactants increased,leading to a high dispersion of C-B at the nanoscale.After drying of the PVBO precursor,the C/B2O3 molar ratio was controlled at（3.1–2.9）,which is less than the stoichiometric ratio of 3.5,by the pyrolysis of the precursor at 650 oC for 2 h in air.The XRD analysis of the final product shows that high purity semi-equiaxed grains and fiber-like shape nanocrystalline boron carbide powder was synthesized by the heat treatment of the pyrolyzed precursor at 1400 oC for 4 h in an Ar flow.Compared to previous reports,it is the first time to report the formation of a fiber-like shape boron carbide by carbothermal reduction route at a low temperature as 1400 oC.The CR method has many drawbacks such as the high control needed for the preparation of a PVBO precursor,and the high consumption of water,etc.To overcome these problem,reaction of PVA with boric acid in a solid-state phase was proposed,however,there was no data about this reaction in the literature.Nano plated,and high-purity boron carbide（B4C）powder was synthesized via a novel method,based on a solid-state reaction（SSR）of poly（vinyl alcohol）PVA and boric acid at（200-250）oC in air.The FTIR analysis proved the occurrence of a cross-linking between PVA and boric acid.The obtained product,a new-type of polyvinyl borate（PVBO）,was consecutively pyrolyzed at（700-800）oC for 120 min in air to obtain the preceramic precursor（S1）.To prepare the preceramic precursor（S2）,PVBO was ground,heat treated at 250 oC for 120 min,followed by pyrolysis at（700-800）oC for 120 min in air.The preceramic precursors（S1＆S2）were then heat treated at（1375-1475）oC in an Ar flow for（180-120）min,respectively.XRD analysis shows that high purity B4C obtained from S2（pyrolyzed at 750 oC）by the heat treatment at 1475 oC.Compared to previous methods（commercial or sol-gel etc.）,this approach is cost-effective,highly promising,and established a new reaction route in the field of polymer-derived ceramic（PDC）.The third approach aims at developing a solid-state reaction-pyrolysis process（SRPP）of poly（vinyl alcohol）PVA and boric acid for the synthesis of boron carbide.PVA and BA were dry-mixed,solid-state reacted by heating at（200–250）oC in air and were directly pyrolyzed at（700–800）oC in air to obtain preceramic precursors.By varying the holding time at 250 oC from 210 to 270 min,its effects on the purity of the final product were investigated.The preceramic precursors were ground,and heat treated at 1475 oC for 120 min in a flow of Ar.The XRD＆FE-SEM analyses show that a high purity boron carbide powder with nanosized particles was obtained using this promising approach.Finally,nano spherical particles and rod-like shape B4C synthesized by a solid-state polymerization（SSP）of PVA and BA,and through performing the reaction of their dry mixture under vacuum at（200–250）oC.FTIR analysis shows the presence of（B-O-C）bond,which confirms the cross-linking of PVA and BA.The formed PVBO precursor was ground,heated at 250 oC for 120 min,and pyrolyzed at（650–800）oC for 120 min in air.The XRD analysis shows that a high purity boron carbide was obtained from the preceramic precursor S6（pyrolyzed at 700 oC）by heat treatment at 1475 oC for 120 min in the flow of Ar.The SSR,SRPP,and SSP solved the problem that lacking the CR to be as alternative method to produce B4C in a large-scale.The present methods overcome the problems associated with the industrial technique of synthesis of boron carbide concerning the high temperature of the heat treatment process and nanosized powder.In near future,the present methods will be highly recommended for the synthesis of a high purity and nano-sized boron carbide.