The paper compares low-temperature techniques for boron carbide synthesis. Boron carbide was syn-thesized via reaction between boric acid and various carbon precursors, e.g. phenol-formaldehyde resin, su-crose, carbon black, and potato starch. Initial compositions and carbon precursor preparation techniques were selected for synthesis. The resulting products were characterized by IR spectrometry, X-ray diffrac-tion (XRD) and scanning electron microscopy. Possible boron carbide yields up to 95 % of the theoretical yield as calculated from initial boron contents at temperatures of 1550 oС were demonstrated. XRD con-firmed that the synthesized boron carbide (B4C) has a rhombohedral crystalline structure. Final product morphology may be tailored, ranging from isometric to needle-like crystallite morphology. Nanopowders as processed via high-energy milling may be further used as sintering additive for processing of boron carbide ceramics.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3560

Genusova, T.

Mednikova, A.

Rumyantsev, V.

Zakharova, K.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 2 No 3, 03AET09(4pp) (2013)   2304-1862/2013/2(3)03AET09(4) 03AET09-1  2013 Sumy State University Synthesis of Boron Carbide from Boric Acid and Carbon-Containing Precursors  K. Zakharova*, A. Mednikova†, V. Rumyantsev‡, T. Genusova§  VIRIAL Ltd., Saint-Petersburg, Russia  (Received 10 June 2013; published online 02 September 2013)  The paper compares low-temperature techniques for boron carbide synthesis. Boron carbide was syn-thesized via reaction between boric acid and various carbon precursors, e.g. phenol-formaldehyde resin, su-crose, carbon black, and potato starch. Initial compositions and carbon precursor preparation techniques were selected for synthesis. The resulting products were characterized by IR spectrometry, X-ray diffrac-tion (XRD) and scanning electron microscopy. Possible boron carbide yields up to 95 % of the theoretical yield as calculated from initial boron contents at temperatures of 1550 oС were demonstrated. XRD con-firmed that the synthesized boron carbide (B4C) has a rhombohedral crystalline structure. Final product morphology may be tailored, ranging from isometric to needle-like crystallite morphology. Nanopowders as processed via high-energy milling may be further used as sintering additive for processing of boron carbide ceramics.  Keywords: Boron carbide, Powder, Synthesis, Phenol-formaldehyde resin, Sucrose, Starch, Preceramic polymer   PACS numbers: 81.05.Je, 81.20.Ka                                                                * info@virial.ru † MednikovaAA@virial.ru ‡ info@virial.ru § GenusovaTN@gmail.com 1. INTRODUCTION  Boron carbide (B4C) has a special place among ul-trahard high-melting nonmetals, featuring a unique combination of properties, e.g. excellent hardness (30-40 GPa, Hv10), low density (2.52 x 103 kg/m3), good Young’s modulus (450-470 GPa), resistance to corro-sion, and neutron absorption. Due to this combination of properties, boron carbide is one of the most promis-ing materials for nuclear applications, wear parts and efficient armor systems.  Due to the highly covalent bonding nature in B4С crystals, the major ceramic sintering mechanisms, such as grain-boundary and volume diffusion are retarded in boron carbide. This led to extensive research effort in identifying the new consolidation techniques, as well as alternative raw materials and processing methods in order to facilitate sintering processes. One of the most promising approaches in this field may be processing of submicron and nanosized boron carbide powders, as well as special particle morphologies that may subse-quently be used for ceramics sintering and processing of materials with improved performance.  Boron carbide is commercially produced by the classical process of carbothermal reduction of the boron oxides at high temperatures. An interesting possible alternative to the high-temperature powder techniques may be found in solution chemical methods that use intermediate preceramic polymer products. The results of earlier research in sol-gel processing of boron carbide powders showed that gel synthesizing the intermediate organic/inorganic hybrids before the synthesis leads to the tailored distribution of carbon at molecular level [1-5]. Our paper used similar approach to synthesize bo-ron carbide powder. Our research was aimed at esti-mating the yield of the targeted product at lower syn-thesis temperatures, as well as characterization of the product for its composition and morphology.   2. MATERIALS AND METHODS  Boric acid H3BO3 (as per GOST 9656-75) was used as a starting material. Four different types of carbon precursors were selected: 1) sucrose; 2) potato starch (food grade); 3) phenol-formaldehyde resin (PFR) , grade SF-010 (as per GOST 18694-80); 4) carbon black (PRINTEX V grade, as per GOST 7885-86). The mix-ture of boric acid with carbon black was used as a ref-erence. Optimal premix compositions for each carbon precursor type were identified based on a series of pre-liminary tests, with optimal ratio corresponding to that with excess boric acid, as compared to stoichiometric (30 to 100 % excess). This corresponds to the earlier published findings [5-7]. The process included the premix-processing stage that was implemented by using various techniques, e.g. mechanical mixing; solution mixing with subsequent evaporation and milling; and melting + milling. The compositions and processing techniques for premix processing are given in Table 1. The as-processed pre-mixes were placed into heat-treatment system UTO-1PS. First heat-treatment phase in Ar at Т=800 °С served for carbonization of the carbon-rich component and H3BO3 dehydration. Second stage of heat-treatment was used for actual boron carbide synthesis. The carefully weighed quantity of the premix, prepro-cessed at 800 oС, was placed into a 5-litre graphite crucible, coated with pyrocarbon. Heating ramp up to the preset final temperature was 300 oС/hour. Synthe-sis was carried out in Ar at temperatures of 1300 to  K. ZAKHAROVA, A. MEDNIKOVA, V. RUMYANTSEV , T. GENUSOVA PROC. NAP 2, 03AET09 (2013)   03AET09-2 1550 oC, and at 1900 oС, with dwell time of 1 to 3 hours. The processed samples were characterized by X-ray diffraction (XRD) using the DRON-4 XRD system. Mi-crostructural characterization was carried out in the JSM 6460 scanning electron microscope. The interme-diate products, as obtained at the premix processing stage, were also characterized by infrared spectrometry (using FSM 1201 IR-spectrometer).  The product yield (based on boron) was calculated as per technique detailed in GOST 5744-85. Samples featuring maximum yield were additional-ly milled in the high-energy planetary lab mill (Aktiva-tor 2SL).  3. RESULTS AND DISCUSSION   The IR spectrometry results for all intermediate products showed the presence of В-О-С bond (absorp-tion peak at 1050 cm-1), which confirms the reaction between the boric acid and the polymer carbon precur-sor. This reaction and the nature of the synthesized preceramic polymer have an effect on the boron carbide yield. Precursors with similar boron and carbon con-tents after the calcination at 800 oС  in Ar atmosphere showed different yields (as based on boron), namely: 80 to 95 %, depending on the initial composition and pro-cessing route (see Table 1).  Mixture of boric acid with carbon black yielded neg-ligible amounts of boron carbide when treated under similar conditions. This fact may be attributed to the better synthesis conditions in the porous system that is obtained after the carbonization of the polymer precur-sors. Still, this process and its possible optimization require further research.  The onset of boron carbide synthesis was confirmed by XRD technique in the samples heat-treated at 1350 °С, with main components of the mixture being amorphous carbon and boron anhydride. Rising heat-treatment temperature to 1450 °С led to much higher boron carbide contents. In samples based on optimal initial compositions, heat—treated at 1550 °С, boron carbide crystallites had rhombohedral structure and was the main reaction product (see Fig. 1a,b,c). When premixes with no excess boron were used, reaction products contained disordered carbon as the main com-ponent (see Fig. 1d).  Table 1 – Characterization of the initial premixes and boron carbide powder samples as synthesized at 1550 °С    Sample descrip-tion Processing details Initial com-ponents Boric acid ex-cess, relative to stoichiometric  contents, % Product yield (based on boron), % Phase analy-sis SEB Component mixing Isothermal dwell of premix at Т=175 °С sucrose; boric acid; ethylene glycol 100 80 Boron carbide, carbon SB Melting of components on Si bath at Т=165 °С; milling sucrose; boric acid; 30 95 Boron carbide, carbon KKB Evaporation of the wa-ter-based solution of boric acid and starch until gelation. potato starch; boric acid 30 88 Boron carbide, carbon FB2 evaporation of the etha-nol-based solution of the boric acid and PFR; milling PFR; boric acid 100 90 Boron carbide, carbon FB1 evaporation of the etha-nol-based solution of the boric acid and PFR; milling PFR; boric acid 0 negligible Boron carbide (negligible), disordered carbon TUB Mechanical mixing of the components in etha-nol (12 hours); drying; milling carbon (tech grade); boric acid 0 negligible Boron carbide (negligible), disordered carbon  SYNTHESIS OF BORON CARBIDE FROM BORIC ACID… PROC. NAP 2, 03AET09 (2013)   03AET09-3  a  b  c  d  Fig. 1 – X-ray diffraction patterns of the different boron carbide powder samples: SEB (a), SB (b), FB2  (с), FB1 (d)  When sucrose was used for boron carbide synthesis (SEB sample) with significant boric acid excess, the B4C product predominantly consisted of coarse needle-shaped crystals (see Fig. 2a). When boric acid content in the premix was reduced, and the premix was melt-processed (SB sample) the product yield was maxim-ized, while boron carbide was obtained as single iso-metric crystals (see Fig. 2b). Product morphology also depends on the component type and ratio in the initial premix. When PFR was used as carbon source, the boron carbide was obtained as coarse well-faceted crystals coalesced into agglomer-ates (see Fig. 2c). At lower В : С ratios the crystals are growing on the carbon component residue (see Fig. 2d).  K. ZAKHAROVA, A. MEDNIKOVA, V. RUMYANTSEV , T. GENUSOVA PROC. NAP 2, 03AET09 (2013)   03AET09-4    a       b     c        d  Fig. 2 – Scanning electron micrographs of the different boron carbide powder samples: SEB (a), SB (b), FB2  (с), FB1 (d)  4. CONCLUSIONS  The results of experiments showed that the low-temperature synthesis process using preceramic poly-mer-containing premixes, as obtained through reaction of the boric acid with organic polymers, it is possible to achieve boron carbide yields of up to 95 % of the initial boron contents. Boron carbide (B4C), as processed by the developed technique, shows rhombohedral crystalline structure. Morphology of the final product may be tailored, rang-ing from isometric to needle-shaped crystallites. High-energy milling of the synthesized product was an efficient way to obtain boron carbide powder with particles sized of 10 to 150 nm.   REFERENCES  1. I. Hasegawa, Y. Fujii, T. Takayama, K. Yamada, J. Mater. Sci. Lett. 18 No20, 1629 (1999). 2. F. Golestani-Farda, H.R. Rezaiea, N. Ehsani, J. Alloys. Comp. 509 No37, 9164 (2011). 3. A. Najafi, F. Golestani-Fard, H.R. Rezaie, N. Ehsani, Ceram. Int. 38 No5, 3583 (2012).  4. A. Sudoh, H. Konno, H. Habazaki, H. Kiyono, J. TANSO No226, 8 (2007). 5. T.R. Pilladi, K. Ananthasivan, S. Anthonysamy, V.  Ganesan, J. Mater. Sci. 47 No4, 1710 (2012) 6. WO9009348, publ. 23.08.1990. 7. S. Corradettia, S. Carturana, L. Biasettoa, A. Andrighettoa, P. Colomboe, J. Nucl Mater. 432 No1–3, 212 (2013).   

Synthesis of Boron Carbide from Boric Acid and Carbon-Containing Precursors

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 2 No 3, 03AET09(4pp) (2013) 
 
 
2304-1862/2013/2(3)03AET09(4) 03AET09-1  2013 Sumy State University 
Synthesis of Boron Carbide from Boric Acid and Carbon-Containing Precursors 
 
K. Zakharova*, A. Mednikova†, V. Rumyantsev‡, T. Genusova§ 
 
VIRIAL Ltd., Saint-Petersburg, Russia 
 
(Received 10 June 2013; published online 02 September 2013) 
 
The paper compares low-temperature techniques for boron carbide synthesis. Boron carbide was syn-
thesized via reaction between boric acid and various carbon precursors, e.g. phenol-formaldehyde resin, su-
crose, carbon black, and potato starch. Initial compositions and carbon precursor preparation techniques 
were selected for synthesis. The resulting products were characterized by IR spectrometry, X-ray diffrac-
tion (XRD) and scanning electron microscopy. Possible boron carbide yields up to 95 % of the theoretical 
yield as calculated from initial boron contents at temperatures of 1550 oС were demonstrated. XRD con-
firmed that the synthesized boron carbide (B4C) has a rhombohedral crystalline structure. Final product 
morphology may be tailored, ranging from isometric to needle-like crystallite morphology. Nanopowders as 
processed via high-energy milling may be further used as sintering additive for processing of boron carbide 
ceramics. 
 
Keywords: Boron carbide, Powder, Synthesis, Phenol-formaldehyde resin, Sucrose, Starch, Preceramic 
polymer 
 
 PACS numbers: 81.05.Je, 81.20.Ka 
 
 
                                                             
*
 info@virial.ru 
† MednikovaAA@virial.ru 
‡ info@virial.ru 
§ GenusovaTN@gmail.com 
1. INTRODUCTION 
 
Boron carbide (B4C) has a special place among ul-
trahard high-melting nonmetals, featuring a unique 
combination of properties, e.g. excellent hardness (30-
40 GPa, Hv10), low density (2.52 x 103 kg/m3), good 
Young’s modulus (450-470 GPa), resistance to corro-
sion, and neutron absorption. Due to this combination 
of properties, boron carbide is one of the most promis-
ing materials for nuclear applications, wear parts and 
efficient armor systems.  
Due to the highly covalent bonding nature in B4С 
crystals, the major ceramic sintering mechanisms, such 
as grain-boundary and volume diffusion are retarded in 
boron carbide. This led to extensive research effort in 
identifying the new consolidation techniques, as well as 
alternative raw materials and processing methods in 
order to facilitate sintering processes. One of the most 
promising approaches in this field may be processing of 
submicron and nanosized boron carbide powders, as 
well as special particle morphologies that may subse-
quently be used for ceramics sintering and processing 
of materials with improved performance. 
 Boron carbide is commercially produced by the 
classical process of carbothermal reduction of the boron 
oxides at high temperatures. An interesting possible 
alternative to the high-temperature powder techniques 
may be found in solution chemical methods that use 
intermediate preceramic polymer products. The results 
of earlier research in sol-gel processing of boron carbide 
powders showed that gel synthesizing the intermediate 
organic/inorganic hybrids before the synthesis leads to 
the tailored distribution of carbon at molecular level [1-
5]. Our paper used similar approach to synthesize bo-
ron carbide powder. Our research was aimed at esti-
mating the yield of the targeted product at lower syn-
thesis temperatures, as well as characterization of the 
product for its composition and morphology.  
 
2. MATERIALS AND METHODS 
 
Boric acid H3BO3 (as per GOST 9656-75) was used 
as a starting material. Four different types of carbon 
precursors were selected: 1) sucrose; 2) potato starch 
(food grade); 3) phenol-formaldehyde resin (PFR) , 
grade SF-010 (as per GOST 18694-80); 4) carbon black 
(PRINTEX V grade, as per GOST 7885-86). The mix-
ture of boric acid with carbon black was used as a ref-
erence. Optimal premix compositions for each carbon 
precursor type were identified based on a series of pre-
liminary tests, with optimal ratio corresponding to that 
with excess boric acid, as compared to stoichiometric 
(30 to 100 % excess). This corresponds to the earlier 
published findings [5-7]. 
The process included the premix-processing stage 
that was implemented by using various techniques, e.g. 
mechanical mixing; solution mixing with subsequent 
evaporation and milling; and melting + milling. The 
compositions and processing techniques for premix 
processing are given in Table 1. The as-processed pre-
mixes were placed into heat-treatment system UTO-
1PS. First heat-treatment phase in Ar at Т=800 °С 
served for carbonization of the carbon-rich component 
and H3BO3 dehydration. Second stage of heat-
treatment was used for actual boron carbide synthesis. 
The carefully weighed quantity of the premix, prepro-
cessed at 800 oС, was placed into a 5-litre graphite 
crucible, coated with pyrocarbon. Heating ramp up to 
the preset final temperature was 300 oС/hour. Synthe-
sis was carried out in Ar at temperatures of 1300 to 
 K. ZAKHAROVA, A. MEDNIKOVA, V. RUMYANTSEV , T. GENUSOVA PROC. NAP 2, 03AET09 (2013) 
 
 
03AET09-2 
1550 oC, and at 1900 oС, with dwell time of 1 to 3 
hours. 
The processed samples were characterized by X-ray 
diffraction (XRD) using the DRON-4 XRD system. Mi-
crostructural characterization was carried out in the 
JSM 6460 scanning electron microscope. The interme-
diate products, as obtained at the premix processing 
stage, were also characterized by infrared spectrometry 
(using FSM 1201 IR-spectrometer).  
The product yield (based on boron) was calculated 
as per technique detailed in GOST 5744-85. 
Samples featuring maximum yield were additional-
ly milled in the high-energy planetary lab mill (Aktiva-
tor 2SL). 
 
3. RESULTS AND DISCUSSION  
 
The IR spectrometry results for all intermediate 
products showed the presence of В-О-С bond (absorp-
tion peak at 1050 cm-1), which confirms the reaction 
between the boric acid and the polymer carbon precur-
sor. This reaction and the nature of the synthesized 
preceramic polymer have an effect on the boron carbide 
yield. Precursors with similar boron and carbon con-
tents after the calcination at 800 oС  in Ar atmosphere 
showed different yields (as based on boron), namely: 80 
to 95 %, depending on the initial composition and pro-
cessing route (see Table 1).  
Mixture of boric acid with carbon black yielded neg-
ligible amounts of boron carbide when treated under 
similar conditions. This fact may be attributed to the 
better synthesis conditions in the porous system that is 
obtained after the carbonization of the polymer precur-
sors. Still, this process and its possible optimization 
require further research.  
The onset of boron carbide synthesis was confirmed 
by XRD technique in the samples heat-treated at 
1350 °С, with main components of the mixture being 
amorphous carbon and boron anhydride. Rising heat-
treatment temperature to 1450 °С led to much higher 
boron carbide contents. In samples based on optimal 
initial compositions, heat—treated at 1550 °С, boron 
carbide crystallites had rhombohedral structure and 
was the main reaction product (see Fig. 1a,b,c). When 
premixes with no excess boron were used, reaction 
products contained disordered carbon as the main com-
ponent (see Fig. 1d). 
 
Table 1 – Characterization of the initial premixes and boron carbide powder samples as synthesized at 1550 °С 
 
 
 
Sample 
descrip-
tion 
Processing details 
Initial com-
ponents 
Boric acid ex-
cess, relative to 
stoichiometric  
contents, % 
Product 
yield 
(based on 
boron), % 
Phase analy-
sis 
SEB 
Component mixing 
Isothermal dwell of 
premix at Т=175 °С 
sucrose; boric 
acid; ethylene 
glycol 
100 80 
Boron carbide, 
carbon 
SB 
Melting of components 
on Si bath at Т=165 °С; 
milling 
sucrose; boric 
acid; 
30 
95 Boron carbide, 
carbon 
KKB 
Evaporation of the wa-
ter-based solution of 
boric acid and starch 
until gelation. 
potato starch; 
boric acid 
30 
88 Boron carbide, 
carbon 
FB2 
evaporation of the etha-
nol-based solution of the 
boric acid and PFR; 
milling 
PFR; boric 
acid 
100 90 
Boron carbide, 
carbon 
FB1 
evaporation of the etha-
nol-based solution of the 
boric acid and PFR; 
milling 
PFR; boric 
acid 
0 
negligible 
Boron carbide 
(negligible), 
disordered 
carbon 
TUB 
Mechanical mixing of 
the components in etha-
nol (12 hours); drying; 
milling 
carbon (tech 
grade); boric 
acid 
0 
negligible 
Boron carbide 
(negligible), 
disordered 
carbon 
 SYNTHESIS OF BORON CARBIDE FROM BORIC ACID… PROC. NAP 2, 03AET09 (2013) 
 
 
03AET09-3 
 
a 
 
b 
 
c 
 
d 
 
Fig. 1 – X-ray diffraction patterns of the different boron carbide powder samples: SEB (a), SB (b), FB2  (с), FB1 (d) 
 
When sucrose was used for boron carbide synthesis 
(SEB sample) with significant boric acid excess, the 
B4C product predominantly consisted of coarse needle-
shaped crystals (see Fig. 2a). When boric acid content 
in the premix was reduced, and the premix was melt-
processed (SB sample) the product yield was maxim-
ized, while boron carbide was obtained as single iso-
metric crystals (see Fig. 2b). 
Product morphology also depends on the component 
type and ratio in the initial premix. When PFR was 
used as carbon source, the boron carbide was obtained 
as coarse well-faceted crystals coalesced into agglomer-
ates (see Fig. 2c). At lower В : С ratios the crystals are 
growing on the carbon component residue (see Fig. 2d). 
 K. ZAKHAROVA, A. MEDNIKOVA, V. RUMYANTSEV , T. GENUSOVA PROC. NAP 2, 03AET09 (2013) 
 
 
03AET09-4 
  
 
a       b 
 
  
 
c        d 
 
Fig. 2 – Scanning electron micrographs of the different boron carbide powder samples: SEB (a), SB (b), FB2  (с), FB1 (d) 
 
4. CONCLUSIONS 
 
The results of experiments showed that the low-
temperature synthesis process using preceramic poly-
mer-containing premixes, as obtained through reaction 
of the boric acid with organic polymers, it is possible to 
achieve boron carbide yields of up to 95 % of the initial 
boron contents. 
Boron carbide (B4C), as processed by the developed 
technique, shows rhombohedral crystalline structure. 
Morphology of the final product may be tailored, rang-
ing from isometric to needle-shaped crystallites. 
High-energy milling of the synthesized product was 
an efficient way to obtain boron carbide powder with 
particles sized of 10 to 150 nm. 
 
 
REFERENCES 
 
1. I. Hasegawa, Y. Fujii, T. Takayama, K. Yamada, J. Mater. 
Sci. Lett. 18 No20, 1629 (1999). 
2. F. Golestani-Farda, H.R. Rezaiea, N. Ehsani, J. Alloys. 
Comp. 509 No37, 9164 (2011). 
3. A. Najafi, F. Golestani-Fard, H.R. Rezaie, N. Ehsani, 
Ceram. Int. 38 No5, 3583 (2012).  
4. A. Sudoh, H. Konno, H. Habazaki, H. Kiyono, J. TANSO 
No226, 8 (2007). 
5. T.R. Pilladi, K. Ananthasivan, S. Anthonysamy, 
V.  Ganesan, J. Mater. Sci. 47 No4, 1710 (2012) 
6. WO9009348, publ. 23.08.1990. 
7. S. Corradettia, S. Carturana, L. Biasettoa, 
A. Andrighettoa, P. Colomboe, J. Nucl Mater. 432 No1–3, 
212 (2013).  
 


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Synthesis of Boron Carbide from Boric Acid and Carbon-Containing Precursors

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