Dynamic / thermochemical method: A novel approach in the synthesis of
B
4
C powder
Hamza Boussebha
a, *
, Sinan Bakan
b
, Ali Osman Kurt
c
a
Sakarya University, Research and Development Center (SARGEM), Powder Research and Development Group, Esentepe Campus, 54187, Sakarya, Turkey
b
Fatih Sultan Mehmet Vakif University, Haliç Yerles ¸kesi, Sütlüce Mah. Karaa gaç Cad. No:12 Beyo glu,
_
Istanbul, Turkey
c
Sakarya University, Department of Metallurgy and Materials Engineering, Esentepe Campus, 54187, Sakarya, Turkey
ARTICLE INFO
Keywords:
Boron carbide
Thermochemical method
Carbothermal reduction
Advanced ceramics
ABSTRACT
The synthesis of high quality B
4
C powders with high purity, uniaxial shape and homogeneous size distribution,
has been hard to obtain. Current production methods take place at temperatures above 1800
C, yielding high free
carbon and large particle size. In this study, using a novel and patented approach, a reaction temperature of 1500
C for 1 h was sufficient to synthesize fine B
4
C powders from boron oxide (B
2
O
3
) and carbon black (C). This
technique is based on the dynamic/thermochemical method (DTM), in which B
2
O
3
and C powders are granulated
before being charged into an atmosphere-controlled rotary type furnace. The granulation process and parameters
of raw materials were the key to obtain high purity B
4
C powders, with equiaxed-grains and homogenous dis-
tribution with an average size of 10 μm.
1. Introduction
With the title of “black diamond” bestowed upon it, boron carbide
(B
4
C), possesses a low density (2.52 g/cm
3
)[1], high hardness (29.1
GPa) [2], high elastic modulus (470 GPa) [3], high melting point (2540
C) [4], an outstanding chemical resistance [5] and a high neutron ab-
sorption cross-section (
10
B
X
C, x > 4) [6]. These properties promote B
4
C
as an excellent choice for armor and abrasive applications. Boron carbide
is commonly obtained via magnesiothermic [7] or carbothermic (also
named carbothermal) reduction (CR) [8], mechanothermal synthesis [5],
synthesis from boron (B) and carbon mixture [9], synthesis from polymer
precursors [10], besides vapor phase reactions, ion beam synthesis and
vapor liquid solid (VLS) growth, usually desired in the synthesis of B
4
C
for surface coating [2]. Although there exist multiple approaches to
synthesize B
4
C powder, the carbothermic reduction of either boric acid
(H
3
BO
3
) or boron anhydride/boron oxide (B
2
O
3
), which are both inex-
pensive starting materials, is the commercially preferred method, due to
its simplicity and economic advantages. The general reactions of boron
carbide synthesis are given in Equations (1) to (5) [8][11]. Despite being
the widely used method, carbothermic reduction, has the major disad-
vantage of boron loss in form of its oxides [9]. Hence, the powders
synthesized in this way, usually contain a high amount of free carbon,
which has a detrimental effect on the mechanical properties of the
sintered boron carbide products. The presence of free carbon is based on
the binary phase diagram B–C. Since B
4
C is in equilibrium with carbon in
a range that enlarges at high temperature to the carbon-rich side, a
super-saturation can take place during the cooling process, causing a
precipitation of free carbon [8].
2B
2
O
3
þ 7C → B
4
C þ 6 CO (1)
4H
3
BO
3
þ 7C → B
4
C þ 6 CO þ 6H
2
O (2)
Latter reaction proceeds in three steps:
4H
3
BO
3
→ B
2
O
3
þ 6H
2
O (3)
B
2
O
3
þ 3 CO → 2B þ 3 CO
2
(4)
C4 B þ C → B
4
C (5)
The carbothermic reduction is extremely endothermic requiring
16,800.00 kJ/mol or 9.10 kWh/kg of B
4
C[12]. In the commercial
method, the process takes place in an electrical arc furnace where B
2
O
3
/C
mixture is heated above 2000
C, resulting a volatilization of boron, and
subsequently precipitation of free carbon. Some studies have suggested
that the presence of a controlled small amount of free carbon can be
useful during sintering. Chen et al. [13]. reported that a carbon excess
enhances the densification and inhibits grain growth. Nevertheless, Yong
* Corresponding author.
E-mail address: hamza.boussebha@ogr.sakarya.edu.tr (H. Boussebha).
Contents lists available at ScienceDirect
Open Ceramics
journal homepage: www.editorialmanager.com/oceram
https://doi.org/10.1016/j.oceram.2021.100133
Received 30 March 2021; Received in revised form 21 May 2021; Accepted 23 May 2021
Available online 28 May 2021
2666-5395/© 2021 The Author(s). Published by Elsevier Ltd on behalf of European Ceramic Society. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Open Ceramics 6 (2021) 100133