Preparation of Aluminium dodecaboride (AlB12) powder by Self-propagating High-temperature Synthesis (SHS)

Most of the borides are crystals with high hardness and melting point [1-4]. Stable chemical properties and a wide range of applications make it widely used in composite materials, semiconductors, and in various areas of national defense, such as radiation protection [5-8]. Among them, AlB12 has a special electronic structure and bonding characteristics [9,10]. It can effectively adjust the conductivity of semiconductor materials, and thus is extensively employed in conductors and semiconductor materials. In addition to the above characteristics, the content of boron in AlB12 is extremely high, reaching 82.8%, which is very promising as neutron shielding material [11-13].


Introduction
Most of the borides are crystals with high hardness and melting point [1][2][3][4]. Stable chemical properties and a wide range of applications make it widely used in composite materials, semiconductors, and in various areas of national defense, such as radiation protection [5][6][7][8]. Among them, AlB 12 has a special electronic structure and bonding characteristics [9,10].
It can effectively adjust the conductivity of semiconductor materials, and thus is extensively employed in conductors and semiconductor materials. In addition to the above characteristics, the content of boron in AlB 12 is extremely high, reaching 82.8%, which is very promising as neutron shielding material [11][12][13].
Ceramic powders are usually synthesized by traditional sintering methods [14][15][16]. However, the use of this method to synthesize ceramic powder takes a long time, consumes a great deal of energy and pollution [17]. Self-propagating hightemperature synthesis (SHS) is a unique technique for synthesizing materials by self-heating and self-conduction of high chemical reaction heat between reactants. This technology was fi rst discovered by Merzhanov et al., in their research on the combustion of solid propellants in rockets and was announced in 1967. Compared with the conventional sintering method, the advantages of the SHS method can be summarized as follows: (1) It is time saving and makes full use of energy [18]. (2) It requires only simple equipment and processes [19].
(3) The high product purity and product conversion rate are close to 100% [20]. (4) It can not only produce ceramic powder, but if the proper amount of pressure is applied at the same time, high-density combustion products can also be produced Citation: Wang  The phase analysis of the synthesized powder was carried out using a n X-ray diffractometer (XRD, X'Pert Pro MRD, Netherlands) with a Philips diffractometer using Cu Ka.
The microstructure of powders and elements analysis were investigated using a scanning electron microscope with EDS detector (SEM, S-3400N, Japan).
This article focuses on the study of two reaction systems, system 1: Al and B 2 O 3 , and system 2: Mg, Al, and B 2 O 3 . Two experimental atmospheres are used in both systems (Table 1).
In the Al-B 2 O 3 system, the following chemical reactions mainly occur: In the Mg-Al-B 2 O 3 system, the following chemical reactions mainly occur:  Figure 1 is the X-ray diffraction pattern of Al and B 2 O 3 prepared under both air conditions (before and after pickling) and argon conditions (before and after pickling) respectively. It can be seen from the fi gure that in either air or argon conditions, irremovable Al 2 O is found in the bottom. Analysis of its crystal Mg+Al+B O Ar After pickling    to prepare AlB 12, and using the self-propagating method, the purity of AlB 12 in the prepared product is low, and the B content is insuffi cient.

Summary
The phase analysis results of preparing AlB 12 using Al and B 2 O 3 as raw materials shows that there are -Al 2 O 3 impurities in the self-propagating powder regardless of either the air condition or the argon condition, and it cannot be removed.
Consequently, the purity of the prepared AlB 12 is not high.

Notes
The authors declare that they have no competing fi nancial interest.