Effect of boron oxide/carbon arrangement of precursor derived from condensed polymer-boric acid product on low-temperature synthesis of boron carbide powder

Abstract

The effect of the boron oxide (B 2 O 3 )/carbon arrangement of the precursor on the low-temperature synthesis of boron carbide (B 4 C) powder was investigated in this study. The precursor was prepared by low-temperature heat treatment without thermal decomposition and subsequent pyrolysis in air of the condensed product formed from poly(vinyl alcohol) (PVA) and boric acid. The dispersion state of B 2 O 3 particles in the carbon matrix of the precursor significantly affected the acceleration of the synthesis reaction. Crystalline B 4 C powder with little free carbon was obtained by heat treatment at 1100°C, which was also the critical formation temperature, for 20 h in an Ar flow starting from a precursor with a B 2 O 3 /carbon structure homogeneously arranged at the nanometer scale.

In-Situ Carbon Control in the Preparation of Precursors to Boron Carbide by a Non-Aqueous Solution Technique

“…6 suggests that H 3 BO 3 forms as a homogeneous coating on the carbon matrix. This finding is contrary to earlier work on solution based methods [3,6,7,8,18] in which it is proposed that boron at this stage of processing is B 2 O 3 . Based on the ATR-FTIR data shown in Fig.…”

“…Bulk industrial synthesis methods are commonly undertaken at high temperature, followed by milling and hot pressing and/or sintering to shape a product [1,2]. However, the formation of excess free carbon during these synthesis methods is problematic [2,3].…”

“…For example, the coarse-grained boron carbide powder requires intensive milling to generate a finer powder suitable for sintering; the intense milling also results in contamination from grinding media. Because of these issues, research is focused on alternative lower temperature synthesis methods that result in a fine powder with less residual carbon [3,[6][7][8]. The use of catalysts to remove residual carbon has been explored [9] 4 C, using solu y Weimer an ation tempera application o r specialised 6,17].…”

Microstructure in precursor formed by controlling composition of condensed boric acid-poly(vinyl alcohol) product for low-temperature synthesis of boron carbide powder

“…Thus, PVA is useful as a carbon source for the low-temperature synthesis of B 4 C powder. The morphology of the precursor obtained by the thermal decomposition of the condensed H 3 BO 3 -PVA product in air exhibits the dispersion of B 2 O 3 particles in a carbon matrix, 11) which is similar to the sea-island structure of a polymer alloy. This indicates that the morphological characteristics of a matrix polymer strongly determine the morphology of the precursor.…”

“…11) It is known that the phase-separated morphology of a polymer alloy is related to the volume fraction of each component. Furthermore, the number of hydroxyl groups of PVA, which react with H 3 BO 3 , in a condensed product increases with increasing PVA content, increasing the dispersion of H 3 BO 3 .…”