February AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y / M A R C H 2 0 1 9 2 4 micrograph of PE MoAlB as an example. Thereafter, PE MoAlB particulates were used to fabricate a composite with cel- lulose acetate (CA) by solvent casting (Fig. 3b1). Figures 3(b2-b4) are schema- tics of solvent casting CA-PE MoAlB composites. Critical steps during the fabrication process are sonication in acetone (Fig. 3b2), dissolution of CA in acetone (Fig. 3b3), and solvent casting of the compositions (Fig. 3b4). Termi- nology used to designate composites in this study is CA-vol% MoAlB etchant. For example, CA-1vol% 12M HCl MoAlB implies that the cellulose-acetate com- posite is reinforced with 1 vol% PE MoAlB, where PE MoAlB is obtained from etching MoAlB with 12M HCl. Figures 3(c1-c3) show SEM mi- crostructures of polished surfaces of CA-1 vol% PE MoAlB composites. In all composites, PE MoAlB particulates are well dispersed in the polymer matrix. Figures 4(a-d) summarize the tensile strength behavior of the composites. Solvent-cast CA has a tensile strength of 50.8±10.9 MPa and shows brittle fail- ure (Fig. 4a). In general, the addition of both MoAlB and PE MoAlB particulates im- proved mechanical properties and duc- tility of the composites (Figs. 4a-d). For example, tensile strength increased by 1.4 times to ~71 MPa compared with CA after the addition of 0.5 and 1 vol% MoAlB-12M HCl-0.37M LiF par- ticulates (Figs. 4a-b). Comparatively, CA-1vol% MoAlB (milled), CA-1vol% 12M HCl MoAlB, and CA-1vol% MoAlB- 12M HCl-0.1M LiF showed similar strength of ~64.5, ~64.8, and ~62 MPa, respectively. In addition, CA-1 vol% MoAlB-12M HCl-0.37M LiF and CA-1vol% MoAlB-12M HCl-0.1M LiF were more ductile than the other compositions (Figs. 4a-b). However, after the addition of 2 vol% particulates, milled MoAlB particulates performed better than PE MoAlB and had a tensile strength of ~84.2 MPa, which is 1.65 times better than pure CA. The exact mechanism for this behavior is not yet clear and re- Fig. 3 — Schematics of the fabrication of PE MoAlB particulates: (a1) MoAlB template [8,14] ; (a2) partial etching of MoAlB; and (a3) FESEMmicrograph of a PE MoAlB. Schematics of fabricating cellulose acetate (CA)-PE MoAlB composites: (b1) PE MoAlB; (b2) sonication in acetone; (b3) stirring of the suspension with CA for 24 h; and (b4) solvent casting of CA-PE MoAlB composites. BSE SEMmicrographs of (c1) CA-1 vol%MoAlB- 12M HCl; (c2) CA- 1 vol%MoAlB-12 M HCl-0.1M LiF; and (c3) CA-MoAlB-12M HCl-0.37M LiF composites. (a1) (a2) (a3) quires more study to understand the fundamental process. In summary, the authors demon- strated that 0.37 mol MoAlB can be successfully partially etched (PE MoAlB) by using HCl and LiF-HCl etchants (12 M HCl, 12 M HCl-0.1M LiF, and 12 M HCl-0.37M LiF). Further, the par- ticulates can be dry processed and used as reinforcing particulates to fabricate polymer-matrix composites. Based on this research, the authors conclude that MoAlB and their particu- late derivatives can be used as property modifiers in polymer matrices, opening newavenues for potential applicationof the materials. MATERIALS AND METHODS For details about the manufac- turing of MoAlB particulates, refer to Ref. 13. MoAlB particulates were partial- ly etched with ~60 ml of 12 M HCl (ACS reagent 37%, Sigma Aldrich, St. Louis) mixed with 0.15 g (~0.1 M) and 0.16 g (0.38 M) LiF (BioUltra, ≥99.0%, Sigma Aldrich). Initially, the required amount of LiF was dissolved in 60 ml of 12 M HCl by stirring in a plastic container on a heated plate by a Teflon coated magnetic stir- rer at ~40 o C for ~5 min. Thereaf- ter, 3 g (~0.37 M) of MoAlB was added to the stirring solution. The resulting suspension was stirred for ~24 h at ~40 o C. The resulting suspension was then centrifuged at ~3000 rpm for 5 min. The resulting filtrate was drained, and fresh DI (distilled) water was added to the residue. The suspension was centrifuged again for 5 min. This cycle was continued for several cycles un- til the pH was 6. In addition, a separate experiment was per- formed where ~3 g of MoAlB was treated with ~60 ml of 12 M HCl. The etched particulates were washed by following the proce- dure described above. The resulting wet mixture was then dried at 100 o C for 24 h to obtain partially etched surfaces (PE MoAlB). The dried powers were ground in a mortar (b1) (b2) (b4) (b3) (c1) (c2) (c3)