Strengthening of borosilicate glass by controlled crystallisation for lightweight bulletproof materials

For development of lightweight bulletproof glass window, TiO2 added as a nucleating agent to borosilicate glass was crystallised by 2-step heat-treatment. The glass transition temperature (Tg) and crystallisation temperature (Tc) were 595°C, 810°C, respectively. The maximum nucleation rate was 7.3 × 1010 mm–3 hr–1 at 600°C and the maximum crystal growth speed was 1.73 nm/min at 810°C. The maximum 3-point bending strength was 563 MPa when the crystal volume fraction and crystal size were 36.1%, 53.4 nm with number of crystals per unit volume of 4.525 × 1010 mm–3 at 600°C for 1 hr, 810°C for 30 min. The Vickers' hardness and fracture toughness of same crystal volume fraction were 736 kg/mm2 and 1.0779 MPa m1/2 which were about 220%, 17%, 44% higher than borosilicate glass. Thus, the bulletproof materials were replaced by crystallised borosilicate glass, which can be expected to be thinner and lightweight.