Study on optical phonon vibration and gamma ray shielding properties of composite geopolymer fly ash-metal

Abstract

Absorption properties of geopolymer from fly ash (FA) as a matrix, graphite and nickel or graphite and iron powder as a filler have been carried out by applying Cs-137 gamma ray source. Composite geopolymer was produced by the activating an alkaline solution and heated at 70 °C for 1 h. The optical phonon vibration determined from the quantitative analysis of Fourier transform infra-red (FTIR) spectra by using Krames Kronig (KK) relations. The difference between two optical phonon mode (LO-TO), longitudinal optical (LO) and transversal optical (TO) provided information of the stability bonding formation structure of composite geopolymer, for A-2 (graphite and nickel as a filler) shows the difference is 192 cm−1 and for A-3 (graphite and iron as a filler) shows the difference is 222 cm−1. The higher differences of optical phonon vibration mode is more stable bonding connection in composite compared with the lower differences. The TO mode was confirmed by the main peak position of imaginary dielectric function (ε2). The higher wavelength peak position of the LO for A-3 which confirmed by the energy loss function (ELF) (Im (−1/ε) compared with the A-2 due to the large of atomic radius of Fe (1.56 Å) compared with Ni (1.49 Å). The plasma frequency identified from the ELF is 1600 cm1 for A-2 and 1757 cm−1 for A-3. The absorption properties of sample A-3 by the attenuation coefficient 0.174 ± 0.008 cm−1 is higher and more effective than the sample A-2. The existence of large empty space on the sample A-2 is evidenced by its value of MFP which is higher than the sample A-3. In this study shows that the higher differences of two optical phonon vibration mode strongly influenced to the absorption properties which shows A-3 (graphite and iron) more effective than the A-2 (graphite and nickel) as a shield due to the strong bonding connection Al–Fe–Si formed in composite geopolymer.