Laser desorption/ionization mass spectrometry of Li1.999Ta0.005SiO3

Abstract

In the last couple of decades the scientific is making great efforts to investigate the phenomenon of laser-matter interaction, because these knowledge can directly positively influence on technological innovations in the field of materials. This phenomenon are still not fully invetigate since involves a number physical and chemical processes, which take place simultaneously or separated in time and space [1]. The laser desorption/ionization (LDI) implies the following processes: the laser provide a pulse of energy to sample (for a few ns), the sample increases in temperature quickly ( to several thousand degrees), so lead to the production ions, neutrals and electrons in the gass phase [2]. The aim of this paper is to examine the products of the gas phase formed during the interaction of laser- Li1.999Ta0.005SiO3. The Li1.999Ta0.005SiO3 ceramics has a wide application because the melting of lithium metasilicate is used for the calibration of thermocouples, as a flux in glazes and ceramic enamels, dental glass, nuclear waste immobilization as well as ceramic materials for fusion reactors. The knowledge gained should contribute to a better understanding behavior of Li1.999Ta0.005SiO3 in extreme conditions. The experiments were performed on a commercial matrix-assisted laser desorption/ionization mass spectrometer (MALDI MS) with time of flight mass analyzer (Voyager-DE PRO, Sciex, USA), equipped with a nitrogen pulse laser (pulse duration of 3 ns, 20 Hz, and wavelength of 337 nm). The mass spectra were obtained using the LDI (without matrices) positive and negative reflector modes. It is known that the LDI MS is an efficient method for the production and detection of homogeneous and heterogeneous clusters [3]. Preliminary results shows that the ion signals in the negative ion LDI mass spectrum of Li1.999Ta0.005SiO3 correspond to the following species: m/z 59.89 SiO2 - (calcd 59.97), m/z 71.90 Si2O- (calcd 71.95), m/z 83.90 Si3 - (calcd 83.93), m/z 95.91 Si(OH)4 - (calcd 95.99), m/z107.91 Si2(OH)2(H2O)- (calcd 107.97), m/z 119.92 Si2O4 - (calcd 119.93), m/z 120.95 Si2O3(OH)- (calcd 120.94), m/z 131.93 Si3O3 - (calcd 131.92), m/z 143.92 Si2(OH)2(H2O)3 - (calcd 143.99). The ion signals in the positive mode were attributed to the following cations: LiSi(OH)+ (m/z 52.02, calcd 51.99), Li3(OH)(H2O)+ (m/z 56.04, calcd 56.06), Li2SiO+ (m/z 58.05 calcd 58.00), Li3Si2H2(H2O)+ (m/z 97.15 calcd 97.03), Li5Si2H2O+ (m/z 109.10, calcd 109.04). The results show that silicon-oxygen cluster ions were formed in the negative mode, while lithiumsilicon clusters were detected in the positive mode.