Observation of incipient particle formation during flame synthesis by tandem differential mobility analysis-mass spectrometry (DMA-MS)

Abstract

While flame aerosol reactor (FLAR) synthesis of nanoparticles is widely used to produce a range of nanomaterials, incipient particle formation by nucleation and vapor condensation is not well understood. This gap in our knowledge of incipient particle formation is caused by limitations in instruments, where, during measurements, the high diffusivity of sub 3 nm particles significantly affects resolution and transport loss. This work used a high resolution Differential Mobility Analyzer (DMA) and an Atmospheric Pressure Interface-Mass Spectrometer (APi-TOF) to observe incipient particle formation during flame synthesis. By tandemly applying these two instruments, Differential Mobility Analysis-Mass Spectrometry (DMA-MS) measured the size and mass of the incipient particles simultaneously, and the effective density of the sub 3 nm particles was estimated. The APi-TOF further provided the chemical compositions of the detected particles based on highly accurate masses and isotope distributions. This study investigated the incipient particle formation in flames with and without the addition of synthesis precursors. Results from FLAR using two types of precursors including tetraethyl orthosilicate (TEOS) and titanium isopropoxide (TTIP) are presented. The effect of the precursor feed rates on incipient particle growth was also investigated.

The high charge fraction of flame-generated particles in the size range below 3 nm measured by enhanced particle detectors

“…Therefore, it would be worthwhile to conduct as collision cross section area, atom arrangement, etc [29]. However, in order to obtain the particle mobility and mass simultaneously, a tandem arrangement of the DMA and mass spectrometer, and more complex data analysis are required, which can be found in a recent study of the same group [4].…”

“…In recent years, the demand for precise control of functional flame-synthesized nanoparticle properties, such as their size, morphology, and crystal phase, has led to a growing interest in studying particle formation mechanisms in high temperature systems. While synthesizing nanoparticles, the flame generates a large amount of ions and charged particles due to the chemical ionization and thermal ionization reactions [1][2][3][4]. The existence of these ions makes the flame a quasi-neutral plasma that significantly impacts particle formation and growth processes that eventually determine the properties of the synthesized nanomaterials.…”

Influence of flame-generated ions on the simultaneous charging and coagulation of nanoparticles during combustion

“…According to Fuchs' charging theory (1963), the only unknown parameters in calculating the ion-particle combination coefficient are the positive and negative ion mobilities and masses. Ideally, the mobility and mass of an ion should be measured with a tandem DMA-MS setup, where these values are obtained at the same time (Maißer et al 2015;Wang et al 2017b). Due to the instrument limitation, ion mobility was the only parameter measured in this study.…”

“…A premixed flat flame was used in this study to measure ion mobility distributions, due to its high stability, uniformity, and broad usage. A detailed description of the setup can be found elsewhere (Wang et al 2017b). The combustion mixture was composed of methane (CH 4 , Airgas Inc., Radnor, PA, USA), oxygen (O 2 , Airgas Inc.), and nitrogen (N 2 , Airgas Inc.) whose flow rates were controlled by mass flow controllers (MKS Inc., Andover, MA, USA).…”

The initial stages of multicomponent particle formation during the gas phase combustion synthesis of mixed SiO2/TiO2

“…Single component SiO 2 and multicomponent SiO 2 / TiO 2 clusters were generated using a premixed methane air flat flame aerosol reactor (Wang et al 2017a(Wang et al , 2017b. Figure 1 displays the experimental setup where methane (CH 4 , >99.95%, Linde AG, Munich, Germany), oxygen (O 2 , >99.95%, Linde AG, Munich, Germany), nitrogen carrier gas (N 2 , >99.95%, Linde AG, Munich, Germany), and gaseous precursor were premixed and stabilized over a 1.91 cm diameter flat flame burner head.…”