TY - THES

T1 - Charging of calcite(100) surface by contact with mineral particles studied by Kelvin Probe Force Microscopy

AU - Klima, Stefan

N1 - embargoed until 17-06-2020

PY - 2015

Y1 - 2015

N2 - Contact charging of mineral particles is an important topic within the framework of the industrially applied triboelectrostatic separation (TS) in mineral processing. During TS, charge is transferred between touching particles yielding positive/negative net charges on them. So far, the mechanism of charge transfer upon contact is still not well understood. In this work, the smallest subprocess - which is the contact electrification upon contact with a single particle - has been investigated in order to deepen insight into the charging behaviour. As a model system, the charging behaviour of a calcite(100) surface in contact with a single micrometer size mineral particle was investigated. For this purpose, a combination of atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) was employed. An AFM based technique to rub a single, few 10 µm large particle with defined force and speed on a surface was developed. The rubbing experiments with a particle glued to an AFM cantilever were done at two contact forces and at three different temperatures. After rubbing, the charging was monitored by measuring the local contact potential difference (CPD) using KPFM. Additionally, AFM force distance (FD) curves were recorded in order to quantify the occurring electrostatic forces. The surface analysis was performed using a standard conductive AFM tip. The analysed area (50 x 50 µm2) was significantly larger than the rubbed area (20 x 20 µm2). This allowed also to observe possible long range influences on the surrounding area. The change of the CPD depends on the rubbing material. Rubbing with a calcite particle leads to a decrease of the CPD, whereas rubbing with a quartz particle increases the CPD of the calcite(100) surface. An analysis of the temporal evolution of the CPD indicated an exponential decay of the introduced charge. FD curves revealed maximum electrostatic forces of ~45 pN, acting between AFM probe and charged areas. All of the conducted experiments demonstrate the applicability of the developed technique to study surface charging due to rubbing in triboelectrostatic separation.

AB - Contact charging of mineral particles is an important topic within the framework of the industrially applied triboelectrostatic separation (TS) in mineral processing. During TS, charge is transferred between touching particles yielding positive/negative net charges on them. So far, the mechanism of charge transfer upon contact is still not well understood. In this work, the smallest subprocess - which is the contact electrification upon contact with a single particle - has been investigated in order to deepen insight into the charging behaviour. As a model system, the charging behaviour of a calcite(100) surface in contact with a single micrometer size mineral particle was investigated. For this purpose, a combination of atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) was employed. An AFM based technique to rub a single, few 10 µm large particle with defined force and speed on a surface was developed. The rubbing experiments with a particle glued to an AFM cantilever were done at two contact forces and at three different temperatures. After rubbing, the charging was monitored by measuring the local contact potential difference (CPD) using KPFM. Additionally, AFM force distance (FD) curves were recorded in order to quantify the occurring electrostatic forces. The surface analysis was performed using a standard conductive AFM tip. The analysed area (50 x 50 µm2) was significantly larger than the rubbed area (20 x 20 µm2). This allowed also to observe possible long range influences on the surrounding area. The change of the CPD depends on the rubbing material. Rubbing with a calcite particle leads to a decrease of the CPD, whereas rubbing with a quartz particle increases the CPD of the calcite(100) surface. An analysis of the temporal evolution of the CPD indicated an exponential decay of the introduced charge. FD curves revealed maximum electrostatic forces of ~45 pN, acting between AFM probe and charged areas. All of the conducted experiments demonstrate the applicability of the developed technique to study surface charging due to rubbing in triboelectrostatic separation.

KW - AFM

KW - KPFM

KW - Kraft-Abstandskurven

KW - Kontakt Potential Differenz (CPD)

KW - Kontaktaufladung

KW - mineralische Partikel

KW - AFM

KW - KPFM

KW - force distance curve

KW - contact potential difference (CPD)

KW - contact charging

KW - mineral particles

M3 - Diploma Thesis

ER -