PSI - Issue 13

Igor Bunin et al. / Procedia Structural Integrity 13 (2018) 1971–1976 Author name / Structural Integrity Procedia 00 (2018) 000–000

1973

3

Table 1. Chemical composition of calcium-bearing minerals, wt %.

Mineral

Ca

W

F

Si

Fe

Al

Mg

Sr

Ba

S

Pb

Mn N/d N/d

Scheelite – CaWO 4 Fluorite – CaF 2 Calcite – CaCO 3

57.11 53.50 40.68

14.08

0.29

0.52 0.15 0.11

0.42 0.01 0.10

0.43 0.15 0.05

0.06 N/d 0.03

N/d 0.03 0.01

N/d 0.03 0.02

0.48 N/d N/d

0.15 N/d N/d

N/d N/d

39.58

0.85

0.002

Calcite (CaCO 3 ) specimens were presented with pop-offs along mineral cleavage (up to 1×1 cm in size) of calcite crystal (Iceland spar). The mineral is colorless, transparent, with glass luster and stepped break-line. Calcite exhibits perfect mineral cleavage in rhomb directions. Mohs’ hardness equal to 3. Table 2. Phase and chemical composition of kimberlite rock-forming minerals, wt %. Mineral MgO SiO 2 Fe 2 O 3 CaO Al 2 O 3 S Ni Cr Br Serpentine 36.56 41.12 5.57 0.18 0.83 0.24 0.37 0.26 – Olivine 46.04 39.60 11.10 0.68 0.28 0.17 0.37 0.01 0.13 Serpentine specimen (lizardite – Mg 3 SiO 5 (OH) 4 , antigorite – (Mg, Fe) 3 Si 2 O 5 (OH) 4 ) is dark-green in color with greasy luster and Mohs’ hardness 2.5–4. The microinclusions of sulfides (millerite NiS) and oxides (chromite FeCr 2 O 4 , magnesiochromite MgCr 2 O 4 ) of less than 0.01 mm in size were detected at the polished mineral surface. Olivine specimen (Mg, Fe) 2 [SiO 4 ]) mainly consists of 0.5-3 mm forsterite grains with minor impurity of magnetite. The mineral hardness in Mohs’ scale is high (Mohs’ hardness is equal to 6.5–7), mineral cleavage is moderate in a single direction. Some moderately-rounded grains (less than 5%) are covered with magnetite “shirt”. We conducted the treatment of mineral specimens with high-voltage nanosecond video-pulses. Pulse duration was no longer than 10 ns, the strength of the electric component of the field was ~10 7 V/m, the energy in each pulse was 0.1 J, the pulse repetition frequency was 100 Hz, and the range of varying the treatment time treat t was 10–150 s (the dose of the electromagnetic pulsed radiation was imp N =10 3 –1.5×10 4 pulses). Before treatment, the samples were wetted with distilled water in an S:L ratio of 5:1 to increase the efficiency of the electromagnetic pulse impact. 2.2. Analysis techniques We used X-ray photoelectron spectroscopy (XPES) and Diffuse reflectance infrared Fourier transform spectroscopy (FTIR, DRIFTS) to analyze the phase composition of the surfaces of mineral particles. To acquire the X-ray photoelectron (XPE) spectra, we used a Kratos Axis Ultra DLD spectrometer with a monochromatic Al K α X-ray radiation source. The IR-spectra of the diffuse reflection of mineral powders were recorded over a 400–4000 cm –1 range of varying wave numbers with a resolution of 4 cm –1 using an IRAffinity-1 IR-spectrometer (Shimadzu) equipped with a DRS-8000 diffuse-reflection attachment. The adsorption of Hammett indicators from aqueous media was used to analyze the acid– base centres (functional chemical composition) of the Ca-bearing mineral surfaces; we performed the spectrophotometric measurements using a UV-1700 spectrophotometer (Shimadzu). The morphological and chemical properties of mineral surface were studied using analytical electronic microscopy (SEM–EDX; scanning electronic microscope LEO 1420VP, and energy-dispersive spectrometer Oxford INCA Energy 350). Nanoscale features of surface relief (Z–coordinate was less than 100 nm) have been studied by atomic force microscopy (AFM; INTEGRA Prima, NT-MDT) in semi-contact mode. The cantilever (NSG10/Au) has a resonance frequency of 240 kHz and a force constant of 11.8 N/m; tip curvature radius was 35 nm. We estimated the microhardness of Ca-bearing and rock-forming minerals in the initial state and after electric pulse treatment of polished mineral sections using Vickers’ method ( HV , MPa; under ISO 6507-1: 2005) at PMT-3M microhardness tester (LOMO, Russia). Vickers’ microhardness value was calculated using standard equation: 6 2 / ) 10 (0.189   P d HV , where P – normal load applied to diamond tip, N; d – arithmetic average lengths of both indent diagonals, μm. Experimental procedure runs as follows: microhardness of minerals was measured before and after HPEMP treatment at flat-parallel polished plates in middle and peripheral areas of sections under experimental loads (P, g) on an indenter (calcite – 50 g, scheelite and fluorite – 100 g, serpentine and olivine – 200 g; loading time was 10–15 seconds). We studied the relationships between relative variations in microhardness of minerals under HPEMP irradiation versus the pulsed treatment time treat t : ) / ,% ( 0 0 i i i HV HV HV  , where i HV 0 – microhardness of i -th specimen in initial state; i HV – microhardness of i -th specimen after electric pulse treatment.