Pumices have been used in cement, concrete, brick, and ceramic industries as an additive and aggregate material. It will be important to study pumice types by using a different tool as EPR which is a new technique for related material to be used for industrial aims. Electron spin resonance (ESR) spectra of the pumice types were taken by EMX-type spectrometer. Also, the current-voltage (
Pumice is a porous, natural glass formed from volcanic activity and contains relatively high concentrations of silica, aluminum, and iron. Pumice has been used as an adsorbent and as photo catalysts in water treatment. It was selected as the catalyst in the present study because of its excellent chemical and configurable properties, such as high mechanical strength and chemical stability [
Pumice may be used in regions where radiation is effective. It can easily be used in walls and coverings of medical buildings and nuclear reactors [
Pumice brings many advantages due to its superior properties like its low density, high heat and noise insulation, air conditioning characteristic, easy plaster retaining, perfect acoustic feature, and elasticity in case of seismic load and behaviors. However, it may be considered as a disadvantage that it causes disintegration in concrete due to low density and due to prior water absorption and additional water absorption amount during preparation of concrete mixture and the risk related to flocculation due to contact of aggregates with cement during concrete pouring [
Due to the fact that these pumice types (pumice, CDS, and PTS) can be used in different applications including boron industries and building process or as a radiation shielding material, it will be important to study pumice types by using a different tool as EPR which is a new technique for related material to be used for industrial aims.
Electron paramagnetic resonance (EPR) is the resonant absorption of electromagnetic radiation by a paramagnetic particle (atom, molecule, or ion), having nonzero electronic spin due to unpaired electrons in its outer shells, and it is a very powerful nondestructive technique used for the study of the electronic structure of paramagnetic centers, for example, transition metal ions such as copper, chromium, and nickel in a large variety of organic and inorganic compounds. The flipping of spins induced in a paramagnetic system embedded in a static magnetic field by the absorption of the electromagnetic radiation is the physical principle behind the EPR technique. For a system with a spin
Chemical analyses of the volcanic rocks are taken by X-ray fluorescence (XRF) instrument. Operating conditions of the Philips PW-2400 XRF instrument were set at 60 kV and 50 mA. The compositions of the pumice samples were checked by X-ray powder diffraction. By comparing the positions of the diffraction peaks against that of the ICDD cards; the target material was identified. Loss of ignition (LOI) of the samples was measured by weighing the samples before and after heating up to 1000°C. Lower detection limits are 0.01 wt.% for all element species.
Electron paramagnetic resonance (EPR) spectra of the volcanic rocks samples were taken by high sensitive conventional X-band (9.5 GHz) Bruker EMX-type spectrometer at room temperature.
The current-voltage (
Figure
SEM images: (a) pumice, (b) PTS, and (c) CDS.
Figure
EDS analysis: (a) pumice, (b) PTS, and (c) CDS.
A new approach was introduced for the analysis of complex civil engineering problems using EPR. The capabilities of the EPR methodology were illustrated by applying it to two practical problems involving the prediction of the stability status of slopes and the compressive strength of rubber concrete [
EPR spectra were taken for Fe+ ion. The broad EPR lines stem from strong dipolar interactions of their unpaired magnetic moments. Samples were measured using an X-band (9.53 GHz) EPR spectrometer with modulation of magnetic field of 10 kHz. EPR spectra were measured with attention of 23 dB to avoid microwave saturation of resonance absorption curves. Figure
X-band EPR spectra of the volcanic rocks: (a) pumice, (b) CDS, and (c) PTS.
The lines were observed in these resonance absorption curves in Figure
Free radicals are generally highly unstable and have very short residence time. However, the certain free radicals have persisted for much longer duration because they were trapped in a stable cell wall matrix [
Based on our EPR measurements it is possible to conclude that, similarly as in the investigation of the hardening during the sol-gel processes, the presence of Mn2+ ions in the cements can be used for the characterization of the kinetic parameters of the solidification and hardening of cement slurries [
The three lines were observed in this resonance absorption curves in Figure
Four-point probe technique was employed during the in-plane conductivity measurements, which were designed according to the property of the samples. The typical spot bias current (
The surface resistivity and conductivity values are obtained by four-point probe measurement techniques. The source current (
The surface resistance measurements.
Samples |
|
|
Surface resistivity × 108 |
Conductivity × 10−9 |
---|---|---|---|---|
CDS | 8.04539 | 1.07199 | 6.03857 | 1.65602 |
PTS | 8.02811 | 0.48724 | 2.75057 | 3.63561 |
Pumice | 8.96023 | 1.14774 | 5.80514 | 1.72261 |
As seen in Table
As seen in Table
Qualitative and quantitative analysis for pumice types.
Element (line K |
Conc. (wt%) | |
---|---|---|
Pumice | O | 65.779 |
Al | 7.254 | |
Si | 24.400 | |
K | 2.436 | |
Ca | 0.130 | |
|
||
PTS | O | 69.187 |
Al | 7.035 | |
Si | 19.077 | |
Ca | 2.083 | |
Fe | 2.617 | |
|
||
CDS | O | 69.735 |
Al | 5.681 | |
Si | 14.974 | |
Ca | 2.871 | |
Fe | 6.739 |
Shielding is particularly needed for underground vaults containing transformers and other electronics that are relevant to electric power and telecommunication. The main mechanism for electromagnetic interference shielding using conductive materials is reflection. Another mechanism is absorption. The loss is due to absorption increase with increasing frequency [
Ramezanianpour et al. show that although in concretes with similar cementations materials different relationships can be found, but generally because of different mechanisms of compressive strength and electrical resistivity, there is no appropriate relationship between them. Consequently it is not recommended to use electrical resistivity as an indicator for evaluation of compressive strength. But SR (surface resistivity) can be used as an electrical indicator of concrete chloride penetration resistance [
Current biases variation of surface resistivity for the volcanic rocks.
The elemental compositional differences are present between the volcanic rocks with energy dispersive spectrometer (EDS) measurement. EDS measurements of all the samples were made on a point which was a selected area from the SEM micrographs. EDS analysis with SEM micrographs illustrating that pore size increased with iron (Fe) appearance and decreased with silicon (Si) concentration in the elemental composition of samples, shown in Table
EPR studies have shown that the three lines (1500 G (
The lowest compression strength is seen in concretes containing pumice. This state may be attributed to pumice’s porous structure. There is a correlation between
Pumice develops flexibility due to its high amorphous structure. The most flexible sample as PTS having a value of
As seen in Table
As a result, we have recommended CDS as an aggregator in terms of shielding rather than PTS and pumice.
The authors declare that there is no conflict of interests regarding the publication of this paper.