White and some colored marbles as alternative radiation shielding materials for applications

ABSTRACT

In this paper, the radiation shielding parameters such as linear attenuation coefficients (LAC, µ), mass attenuation coefficients (MAC, µ/ρ), effective atomic numbers (Z_eff), effective electron densities (N_eff), half value of layers (HVL), mean free paths (MFP) and buildup factors (exposure (EBF) and energy absorption (EABF)) were investigated for cream (M1), pink (M2), white (M3), maroon (M4) and green (M5) marbles. Attenuation coefficients were measured in the energy region 31.18–661.66 keV photon energies. The values of Z_eff and N_eff were then calculated using these coefficients with logarithmic interpolation method, and HVLs and MFPs were calculated using the values of LAC of marble samples at the same photon energies. The experimental results were compared with the theoretical values obtained from WinXCom program, and good agreements were observed between the experimental and theoretical results. HVLs and MFPs of all marble samples were compared with those of some concretes, glasses and commercial radiation shielding glasses (SCHOTT Co.). The studied marbles were better radiation shielding materials than standard shielding concretes due to lower HVL and MFP values lower than the ordinary concrete. Finally, EBFs and EABFs of the marbles were calculated in the energy region 0.015–1?MeV up to penetration depths of 40 mfps by Geometric Progression method (G-P), and the results were discussed in terms of photon energies and chemical compositions of the marbles.     

Analytical investigation of calcium oxalate films on marble monuments

This paper describes an analytical approach to investigate the origin of oxalate films on marble. Calcium oxalate films were collected on buildings of historical importance in Lucca and Pisa (Italy) and characterised by optical microscopy (OM), scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX), Fourier transform infrared (FTIR) spectroscopy (equipped with diamond cell), and gas chromatography-mass spectrometry (GC-MS). The morphology of the films was investigated by optical and electronic microscopy. FTIR analyses highlighted the presence of calcium oxalate (both as whewellite and weddellite), gypsum, calcite, nitrates, silicates and apatite, while EDX maps showed the distribution of elements. Several samples showed traces of organic compounds, identified by GC-MS as paraffin wax, lipids of animal origin and egg. The correlation between organic material and oxalate contents suggests the origin of the films from degradation processes of past surface treatment.     

Waste marble dust-filled sustainable polymer composite selection using a multi-criteria decision-making technique

This research works with the optimal design of marble dust-filled polymer composites using a multi-criteria decision-making (MCDM) technique. Polylactic acid (PLA) and recycled polyethylene terephthalate (rPET)-based composites containing 0, 5, 10, and 20 wt% of marble dust were developed and evaluated for various physicomechanical and wear properties. The results showed that the incorporation of marble dust improved the modulus and hardness of both PLA and rPET. Moreover, a marginal improvement in flexural strength was noted while the tensile and impact strength of the matrices were deteriorating due to marble dust addition. The outcomes of wear analysis demonstrated an improvement in wear resistance up until 10 wt% filler reinforcement, after which the incidence of dust particles peeling off from the matrix was observed, thereby reducing its efficiency. The best tensile modulus of 3.23 GPa, flexural modulus of 4.39 GPa, and hardness of 83.95 Shore D were obtained for 20 wt% marble dust-filled PLA composites. The lowest density of 1.24 g/cc and the highest tensile strength of 57.94 MPa were recorded for neat PLA, while the highest impact strength of 30.94 kJ/m² was recorded for neat rPET. The lowest wear of 0.01 g was obtained for the rPET containing 5 wt% marble dust content. The experimental results revealed that for the examined criteria, the order of composite preference is not the same. Therefore, the optimal composite was identified by adopting a preference selection index-based MCDM technique. The findings demonstrated that the 10 wt% marble dust-filled PLA composite appears to be the best solution with favorable physical, mechanical, and wear properties.     

Methodologies for laboratory Laser Induced Breakdown Spectroscopy semi-quantitative and quantitative analysis—A review

Since its early applications, Laser Induced Breakdown Spectroscopy has been recognized as a useful tool for solid state chemical analysis. However the quantitative accuracy of the technique depends on the complex processes involved in laser induced plasma formation, ablation, atomization, excitation and ion recombination. Problems arising from laser target coupling, matrix effect, fractionation in target vaporization, local thermodynamic equilibrium assumption and interferences from additional air ionization should be properly addressed in order to obtain reliable quantitative results in laboratory to be used as starting point during field campaigns.     

Radiometric analysis and radiological hazards of Chinese commercial marble

The activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in commercial marble materials have been determined using a NaI(Tl) γ-ray spectrometer with a matrix-inversion-based spectral stripping technique. Knowledge of radioactivity present in marble materials enables one to assess any possible radiological risks to human health. The concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in Chinese commercial marble range from 8.4 to 157.4, 5.6 to 165.5 and 44.1 to 1352.7 Bq kg^?1, respectively. The natural radionuclide concentration varied with color and production site of commercial marble. The activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in white, gray, black, green and yellow marble samples are comparatively smaller than those in brown and red marble samples. The radium equivalent activity (Ra_eq), the external hazard index (H _ex), the internal hazard index (H _in) and the annual gonadal dose equivalent were also calculated and compared with the internationally recommended values. One type of brown commercial marble (TSB) of China does not satisfy the universal standards.     

Efficiency and resistance of the artificial oxalate protection treatment on marble against chemical weathering

The artificial oxalate protection method was analyzed in laboratory experiments in order to achieve an optimum treatment application and concentration giving rise to its most effective protective nature. Spectroscopic (Fourier transform infrared, Micro-Raman and UV-vis colorimetry), microscopic (scanning electron microscope) and contact-angle analyses were carried out to characterize Carrara marble samples before and after application of the treatment to validate its efficiency. The resistance effects against chemical weathering were subsequently observed in a lab-controlled weak acid rain experiment. An acid spray at pH 5.5, representative of normal rain was used to provoke degrade of natural marble, marble treated with the artificial oxalate protective at concentrations of 0.4 and 5% and marble treated with a commercial organic silicon product. Run-off solutions sampled at timely intervals were tested for any change in pH followed by ion chromatography measurements for the presence of calcium ions in solution. The chromatography results of the oxalate treatment applied at a 5% concentration are analogous to an organic commercial product indicating its validity as a method for the conservation of carbonate substrates conferring protection to stone materials against acid environments.     

大理岩微裂隙与其力学性质间的关系

香港元朗地区发育有大量的大理岩, 它的力学性质直接影响该区的建筑安全。我们采用超声测量技术、单轴压缩试验和岩石薄片的镜下观测等方法了解其内部的结构变化及其力学性质。得出的结论是：该区的大理岩力学性质变化很大。一般的说, 致密的黑色大理岩超声波速度高, 抗压强度大且具有脆性特征, P波速度6.2～6.5km·s-1, S波速度3.0～3.60km·s-1, 抗压强度在88～166MPa;而那些颗粒较粗的白色或灰色大理岩, 超声波速度变化很大, 抗压强度小且具有韧性特征, P波速度在4.2～6.9km·s-1, S波速度2.4～3.20km·s-1, 抗压强度在52～63MPa之间。P波速度与裂隙密度成反比关系。抗压强度与裂隙密度成线性反比关系, 而且对脆性大理岩, 其曲线斜率要比韧性大理岩的曲线斜率大出许多倍。     

Lead separation by sorption onto powdered marble waste

Batch adsorption experiments were carried out, aiming to remove lead ions from aqueous solutions and water samples using powdered marble wastes (PMW) as an effective inorganic sorbent, which is cheap, widespread, and may represent an environmental problem. The main parameters (i.e., solution pH, sorbent and lead concentration, shaking time, and temperature) influencing the sorption process, were investigated. The results obtained showed that the sorption of Pb²⁺ ions onto PMW was fitted well with the linear Freundlich and Langmuir models over the concentration range studied. From the Dubinin–Radushkevick (D–R) isotherm model it was found that the adsorption was chemical in nature. Thermodynamic parameters viz. the change in Gibbs free energy change (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were also calculated. These parameters indicated that the adsorption process of Pb²⁺ ions on PMW was spontaneous and endothermic in nature. Under the optimum experimental conditions employed, the removal of about 100% of Pb²⁺ ions was attained. The procedure was successfully applied to remove lead ions from aqueous and different natural water samples. Moreover, the adsorption mechanism is suggested.     

Raw and treated marble wastes reuse as low cost materials for phosphorus removal from aqueous solutions: Efficiencies and mechanisms

Phosphorus removal from synthetic solutions by raw and calcined powdered marble wastes (RPMW and CPMW) has been investigated in batch mode under different experimental conditions. The results showed that RPMW and CPMW have high removal efficiencies, especially in acidic media. The maximum phosphorus removal capacities were evaluated to 103.9 and 181.2 mg·g⁻¹ at an initial pH and an aqueous concentration of 5 and 350 mg·L⁻¹, respectively. Phosphorus removal by RPMW occurred mainly through adsorption. However, for CPMW, phosphorus was removed not only by adsorption, but also by precipitation as calcium phosphate complexes. Specific analyses using scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy confirmed that this precipitate is most probably hydroxyapatite. On the other hand, CPMW have demonstrated an important ability in removing phosphorus from highly concentrated dairy wastewater (C_0,P = 1000 mg·L⁻¹) since only one dosage of 10 g·L⁻¹ was enough to ensure more than 97% of phosphorus removal.