Identification of photoluminescence features of an epoxy resin based on components features and curing effects

Photoluminescence features in a commercial grade cured DGEBA-based epoxy resin have been investigated with as objective to determine which of the material compounds are responsible for cured resin emissions. The origin of the bands has been approached by considering photoluminescence of base resin and hardener taken separately, of their mixture, and in the course of curing. Most of the bands observed in the cured resin could be interpreted based on those found in the components taken separately. Fluorescence of the cured resin appears dominated by two broad bands that are characteristic of the hardener and exhibits a blue shift by up to 30 nm in the course of curing which could be used for cure monitoring purpose of the investigated system. Fluorescence of the base resin is clearly detected in the resin cured with tertiary amine as catalyser. However, it is very weak if the catalyser is not added. Two phosphorescence processes have been isolated in the cured resin, one of them being related to the base resin. Finally, a chemiluminescence spectrum has been recorded in the course of curing, which has been related to either curing-related reactions or to an oxidation process.     

Thermoluminescence kinetic analysis of basaltic rocks using a generalized model for exponential distribution of activation energies

A new general order Thermoluminescence (TL) model for exponential distribution of activation energies has been presented. In the proposed model an effective kinetic-order has been introduced as an additional adjustable parameter. This makes it possible to take the re-trapping into account and would give a better estimate of the activation energy compared with the first order kinetics model. The proposed model has been applied to the basaltic rocks from central zone of Iran. The obtained results show that the proposed model gives a better fit to the experimental peaks compared to the first order model.     

Analysis of thermoluminescence kinetics of Mg2SiO4:Tb compounds employing an interactive model

The kinetics involved in the thermoluminescence (TL) of Mg₂SiO₄:Tb compounds has been investigated by unfolding glow curves employing both the General Order model and a model that takes into account interactions among traps. The dependence of the glow curve shape on dose is only correctly described if interaction among traps is included in the analysis.     

Study on TL and OSL characteristics of indigenously developed CaF2:Mn phosphor

CaF₂:Mn phosphor is known for its high thermoluminescent sensitivity and dose linearity up to few kGy. In the present study CaF₂ phosphor with different concentration of Mn dopant was prepared and was characterized through different techniques. The phosphor was prepared through chemical root using CaCO₃, HF acid and MnCl₂ as raw materials following co-precipitation method. TL sensitivity of the prepared phosphor was compared with other well established phosphors used for radiation dosimetry. It was found that the TL sensitivity is higher by a factor of 10 with respect to LiF:Mg, Ti, TLD-100 and half to that of CaSO₄:Dy (0.05 mol%) phosphor. X-ray diffraction, TL emission spectrum and ESR spectrum taken of the prepared phosphor confirms the crystal structure, Mn²⁺ emission and incorporation Mn in the crystal, respectively. No significant fading of the dosimetric peak was observed of the prepared phosphor for a storage period of 45 days. The dose linearity of the phosphor was found to be in the range of 50 Gy-3 kGy within an uncertainty of about 10%. An attempt was made to determine the kinetic parameters of TL glow curve and the parameters related to optically stimulated luminescence. In view of its long range of dose linearity, it can be used for the dosimetry of commercial irradiator generally used for the irradiation of food and grains in our country.     

Turbulence of Capillary Waves on the Surface of Quantum Liquids

The techniques developed earlier for study of turbulence on the surface of liquid hydrogen was used for generation of nonlinear waves on the charged surface of liquid ⁴He. This permitted us to observe for the first time capillary turbulence on the surface of liquid ⁴He in normal and superfluid state, and to expand in a few times the relative width of the inertial interval, where the Kolmogorov-Zakharov spectrum of turbulence was observed.     

CaF2:Tm (TLD-300) thermoluminescent response and glow curve induced by γ-rays and ions

The thermoluminescent response of CaF₂:Tm after exposure to ⁶⁰Co γ-rays at doses from 0.44 Gy to 8.75 kGy and to low fluences (10⁵ ∼ 10⁸ cm⁻²) of 25 and 40 MeV ¹H, 75 and 120 MeV ³He, 180, 300 and 480 MeV ¹²C, 400 MeV ¹⁶O and 800 MeV ²⁰Ne ion beams, spanning a LET interval up to about 500 keV/μm, has been investigated. A careful deconvolution analysis of the glow curve has been performed in order to obtain information for individual peaks. The region of linear response to gammas extends up to ≈1 Gy, while that for ions includes the complete dose interval covered in the study (up to ≈1.3 Gy). The ratio between the high- and low-temperature structures in the glow curve is correlated with radiation quality and dependence on ion identity, besides LET, is strongly suggested by the data. The thermoluminescent efficiency to ion exposure, with respect to irradiation with ⁶⁰Co γ-rays, shows a different dependence on LET for each of the peaks. In general terms, the efficiency reaches a maximum between 1.2 and 1.4 near 6 keV/μm and decreases for higher LET. Peak 3 displays a unique trend, its relative efficiency is always less than 1.0 and shows a strong monotonic inverse dependence with LET.     

Pressure Effects on Superconducting and Magnetic Transitions in Layered Sodium Cobalt Oxides, NaxCoO2

Magnetoresistance for field close to the parallel to the superconducting planes direction has been studied in organic superconductor κ-(BEDT-TTF)₂Cu[N(CN)₂]Br. The results show a first order phase transition between the superconducting state and the normal state at the upper critical field H_c2. The 1^st order transition is evidenced by the hysteretic behavior in the magnetoresistance as a function of field or angle between the field and the plane. A possible model is discussed.     

Active control of oxygen in molten lead-bismuth eutectic systems to prevent steel corrosion and coolant contamination

The thermodynamic basis for controlling oxygen level in lead-bismuth to prevent steel corrosion and coolant contamination is examined. The operational conditions, including the thermodynamic activity of oxygen, cover gas oxygen partial pressure, mixtures of H₂ and H₂O (steam) to obtain such low oxygen partial pressure (<10⁻²⁴ atm or around 10⁻⁶ wt% in lead-bismuth), and the voltage signals of one type of oxygen sensors (with a solid electrolyte and molten bismuth reference electrode) are calculated. These results provide the guidance to implement the oxygen control technique.     

In vitro electrochemical corrosion behavior of functionally graded diamond-like carbon coatings on biomedical Nitinol alloy

The anti-corrosion property plays an important role in determining the biocompatibility of metal implants. In this study, functionally graded diamond-like carbon coatings were deposited on the Nitinol substrate by hybrid magnetron sputtering and plasma enhanced chemical vapor deposition. A scratch test was adapted to study the adhesion strength of the coatings. The Si/SiC graded layer (up to 150 nm thick) provided good adhesion between the coating and the substrate, up to approximately 47.17 ± 2.1 N. The effectiveness of corrosion protection for the coated specimen was investigated in Tyrode's simulated body fluid. It was found that adhesion strength had a great influence on the effectiveness of corrosion protection, and the better adhesion strength, the better corrosion resistance. Compared to the others, the coating with a 150 nm thick Si/SiC graded layer provided better corrosion protection, and there existed no large amount of debonding and cracking of the coating around corrosion pits after the potentiodynamic polarization tests.     

Role of silicon in the formation of the corrosion resistance of austenitic materials for cryogenic engineering

The effect of silicon on the operational efficiency and corrosion resistance of low-temperature equipment made of 12Kh18N12T chromium-nickel steel has been studied. The specific features of the cryogenic equipment consist in high-temperature heating procedures between operation periods. Equipment for gas liquefaction and cleaning aimed at the restoration of the operational efficiency of filtration and catalysis systems serves as an example. The heating temperature of this equipment can reach 800°C. Experimental steels containing 0.09–1.03 wt % Si are subjected to intercrystalline corrosion tests. Upon heating to 550–600°C, silicon is found to increase the corrosion resistance of the steel, and, upon heating at higher temperatures, silicon plays a negative role. This is caused by the distribution of silicon atoms along grain boundaries, namely, a nonuniform silicon distribution with the formation of high-and low-concentration regions, i.e., the formation of clusters of silicon-phase preprecipitates.