Effect Of Different Impurities Research Articles

Physico-chemical properties of γ-irradiated International Simple Glass (ISG) nuclear waste simulants with low levels of iron impurities

The effect of γ-irradiation on physico-chemical properties of International Simple Glass (ISG) nuclear waste glass simulants with low iron impurities was investigated. The study was performed on glasses produced by Corning Inc. (named ISG-1, ISG-2) following a 0.95 MGy dose. Fourier-transform infrared and Raman spectroscopy, chemical durability tests, dilatometry, differential scanning calorimetry, electron paramagnetic resonance (EPR), optical absorption, and photoluminescence (PL) spectroscopy appraisals were done in comparison with pristine glasses. The data indicated that structural, chemical, and thermal properties were not significantly altered following γ-ray exposure. EPR spectroscopy showed radiogenic signatures from spin defects for the γ-irradiated glasses which were absent in the pristine. Optical absorption also changed significantly for the γ-irradiated glasses which exhibited defects-related features around 3.45 and 2.25 eV. The optical band gap and Urbach energies were then determined and compared with those obtained for the γ-irradiated original ISG produced by Mo-SCI Corporation. PL spectroscopy revealed distinct changes after irradiation showing enhanced high-energy emission, contrasting with the γ-irradiated original ISG. The effects of thermal treatment on optical properties of γ-irradiated glasses were finally evaluated. Potential causes at the origin of the contrasting results are discussed based on the effects of different impurities.

Experimental study of impurity effects on convective mixing in Hele-Shaw cell with application to CO2 geological sequestration

Density-driven convective mixing, i.e., convective fingering, has been identified to enhance CO2 dissolution trapping in deep saline aquifers. In this study, a series of experiments in Hele-Shaw cells were conducted, and the effects of common impurities (N2, O2, and/or Ar) on the occurrence and development of the convective mixing process were compared and analyzed. It is demonstrated that the existence of these impurities, whether single or their mixture, delayed the onset of convection. However, the subsequent fingering development, including the mixing length and fingering footprint, exhibited different patterns and trends depending on the species and compositions of the impurities. The development and growth of the convective fingers displayed non-monotonic characteristics as a function of the concentration of single impurity Ar. Furthermore, the multiple impurities containing Ar had the potential to enhance the fingering development, especially during the advanced stage. Other than these cases involving Ar, the inclusion of other impurities (N2, and/or O2) was found to weaken the fingering development compared with the pure CO2 case. Nevertheless, the results of dissolved CO2 inventory suggested that the effects of different impurities at the same content, both single and multiple, might be similar to each other in the long term, except for the three-impurity case involving Ar. The laboratory experiments in the present study can help establishing a better understanding of the effects of multiple impurities in the application of impure CO2 geological sequestration.

The effect of impurities in zirconium on the formation and mechanical properties of Zr55Cu30Al10Ni5 metallic glass

Minor alloying has been developed as an effective method to modify and optimize various properties of bulk metallic glasses (BMG). In this work, as inevitable minor alloying elements, two major impurities, hafnium (Hf) and oxygen (O) were quantitatively confirmed to co-exist in two zirconium (Zr) raw materials with different grades of impurities. The effects of these two impurities on the thermal properties, crystallization behavior, glass-forming ability (GFA), and mechanical properties of the nominal Zr55Cu30Al10Ni5 BMG were systematically studied. The O impurity was found to promote the formation of the Al5Ni3Zr2 intermetallic compound phase, which could account for the poor GFA, thermal stability, and plasticity associated with BMGs with higher O content in the Zr raw material. In contrast, although the impurity of Hf has a much higher content than O, a negligible effect of Hf on the Zr55Cu30Al10Ni5 BMG was revealed. These findings were further confirmed by deliberately adding extra O and Hf with designed contents into the Zr55Cu30Al10Ni5 BMG. Our results clarify the effects of different impurities in Zr raw materials on the Zr-based BMG and will help guide industrial production and applications of Zr-based BMGs.

Influence of Mix Water Quality on Compressive Strength of Making Concrete

The influence of concrete mixing water quality on the compressive strength of concretes was investigated in this study. During the study, the compressive strength (CS) of the concretes was determined at 7, 14, and 28 days age. This study used 8 types of water of varying qualities as concrete mixing water (water with 71 UTN impurity level, water with 250 UTN impurity level, water with 1000 UTN impurity level, well-sourced water, acidified water, and alkaline water). Potable water was used as reference water. The results indicated that the lowest CS has been obtained by using alkaline water at a concrete age of 7 days while the usage of water with 250 UTN impurity level as a concrete mixing water yielded the highest CS. in addition, the lowest CS has been obtained when using a mixing water of alkaline at a concrete age of 14 days while the highest CS resulted from using water with 71 and 250 UTN impurities levels. Furthermore, the usage of water with 71 UTN impurities level and an acidic water as a concrete water mixing gave the lowest CS at twenty eight days concrete age, while using magnetic water and water with 250 UTN impurities as concrete mixing water resulted in the highest CS. The use of water with 250 UTN impurities as concrete mixing water favored CS development at all concrete ages. These obtained results have shown a various effects of different impurities which significantly indicate that only a few water impurities affect the concrete’s CS seriously..

Effect of Impurities on the Initiation of the Methanol-to-Olefins Process: Kinetic Modeling Based on Ab Initio Rate Constants

The relevance of a selection of organic impurities for the initiation of the MTO process was quantified in a kinetic model comprising 107 elementary steps with ab initio computed reaction barriers (MP2:DFT). This model includes a representative part of the autocatalytic olefin cycle as well as a direct initiation mechanism starting from methanol through CO-mediated direct C–C bond formation. We find that the effect of different impurities on the olefin evolution varies with the type of impurity and their partial pressures. The reactivity of the considered impurities for initiating the olefin cycle increases in the order formaldehyde < di-methoxy methane < CO < methyl acetate < ethanol < ethene < propene. In our kinetic model, already extremely low quantities of impurities such as ethanol lead to faster initiation than through direct C–C bond formation which only matters in complete absence of impurities. Graphic

Investigating the effect of different impurities on plasma detachment in linear plasma machine Magnum-PSI

To achieve a tolerable heat and particle flux to the divertor target of fusion reactors, the so-called plasma detachment is essential to be set up and controlled. Impurity seeding facilitates the achievement of such a regime, mostly due to the enhanced plasma radiation led by the excitation-relaxation cycle of such species. Little is known about the impurity-induced plasma chemical processes occurring in the divertor region during detachment operation. In this work, the influence of three different impurities, i.e., N2, Ar, and He, on detachment performance is studied. To do so, experimental campaigns on the linear plasma machine Magnum-PSI have been carried out. Results highlight the beneficial role of N2 + H2 seeding, decreasing the plasma pressure in front of the target, leading to a reduced heat load compared to the pure H2 seeding case. An opposite trend has been found concerning He and Ar puffing. In fact, injection of H2 + He and H2 + Ar gas mixtures led to an increased heat flux. To address the importance of different plasma-chemical reaction paths, global plasma models have been used. The resulting reduced reaction schemes for Ar + H2, He + H2, and N2 + H2 have been implemented in B2.5-Eunomia, a coupled code consisting of a Monte Carlo code treating the transport of neutrals and a fluid code solving plasma equations. Simulation results qualitatively reproduce the favorable effect of N2, while confirming the deteriorating effect of He and Ar on a detachedlike hydrogen plasma. We point the synergetic role of H2 + N2 to be due to molecular-driven ion recombination, i.e., N-molecular-assisted recombination (MAR). A direct comparison of the collision frequency between N-MAR and MAR is showed, highlighting the crucial importance of the former in reducing the ion and heat flux to the target plate.

Catalysts for Fatty Alcohol Production from Renewable Resources

AbstractFatty alcohols may be produced through the processing of fatty acids or their esters derived from palm or coconut oils. Fatty alcohol technology can be classified into two categories (a) a slurry‐phase process in which the fatty acid or its ester is converted into alcohol using a powdered catalyst and (b) fixed bed technology in which the fatty acid or its ester is processed over a formed catalyst, e.g. tablets or extrudates. Historically copper‐based catalysts are employed for achieving ester hydrogenolysis. In recent years, studies were also focused on precious metal catalysts for this process. This paper will critically review existing literature pertaining to the catalysts that operate at diverse conditions, handle different feedstocks, and are compatible with a variety of unit operations used by the fatty alcohol manufacturers. There is an effort to develop environmentally friendly non‐chrome copper catalyst in this process. Some recent progress on bimetallic Cu‐Fe catalyst and understanding Cu‐Fe interaction has been reported. Current development on homogenous catalysts in this process was carefully reviewed. The catalyst deactivation mechanism has been investigated and effect of different impurities, mainly phosphorous, sulfur, chloride, water, glycerine and free fatty acid was thoroughly reviewed.

LEFM-Based Fatigue Life Assessment of Anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; Pipeline under Inner Pressure Fluctuation

Natural or anthropogenic CO2pipelines have been in operation in USA, Europe and North Africa for almost three decades, which are aimed at implementing EOR(enhanced oil recovery) technology and (more importantly) developing CCS(carbon capture and storage) technology. At present, there is no specific pipe standard for CO2transportation pipelines. Instead, oil &amp; gas pipeline system is directly introduced into the field of CO2transportation piping. Therefore, the technical details for oil &amp; gas pipelines transporting supercritical CO2should be carefully taken into consideration due to the relevant effects of different impurities in the transported CO2and the different transportation environment for these two mediums, i.e. oil&amp;gas mixture and CO2. For the application of anthropogenic CO2pipe transportation technique, this paper will address a FE-based method which can evaluate fatigue life of a supercritical CO2 transmission pipeline containing an inner crack. Specifically, a portion of welded round steel pipeline is selected as the object of our analysis. And under the inner pressure fluctuation scenarios, an FRANC2D finite element procedure is generated to simulate mode-I crack extension from a given inner edge crack and to calculate the corresponding stress intension factors(SIFs) varied with different cracking depths. Afterwards, considering the effects of crack closure, the Paris equation is modified to build an integral analysis method for the fatigue life evaluation of CO2pipeline. Thus, the relation between the fatigue life and the inner pressure fluctuation range can be determined by performing the proposed fatigue crack growth analysis, which can also provide a LEFM-based pipeline selection method in terms of fatigue durability other than the conventional method coming from the structural strength theory.

Finite Element Based Fatigue Life Evaluation of Anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; Pipeline Containing an Inner Defect

The great effort for reducing emissions of CO2 to atmosphere will inevitably involve the carry-out process of Carbon Capture and Storage(CCS), a novel plan which intends to capture and store anthropogenic CO2 produced at many existing industrial sources, such as power stations and petrochemical works. In particular, anthropogenic CO2 pipeline transportation from the energy plant to the remote sequestration area(both onshore and offshore) is a fundamental issue regarding the feasibility of applying the CCS technology. CO2 pipelines have been in operation in USA, Europe and North Africa for almost three decades. However, the technical challenges for pipelines transporting CO2 due to the relevant effects of different impurities coming from flue gases, are still needed to get people to take up, especially for China which is focusing on the roll-out of CCS. This paper will address a FE-based method which can assess residual life of a supercritical CO2 transmission pipeline containing an inner defect induced crack. Specifically, a portion of welded round steel pipeline is selected as the object of our analysis and an ANSYS finite element procedure is generated to simulate the stress state of an element volume along the radial direction and hence to calculate the effective stress due to the effects of crack closure. Afterwards, combining the effective stress we get in the above numeric analysis, the Paris equation is modified to build an integral analysis method for the residual life evaluation of CO2 pipeline. Lastly, in order to verify the validity of the proposed method, a pipeline example in a published paper is used as the benchmark model, the full-scale test results of which are compared with those from our method. Based on this, a section of CO2 pipeline, with an initial defect (assumed as a crack source), is analyzed and its residual life is evaluated by using the presented method. The analysis of numerical results indicates that the method presented in this paper can give us a valuable reference to life-evaluation for CO2 pipeline in CCS.

TlBr crystal growth, purification and characterisation

TlBr single crystals are promising materials as room temperature X- and gamma ray detectors. However, the TlBr detector performance is generally limited by the quality of the initial crystal material. In this work, the chemical aspects of synthesis, purification, and crystal growth are emphasised. The aim of this paper was to develop characterisation methods for TlBr and study the effect of different impurities on the properties of TlBr. Samples of different types were selected for the investigations, viz. melt grown crystals and material precipitated from water solution. One important topic in the research was to study the purification of TlBr crystals by annealing in pure water. In this paper, the materials were characterised by X-ray diffraction, FTIR spectroscopy, I–V measurements and trace element analysis.

Effects of various dopants on NaCl and KCl glow curves

We have measured the thermoluminescence of a number of NaCl and KCl crystals following irradiation at ambient temperature with the same dose (10 kGy) of Co-60 γ rays. We compare the TL of pure samples and of samples doped with europium and calcium ions. In the case of NaCl, additional impurities (Ni, Pb, Sr and Cr) have been investigated. The effects of irradiation are determined using optical absorption and thermoluminescence. Factors investigated include the effects of different dopants on TL glow curves and the effects of thermal annealing samples at 400 °C before the irradiation. Changes in TL glow curves relating to changes in the state of aggregation of the impurities produced by pre-irradiation annealing are reported in this paper. Perhaps the most significant effect is a temperature shift of the main glow peak in pre-annealed compared to not pre-annealed samples in the case of Eu doped NaCl. The magnitude of the shift depends on the concentration of the Eu dopant. Shifts are also observed for Ni and Sr impurities in NaCl, but not for Ca and Cr impurities in NaCl. In the case of KCl, glow peaks generally occur at similar temperatures in doped samples and do not shift when doped samples are pre-annealed. Here the main effect of different impurities is to influence the size of the emission and not the structure of the glow curve. Results are discussed in terms of current theories of thermoluminescence.

A Piezocatalytic Sensor for Determining Fuel Gases in Air: Principles of Operation and Performance Characteristics

A new type of sensor for determining fuel gases in air is described. The sensor consists of a differential circuit of two thermosensitive piezoelectric quartz resonators, one of which contains the thin layer of an oxidation catalyst. In the presence of a fuel gas in the flow of air, the active resonator with a catalytic layer heats up compared to the reference resonator. The difference between the oscillation frequencies of the two resonators serves as an analytical signal. The performance characteristics of resonators of different types (open and sealed) were determined, and the effect of different impurities (hydrogen, methane, and organic vapors) was studied. The detection limits for impurities estimated from the 3-σ test were found to be at a level of 10–2 vol %.

The Influence of Impurities on Crystallization Kinetics of Sodium Chloride

The influence of impurities on the crystallization kinetics of NaCl was investigated in a fluidized bed crystallizer. The growth and dissolution rates were related to the supersaturation and impurity concentrations. The effect of different impurities on the growth rate of NaCl crystals can be divided into thermodynamic effects where the impurities influence the solubility and kinetic effects where the impurities will suppress the growth rate compared to the pure NaCl. A mathematical model describing crystal growth rates from aqueous solution as a function of impurity concentration is presented. The model explains impurity concentration effects on the crystal growth rate in terms of an impurity effectiveness factor and a Langmuir adsorption isotherm for the impurity.

Effects of impurities on growth habit of KDP crystal

The effects of metaphosphate, boric acid and quaternary ammonium cations with different concentration on the growth habit of KDP crystal are reported. The results are analyzed and discussed, which show that the effects of different impurities on the growth habit of KDP are not the same. It is due to the different adsorption mechanism of the impurities.

Evolution of the mechanical stress on PECVD silicon oxide films under thermal processing

Plasma enhanced chemical vapor deposited (PECVD) silicon oxides obtained from SiH4 and N2O as reactant gases are being extensively studied nowadays. This interest is based on potential uses in microelectronics, integrated optics technology [1, 2] and as a basic material for fundamental studies about the luminescent properties of silicon-based nanostructures and silicon oxide defect centers [3]. The composition and physical properties of these oxides strongly depend on the deposition parameters, the precursor gas flow ratio, R= [N2O]/[SiH4], and the deposition temperature, td, being the most important of them [4]. During deposition, impurities such as hydrogen, nitrogen and water are incorporated into the a-SiOX network. Furthermore, moisture can be absorbed from the atmosphere after the deposition process, thus enhancing bond absorption and transmission losses. Thermal processing to achieve impurity effusion will often cause structural changes, significantly changing the film stress and affecting the film integrity. In a previous work [5] we studied the effect of rapid thermal annealing (RTA) at 900 ◦C on the stress values of PECVD silicon oxide films deposited at 300 ◦C as a function of flow ratio. The differences between the curves obtained before and after RTA were explained on the basis of the layer composition (oxygen content) and the hydrogen incorporation during the deposition process. No differences were established between the effect of different impurities as, for example, Si-H and Si-OH groups. It was also demonstrated by infrared spectroscopy (FTIR) that for the as-deposited films a sort of complementary effect exists, i.e., for low R-values the films are Si-rich with a high concentration of Si-H bonds and as R increases more stoichiometric films are obtained with lower bonded hydrogen content. To clarify the role of the different impurities in the stress behavior during thermal processing of the as-deposited oxides, thermal cycles up to 300 ◦C followed by RTA at 900 ◦C in inert atmospheres were accomplished and the preliminary results are presented here. Samples obtained with two extreme R-values (5.5 and 20.7) and different deposition temperatures, ranging from 200 to 350 ◦C, were used. A similar analysis

Pinning of charge density waves by strong impurities

Starting with the energy functional of the charge density wave, the distribution of phase distortions due to impurities coupling strongly to the charge density wave phase is calculated. The inclusion of interference effects of different impurities allows an estimation of the phase coherence length. The results are found to be consistent with those obtained by the phenomenological ansatz of individual pinning.

Impurity effects on metallic cohesion: Lithium-row atoms in nickel clusters.

We present results from a theoretical study of the localized bonding in atomic clusters consisting of octahedral nickel hosts and interstitial atoms from the lithium row of the Periodic Table. Trends in impurity binding energies and the effects of impurities on the elastic properties of the host are established by comparison of total energies and interatomic forces of the doped clusters with results for the bare host. Properties of the host cluster are strongly dependent upon impurity atom type. An orbital analysis identifies the microchemical mechanisms through which the elastic properties of the host respond to changes in impurity-host bond character, as we progress from strongly electropositive lithium to strongly electronegative fluorine. The tendency of Li and F to form ionic bonds destabilizes and weakens the Ni host cluster. A bonding mode which is predominantly covalent characterizes the remainder of the first-row series. A nonuniform variation of impurity-induced strain and elastic properties of the host is found, with midrow atoms B, C, and N effecting an appreciable strengthening of the host. Trends in the stability and strengthening character of the midrow series of atoms is a result of competing atom size and covalency effects. There is good qualitative correspondence betweenmore » the trends and relative effects of different impurities in this study and the observed effects of first-row impurities on the cohesive properties of metallic host interfaces. This relationship suggests the microchemical properties of the cluster model may serve to identify atomic-level factors important to understanding macroscopic impurity effects in grain-boundary segregation.« less