Effect Of Chromium Concentration Research Articles

Effect of chromium substitution on the dielectric, ferroelectric and piezoelectric properties of PLNZNT ceramics (P=Pb2+, L=La3+, N=Nd3+, Z=Zr4+, N=Nb5+, T=Ti4+)

Piezoelectricity is one of the renewable and clean electrical energy sources, as it is generated from materials specially manufactured for this purpose in proportions and scales called piezoelectric materials, that is, electricity resulting from mechanical work that produces the electric field, and this is known as the direct piezoelectric effect. An inverse mechanical effect can also be observed when an electric field is applied to the same piezoelectric material that deforms and returns to its original shape after the electric field is removed. In order to contribute to improving the properties of these materials that have been prepared from insulating ceramic materials having an equivalent formula: Pb0.975 La0.015 Nd0.01 [(Zr 0,524 Ti 0,476) 0.9875 -3/4 z Nb0.005 Crz]O3 abbreviated PLNZCNT (z = 0%, 0.5%, 0.75%, 1%, 1.25%, 1,5% and 2%). The formation of pure single-phase perovskite compounds of tetragonal symmetry for all samples was confirmed by X-ray diffraction (XRD) analyzes. The scanning electron micrographs show that the grains have melted, most of the separating walls have disappeared, and the average grain size has increased. Information about the effects of chromium concentration on the measured properties was obtained based on temperature and frequency measurements of the dielectric properties of PLNZNT ceramics, represented by an increase in Curie temperature with increasing Cr3+ concentration. The ferroelectric properties of materials are characterized by the presence of a polarization hysteresis cycle as a function of the applied electric field (P-E). To measure the piezoelectric and electromechanical properties at room temperature, was used by the standard resonance and anti-resonance method. It was found that the sample E2 (0.75%) sintered at 1200°C achieves excellent dielectric, ferroelectric and piezoelectric properties (𝜺r=24394.51, tan δ =0.072 and Tc = 378K). The values of saturated electric polarization (Ps=29.61 µC/cm²), remnant electric polarization (Pr=24.63 µC/cm²) and coercive electric field (Ec=0.905kV/mm), as well as piezoelectric charge coefficient (d33 = 435 pC/N) for sample E2 (0.75%).

The effect of chromium concentration on luminescent properties of alkali-alumina-borate glass-ceramics

Alkali alumina-borate glass-ceramics doped with different concentration of Cr3+ ions was prepared by conventional melt-quenching technique. Luminescent glass-ceramics was derived by volume crystallization of the precursor glass via two-stage heat treatment. The phase transition temperatures, structure, spectral and luminescent properties of the glass-ceramics were determined by differential scanning calorimetry (DSC), X-ray diffraction (XRD), optical absorption, photo- and cathodoluminescent spectroscopy. The XRD studies revealed the LiAl7B4O17: Cr3+ nanocrystals nucleation (mean size of 20–23 nm) during the heat treatment. The photoluminescence spectra consisted of three intense bands in the 685–715 nm region. The maximum quantum yield value under 532 nm excitation was 30%. The difference between photoluminescence (PL) and cathodoluminescence (CL) decay kinetics is presented and possible nature of this phenomenon is discussed.

Effect of chromium concentration on the structural, magnetic and electrical properties of praseodymium-calcium manganite

The influence of Cr doping on magnetic, magnetocaloric and electrical properties in a polycrystalline sample of Pr0.7Ca0.3MnO3 is investigated. Structural studies show that our samples are single phase. The magnetization shows that the Pr0.7Ca0.3Mn1−xCrxO3 ceramics exhibit a paramagnetic–ferromagnetic transition with a large magnetic entropy change. The relative cooling power (RCP) values are comparable to those of other manganite. DC conductance GDC measurements show that all samples are characterized by a semiconductor behavior. It is found that GDC decreases by two decades when increasing chromium concentrations. For the parent compound, dc-conductance is characterized by the appearance of a saturation region at a specific temperature (Tsat = 200 K). For the doped compound, Tsat go beyond room temperature. Conduction mechanism is found to be dominated by the small polaron hopping (SPH) process at high temperature and by variable range hopping one (VRH) at low temperature. AC conductance study confirms that the conductivity is governed by hopping process and obeys to the Jonscher universal power law. The exponent ‘n’ variation with temperature is in good agreement with Mott theory. Its variation as a function of chromium content indicates that the material turns from metallic to semi-insulating behavior when chromium composition increases. Impedance analysis proves the presence of electrical relaxation phenomenon in the material and confirms that grain boundaries played a main role in the conduction process.

Calcium alginate as an eco-friendly supporting material for Baker’s yeast strain in chromium bioremediation

In this study, Baker’s yeast strain (Saccharomyces cerevisiae) biomass was immobilized in alginate extract 3% forming Biomass/Polymer Matrices Beads (BPMB). These beads were investigated for chromium biosorption from aqueous solution. Factors such as solution pH, contact times, temperature values, stirring rates, BPMB dosages and initial chromium ions concentrations were experimentally tested using repeated-batch process to determine the sorption capacity for chromium (VI) ions. Batch experiments were conducted at pH range from 1.5 to 7.5. The optimum pH value was 3.5 for direct chromium removal. The effect of chromium concentration was studied using different concentrations from 200 to 1000ppm. Freundlich’s isothermal model showed better representation of data than Langmuir’s isothermal model with correlation coefficient 0.922. The maximum biosorption capacity of chromium was found to be 154mgg−1 at initial concentration 200ppm under optimum conditions. At the end of the experiments, BPMB were investigated for chromium biosorption from tannery effluent sample. Results showed decrease in chromium concentration up to 85%. The availability of recycling of the BPMB was also studied for three subsequent cycles. The surface sequestration of metal ions by BPMB was characterized before and after metal binding using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray analysis (EDXA) and FTIR spectroscopy in order to determine the mechanisms of chromium biosorption.

Evaluation of Phytoremediation Potential of <i>Catharanthus roseus</i> with Respect to Chromium Contamination

A major environmental concern due to dispersal of industrial and urban wastes generated by human activities is the contamination of soil. The release of heavy metals into the terrestrial ecosystem is a major problem. Accumulation of heavy metals in environment and particularly in soil is a serious environmental concern, as the accumulated heavy metal ions can find their way into living organisms via contamination of ground water or food chain. This praxis urgently requires and demands governmental regulations in India. Two samples of sludge were collected from Banthar Industrial Pollution Control Company (BIPCC), UP State Industrial Development Corporation (UPSIDC), Leather Technology Park, Banthar, Unnao, India. In the present study, the phytoremediation potential of Catharanthus roseus, a valued medicinal plant, with respect to chromium has been analyzed. C. roseus was shown to absorb up to about 38% of the amount of Cr present in primary and secondary sludge amended soil through roots and accumulate it to about 22% in leaves. Effect of chromium concentration on the status of antioxidant enzyme peroxidase (POD) and detoxification enzyme glutathione-S-transferase (GST) from C. roseus leaves was also observed and determined. Increased expressions of POD and GST were observed on native PAGE under stress conditions as compared to control. C. roseus can well tolerate low amounts of chromium (and accumulate it to about 22% in leaves) and can, thus, prove useful in the reclamation and remediation of chromium contaminated soil and land.

The influence of Cr content on the microstructure and mechanical properties of AlSi 9Cu 3(Fe) die-casting alloys

The effect of chromium concentration on the microstructure and mechanical properties of a high-pressure die-cast AlSi 9Cu 3(Fe) alloy is reported. The Cr content ranges within the composition tolerance limits of the standard EN AB-46000 alloy, from 0.057 up to 0.15 wt.%. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes occurring with Cr addition. The results indicate that the morphology of the primary and proeutectic α-Al x (Fe,Mn,Cr) y Si z intermetallics are mainly polyhedral, star-like and blocky. The area fraction and the size of intermetallic compounds increases as the Cr content increases. At the holding temperature used for the different EN AB-46000 type alloys, sludge forms mainly in the shot sleeve before the melt entered the die cavity and segregates in the central region of the cross-section of the castings. The entrapped sludge, whose value can be estimated from the sludge factor by a linear relationship, affects the ultimate tensile strength and the ductility of the alloy at the highest Cr level.

Effect of chromium concentration on microstructure and properties of Fe–3.5B alloy

The cast low carbon Fe–3.5B alloys containing various chromium concentrations were prepared in a 10 kg medium frequency induction furnace and the effects of chromium concentration on microstructure and properties of Fe–3.5B alloys have been examined by means of optical microscope (OM), scanning electron microscope (SEM), back-scattered electron microscope (BSE), electron probe microanalyzer (EPMA), energy dispersive spectrum (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and Vickers hardness. As a result, the as-cast structures of Fe–3.5B– XCr ( X = 0, 2, 5, 8, 12, 18, mass fraction) alloys are mainly composed of dendrite ferrite, martensite, pearlite and boride. The boride in the alloy without chromium addition comprises the eutectic Fe 2B, which is continuous netlike or fish-bone structure distributed over the metallic matrix. With the increase of chromium concentration in Fe–3.5B alloy, matrix structure turns into the supersaturated α-Fe solid solution while the morphology of boride becomes dispersed due to the transformation of boride from simple Fe 2B to (Fe,Cr) 2B when the chromium concentration in Fe–3.5B alloy exceeds 8 wt.%. Meanwhile, some primary M 2B-type borides may precipitate under this condition. The bulk hardness of the as-cast alloy ranges from 41.8 to 46.8 HRC. However, the bulk hardness of the heat treated alloy rises first and falls later mainly because of the morphology variation of structure. Fracture toughness of boride is improved gradually owing to the entrance of chromium into Fe 2B, which may be attributed to the change of spatial structure of boride.

810 高応力下におけるNi-Cr系合金の高温水中酸化挙動に及ぼすCr濃度の影響(材料・設計(8))

810 高応力下におけるNi-Cr系合金の高温水中酸化挙動に及ぼすCr濃度の影響(材料・設計(8))

The charge percolation mechanism and simulation of Ziegler-Natta polymerizations, Part VII: Effects of the distribution of chromium active centers on silica on the polymerization of ethylene

The charge percolation mechanism (CPM) of olefin polymerization in the presence of transition metal compounds has been applied to explain the polymerization of ethylene by silica supported chromium oxide. In the previous work of this series, the fundamental issues and mechanism of this polymeri?zation were presented. In this work the compatibility of the CPM with the em?pirical findings is confirmed. The CPM has been applied to explain: the appea?rance of an induction period; the deactivation of active centers and the forma?tion of oligomers; the effects of chromium concentration on the silica surface, the silica surface discontinuity and the pore size of silica on polymerization and the formation of the structure of polyethylene. A mathematical model has been derived to explain the effects of the CrOx/SiO2 ratio on the productivity of Phil?lips catalysts in the polymerization of ethylene. The empirical findings have also been confirmed by computer simulations.

Effect of Chromium Concentration on the Electrical Properties of NiCr Thin Films Resistor Deposited at Room Temperature by Magnetron Cosputtering Technique

NiCr films, thick, were prepared on substrates at room temperature as a function of chromium concentration by the cosputtering technique. The crystalline nature and electrical properties of the NiCr films were investigated as a function of chromium concentration. The films with a chromium concentration up to 39% showed a crystalline structure having a low resistivity, a high root-mean-square (rms) roughness, and positive temperature coefficient of resistivity (TCR) values. The films with a chromium concentration above 39% exhibited the amorphous structure with negative TCR values. The TCR values of the films with a chromium concentration of 39 and 42% are approximately and , respectively. The TCR values approaching zero can be established by controlling the chromium concentration in the NiCr films.

Effect of Chromium Concentration in Metal Alloys on Biofilm Formation in a Dynamic System

Effect of Chromium Concentration in Metal Alloys on Biofilm Formation in a Dynamic System

The Effects of Chromium Concentration on Magnetically Polarized Heat-Treated Steel Torque Transducer Shafts

We have discovered that a large enhancement in transducer sensitivity can be gained by increasing the chromium concentration of the steel to as high as the 12% level (with nickel concentrations under 1%), without the sacrifice of any essential mechanical properties. Beyond this optimal concentration level, the enhancement in the sensitivity appears to have saturated and then gradually disappears as additional chromium is added. Among the steel shafts we investigated were four types, W-1, S-7, D-2, and F-255, with transducer sensitivities of 15.1, 40.3, 71.1, and 25.2 /spl infin/G/psi, respectively. Additionally, the S-7 and D-2 magnetic transducers exhibited still further increases in their sensitivity following their standard heat treatments, with the greatest increase occurring for the D-2 sample.

Effect of chromium concentration on site selective luminescence in nearly stoichiometric lithium niobate crystals

Abstract The optical luminescence of nearly stoichiometric Cr3+ doped LiNbO3 crystals is examined as a function of Cr3+ doping ions concentration. Our interest in this paper is only the evolution of the 2E → 4A2 transition with the chromium concentration and the comparison with the literature results obtained on the congruent crystals

The effect of chromium enrichment in the film formed by surface treatments on the corrosion resistance of type 430 stainless steel

The effect of chromium concentration in the surface film formed by surface treatments on the corrosion resistance of Type 430 stainless steel was studied. It was found that the chromium content depends on the surface treatment method. HNO3 treatments result in a significant enrichment of chromium in the surface film on the Type 430 stainless steel, and the chromium enrichment increases with increasing HNO3 concentration. The pitting potential (Ep), corrosion potential (Ec) and polarization resistance (Rp) are changed by the chromium enrichment (SCr) in the surface film formed by treatment. The higher the SCr value, the higher the Ep, Ec and Rp values.

Studies on Chromium from the Standpoint of Plant Nutrition(Part 1) : Effect of Chromium Concentration on Germination and Growth of Several Kinds of Plant

Studies on Chromium from the Standpoint of Plant Nutrition(Part 1) : Effect of Chromium Concentration on Germination and Growth of Several Kinds of Plant