Effect Of Calcium Addition Research Articles

Effect of calcium addition on catalytic ethanol steam reforming of Ni/Al 2O 3: I. Catalytic stability, electronic properties and coking mechanism

Ca-modified Ni/Al 2O 3 catalysts with various Ca loadings of 0, 3, 5 and 7 wt% were studied for low temperature catalytic ethanol steam reforming (ESR). Catalyst with 3 wt% of Ca remains stable at 673 K for at least 24 h, while 0 wt%, 5 wt% and 7 wt% Ca modified catalysts deactivate easily. The addition of Ca increases the particle size of active Ni which promotes the formation of un-reactive and encapsulating carbons, undermining the stability of highly loaded (7 wt%) Ca-modified Ni catalyst. XPS valence band shows that the presence of Ca increases the density of Ni 3d band valence electrons which helps in dissociation of methane and deactivates the catalysts, as in the case of nickel catalysts supported on 7 wt% of Ca on Al 2O 3. Excellent catalytic performance of 10Ni/3Ca-Al 2O 3 is due to the effective coke removal and the amorphous nature of coke deposition. Optimized Ca loading was found to play a critical role in coke removal, through its effect on Ni particle size, valence band of catalyst and steam gasification of coke.

Effect of calcium addition on catalytic ethanol steam reforming of Ni/Al 2O 3: II. Acidity/basicity, water adsorption and catalytic activity

The effect of Ca modification to Ni/Al 2O 3 catalysts in ethanol steam reforming was studied by using a 5-channel micro-reactor, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and temperature-programmed desorption (TPD) of probe molecules H 2O, NH 3, CO 2 and ethanol. Both Al 2O 3 and Ca-modified Al 2O 3 supports are not catalytically active for the ethanol reforming. But in the presence of the active metal Ni, the catalytic performance of Ni/Ca-Al 2O 3 is far more superior to Ni/Al 2O 3 for low temperature H 2 production. The introduction of Ca greatly reduces the acidity of Al 2O 3, depressing ethanol dehydration and ethylene formation. It brings about positive attributes such as increasing water adsorption, providing Ni catalyst the proximity and abundance of adsorbed OH groups. The involvement of OH groups in the reactions in turn enhances the ethanol adsorption, stabilizes its adsorbate intermediates for further conversions to H 2, CH 4 and CO 2 at relatively low temperatures. This paper therefore serves to illustrate the importance of acidity and steam adsorption capacity in the design of the catalysts for ethanol steam reforming.

Composition of poorly and non-coagulating bovine milk and effect of calcium addition

Ninety-nine individual milk samples from 37 cows in lactation week 10-35, selected for producing well or poorly/non-coagulating milk, were compared regarding protein composition, total calcium content, casein micelle size, pH, and coagulating properties after addition of 0·05% CaCl₂. The results showed that a low κ-casein concentration in milk was a risk factor for non-coagulation. CaCl₂ addition improved coagulating properties (coagulation time, curd firmness) of nearly all samples and eliminated differences between poorly/non-coagulating and well-coagulating milk, particularly regarding curd firmness. A second, independent data set with 18 non-coagulating or well-coagulating milk samples were analysed for protein composition, where indications of a similar association with κ-casein was observed.

Effect of Calcium Additions on N–A–S–H Cementitious Gels

This paper reports a research on the properties of synthetic sodium aluminosilicate hydrate gels as models for the gels arising in alkali‐activated aluminosilicate systems. The interaction between these N–A–S–H gels and aqueous calcium was studied to explore a potential consequence of mixing conventional Portland cements and alkali‐activated systems. The properties of two N–A–S–H gels (with Si/Al=1 and 2) synthesized in highly alkaline media, in the presence of calcium are reported. N–A–S–H gels were synthesized using aluminum nitrate, sodium hydroxide, and a sodium silicate. FTIR, NMR, and TEM/EDX techniques were used to characterize N–A–S–H gels before and after adding calcium. The results obtained show that calcium is uptaken in N–A–S–H gels resulting in a modification of the chemical composition due to the substitution of sodium per calcium.

Effects of calcium addition on as-cast microstructure and mechanical properties of Mg-5Zn-5Sn alloy

The effects of Ca addition on the as-cast microstructure and mechanical properties of the Mg-5Zn-5Sn (mass fraction, %) alloy were investigated. The results indicate that an addition of 0.5%-1.5% (mass fraction) Ca to the Mg-5Zn-5Sn alloy not only refines the as-cast microstructure of the alloy but also causes the formation of the primary and/or eutectic CaMgSn phases with high thermal stability; an increase in Ca amount from 0.5% to 1.5% (mass fraction) increases the amount and size of the CaMgSn phase. In addition, Ca addition to the Mg-5Zn-5Sn alloy improves not only the tensile properties at room temperature and 150 °C but also the creep properties. Among the Ca-containing Mg-5Zn-5Sn alloys, the one added 0.5% (mass fraction) Ca obtains the optimum ultimate tensile strength and elongation at room temperature and 150 °C, however, the alloy added 1.5% (mass fraction) Ca exhibits the optimum yield strength and creep properties.

EPR as a Tool to Study the Dynamic of Tropomyosin in the Muscle Fiber - Use of a Bifunctional Spin Label

Tropomyosin (Tm), an alpha-helical coiled-coil protein, is a key regulatory protein in muscle contraction. Little is known about the role of Tm dynamics in muscle regulation and more specifically dynamics in the three states of the thin filament. In this work, the flexibility of four different regions of Tm was determined with Saturation Transfer Electron Paramagnetic Resonance (ST-EPR). The use of bi-functional labels allowed us to immobilize the probe and prevent the motion of the label with respect to protein surface. The rotational correlation time of the bi-functional spin label on Tm was 40 ns compared to 25 ns for a conventional mono-dentate spin label. The spin label was attached to i, i+4 positions of the coiled-coil, obtained by cysteine mutagenesis. The bi-functionally labeled Tm di-mutants were reconstituted into “ghost muscle fibers” from which the myosin filaments and intrinsic regulatory proteins (tropomyosin, troponin) were removed. The filaments were reconsituted with Tn and decorated with myosin S1. We found that there is a gradient of flexibility of Tm along its length in the muscle fiber with the C-terminus mutant A268C/E272C being less mobile (two-fold), as compared to the rest of the mutants. Introduction of troponin decreases the flexibility of the four mutants, specifically the two mid-region mutants H153C/D157C and G188C/E192C by 25% and 30% respectively. The addition of calcium did show a decrease in the flexibility of the C terminus mutant A268C/E272C by 20%. The effect of calcium addition on the two other mutants and the effect of addition of S1 on the four mutants were not significant. Thus, although there is a gradient of flexibility in Tm, its dynamics does not change within different states of thin filament activation.

Refinement role of electromagnetic stirring and calcium in AZ91 magnesium alloy

Effects of calcium addition and electromagnetic stirring on the microstructure of AZ91 magnesium alloy and refinement mechanism were investigated. The results show that calcium addition ranging from 0.1wt% to 0.3 wt% does not lead to formation of any new phases but cause the refi nement of as-cast microstructure.However, combined calcium alloying and electromagnetic stirring significantly decrease the grain size, change the morphologies of the β-Mg17Al12 phases,and reduce their volume percentage. The minimum grain size of AZ91 alloy is obtained in the case of the addition of 0.2 wt%Ca with exciting voltage of 100 V. The microstructural refi nement is attributed to the increase of the degree of undercooling and nucleation temperature of primary α-Mg phases on the basis of DTA analysis results.

Effect of Calcium on Calmodulin Bound to the IQ Motifs of Myosin V

The long neck of unconventional myosin V is composed of six tandem "IQ motifs," which are fully occupied by calmodulin (CaM) in the absence of calcium. Calcium regulates the activity, the folded-to-extended conformational transition, and the processive run length of myosin V, and thus, it is important to understand how calcium affects CaM binding to the IQ motifs. Here we used electron cryomicroscopy together with computer-based docking of crystal structures into three-dimensional reconstructions of actin decorated with a motor domain-two IQ complex to provide an atomic model of myosin V in the presence of calcium. Calcium causes a major rearrangement of the bound CaMs, dissociation of CaM bound to IQ motif 2, and propagated changes in the motor domain. Tryptophan fluorescence spectroscopy showed that calcium-CaM binds to IQ motifs 1, 3, and 5 in a different conformation than apoCaM. Proteolytic cleavage was consistent with CaM preferentially dissociating from the second IQ motif. The enzymatic and mechanical functions of myosin V can, therefore, be modulated both by calcium-dependent conformational changes of bound CaM as well as by CaM dissociation.

Effect of Calcium Addition and Heat Treatment on the Al-Zn-In Alloys as Sacrificial Anode

Aluminium alloys are successfully used in marine and offshore structure in purpose of cathodic protection. Aluminium itself has poor electrochemical properties for sacrificial anode applications. Hence it is alloyed with other elements to improve its characteristics. This study was conducted to investigate the influence of calcium addition and also heat treatment on the potential and current capacity of Al-Zn-In anodes. The electrochemical performance of these anodes was evaluated by electrochemical test based on NACE standard method. SEM and EDAX analyses were used to examine the surface structure of the anodic materials. The results were then compared with those of the base alloy without calcium and untreated specimens to understand the behaviour of the anode after alloying and heat treatment.

The role of calcium in microstructural refinement of AZ91 magnesium alloy

The effect of calcium addition on the microstructures of AZ91 magnesium alloy was investigated. It was found that a small amount of calcium in AZ91 alloy produced a large decrease in the α-Mg grain size and the dispersed fine β-Mg17Al12 phases. In addition, some Al4 Ca particles were found to exist in the AZ91 alloy containing 0.5wt% Ca. EDS analysis and water-quenched technique revealed that the grain-refining mechanism of calcium for the AZ91 alloys was mainly attributed to the role of restricting growth of calcium in the primary α−Mg crystals.

Impacts of calcium addition and different oil types and levels on in vitro rumen fermentation and digestibility

This in vitro study was designed to investigate the effects of calcium addition to substrates differing in source and level of oil on fermentation, gas production, and digestibility parameters. Substrates were made from basal mixtures containing three levels of calcium salt (0, 1, and 2% CaCl2) to contain three levels (3, 6, and 9%) of two types (sunflower and soy) of oil. After collecting from two Holstein bulls and mixing with buffer, rumen fluid was used to incubate the resulting 18 mixtures in duplicate. Ionizable calcium, pH and NH3–N concentration were measured during incubation. Gas production was measured at 6, 12, 24, and 48 h after incubation. Kinetics parameters of gas production and in vitro dry matter digestibility (IVDMD) were calculated from regression coefficients of an exponential equation and a linear equation, respectively. Data were analysed using 3-way ANOVA with repeated measure option in which the parameter time was a subplot. Oil type did not affect pH and ionizable calcium concentration. There were linear increases and decreases in pH and ionizable calcium concentration in response to increasing oil and calcium levels, respectively. However, with increasing oil levels there were no interactions between calcium addition and oil level on pH and ionizable calcium concentration. None of the treatments affected NH3–N concentration. The amount of gas produced from substrates containing sunflower oil was greater than soy oil (41.7 vs. 40.5 ml). Cumulative gas production and amount of gas production from insoluble but slowly fermentable portion of the supplemental mixtures linearly decreased and linearly increased as oil and calcium levels increased in the substrates, respectively. However, interactions of calcium addition and oil level on gas production and kinetics of gas production were lacking. Oil type did not affect IVDMD. Despite lacking main effects, interaction of calcium addition and oil level indicated that increasing calcium level alleviated depression in IVDMD resulting from increasing oil level. In conclusion, increasing oil level depressed, whereas calcium addition stimulated ruminal fermentation. Improvement in IVDMD may partially support that calcium addition alleviates the adverse effects of oil and that more calcium is needed when diets are supplemented with increasing amounts of oil.

Effect of calcium additions on the creep behavior of magnesium die-cast alloy ZA85

Magnesium alloys are typically used for weight saving in a wide range of technical applications, but the most common alloys are limited to low temperatures. Magnesium die-cast alloys with zinc (ZA85, 8 wt pct Zn, 5 wt pct A1) as the major alloy addition show an acceptable die castability and creep resistance, and more recent investigations revealed that their creep strength can be significantly improved by adding small amounts of Ca. In this work, the creep behavior of ZA85 and alloys containing 0.3 and 0.9 wt pct Ca in die-cast and preannealed conditions was investigated. The correlation of creep test results with microstructural investigations showed that dislocation-based creep is the rate controlling mechanism for the high-temperature deformation in the entire stress regime from 20 to 100 MPa, and the formation and growth of small incoherent precipitates controls the creep behavior. For the creep tests at stresses above 40 MPa, it has been found that the creep behavior can be described phenomenologically on the basis of a threshold creep model. The addition of Ca was found to lead to an increase in threshold stress, and it is argued that the segregation of Ca to the precipitate/matrix interface leads to a stronger dislocation core relaxation at this interface, thereby increasing the creep resistance of the Ca containing alloys.

Effects of calcium additions on microstructure and creep behaviour of AE42 alloy

The as cast microstructure of alloy AE42 is composed of the α-Mg matrix and Al11RE3 compound, which is unstable and decomposes to Al2RE and Mg17Al12 (β) at temperatures above 150°C. A small amount of calcium added to the AE42 alloy results in a significant microstructure refinement and formation of Al2Ca compound, which shows two kinds of morphologies: eutectic lamellar at grain boundaries of the α matrix and tiny lamellar in the matrix grains. With the increase of added calcium the volume fraction of Al2Ca increases, while Al11RE3 decreases in the AE42 alloy. Creep resistance of the alloy is significantly improved with calcium addition. The microstructure of the specimen after creep tests at 175°C and 70 MPa with 2% of calcium addition has no obvious changes compared to that before the creep test, indicating Al2Ca has high thermal stability, which is the key factor in creep resistance improvement.

Selective catalytic reduction of NO to N2 with copper and cobalt exchanged ZSM-5 zeolites: the effect of calcium addition

ZSM-5 catalysts containing either Cu or Co cations individually or Cu/Ca or Co/Ca cation combinations were prepared by ion exchange. These materials were tested as catalysts for the reduction of NO to N2 in the presence of propane or methane. Cu2+ and [Cu-O-Cu]2+ species were identified in ion exchangeable sites in the copper-containing catalysts. The amount of the latter cation increased with increasing copper content and in the presence of Ca2+ and was the most active in the reduction of NO. However, at temperatures higher than 400 ºC its activity decreased markedly. For cobalt-exchanged zeolites, Co2+ in charge-compensation sites or Co3+ in extra-framework precipitates were present in the catalysts. It was verified that the amount of Co3+ diminished with the presence of Ca2+. For the catalysts prepared in this study no significant differences in specific activity for the reduction of NO or for methane oxidation were observed in the presence of calcium.

Effect of calcium additives on physicochemical aspects of cell wall pectin and sensory attributes of canned peach (Prunus persica (L) Batsch cv Andross)

AbstractQuality evaluation of calcium‐treated processed peaches was determined by physical, chemical and sensory analyses. Textural and structural properties of canned peaches indicated that calcium‐treated peaches gained better firmness retention and greater proportion of uronic acids between the insoluble and water‐soluble pectin fraction than untreated peaches, probably because of higher cell wall calcium content. However, a direct relationship cannot be established between calcium and uronic acid content in pectin fractions. A range of sensory descriptors assessed by a trained panel provided results that challenge accepted interpretations in the field of quality evaluation. The results indicated the possibility of processing high quality calcium‐treated canned peaches with acceptable qualitative features. Calcium lactate is suggested as a potential calcium source in the peach canning industry, since it provided both better textural features and sensory attributes. The interactions among calcium, the physicochemical properties of the cell wall framework and sensory attributes are discussed. Copyright © 2005 Society of Chemical Industry

Inclusion control of ferritic stainless steel by aluminum deoxidation and calcium treatment

A thermodynamic equilibrium between aluminum and oxygen and inclusion morphology in the Fe-16Cr stainless steel were investigated to understand the fundamentals of the aluminum deoxidation technology for ferritic stainless steels. Further, the effect of calcium addition on the changes in chemistry and morphology of inclusions was discussed. The measured results for the aluminum-oxygen equilibria exhibit relatively good agreement with the calculated values, indicating that an introduction of the first-and second-order interaction parameters, recently reported, is reasonable to numerically express the aluminum deoxidation equilibrium in a ferritic stainless steel. In the composition of dissolved aluminum content greater than about 60 ppm, pure alumina particles were observed, while the alumino-manganese silicates containing Cr2O3 appeared at less than 20 mass ppm of dissolved aluminum. The formation of calcium aluminate inclusions after Ca treatment can be discussed based on the thermodynamic equilibria among calcium, aluminum, and oxygen in the steel melt. In the composition of steel melt with relatively high content of calcium and low aluminum, the log (\(X_{CaO} /X_{Al_2 O_3 } \)) of inclusions linearly increases by increasing the log [aCa/aAl2·aO2] with the slope close to unity. However, the slope of the line is significantly lower than the expected value in the composition of steel melt with relatively low calcium and high aluminum contents.

A thousandfold creep strengthening by Ca addition in die-cast AM50 magnesium alloy

The effect of calcium addition on the microstructure and creep strength of the die-cast AM50 magnesium alloy was investigated. The α-Mg grains with the diameter of 4.9 µm are surrounded by the eutectic phases for the AM50-1.72 mass pct Ca alloy, while the β(Mg17Al12) particles are located mainly on the grain boundaries of the α grains for the AM50 alloy. The minimum creep rates of the AM50-1.72 mass pct Ca alloy are three orders of magnitude lower than those of the AM50 alloy at 423 K typically below 120 MPa. The thousandfold creep strengthening by the Ca addition is ascribed to the thermally stable eutectic phases appearing in the AM50-1.72 mass pct Ca alloy, which is expected to yield effective grain boundary strengthening or to resist the plastic flow of the α-Mg grains.

Calcium addition in straw gasification ☆

The present work focuses on the influence of calcium addition in gasification. The inorganic–organic element interaction as well as the detailed inorganic–inorganic elements interaction has been studied. The effect of calcium addition as calcium sugar/molasses solutions to straw significantly affected the ash chemistry and the ash sintering tendency but much less the char reactivity. Thermo balance test are made and high-temperature X-ray diffraction measurements are performed, the experimental results indicate that with calcium addition major inorganic–inorganic reactions take place very late in the char conversion process. Comprehensive global equilibrium calculations predicted important characteristics of the inorganic ash residue. Equilibrium calculations predict the formation of liquid salt if sufficient amounts of Ca are added and according to experiments as well as calculations calcium binds silicon primarily as calcium silicates and less as potassium calcium silicates.

The effect of calcium additions on the oxidation behavior in magnesium alloys

Our previous study found that the thermal conductivity of nonflammable Mg-Al-Ca alloys is improved by heat treatment. Heat-treated Mg-Al-Ca alloys exhibited a high thermal conductivity of 100–130 W m−1 K−1 because of C15 (Al2Ca) compound precipitation in the α-Mg phase. In this study, the optimal heat treatment condition and the effect of C15 precipitation behavior on thermal conductivity were investigated using Mg91.98Al5Ca3Mn0.02 alloys. The thermal conductivity saturated at approximately 120 W m−1 K−1 in the shortest time at a heat treatment temperature of 673 K. This suggests that the nucleation rate of the C15 compounds could reach the highest at 673 K. Through the formation of dense, long, and thick C15 compounds, thermal conductivity increased with decreasing Al concentration in the α-Mg matrix.

The effect of calcium addition on the rheological properties of a soft cheese at various stages of manufacture

The effects of calcium on the rheology of a model soft cheese at different stages of manufacture have been assessed. Several batches of reconstituted skim milk with 9% w/v and four calcium concentrations (0.14, 0.35, 0.88, 2.2 mM) were used to make a soft stretchable cheese whose rheological characteristics, G' (storage modulus or elastic component) and G' (loss modulus or viscous component), at different stages of manufacture, were measured using a Stress Controlled Rheometer. Calcium had a significant effect on the rheology of the soft cheese; however, it affected each rheological parameter differently.