Papers by Keyword: Substitution

Abstract: Lead-free (Ba1-xCax)(Ti0.96Zr0.02Sn0.02)O3 (BCTZS) (x=0, 0.01, 0.02, 0.03) ceramics were prepared using conventional solid-state reaction technique. The effects of Ca content on the microstructure and electrical properties of the BCTZS ceramics were investigated. High piezoelctric coefficient was obtained for the sample at x=0.02.

Abstract: In this paper, a batch of M- type strontium hexaferrite samples with nominal composition of SrFe_12-xCo_xO₁₉(where x= 0- 2), have been synthesized via sol- gel method. In the synthesis of samples, first a precursor gel was prepared, and then dry- gel was calcined at 1000°C for 2 hours to obtain the nano- SrFe_12-xCo_xO₁₉. The XRD results revealed that for SrFe12-xCoxO19 samples with x≤0.5, all of them have single- phase hexaferrite structure and also this data suggests that the F ³⁺ ions are substituted by Co²⁺ ions in the crystallography sites of the SrFe_12-xCo_xO₁₉, but for the samples with x>0.5, the second phase of CoFe2O4 is appeared and suggests that the Co²⁺ ions also make a distinct phase in the samples. The magnetic properties, such as saturation magnetization (Ms), magnetic remanence (Mr), magnetic coercivity (Hc), squareness ratio (Mr/Ms), crystalline anisotropy field (Ha), energy product [(BH)max] and the susceptibility χ as the derivative of M with respect to H of the upper branch of the hysteresis loop were discussed by measurements of M-H curves with vibrating sample magnetometer (VSM). The magnetic measurements revealed that the coercively (Hc) values of all the samples decrease with increasing dopant contents.

Abstract: To study the effect of K and Mn substitution on simultaneous removal of NOx and particulate materials (PM), a series of La_1-xK_xCo_1-yMn_yO₃ (x, y=0.1, 0.2, 0.3, 0.4, 0.5) perovskite-type catalysts were synthesized by complex-combustion method. The catalytic performances of the catalysts were evaluated by temperature-programmed oxidation reaction (TPO). And the catalysts were characterized by XRD, FT-IR, H₂-TPR techniques. After introducing K and Mn to LaCoO₃ simultaneously, all the samples possess perovskite-type structures and the B-site ions form higher average oxidation state enhancing the catalytic performance obviously. La_0.8K_0.2Co_0.7Mn_0.3O₃ catalyst exhibits not only the lowest T _i(297 °C) temperature but also the lowest Tm (343 °C) temperature. Meanwhile, the NO reduction percentage over this catalyst can reach 97%.

Abstract: When the products are withdrawn from the market, some capacity is reserved for a certain time because the manufacturer is responsible for providing after-sale service during the entire quality guarantee period. We consider a capacity reservation problem of a semiconductor manufacturer with two kinds of products and the corresponding demands are random. The demands can be substituted when one type of capacity has been depleted. The optimization goal is to determine the reserved capacity for each type of product. The problem is formulated by a stochastic programming model in which the objective is to minimize the total service cost of the manufacturer. We show that the concavity and convexity of the optimal function is depended on the joint distribution function density of the products. An iterative algorithm is designed to find the optimal capacity conservation quantities and a numerical experiment is used to illustrate its effectiveness.

Abstract: The ionic substitutions have been proposed as a tool to improve the biological performance of hydroxyapatite (HAp) based materials. In the present work, the systems of Ca_(10-x)Mg_x(PO₄)₆(OH)₂ (MgHAp, x = 0, 1, 2, and 3) were successfully synthesized by solgel method. To obtain nanocrystalline of MgHAp, the prepared precursors were calcined in air at 600 °C for 2 h. The samples were characterized by Xray diffraction (XRD) and transmission electron microscope (TEM) observation. The XRD results confirm the formation of pure phase of HAp with the lattice parameter a in the range of 0.94170.9479 nm and c of 0.68410.6919 nm. The crystallite sizes of the powder are found to be 3546 nm as evaluated by the XRD line broadening method. The morphology of the samples are spherical shape of diameter less than 100 nm as evaluated by TEM. The corresponding selected area electron diffraction (SAED) analysis further confirms the formation of hexagonal structure of HAp.

Abstract: The removal of arsenic from synthetic arsenic contaminated water sample by precipitating arsenic (in the form of arsenate oxyanion) with calcium phosphate hydroxyapatite, HAp, was studied under conditions that induce arsenate incorporated calcium phosphate hydroxyapatite, Ca (P/As)HAp, to form. Arsenate is able to substitute for a fraction of the phosphate in HAp host material as it forms. Consequently, arsenic is successfully removed from the contaminated water achieving up to 99% arsenic removal from 25 ppm initial arsenic concentration. The Ca:(P+As) and P:As mole ratios were found to play an important role in arsenic removal efficiency. Higher Ca:(P+As) and P:As mole ratios give higher arsenic removal efficiency. Surprisingly, the pH of the initial anion solution, a key parameter in arsenic speciation, was found to not have a significant effect on arsenic removal by this process. The advantage of this process is that the precipitation can occur rapidly at relatively low levels of arsenic contamination, implying an easy and inexpensive process for arsenic removal can be developed based on this approach.

Abstract: Simulations are performed on atom substitution character in Ni-Al-V alloy based on microscopic phase-field model at 1046K. It was showed that the ordering of both Al and V atoms take place simultaneously during the precipitation process of Ni-Al-V alloy, V atoms substitute the Al sublattice in L1₂ phases, and they prefer β-sites to α-sites. Both of Al and V occupy the β-sites and complex phases Ni₃(Al_1-xV_x)are formed; V atoms substitute the Al sublattice, the D0₂₂ phases are formed at the boundary of L1₂ phases.

Abstract: Polycrystalline Ca_3-xMg_xCo₄O₉(x=0-0.3)ceramics were prepared by the sol–gel method combined with the ordinary pressing sintering and the thermoelectric properties were measured from room temperature to 673 K. The substitution of Mg²⁺ for Ca²⁺ had a greater impact on the thermoelectric properties of Ca₃Co₄O₉. The electrical conductivity and the thermal conductivity reduced significantly with increasing Mg content, and the Seebeck coefficient increased simultaneously. The influence of Mg doping on the thermal conductivity is mainly embodied in the lattice thermal conductivity of Ca₃Co₄O₉. The lattice thermal conductivity showed a significant change with the increase of the dopant content, while the carrier thermal conductivity had no obvious change with the doping increasing. These results indicated that the thermoelectric properties of the material could be optimized remarkably with the substitution of Mg. The figure of merit Z reached 1.08×10^-4 K^-1 at 573 K for the sample of Ca_2.8Mg_0.2Co₄O₉.

Abstract: This paper adds to the growing literature on the vertically specialized collaboration of modularity firms by applying a model in which complement and core products collaborate with each other in a network situation. More specifically, it investigates the influence of the complement’s network strength on the equilibrium price and output of the core product. The results thus characterize the relationship between the complement’s and the core products’ network strength during collaboration.

Abstract: Polycrystalline Ca_3-xMg_xCo₄O₉（x=0-0.3）ceramics were prepared by the sol–gel method combined with the ordinary pressing sintering and the thermal conductivities were measured from room temperature to 673 K. The influence of Mg²⁺ substitution for Ca²⁺ on the thermal conductivities of Ca₃Co₄O₉ ceramics was investigated systematically. The influence of Mg doping on the thermal conductivities is mainly embodied in the lattice thermal conductivities, which shows a significant decrease with the increase of the dopant content for the samples with x ≤ 0.2, while the carrier thermal conductivity had no obvious change with Mg doping increasing. These results indicated that the thermal conductivities of the material could be reduced remarkably with the substitution of Mg from 1.427 W/m·K to 0.731 W/m·K at 573 K with x = 0.2.