Gibbs energies of formation of intermetallic phases in the systems Pt Mg, Pt Ca and Pt Ba and some applications

The standard Gibbs energies of formation of platinum-rich intermetallic compounds in the systems Pt-Mg, Pt-Ca, and Pt-Ba have been measured in the temperature range of 950 to 1200 K using solid-state galvanic cells based on MgF2, CaF2, and BaF2 as solid electrolytes. The results are summarized by the following equations: ΔG° (MgPt7) = −256,100 + 16.5T (±2000) J/mol ΔG° (MgPt3) = −217,400 + 10.7T (±2000) J/mol ΔG° (CaPt5) = −297,500 + 13.0T (±5000) J/mol ΔG° (Ca2Pt7) = −551,800 + 22.3T (±5000) J/mol ΔG° (CaPt2) = −245,400 + 9.3T (±5000) J/mol ΔG° (BaPt5) = −238,700 + 8.1T (±4000) J/mol ΔG° (BaPt2) = −197,300 + 4.0T (±4000) J/mol where solid platinum and liquid alkaline earth metals are selected as the standard states. The relatively large error estimates reflect the uncertainties in the auxiliary thermodynamic data used in the calculation. Because of the strong interaction between platinum and alkaline earth metals, it is possible to reduce oxides of Group ILA metals by hydrogen at high temperature in the presence of platinum. The alkaline earth metals can be recovered from the resulting intermetallic compounds by distillation, regenerating platinum for recycling. The platinum-slag-gas equilibration technique for the study of the activities of FeO, MnO, or Cr2O3 in slags containing MgO, CaO, or BaO is feasible provided oxygen partial pressure in the gas is maintained above that corresponding to the coexistence of Fe and “FeO.”

Alloy oxide equilibria in the system Ca Al O at 1373 K

The tie lines delineating equilibria between different oxides of the Ca-Al-O system and liquid Ca-Al alloy has been determined at 1373 K. Equilibration of the alloy with two adjacent oxide phases in the CaO-Al2O3 pseudo-binary system was established in a closed cell made of iron. Equilibrium oxide phases were confirmed by x-ray analysis and alloy compositions were determined by chemical analysis. The compound 12CaO.7Al2O3 Ca12Al14O33 was found to be a stable phase in equilibrium with calcium alloys. The experimental diagram is consistent with that calculated from the free energies of formation of the oxide phases and activities in liquid Ca-Al alloys at 1373 K reported in the literature.

Phase relations in the system Ca-Ta-O and thermodynamics of calcium tantalates in relation to calciothermic reduction of Ta2O5

Phase equilibria of the system Ca-Ta-O is established by equilibrating eleven samples at 1200 K for prolonged periods and phase identification in quenched samples by optical and scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Four ternary oxides are identified: CaTa4O11, CaTa2O6, Ca2Ta2O7 and Ca4Ta2O9. Isothermal section of the phase diagram is composed using the results. Thermodynamic properties of the ternary oxides are measured in the temperature range from 975 to 1275 K employing solid-state galvanic cells incorporating single crystal CaF2 as the solid electrolyte. The cells essentially measure the chemical potentials of CaO in two-phase fields (Ta2O5 + CaTa4O11), (CaTa4O11 + CaTa2O6), (CaTa2O6 + Ca2Ta2O7), and (Ca2Ta2O7 + Ca4Ta2O9) of the pseudo-binary system CaO-Ta2O5. The standard Gibbs energies of formation of the four ternary oxides from their component binary oxides Ta2O5 and CaO are given by: Delta G(f)((ox))(o) (CaTa4O11) (+/- 482)/J mol(-1) = -58644+21.497 (T/K) Delta G(f)((ox))(o) (CaTa2O6) (+/- 618)/J mol(-1) = -55122+21.893 (T/K) Delta G(f)((ox))(o) (Ca2Ta2O7) (+/- 729)/J mol(-1) = -82562+31.843 (T/K) Delta G(f)((ox))(o) (Ca4Ta2O9) (+/- 955)/J mol(-1) = -126598+48.859 (T/K) The Gibbs energy of formation of the four ternary compounds obtained in this study differs significantly from that reported in the literature. The thermodynamic data and phase diagram are used for understanding the mechanism and kinetics of calciothermic and electrochemical reduction of Ta2O5 to metal. (C) 2014 Elsevier B.V. All rights reserved.

Chemical bond characteristics, thermal expansion property and compressibility of AR(2)O(4) (A = Ca, Sr, Ba; R = rare earths)

Theoretical researches were performed on the CaFe2O4-type binary rare earth oxides AR(2)O(4) (A = Ca, Sr, Ba; R = rare earths) by using chemical bond theory of dielectric description. The chemical bond properties of these crystals were explored, and then the thermal expansion property and compressibility were studied. The theoretical values of linear thermal expansion coefficient (LTEC) and bulk modulus were presented. The calculations revealed that the LTECs and the bulk moduli do have linear relationship with the ionic radii of the rare earths. In the cases of Sc and Y, both the LTEC and bulk modulus values are larger than the lanthanide series. We attribute this to the difference in the electronic configuration between Sc (Y) and lanthanide series. For SrY2O4 and BaY2O4 crystals, the theoretical values of LTEC and bulk modulus agree well with experimental ones.

THE VALENCY AND SPECTRA OF SAMARIUM IONS IN MF(2)-MGF2 (M=CA, SR, BA)

The phosphors MMgF(4)(M = Ca, Sr, Ba) doped with samarium ions are synthesized in different atmospheres using solid phase reaction at high temperature. Samarium has been first stabilized in the divalent state in SrMgF4 and BaMgF4 matrices. Effects of matrices on the valent state of samarium ions are briefly discussed.

喀斯特石灰土-灌丛系统主要养分含量分布特征研究---以贵阳花溪杨中石灰土-灌丛系统Ca���Mg、 K 、P为例

本论文通过对贵州贵阳花溪杨中喀斯特山区的植被调查与土壤样品分析, 研究土壤-植被中Ca���Mg、 K、P分布特征、变化规律及其影响因素，并在此基础上尝试Ca���位素的预处理研究，以期为喀斯特地区土壤-植被中Ca���Mg、 K、P（尤其是Ca���的生物地球化学循环研究奠定基础，同时为植被演替、物质循环研究和退耕还林还草的人工恢复提供植物自身的营养依据。本次研究取得如下认识： 1.受石灰岩母岩控制，土壤样品元素含量的特征为：CaO>MgO>K2O> P2O5。同一元素沿海拔变化有一定的相关性，并且相关性随元素的不同存在差异：随海拔高度的增加CaO含量有升高的趋势，而MgO 、K2O、Na2O含量都有所降低。表层土壤中K2O-Na2O含量正相关变化，CaO-K2O含量负相关变化。并且从土壤表层到底层在剖面-1中随深度增加，CaO、MgO、K2O含量升高，而P2O5的含量则有上升的趋势。土壤中元素的上述分布特征主要与石灰岩的风化成土作用过程中不同分化程度土壤Ca���淋失和来自高处的富钙雨水输入有关。 2.喀斯特生态环境富钙的这一特点对喀斯特灌丛植物的种类成分和营养元素含量有很大影响。地貌部位、海拔高度对植物Ca���Mg 、K、P含量也有不同程度的影响。植物Ca���Mg 、K、P含量由高到低依次为：Ca > K > Mg >P。苔藓与其它植物比较， Ca���Mg、 K、P的含量都小于其它三类较高等的植物，这一现象与其自身的生物学特性有关：苔藓植物组织结构简单，不具备发达的输导组织，不具备真正的根系，不利于从土壤等基质中吸收营养。在、灌草、灌木、藤本三类植物营养元素之间Ca –P含量具有负相关变化，Mg –P含量具有正相关变化；在所分析的植物种，P- K含量变化呈正相关，并且植物叶片Ca/K比值随着P含量的增加而显著地以指数形式减小。这是因为植物体内的K和P对于Ca���说起着平衡离子（counter ion）的作用。 3. 生境中基岩裸露和土体浅薄的特点，极大地制约了喀斯特灌丛的发育，喀斯特生境的富含钙的特点对喀斯特灌丛植物的种类成分和元素含量有很大的影响。但是杨中灌丛群落植物Ca���Mg、K、P含量和对应土壤CaO、MgO、K2O和P2O5含量相关性不明显。植物Ca���Mg、K、P元素虽主要来源于土壤，但因其含量受元素地球化学性质、植物种类、土壤元素对植物有效态的含量等因素的制约，而使植物元素含量和土壤元素的含量没有明显的相关性． 4.从Ca���位素的预处理研究来看，离子交换分离法对去除样品中的杂质效果较好。在以后测定过程中，有利于增强离子流稳定性和强度, 提高测量精度和准确度，与沉淀法相比较，此法适宜作为钙同位素样品的前处理方法。 关键词： 喀斯特 石灰土-灌丛系统 Ca���Mg、K、P含量分布 钙同位素 环境地球化学

Textural and structural properties of bioactive glasses in the system CaO-SiO2

Gel-derived CaO-SiO2 binary glasses of CaO mole fractions 0. 2, 0.3 and 0. 4 have been prepared and characterised. Pore diameter specific pore volume, skeletal density and porosity were found to increase with increasing CaO-content, whereas a concomitant decrease in specific surface area was observed. Si-29 NMR indicated that the 0.2 CaO mole fraction glass consisted of higly polymerized Q(4) and Q(3) silicate species, with some Q(2) units. With increasing CaO mole fraction, these silicate species became progressively depolymerised such that isolated SiO4 tetrahedra were detected within the 0.4 CaO glass matrix. Unusually, the glasses retained a proportion of Q(4) and Q(3) species as the CaO mole fraction was increased. All glass formulations exhibited in vitro bioactivity. The rate of hydroxyapatite precipitation followed the order 0.2 CaO > 0.4 CaO > > 0.3 CaO, an effect that is attributed to differences in the rate of dissolution of calcium from these glasses. This, in turn, appears to be dependent upon the proportion of Ca 21 participating in the formation of the glassy network.

三藥齋重訂本草綱目San yue zhai chong ding ben cao gang mu.Traité des simples, réédition de la salle San yue.

Édition de 1735, imitée de celle de 1717 (Chinois 5264-5271, article I). Préfaces, table, avertissement, dédicace, introduction.3 livres de figures (manque le texte).

Apoyo social e ideación suicida en pacientes con cáncer

El diagnóstico de cáncer ha sido asociado con un alto riesgo de presentar ideación suicida en comparación con la población no oncológica, sin embargo se ha considerado al apoyo social como un factor protector para la ocurrencia de esta conducta. La presente investigación tuvo como objetivo identificar la relación entre el apoyo social percibido y la ideación suicida en 90 pacientes oncológicos adultos en Bogotá, bajo la hipótesis de que a mayor apoyo social percibido, menor presencia de ideación suicida. Se midió la variable de apoyo social a través del cuestionario Duke UNC y la ideación suicida a través de cuatro instrumentos: Escala de Ideación Suicida (SSI), Escala de Desesperanza de Beck (BHS), el ítem 9 del Inventario de Depresión de Beck (BDI-IA) y una entrevista semiestructurada. Los resultados mostraron que no existe relación entre el apoyo social percibido y la ideación suicida. Por otro lado se identificó una prevalencia de suicidio entre 5,6% y 22,77%, confirmando que el paciente con cáncer considera el suicidio y es fundamental evaluar esta variable en esta población. Se considera importante continuar con la realización de investigaciones que permitan generalizar los resultados a la población oncológica colombiana.

Les vrais principes de la lecture (1763) de Viard : aproximación a un primer planteamiento didáctico de la fonética francesa.

La autora presenta un estudio del libro de Nicolas-Antoine Viard, Les vrais Principes de la Lecture (1763). En él se destacan dos rasgos innovadores para su época: la reflexión pedagógica y la elaboración de un incipiente manual de Didáctica de la Fonética Francesa. Esta obra es un verdadero manual de pronunciación, ya que presenta tanto un contenido científico, como su aplicación o su reflexión didáctica. Viard elaboró un manual dirigido tanto alumno como al profesor y mostró la metodología que lo rige. Respecto del profesor, no sólo le presenta una organización jerarquizada y progresiva de los contenidos, sino que además le procura consignas de utilización. En cuanto a la metodología, que debe ser operativa (rapidez, facilidad y eficacia del aprendizaje) tales rasgos aparecen en esta misma triple vertiente. En, definitiva, la materia que trata y su forma de presentarla sitúan la obra como uno de los fundamentos básicos de la pirámide que a lo largo de la historia de la educación ha culminado en nuestra actual Didáctica de la Fonética Francesa..

A method for Ca, Fe, Ga, Na, Si and Zn determination in alumina by inductively coupled plasma optical emission spectrometry after aluminum precipitation

In this present work a method for the determination of Ca, Fe, Ga, Na, Si and Zn in alumina (Al(2)O(3)) by inductively coupled plasma optical emission spectrometry (ICP OES) with axial viewing is presented. Preliminary studies revealed intense aluminum spectral interference over the majority of elements and reaction between aluminum and quartz to form aluminosilicate, reducing drastically the lifetime of the torch. To overcome these problems alumina samples (250 mg) were dissolved with 5 mL HCl + 1.5 mLH(2)SO(4) + 1.5 mL H(2)O in a microwave oven. After complete dissolution the volume was completed to 20 mL and aluminum was precipitated as Al(OH)(3) with NH(3) (by bubbling NH(3) into the solution up to a pH similar to 8, for 10 min). The use of internal standards (Fe/Be, Ga/Dy, Zn/In and Na/Sc) was essential to obtain precise and accurate results. The reliability of the proposed method was checked by analysis of alumina certified reference material (Alumina Reduction Grade-699, NIST). The found concentrations (0.037%w(-1) CaO, 0.013% w w(-1) Fe(2)O(3), 0.012%w w(-1)Ga(2)O(3), 0.49% w w(-1) Na(2)O, 0.014% w w(-1) SiO(2) and 0.013% w w(-1) ZnO) presented no statistical differences compared to the certified values at a 95% confidence level. (C) 2011 Elsevier B.V. All rights reserved.

Variabilidade espacial do pH, Ca, Mg e V% do solo em diferentes formas do relevo sob cultivo de cana-de-açúcar

Em uma paisagem natural, os solos apresentam uma ampla variação dos atributos químicos, tanto vertical como horizontal, resultante da interação dos diversos fatores de formação envolvidos. Este trabalho foi desenvolvido em Guariba-SP, com o objetivo de avaliar a variabilidade espacial do pH, cálcio (Ca), magnésio (Mg) e saturação por bases (V%) em um Latossolo Vermelho eutroférrico sob cultivo de cana-de-açúcar, utilizando-se métodos da estatística clássica, análise geoestatística e técnica de interpolação de dados, com a finalidade de observar padrões de ocorrência destes atributos na paisagem. No terço inferior da encosta, após análise detalhada da variação do gradiente do declive, caracterizaram-se dois compartimentos (I e II), sob os quais os solos foram amostrados nos pontos de cruzamento de uma malha, com intervalos regulares de 50m, perfazendo um total de 206 pontos, nas profundidades de 0,0-0,2m e 0,6-0,8m. Os maiores alcances foram observados na profundidade de 0,0-0,2m para todos os atributos estudados, com exceção do cálcio que apresentou comportamento inverso, refletindo os efeitos do maior grau de intemperismo e do manejo na variabilidade natural dos solos. Pequenas variações, nas formas do relevo, condicionam variabilidade diferenciada para os atributos químicos.

High sinterability of Ca-PZT, synthesized by polymeric and partial oxalate process

This study includes Ca-PZT in the morphotropic phase boundary, MPB process combining the Pechini method, (ZT) and the Partial oxalate method (Ca-PZT) by obtaining single phase particles of ZT phase with a high specific surface area (similar to 110 m(2)/g at 550 degrees C) and narrow particle size distribution. Lead and calcium oxalates were precipitated onto the ZT particle surface and reacted to a solid state interface ZT/Ca-PZT/PbO-CaO. A deviation of a coexistence region from F-T- and F-R-phases to F-R-phase (Zr rich region) was observed. Strong surface area reduction occurs by Ca-PZT crystallization at about 700 degreesC, and demonstrated high sinterability (2.40 m(2)/g - 350 nm) with apparent densities near to 99.9%. Different processing methods did not demonstrate superior results. Studies of calcined powder shows a high sinterability of powder calcined 3 h at 700 degrees C and sintered 3 h at 1000 degreesC coming up to 99.8% of relative density. (C) 2001 Kluwer Academic Publishers.

Structural refinement and photoluminescence properties of cube-like (Ca 1-xCu x)TiO 3 crystals synthesized by the microwave-hydrothermal method

In this work, (Ca 1-xCu x)TiO 3 crystals with (x = 0, 0.01 and 0.02), labeled as CTO, CCTO1 and CCTO2, were synthesized by the microwave-hydrothermal method at 140°C for 32 min. XRD patterns (Fig. 1), Rietveld refinement and FT-Raman spectroscopy indicated that these crystals present orthorhombic structure Pbnm. Micro-Raman and XANES spectra suggested that the substitution of Ca by Cu in A-site promoted a displacement of the [TiO6]-[TiO6] clusters adjacent from its symmetric center, which leads distortions on the [CaO 12] clusters neighboring and consequently cause the strains into the CaTiO3 lattice. FE-SEM images showed that these crystals have an irregular shape as cube like probably indicating an Ostwald-ripening and self-assemble as dominant mechanisms to crystals growth. The powders presented an intense PL blue-emission.

Fluorcalciomicrolite, (Ca,Na,□)2Ta2O6F, a new microlite-group mineral from Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil

Fluorcalciomicrolite, (Ca,Na,□)2Ta2O6F, is a new microlite-group, pyrochlore supergroup mineral approved by the CNMNC (IMA 2012-036). It occurs as an accessory mineral in the Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil. Associated minerals include: microcline, albite, quartz, muscovite, spodumene, "lepidolite", cassiterite, tantalite-(Mn), monazite-(Ce), fluorite, "apatite", beryl, "garnet", epidote, magnetite, gahnite, zircon, "tourmaline", bityite, hydrokenomicrolite, and other microlite-group minerals under study. Fluorcalciomicrolite occurs as euhedral, untwinned, octahedral crystals 0.1-1.5 mm in size, occasionally modified by rhombododecahedral faces. The crystals are colourless and translucent; the streak is white, and the lustre is adamantine to resinous. It does not fluoresce under ultraviolet light. Mohs' hardness is 4½- 5, tenacity is brittle. Cleavage is not observed; fracture is conchoidal. The calculated density is 6.160 g/cm3. The mineral is isotropic, ncalc. = 1.992. The Raman spectrum is dominated by bands of B-X octahedral bond stretching and X-B-X bending modes.The chemical composition (n = 6) is (by wavelength dispersive spectroscopy, H2O calculated to obtain charge balance, wt.%): Na2O 4.68, CaO 11.24, MnO 0.01, SrO 0.04, BaO 0.02, SnO2 0.63, UO2 0.02, Nb2O5 3.47, Ta2O5 76.02, F 2.80, H2O 0.48, O=F -1.18, total 98.23. The empirical formula, based on 2 cations at the B site, is (Ca1.07Na0.81□0.12)∑2.00(Ta1.84Nb0.14Sn0.02)∑2.00 [O5.93(OH)0.07]6.00[F0.79(OH)0.21]. The strongest eight X-ray powder-diffraction lines [d in Å(I)(hkl)] are: 5.997(59)(111), 3.138(83)(311), 3.005(100)(222), 2.602(29)(400), 2.004(23)(511), 1.841(23)(440), 1.589(25)(533), and 1.504(24)(444). The crystal structure refinement (R1 = 0.0132) gave the following data: cubic, Fd3m, a = 10.4191(6) Å, V = 1131.07(11) Å3, Z = 8.