CaO-SiO_2-Na_2O-CaF_2-Al_2O_3-MgO保护渣系的Al_2O_3吸收速率和粘度

采用CaO -SiO2 -Na2 O -CaF2 -Al2 O3-MgO渣系 ,通过测定熔渣的粘度和Al2 O3吸收速率 ,研究连铸保护渣的Al2 O3吸收速率与粘度及化学成分之间的关系。在一定条件下 ,当CaO SiO2 为1 .2左右时 ,粘度达到最小值 ,Al2 O3吸收速率达到最大值 ,分别为 0 .1 0Pa·s、8.4 0 3× 1 0 - 4 kg·m- 2 ·s- 1 。随着渣中Na2 CO3含量、CaF2 含量和MgO含量的增加 ,粘度减小 ,Al2 O3吸收速率增大。随着渣中Al2 O3含量的增加 ,粘度增大 ,Al2 O3吸收速率减小。粘度为Al2 O3吸收速率的主要控制因素。随着熔渣粘度的增加 ,连铸保护渣的Al2 O3吸收速率逐渐减小。     

Thermodynamic study of BaCuO2 and BaCu2O2

The Gibbs energy changes for the syntheses of the interceramic compounds of BaCuO₂ and BaCu₂O₂ were investigated as a basic study in the Y-Ba-Cu-O system that includes a superconductor, YBa₂Cu₃O_6.5+x . For the compound BaCuO₂, thermogravimetry with CO₂-O₂-N₂ gas mixtures was employed, and equilibrium temperatures were determined at which CO₂ partial pressures in the gas mixtures were equilibrated with mixed powder of BaCuO₂, CuO, and BaCO₃. The Gibbs energy change for the reaction of BaCO₃ + CuO = BaCuO₂ + CO₂ was determined from the relation between CO₂ partial pressure and equilibrium temperature, taking into consideration the effect of CO₂ dissolution in BaCuO₂. For the study on BaCu₂O₂, electromotive force (emf) measurement using yttria-stabilized zirconia solid electrolyte was conducted. A technique using two cells was applied to the emf measurement for minimizing the effect of dispersion of oxygen from samples, and the Gibbs energy change for the reaction of BaCuO₂ + CuO = BaCu₂O₂ + 1/2O₂ was decided from the measured O₂ partial pressure.     

Biological activity and phosphorylation of 2'-azido-2'-deoxyuridine and 2'-azido-2'-deoxycytidine

2'-Azido-2'-deoxyuridine and 2'-azido-2'-deoxycytidine were evaluated for their inhibitory activity against ribonucleotide reductase and for subsequent cell growth inhibition. Their mono- and di-phosphates were synthesized and their inhibitory activities against the reductase were also determined in a permeabilized cell system, along with the two nucleosides. The results of the present study identify the first phosphorylation step involved in the conversion of the two azidonucleosides to the corresponding diphosphates to be rate-limiting in the overall activation.     

Raman spectroscopy of the structures of Li2O-SiO2 and Li2O-GeO2 melts

An analysis of the Li₂O-SiO₂ and Li₂O-GeO₂ systems in the temperature range from 298 to 1373 K has been performed by Raman spectroscopy. A comparison of the spectroscopic data for the crystalline phases, glasses, and melts allowed us to determine the main anion groups existing in these systems and to establish the structural changes induced by changes in the temperature and composition.     

The free energies of mixing of melts in the systems 2FeO-SiO2-2MnO-SiO2 and 2.33FeO-TiO2-2.33MnOTiO2

The free energies of mixing in melts in the system 2FeO · SiO₂-2MnO · SiO₂ at 1450°C and the system 2.33FeO · TiO₂-2.33MnO · TiO₂ at 1475°C have been obtained from measurement of the equilibrium Mn + FeO = Fe + MnO established between the melts and ironmanganese foils. Both systems exhibit ideal silicate mixing. The phase diagram for the system 2FeO-SiO₂-2MnO ·SiO₂ is calculated.     

CaO-SiO2-Na2O-CaF2-Al2O3-MgO渣系的粘性活化能

采用CaO-Si02-Na20-CaF2-Al2O3-MgO渣系，通过测定粘度和粘性活化能，建立二次回归正交设计模型，借此研究了粘性特征与碱度、Na20含量、CaF2含量、Al2O3含量及MgO含量之间的关系，为设计开发连铸保护渣提供了理论依据。研究结果表明，粘性活化能随着渣中碱度、Na2C03含量和CaF2含量的增加而减小；Al2O3和MgO对粘性活化能的影响与碱度密切相关。连铸保护渣的粘度和粘性活化能具有相似的变化规律。     

Thermodynamic behavior of phosphorus in CaO-CaF2-SiO2 and CaO-Na2O-SiO2 systems

In order to understand the thermodynamic behavior of phosphorus, such as the polymerization of phosphate ions in slag melts, the influence of phosphorus content of slag melts on the partition of phosphorus between slags and carbon-saturated iron or silver was investigated for the CaO-CaF₂-SiO₂ and CaO-Na₂O-SiO₂ systems at 1573 and 1473 K, respectively. The predominant species changes from PO ₄ ³ to P₂O₇ ^4-approximately at 2 mass pct of phosphorus in slag melts, which is defined as the critical phosphorus content, for the CaO-CaF₂-SiO₂ system which is doubly saturated with CaO and 3CaO · SiO₂. The critical phosphorus content was found to be about 1 mass pct for the CaO-CaF₂-SiO₂ melts saturated with 2CaO · SiO₂. On the other hand, in the case of the 20CaO-35Na₂O-45SiO₂ system, PO₄/^3- is the predominant species until the slag becomes saturated with Ca₃(PO₄)₂. No effect of sulfur on the phosphorus partition ratio was observed for the CaO-CaF₂-SiO₂ system. Formerly Undergraduate Student, Department of Metallurgy, The University of Tokyo.     

Preparation of 2'-thio-2'-deoxycytidine 2':3'-phosphorothioate

The synthesis of a novel ribonucleotide analog 2'-thio-2' deoxycytidine 2':3'-O,S-phosphorothioate is described. In the first step, 2,2'-anhydro 1-beta-D-arabinosylcytosine was thiophosphorylated by the action of dithiophosphate, a process which gave predominantly the 3'-O-phosphorothioate isomer. An intramolecular displacement reaction led to the formation of the title compound. Structure and reactivity of this thioanalog differ substantially from 2':3'-CMP.     

BaF2-CaF2-CaCl2三元系熔盐电解体系的物理化学性质

研究了BaF2-CaF2-CaCl2三元系电解质体系的物理化学性质,为熔盐电解法制备Al-Ca合金奠定基础.采用阿基米德法,测定了BaF2-CaF2-CaCl2体系的密度;采用差热-热重分析法,测定了BaF2-CaF2-CaCl2体系初晶温度;采用连续变化电导池常数(CVCC)法,测定了BaF2-CaF2-CaCl2体系的电导率;采用循环伏安法研究了该体系的电化学行为.