Thermodynamics and phase diagrams in the binary systems Na2O-SiO2, Na2O-GeO2, Na2O-B2O3, Li2O-B2O3, CaO-B2O3, SrO-B2O3, and BaO-B2O3

We applied our model to the enthalpy of mixing data of the binary systems Na₂O-SiO₂, Na₂O-GeO₂, Na₂O-B₂O₃, Li₂O-B₂O₃, CaO-B₂O₃, SrO-B₂O₃, and BaO-B₂O₃. The most stable composition in the liquid, that is where the enthalpy of mixing is most negative, is with a metal-oxygen ratio of 4 to 3, for monovalent metals (Na and Li) and 3 to 4 for divalent metals (Ba and Ca) in liquid silicates or borates. The same applies to the CaO-SiO₂, CaO-Al₂O₃, PbO-B₂O₃, PbO-SiO₂, ZnO-B₂O₃, and ZnO-SiO₂ systems. The oxygen to metal ratio, its constant value in various types of systems, reflects and describes the structure of the liquid. Using the analyzed enthalpies of mixing data and the available phase diagrams, we calculated the enthalpies of formation of the various binary compounds. The results are in excellent agreement with data in the literature that were obtained from direct solid-solid calorimetry.     

Optical properties of heusler alloys Co2FeSi, Co2FeAl, Co2CrAl, and Co2CrGa

The results of an investigation of optical properties and the calculations of the electronic structure of Co₂FeSi, Co₂FeAl, Co₂CrAl, and Co₂CrGa Heusler alloys are presented. The main focus of our attention is the study of the spectral dependence of the real part (?₁) and imaginary part (?₂) of the dielectric constant in the range of wavelengths λ = 0.3–13 μm using the ellipsometric method. An anomalous behavior of the optical conductivity σ(ω) has been found in the infrared range in the Co₂CrAl and Co₂CrGa alloys, which differs substantially from that in the Co₂FeSi and Co₂FeAl alloys. The results obtained are discussed based on the calculations of the electronic structure.     

The oxidation of ZrB2, TaB2, NbB2, and W2B5 in atomic oxygen and by anodic polarization

The oxidation of ZrB₂, TaB₂, NbB₂, and W₂B₅ in atomic oxygen and by anodic polarization was studied. All the investigated materials, both in the gas medium and in the electrolyte, were highly resistant to corrosion. The composition of the surface compounds was examined during the oxidation. High resistance to oxidation is explained by the B₂O₃ oxide. Oxidation of borides in both atomic oxygen and in 1N H₂SO₄ takes place at comparable rates, the corrosion resistance in the two media being similar.     

Anisotropic elastic constants and thermal expansivities in monocrystal CrB2, TiB2, and ZrB2

The elastic constants and thermal expansivities in monocrystals of three transition-metal diborides with the AlB₂ structure, CrB₂, TiB₂, and ZrB₂, have been investigated in the temperature ranges from 300 to 1373 K and from 300 to 1073 K. The anisotropic parameters deduced from the measured elastic constants and thermal expansivities indicate that of the three diborides, the anisotropy is the most and least significant in CrB₂ and ZrB₂, respectively. The factors determining the significance in anisotropy in atomic bonding in AlB₂-type diborides are analyzed by an approach similar to the valence-force-field method and are discussed in terms of the deformation of the electronic charge around the metal atoms occurring to fit themselves in the (0 0 0 1) basal plane.     

Editorial board page for “Crystallography Reviews”, Volume 2, Number 2

Abstract

This is a scanned image of the original Editorial Board page(s) for this issue.     

Editorial board page for “Welding International”, Volume 2, Number 2

Abstract

This is a scanned image of the original Editorial Board page(s) for this issue     

Structure,composition, morphology,photoluminescence and cathodoluminescence properties of ZnGeN2 and ZnGeN2:Mn2+ for field emission displays

Yellowish-orange-emitting ZnGeN₂ and orange-red-emitting ZnGeN₂:Mn were synthesized by a facile and mild gas-reduction–nitridation reaction at 1153 K under NH₃ flow with air-stable raw materials ZnO, GeO₂ and MnCO₃. The structure, composition, morphology, photoluminescence and cathodoluminescence properties of ZnGeN₂ doped with or without Mn²⁺ were systematically investigated. Rietveld refinements show that the as-synthesized samples are obtained as single-phase compounds and crystallize as an orthorhombic structure with a space group of Pna2₁. The actual chemical composition of the as-prepared ZnGeN₂ determined by energy dispersive X-ray spectroscopy suggests that the Ge vacancy defects probably exist in the host. The SEM image reveals that the Zn_0.99Mn_0.01GeN₂ particles form aggregates ～500–600 nm in size. The diffuse reflection spectrum and photoluminescence excitation spectrum confirm that the band edge absorption of ZnGeN₂ at low energy is 3.3 eV (～376 nm). Upon UV light excitation and electron beam excitation, ZnGeN₂ gives an intense yellowish-orange emission around 580–600 nm, associated with a deep defect level due to the Ge vacancy defects, and ZnGeN₂:Mn shows an intense red emission at 610 nm due to the ⁴T_1g(⁴G) → 6A_1g(⁶S) of Mn²⁺. The unusual red emission of Mn²⁺ in tetrahedral Zn²⁺ sites is attributed to the strong nephelauxetic effect between Mn²⁺ and the surrounding tetrahedrally coordinated nitrogen. The photoluminescence and cathodoluminescence emission colors of ZnGeN₂:Mn have a high color purity of ～93–98%. These results demonstrate that ZnGeN₂:Mn is a novel, promising red-emitting nitride, potentially applicable to field emission displays with brilliant color-rendering properties and a large color gamut.     

Wetting characteristics of CaO−SiO2−Al2O3 ternary slag on refractory oxides, Al2O3, SiO2 and TiO2

The wettabilities of the metallurgical slag, CaO−55.2 wt.%SiO₂−15 wt.%Al₂O₃ on refractory oxides, Al₂O₃, SiO₂ and TiO₂ were investigated at temperatures of 1350, 1400 and 1470°C. Contact angle measurements were performed using a combination of the sessile drop method and the X-ray fluoroscopic technique. The contact angle was obtained from the numerical solution of the Young-Laplace equation. The steady contact angles obtained were 31°, 24°, and 15° for SiO₂, Al₂O₃ and TiO₂ at 1470°C, respectively. The spreading rate of the liquid slag was characterized by the formation of cognate interface between the liquid slag and solid oxide, and further enhanced by the formation of a diffuse layer around the slag drop at higher temperatures.     

LiF－CaF_2，NaF－CaF_2和KF－CaF_2系熔体热力学参量及相图的计算

本文将ＤＣＡ模型应用于ＬｉＦ－ＣａＦ２，ＮａＦ－ＣａＦ２和ＫＦ－ＣａＦ２熔体，并假设在这些熔体中存在络合离子．利用已有的上述混合熔体量热和熔盐相图的实验数据估计了熔体模型中的参数，并计算了熔体的混合热力学参量及相图．计算结果与实验结果吻合较好．     

Polarization of the H2, CO, CO2|Ni and H2S, H2, CO, CO2|Ni electrodes in molten sodium carbonate

Reactions at the H₂,CO,CO₂,Ni and H₂S,H₂,CO,CO₂|Ni electrodes in molten sodium carbonate at 1000°C have been studied in detail by means of computer-assisted analysis of potentiostatic polarization curves. Calculated curves accounting for charge transfer polarization, concentration polarization, ohmic loss and passivation arc matched to experimental curves by a series of successive approximations. Kinetic parameters thus determined are interpreted via rate theory and hypotheses concerning the identity of individual electrode reactions. Previous work with the CO,CO₂|Ni electrode was satisfactorily modelled by five anodic reactions: oxidation of physically dissolved CO, oxidation of chemically dissolved CO, oxidation of Ni to Ni²⁺, oxidation of NiO to Ni₂O₃ and oxidation of carbonate, occurring at progressively increasing overpotentials. At the H₂,CO,CO₂|Ni electrode, in addition to these reactions (oxidation of physically dissolved CO was not seen at the P_co values employed) oxidation of H₂ was observed at low anodic overpotentials. These experiments also clearly delineated an additional reaction postulated to be oxidation of Ni₂O₃ to NiO₂. Reactions at the H₂S,H₂,CO,CO₂|Ni electrode were identical to those at the H₂,CO,CO₂|Ni electrode save that the diffusion-limited current for oxidation of chemically dissolved CO increased linearly with . This is attributed to the occurrence of chemically dissolved CO as a sulfide species, e.g. COHS⁻, in addition to the CO₂^2- found under CO, CO₂ atmospheres. In support of this mechanism, the reaction did not display diffusion control when 0.5% Na₂S was added to the electrolyte, suggesting a high level of, e.g., COS^2-. Total cell pressure was 1 atm; in the sulfide experiments P_H2S varied from 0.000027 to 0.027 atm, with P_{H2 = 0.5 atm} and P_co = P_co2 = 0.25 atm.     

N2，CO2，O2与铀初期反应动力学研究

采用微压PVT方法测定了323K下N2、CO2和O2在清洁铀表面的饱和吸附量及反应概率,对比分析了3种活性气体的反应活性及动力学性质。结果表明,N2、CO2和O2同呈吸附量(覆盖度)趋近一个极大值,反应概率随吸附量增加而减少的特征;反应活性强弱关系为O2>CO2>N2,饱和吸附量关系为NO2≈2.4NCO2≈7NN2。气体与铀的初期反应动力学进程依赖于表面产物层组成和厚度对分子解离和粒子扩散过程的影响,铀氮化物和铀碳化物(或含氧碳化物)较铀氧化物对气体反应动力学进程具有更强的阻抑效应。     

Yb2Ge,Eu2Ge and Eu2Si: new PbCl2-type compounds

The intermetallic compounds Yb₂Ge, Eu₂Ge and Eu₂Si were synthesized from the elements by HF melting in tantalum crucibles. The three phases crystallize in the PbCl₂ structure type, as shown by Rietveld refinement of powder pattern intensity data. The structure of Yb₂Ge was confirmed by a single crystal study.     

Fe-15Ce合金在H2-CO2、H2-H2S及H2-H2S-CO2气氛下的腐蚀

研究了600℃时Fe-15Ce合金在H2-CO2、H2-H2S及H2-H2S-CO2 3种气氛中的腐蚀行为，Fe-15Ce合金腐蚀后发生了Ce的内氧化或形成了复杂的腐蚀产物膜，而未出现Ce的选择性氧化或硫化，这主要是合金中存在着两相及Ce在Fe中极低的溶解度的结果。Fe-15Ce合金在本实验条件下的氧化-硫化腐蚀速度低于相同温度、压力下的纯硫化。     

A model for the oxidation of ZrB2, HfB2 and TiB2

A mechanistic model that interprets the oxidation behavior of the diborides of Zr, Hf and Ti in the temperature range of ∼1000–1800 °C was formulated. Available thermodynamic data and literature data for vapor pressures and diffusivities were used to evaluate the model. Good correspondence was obtained between theory and experiments for weight gain, recession and scale thickness as functions of temperature and oxygen partial pressure. At temperatures below about 1400 °C, the rate-limiting step is the diffusion of dissolved oxygen through a film of liquid boria in capillaries at the base of the oxidation product. At higher temperatures, the boria is lost by evaporation, and the oxidation rate is limited by Knudsen diffusion of molecular oxygen through the capillaries between nearly columnar blocks of the oxide, MO₂.     

添加SnO_2组元对RuO_2 SnO_2 TiO_2/Ti钛阳极组织形貌的影响

通过溶胶凝胶 (Sol gel)法经涂刷、烧结、退火等工艺制备了添加不同含量SnO2 的RuO2 SnO2 TiO2 /Ti三元涂层钛阳极。并通过X射线衍射 (XRD)、差热分析 (DTA)、透射电子显微 (TEM )分析了SnO2 组元对RuO2 TiO2 SnO2 /Ti阳极涂层组织、晶粒尺寸和外观形貌的影响。结果表明 ,所获三元涂层颗粒尺寸细小 ,均为纳米结构 ,且添加SnO2 组元后有显著细化涂层晶粒的效果。在不同退火温度下 ,随SnO2 含量的增加 ,涂层晶粒均能发生一定程度的细化。所获三元阳极涂层主要组成物相为金红石 (Ru ,Sn ,Ti)O2 固溶体 ,SnO2 组元含量较高的涂层出现不同成分金红石相共存的现象 ;当涂层退火温度由 45 0℃升高至 6 0 0℃后 ,SnO2 组元不能阻止 (Ru ,Sn ,Ti)O2 固溶体脱溶分解 ,并析出六方晶系Ru单质 ;添加SnO2 组元的RuO2 SnO2 TiO2 涂层晶粒外观呈较理想等轴状特征     

Oxidation of molten Al-Mg alloy in air,air-SO2, and air-H2S atmospheres

Rates of oxidation of 8 g samples of molten Al-Mg alloys in air, air-SO₂, and air-H₂S atmospheres were determined at 750°C by gravimetry. Weight gains in air containing 10 or more volume percent SO₂ averaged 0.2 % in up to 100 hr, whereas samples heated in air alone gained over 5% weight in 20 hr and 10% in 70 hr. Heating for only 1 hr in SO₂ concentrations of 10% or greater prevented extensive oxidation during additional heating in air alone. H₂S was more effective than SO₂ heating for as little as 1/2hr in 0.25 vol. % H₂S prevented extensive oxidation during subsequent heating for at least 90 hr in air alone. The inhibiting effect of either SO₂ or H₂S probably involves oxidation to SO₃. This reacts with portions of the initial protective amorphous MgO film to form MgSO₄, which has a high volume quotient and maintains protection as nonprotective crystalline MgO forms at the end of an induction period.     

TiO_2 sensitized by red-, green-, blue-emissive carbon dots for enhanced H_2 production

Carbon dots(Cdots) with a broad light absorption range could be a potential stable sensitizer for TiO_2,which is an excellent ultraviolet(UV) response photocatalyst. Herein, we systematically investigated the different color emissive Cdots-sensitized TiO_2 for H_2 production.Firstly, all kinds of Cdots enhanced the photocatalytic properties of TiO_2. All the Cdots-sensitized TiO_2 exhibits visible light H_2 production due to their absorption in the visible light region. The photocurrent and H_2 production amount display strong dependence on the light absorption range of Cdots. The blue-emissive Cdots endow the weak H_2 production rate due to its weak absorption in the visible light. The enhanced photocatalytic activities are mainly contributed to the strong light absorbance and high-efficient charge separation. The light absorption of green-and red-emissive Cdots is another main factor for the high catalytic activities besides charge separation.     

X-射线荧光光谱法快速测定电解质的BR、CaF2、MgF2、KF及Al2O3含量

本文对采用直接压片X-射线荧光光谱测定电解质分子比及其氧化铝和杂质元素含量的方法进行了探讨与研究，试验结果表明诚方法分析结果可靠。可快速分析电解质的成分组成。能满足电解槽的控制需要。     

RECl_3-CaCl_2-MgCl_2 TERNARY PHASE DIAGRAMS(RE:La,Ce,Pr,Nd)

Nine sub-binary phase diagrams of the RECl_3-CaCl_2,RECl_3-MgCl_2 and CaCl_2-MgCl_2 systems,andthermodynamic data for these systems are critically assessed and optimized.Using Hillert model and takingMgCl_2 as an asymmetric component,the ternary phase diagrams or the RECl_3-CaCl_2-MgCl_2 systems are predtcted.As well,the determination of asymmetric component in the asymmetric model is investigated.     

Polymorphism in 2-Amino-2-Methyl-l,3 propanediol plastic crystal

Several techniques were used to characterize the polymorphism in polyalcohol 2-amino-2-methyl-1, 3 propanediol, (CH₂OH)₂CH₃C NH₂, which exhibits a solid crystalline plastic phase. Three equilibrium and two nonequilibrium states were determined in the temperature range from 0 to 150 °. One of the nonequilibrium states reveals characteristics of a glassy crystal, a frozen state from the plastic phase. Although different results agree with this affirmation, further analysis is needed to verify the glassy crystal definition of Suga and Seki [68Ada].