Rapid solidification of cryolite and cryolite–alumina melts

Abstract  

Rapid solidification processing (with a cooling rate in the interval 10⁵–10⁶ K s⁻¹) was used to prepare deeply undercooled cryolite–alumina melts. These samples were analyzed by XRD, infrared, and Raman spectroscopy. Besides cryolite, the amorphous phase and a low amount of ι-Al₂O₃ were detected. Annealing of the quenched sample revealed the transformation of metastable amorphous phases into different products depending on the annealing conditions. The results obtained showed that all of the elements (Na, Al, O, and F) are probably present in the amorphous parts of the quenched samples.     

Nanotubes Made from Deeply Undercooled Cryolite/Alumina Melts

The rapid‐solidification processing (by a cooling rate of 10⁵–10⁶ K/s) was used for the preparation of deeply undercooled cryolite/alumina (Na₃AlF₆/Al₂O₃) melts. We found a mass of nanotubes on the surface of these undercooled melts. The nanotubes were preferentially located on the defect places of the surface with the following approximate dimensions: base≈100×100 nm, length≈1000 nm. The solidified samples with the nanotubes on the surface were analyzed by scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD), and infrared spectroscopy (IR).     

Thermodynamics of Zr<Subscript>52.5</Subscript>Cu<Subscript>17.9</Subscript>Ni<Subscript>14.6</Subscript>Al<Subscript>10</Subscript>Ti<Subscript>5</Subscript> bulk metallic glass forming alloy

Recently, multicomponent glass forming alloys have been found which exhibit extraordinary glass forming ability and cooling rates of less than 100 K/s are sufficient to suppress nucleation of crystalline phases and consequently bulk metallic glass (BMG) is formed. The undercooled melts of BMG systems have high thermal stability in the undercooled region. Therefore, it is interesting to study the thermodynamics of such materials. This article investigates the thermodynamic behavior of a BMG system namely Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ by estimating the Gibbs free energy difference ΔG, entropy difference ΔS, enthalpy difference ΔH between the undercooled liquid and corresponding equilibrium crystalline solid phase, in the entire temperature range from T _m to T _K. Glass forming ability (GFA) of this system has been investigated through various GFA parameters indicating the degree of ease of glass formation.     

Transitions among five polymorphs of chlorpropamide near the melting point

Five polymorphs of chlorpropamide (α, β, δ, γ, and ε) were investigated near the melting point by using DSC. Structure of samples was tested by X-ray powder diffraction. Four first polymorphs were found to transform into ε-polymorph, which melts at T _m=128°C, Δ_m H=24 kJ mol⁻¹. Enthalpy of the polymorph transitions ranges from +3 kJ mol⁻¹ for α→ε to −0.8 kJ mol⁻¹ for β→ε. Structure of three first polymorphs was published elsewhere, and the structure of δ-polymorph is published for the first time. XRPD patterns for all polymorphs are reported, together with the atomic coordinates for the δ-polymorph.     

Solubility of europium oxides in NaI melts at 700°C

The solubility product of EuO (pP _EuO = 8.65 ± 0.5) and its dissociation constant (pK _EuO = 5.67 ± 0.5) in NaI melts at 700°C have been determined by potentiometric titration with the use of a Pt(O₂)|ZrO₂(Y₂O₃) membrane oxygen electrode. Estimated on the basis of these parameters, the total solubility of EuO in NaI melts (1.12 × 10⁻³ mol/kg, logs _EuO = −2.95) is close to the value obtained by the consecutive additions method (2.8 × 10⁻³ mol/kg, logs _EuO = −2.55). The values obtained show that Eu²⁺ (EuI₂) is a stable cationic activator in NaI melt, but it yet cannot be recommended as an agent for the removal of oxygen-containing admixtures from this melt.     

Electrodeposition of magnesium–lithium–dysprosium ternary alloys with controlled components from dysprosium oxide assisted by magnesium chloride in molten chlorides

In the work, Gibbs energy showed that MgCl₂ can chloridize Dy₂O₃ and release Dy(III) ions in the LiCl–KCl–MgCl₂–Dy₂O₃ melts. Dy(III) ions were observed by cyclic voltammetry, square wave voltammetry in melts. X-ray diffraction (XRD) pattern of melts indicated that Dy₂O₃ was chlorinated by MgCl₂ and formed DyCl₃. XRD pattern of non-dissolved residue, which was left after the melts were washed with water to remove the soluble salt, showed that the new compounds (i.e., DyOCl, MgO, and Dy(OH)₃) were produced. The concentration of Dy(III) reached a maximum when the concentration of Mg(II) ions exceeded 8?×?10^?4 mol cm^?3 in melts by inductive coupled plasma atomic emission spectrometer analyses of melts. Galvanostatic electrolysis was conducted to extract Dy element from LiCl–KCl–MgCl₂–Dy₂O₃ melts by forming Mg–Li–Dy alloys. The components of Dy and Li in alloys were controlled within a small range by the concentration of MgCl₂ in melts, current density, and additions of Dy₂O₃. XRD patterns of alloys indicated that Mg₃Dy phase was formed. Scanning electron microscope images with energy-dispersive X-ray spectroscopy showed that Dy elements were mainly distributed in the grain boundary. Grain size was refined, due to a more content of Dy elements in alloys by optical microscopy images.     

Analysis of thermodynamic behaviour of bulk metallic glass forming melts and glass forming ability

The thermodynamic behaviour of bulk metallic glass (BMG) forming melts have been studied by analyzing the temperature dependence of the Gibbs free energy difference (∆G), entropy difference (∆S) and enthalpy difference (∆H)between the undercooled melt and the corresponding equilibrium solid phases. The study is made by calculating∆G, ∆S and ∆H in the entire temperature range T _m (melting temperature) to T _g (glass transition temperature) using the expressions obtained on the basis of Taylor’s series expansion. The entire analysis is made for La-based five samples of BMGs; La₅₅Al₂₅Ni_20, La₅₅Al₂₅Ni₁₅Cu₅, La₅₅Al₂₅Ni₁₀Cu₁₀, La₅₅Al₂₅Ni₅Cu_15, and La₅₅Al₂₅Ni₅Cu₁₀Co₅ and a comparative study is also performed between present results and results obtained in the framework of expressions proposed by earlier workers. An attempt has also been made to study the glass forming ability for BMGs.     

The influence of the composition of CsCl-LiCl-YCl<Subscript>3</Subscript> melts on their acid properties at 973 K

The acid properties of CsCl-xLiCl and CsCl-LiCl + xYCl₃ melts were studied at 973 K by the potentiometric method with the use of a Pt(O₂)|ZrO₂(Y₂O₃) oxygen electrode. The acidity of these melts increased as x grew. The oxobasicity index values (pI _L) were estimated, they were 3.84 for 2CsCl-LiCl and 5.55 for 0.875(2CsCl + LiCl) + 0.125YCl₃ melts. The acid properties of mixed “alkali metal halide-rare-earth metal halide” melts were close to each other, and the presence of Li⁺ cations in such melts did not influence their pI _L values because of the leveling of their acid properties.     

Thermodynamic properties of Ni-Ga melts

The partial mixing enthalpies of the components (Δ_m $ \bar H $ \bar H _i ) of the Ni-Ga melts were measured using the high-temperature isoperibolic calorimetry at 1770 ± 5 K in wide concentration interval. The limiting partial mixing enthalpy of gallium in a liquid nickel (Δ_m $ \bar H $ \bar H _Ga^∞) is −95.5 ± 19.8 kJ mol⁻¹, and similar function of nickel in liquid gallium (Δ_m $ \bar H $ \bar H _Ni^∞) is −74.5 ± 16.4 kJ mol⁻¹. The integral mixing enthalpy of liquid alloys of this system was calculated from partial enthalpies for the whole concentration area (Δ_m H _min = −32.1 ± 2.7 kJ mol⁻¹ at x _Ni = 0.5). The Δ_m H value of liquid nickel-gallium alloys independence of the temperature is confirmed. Enthalpies of formation of liquid (Δ_m H) phases of Ni-Ga system were compared with ones for solid (Δ_f H) phases of this system. An analysis of d-metals influence on formation energy of Ga-d-Me melts was made using the values of Δ_f H for intermediate phases of these systems. The article was translated by the authors.     

Effect of annealing temperatures and of high content of the iron ion (Fe<Superscript>3+</Superscript>)-doping on transition anatase–rutile phase of nanocrystalline TiO<Subscript>2</Subscript> thin films prepared by sol–gel spin coating

Titanium dioxide doped with iron (III) was prepared by sol–gel Spin Coating method. The phase structures, morphologies, particle size of the doped TiO₂ have been characterized by X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM) and ultraviolet–visible (UV–Vis) spectrophotometer. The XRD and Raman results show that the 10% Fe³⁺-doped TiO₂ thin films crystallize in anatase phase between 600 and 800 °C, and into the anatase–rutile phase at 1,000 °C, and further into the rutile phase when the content of Fe³⁺ increases (20%). The grain size calculated from XRD patterns shows that the crystallinity of the obtained anatase particles increased from 39.4 to 43.4 nm as the temperature of annealing increase, whereas the size of rutile crystallites increases, with increasing Fe³⁺ concentrations from 36.9 to 38.1 nm. The AFM surface morphology results confirmed that the particle size increases by increasing the annealing temperature and also with an increasing of Fe³⁺ content. The optical band gap (E _g) of the films was determined by the UV–Vis spectrophotometer. We have found that the optical band gap decreased with an increasing of annealing temperatures and also with an increasing of Fe³⁺ content.     

Thermophysical Investigations of the Polymorphous Phases of Calcium Carbonate

1. Results of thermodynamic and kinetic investigations for the different crystalline calcium carbonate phases and their phase transition data are reported and summarized (vaterite: V; aragonite: A; calcite: C). A→C: T _tr=455±10°C, Δ_tr H=403±8 J mol^–1 at T _tr, V→C: T _tr=320–460°C, depending on the way of preparation,Δ_tr H=–3.2±0.1 kJ mol^–1 at T _tr,Δ_tr H=–3.4±0.9 kJ mol^–1 at 40°C, S _V ^Θ= 93.6±0.5 J (K mol)^–1, A→C: E _A=370±10 kJ mol^–1; XRD only, V→C: E _A=250±10 kJ mol^–1; thermally activated, iso- and non-isothermal, XRD 2. Preliminary results on the preparation and investigation of inhibitor-free non-crystalline calcium carbonate (NCC) are presented. NCC→C: T _tr=276±10°C,Δ_tr H=–15.0±3 kJ mol^–1 at T _tr, T _tr – transition temperature, Δ_tr H – transition enthalpy, S ^Θ – standard entropy, E _A – activation energy. 3. Biologically formed internal shell of Sepia officinalis seems to be composed of ca 96% aragonite and 4% non-crystalline calcium carbonate. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal characterization of montmorillonite clays saturated with various cations

Emanation thermal analysis (ETA), thermogravimetry and high temperature XRD were used to characterize the thermal behavior during dehydration of natural Na montmorillonite (Upton Wyoming, USA) and homoionic montmorillonite (MMT) samples saturated with different cations, i.e. Li⁺, Cs⁺, NH₄⁺, Mg²⁺ and Al³⁺. ETA results characterized radon mobility and microstructure changes that accompanied the mass loss of the samples due to dehydration on heating in air. A collapse of interlayer space between the silicate sheets after water release from the MMT samples was characterized by a decrease of the radon release rate, ΔE. Decreases in c-axis basal spacing (d ₀₀₁) values determined from XRD patterns for the different montmorillonite samples follow the sequence:

载银羟基磷灰石抗菌粉体和陶瓷的制备及抗菌性能

采用水热法一步合成载银羟基磷灰石抗菌粉体(Ag-HA),并将其应用于抗菌陶瓷的制备。研究结果表明水热条件下HA实际载银量与AgNO₃加入量存在较好的线性关系。XRD和TEM分析结果显示Ag-HA与HA具有相同的晶体结构,水热条件下Ag⁺取代Ca²⁺在HA晶体中的位置,生成Ag_xCa_10-x(PO₄)₆(OH)₂。Ag-HA长度随Ag⁺掺入量的增加而增大,当Ag⁺掺入量增加至1.50%时,Ag-HA由棒状生长为晶须状。选择4.50% Ag-HA作为抗菌粉体,其掺入量为9wt%时,陶瓷的抗菌率>99.9%,此时釉料中Ag₃PO₄含量为0.56%,低于目前研究中釉料中Ag₃PO₄添加量(2wt%~4wt%),不但在一定程度上解决了抗菌陶瓷产品成本较高的问题,而且满足JC/T 897-2002(抗菌陶瓷制品抗菌性能)对抗菌陶瓷抗菌性能的要求。     

Analysis of Thermodynamic Parameters of Glass Forming Polymeric Melts

The temperature dependence of the Gibbs free energy difference (ΔG), enthalpy difference (ΔH) and entropy difference (ΔS) between the undercooled meltand the corresponding equilibrium solid has been analysed for glass forming polymeric materials by calculating ΔG, ΔH and ΔS within the framework of the hole theory of liquids. The study is made for nine samples of glass forming polymeric melts; polypropylene oxide (PPO), polyamid-6 (PA-6), polytetramethylene oxide (PTMO), polyethylene oxide (PEO), polystyrene (PS), polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET) and polybutadiene (PB) and three simple organic liquids: tri-α-naphthyl benzene (tri-α-NB), o-terphenyl (o-ter) and phenyl salicylate (salol) in the entire temperature range T _m (melting temperature) to T _g (glass transition temperature). The ideal glass transition temperature (T _K) and the residual entropy (ΔS _R) of these samples have also been studied due to their important role in the study of the glass forming ability of materials. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heat capacity and thermal expansion coefficient of rare earth uranates RE<Subscript>6</Subscript>UO<Subscript>12</Subscript> (RE = Nd,Gd and Eu)

Rare earth uranates Nd₆UO₁₂, Gd₆UO₁₂ and Eu₆UO₁₂ were prepared by combustion synthesis and characterized by XRD. Single-phase rhombohedral structure was observed for all the above compounds. Heat capacity measurements were carried out on Nd₆UO₁₂ and Gd₆UO₁₂ with differential scanning calorimetry in the temperature range 298–800 K. Enthalpy, entropy and Gibbs energy functions were computed. Heat capacity values of Nd₆UO₁₂ and Gd₆UO₁₂ at 298 K are 436 and 400 J K⁻¹ mol⁻¹, respectively. Thermal expansion characteristics were studied using high temperature X-ray diffraction (HTXRD) in the temperature range 298–873 K. The coefficients of thermal expansion measured for Eu₆UO₁₂ are 10.5 × 10⁻⁶ and 7.3 × 10⁻⁶ K⁻¹ along a- and c-axis, respectively. Similarly, the coefficients of thermal expansion of Gd₆UO₁₂ along a-axis are 10.0 × 10⁻⁶ K⁻¹ and along c-axis is 9.7 × 10⁻⁶ K⁻¹.     

Thermodynamic properties of Eu-Sn melts

Partial and integral mixing enthalpies of melts of the Eu-Sn system were determined by calorimetry at 1300 (1250) K in the concentration intervals 0 < x _Sn < 0.16 and 0.7 < x _Sn < 1. It was found that the first partial mixing enthalpies of Sn and Eu were −215.6 ± 10.6 and −161.2 ± 7.6 kJ/mol, respectively. The thermodynamic properties of the Eu-Sn alloys were modeled using the theory of ideal associated solutions over a wide interval of concentrations and temperatures. In was found that the activities of components exhibit strong negative deviations from Raoult’s law. At minimum, the calculated integral Gibbs energies of mixing reach −43.4 kJ/mol at x _Sn = 0.48; ΔG ^ex = −36 kJ/mol, ΔS ^ex = −22 J/(mol K).     

Structural characterization and dielectric properties of the solid solutions AgPb(Sb,Bi)S3

The new solid solutions AgPbSb_1 − x Bi _x S₃ were prepared by solid state reactions. The phases were characterized by powder X-ray diffractions (XRD), scanning electron microscopy, and thermal analysis. The XRD patterns of different members (x = 0.5, 0.7, 0.8, and 1.0) are consistent with pure phases crystallizing in the cubic PbS-type structure. The electrical characterization was carried out using ac impedance spectroscopy and dc methods. The temperature dependence of the dc conductivity shows typical semiconductor Arrhenius behavior. The impedance measurements were performed in the frequency range of 0.1 Hz to 10 MHz and at the temperature range of 15 °C to 350 °C. The ac conductivity conforms to Jonscher’s universal power law. The frequency dependence of the dielectric permittivity follows the normal dielectric material behavior, and the relaxation is thermally activated. The frequency and temperature dependences of the electrical data are found to follow Summerfield scaling formalism.     

Preparation and characterization of lithium ion conducting ionic liquid-based biodegradable corn starch polymer electrolytes

Thin films of biodegradable corn starch-based biopolymer electrolytes were prepared by solution casting technique. Lithium hexafluorophosphate (LiPF₆) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BmImTf) were employed as lithium salt and ionic liquid, respectively. With reference to the temperature dependence study, Arrhenius relationship was observed. The highest ionic conductivity of (6.00 ± 0.01) × 10⁻⁴ S cm⁻¹ was obtained at 80 °C. Based on x-ray diffraction (XRD) result, the peaks became broader with doping of ionic liquid revealing the higher amorphous region of the biopolymer electrolytes. Ionic liquid-based biopolymer electrolytes exhibited lower glass transition temperature (T _g).     

Kinetic characterization of the reduction of silica supported cobalt catalysts

Abstact  The reduction process of silica supported cobalt catalyst was studied by thermal analysis technique. The reduction of the catalyst proceeds in two steps:

具有磁性-多色发光-热性能的MWCNTs负载NaGdF4:Tb3+,Eu3+多功能复合纳米材料

采用液相法成功制备了MWCNTs负载NaGdF_4∶Tb~(3+),Eu~(3+)纳米粒子的磁光热多功能复合纳米材料,并用XRD,SEM和EDS对其结构、组成和形貌进行了表征,结果表明:NaGdF_4∶Tb~(3+),Eu~(3+)纳米粒子为六方晶相,形貌为球形且尺寸分布均匀,直径大约为25 nm,并且均匀的包覆在MWCNTs的表面;通过PL,VSM和HTC对复合纳米材料的发光性能,磁性能和光热转换性能进行了表征,采用MTT法对多功能复合纳米材料的生物相容性进行了评估,结果表明:MWCNTs-NaGdF_4∶Tb~(3+),Eu~(3+)复合纳米材料具有良好的多色发光性能、磁性能、光热转换性能、低的毒性和良好的生物相容性。该种磁光热多功能复合纳米材料在生物标记、生物成像、肿瘤诊疗等领域有着广泛的应用前景。