Kinetic analysis of the isochronal crystallization of Ti40Zr25Ni8Cu9Be18 metallic glass

The isochronal crystallization kinetics of the Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ metallic glass has been investigated by differential scanning calorimetry (DSC). Results indicate that the two crystallization events of this metallic glass cannot be well-described by the classic Johnson-Mehl-Avrami (JMA) kinetic equation. The kinetic equation considering the impingement effect has been found more applicable for describing the isochronal crystallization kinetics of this amorphous alloy. Accurate values of kinetic parameters were determined by fitting the theoretical DSC data to experimental curves. The kinetic parameters change in different crystallization stages and show strong heating rate dependence. Reasons of the deviation from the JMA kinetics for the isochronal crystallization of Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ metallic glass were discussed.     

Computer modelling of the non-isothermal crystallization kinetics of electroless nickel-phosphorus deposits

Non-isothermal differential scanning calorimetry (DSC) data of electroless nickel-phosphorus (EN) samples with three different phosphorus contents (9, 12 and 16 wt%) has been used in the computer modelling of crystallization kinetics based upon the Johnson-Mehl-Avrami (JMA) theory. The major crystallization processes of the EN samples are complex and could involve multiple reactions, as indicated by the corresponding DSC curves obtained at the heating rates of 5-50 °C/min. The degrees of transformation for major crystallization process of the samples were calculated from those DSC experimental data. Computer simulations of the degree of transformation as well as the corresponding DSC curves were performed using the JMA models, and the results were compared to those from the experiments. It was found that the JMA models could perform within the experimental accuracy of the samples with high (12 and 16 wt%) phosphorus contents. However, satisfactory application of the model to a sample with medium (9 wt%) phosphorus content was not achieved, probably due to the presence of crystalline phase in the deposit prior to crystallization process. The derived JMA kinetic exponents (n) are compared and discussed upon their kinetic interpretation to the non-isothermal crystallization processes of the samples.     

Crystallization processes of Ag–Ge–Se superionic glasses

The interest in superionic systems has increased in recent years because of the potential application of these materials as solid electrolytes. In this field, amorphous materials present important advantages when compared to the crystalline solids: larger conductivity, isotropy and absence of grain boundaries. In this work, amorphous alloys of compositions (Ge₂₅Se₇₅)_100−yAg_y with y=10, 15, 20 and 25 at.% have been studied. Amorphous samples in bulk were obtained from the liquid by water quenching (melt-quenching technique). The crystallization kinetics of the amorphous alloys have been studied under continuous heating and isothermal conditions by means of differential scanning calorimetry. A glass transition and two exothermic transformations were observed in all the samples. The quenched samples and the crystallization products have been characterized by X-ray diffraction. The primary crystallization of the ternary phase Ag₈GeSe₆ and the secondary phase GeSe₂ was observed. The glass and crystallization temperatures, the activation energy and the crystallization enthalpy are reported. The first step of the crystallization of the Ag₈GeSe₆ phase in all the (Ge₂₅Se₇₅)_100−yAg_y samples is modelled taking into account the Johnson–Mehl–Avrami–Kolmogorov theory and considering that the changes in the composition only modify the viscosity of the undercooled liquid. The transformation diagrams (TTT and THRT) are calculated and the glass forming ability is analyzed. The experimental results are discussed and correlated with the structures proposed for the glass. The present results and conclusions are also compared with those reported by other authors.     

Fabrication of fluorine-doped silica glasses by the sol-gel method

Fluorine-doped silica glasses are produced by the sol-gel method for optical fiber preforms. In order to dope fluorine into silica glass, fluorinated silicon alkoxide, Si(OC₂H₅)₃F, is titrated into SiO₂ sol solutions. The fluorine content in silica glass depends on: the fluorine concentration in the gel, the specific surface area of SiO₂ particles and the heating rate in the sintering process. Fluorine-doped silica glass with a maximum relative refractive index difference of −0.93% is obtained. Using this technique, optical fibers with a triangular refractive index profile are fabricated with a minimum optical loss of 1.6 dB/km at 1.69 μm wavelength.     

Influence of the nucleation time-lag on the activation energy in non-isothermal crystallization

In the present work, the influence of the nucleation time-lag on the non-isothermal glass crystallization is discussed. Differential thermal analysis (DTA) results of an iron-rich glass nucleated by Cr₂O₃ were obtained at different heating rates. The activation energy of crystallization, E_c, and the Avrami parameter, m, estimated by Kissinger's and Ozawa's equations were shown to be dependent on the heating rate. The value of E_c, obtained at 2.5, 5 and 7.5 K/min heating rates was calculated as 299 kJ/mol, while the value of E_c, obtained at 10, 15 and 20 K/min was as 499 kJ/mol. The value of m for ‘low' and ‘high' heating rates were 2.57 and 1.45, respectively. The results were interpreted on the basis of the non-steady state nature of the nucleation process. It was assumed that at high heating rates no nucleation takes place and the crystals grow on a existing fixed number of nuclei; the activation energy of crystal growth, E_g, can be estimated by applying the Kissinger equations. At low heating rates nucleation occurs and the number of nuclei formed is influenced by the heating rate; E_g can be estimated by the Matusita and Sakka equation.     

Thermal stability and crystallization kinetics of new As–Ge–Se–Sb glasses

Thermal stability and crystallization kinetics of As₁₄Ge₁₄Se_72−xSb_x (where x = 3, 6, 9, 12 and 15 at.%) glasses are studied by the differential scanning calorimetry. The values of the glass transition temperature (T_g) and the peak temperature of crystallization (T_p) are found to be dependent on heating rate and antimony content. From the heating rate dependence of T_g and T_p the values of the activation energy for glass transition (E_t) and the activation energy for crystallization (E_c) are evaluated and their composition dependence discussed. Crystallization studies have been made under non-isothermal conditions with the samples heated at several uniform rates. Using a recent analysis developed for non-isothermal crystallization studies, information on some aspects of the crystallization process has been obtained. The stability calculations emphasized that the thermal stability decreases with increasing the Sb content.     

共沉淀法合成ZnMoO4粉体及其抗菌性能

以Zn(NO₃)₂·6H₂O、(NH₄)₆Mo₇O₂₄·4H₂O为主要原料,采用共沉淀法合成ZnMoO₄粉体。利用XRD、SEM等测试方法对合成样品的物相组成、微观结构进行表征。以培养的大肠杆菌为消杀对象,研究了不同热处理温度下的样品对大肠杆菌的抗菌性能。结果表明,前驱体主要为非晶态,含少量ZnMoO₄、Zn₂Mo₃O₈、Zn(OH)₂和MoO₃;前驱体经400~600 ℃、保温30 min热处理,其产物转化为ZnMoO₄,且随着热处理温度的升高,合成的ZnMoO₄晶型逐渐完善,抗菌性能增加,当热处理温度为600 ℃时,可以获得结晶良好的ZnMoO₄,其晶粒呈颗粒状和片状,平均粒径约为1.5 μm。不同热处理温度合成的ZnMoO₄均具有一定的抗菌性能,其中经600 ℃热处理得到的ZnMoO₄具有最佳抗菌性能,经过24 h抗菌检测,其抗菌率达到99.2%,在商用涂料料浆中外加5%的ZnMoO₄粉体,所制备涂层对大肠杆菌的抗菌率达到95.7%,表明ZnMoO₄及其涂料具有良好的应用前景。     

微波加热制备含稀土(La2O3)矿渣微晶玻璃研究

利用矿渣制备微晶玻璃是提高矿产资源利用率的主要形式之一。本文以白云鄂博尾矿为原料,采用微波一步法制备了CaO-MgO-Al₂O₃-SiO₂(CMAS)系辉石相矿渣微晶玻璃。选择835 ℃作为晶化温度,研究了微波加热对微晶玻璃析晶行为和微观组织的影响。以La₂O₃作为研究变量探讨了La₂O₃添加对矿渣微晶玻璃析晶行为的作用。与传统的热处理制度相比,微波加热可以在较短的时间内达到较高的析晶效果。同时La₂O₃的添加促进了晶粒细化。由拉曼光谱分析,La离子添加会导致玻璃网络中桥氧的增多,促进了辉石相析晶。在La的添加量为4%(质量分数)时硬度最高,达到了829.22 MPa。     

In vitro degradation studies of calcium phosphate glass ceramics prepared by controlled crystallization

Calcium phosphate glass ceramics with incorporation of small additions of two nucleating agents, MgO and K₂O were prepared in the metaphosphate and pyrophosphate region, using an appropriate two-step heat treatment of controlled crystallization defined by differential thermal analysis results. Identification and quantification of crystalline phases precipitated from the calcium phosphate glass were performed using X-ray diffraction and Rietveld analysis. The β-Ca₂P₂O₇ (β-DCP), KCa(PO₃)₃, β-Ca(PO₃)₂ and Ca₄P₆O₁₉ phases were detected in the glass ceramics. In order to evaluate the degradation of the glass ceramics prepared, degradation studies were carried out during 42 days in Tris-HCl solution at 37 °C, pH 7.4, using granules in the range of 355–415 μm. The materials presented a weight loss ranging up to 12%. The ions leached during the immersion mainly originated from the KCa(PO₃)₃ phase, probably due to the presence of K⁺ ion in the calcium metaphosphate, and the residual glassy phase. The structural changes at the surface of materials during degradation have been analyzed by Fourier transform infrared spectroscopy and X-ray diffraction. Results showed that significant surface changes occurred with immersion time, with the decrease of KCa(PO₃)₃, β-Ca₂P₂O₇ and β-Ca(PO₃)₂ phases occurring at different periods of immersion. This study has demonstrated an easy way to prepared calcium phosphate materials with specific calcium phosphate phases and crystallization, and therefore specific degradation rates.     

AgBr/TiO2纳米纤维的制备及其光催化性能研究

以钛酸丁酯、聚乙烯吡咯烷酮(PVP)、无水乙醇为原料,利用静电纺丝技术制备出Ti(OC4H9)4/PVP纳米纤维,经500～1000℃高温煅烧制得TiO2纳米纤维,再通过水热法将AgBr纳米颗粒负载到TiO2纳米纤维表面.利用X射线衍射仪、场发射扫描电镜、差热-热重分析对AgBr/TiO2纳米纤维进行表征分析.利用甲基...     

Internal friction and structural relaxation of amorphous Fe---Mn---P alloys

Measurements of internal friction and dynamic modulus have been carried out on amorphous Fe_83−xMn_xP₁₇(x=9,12, or 15) alloys in the temperature range 300–800 K, as a function of applied frequency, by a forced oscillation method. The characteristic transition temperatures and activation energies for crystallization were measured by differential scanning calorimetry (DSC). The viscous flow of the sample was measured using a thermomechanical analyzer (TMA) under continuous heating conditions. Internal friction increases rapidly with temperature starting from 450 K for 0.1 Hz, 474 K for 0.5 Hz, 486 K for 1.0 Hz, 511 K for 5 Hz, and 525 K for 10 Hz for the Fe₇₄Mn₉P₁₇ specimen. It was found that the internal friction peak temperature was very closely the same as the steady state viscous flow temperature from the TMA curves for Fe₇₄Mn₉P₁₇ and Fe₆₈Mn₁₅P₁₇ but not for Fe₇₁Mn₁₂P₁₇. It is assumed that the internal friction peak does not correspond to the glass transition temperature or crystallization temperature for these alloy systems. Two maxima in the free-volume fraction and two minima in the viscosity were also found for the samples which exhibit a ‘mid-contraction’ in their TMA displacement curves. The internal friction peak occurred at the steady state viscous flow temperature. This occurrence means that the origin of the internal friction peak is related to the viscous flow behavior and free-volume fluctuation for this alloy system.     

原位ATR-IR光谱实时研究DKDP的结晶过程

采用全反模式的红外(ATR-IR)光谱实时研究了不同氘含量KH_2-xD_xPO₄(DKDP)晶体的结晶过程,其中DKDP溶液氘含量范围为0到99%。通过υ₁(PO₄)和υ₃(PO₄)振动表征了DKDP结晶溶液中(H₂PO₄^-)_1-x(D₂PO₄^-)_x离子基团浓度的变化。υ₁(PO₄)振动强度的变化和υ₃(PO₄)振动宽度的变化说明生长溶液中的(H₂PO₄^-)_1-x(D₂PO₄^-)_x离子浓度随着测试时间延长而不断增大。同时,δ(P—O…H/D—O—P)振动峰的形成说明DKDP晶体的生长基元为(H₂PO₄^-)_n-x(D₂PO₄^-)_x离子团簇。波数在1 448 cm^-1到1 653 cm^-1范围内H—O—H和D—O—D振动强度的变化解释了DKDP晶体在结晶过程中氘含量分布不均的现象。     

Properties of ZrO2---Al2O3 composite powders prepared from Zr---Al metallo-organic compounds

Zr---Al metallo-organic compounds (zircoaluminates), having (CH₂)₄COOH, (CH₂)₁₂CH₃ and (CH₂)₂NH₂ as the organofunctional groups, were treated preliminary by (1) spray-drying, (2) gelation of addition of 10% NH₄OH aqueous solution followed by spray-drying and (3) rotary evaporation under a reduced pressure. After the treatment they were heated in air to prepare ZrO₂---Al₂O₃ composite powders. The IR and DTA profiles for the treated compounds indicated that the procedures modified the structures for the zircoaluminates. The stability of tetragonal ZrO₂ for the ZrO₂---Al₂O₃ composite powder were dependent on the modification in the structure for the zircoaluminates. Balloon shaped particles, 0.5–2 μm in diameter, were obtained through procedure (1) and spherical particles, 1–4 μm in diameter, through (2). Tetragonal ZrO₂ grains, 0.1–0.2 μm in diameter, were dispersed in the particles when heated at 1400°C.     

草酸配体修饰的锆取代型硅钨-氧簇合物的合成、结构和电化学性质研究

通过水热反应,成功合成了一个草酸配体修饰的四核锆取代的夹心型硅钨-氧簇合物H₁₂Na₂[Zr₄(μ₃-O)₂(μ₂-OH)₂(Ox)₂(α-SiW₁₀O₃₇)₂]·22H₂O (Ox=oxalic acid)。该夹心型硅钨-氧簇是由两个{α-SiW₁₀O₃₇}簇块通过一个{Zr₄(μ₃-O)₂(μ₂-OH)₂(Ox)₂}簇连接构成的。通过X-射线单晶衍射、IR、TG以及元素分析对该簇合物进行表征。晶体结构分析表明: 该簇合物结晶于单斜晶系,P2₁/c空间群,a=2.132 2 (6) nm, b=1.271 6 (4) nm, c=2.223 1 (7) nm, β=110.933(4)°,V=5.629 9(3) nm³,Z=2,R₁=0.061 5,wR₂=0.164 4。电化学和电催化性质研究表明标题簇合物对NO^-₂的还原有很好的电催化效果。     

(La0.95 Eu0.05)F3纳米晶的自牺牲模板法合成及其下转换发光性能研究

利用自牺牲模板法以一种新型稀土层状化合物(La0.95 Eu0.05)2(OH)4SO4·2H2O为模板成功合成出(La0.95 Eu0.05)F3纳米晶并研究其下转换发光性能.采用X射线衍射仪(XRD)、傅里叶红外变换(FT-IR)、场发射扫描电子显微镜(FE-SEM)及荧光光谱仪对合成产物的物相和荧光性能进行表征....     

5-溴-2-(4-甲基哌啶-1-基)嘧啶的晶体结构及密度泛函理论研究

嘧啶类衍生物在医药、化工和功能材料等领域有着重要应用。在药物研发,特别是抗癌药物研发领域中,5-溴-2-(4-甲基哌啶-1-基)嘧啶是一种含嘧啶环的重要中间体。本文通过一步芳香亲核取代反应合成了5-溴-2-(4-甲基哌啶-1-基)嘧啶,经溶液结晶法获得其单晶体,并进行了晶体学分析(晶系:正交晶系,空间群:P2₁2₁2₁,晶胞:a=10.181 42(6) nm, b=17.620 0(8) nm, c=10.179 02(5) nm,Z=4,ρ_c＝1.478 g·cm^-3,R=0.056 6,wR=0.168 8)。标题化合物的最优结构和前线轨道能量在B3LYP/6-311G(d, p)模式下使用密度泛函理论(DFT)计算得到,经DFT优化的结果与实验确定的数据相近。此外,为进一步揭示标题化合物的物理化学性质,通过DFT进一步研究了分子的静电式和前线分子轨道。     

Influence of chlorine-fluorine substitution on the electrical properties of some fluoride glasses

Study of electrical properties of two series of glasses (ZrF₄)₅₄(BaF₂)₃₀(ThF₄)₅(LaF₃)₃(RbF)_8(1−x)(RbCl)_8x (0 x 1) and (ZrF₄)₅₀(BaF₂)₃₀(ThF₄)₅(LaF₃)₃(RbF)_12(1−x)(RbCl)_12x (0 x 1) demonstrates the existence of a mixed mobile anion effect in these anion-conducting glasses. The effective medium approach has been applied to these materials: a satisfactory fitting is obtained as a function of the Cl/(Cl + F) ratio and temperature; the ionic transport in these glasses takes place along preferential pathways.     

一例含阴离子水簇的钴配合物的合成、结构及理论研究

金属配合物中的水簇研究为研究宏观意义上的水以及与蛋白质分子有关的水分子提供了有效途径。本文合成了一个含有阴离子水簇的带状超分子配合物[Co(2,2-bipy)₂(N₃)₂](N₃)_0.5Cl_0.5·2H₂O(1,2, 2-bipy=2, 2-联吡啶)。单晶结构解析表明,配合物属于三斜晶系,P-1空间群,晶胞参数为:a=0.822 54(7) nm,b=1.175 58(9) nm,c=1.237 06(10) nm,α=91.379 0(10)°,β=92.151 0(10)°,γ=108.119 0(10)°,V=1.135 27(16) nm³,由一个单核[Co(2,2-bipy)₂(N₃)₂]⁺配合物阳离子、两个非配位水分子、0.5个游离的叠氮离子和0.5个氯离子组成,叠氮离子和氯离子位置无序,占有率各为50%。两个客体水分子通过强烈的分子间氢键作用形成了环状水四聚体,且与无序的N^-₃和Cl^-通过氢键作用形成了一个[(H₂O)₄(N₃)Cl]^2- 阴离子水簇。此外,本文基于密度泛函理论(DFT)对配合物[Co(2,2-bipy)₂(N₃)₂]⁺阳离子进行了量子化学计算,分析了其单点能和原子电荷,并计算了中心金属离子的氧化态,计算结果与实验相吻合。     

Growth and characterization of KY(WO4)2 crystals

Single-crystal growth of KY(WO₄)₂ (KYW) by top-seeded solution growth technique has been investigated. The effects of seed orientation, temperature gradient experienced by the growing crystal and rate of crystallization on crystal quality are reported. The best results are obtained when the growth is seeded along the 0 1 0 direction. Minute deviations from this growth direction are found to be detrimental to crystal perfection. The differential thermal analysis shows that the amount of super-cooling required for dissolution and crystallization of KYW in the flux is only 5° and this promotes an easy formation of tiny crystallites in the solution. Consequently, the crystal rotation and the solution cooling rates are found to have pronounced effects on the growth of KYW crystal.     

基于有机羧酸配体的Co(Ⅲ)/Cu(Ⅱ)配合物的合成、结构及表征

在溶剂热条件下,以含卤素有机羧酸3-溴-吡啶-2,6-二甲酸(H₂L)为配体,以硝酸钴、硝酸铜为金属源,合成了两例配合物:[Co(L′)₃](1)和[Cu(L′)₂]_n(2)(HL′=5-溴-吡啶-2-甲酸),通过元素分析(EA)、X射线单晶衍射(SXRD)、X射线粉末衍射(PXRD)、红外光谱(IR)和热重分析(TGA)进行结构表征。X射线单晶衍射结果表明,配体H₂L在反应过程中发生脱羧现象,生成单羧酸配体5-溴-吡啶-2-甲酸。在配合物1中,每个Co(Ⅲ)都位于略微扭曲的八面体几何构型中,不对称单元中含有两个单核单元,单核单元通过C—H…O氢键形成三维超分子结构。配合物2的不对称单元中含有一个Cu(Ⅱ),两个脱质子的L′^-配体,每个Cu(Ⅱ)都是六配位的,位于扭曲的八面体几何构型中。Cu(Ⅱ)由配体连接生成1D链结构,通过C—H…O氢键形成三维超分子结构。此外,研究了两例配合物的热稳定性能。