Sinter-crystallization of a glass obtained from basaltic tuffs

Glass-ceramic materials, obtained by sinter-crystallization of melted alkaline-olivine basaltic tuffs, were investigated. The kinetics of bulk crystallization was evaluated by differential thermal analysis (DTA) at different heating rates. The phase formation and the sintering behavior of glass powders (<75 μm) were studied in air and in nitrogen atmospheres by DTA and dilatometry, respectively. The crystalline phases formed were identified by X-ray diffraction. The DTA traces showed an unusual phase formation behavior with a higher crystallization trend for the bulk samples. The crystallization activation energy was evaluated as 590 ± 20 kJ/mol in the range 1080–1110 K. A value of about 3 of the Avrami constant, corresponding to three-dimensional growth on a fixed number of nuclei, was evaluated by Ozawa and Augis–Bennet methods. The densification at low-temperatures is reduced by the intensive crystallization process in both air and nitrogen atmospheres. The sintering starts again at 1150–1250 K. In air atmospheres, due to the FeO oxidation, the sintering temperature increases and the percentage of formed crystal phase decreases by 15–20%.     

Evaluation of glass ionomer cements properties obtained from niobium silicate glasses prepared by chemical process

Glass ionomer cements (GICs) are glass and polymer composite materials. These materials currently find use in the dental field. The purpose of this work is to obtain systems based on composition 4.5SiO₂–3Al₂O₃–XNb₂O₅–2CaO to be used in Dentistry. The systems were prepared by chemical route at 700 °C. The results obtained by XRD and DTA showed that all systems prepared are glasses. The structures of the obtained glasses were compared to commercial material using ²⁷Al and ²⁹Si MAS NMR. The analysis of MAS NMR spectra indicated that the systems developed and commercial material are formed by SiO₄ and AlO₄ linked tetrahedra. The properties of glass ionomer cements based on the glasses prepared with several niobium contents were studied. Setting and working times of the cement pastes, microhardness and diametral tensile strength were evaluated for the experimental GICs and commercial luting cements. It was concluded that setting time of the cement pastes increased with increasing niobium content of the glasses (X). The properties to the GICs such as setting time and microhardness were influenced by niobium content.     

溶胶-凝胶法制备尖晶石型ZnFe2O4粉体的研究

以硝酸铁、硝酸锌为原料,柠檬酸为络合剂,采用溶胶-凝胶法制备了尖晶石型ZnFe2 O4粉体.通过热重-差热分析(TG-DTA)、X射线衍射仪(XRD)、扫描电镜(SEM)、X射线能谱仪(EDS)、透射电镜(TEM)等方法对制备的ZnFe2O4粉体进行了分析测试与表征,并对其合成机理进行探讨.研究表明:滴定溶液的pH =4时最有利于柠檬酸对Fe3+、Zn2+的络合.在600 ～ 1000℃下,随着合成温度的提高,制备的ZnFe2O4粉体晶型发育逐步完整,确定较好的合成温度为900℃.相同条件下,适当延长保温时间,有助于ZnFe2O4粉体的合成.     

添加剂促进锌铝尖晶石生成机理研究

以氧化铝和氧化锌为原料,采用固相反应法合成锌铝尖晶石,将试样在800～1500℃进行烧结,研究了添加剂对矿物组成和微观结构的影响,采用XRD、SEM和EDS等手段对烧后试样的物相组成和显微结构进行表征.结果表明:在800℃时,空白样的主晶相为氧化锌,次晶相为锌铝尖晶石,添加ZrO2的试样主晶相为锌铝尖晶石,次晶相为氧化锌和氧化锆,添加TiO2的试样,主晶相为锌铝尖晶石,次晶相为钛酸锌,两种添加剂均有促进锌铝尖晶石生成的作用,添加TiO2和ZrO2的试样晶粒尺寸均比空白样大;1500℃时,氧化钛与氧化铝反应生成钛酸铝,当TiO2含量在1;～5;之间时,随着TiO2含量增加,锌铝尖晶石晶粒尺寸增大.     

Waveguide produced by fiber on glass method using Er-doped tellurite glass

We report the fabrication of waveguides using the fiber on glass (FOG) method. Taking advantage of a Thermal Mechanical Analyzer (Shimadzu TMA-50), we were able to produce a new type of waveguide by coupling an erbium doped fiber core onto a planar glass substrate. Both optical fiber core and substrate were fabricated from tellurite glass. Important thermal characteristics of the substrate and fiber like the transition temperature T_g, the temperature for the crystallization onset T_x and the maximum crystallization temperature T_c were determined by Differential Thermal Analysis (DTA). The thermal expansion coefficient of the tellurite glass was determined by Thermal Mechanical Analysis (TMA).     

电熔镁铝尖晶石和轻烧镁粉对合成镁铁铝系复合尖晶石的影响

本文研究电熔镁铝尖晶石和轻烧镁粉对合成镁铁铝复合尖晶石的影响.电熔镁铝尖晶石和轻烧镁粉分别与氢氧化铁、活性氧化铝混合均匀制得φ20 mm×10 mm的试样,在空气气氛烧结条件下,于1550℃×6 h高温烧成.采用XRD、SEM和EDS等手段对烧后试样的物相组成和显微结构进行表征.结果表明:加入电熔镁铝尖晶石的试样中存在刚玉相、赤铁矿、铁铝尖晶石相和镁铁铝复合尖晶石相四种矿物相,镁铁铝复合尖晶石的化学式为Mg796Al15.31Fe0.68O32;加入轻烧镁粉的试样中存在刚玉相、铁铝尖晶石相和镁铁铝复合尖晶石相三种矿物相,镁铁铝复合尖晶石的化学式为Al15.71Mg3.35Fe4.94O32;加入电熔镁铝尖晶石的试样中铁铝尖晶石的晶粒尺寸和镁铁铝复合尖晶石相差无几,加入轻烧镁粉的试样中铁铝尖晶石的晶粒尺寸明显大于镁铁铝复合尖晶石.     

Silicate nanoparticles by bioleaching of glass and modification of the glass surface

Bioleaching is examined as a low temperature (50 °C) soft chemical approach to nanosynthesis and surface processing. We demonstrate that fungus based bioleaching of borosilicate glass enables synthesis of nearly monodispersed ultrafine (∼5 ± 0.5 nm) silicate nanoparticles. Using various techniques such as X-ray diffraction, X-ray photoelectron spectroscopy and FTIR we compare the constitution and composition of the nanoparticles with that of the parent glass, and establish the basic similarities between the two. The bioleaching process is shown to enhance the non-bridging oxygen component and correspondingly influence the Si-O-Si network. The root mean square roughness of glass surface is seen to increase from 1.27 nm for bare glass to 2.52 nm for 15 h fungal processed case, this increase being equivalent to that for glass annealed at 500 °C.     

Structure of lanthanum prepared by quenching from a liquid state

The structure of lanthanum quenched from a liquid state at cooling rates of 2.5 × 10⁵–10⁷ K/s is investigated. It is shown that a mixture of the face-centered cubic β-La phase stable above 583 K and the metastable lanthanum modification with a seven-layer hexagonal lattice consisting of alternating atomic layers ABCABAC… is formed in rapidly cooled foils. A mechanism is proposed for the formation of the metastable polytype, according to which the polytype is formed as a result of saturation of the main β-phase with well-ordered stacking faults.     

自增韧和增强的镁铝尖晶石透明陶瓷

用化学配比n为1.0,1.3,1.5和1.8的MgO·nAl2O3粉体分别制备出了镁铝尖晶石透明陶瓷MA1.0,MA1.3,MA1.5和MA1.8.这些陶瓷是通过真空烧结和热等静压两步烧结方法制得的.由于第二相物质氧化铝晶粒的析出,陶瓷相对密度随着化学配比的增高而降低.然而,与化学配比陶瓷相比,这些非化学配比陶瓷表现出了较高的机械性能,陶瓷断面的扫描电镜照片显示非化学配比陶瓷多为穿晶断裂模式,这种断裂模式对陶瓷的强韧化作出了主要贡献.     

Lactose-based molecular alloys obtained by solid state vitrification

In this paper, we report the possibility to form glassy amorphous molecular alloys α-lactose/mannitol and α-lactose/budesonide by milling together pure crystalline powders of α-lactose and mannitol on the one hand, and pure crystalline powders of α-lactose and budesonide on the other hand. It is also shown that upon milling, pure mannitol undergoes a polymorphic transformation from the stable form β towards the metastable form α, while pure budesonide undergoes a complete amorphization. The results have been established by differential scanning calorimetry and by powder X-ray diffraction.     

透明多晶尖晶石的制备研究

本文报道了采用高纯、超细的尖晶石粉末作为起始原料,用真空烧结法结合热等静压后处理技术制备透明多晶尖晶石材料,合成的原料纯度较高、粒度小、粒径分布窄.测试了尖晶石的透过率、抗弯强度、硬度、热膨胀系数等主要物理性能.制备的多晶尖晶石材料从紫外、可见光到近红外波段的透过率在75;以上.     

Silica glass tubes by new sol-gel method

Silica glass tubes were prepared by following a new sol-gel method. The pH of the sol containing hydrolyzed Si(OC₂H₅)₄ with HCl and colloidal silica was adjusted by adding ammonia solution. Sol was poured into a cylindrical tube and gelled while rotating cylinder at 1000 rpm to form a tube-shaped gel. Then the gel was dried carefully to be tube dry-gel and finally sintered to become a clear silica glass tube.

The effects were examined of the speed of rotation before and after gelation, to form the tubular gel, upon the shape and appearance of the derived tubes. The best speed of rotation was about 1000 rpm, and an adequate long period of rotation after gelation was necessary to maintain the tube shape. One of the large silica tubes had dimensions of 26 mm outside diameter, 13 mm internal diameter and 1000 mm length, and the ovality of the silica glass tube was 0.02%.

The derived tube can be applied in a silica glass tube for an optical fiber fabrication process or in a furnace tube for IC production.     

Luminescent porphyrinosilica obtained by the sol–gel method

Hybrid materials consisting of a substituted porphyrinic macrocycle covalently bonded to a porous silica matrix have been prepared. The organic macrocycle 5,10,15,20-tetra-(p-hydroxy)phenylporphyrin, H₂T(p-OH)PP, has been covalently bonded to silica gel porous networks, obtained by sol–gel reactions, by means of 3-isocyanatopropyl-triethoxysilane (IPTES), whose molecules act as bridges between the silica precursor tetraethoxysilane (TEOS) and the porphyrinic H₂T(p-OH)PP macrocycles. Electronic absorption spectra show Soret and Q bands characteristic of trapped porphyrins inside the silica networks. Infrared spectroscopy monitoring has been employed to demonstrate the formation of covalent bonds between some substituents of the porphyrin molecules and the isocyanato group of IPTES.     

Reduction of copper in soda-lime-silicate glass by hydrogen

The reduction of copper in soda-lime-silicate glasses by hydrogen was measured as a function of time and copper content within the temperature range 440 to 650°C. Copper is reduced to the metallic state in a surface layer whose thickness increases with time and temperature and decreases with copper content. A well developed periodical precipitation of copper particles is observed in the reduced layer. The reduction is accompanied by an alteration of the glass composition in which there is an increase of the copper content and a reduction of the calcium content. The growth kinetic of the reduced layer, followed by optical spectroscopy and measurement of the layer thickness, is analyzed with regard to the tarnishing model.     

Fine-patterning on glass substrates by the sol-gel method

A novel process has been developed to form fine patterns on glass substrates. The process consists of the following steps: (1) coating of gel film on a substrate, (2) patterning on the gel film, and (3) heat-treatment. The key point in this process is the control of hardening of the gel films by the addition of organic polymers such as polyethylene glycol (PEG). The addition of PEG increased the viscosity of the coating solutions and delayed the gelation time, but had little effect on the optical properties of the resultant heat-treated glass films. The newly developed process is expected to be applicable to the formation of the optical devices such as diffraction gratings and pre-groovesof optical memory disks.     

IR investigation of density changes of silica glass and soda-lime silicate glass caused by microhardness indentation

Density changes of silica glass and soda-lime silicate glass caused by ball indentation and Vickers indentation were investigated. The IR reflection peak shift of the silica structural band was monitored to determine the extent of the fictive temperature change and the corresponding density change. Under the central portion of the ball indentation, the density of silica glass increased while a change in the soda-lime silicate glass structure was not clear. On the other hand, in the vicinity of the Vickers indentation, the opposite trend was observed. Namely, soda-lime silicate glass exhibited the structural change corresponding to the density decrease, while the structural change of the silica glass was uncertain. The initial density of the silica glass influenced the change of density under ball indentation in such a way that the initial density difference of the glass samples was reduced.     

Synthesis of silica aerogel blanket by ambient drying method using water glass based precursor and glass wool modified by alumina sol

Silica aerogel blankets have been synthesized by ambient drying technique using cheap water glass as the silica source and glass wool modified by alumina sol. One step solvent exchange and surface modification were simultaneously conducted by immersing the wet hydrogel blanket in EtOH/TMCS/hexane solution. The synthesized silica aerogel blanket was light with the density of 0.143-0.104 g/cm³ and 89.4-95% porosity. The microstructure of silica aerogel blanket exhibits a porous structure consisting of glass fibers of diameter ∼2.5 μm interconnected with solid silica clusters (5-20 μm).