Effect of Al2O3 on phase separation and crystallization in ZnO---Al2O3---B2O3---SiO2 glasses

The effect of alumina on the phase separation and the crystallization of the glasses of composition (mol%) 18ZnO·30B₂O₃·52SiO₂ and O-40 Al₂O₃ was studied using an electron microscope and IR spectroscopy. The main crystalline phase appears in the microphase for which the compositions are not nearer to the crystal stoichiometry than the mean. The addition of Al₂O₃ suppresses the immiscibility but enhances the crystallizability.     

Solidification of superalloy in a SiO2–ZrO2–B2O3 coating mould

The preparation of glass-lined coating mould from gels in the ternary system of SiO₂–ZrO₂–B₂O₃ has been investigated. The crystallization characterization and high temperature structure stability of this coating mould are demonstrated. We can find that the crystallization of t-ZrO₂ as well as the tetragonal to monoclinic phase transformation are, respectively, retarded and impeded owing to the encasement of SiO₂ matrix. While the inhibitive effect of B₂O₃ on crystallization of the SiO₂–ZrO₂–B₂O₃ coating mould is explained. Finally, DD3 single crystal superalloy melt can realize highly undercooled rapid solidification by adopting this coating mould, which further evinces that SiO₂–ZrO₂–B₂O₃ coating mould has an ideal nucleation inhibition for superalloy.     

The influence of the crystallization process on the internal friction of some oxide glasses

The influence of phase separation and crystallization on the internal friction of some oxide glasses is reviewed and discussed. In alkali-containing glasses, the internal friction peak caused by stress-induced diffusion of alkali ions decreases in magnitude and shifts to higher temperature slightly due to phase separation. And in alkali-free glasses phase separation only exerts a minor decrease upon the background of internal friction curves, whereas crystallization influences the internal friction of these glasses more strongly. Because of crystallization, in alkali-containing glasses alkali ions might diffuse in a residual glass phase and a crystal phase, respectively. This might cause corresponding internal friction peaks. And in alkali-free glasses, no evident internal friction peak is observed. However, the author found a high and wide internal friction peak at about 100°C in the crystallized MgO·Al₂O₃·SiO₂·TiO₂ and ZnO·Al₂O₃·SiO₂·ZrO₂ glasses. The peak occurring in the two glasses studied is probably connected with glass crystallization and crystallized crystals.     

Al2O3-TiO2 and Al2TiO5 ceramic materials by the sol-gel process

Ceramic materials with a very low thermal expansion coefficient are synthesized by the sol-gel process. The binary gel is obtained by hydrolysis and polycondensation reactions of organometallic compounds of aluminium and titanium. The thermal evolution of the amorphous powder is followed by DTA and TGA measurements. Structural evolution is followed using X-ray diffraction. The crystallization of the TiO₂ rutile and Al₂O₃ corindon starts at 700 and 900°C respectively. The transformation of Al₂O₃ and TiO₂ into Al₂TiO₅ appears between 1200 and 1300°C. The densification of the powder is performed by the hot pressing process. The shrinkage of the powder was previously followed by dilatometric measurements. The physical properties of the final material are studied as a function of pressing parameters.     

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.     

Structure and thermal stability of MOCVD ZrO2 films on Si (1 0 0)

The structure and thermal stability of ZrO₂ films grown on Si (1 0 0) substrates by metalorganic chemical vapor deposition have been studied by high-resolution transmission electron microscopy, selected area electron diffraction and X-ray energy dispersive spectroscopy. As-deposited films consist of tetragonal ZrO₂ nanocrystallites and an amorphous Zr silicate interfacial layer. After annealing at 850°C, some monoclinic phase is formed, and the grain size is increased. Annealing a 6 nm thick film at 850°C in O₂ revealed that the growth of the interfacial layer is at the expense of the ZrO₂ layer. In a 3.0 nm thick Zr silicate interfacial layer, there is a 0.9 nm Zr-free SiO₂ region right above the Si substrate. These observations suggest that oxygen reacted with the Si substrate to grow SiO₂, and SiO₂ reacted with ZrO₂ to form a Zr silicate interfacial layer during the deposition and annealing. Oxygen diffusion through the tetragonal ZrO₂ phase was found to be relatively easier than through the monoclinic phase.     

Migration of Cu ions in Cu2O---Al2O3---SiO2 glasses on heating in air

The behavior of copper ions in the Cu₂O·Al₂O₃·4SiO₂ (in moles) glass on heating in air at temperatures up to 500°C was studied. When the glass, in which about 90% of Cu was present as Cu⁺ ions, was heated in air above 300°C, a CuO layer was formed on the surface. The amount of CuO was increased with heating temperature and time, corresponding to the decrease in weight of the glass. Furthermore, the fraction of Cu²⁺ ions in the glass increased. These observations suggest that oxygens do not diffuse into the glass, but Cu⁺ ions migrate to the surface from the interior to balance the surplus positive charge produced by the oxidation of Cu⁺ to Cu²⁺ ions inside the glass. The following reaction scheme for the formation of the CuO layer was proposed; 2Cu⁺(interior) + ₂¹O₂(surface) → Cu²⁺(interior) + CuO(surface).     

Effect of CaO on the surface morphology and strength of water soaked Na2O–B2O3–Al2O3–SiO2 vitrified bond

The surface morphology of Na₂O–B₂O₃–Al₂O₃–SiO₂ vitrified bond with and without calcium oxide was studied by soaking vitrified bonded microcrystalline alumina composites in water. The content of water introduced to the vitrified bond was determined by thermal gravity analysis, and the effects of water and calcium on the phase separation and nucleation of the vitrified bond were investigated using scanning electron microscope and energy-dispersive X-ray spectrometer. Soaked in water for 72 h, the Na₂O–B₂O₃–Al₂O₃–SiO₂ vitrified bond presented a porous surface, and its bending strength declined with increasing sintering temperature. However, the Na₂O–CaO–B₂O₃–Al₂O₃–SiO₂ vitrified bond was more durable against aqueous coolant even needle-shape crystals were found clustered on the surface of the vitrified bond. The crystals were enriched with aluminosilicate tested by energy-dispersive X-ray spectrums. The appearance of crystals lessened the dissolution of the vitrified bond and made the bending strength increase in the sintering temperature region between 870 °C and 930 °C.     

Surface modification of SiO2 glass by laser processing

Various oxide films on SiO₂ glass substrates were irradiated by a laser beam. A continuous CO₂ laser source (wavelength 10.6 μm) was used for this purpose; the composition change at the surface layer was determined by Rutherford backscattering spectrometry (RBS). All the alkaline-earth oxides as well as those of lanthanum and yttrium, entered the glass after treatment. ZrO₂ and CeO₂, however, did not enter the SiO₂ glass due to laser irradiation. It is interesting, however, that a film of ZrO₂ + Al₂O mixture easily entered into the SiO₂ glass by laser processing. The conditions and mechanism of laser-enhanced interaction of ZrO₂ or other oxide films with SiO₂ glass surfaces are discussed especially in view of their structural behaviour in glass.     

Mössbauer studies on some glasses and crystals in the Na2O---Fe2O3---SiO2 system

Mössbauer absorption measurements have been made at room temperature on ⁵⁷Fe in iron sodium silicate glasses containing 3–15 mol% Fe₂O₃ and various iron alkali silicate crystals in order to study the state of iron in these glasses. The spectra of all the glasses gave one doublet with a quadrupole splitting varying from 0.73–0.78 mm s⁻¹, while those of Na₂O · Fe₂O₃ · 4 SiO₂ and 5 Na₂O · Fe₂O₃ · 8 SiO₂ crystals showed much smaller quadrupole splitting, 0.28 mm s⁻¹ and 0.10 mm s⁻¹, respectively, and an asymmetrical doublet of much narrower linewidth. When sodium was replaced by other alkali metals of larger size, such as K and Cs, in MFeSi₂O₆ and MFeSi₃O₈ crystals, the quadrupole splitting became wider and approached to 0.73 mm s⁻¹. Such a variation was not observed for glasses. These results suggest that a larger number of non-identical sites exist in iron sodium silicate glasses than in the corresponding crystals.     

The effect of MgO on the thermodynamics of the Fe/Fe-redox equilibrium and the incorporation of iron in soda-magnesia-aluminosilicate melts

Melts with the basic compositions 10Na₂O · 10MgO · xAl₂O₃ · (80−x)SiO₂ (x=0, 5, 10, 15 and 20), 10Na₂O · xMgO · 10Al₂O₃ · (80−x)SiO₂ (x=5, 10, 15 and 20) and xNa₂O · 10MgO · 10Al₂O₃ · (80−x)SiO₂ (x=5, 10 and 15) all doped with 0.25 mol% Fe₂O₃ were studied using square-wave voltammetry. The temperatures applied were in the range of 1000–1600 °C. The square-wave voltammograms recorded show peaks caused by the reduction of Fe³⁺ to Fe²⁺. The attributed peak potentials measured decreased linearly with decreasing temperatures. Increasing the MgO-concentration led to more negative peak potentials. Introducing alumina in the melt first resulted in less negative peak potentials. If the molar Al₂O₃-concentration is equal to that of Na₂O (=10 mol%) the peak potentials are least negative. Further increase of the Al₂O₃-concentration led to more negative peak potentials. The variation of the Na₂O-concentration led to a maximum in the peak potentials at an Na₂O-concentration of 10 mol%. An empirical formula which allows the calculation of standard potentials from the chemical composition is proposed. Furthermore, a structural explanation for the effect of the chemical composition is given. Especially, the incorporation of Al₂O₃ as AlO₄⁻-tetrahedra at [Al₂O₃] < [Na₂O] and as network modifier at larger concentrations was structurally explained by the similarities of Fe²⁺ and Mg²⁺, with respect to cation radii and metal–oxygen bond lengths.     

Facile synthesis of submicron BaTiO3 crystallites by a liquid–solid reaction method

Uniform, submicron BaTiO₃ crystallites in tetragonal structure were synthesized by a novel low-temperature liquid–solid reaction method mainly via two simple steps: firstly, BaO₂·H₂O₂ submicron particles of about 130–450 nm were precipitated from the reaction of BaCl₂ and H₂O₂ in a slightly alkaline (pH 8) aqueous solution under the ambient condition; secondly, tetragonal phase BaTiO₃ submicrocrystals with the size in the range of 180 to 400 nm could be produced by subjecting the as-prepared BaO₂·H₂O₂ and commercial TiO₂ submicron particles to thermal treatment in air at 700 °C for 10 h. The as-obtained products were characterized by X-ray powder diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and inductively coupled plasma-atomic emission spectroscopy, and scanning electron microscopy.     

Hydrolytic resistance of Na2O---B2O3---SiO2 gels prepared by sol-gel process

Alkoxide derived gels were prepared in the system Na₂O---B₂O₃---SiO₂. The gel compositions were situated in the liquid-liquid immiscibility area of the phase equilibrium diagram.

Hydrolytic resistance tests were performed on the gels heat-treated at temperatures ranging between 120 to 850 °C. The Na₂O, B₂O₃ and SiO₂ extracted from the attack gels were analyzed. The experimental results indicate that the amount of B₂O₃ has a significant influence on the chemical durability of the heat-treated gels. At temperatures of 850 °C the greater the B₂O₃ mol% the greater are the amounts of Na₂O and B₂O₃ extracted. Different behaviour was observed for gels heat-treated at 600 °C where the amounts of B₂O₃ and Na₂O extracted slightly increases as the B₂O₃ mol% increases. Small amounts of extracted SiO₂ were always observed.

These results are complemented with other measurements so that an explanation of the controlling mechanism is given.     

Precipitation of In2O3 nano-crystallites from glasses in the system Na2O/B2O3/Al2O3/In2O3

Glasses in the system Na₂O/B₂O₃/Al₂O₃/In₂O₃ were melted and subsequently tempered in the range from 500 to 700 °C. Depending on the chemical composition, various crystalline phases were observed. From samples without Al₂O₃, In₂O₃ could not be crystallized from homogeneous glasses, because either spontaneous In₂O₃ crystallization occurred during cooling, or other phases such as NaInO₂ were formed during tempering. The addition of alumina, however, controlled the crystallization of In₂O₃. Depending on the crystallization temperature applied, the crystallite sizes were in the range from 13 to 53 nm. The glass matrix can be dissolved by soaking the powdered glass in water. This procedure can be used to prepare nano-crystalline In₂O₃-powders.     

Structural transformation of the TiO2---SiO2 system gel during heat-treatment

The gel formation of the (100-x)TiO₂·xSiO₂ (x = 0–10 mol%) system has been studied. The progressive elimination of residues was followed by DTA and TGA curves. DTA curves showed that the formation of anatase during heat treatment could be sensibly slowed down with the increase of SiO₂. The relationship between the gel composition and crystallization temperature of anatase has been systematically investigated. The X-ray diffraction spectra demonstrated that the crystallization temperature of anatase is 400°C for TiO₂ gel and 430°C for 90TiO₂ - 10SiO₂ gel. The infrared absorption spectra were used to follow the structural transformation of gels heat-treated at different temperatures. With the help of EPR it is evident that titanium ions exist only in tetravalence.     

TOPCon太阳电池发射极Al2O3/SiNx与SiO2/Al2O3/SiNx叠层膜钝化性能的比较

本文对TOPCon电池发射结的叠层钝化膜进行了研究,对比了3种不同叠层钝化膜(SiO₂/SiN_x、Al₂O₃(1.5 nm)/SiN_x、SiO₂/Al₂O₃(1.5 nm)/SiN_x)的钝化性能。结果表明:Al₂O₃(1.5 nm)/SiN_x的钝化性能优于SiO₂/SiN_x,SiO₂/Al₂O₃(1.5 nm)/SiN_x的钝化水平最佳,隐开路电压均值可达到705 mV。基于Al₂O₃/SiN_x叠层膜研究了Al₂O₃厚度(1.5 nm、3 nm和5 nm)对钝化性能和电池转换效率的影响。当Al₂O₃厚度由1.5 nm增加到3 nm时,钝化性能得到明显提升,隐开路电压均值提高了20 mV,达到707 mV,对应电池的光电转换效率升高了0.23个百分点,与SiO₂/Al₂O₃(1.5 nm)/SiN_x叠层膜电池的转换效率持平。然而,当Al₂O₃厚度继续增加至5 nm时,隐开路电压均值保持不变。因此可以使用Al₂O₃(3 nm)/SiN_x叠层膜代替SiO₂/Al₂O₃(1.5 nm)/SiN_x叠层膜,不仅简化了电池的工艺步骤,而且降低了生产成本。     

Surface modification of a TiO2 film electrode prepared by the sol-gel method and its effect on photoelectrochemical behavior

The surface of a TiO₂ film electrode, about 1 μm thick, prepared by the sol-gel method, was modified by being additionally coated with about 0.1 μm thick TiO₂---SiO₂, TiO₂---ZrO₂ or TiO₂---Al₂O₃ films. The effect of the additional coating on the photoelectrochemical properties of a TiO₂ film electrode was investigated in detail. On addition of the second additive to TiO₂, the flat band potential was shifted toward negative potential for SiO₂ and positive potential for ZrO₂ and Al₂O₃, which is attributed to the change in the point of zero zeta potential (pzzp), not in the electron affinity (EA). However, enhancement in photocurrent was not observed for all the cases.     

XAS study of lanthanum coordination environments in glasses of the system K2O---SiO2---La2O3

The La L₁ and L₃ XANES and L₃ EXAFS have been investigated for the series of glasses 10K₂O---50SiO₂---x La₂O₃ (x = 1, 5, 10) and (10 − x)K₂O---40SiO₂−(x/3)La₂O₃ (x = 7.5, 5, 2.5) and model compounds La₂O₃, LaAlO₃, LaPO₄, La₂NiO₄, La₂CuO₄ and La(OH)₃. An edge resonance at 25 eV above the L₁ edge in the glass spectra is concentration-dependent, decreasing in intensity with increasing lanthanum concentration. The 2s → nd forbidden transition increases with La₂O₃ concentration, indicating a reduction in the ‘average’ site symmetry of the first coordination shell of La. Mapping _X(k) space, which is a new and promising technique, was employed to extract bond distance, coordination number and thermal parameters from the EXAFS. By this method, one calculates the complete _X(k) space a function of all physically reasonable values of the adjusted parameters in all possible combinations. The advantage in this method is the assurance of a global minimum. Bond lengths were comparable to those obtained by Fourier transforming the phase corrected EXAFS. The values are 2.42 Å (± 0.03 Å) for La---O. The coordination numbers (N ≤ 7 ± 1.5) were derived by mapping and comparison to the published structures for other La compounds. _X(k) mapping is compared with least-squares fitting the data, and the correlation between the Debye-Waller factor and coordination number is also discussed.     

Glass formation and crystallization in the ZrO2---Al2O3---P2O5 system

The glass formation of the ZrO₂---Al₂O₃---P₂O₅ system in the high phosphate region is determined. The crystallization process and the crystal types formed during heat treatment have been studied. The structure of these glasses is discussed.     

Hydrothermal growth of single-crystal CaV6O16·3H2O nanoribbons

CaV₆O₁₆·3H₂O nanoribbons have been prepared by the hydrothermal method in the presence of sodium dodecyl sulfate (SDS) at 160°C for 10 h. X-ray diffraction pattern indicates that the sample is monoclinic phase of CaV₆O₁₆·3H₂O with the lattice contents a=12.18 Å, b=3.598 Å, c=18.39 Å, β=118.03°. Field emission scanning electron microscopy shows that the nanoribbons have widths in the range of 150–500 nm, thicknesses of 30–60 nm and lengths of 500 mm X-ray photoelectron spectrum measurements further confirm the formation of the CaV₆O₁₆·3H₂O phase. The formation of CaV₆O₁₆·3H₂O nanoribbons is a self-assembling process, in which surfactant SDS plays the role of soft template.