Fabrication of hollow glass microspheres in the Na2O-B2O3-SiO2 system from metal alkoxides

Hollow glass microspheres (HGS) for laser fusion targets were fabricated in the system Na₂O-B₂O₃-SiO₂ from NaOCH₃, B(OCH₃)₃ and Si(OC₂H₅)₄. Gel powders prepared from metal alkoxides and urea liberate H₂O, CO₂ and NH₃ gases, evolution of which takes place completely at about 500° C. The precursor of HGS is formed by the encapsulation of these gas components in the glass layer formed at the surface of the powder. HGS are produced from the gel powders having both a melting temperature lower than about 1000° C and a viscosity at that temperature lower than 10⁵ P. In the Na₂O-B₂O₃-SiO₂ system, the compositions from which HGS are produced are those containing 55–75 wt% SiO₂ and 0–20 wt% B₂O₃. HGS ranging from 100–500m diameter and 0.5–7.0m wall thickness are obtained by change of urea content.     

Structural and microstructural transitions during phase separation and crystallization of Al2O3-SiO2-P2O5-Y2O3 glass

A highly refractory glass in the system Al₂O₃-SiO₂-P₂O₅-Y₂O₃ has been designed and produced such that, upon heating, an essentially fully crystalline glass—ceramic evolves containing mullite (nominally 3Al₂O₃·2SiO₂) and xenotime (YPO₄) as the final principal phases. Phase separation in this glass occurred during cooling from the melt and continued during annealing. XPS of the Al 2p, P 2p and the Y 3d electrons revealed that the average chemical environment of each of these elements is measurably different in the annealed glass and in the completely crystallized material. This indicates that the compositions of the separated glass phases are very different from those of the crystal phases which form from them. Additional rearrangement of the glass structure was observed at 1173 K. Extensive formation of mullite was initially detected at 1223 K and was followed by the crystallization of xenotime and the transient compounds of Y₄Al₂O₉, Y₂Si₂O₇, AlPO₄ and YP₅O₁₄. The optimum crystal nucleation and crystallization temperatures of 1173 and 1473 K, respectively, were determined from DTA, XRD, SEM and TEM studies.     

Characterization and study of Na2O-B2O3-SiO2 glasses prepared by the sol-gel method

The sol-gel procedure has been used to prepare vitreous materials whose compositions are situated in the liquid-liquid immiscibility area of the Na₂O-B₂O₃ SiO₂ phase equilibrium diagram. Gels were prepared from different precursors and under different experimental conditions. After determining optimum conditions for gelling and heat-treatment, the gels were characterized with the aid of thermal analysis, X-ray diffraction, density and specific surface area measurements, as well as infrared and near-infrared spectroscopy. The textures of the samples and their microstructures were studied by means of scanning electron microscopy and transmission electron microscopy, respectively. The phase separation in the gels was compared to the same phenomenon in one of the glasses of identical composition, but prepared by conventional melting.     

Na2O-B2O3-SiO2玻璃焊料连接碳化硅陶瓷接口抗热震性能

采用水淬法对以Na₂O-B₂O₃-SiO₂体系玻璃焊料连接的常压烧结碳化硅试条的抗热震性能进行了研究. 对不同温度下淬火后接口以及断面处微观结构进行了比较与分析, 并对比了不同淬火温度以及固定淬火温度为150℃时多次热循环后连接试条的残余弯曲强度. 结果表明, 对于单次淬火, 当淬火温度为150℃时, 由于热应力引起中间层内部微裂纹扩展, 导致残余弯曲强度迅速降低到(152±28) MPa. 淬火温度在150℃~320℃时, 中间层内部裂纹保持在亚临界状态, 相应弯曲强度基本保持在140 MPa. 继续升高淬火温度至420℃时, 裂纹进一步扩展, 试条残余弯曲强度迅速降低至(32±8) MPa. 对于多次热循环, 当淬火温度固定在150℃时, 经多次热循环, 残余弯曲强度与热循环次数变化不明显, 基本保持在120 MPa左右, 这说明在150℃以下淬火, 连接试条具有较好的抗热循环冲击性能.     

A structural study of metastable tetragonal zirconia in an Al2O3-ZrO2-SiO2-Na2O glass ceramic system

The structural and microstructural properties (crystalline system at the beginning of crystallization, lattice disorder and crystallite size) of metastable zirconia have been studied by an X-ray line broadening analysis using simplified methods based on suitably assumed functions describing the diffraction profiles. Metastable tetragonal zirconia has been crystallized at 970, 1000 and 1050° C, respectively, starting from an Al₂O₃-ZrO₂-SiO₂Na₂O glassy system with a chemical composition very close to that of well known electromelted refractory materials. In the present work we have definitely shown the presence, inside the crystallized zirconia phase, of internal microstrains having values ranging approximately between 2 and 4×10^–3. Moreover, we have confirmed the peculiar smallness in size of precipitated zirconia crystallites ( 200 Å). Therefore, in the present system, the stabilization of the tetragonal form of ZrO₂ with respect to the stable monoclinic one can be explained in terms of a contribution to the amount of free energy due to strain energy, in addition to the previously hypothesized surface energy. The observed strong line broadening for some samples treated at lower temperatures (970 and 1000° C) gives rise to an apparent cubic lattice pattern; but the asymmetry of each apparent single line masks unequivocally a tetragonal doublet. This latter conclusion disagrees with some hypotheses on the existence of a cubic metastable form of ZrO₂ which could originate at the beginning of zirconia crystallization.     

Preparation and non-linear optical properties of CdS quantum dots in Na2O-B2O3-SiO2 glasses by the sol-gel technique

Non-linear optical properties of CdS quantum dots embedded in the sol-gel derived Na₂O-B₂O₃-SiO₂x³ glass matrix have been studied using nanosecond degenerate four-wave mixing (DFWM), pump-probe experiments, and time-resolved subpicosecond DFWM measurements. The concentration of CdS microcrystallites was varied from 1.4 to 10.2 wt% while the particle size was controlled to be in the range of 3–6 nm in diameter so that the confinement effects can be realized. The third-order susceptibility, ³, was determined to be of the order of 10^–7-10^–6 e.s.u. near the resonant wavelength between 450 and 470 nm by the nanosecond DFWM and pump-probe experiments, and of the order of 10^–11-10^–10 e.s.u. at the off-resonant wavelength, 580 nm, by a time-resolved DFWM measurement with 400 fs laser pulse. The decay time changed from 0.5 to 50 picoseconds as a function of the size, size distribution and number density of CdS microcrystallites in the glasses. Photodarkening reduced the optical non-linearity of the melt-quenched samples by a factor of 20, while it had no appreciable effect on that of the sol-gel derived samples.[/p]     

K_2O－B_2O_3－SiO_2玻璃成分对析晶性能的影响

本文利用ＤＴＡ、ＸＲＤ、ＴＥＭ、ＳＥＭ等技术研究了三种Ｋ２Ｏ－Ｂ２Ｏ３－ＳｉＯ２玻璃的析晶性能。结果表明，Ｋ２Ｏ－Ｂ２Ｏ３－ＳｉＯ２玻璃的析晶由分相引起，分相和析晶能力受成分影响较大。随Ｂ２Ｏ３和Ｋ２Ｏ含量增多及Ｋ２Ｏ／Ｂ２Ｏ３比值的降低，析晶加强。析晶中主晶相类别尚未查清，次晶相确定为α－方石英。     

Glass formation and phase transformations in plasma prepared Al2O3-SiO2 powders

The structure of Al₂O₃-SiO₂ sub-micron powders prepared by oxidation of mixed aluminium-silicon halides in an oxygen-argon high frequency plasma flame has been studied. The powders were completely amorphous up to at least 52 wt % Al₂O₃ and partially amorphous in the range 52 to 88 wt % Al₂O₃. The crystalline phase was mullite up to 75 wt % Al₂O₃ but at higher Al₂O₃ contents a metastable solid solution of SiO₂ in -Al₂O₃ was observed in addition to mullite. Amorphous particles crystallized to mullite on heating to 1000°C, independently of composition. Extension of glass formation towards the high Al₂O₃ end of the Al₂O₃-SiO₂ system as the cooling rate is increased and particle size decreased, may be explained by the effect of viscosity on the nucleation rate of mullite from liquid, for Al₂O₃ contents up to 60 wt %. The viscosity change is relatively small as the Al₂O₃ content is increased beyond 60% and it is suggested that the change in nucleus-liquid interfacial energy with composition is the predominant factor controlling nucleation rate in this range. At Al₂O₃ concentrations greater than approximately 80 wt %, -Al₂O₃ is the phase which nucleates from the melt. A double DTA peak was observed for powders containing more than 80 wt % Al₂O₃. The lower temperature peak is believed to arise from the formation of mullite from a metastable solution of SiO₂ in -Al₂O₃, and the higher temperature peak from crystallization of mullite from the amorphous phase. The presence of SiO₂ in solution in metastable Al₂O₃ increases the temperature of transformation to -Al₂O₃ to greater than 1500° C compared with 1230° C for pure Al₂O₃.     

复合Al_2O_3-SiO_2纳米颗粒的摩擦学性能研究

以硅烷偶联剂为改性剂对复合Al2O3-SiO2纳米颗粒进行原位改性,实现其在润滑油中均匀稳定的单分散。将改性后的复合Al2O3-SiO2纳米颗粒分别按质量分数为0、0.05%、0.1%、0.5%、1.0%的量加入到润滑油中制成试样,进行四球试验和止推圈试验。对摩擦实验中的摩擦系数、磨斑直径、磨损量、摩擦副表面形貌进行分析。结果表明:当复合Al2O3-SiO2纳米颗粒添加质量分数为0.5%时,摩擦系数和磨斑直径最小,止推圈的磨损量出现负磨损,摩擦表面的磨痕明显的变浅、变窄。说明摩擦过程中,复合Al2O3-SiO2纳米颗粒沉积在摩擦副表面,形成一层保护膜有效的保护了摩擦表面,抗磨减摩作用显著。     

The corrosion resistance of high ZrO2 fusion-cast Al2O3-ZrO2-SiO2 glass refractories in soda lime glass

The corrosion resistance to soda lime glass of fusion-cast high zirconia Al₂O₃-ZrO₂-SiO₂ compositions is evaluated. It is concluded that these materials offer no improvement in corrosion resistance over the typical commercially available 40 wt% zirconia refractory in this glass. Furthermore, it is concluded that an optimum mixture of alumina and zirconia exists which has better corrosion resistance to soda lime glass than either end member. Finally, it is suggested that this trend in corrosion resistance is due to the interdependent solubilities of alumina and zirconia in the glass.     

Phase formation kinetics in SrO-Al2O3-SiO2-B2O3 glass

Phase formation in Sr-celsian glass, containing 3 wt% B₂O₃ (SA2SB), was investigated by using non-isothermal and isothermal kinetic analyses. While stoichiometric celsian (SA2S) glass showed two-stage crystallization of glass, from glassy state to hexacelsian and from hexacelsian to monocelsian, SA2SB glass showed direct crystallization of glass to monocelsian, resulting in considerable decrease in the temperature of monocelsian formation. The activation energy for monocelsian formation in SA2SB glass was 390 kJ/mol, which is lower than those for hexacelsian and monocelsian formation respectively in SA2S glass. The Avrami exponent of SA2SB glass was 2.0, indicating two-dimensional crystal growth with interface-controlled mechanism at a zero nucleation rate.     

Al2O3-SiO2气凝胶的制备及性能研究

以正硅酸乙酯(TEOS)和仲丁醇铝(ASB)为硅源和铝源,采用溶胶-凝胶和超临界干燥工艺制备出了高比表面积的Al2O3-SiO2块状气凝胶,研究了不同溶胶配比及热处理温度对气凝胶结构的影响,利用红外光谱、氮气吸附、X射线衍射和扫描电子显微镜等手段对气凝胶的性能和鲒构进行了分析.结果表明,随Al/Si摩尔比增大,Al2O3-SiO2气凝胶凝胶时间逐渐缩短,比表面积(1000℃)先增后减,当Al/Si摩尔比为4∶1时,比表面积最高,为444.5m2/g;1200℃,Al/Si为8∶1时比表面积最高,为115m2/g,具有较好的高温热稳定性.红外分析表明Al2O3-SiO2气凝胶存在Al-O-Si键;在1000℃热处理后,Al2O3-SiO2气凝胶中Si含量减少到一定程度才会出现γ-Al2O3.通过SEM观察表明Al2O3-SiO2气凝胶粒子较Al2O3气凝胶小.     

EPR and optical absorption of Cr3+ in binary Na2O-B2O3 glasses

The optical absorption and EPR spectra of Cr³⁺ in binary sodium borate glasses have been studied as functions of chromium concentration and Na₂O/B₂O₃ ratio in the glass; the ligand field and EPR parameters have been calculated and were found to be independent of Cr₃₊ concentration in any particular glass. In low-alkali borate glasses (Na₂O = 11 or 14 mol %) a single symmetrical EPR line was observed with g _¦=g =1.984±0.001 corresponding to perfect octahedral symmetry of the Cr³⁺ ion in these glasses. With increasing Na₂O content of the glass, the EPR line becomes more asymmetric (characteristic two-peaked pattern); this has been explained as being due to axial elongation of the six co-ordinated Cr³⁺-complex in these glasses.     

氧化铝-氧化硅系纳米粉体的制备及稀土掺杂改性研究

采用液相化学包覆沉淀法制备了Al2O3-SiO2及稀土元素Ce／Pr掺杂的Al2O3-SiO2系复合氧化物纳米粉体，通过XRD、TEM和BET分析手段对粉体的相组成、结构和形态进行了研究，并对8～15μm的红外波段下的发射率进行了测试。实验发现，在800℃的煅烧温度下可以获得Al2O3-SiO2系缺位反尖晶石型结构，尺度约为100nm的椭球形且红外发射率较高的纳米粉体。掺杂稀土Ce、Pr对此纳米粉体的形貌与红外特性均有影响，掺杂2％mol稀土Pr的Al2O3-SiO2系统红外发射率达92％。     

溶胶—凝胶法制备Al2O3—SiO2陶瓷薄膜的研究

研究了溶胶－凝胶（Ｓｏｌ－Ｇｅｌ）法制备Ａｌ２Ｏ３－ＳｉＯ２体系多孔的陶瓷膜过程中的溶胶、凝胶反应，通过冷冻复型法观察到溶胶颗粒的微观形貌，认为组分之间的去极化作用是导致溶胶颗粒团聚的原因，利用ＦＴＩＲ地复合交的热处理过程反应情况进行观察，结果表明，组分各自的相变互不影响，也不发生反应，由此可制得保持各组分特性的Ａｌ２Ｏ３－ＳｉＯ２复合陶瓷薄复合薄膜的ＴＥＭ形貌表明，组分在溶胶状太的去极化作用地致