Magnetic susceptibility of lithium borosilicate glasses containing metal oxide

Lithium borosilicate glasses with different chromium, manganese and cobalt contents were prepared and heat treated at 480, 580 and 680° C for 5 h. The magnetic susceptibilities of untreated and heat-treated samples were measured. The magnetic susceptibility was found to increase as the Cr₂O₃, MnO or CoO content increased. The values for magnetic susceptibility were co-related to the relative proportion of valence states of transition elements. The magnetic susceptibilities were found to have random behaviour with heat-treatment temperatures. Samples containing Cr₂O₃ showed transformations from diamagnetic to paramagnetic behaviour with the increase in Cr₂O₃ content, which may be due to the change of chromium ions from the high valence to the low valence state.     

Sol-gel synthesis, characterization and impedance studies of lithium borosilicate glass

Densified xerogels of lithium borosilicate (LBS) were synthesized through sol-gel process by varying modifier to formers (m/f) ratios. XRD and FTIR spectra were recorded for dried LBS gel samples heat-treated at different temperatures and the gel to glass to crystalline changes were studied. Also, all LBS samples were characterized by XRD, FTIR and DSC techniques. Impedance measurements were made on all LBS samples at different temperatures and the impedance data were analyzed using Boukamp equivalent circuit software. Conductivity of each m/f ratios of LBS samples were calculated from the analyzed impedance data and 20% Li₂O-80% [0.2 B₂O₃ + 0.8 SiO₂] composition showed the best conductivity σ = 8.83 (±0.02) × 10⁻⁸ Scm⁻¹ at 443 K. The activation energy (E_a) is obtained from the temperature dependent of conductivity data fitted to Arrhenius equation and it is found to be 0.64 eV (±0.02). The observed variation of conductivity with m/f ratios of LBS samples was explained using weak electrolyte model.     

Magnetic and electrical properties of lithium borosilicate glasses containing nickel and iron oxides

Measurements of a.c. conductivity, dielectric constants, Mo¨ssbauer spectra and magnetic susceptibility were carried out on samples of composition: 20LiO₂, 31B₂O₅, 34SiO₂, 15 – x NiO, xFe₂O₃ where x = 2.5, 5, 7.5, 10 and 12.5 mol %. It was found that when x is changed from 2.5 to 10 mol % NiO, the conductivity decreases due to the increase of the bridging oxygen ions. When x is increased to greater than 10 mol % NiO, the conductivity increases because of the decrease of the ratio of Fe²⁺Fe³⁺ ions as confirmed from Mo¨ssbauer data. The conductivity has a distinct minimum at 10 mol % NiO. Distribution of relaxation processes was also studied, and two processes were adequate to describe the present experimental data.     

Surface texture modification of spin-coated SiO2 xerogel thin films by TMCS silylation

The SiO₂ xerogel thin films were deposited successfully by sol?Cgel technique via the acid-catalyzed hydrolysis and condensation of tetraethylorthosilicate (TEOS) with ethanol as a solvent. Further, the deposited thin films were treated wet chemically by trimethylchlorosilane (TMCS) and hexane solution with 10% and 15% volume ratio to remove the hydroxyl groups from the surface of deposited SiO₂ thin films. These as deposited and surface-modified films were characterized by ellipsometer, Fourier transform infrared (FTIR) spectrometer and contact angle meter. The presence of 2900 and 850?cm^?1 peaks of CH₃ vibrations in FTIR spectra of surface-modified films confirms the hydrphobisation of SiO₂ surface. The maximum contact angle of 108·7° was observed for the surface-modified film at 10% TMCS.     

Sintering of titanate based dielectrics doped with lithium fluoride and calcium borosilicate glass

The effect of LiF and CBS glass additives on the microstructure and dielectric property of BaTiO₃ (BT) ceramics was studied. The phase of BaLiF₃ was observed from the interaction between BT and LiF when the samples were sintered at 900 °C for 1 h. Crystal grains with Ba and F in atomic ratios of 1:3 were observed from the SEM and TEM analysis of the microstructures. Abnormal grain growth (AGG) was observed to occur in the BT ceramics sintered at 950 °C. Further improvement to the composition was achieved by employing a two-stage process. This included CBS glass shell coating of the BT particles in the first stage, and the addition of LiF in the second stage. The composition thus formed had very good permittivity (1725) and an extremely low dielectric loss value (0.008).     

Thermal shock resistance of SiC fibrerein-forced borosilicate glass and lithium aluminosilicate matrix composites

Thermal shock resistance of an SiC fibre-(Nicalon®) reinforced borosilicate glass (Pyrex) and lithium aluminosilicate (LAS) matrix composite has been investigated experimentally in the temperature range 0–1000 K. Longitudinal Young's modulus and flexure strength of the composites after thermal shock were obtained as a function of thermal shock temperature. The results are discussed with the observed damage of the composite. The borosilicate glass matrix composite showed multiple cracking of the glass matrix perpendicular to the fibre axis when the thermal shock temperature was above 600 K. Decreases in Young's modulus and flexure strength were also recognized after multiple cracking of the matrix was initiated. On the other hand, the LAS matrix composite showed no damage at thermal shock temperatures below 800 K. However, at 800 K and above, microcracking of the matrix along the fibre axis was observed. After thermal shock, no decrease in the flexure strength was recognized, while the Young's modulus decreased due to microcracking of the matrix when the thermal shock temperatures were 800 K and above. It was found that the major advantage of the composite against thermal shock was to retain non-catastrophic failure properties even after the development of thermally induced damage in the composite.     

Preparation and characterization of mesoporous lithium borosilicate material via the sol–gel process

The lithium borosilicate gels were prepared from the cohydrolysis of the tetraehtylorthosilicate (Si(C₂H₅O)₄) and triethylborate (B(C₂H₅O)₃) by using an ethanolic solution of tetradecyltrimethylammonium bromide (TTAB) as surfactant. The Li⁺ ions were introduced from an acidic solution of lithium carbonate (Li₂CO₃). Depending on the B/Si, Li/Si and TTAB/Si molar ratios at pH equal to 1 and at room temperature, monolithic and transparent colourless gels were obtained. The structure of the gel was investigated by infrared spectroscopy (IR), ²⁹Si, ¹¹B and ⁷Li solid-state magnetic resonance (MAS NMR) and by thermal analysis (DTA–TG). The results show the possibility of obtaining a borosilicate network via B–O–Si bonds in which Li⁺ ions were dispersed. The adsorption–desorption isotherms of the xerogel were characteristic of mesoporous materials. These materials may provide a greater free volume through which conducting ions can move.     

Sn(Sb)O2凝胶结构模型及试验研究

对Sn(Sb)O2干凝胶的结构进行了试验及模拟研究，通过BET－N2吸附及XRD分析，详细研究了SnO2凝胶在200－600℃干燥过程中凝胶骨架纳米结构及其变化规律，并研究了掺杂元素Sb对纳米结构演变的影响。研究发现：SnO2干凝胶为1－10nm的纳米多孔结构，其结构特征符合圆柱体通孔模型；随着固化温度的升高，凝胶骨架粗化，但结构特征相似性不变，孔体积率也基本不变；Sb的增加有细化骨架的作用。     

Structure,composition and electrophysical properties of heat-treated single-crystal AB films

The results of electron diffraction investigations and a study of the electrophysical properties (specific resistance ?, mobility of charge carriers μ) of original and air annealed epitaxial A^IIB^VI (CdS, CdSe, ZnS and ZnSe) films are reported.     

Infrared spectra,X-ray investigations and electrical conductivity of lithium borosilicate glasses containing transition metal oxides

The conductivities of lithium borosilicate glasses containing 2.5 mol % V₂O₅, MnO, Cr₂O₃, Fe₂O₃ and CoO were measured for untreated and heat-treated glasses (for 5 h at 480, 580 and 680°C). Both IR and X-ray diffraction techniques were used to investigate the microstructure of these glasses before and after heat-treatment. Lithium metasilicate and lithium metaborate were the main separated phases in addition to lithium disilicate in samples containing Fe₂O₃. The silicon ions are coordinated to four oxygens in tetrahedral coordination and some borons changed from triangular to tetrahedral.     

Role of lithium borosilicate glass in the decomposition of MgTiO3-based dielectric ceramic during sintering

The decomposition behaviour of 0.9MgTiO₃–0.1CaTiO₃ dielectric ceramic during a liquid phase sintering by lithium borosilicate (LBS) glass was studied. The decompositions of MgTiO₃ into MgTi₂O₅ and Mg₂TiO₄ were apparent during the sintering although the reactions are thermodynamically unfavourable in glass-free compositions. The role of the LBS glass in favouring the decomposition reaction was investigated in terms of the thermodynamic activity of the reaction product in the glass. The decomposition reactions were not necessarily harmful because of the high dielectric performance of the decomposition products, MgTi₂O₅ (17.4 permittivity; 47,000 GHz quality factor) and Mg₂TiO₄ (14.4 and 55,000 GHz, respectively).     

Phase evolution and dielectric properties of MgTi2O5 ceramic sintered with lithium borosilicate glass

Phase evolution, densification, and dielectric properties of MgTi₂O₅ dielectric ceramic, sintered with lithium borosilicate (LBS) glass, were studied. Reaction between LBS glass and MgTi₂O₅ was significant in forming secondary phases such as TiO₂ and (Mg,Ti)₂(BO₃)O. The glass addition was not necessarily deleterious to the dielectric properties due to the formation of TiO₂: permittivity increased and temperature coefficient of resonance frequency could be tuned to zero with the addition of LBS glass, although the inevitable glass-induced decrease of quality factor was not retarded by the formation of TiO₂. The sintered specimen with 10 wt% LBS fired at 950 °C for 2 h showed permittivity of 19.3, quality factor of 6800 GHz, and τ_f of −16 ppm/°C.     

魔芋葡甘聚糖基干凝胶的制备与性能表征

以魔芋葡甘聚糖(KGM)和淀粉等几种植物多糖为原料,通过溶胶-凝胶及冷冻干燥法制备魔芋葡甘聚糖基干凝胶。通过质构仪、扫描电镜(SEM)、比表面积分析、水蒸气吸附平衡、差示扫描热量法(DSC)和热重分析(TGA)研究了此干凝胶的结构和性能。结果表明,制备的干凝胶表面光滑平整,没有皱缩、裂纹和塌陷。干凝胶内部呈三维空间网状结构。N2吸附表明干凝胶比表面积为51.84m2/g,平均孔径为50nm。此干凝胶样品在RH50%～80%的环境中吸湿量约6%～16%,仍能保持原有的形态不变。在169℃以内具有良好的热稳定性。     

Structure and electrical properties of sputtered lithium cobaltite thin films

Li_xCoO_y films with x<1 and y>2 have been prepared by radio-frequency (rf) sputtering from high temperature (HT) LiCoO₂ targets. Their structures have been examined with high resolution electron microscopy. Conductivities have been studied between 77 and 400 K. The electrochemical behaviour of film electrodes have been investigated with Li/LiClO₄-PC/Li_xCoO_y cells. The annealed films consist of nanocrystalline domains with amorphous boundaries. Electrical conductivities appear to arise from variable-range hopping (VRH) of holes. The films form good electrodes with operating potentials between 2.7 and 3.8 V. The observations have been discussed on the basis of a tentative and heuristic molecular orbital based energy band diagram.     

Characterization of brown ferric oxide hydrate xerogel

Ferric chloride solution was neutralized using sodium hydroxide as the precipitant to the extent that the final pH of the suspension was 7. After thorough washing the precipitated gel was dried in air at 60° C for 24 h to yield brown ferric oxide hydrate xerogel. The xerogel was examined at room temperature using infrared (IR) spectroscopy, powder X-ray diffraction (XRD), electron optical measurements, magnetometry and Mössbauer resonance spectroscopy. It has been concluded that the structural, morphological and magnetic characteristics of the xerogel are identifiable with those of the protoferrihydrite phase.