Addition Of Li2O Research Articles

Effects of Li<SUB>2</SUB>O on Densification, Microstructure and Thermal Property of Spark Plasma Sintered AlN Ceramics

A newly developed rapid densify technique, spark plasma sintering (SPS), is used to prepare full-densified aluminum nitride (AlN) ceramics which are poorly sinterable. Some sintering aids are also used to promote the AlN ceramics' densification and improve its thermal conductivity. In this work, effects of sintering aid Li2O on densifica- tion, microstructure and thermal property of SPS sintered AlN ceramics were investigated. Results suggest that the ini- tial sintering temperature of AlN samples reduce from 1550℃ to lower than 1200℃ with 1.0wt% Li2O and 1.5wt% Sm2O3 (or Y2O3) adding as sintering aids . With Li2O addition, AlN compacts can be fully densified at 1650℃. The microstructure of AlN compacts indicates that Li2O is beneficial to generate aluminate liquid phase with better wet- tability and promote the densification of AlN ceramics, but it is unable to obtain higher relative density of AlN com- pacts because the escapement of gas phase though out liquid phase is very difficult in a rapid sintering process. Meanwhile, Li2O addition affects the growth of AlN grains, and the better wettability of aluminate with AlN grain in- duces the homogeneous distribution of grain boundary phase. The deterioration of thermal conductivity of AlN ceram- ics is caused by the fact that the scattering of phonon is enhanced by small grain size and the secondary phase spreading adequately along the AlN grain boundaries. The thermal conductivity of AlN samples with 1.0wt% Li2O and 1.5wt%Sm2O3 as sintering aids is lower than that of sample only with Sm2O3 as sintering aids.

Influence of CaF2 and Li2O on the Viscous Behavior of Calcium Silicate Melts Containing 12 wt pct Na2O

Understanding the viscous behavior of silica-based molten fluxes is essential in maintaining the reliability of steel casting operations and in preventing breakouts. In particular, high concentrations of aluminum in recently developed transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) steels tend to promote reduction of silica in the mold fluxes that result in the formation of alumina, which in turn increases the viscosity. To counteract this effect, significant amounts of fluidizers such as CaF2 and Li2O are required to ensure that mold fluxes have acceptable lubrication and heat transfer characteristics. The viscous behavior of the slag system based on CaO-SiO2-12 wt pct Na2O with various concentrations of CaF2 and Li2O has been studied using the rotating spindle method to understand the effects on the viscosity with these additives. CaF2 additions up to 8 wt pct were effective in decreasing the viscosity by breaking the network structure of molten fluxes, but CaF2 concentrations above this level had a negligible effect on viscosity. Li2O additions up to 2 wt pct were also effective in decreasing the viscosity, but the effect was comparatively negligible above 2 wt pct. Using Fourier transform infrared (FTIR) analysis of as-quenched slag samples, it was concluded that the viscosity was controlled more effectively by changing the larger complex silicate structures of rings and chains than by changing the amounts of simpler dimers and monomers.

Effect of Li2O Addition on Crystallization Behavior of CaO–Al2O3–MgO Based Inclusions

The crystallization behavior of CaO–Al2O3–MgO oxide powder which is one of the major non-metallic inclusions in Al-killed steel was systematically examined in the present study. 33mass%CaO–62mass% Al2O3–5mass%MgO and 30mass%CaO–57mass% Al2O3–5mass%MgO–8mass%Li2O glass powders were heat-treated at 1073–1673 K for 8–512 s under air.CaO–Al2O3–MgO glass was found to be crystallized immediately after the heat treatments. Moreover, it was revealed that the addition of Li2O accelerated the crystallization of the glass powders, and controlled aggregation of crystal particles. Additionally, the indentation hardness of crystallized glasses after 512 s heat-treatments was investigated by using a nano-indenter. The addition of Li2O had the effect of lowering the hardness of samples, which indicates that Li2O would improve the deformation behavior of aluminate based inclusions.

Density and Surface Tension of CaO–SiO2–Al2O3–R2O (R=Li, Na, K) Melts

In the present work, we measured the density and the surface tension of CaO–SiO2–Al2O3–R2O (CaO/SiO2=0.67, Al2O3=20 mass%, R2O=10.8 mol%, R=Li, Na, K) quaternary melts at elevated temperature using the double-bob Archimedean method and the ring method, respectively. The density of the CaO–SiO2–Al2O3–R2O melts decreased with temperature due to the thermal expansion of the melts. In addition, the density of the CaO–SiO2–Al2O3 ternary melt decreased with the addition of the alkali oxides. We converted the density into the molar volume to have a consideration on the microstructure of the melts. The molar volumes of the CaO–SiO2–Al2O3–R2O melts are proportional to cube of the cationic radius for the alkali ions, which indicates the structural roles of the alkali oxides are mainly charge compensator to AlO45– anions. The surface tension of the CaO–SiO2–Al2O3–R2O melts changed only slightly with temperature. The surface tension of the CaO–SiO2–Al2O3 ternary melt increased with the addition of Li2O. In contrast, the surface tension decreased with the addition of Na2O or K2O. As for quaternary system, the surface tension increased with the ionic potential of the additive alkali ions; it is the same tendency with the binary alkali silicate melts. However, the mechanism of the surface tension change with the addition of the alkali oxides has not been clarified in the present study.

Effect of CaF2 and Li2O Additives on the Viscosity of CaO–SiO2–Na2O Slags

High aluminum containing steels react vigorously with silica-based mold fluxes to form alumina. The change in alumina content increases the viscosity and thus silica-based mold fluxes are compensated with significant amounts of Na2O, CaF2, and Li2O to ensure both lubrication and heat transfer control. Detailed viscosity studies using the rotating spindle method showed that additions of CaF2 up to 8 wt% in the CaO–SiO2–12wt%Na2O system at a constant CaO/SiO2 ratio of 0.8 decreases the viscosity by breaking the network structure of molten fluxes, but is negligible above 8 wt%. A similar modification of the network was observed for Li2O up to 2 wt%. The viscosity data was correlated with the XPS analysis and verified CaF2 and Li2O as effective in modifying complex silicate structures into simpler silicate structures depending on the availability of complex silicates and thus was limited to below certain concentrations.

Low temperature sintering of .ALPHA.-cordierite ceramics with low thermal expansion using Li2O-Bi2O3 as a sintering additive

Low temperature sintering of α-cordierite ceramics with low coefficient of thermal expansion was attained using Li2O–Bi2O3 sintering additive. High purity α-cordierite could be synthesized at 1270°C using high purity and fine amorphous silica, α-alumina and magnesium oxide powder mixture via the solid state reaction route. The mixture was calcined at 1240°C, pulverized, compacted, and at first sintered without sintering additive. High density and outstanding characteristics cordierite ceramics was obtained. However, sintering temperature reached 1430°C, which was extremely high. By adding 3 mass % of the additive, the sintering temperature could be lowered from 1430 to 1050°C. Its relative density reached 97%, its flexural strength, however, decreased from 243 to 120 MPa. Its thermal expansion coefficient (from R.T. to 800°C) decreased slightly from 1.8 × 10−6/K to 1.6 × 10−6/K. Its dielectric constant increased slightly from 4.9 to 5.2 accompanied with considerable increase in loss tangent from 1.3 × 10−4 to 6.1 × 10−4 at 14 GHz, which were, however, low enough at this high frequency range. These results indicated that the addition of Li2O–Bi2O3 sintering additive had negligibly small effects on the properties of the sintered sample except mechanical properties and the loss tangent. These properties were found more excellent or at least comparable compared with the best properties previously reported and suitable for substrate materials on micro-electronic applications.

Low temperature sintering of barium titanate based ceramics with high dielectric constant for LTCC applications

The sintering temperature of BaTiO 3 powder was reduced to 900 °C due to the ZnO–B 2O 3–Li 2O–Nb 2O 5–Co 2O 3 addition. Excellent densification was achieved after sintering at 900 °C for 2 h. The low sintering temperature of newly developed capacitor materials allows a co-firing with pure silver electrodes. The dielectric constant and the temperature stability of the dielectric constant are strongly correlated with the composition of the ZnO–B 2O 3–Li 2O additives. A high dielectric constant up to 3000 and a dielectric loss less than 0.024 were measured on multilayer capacitors sintered at 900 °C with silver inner electrodes.

Direct conversion of ethanol into ethylene oxide on gold-based catalysts: Effect of CeO x and Li 2O addition on the selectivity

Results are presented concerning the behavior of alumina-supported gold catalysts and the effects of addition of Li 2O and CeO x on the oxidation, dehydrogenation and dehydration reactions of ethanol. Pure alumina mainly acts as an acidic catalyst and produces diethyl ether and ethylene. Gold particles play an important role in converting ethanol into ethylene oxide and acetaldehyde. Addition of Li 2O influences the selectivity by suppressing the formation of diethyl ether and ethylene. With the Au/Li 2O/Al 2O 3 catalysts, a high selectivity toward ethylene oxide can be obtained. The influence of the oxygen concentration on the gas flow is investigated. It is suggested that at low concentrations, the role of oxygen is mainly to prevent coke formation on the catalytic surface.

Effect of Additives on the Refractive Index of B2O3-SiO2-Al2O3 Glasses for Photolithographic Process in Electronic Micro Devices

In fabricating plasma display panels, the photolithographic process is used to form patterns of barrier ribs with high accuracy and high aspect ratio. It is important in the photolithographic process to control the refractive index of the photosensitive paste. The composition of this paste for photolithography is based on the B2O3-SiO2-Al2O3 glass system, including additives of alkali oxides and rare earth oxides. In this work, we investigated the density, structure and refractive index of glasses based on the B2O3-SiO2-Al2O3 system with the addition of Li2O, K2O, Na2O, CaO, SrO, and MgO. The refractive index of the glasses containing K2O, Na2O and CaO was similar to that of the [BO3] fraction while that of the SrO, MgO and Li2O containing glasses were not correlated with the coordination fraction. The coordination number of the boron atoms was measured by MAS NMR. The refractive index increased with a decrease of molar volume due to the increase in the number of non-bridging oxygen atoms and the polarizability. The lowest refractive index (1.485) in this study was that of the B2O3-SiO2-Al2O3-K2O glass system due to the larger ionic radius of K+. Based on our results, it has been determined that the refractive index of the B2O3-SiO2-Al2O3 system should be controlled by the addition of alkali oxides and alkali earth oxides for proper formation of the photosensitive paste.

Direct conversion of ethanol into ethylene oxide on copper and silver nanoparticles: Effect of addition of CeO x and Li 2O

The behavior of nanoparticles of copper and silver on an alumina support in the oxidation and dehydrogenation of ethanol is investigated. Pure alumina mainly acts as an acidic catalyst and produces diethyl ether and ethylene. Addition of copper and silver nanoparticles results in a direct conversion of ethanol into ethylene oxide. Addition of Li 2O influences the selectivity by suppressing the formation of diethyl ether and ethylene. Using Ag/Li 2O/Al 2O 3 and Cu/Li 2O/Al 2O 3 catalysts it is possible to obtain high selectivity towards ethylene oxide at a temperature of 200 ° C. It is suggested that at low concentrations the main role of oxygen is to prevent coke formation on the catalytic surface. Addition of CeO x results in higher selectivities towards CO.

Influence of Li2O Addition on Physical Properties of Glass-Ceramics Fabricated Using a Coal Bottom Ash

Influence of Li2O Addition on Physical Properties of Glass-Ceramics Fabricated Using a Coal Bottom Ash

Interface-mediated electrochemical effects in lithium/polymer-ceramic cells

The paper presents and discusses a method to achieve beneficial electrochemical effects mediated by interfaces in an ionic conducting polymer matrix. The beneficial effects include enhanced ionic transport, catalysis of anodic oxidation reaction, and stabilization of the lithium-electrolyte interface in lithium-based electrochemical cells. Polyethylene oxide (PEO) doped with LiN(SO 2CF 2CF 3) 2 (LiBETI) was chosen as the ion conducting polymer matrix. The polymer-ceramic (PC) composite electrolytes from the PEO:LiBETI-BN and PEO:LiBETI-Li 2O systems were optimized to achieve high conductivity, reduce charge-transfer resistance, and stabilize the solid electrolyte interface (SEI) layer at the lithium anode. Both BN and Li 2O were effective in enhancing interface-mediated lithium ion transport. The charge-transfer resistance was reduced by orders of magnitude and the long-term stability of the cells was improved remarkably due to the addition of BN and Li 2O in the PEO:LiBETI polymer matrix. AC impedance spectroscopy was used to investigate the phenomenon by measuring the time- and temperature-dependent electrical behavior of the aforementioned materials and cells. The interface-mediated effects due to the addition of BN and Li 2O dielectrics contributed to the improved cell properties.

Solubility of Pu and rare-earths in LiCl-Li2O melt

Abstract The solubility of Pu and rare-earths (REs) were measured in LiClLi2O melt where individually the oxides precipitated. The solubility of Pu(III) was measured at 923 K as a function of Li2O concentration. After every addition of Li2O to increase the Li2O concentration in the melt, the Pu concentration increased and showed a saturation in several hours. The stepwise variation means that the Pu concentrations at the saturation are regarded as the Pu solubility at the respective Li2O concentrations. The solubility of Nd(III), Gd(III), Pu(IV), and Ce(IV) were also measured as a fanction of Li2O concentration, and all of them increased with increased Li2O concentration. Especially, the solubility of the trivalent Pu and REs were related almost proportionally with the Li2O concentration. The solubility of La(III) and Pr(III) were measured in molten LiCl saturated with Li2O between 883 and 973 K. The logarithmic solubility was related linearly with the reciprocal temperature. The systematic measurement indicated that the solubility was higher for the element with a larger ionic radius as to the trivalent Pu and REs.

R&D of a Li2TiO3 pebble bed for a test blanket module in JAEA

At JAEA, a test blanket module (TBM) with a water-cooled solid breeder is being developed. This paper presents recent achievements of research activities for the TBM, particularly addressing the pebble bed of the tritium breeder materials and tritium behaviour. For the breeder material, the chemical stability of Li2TiO3 was improved using Li2O additives. To analyse the pebble bed behaviour, thermomechanical properties of the Li2TiO3 pebble bed were assessed experimentally. To verify the pebble bed's nuclear properties, the activation foil method was proposed and a preliminary experiment was conducted. To reduce the tritium permeation, the chemical densified coating method was developed and the coating was attached to F82H steel. For tritium behaviour, the tritium recovery system was modified in consideration of the design change of the TBM.

Effect of Li 2O on structure and optical properties of lithium bismosilicate glasses

Bismuth–silicate glasses containing lithium oxide having composition xLi 2O·(85 − x)Bi 2O 3·15SiO 2 (5 ≤ x ≤ 45 mol%) were prepared by melt quench technique. Density, molar volume and glass transition temperature for all the glass samples were measured. IR spectroscopy was used for structural studies of these glasses in the range from 400 to 1400 cm −1. The increase of Li 2O content in glass matrix results in the decrease of the Si–O–Si bond angle and increase in the covalence nature of Bi–O bond. IR spectra suggest the presence of distorted [BiO 6] octahedral units and the degree of distortion increases with the addition of Li 2O in these glasses. The optical transmission spectra in the wavelength range from 200 to 3300 nm were recorded and optical band gap ( E g) was calculated. The values of E g lie in between 2.81 and 2.98 eV. The values of average electronic oxide polarizability as well as optical basicity in these glasses were found to be dependent directly on Bi 2O 3/Li 2O ratio.

EPR and Optical Studies of Mo5+ Ions in Lithium Molybdoborate Glasses

Electron paramagnetic resonance (EPR) and optical absorption studies of Li2O–MoO3–B2O3 with varying concentrations of Li2O, MoO3 and B2O3 have been carried out at room temperature. Two series of glasses, one with constant MoO3 (CM) and another with constant borate (CB), have been investigated. Characteristic EPR spectra of Mo5+ have been observed centered around g ≅ 2.00, which are attributed to Mo5+ ion in an octahedral coordination sphere with an axial distortion. The spectra also show strong dependence on the concentration of Li2O and B2O3. Spin concentrations (N) and magnetic susceptibilities (χ) have been calculated. In the CM series, the N values decrease with increasing Li2O content up to 30 mol%, while in the CB series variation of N is found to increase initially up to 20 mol%, and with further increase in the Li2O content the N values tend to decrease. The variation of magnetic susceptibilities is almost similar to that observed with the variation of N. From the optical absorption spectra, an absorption edge (α) has been evaluated. In the CM series, the values of α show a blueshift. On the other hand, in the CB series a redshift is observed. The observed variations in spectral parameters are explained by considering the molybdoborate network. Addition of Li2O to the CM and CB series results in modification of [MoO6/2]0 → [MoOO5/2]− and [BO3/2]0 → [BO4/2]− → [BOO2/2]− groups, respectively, leading to creation of nonbridging oxygens. The optical basicity of the glasses has been evaluated in both the CM and the CB glasses. The optical basicity can be used to classify the covalent-to-ionic ratios of the glass, since an increasing optical basicity indicates decreasing covalency. It is observed that the covalency between Mo5+ ions and oxygen ligands increases in the CB series, whereas in the CM series the covalency between Mo5+ ions and oxygen ligands decreases.

A comparative study of oxidation of methanol on [formula omitted]-Al 2O 3 supported group IB metal catalysts

Results are presented concerning the behavior of alumina supported Cu, Ag and Au (M) catalysts and the effect of addition of Li 2O and CeO x on the dehydrogenation and oxidation of methanol. The γ -Al 2O 3 used is able to dehydrogenate methanol to formaldehyde and the addition of a metal to the support increases the CO production. A two-step reaction mechanism is proposed: in the first step, CH 3OH is dehydrogenated on alumina to formaldehyde; in the second step, the formaldehyde reacts on M to CO or CO 2. Another mechanism is proposed for good oxidizing catalysts: methanol reacts directly on M and is oxidized to CO 2. The addition of the co-catalyst CeO x to the catalysts has a beneficial effect on the oxidation of methanol to CO 2 because of its ability to provide oxygen. We suggest that Li 2O blocks the adsorption site for methanol on alumina, and hence, decreasing the formation of formaldehyde.

A comparative study of the selective oxidation of NH 3 to N 2 over gold, silver and copper catalysts and the effect of addition of Li 2O and CeO x

This paper describes the selective oxidation of ammonia into nitrogen over copper, silver and gold catalysts between room temperature and 400 ° C using different NH 3/O 2 ratios. The effect of addition of CeO x and Li 2O on the activity and selectivity is also discussed. The results show that copper and silver are very active and selective toward N 2. However the multicomponent catalysts: M/Li 2O/CeO x /Al 2O 3 (M: Au, Ag, Cu) perform the best. On all three metal containing catalysts the activity and selectivity is influenced by the particle size and the interaction between metal particles and support.

Effect of alkali metal on the properties of Bi-based glass powders prepared by spray pyrolysis

Bismuth-based glass powders with different quantities of Li2O were directly prepared by high-temperature spray pyrolysis. The bismuth-based glass powders were completely spherical and submicron in size irrespective of the quantities of the Li2O additive. The high optical transmittances of the dielectric layers formed from the glass powders obtained by spray pyrolysis were due to the decrease in the glass-transition temperatures of the glass powders with the addition of Li2O. The ‘yellowing phenomenon’ was not observed in the dielectric layers formed from the glass powders obtained by spray pyrolysis, whereas it occurred in the dielectric layers formed from the glass powders obtained through the conventional melting process.

Improvement of response characteristics of TiO 2 humidity sensors by simultaneous addition of Li 2O and V 2O 5

Porous TiO 2 ceramics were prepared by adding various amounts of Li 2O and V 2O 5 and the humidity sensitivity of the resulting ceramics was investigated by means of electrical measurements, scanning electron microscopy and mercury intrusion porosimetry. Simultaneous addition of Li 2O and V 2O 5 to TiO 2 enabled sintering at temperatures as low as 700 °C and also decreased the impedance of the ceramics. Furthermore, in the ceramics including these additives simultaneously, excellent humidity sensitivity as well as good response characteristics were observed. The microstructures of these ceramics depended on the firing temperature and the amount and ratio of Li 2O/V 2O 5, and optimum humidity sensitivity was observed for the sample including both 0.25 mol% Li 2O and 0.75 mol% V 2O 5 fired at 700 °C. These results indicated that the humidity sensitivity and its response characteristics were closely related to the microstructure, and that improving the uniformity of microstructure is important for improving humidity sensitivity and its response characteristics.