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1.
Bondability and interfacial reaction between dielectric and insulator layers have been examined to obtain a basic understanding of bonding mechanisms. Lead-containing complex perovskite was used as a dielectric material. Two kinds of glass-ceramics were used as insulator material; lead borosilicate glass containing Al 2O 3 (insulator A) and the same containing Al 2O 3 and M gO (insulator B). Dielectric and insulator layers did not bond when insulator A was used. When insulator B was used, however, strong bonding was achieved between the two layers by firing the powder compacts at temperatures between 800° and 1000°C. Addition of M gO to lead borosilicate glass increased the thermal expansion coefficient to that of the dielectric and enhanced the formation of reaction layers, resulting in good bonding. Two reaction layers were identified. The main reaction products were enstatite and bredigite for one layer contacting the dielectric, and enstatite and a compound with the same diffraction pattern as that of faujasite for the other layers contacting insulator B. 相似文献
2.
A glass of composition: SiO 2 = 59·84%; Al 2O 3 = 11·45%; MgO = 15·34%; TiO 2 = 4·23%; K 2O = 3·80%; Na 2O = 2·48%; CaO = 1·08%; Fe 2O 3 = 1·78%; was prepared from porphyric sands by addition of MgO and TiO 2. The quenched glass is demixed on a very fine scale. The non-isothermal devitrification has been studied. Three-dimensional crystal growth has been observed. The experimental data suggest a mechanism controlled by the crystal-glass interface reaction. The crystal growth activation energy E c = 467 ± 20 kJ/mole has been evaluated. The temperature of most efficient nucleation is approximately T N = 720°C. 相似文献
3.
A novel catalyst based on copper-silver was developed to solve the contradiction between the high conversion temperature of Cu-based catalyst and low N 2 selectivity of Ag-based catalyst during selective oxidation of ammonium gas. The Cu-Ag-based catalyst (Cu 5 wt.%-Ag 5 wt.%/Al 2O 3) displayed a relatively low complete conversion temperature (<320 °C) with a high N 2 selectivity (>95%). Increasing loading of Cu and Ag decreases N 2 selectivity. The low N 2 selectivity of Ag-based catalyst is possibly related to the formation of Ag 2O crystals. Improvement of N 2 selectivity of Ag-based catalyst was obtained by doping Cu to decrease crystallized Ag 2O phase. The temperature programmed reaction (TPR) data show that N 2O is the main byproduct of oxidation of ammonia at temperature lower than 200 °C. Two bands of nitrate species at 1541 and 1302 cm −1 were observed on Ag 10 wt.%/Al 2O 3 at the temperature higher than 250 °C, which indicates the formation of NO x during the selective catalytic oxidation of ammonia. No nitrate species was observed on Cu 10 wt.%/Al 2O 3 and Cu 5 wt.%-Ag 5 wt.%/Al 2O 3, while only one nitrate species (1543 cm −1) existed on Cu 10 wt.%-Ag 10 wt.%/Al 2O 3. We proposed that mixing Ag with Cu inhibited the formation of NO x during the selective catalytic oxidation of ammonia over Cu-Ag/Al 2O 3. 相似文献
4.
The formation of ettringite (3CaO · Al 2O 3 · 3CaSO 4 · 32H 2O) and monosulfate (3CaO · Al 2O 3 · CaSO 4 · 12H 2O) from tricalcium aluminate (3CaO · Al 2O 3) and gypsum (CaSO 4 · 2H 2O) in sodium hydroxide (NaOH) solutions was investigated by isothermal calorimetry and X-ray diffraction analyses. Tricalcium aluminate/gypsum mixtures with a molar aluminate-to-sulfate ratio of 1:3 were hydrated at constant temperatures from 40 to 80°C in deionized water and 200 and 500 mM of NaOH solutions. Ettringite was the only crystalline phase ultimately formed between 40 and 80°C, regardless of whether hydration was carried out in deionized water or sodium hydroxide solutions. The rates of ettringite formation were retarded in sodium hydroxide solutions at all temperatures when compared to hydration in deionized water. The apparent activation energy for the conversion of the tricalcium aluminate/gypsum mixture to ettringite was observed to depend on the concentration of sodium hydroxide. 相似文献
5.
玻璃由于优异的电学性能在电子封接领域的应用越来越广泛。本文以硼铝硅酸盐玻璃为基础玻璃体系,采用高温熔融法制备了低介电封接玻璃。通过拉曼光谱、热膨胀系数测定仪、密度计、弯曲梁低温测试仪、精密阻抗分析仪等对样品性能进行表征,研究了碱金属氧化物对低介电玻璃的结构与性能的影响。研究结果表明:碱金属氧化物R 2O总量保持不变,随着Li 2O取代量的增加,玻璃结构中[BO 3]含量先降低后增加,同时[AlO 4]增加、[AlO 6]降低;玻璃的热膨胀系数先降低后升高,密度变化趋势与之相反,且均在LN-3(Na 2O与Li 2O质量比为1.0:1.0)组出现极值;特征温度先升高后降低,最后Na 2O被完全取代后呈现再次升高的趋势;玻璃介电常数和介电损耗先降低后升高,且混合碱金属玻璃的介电常数和介电损耗均低于单一碱金属玻璃。 相似文献
6.
The effect of deposition and order of potassium introduction on the texture and activity of Mo/γ-Al 2O 3 catalysts in water gas shift (WGS) reaction was investigated. The samples were synthesised by incipient wetness impregnation of the carrier with aqueous solutions of the corresponding salts followed by drying and calcination after each deposition step. The prepared catalyst precursors were sulphided at 400°C for 2 h with 6% H 2S in H 2 before testing in WGS reaction in a glass flow apparatus at 400°C under atmospheric pressure. The results show that potassium deposition alone on the bare γ-Al2O3 (sample K/Al2O3) decreases the specific surface after calcination by blocking the constrictions between the pores in the primary porous texture. In the WGS reaction conditions part of the pores are deblocked and a redistribution in the pore volumes occurs. The deposition of the Mo (sample Mo/Al2O3) also results in a decrease in both specific surface and total pore volume with respect to the bare support. However after catalytic activity test no substantial changes in its texture were observed. The addition of K to the Mo (sample KMo/Al2O3) leads to nonuniformity in distribution of molybdenum–oxygen entities due to partial migration of the MoOx species to the external surface. The specific surface is not changed during the reaction test. The deposition of Mo on K/Al2O3 contributes to the uniform distribution of oxomolybdenum species in the porous texture of the support. This uniformity is preserved to a high extent in the catalytic reaction as well. The activity in the synthesised samples in the WGS reaction decreases in the order MoK/Al2O3 > Mo/Al2O3 > KMo/Al2O3. 相似文献
7.
Well crystallised aluminium borate Al 18B 4O 33 has been synthesised from alumina and boric acid with a BET area of 18 m 2/g after calcination at 1100 °C. Afterwards, 2 wt.% Pd/Al 18B 4O 33 was prepared by conventional impregnation of Pd(NO 3) 2 aqueous solution and calcination in air at 500 °C. The catalytic activity of Pd/Al 18B 4O 33 in the complete oxidation of methane was measured between 300 and 900 °C and compared with that of Pd/Al 2O 3. Pd/Al 18B 4O 33 exhibited a much lower activity than Pd/Al 2O 3 when treated in hydrogen at 500 °C or aged in O 2/H 2O (90:10) at 800 °C prior to catalytic testing. Surprisingly, a catalytic reaction run up to 900 °C in the reaction mixture induced a steep increase of the catalytic activity of Pd/Al 18B 4O 33 which became as active as Pd/Al 2O 3. Moreover, the decrease of the catalytic activity observed around 750 °C for Pd/Al 2O 3 and attributed to PdO decomposition into metallic Pd was significantly shifted to higher temperatures (820 °C) in the case of Pd/Al 18B 4O 33. The existence of two distinct types of PdO species formed on Al 18B 4O 33 and being, respectively, responsible for the improvement of the activity at low and high temperature was proposed on the basis of diffuse reflectance spectroscopy and temperature-programmed desorption of O 2. 相似文献
8.
The chemical composition of cristobalite, tridymite, glass, and accessory phases of different zones of used silica bricks taken from the roof of a glass tank was studied with a high resolution microprobe. Tridymite and cristobalite contain as impurities TiO 2 (≤ 0.36 wt%), Al 2O 3 (≤ 0.37 wt%), and Na 2O (≤ 0.27 wt%). Main constituents of the glass phase coexisting with crystalline silica are: SiO 2 (74 to 60 wt%), TiO 2 (0.4 to 9 wt%), Al 2O 3 (1 to 5 wt%), Fe 2O 3 (0.3 to 3 wt%), CaO (5 to 20 wt%), and Na 2O (8 to 17 wt%). Temperature curves within the bricks during operation of the glass tank have been estimated using direct temperature measurement at the hot front of the bricks, and the transition temperatures of cristobalite to tridymite ( 1450°C), and of - to β-wollastonite ( 1200°C). Microchemical data and supposed temperatures were correlated with the Nernst distribution law. The applicability of the Nernst law shows that local equilibrium conditions were reached during the use of the bricks; they have been preserved during cooling of bricks. The results of the Nernst law cation distribution imply that structural saturation with Al 2O 3, TiO 2, and Na 2O was not reached in the investigated composition range. Al 3+ is believed to substitute Si 4+ at tetrahedral lattice sites. Al 3+ substitution is favoured with decreasing temperature in relation to the Al 2O 3 content in the glass phase. Al 3+ → Si 4+ substitution produces charge deficiency, which is compensated by interstitial entry of Na + into structural channels and voids of tridymite and cristobalite. Ti 4+ incorporation into the cristobalite and tridymite structures is favoured at higher temperatures with respect to the TiO 2 content of the glass phase. The close reciprocal dependence between Al 3+ and Ti 4+ in silica may indicate that Ti 4+ is tetrahedrally incorporated as well. 相似文献
9.
Five Si 3N 4---Al 2O 3 ceramic grades were prepared by hot pressing at 1650°C. Backscattered electron micrographs revealed four different phases. Quantitative electron probe microanalysis allowed the identification of these phases as X-sialon, -Al 2O 3, O'-sialon and β-sialon. The maximum solubility of Al 2O 3 in Si 3N 4 and in Si 2N 2O at 1650°C was determined as well as the chemical composition of X-sialon. Based on these results, a slightly revised phase diagram is proposed. The general features describing the microstructure of the various phases have been investigated by transmission electron microscopy. The influence of the various phases on the mechanical properties was investigated; hardness, fracture toughness and elastic modulus were measured. The oxidation behaviour has been studied in air at 1300°C and 1450°C. The metastable phase diagram of Al 2O 3---SiO 2 in the absence of mullite can be used to predict the oxidation products and relative amounts formed in the oxide layers. 相似文献
10.
In situ growth of needlelike LaAl 11O 18 grains reinforcing Al 2O 3 composites can be fabricated by a coprecipitation method using La(NO 3) 3√6H 2O and Al(NO 3) 3√9H 2O as starting materials. The new two-step process involved firstly preparing needlelike LaAl 11O 18 grains distributed homogeneously in Al 2O 3 powder and then pressureless sintering the composite powders. The Al 2O 3/25 vol.%LaAl 11O 18 samples pressureless sintered at 1550°C for 4 h achieve relative density up to 96.5% and exhibit a bending strength of 420±30 MPa and a fracture toughness of 4.3±0.4 MPa m 1/2. 相似文献
11.
An approach to select appropriate network modifiers to tailor the thermal and dielectric properties of zinc borosilicate (ZBS) glass has been explored to apply the glass composition to a dielectric layer of plasma display panels. Based on ionic field strength of the modifiers and the ionic polarizability of the corresponding crystalline form, Bi 2O 3 and Na 2O modifiers have been selected to modify the thermal and dielectric properties of the glass toward the required properties for the application (440< T g<460°C, 7.5 × 10 −6−6/K, and 10< K <15). Bi2O3 addition to ZBS could meet all the required properties simultaneously at a given addition range (8.5–14 mol%), while the addition of Na2O could not meet all the properties at a single composition range. 相似文献
12.
采用活化Mo-Mn法和活性金属钎焊(AMB)工艺对Al 2O 3陶瓷进行金属化处理,分别研究了两种金属化工艺的界面形貌、新相的形成及显微结构的演变,并测试了Al 2O 3/Cu的力学性能和气密性。研究表明:采用活化Mo-Mn法的封接界面处出现玻璃相的迁移,形成了立方相MnAl 2O 4,可以提高封接强度。AMB工艺中活性元素Ti与Al 2O 3反应依次形成厚度为0.64 μm的TiO和1.03 μm的Cu 3Ti 3O。各层间热膨胀系数(CTE)的差异给钎焊接头提供了良好的热弹性相容性且降低了残余应力。活化Mo-Mn法的封接强度((60.2±7.7) MPa)比AMB工艺((43.1±6.9) MPa)高,但在气密性方面两者并无明显差别(均在2.3×10 -11 Pa·m 3·s -1左右)。 相似文献
13.
分别以自制固体碱K 2O/Al 2O 3和Na 3PO 4/MgO为催化剂,1,2-丙二醇为反应溶剂,催化松香与蔗糖合成松香酸蔗糖酯。以酯化率为指标,考察了反应温度、催化剂的负载量、反应时间、松香与蔗糖质量比对松香酸蔗糖酯合成的影响。通过SEM和BET等手段对催化剂进行表征,并对松香酸蔗糖酯的乳化、发泡、表面张力等性能进行测试。结果表明:K 2O/Al 2O 3与Na 3PO 4/MgO比表面积分别为142.52和19.38m 2/g;在松香酸蔗糖酯的合成反应中,催化剂K 2O/Al 2O 3的活性高于Na 3PO 4/MgO。K 2O/Al 2O 3为催化剂时,最优合成工艺条件为反应时间2.5h,反应温度125℃,K 2O/Al 2O 3催化剂用量3%,催化剂中K 2O负载量30%,松香和蔗糖质量比1:2,该条件下酯化率达到98%。合成的松香酸蔗糖酯与市场广泛使用的脂肪酸蔗糖酯相比,具有更好的表面活性。 相似文献
14.
Alumina-supported catalysts containing different transition metals (Ni, Cu, Cr, Mn, Fe and Co) were prepared and tested for their activity in the selective oxidation of ammonia reaction at high temperatures (between 700 and 900 °C) using a synthetic gasification gas mixture. The catalysts were also characterised for their acidic properties by infrared studies of pyridine and ammonia adsorption and reaction/desorption. The Ni/Al 2O 3 and Cr/Al 2O 3 catalyst displayed the highest selective catalytic oxidation (SCO) activity in that temperature range with excellent N 2 selectivities. FT-IR studies of adsorbed pyridine and NH 3 indicate that Lewis acid sites dominate and that NH 3 adsorption on these sites is likely to be the first step in the SCO reaction. FT-IR studies on less active catalysts, particularly on Cu/Al 2O 3 allowed the detection of oxidation intermediates, amide (NH 2), and possibly hydrazine and imido and nitroxyl species. The amide and hydrazine intermediate gives credence to a proposed SCO mechanism involving a hydrazine intermediate, while the proposed imide, =N–H, and/or nitroxyl, HNO species could be intermediates in incomplete oxidation of NH 3 to N 2O. 相似文献
15.
Performance of NO x traps after high-temperature treatments in different redox environments was studied. Two types of treatments were considered: aging and pretreatment. Lean and rich agings were examined for a model NO x trap, Pt–Ba/Al 2O 3. These were done at 950 °C for 3 h, in air and in 1% H 2/N 2, respectively. Lean aging had a severe impact on NO x trap performance, including HC and CO oxidation, and NH 3 and N 2O formation. Rich aging had minimal impact on performance, compared to fresh/degreened performance. Deactivation from lean aging was essentially irreversible due to Pt sintering, but Pt remained dispersed with the rich aging. Pretreatments were examined for a commercially feasible fully formulated NO x trap and two model NO x traps, Pt–Ba/Al 2O 3 and Pt–Ba–Ce/Al 2O 3. Pretreatments were done at 600 °C for 10 min, and used feed gas that simulated diesel exhaust under several conditions. Lean pretreatment severely suppressed NO x, HC, CO, NH 3 and N 2O activities for the ceria-containing NO x traps, but had no impact on Pt–Ba/Al 2O 3. Subsequently, a relatively mild rich pretreatment reversed this deactivation, which appears to be due to a form of Pt–ceria interaction, an effect that is well known from early work on three-way catalysts. Practical applications of results of this work are discussed with respect to NO x traps for light-duty diesel vehicles. 相似文献
16.
Fine powders of submicron-sized crystallites of BaTiO 3 were prepared at 85–130°C by the hydrothermal method, starting from TiO 2.ξH 2O gel and Ba(OH) 2 solution. The products obtained below 110°C incorporated considerable amounts of H 2O and OH − in the lattice. As-prepared BaTiO 3 is cubic and converts to the tetragonal phase after heat treatment at 1200°C, accompanied by the loss of residual OH − ions. Hydrothermal reaction of SnO 2.ξH 2O gel with Ba(OH) 2 at 150–260°C gives rise to the hydrated phase, BaSn(OH) 6.3H 2O, due to the amphoteric nature of SnO 2.ξH 2O which stabilises Sn(OH) 62− anions in basic media. On heating in air or releasing the pressure in situ at 260°C, BaSn(OH) 6.3H 2O converts to BaSnO 3 through an intermediate, BaSnO(OH) 4. Solid solutions of Ba(Ti,Sn)O 3 are directly formed from (TiO 2 + SnO 2)..ξH 2O gel up to 35 mol% SnO 2. At higher Sn contents, the hydrothermal products are mixtures of BaSn(OH) 6.3H 2O and BaTiO 3, which on annealing at 1000°C result in monophasic Ba(Ti,Sn)O 3. The sintering characteristics and the dielectric properties of the ceramics prepared out of these fine powders are presented. The dielectric properties of fine-grained Ba(Ti,Sn)O 3 ceramics are explained on the basis of the prevailing diffuse phase transition behaviour. 相似文献
17.
以分析纯试剂CaCO 3、Al 2O 3和Na 2CO 3为原料,在1350℃烧结1 h合成了Na 2O掺杂铝酸钙熟料,并采用XRD、SEM和EDS等方法研究了Na 2O掺杂CaO-Al 2O 3体系铝酸钙化合物的物相演变规律及熟料浸出性能。结果表明:当CaO和Al 2O 3的摩尔比为1.0时,CaO-Al 2O 3体系铝酸钙由CaO·Al 2O 3和12CaO·7Al 2O 3组成,而Na 2O掺杂铝酸钙熟料由CaO·Al 2O 3、12CaO·7Al 2O 3、Na 2O·Al 2O 3和Na 4Ca 3(AlO 2) 10组成。除形成含Na 2O化合物外,熟料中掺杂的Na 2O固溶于12CaO·7Al 2O 3中,而CaO·Al 2O 3中几乎不含Na 2O。随着熟料中Na 2O掺杂量的升高,12CaO·7Al 2O 3和Na 4Ca 3(AlO 2) 10的含量逐渐增加,CaO·Al 2O 3的含量逐渐降低;12CaO·7Al 2O 3和Na 4Ca 3(AlO 2) 10的结晶度逐渐降低,CaO·Al 2O 3的结晶度逐渐升高。Na 2O的掺杂提高了熟料在碳酸钠溶液中的浸出性能,并且使浸出渣中CaCO 3的空间群由R-3CH、P63/MMC两种转变为只含有R-3CH一种。 相似文献
18.
Oxidation activity and stability under reaction was investigated for a series of mixed oxide catalysts, doped or not by a precious metal (Pd, Pt). The reaction feedstock, containing CO, H 2, CH 4, CO 2 and H 2O, simulated gases issued from H 2 production processes for fuel cells. Contrarily to conventional noble metal catalysts, mixed oxide samples present generally good stability under reaction at high temperature. The activities measured for the perovskite and hexaaluminate catalysts, are however largely lower than that of the reference Pd/Al 2O 3 catalyst. High activities were obtained after impregnation of 1.1 wt.% Pd or 0.8 wt.% Pt on the hexaaluminates samples. Even if Pd/Al 2O 3 was found to present a high activity, this sample suffered from drastic deactivation at 700 °C. Better stability were obtained on perovskite. Furthermore, doping hexaaluminate by Pt led to samples with good activities and high stability. Even if better activities were obtained by doping the hexaaluminate samples by Pd, the Pd/BaAl 12O 19 strongly deactivated, as it was previously observed for the reference catalyst. Interestingly, this Pd deactivation was not observed when Pd was impregnated on the Mn substituted hexaaluminate, leading to a stable and active catalyst. This suggests that it is possible to stabilize the palladium in its oxidized form at high temperature (700 °C) on the surface of some supports. 相似文献
19.
The reaction sintering of Si 2N 2O from an equimolar mixture of Si 3N 4 and SiO 2 with 5 wt% Al 2O 3 addition was investigated in 98 or 980 kPa N 2 at 1600–1850°C. At the initial stage, Si 3N 4 densification occurred through a liquid phase of SiO 2---Al 2O 3 system. Further densification was observed together with the formation and exaggerated grain growth of Si 2N 2O. High N 2 pressure was useful for the prevention of thermal decomposition of Si 2N 2O and bloating of the compact. Among various packing powders, which have various SiO partial pressures, an equimolar mixture of Si 3N 2O and SiO 2 was the most effective for the densification. The effect of N 2 and packing powder on reaction sintering of Si 2N 2O was discussed in relation to observed kinetics and thermodynamic calculations. Bending strength of sintered materials was 310–320 MPa. 相似文献
20.
A multi-component NO x-trap catalyst consisting of Pt and K supported on γ-Al 2O 3 was studied at 250 °C to determine the roles of the individual catalyst components, to identify the adsorbing species during the lean capture cycle, and to assess the effects of H 2O and CO 2 on NO x storage. The Al 2O 3 support was shown to have NO x trapping capability with and without Pt present (at 250 °C Pt/Al 2O 3 adsorbs 2.3 μmols NO x/m 2). NO x is primarily trapped on Al 2O 3 in the form of nitrates with monodentate, chelating and bridged forms apparent in Diffuse Reflectance mid-Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. The addition of K to the catalyst increases the adsorption capacity to 6.2 μmols NO x/m 2, and the primary storage form on K is a free nitrate ion. Quantitative DRIFTS analysis shows that 12% of the nitrates on a Pt/K/Al 2O 3 catalyst are coordinated on the Al 2O 3 support at saturation. When 5% CO2 was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by 45% after 1 h on stream due to the competition of adsorbed free nitrates with carboxylates for adsorption sites. When 5% H2O was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by only 16% after 1 h, but the Al2O3-based nitrates decreased by 92%. Interestingly, with both 5% CO2 and 5% H2O in the feed, the total storage only decreased by 11%, as the hydroxyl groups generated on Al2O3 destabilized the K–CO2 bond; specifically, H2O mitigates the NOx storage capacity losses associated with carboxylate competition. 相似文献
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