Kinetics of Liquid Spreading and Penetration with Application to RuO2−Glass Thick-Film Resistors

The rate of spreading of a spherical liquid droplet on a flat substrate is analyzed using the time-dependent contact angle approach. The constants in the contact angle development equation are explicitly related to physical parameters. Normalized rate of spreading is shown to be independent of the volume of the liquid droplet. A general capillary flow equation incorporating the time-dependent contact angle is used to analyze the kinetics of infiltration of the glass phase into the conductive phase in RuO₂/lead-horosilicate-glass thick-film resistors. The dependence of the kinetics on temperature, interparticle separation, and dissolved alumina content of the glass are discussed with reference to microstructure development in these resistors.     

Effect of O2 Concentration in Firing Atmosphere on Resistance of RuO2-Glass Thick-Film Resistors

The effect of oxygen concentration in the firing atmosphere on the resistance of RuO₂-glass thick-film resistors (TFRs) has been studied using glasses with various compositions. The resistance decreased with increasing oxygen concentration for TFRs made from PbO-containing glasses, but TFRs prepared from PbO-free glasses exhibited no oxygen concentration dependence of resistance. Experimental results suggest that the RuO₂-PbO interaction is responsible for the oxygen concentration dependence of the resistance.     

Sol-Gel Processing and Conduction Mechanism of RuO2-Glass Thick-Film Resistors

Sol-gel processing was used to study the conduction mechanism in RuO₂-glass thick-film resistors (TFRs). The relation between resistance and conductive particle concentration was studied on TFRs with uniformly dispersed RuO₂ particles in lead silicate glass. The resistance-concentration relation was best expressed by the percolation theory, whereas conventional TFRs showed a marked deviation. Conductivity measurements and Auger spectroscopy of glass films heated in contact with RuO₂ films revealed appreciable dissolution of RuO₂ in glass. Summarizing the experimental results, a percolation theory has been proposed as a possible conduction mechanism.     

Effect of Glass-Frit Size Distribution on the Microstructure of RuO2-Based Thick-Film Resistors

Ru0₂-based resistor inks were formulated with four glass-frit particle size distributions. Microstructural features, namely the RuO₂ ring size distribution, were shown to be related to the frit size distribution in the fired resistors.     

Microstructure Development in RuO2-Glass Thick-Film Resistors and Its Effect on the Electrical Resistivity

Microstructure development in RuO₂-glass thick-film resistors has been studied by optical microscopy with special emphasis on the effect of glass particle size and mixing and firing conditions. The microstructure development has been characterized by the coalescence of glass grains, infiltration of glass into RuO₂ particle aggregates, and agglomeration of RuO₂ particles. The resistivity-firing temperature relationship has been correlated with the microstructure development.     

Thermodynamic Properties of RuO2

The free energy change for the reaction RuO₂( s )+4Cu( s ) = 2Cu₂O( s )+Ru( s ) was determined from 600° to 1000°C from emf measurements on a solid oxide galvanic cell using a stabilized ZrO₂ electrolyte. The cell was designed to minimize the reduction of RuO₂ by the gas phase. The results were used to develop an equation for the standard molar free energy of formation of RuO₂:
The standard molar enthalpy and entropy of formation of RuO₂ at 298°K were calculated to be −72,430 ±200 cal/mol and –40.44±0.2 eu, respectively, using the available heat capacity data. The absolute entropy of RuO₂ at 298°K was calculated to be 15.46±0.2 eu.     

Modification of αAI2O3 Platelet/ZrO2 Matrix Interface by Epitaxial Growth of β-AI2O3 on the α-AI2O3

An epitaxial β-alumina crystal growth method was used to modify α-AI₂O₃ platelet surfaces before inclusion as a reinforcing phase in partially stabilized zirconia (3Y-TZP). The as-grown surface phase was Na-β"-AI₂O₃. This was converted to Ca-β"-AI₂O₃ by ion exchange, as the latter is more temperature-stable at composite sintering temperatures. The conditions of formation, thermal stability, and chemical compatibility of these interfacial phases were examined. α-AI₂O₃ platelets with Ca-β"-AI₂O₃ film were incorporated into 3Y-TZP. The β"-AI₂O₃/ZrO₂ interface was found to promote platelet debonding and pullout, thus enhancing the α-AI₂O₃ platelet/crack interactions during the fracture process.     

Effect of Firing Temperature on Electrical and Gas-Sensing Properties of Nano-SnO2-Based Thick-Film Resistors

Nano-SnO₂-based thick-film resistors were fabricated using screen printing technology. To study the effect of firing temperature, sensors were fired in the range 425–850°C. A mixture of tetragonal and orthorhombic SnO₂ was observed in the range 425–700°C. Above 700°C, the presence of majority tetragonal phase was observed. The sheet resistivity and TCR values were one to two orders of magnitude less than the reported values. Sensors fired at 750°C showed the highest sensitivity and selectivity for H₂, CO, and LPG at 140°C, 210°C, and 180°C, respectively, with a response and recovery time of 12 and 22 s.     

Shape of MgAl2O4 Grains in a CaMgSiAlO Glass Matrix

When sintered Al₂O₃ is annealed with CaMgSiAlO glass at 1600°C, polyhedral MgAl₂O₄ grains form and glass pockets are entrapped within the grains. After annealing for 13 h at 1600°C, the liquid pockets show a regular octahedron shape which is expected to represent the equilibrium shape. All grain surfaces in contact with the glass matrix show the same shape. The small grains, which must be shrinking, thus have the equilibrium shape, because their shrinkage shape is is identical to the equilibrium and growth shape. However, the octahedral shape also represents the growth shape for the growing large grains. The grains also form grain boundaries with neighboring grains.     

Crystallization Behavior of CaO–P2O5 Glass with TiO2, SiO2, and Al2O3 Additions

TiO₂ above 4 mol% is an effective nucleating agent for CaO–P₂O₅ glass which also contains substantial SiO₂ and Al₂O₃ additions. Glass ceramics can be made from this glass using a single slow heating ramp with no need for a nucleating heat treatment step. Powder of this composition crystallizes rapidly to β-Ca₂P₂O₇, whereas bulk glass crystallizes from diphasic nuclei consisting of a central cubic Ca-P-Ti-Si-Al oxide phase surrounded by impure AlPO₄ dendrites. Metastable calcium phosphate grows on the AlPO₄ dendrites and later transforms to β-Ca₂P₂O₇.     

Electrical Relaxation in Na2O·3SiO2 Glass

The electrical relaxation associated with alkali diffusion in Na₂O·3SiO₂ glass was studied from 0.2 Hz to 700 kHz at –1° to 163°C. A formalism for analysis of electrical relaxation in conducting dielectrics which associates the nonexponential decay of the electric field to zero and the dispersions in the dielectric constant and the conductivity with a distribution of relaxation times for the electric field was developed and is shown to be in qualitative accord with current molecular theories of electrical relaxation in alkali silicate glasses. A relation between the dc conductivity, the limiting high-frequency dielectric constant, and the average electric field or conductivity relaxation time was derived and is verified experimentally for the Na₂O·3SiO₂ glass. The distribution of electric-field relaxation times for the glass is broad, asymmetric on a logarithmic scale, and weighted in favor of the shorter relaxation times; the distribution narrows with increasing temperature. A reduced electrical relaxation curve which can be used to compare electrical and mechanical relaxations in Na₂O·3SiO₂ glass was generated.     

Glass/Substrate Interaction in Model RuO5-Glass Double-Layer Thick Films

Chemical interaction between RuO₂-glass thick-film resistors and substrates was studied by observing microstructural changes in model double-layer thick films, which were composed of a top glass layer and an RuO₂ layer. The concentration profiles of Al, Pb, and Ru in the film were analyzed. A new glass layer formed on the alumina substrate during firing, the formation of which resulted from dissolution of A1₂O₃ into glass. A mechanism of microstructural changes has been proposed based on the results of EPMA.     

Sodium Transport in the Na2O-H2O-SiO2 Glass System

The variation with water content of dc conductivity and Na diffusion coefficient for the Na₂O · 4siO₂ and Na₂O · 2SiO₂ glass systems was found to be similar to that of the Na₂O.3SiO₂ series reported earlier. The conductivity was estimated for the ternary system Na₂O-H₂O-SiO₂ by combining the present results with the previous data on the Na₂O · 3SiO₂ system. When the conductivity of those glasses with a constant [Na₂O] + [H₂O] content was plotted against water content, a pronounced mixed "alkali" effect was demonstrated. The Haven ratio, calculated by comparison of the dc conductivity to the Na diffusion coefficient at 100°C for each of the three glass systems, was found to increase toward unity with increasing water content. This suggests that the addition of water reduces the number of sodium charge carriers. The subsequent increase in conductivity beyond the minimum with the introduction of larger amounts of water is, probably, due to an increase in the mobility of the Na⁺ ions.     

Effect of As2O3 and NaNO3 on the Solution of O2 in Soda-Lime Glass

The rate at which soda-lime glass absorbed oxygen increased with the addition of arsenious oxide to the batch; the absorption rate increased further when sodium nitrate was substituted for part of the sodium carbonate in the batch. There was little difference, however, between the rate of absorption in melts in a gas furnace and melts in an electric furnace. The rate of absorption increased in all cases as the temperature increased in the range 1065° to 1280°C.     

Internal Friction of Proton-Exchanged Li2O·Al2O3·2SiO2 Glass

Protons were introduced into the surface of an Li₂O·Al₂O₃·2SiO₂ glass fiber (0.5 mm in diameter) by ion exchange in NH₄HSO₄ at 366°C for 21 h. Infrared absorption measurements established that the protons were associated with bridging oxygen ions. After ion exchange, the magnitude of the alkali internal friction peak decreased and a new peak appeared at ∼220°C. This new peak is attributed to the interaction of alkali and hydrogen ions, independent of the presence of nonbridging oxygen ions.     

Melting and Interface Reaction of Mn–Si–O Glass on BaTiO3

A glass with the eutectic composition 3MnO_1.5–2SiO₂ was used to simulate the formation of a liquid phase during sintering of BaTiO₃. Two oxide additives (Mn₂O₃ and SiO₂) performing various functions of the properties of BaTiO₃ were investigated for their crystallization and thermal characteristics at temperatures ≤1400°C. The wetting behavior of the glass, the dissolution of BaTiO₃ in glass melt, the identification of newly formed phases, and the sequential reaction kinetics of the glass/BaTiO₃ system, especially when isothermally treated at 1150°C, were investigated by electron microscopy with quantitative X-ray energy dispersive spectroscopic (Q-EDS) analysis. The evolution of the interfacial reaction of the glass/BaTiO₃ at 1150°C is reported and discussed.     

Matrix Phase in Ceramics with Composition near BaO·Nd2O3·5TiO2

Phase structures of two ceramics of Compositions BaNd₂Ti₅O₁₄ and Ba_3.75Nd_9.5Ti₁₈O₅₄, both of which had earlier been reported to be single-phase materials, were investigated using electron microscopy and an electron probe microanalyzer. It was observed that the amount of secondary phases was much lower in ceramics prepared with the latter composition and that the composition of the matrix phase of both samples was near 4BaO·5 Nd₂O₃·18TiO₂. These results indicate that only the composition Ba_3.75Nd_9.5Ti₁₈O₅₄ is a single-phase composition.     

Low-Fire Processing of Microwave BaTi4O9 Dielectric with BaO–ZnO–B2O3 Glass

The effects of BaO—ZnO–B₂O₃ (BZB) glass addition on the densification and dielectric properties of BaTi₄O₉ (BT4) have been investigated. With increasing BaO content in the BZB glass, the softening and melting points of the resulting BZB glass decrease, but the wetting between BZB and BT4 improves cosiderably. Although the densification temperature is reduced from 1300°C for pure BT4 to 925°C for BT4+BZB dielectric ceramics, the enhancement in densification becomes less significant with increasing BaO content in the BZB glass. The above result is attributed to a chemical reaction taking place at the interface of BZB/BT4 during firing, which becomes less extensive with increasing BaO content in the BZB glass. For the BZB glass with a BaO content in the range of 0–20 mol%, the resulting 90 vol% BT4+10 vol% BZB microwave dielectric has a dielectric constant of 28–33, and a product ( Q × f _r) of quality factor ( Q ) and a resonant frequency ( f _r) of 15 000–20 000 GHz at 6.6 GHz.