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When Bi2O3-containing glasses are melted at relatively high melting temperatures, they often show brown coloration due to the reduced Bi species, which is undesirable as optical glasses. In the present study, the low melting temperature (900°C) compared with conventional ones (1000°–1200°C) was used, in order to avoid the formation of reduced Bi species. ZnO–Bi2O3–B2O3 (ZBiB) glasses were selected for developing molding glasses with low Tg (≤600°C) and high nd (≥1.8). Most ZBiB glasses containing both B2O3≥40 mol% and Bi2O3≤40 mol% have much higher nd (=1.87–2.10) than those of ZnO–Bi2O3–P2O5 glasses (nd=1.68–1.97), much lower Tg (=400°–470°C) than those of Li2O–ZnO–TiO2–B2O3–P2O5 glasses (Tg=550°–570°C), and much lower λ70% (=39–45) than those of commercially available molding glasses (λ70%=44–50) with nd≥1.85. Some of the ZBiB glasses have properties suitable for precision glass molding (Tg=466°C, nd=1.929, λ70%=41 for 10ZnO·30Bi2O3·60B2O3 glass; Tg=440°C, nd=1.946, λ70%=42 for 40ZnO·20Bi2O3·40B2O3 glass). Thus, ZBiB glasses containing both B2O3≥40 mol% and Bi2O3≤40 mol% melted at 900°C are considered to be promising materials as molding glasses with high nd and low λ70%.

Four ferric phosphate compounds were identified in the Fe2O3–P2O5 system and the liquidus surfaces in the subsystems Fe3PO7–FePO4, FePO4–Fe4(P2O7)3, and Fe4(P2O7)3–Fe(PO3)3 were determined. The results are significantly different from those presented by Wentrup in 1935. Fe3PO7 is the stable ferric oxophosphate compound, not Fe4P2O11, and Fe3PO7 decomposes in air at 1090°C. The congruent melting point of FePO4 (1208°C) is similar to what was reported, but Fe4(P2O7)3 melts congruently at 945°C, about 300°C lower than claimed by Wentrup. Fe(PO3)3, for which the melting temperature has not been previously reported, melts congruently at 1205°C. Eutectic points exist at 58.0 mol% Fe2O3 (1070°C), 42.7% Fe2O3 (925°C), and 37.0% Fe2O3 (907°C). The latter two eutectic points bracket the conventional glass-forming range for iron phosphate melts under consideration as alternative hosts for nuclear wastes.

It is demonstrated that the use of ∼0.9 mol% Li2CO3 (LC) as a sintering aid for Sr, K, Nb modified Pb(Zr1−x,Tix)O3 (PZT) ceramics is effective only in the presence of excess PbO (∼2 mol%). It is shown that LC and PbO react to form the compound, Li2PbO3 (LPO) which has a melting temperature of ∼836°C. Using dilatometry, we were able to correlate shrinkage during heating of a green ceramic to the melting of the LPO. Consequently, complete densification and sizeable grain growth are achieved by solution-precipitation of the ceramic through the liquid phase. Importantly, sintering is not particularly effective with such small additions of either LC or PbO alone. In confirmation of this model, the LPO compound was presynthesized and used as the only sintering aid in the same PZT composition. The densification behavior of this mixture compared well with the case of separate additions.

BaCu(B2O5) ceramics were synthesized and their microwave dielectric properties were investigated. BaCu(B2O5) phase was formed at 700°C and melted above 850°C. The BaCu(B2O5) ceramic sintered at 810°C had a dielectric constant (ɛr) of 7.4, a quality factor (Q×f) of 50 000 GHz and a temperature coefficient of resonance frequency (τf) of −32 ppm/°C. As the BaCu(B2O5) ceramic had a low melting temperature and good microwave dielectric properties, it can be used as a low-temperature sintering aid for microwave dielectric materials for low temperature co-fired ceramic application. When BaCu(B2O5) was added to the Ba(Zn1/3Nb2/3)O3 (BZN) ceramic, BZN ceramics were well sintered even at 850°C. BaCu(B2O5) existed as a liquid phase during the sintering and assisted the densification of the BZN ceramic. Good microwave dielectric properties of Q×f=16 000 GHz, ɛr=35, and τf=22.1 ppm/°C were obtained for the BZN+6.0 mol% BaCu(B2O5) ceramic sintered at 875°C for 2 h.

The melting temperature of alpha-silicon nitride, up to a pressure of 37 GPa, was determined by using the diamond-anvil cell technique, together with laser heating and spectroradiometry. The melting temperature varied from 2200 ± 75 K at 3.5 GPa to 3600 ± 200 K at 37 GPa; the extrapolated temperature at 1 atm was estimated to be 2100 ± 75 K.

When Bi2O3 was added to LiAlSiO4 ceramics, Bi12SiO20 secondary phase was formed. Since the melting temperature of Bi12SiO20 ceramics is 880°C, the liquid phase is expected to form during sintering and to assist the densification of LiAlSiO4 ceramics. When 15.0 mol% Bi2O3 was added, the LiAlSiO4 ceramics could be sintered at 900°C, and with 20.0 mol% Bi2O3 they could even be sintered at 875°C. The 15.0 mol% Bi2O3-doped LiAlSiO4 ceramics sintered at 900°C exhibited good microwave dielectric properties, namely, a low er of 4.3, a high Q × f of 62 430 GHz and a small τf of −16.21 ppm/oC.

The densification behavior and mechanical properties of B4C hot-pressed at 2000°C for 1 h with additions of Al2O3 up to 10 vol% were investigated. Sinterability was greatly improved by the addition of a small amount of Al2O3. The improvement was attributed to the enhanced mobility of elements through the Al2O3 near the melting temperature or a reaction product formed at the grain boundaries. As a result of this improvement in the density, mechanical properties, such as hardness, elastic modulus, strength, and fracture toughness, increased remarkably. However, when the amount of Al2O3 exceeded 5 vol%, the level of improvement in the mechanical properties, except for fracture toughness, was reduced presumably because of the high thermal mismatch between B4C and Al2O3.

The pristine strength of 0.5Li2O·0.5K2O·2SiO2 glass measured in 3-point bending under liquid nitrogen was studied as a function of melting time and atmosphere at a constant melting temperature. The atmosphere over the melt was one of the most important parameters affecting the pristine strength. The most significant time-dependent melting effects and the highest strengths resulted from melting in a dry atmosphere of O2 or air. In contrast, vacuum-melted and Ar-melted glasses had the lowest strengths. Melting in N2 or CO2 led to intermediate strengths. The presence of water vapor in the atmosphere during melting was detrimental to strength in those cases where very high strengths had been obtained with dry gases. The introduction of water vapor into those gases which in the dry state had led to low-strength glasses did not significantly affect the strength. The effects of the atmosphere in leading to oxygen-deficient or excess-oxygen glasses on the formation or dissolution of microheterogeneous regions were correlated with the pristine strengths of the glasses.

This paper reports on {beta}-Spodumene glass-ceramic compositions melted and studied. Compositional variations were made in the three major components as well as through minor additions of other oxides. Sintering characteristics and microstructures were studied and values for crystallization temperature, melting temperature, and crystallized thermal expansion coefficient were recorded. It was found that sinterable {beta}-spodumene glass-ceramics could be made with a wide range of properties. Selection of an appropriate composition would be based on desired properties.

An apparatus is described which employs the elongation of a glass fiber under load for the determination of annealing and strain points. The same apparatus is also used by varying the suspended load for the determination of the temperature-viscosity curve between the annealing range and the softening point of the glass. A description is given of measurements made in this manner on a series of three simple soda-lime-silica glasses at theses low temperatures, as well as measurements made in a rotating cylinder viscomcter between the softening point and the melting temperature. Curves are shown for the viscosities of the three glasses in the two temperature ranges and a complete viscosity curve from 500 to 1400°C is given for one of them. It is found that the two methods yield results that fit a smooth curve between these limits of temperature.

The manufacture of opal glass in day tanks has made it necessary to study the corrosion of tank blocks. Opacifiers have to be used in larger quantities than in batches for opal glasses melted in covered pots because of the loss of density due to higher melting temperatures and shorter melting times, and exposure of batch to reactions from the direct flame heat. Experiments have been conducted to ascertain the factors which will allow the use of the lowest amount of opacifiers, the shortest practical melting time with the highest practical melting temperature, and also to minimize the corrosion of the bottom blocks of tanks by application of a cooling system, as well as prevention of separation of batch by practising certain “filling-in” methods of the batch, and as a final result to reduce block stones in the glass. The experiments have resulted in the successful operation of day tanks for opal glass and in prolonging the life of the tanks, and have made possible the manufacture of thin blown dense opal glasses of almost as good quality from tanks as can be produced in pots.

Interpretations are made of experimental and practical aspects of glass structures in terms of a postulated distribution of anionic structures in glass. The existence of effects determined by the “melting history” of a glass is demonstrated by specially programmed experiments on viscosity and tensile strength. The viscosity curve of glass melted at a relatively low temperature lies above that for the same glass which had been previously melted at high temperatures. The two curves merge in the high-temperature region. It also is found that the tensile strength of glass fibers increases as the maximum melting temperature increases.

Melting experiments have established three important eutectics in this system: (1) the Si3N4-Mg2SiO4 binary eutectic composition, 0.07Si3N4+0.93Mg2SiO4 at 1560°C, (2) the Si2N2O-Mg2SiO4 binary eutectic composition, 0.17Si2N2O+ 0.83Mg2SiO4 at 1525°C, and (3) the Si3N4-Si2N2O-Mg2SiO4 ternary eutectic composition, 0.04Si3N4+0.14Si2N2O+0.82Mg2SiO4 at 1515°C. Systematic replacement of MgO with CaO in the ternary eutectic reduced its melting temperature to 1325°C for a CaO/MgO molar ratio of 0.67. The results of this study are discussed in relation to fabrication, microstructure, and high-temperature strengths.

Phase relations in the system Sc2O3-WO3 were characterized. Two stable binary compounds were, found. The 1:3 compound, SC2(WO4)3, melts congruently at 1640°±10°C and forms a simple eutectic with WO3 at ∼90 mol% WO3 and 1309°+10°C. The 3 : 1 compound, Sc6WO12, forms a simple eutectic with the 1:3 compound at -69 mol% WO2, and 1580°+10°C. The melting temperature of SC6WO12 was >1600°C.

The effect of rare-earth oxide additives on the densification of silicon nitride by pressureless sintering at 1600° to 1700°C and by gas pressure sintering under 10 MPa of N2 at 1800° to 2000°C was studied. When a single-component oxide, such as CeO2, Nd2O3, La2O3, Sm2O3, or Y2O3, was used as an additive, the sintering temperature required to reach approximate theoretical density became higher as the melting temperature of the oxide increased. When a mixed oxide additive, such as Y2O3–Ln2O3 (Ln=Ce, Nd, La, Sm), was used, higher densification was achieved below 2000°C because of a lower liquid formation temperature. The sinterability of silicon nitride ceramics with the addition of rare-earth oxides is discussed in relation to the additive compositions.