Effect of Sb2O3 on Thermal Properties of Glasses in Bi2O3–B2O3–SiO2 System

Glasses with compositions 50Bi₂O₃– x Sb₂O₃–10B₂O₃–(40– x ) SiO₂ ( x =0, 1, 3, 5, 8, 10) have been prepared by conventional melt quench technique. Substitution of Sb₂O₃ for SiO₂ exerted an obvious effect on properties of glasses, especially, increased glass transition temperature ( T _g) and crystalline temperature ( T _c) greatly. Results of infrared transmission spectra attributed the effect to the formation of new bridging bonds of Sb–O–B and Sb–O–Si in glass network.     

Glass-Forming Ability and Crystallization Tendency Evaluated by the DTA Method in the Na2O–B2O3–Al2O3 System

In order to evaluate the crystallization tendency of glasses, the ratio of the crystallization temperature to the liquidus temperature ( T _c/ T _L) was obtained by DTA measurement for the Na₂O–B₂O₃ and Na₂O–B₂O₃–Al₂O₃ systems. The critical cooling rate for glass formation ( Q *) was also measured. The measurements were performed in the composition range of (100 − x )Na₂O–( x )B₂O₃, ( x = 25–35 and 60–100 mol%), and (100 − y )0.5Na₂O·0.5B₂O₃−( y )Al₂O₃, ( y = 6–34 mol%). The relationship between T _c/ T _L and Q * was discussed. A linear relationship between T _c/ T _L and log Q * for these systems was found. Furthermore, the relationship between T _c/ T _L and Q * was verified by computer simulation based on the crystallization kinetics of glass or supercooled liquid.     

Effect of Molybdenum on the Structure and on the Crystallization of SiO2–Na2O–CaO–B2O3 Glasses

Crystallization of the poorly durable Na₂MoO₄ phase able to incorporate radioactive cesium must be avoided in SiO₂–Al₂O₃–B₂O₃–Na₂O–CaO glasses developed for the immobilization of Mo-rich nuclear wastes. Increasing amounts of B₂O₃ and MoO₃ were added to a SiO₂–Na₂O–CaO glass, and crystallization tendency was studied. Na₂MoO₄ crystallization tendency decreased with the increase of B₂O₃ concentration whereas the tendency of CaMoO₄ to crystallize increased due to preferential charge compensation of BO₄⁻ entities by Na⁺ ions. ²⁹Si MAS NMR showed that molybdenum acts as a reticulating agent in glass structure. Trivalent actinides surrogate (Nd³⁺) were shown to enter into CaMoO₄ crystals formed in glasses.     

Energetics of La2O3–HfO2–SiO2 Glasses

A series of La₂O₃–HfO₂–SiO₂ glasses, approximately along the join 0.73SiO₂–0.27( x HfO₂–(1− x )La₂O₃), 0< x <0.3), was prepared using containerless processing techniques (aerodynamic levitation combined with laser heating in oxygen). The enthalpy of formation and enthalpy of vitrification at 25°C were obtained from drop solution calorimetry of these glasses and appropriate crystalline compounds in a molten lead borate (2PbO–B₂O₃) solvent at 702°C. The enthalpy of formation from crystalline oxides was exothermic and became less exothermic with increasing HfO₂ content. Heat contents were measured by transposed temperature drop calorimetry and depended linearly on the HfO₂ content. Differential scanning calorimetry showed that both the onset glass transition and the onset crystallization temperature of these glasses increased with increasing HfO₂ content. Upon slow cooling in air, the glasses crystallized to a mixture of baddeleyite, cristobalite, lanthanum disilicate, and hafnon.     

Crystalline Phases and YAG Laser-Induced Crystallization in Sm2O3–Bi2O3–B2O3 Glasses

The glass formation region, crystalline phases, second harmonic (SH) generation, and Nd:yttrium aluminum garnet (YAG) laser-induced crystallization in the Sm₂O₃–Bi₂O₃–B₂O₃ system were clarified. The crystalline phases of Bi₄B₂O₉, Bi₃B₅O₁₂, BiBO₃, Sm _x Bi_{1− x} BO₃, and SmB₃O₆ were formed through the usual crystallization in an electric furnace. The crystallized glasses consisting of BiBO₃ and Sm _x Bi_{1− x} BO₃ showed SH generations. The formation of the nonlinear optical BiB₃O₆ phase was not confirmed. The formation (writing) region of crystal lines consisting of Sm _x Bi_{1− x} BO₃ by YAG laser irradiation was determined, in which Sm₂O₃ contents were∼10 mol%. The present study demonstrates that Sm₂O₃–Bi₂O₃–B₂O₃ glasses are promising materials for optical functional applications.     

Al2O3–ZrO2–SiO2 Ternary Glasses for Molybdenum Oxidation Barriers

The wettability of binary and ternary glasses belonging to SiO₂–Al₂O₃–ZrO₂ diagram has been studied using the sessile drop technique at 1750° and 1800°C. The ternary SiO₂–Al₂O₃–ZrO₂ (90–5–5 wt%) glass has proved to be well appropriated as a molybdenum oxidation barrier coating. The addition of 5 wt% of MoO₂ slightly improves its wettablity at higher temperatures without affecting its oxidation barrier properties. The Mo comes into the glass network as a mixture of Mo⁵⁺, Mo⁴⁺, and Mo⁶⁺. After oxidation at 1000°C in oxygen atmosphere, the molybdenum remains in the glass network as Mo⁶⁺.     

SiO2–PbO–CaO–ZrO2–TiO2–(B2O3–K2O), A New Zirconolite Glass–Ceramic System: Crystallization Behavior and Microstructure Evaluation

Zirconolite (CaZrTi₂O₇) is a mineral that has a high containment capacity for actinides and lanthanides and is considered to be a good candidate for the immobilization of radioactive wastes. The glass–ceramic technique seems to be a very suitable and convenient method to produce zirconolite crystals by precipitating them in a specific glass matrix. In this study, development of a new zirconolite-based glass–ceramic belonging to SiO₂–PbO–CaO–ZrO₂–TiO₂–(B₂O₃–K₂O) system was investigated. The presence of PbO, together with B₂O₃ and K₂O, allowed the preparation of a X-ray diffraction (XRD) amorphous glass with a relatively high concentration of ZrO₂ and TiO₂, which was successfully converted to a glass–ceramic containing 34 wt% of zirconolite after heating at 770°C for 4 h. Differential thermal analysis, XRD, scanning electron microscope, and energy dispersive X-ray spectroscopy were used to determine the crystallization conditions, identify the crystallized phases, determine their compositions and quantities and observe and analyze the microstructures. The zirconolite crystals showed a platelet morphology with a monoclinic structure characterized by a =1.246 nm, b =0.7193 nm, c =1.128 nm, and β=100.508°.     

The Influence of Sb2O3 Addition on the Properties of Low-melting ZnO–P2O5 Glasses

The influence of 0–16 mol% Sb₂O₃ substitution for P₂O₅ on the properties of ZnO–P₂O₅ glasses has been investigated. It was shown that Sb₂O₃ could participate in the glass network and thermal stability of the glasses decreased with increasing Sb₂O₃ content. Glass transition temperature T _g, softening temperature T _s, and water durability all decreased firstly (up to 6 mol% Sb₂O₃ added) and then increased. Substitution of 12 mol% Sb₂O₃ led to a 16°C decrease in T _g and 30°C decrease in T _s, and weight loss of the glass was only 0.42 mg/cm², which is ∼11 times lower than that of the glass without Sb₂O₃ after immersion in deionized water at 90°C for 1 day. The glass containing 12 mol% Sb₂O₃ might be a substitute for Pb-based glasses in some applications.     

Phase Relations in the System Al2O3–B2O3–Nd2O3

The phase relations at a temperature below "subsolidus" in the system Al₂O₃–B₂O₃–Nd₂O₃ are reported. Specimens were prepared from various compositions of Al₂O₃, B₂O₃, and Nd₂O₃ of purity 99.5%, 99.99%, and 99.9%, respectively, and fired at 1100°C. There are six binary compounds and one ternary compound in this system. The ternary compound, NdAl₃(BO₃)₄ (NAB), has a phase transition at 950°C ± 15°C. The high-temperature form of NAB has a second harmonic generation (SHG) efficiency of KH₂PO₄ (KDP) of the order of magnitude of the form which has been used as a good self-activated laser material, and the low-temperature form of NAB has no SHG efficiency.     

Effect of Alkali Metal Oxide Addition on the Sinterability of MgO–B2O3–Al2O3 Glass–Al2O3 Filler Composites

The sintering of a composite of MgO–B₂O₃–Al₂O₃ glass and Al₂O₃ filler is terminated due to the crystallization of Al₄B₂O₉ in the glass. The densification of a composite of MgO–B₂O₃–Al₂O₃ glass and Al₂O₃ filler using pressureless sintering was accomplished by lowering the sintering temperature of the composite. The sintering temperature was lowered by the addition of small amounts of alkali metal oxides to the MgO–B₂O₃–Al₂O₃ glass system. The resultant composite has a four-point bending strength of 280 MPa, a coefficient of thermal expansion (RT—200°C) of 4.4 × 10⁻⁶ K⁻¹, a dielectric constant of 6.0 at 1 MHz, porosity of approximately 1%, and moisture resistance.     

Mullite-Type Structures in the Systems Al2O3–Me2O (Me = Na, K) and Al2O3–B2O3

A morphous solids belonging to the systems Al₂O₃–Me₂O (Me = Na, K) and Al₂O₃–B₂O₃ were prepared by nitrate decomposition, introducing boron in the form of boric acid. Crystalline metastable solids with pseudotetragonal symmetry were obtained from thermal treatment at 850° to 900°C for the compositions Al₆Me_xO_{(9+0.5 x )} ( x ≅ 1; Me = Na, K) and Al_{6- x} B _x O₉ (1 x 3). The resultant solids were stable only within a difinite temperature range and transformed, with further treatment increases, into stable equilibrium phases. The structures of the metastable phases were examined by X-ray diffraction and Fourier transform infrared spectroscopy, and both analyses showed a mullite type of framework, inside of which the atomic coordinates were refined in the Pbam (no. 55) space group. The present results indicate that these silica-free mullite structures are stabilized by two different mechanisms: (1) interstitial occupation of bulky cations (Na⁺, K⁺) or (2) substitution of B for Al in some of the tetrahedral positions.     

Cassiterite Solubility in High-Silica K2O-Al2O3-SiO2 Liquids

The saturation surface of cassiterite, SnO₂, was determined for liquids in the system K₂O–Al₂O₃–SiO₂ as a function of bulk composition and temperature. At fixed K₂O/Al₂O₃ cassiterite solubility varies weakly with SiO₂ concentration (76 to 84 mol%), temperature (1350° to 1550°C), and log ( f _O2) (−0.7 to −5.3). Cassiterite solubility is also approximately independent of composition in liquids with molar ratios of K₂O/Al₂O₃ lessthan equal to 1 (peraluminous liquids). As K₂O/Al₂O₃ increases from 1 (peralkaline liquids), however, cassiterite solubility increases steeply and approximately linearly with K₂O in excess of Al₂O₃. It is proposed that potassium in excess of aluminum combines with Sn⁴⁺ to form quasi-molecular complexes with an effective stoichiometry of K₄SnO₄.     

Effect of B2O3 Addition on the Thermal Properties and Structure of Bulk and Powdered Barium Phosphate Glasses

The glass transition temperature increases and the thermal expansion coefficient and density decrease with increasing B₂O₃ concentration in a series of (100− x )(50BaO–50P₂O₅)− x B₂O₃ where x =0–10 mol% for bulk samples. According to Raman spectroscopy, the bulk BaO–P₂O₅–B₂O₃ (BaP–B) glasses consist of metaphosphate Q ² units with ring-type metaborate, diborate, and PO₄–BO₄ groups. X-ray photoelectron spectroscopy results reveal qualitatively that P–O–B bonds are formed at the surface of BaP–B glass samples ground in laboratory air over 6 mol% B₂O₃ only. The P–O–B bonds are related to the suppression of the crystallization of powdered BaP–B glasses with >6 mol% B₂O₃ during differential thermal analysis.     

Pyrochlore Phases in the System ZnO–Bi2O3–Sb2O5: I. Stoichiometries and Phase Equilibria

Two cubic pyrochlore phases exist in the system ZnO–Bi₂O₃–Sb₂O₅. Neither has the supposed "ideal" stoichiometry, Zn₂Bi₃Sb₃O₁₄. One, P ₁, is a solid solution phase, Zn_{2+ x} Bi_{2.96−( x − y )}Sb_{3.04− y} O_14.04+δ where 0< x <0.13(1), 0< y <0.017(2) and a =10.4285(9)−10.451(1) Å. The other, P ₂, is a line phase, Zn₂Bi_3.08Sb_2.92O_13.92 with a =10.462(2) Å. Subsolidus phase relations at 950°C involving phases P ₁ and P ₂ in the ZnO–Bi₂O₃–Sb₂O₅ phase diagram have been determined.     

Studies in Lithium Oxide Systems: VII, Li2O–B2O2–SiO2

Phase relations in the system Li₂O–B₂O₃–SiO₂ were studied by quenching and solid-state reactions. No ternary compounds were detected in the portion of the system containing less than 53% Li₂O. Compatibility triangles were formed from the binary borate and silicate compounds. Liquidus data obtained by quenching are reported for four joins, Li₂O·2SiO₂–Li₂O·2B₂O₃, Li₂O·SiO₂-Li₂O·2B₂O₃, Li₂O·SiO₂-Li₂O·B₂O₃, and Li₂O·2B₂O₃-SiO₂. The last join cuts across the two-liquid region and is not a true binary system. Some probable ternary invariant points were located in the portion of the system which was quenchable to glass and adjacent to the two-liquid region. Further data on the previously reported immiscible liquid formation are given and the significance is discussed. Data on the thermal expansion behavior of certain glasses are presented.     

The System KAlSiO4–Mg2SiO4–KAlSi2O6

Schairer's study (1954) on phase relations in the system KalSi₂O₆–Mg₂SiO₄–SiO₂ was extended to include the system KalSiO₄–Mg₂SiO₄–KalSi₂O₆. It is shown that this join is ternary; however, the relatively high vapor pressure of the condensed phases prohibits study by the usual quenching techniques. The apparent intersection of the (KalSiO₄–Mg₂SiO₄–SiO₃) join with the primary phase volume of spinel is attributed to loss of the alkali-silicate constituents by vapor transport. This results in the effective bulk composition being moved away from this join toward the primary phase volume of spinel in the system K₂O–MgO–Al₂O₃–SiO₂.     

Sintering and Microwave Dielectric Properties of the LiNb0.63Ti0.4625O3 Ceramics with the B2O3–SiO2 Liquid-Phase Additives

The effect of B₂O₃–SiO₂ liquid-phase additives on the sintering, microstructure, and microwave dielectric properties of LiNb_0.63Ti_0.4625O₃ ceramics was investigated. It was found that the sintering temperature could be lowered easily, and the densification and dielectric properties of LiNb_0.63Ti_0.4625O₃ ceramics could be greatly improved by adding a small amount of B₂O₃–SiO₂ solution additives. No secondary phase was observed for the ceramics with B₂O₃–SiO₂ additives. With the addition of 0.10 wt% B₂O₃–SiO₂, the ceramics sintered at 900°C showed favorable microwave dielectric properties with ɛ_r=71.7, Q × f =4950 GHz, and τ_f=−2.1 ppm/°C. The energy dispersive spectra analysis showed an excellent co-firing interfacial behavior between the LiNb_0.63Ti_0.4625O₃ ceramic and the Ag electrode. It indicated that LiNb_0.63Ti_0.4625O₃ ceramics with B₂O₃–SiO₂ solution additives have a number of potential applications on passive integrated devices based on the low-temperature co-fired ceramics technology.     

Devitrification Kinetics and Mechanism of K2O–CaO–SrO–BaO–B2O3–SiO2 Glass-Ceramic

The devitrification kinetics and mechanism of a low-dielectric, low-temperature, cofirable K₂O–CaO–SrO–BaO–B₂O₃–SiO₂ glass-ceramic have been investigated. Crystalline phases including cristobalite (SiO₂) and pseudowollastonite ((Ca,Ba,Sr) SiO₃) are formed during firing. Activation energy analysis shows that the nucleation of the crystalline phases is controlled by phase separation of the glass. The crystallization kinetics of both cristobalite and pseudowollastonite obey Avrami-like behavior, and the results show an apparent activation energy close to that of the diffusion of alkaline and alkali ions in the glass, suggesting that diffusion is rate limiting. The above conclusion is further supported by analysis of measured growth rates.     

Reduction of Eu3+ to Eu2+ in Aluminoborosilicate Glasses Prepared in Air

Eu₂O₃-doped aluminoborosilicate glasses were prepared in air at high temperature. Luminescence measurements were used to investigate a valence change from Eu³⁺ to Eu²⁺ ions in the aluminoborosilicate glasses. The results showed that the doped Eu³⁺ ions were partially reduced to Eu²⁺ in the Eu₂O₃:RO–Al₂O₃–B₂O₃–SiO₂ (RO=CaO, SrO, BaO, Li₂O) glasses, but not in the Eu₂O₃:RO–Al₂O₃–B₂O₃–SiO₂ (RO=Na₂O, K₂O) glasses. The changes of Eu reduction with different RO components were discussed with the variation of optical basicity of RO and with different valency of R cations. The effects of co-doping BaO and ZnO in aluminoborosilicate glasses on Eu reduction were also investigated and discussed.     

Spectroscopic Properties of Er3+-Doped Na2O–La2O3–Al2O3–SiO2 Glasses

Er³⁺-doped sodium lanthanum aluminosilicate glasses with compositions of (90− x )(0.7SiO₂·0.3Al₂O₃)· x Na₂O·8.2La₂O₃· 0.6Er₂O₃·0.2Yb₂O₃·1Sb₂O₃ (in mol%) ( x = 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ω _t ( t = 2, 4, 6) decreases with increasing Na₂O. Ω₂ decreases rapidly with increasing Na₂O while Ω₄ and Ω₆ decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na₂O. Fluorescence spectra of the ⁴ I _13/2 to ⁴ I _15/2 transition have been measured and the change with Na₂O content is discussed. It is found that the full width at half-maximum decreases with increasing Na₂O.