Boron carbide undergoes stress-induced amorphization when subjected to large non-hydrostatic stresses that exceed its elastic limit. This has been proposed as the source for the abrupt loss of shear ...strength in boron carbide which limits its engineering applications. Si/B co-doping was suggested as one of the means to suppress stress-induced amorphization but this has not been experimentally verified. Here, by utilizing arc melting, we prepared Si/B co-doped boron carbide with increased Si content as compared to conventional methods. Through Raman analysis in conjunction with indention and elemental analyses based on SEM and STEM (ζ-factor microanalysis), it is suggested that Si/B co-doping is a promising avenue for suppressing stress-induced amorphization. A comprehensive characterization of microstructure, chemistry, and structural change of boron carbide as a result of Si/B co-doping was elucidated.
The compositional dependences of bioactivity, thermal properties, atomic structure, and surface morphology have been investigated in the CaO-Na
2
O-SiO
2
-P
2
O
5
system; this system is known as a ...bioglass. 45S5 Bioglass® is known to be a general and highly bioactive material. However, the bioactivity of this glassy material is expected to be improved by modifying the alkali-metal composition. Thermal properties, density, and molar volume were measured to investigate the structural packing. FT-IR spectra and X-ray diffraction were used to confirm the structures of these glasses. The morphology was examined using field emission electron microscopy, and the formation of a Ca-P layer was studied using an energy-dispersive system. This study shows that the tendency to form a calcium phosphate layer is increased with the substitution of K
2
O for Na
2
O.
The density, surface tension, and viscosity of the melts from the PbO‐B2O3‐SiO2 system have been measured at temperatures in the range 1073–1473 K. The effect of composition on these properties was ...also investigated. The density of the melt was found to increase linearly with increasing PbO content. Molar volume was derived from the density data, and its deviation from the additivity of partial molar volumes was calculated. These deviations in molar volume from those obtained from additivity rules have been used along with the ratio of various coordination numbers of boron (as reported by Bray) to discuss the structure of the melts. The surface tension was found to decrease with decreasing SiO2/B2O3 ratio, and to increase in the range of the PbO content between 30 and 60 mol%, showing a maximum at ∼60 mol% PbO, and then decreased with further additions. This result suggested that the surface tension would be affected primarily by the B2O3 content in the range of the PbO content between 30–60 mol%, and mainly by the PbO content in the range of the PbO content >60 mol%, respectively. The viscosity of the melt was found to decrease linearly with increasing PbO content. The results obtained indicate that the increase in viscosity with B2O3 was half that of SiO2 (on a molar basis), and an empirical equation has been proposed for the viscosity as a function of mole fraction.
Density of Bi2O3-B2O3 Binary Melts Hwang, Chawon; Fujino, Shigeru; Morinaga, Kenji
Journal of the American Ceramic Society,
September 2004, Letnik:
87, Številka:
9
Journal Article
Recenzirano
The densities of xBi2O3·(100−x)B2O3 binary melts (x= 0–100 mol%) have been measured systematically in the temperature range of 973 to 1373 K using the Archimedean double‐bob method. In addition, the ...molar volume and coefficient of volume expansion have been determined from these density measurements. The density of melts in the Bi2O3–B2O3 binary system decreased with increasing temperature for all compositions, and increased with increasing Bi2O3 content. The molar volume calculated at 1273 K showed a minimum at around 20–30 mol% Bi2O3. The deviation of molar volume from ideality and the partial molar volumes of B2O3 and Bi2O3 single‐component melts were calculated, and the relationships between these properties and Bi2O3 content were investigated. The Δ(MV) (deviation of molar volume from ideality) was negative in the Bi2O3–B2O3 binary melts and showed a minimum of −7.5 cm3 (−17.3%) at 40 mol% Bi2O3 and 1273 K. The PMV (partial molar volume) of the B2O3 melt decreased with increasing Bi2O3 content, up to 70 mol% Bi2O3, and was constant above 70 mol% Bi2O3. The PMV of the Bi2O3 melt was constant up to 30 mol% B2O3 (considered from the viewpoint of Bi2O3), and then decreased sharply with further addition of B2O3. The coefficient of volume expansion increased sharply up to 20 mol% Bi2O3 and decreased with further addition of Bi2O3 at 1273 K. From this result, it can be inferred that the temperature‐induced structural changes taking place in the melts are greatest at 20 mol% Bi2O3.
Undoped (B4C), B rich (B5.5C), and B/Si co-doped (Si-B6.5C) boron carbides were annealed at 500 °C for up to 21 days to investigate the thermal stability of primary dopants, B and Si. Structural ...changes associated with dedoping were investigated by X-ray diffraction (XRD) and Raman spectroscopy. The stable phase B4C showed no microstructural or lattice parameter changes. Similarly, lattice parameters of B5.5C remained constant, suggesting that B dopant is stable at the given conditions. However, the shortened lattice parameters and reduced Si content of Si-B6.5C over the annealing time indicated that Si dopant was in a metastable state at the annealing temperature. Consequently, Si dedoping led to an increase in amorphization (a loss of local crystalline order) which degrades the ballistic performance of boron carbide. The insight highlights the importance of Si dopant in boron carbide and suggests that rapid processing may be necessary to retain more silicon for better performance.
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Undoped (B4C), B rich (B5.5C), and B/Si co-doped (Si-B6.5C) boron carbides were annealed at 500 °C for up to 21 days to investigate the thermal stability of primary dopants, B and Si. Structural ...changes associated with dedoping were investigated by X-ray diffraction (XRD) and Raman spectroscopy. The stable phase B4C showed no microstructural or lattice parameter changes. Similarly, lattice parameters of B5.5C remained constant, suggesting that B dopant is stable at the given conditions. However, the shortened lattice parameters and reduced Si content of Si-B6.5C over the annealing time indicated that Si dopant was in a metastable state at the annealing temperature. Consequently, Si dedoping led to an increase in amorphization (a loss of local crystalline order) which degrades the ballistic performance of boron carbide. The insight highlights the importance of Si dopant in boron carbide and suggests that rapid processing may be necessary to retain more silicon for better performance.
Glasses in the system 30P
2
O
5
-30B
2
O
3
-40Na
2
O-xTiO
2
(0 ≤ x ≤ 25 mol %) have been prepared by the melt-quenching technique. Increasing the TiO
2
content of the glass structure results in a ...decrease in the molar volume and an increase in the glass transition/softening temperatures. Structural changes were studied by Raman spectroscopy, and
11
B and
31
P solid-state NMR. The observed changes in the spectra and the properties of the studied glasses can be ascribed to several reasons, such as the addition of TiO
2
that results in the formation of distorted Ti octahedral linked to pyrophosphate unit through P-O-Ti bonds. In these glass series, the overall glass network was enhanced by TiO
2
addition, although a depolymerization in the original P-O-P network occurred.
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