Noritaka Saito

Structural Role of Alkali Cations in Calcium Aluminosilicate Glasses as Examined Using Oxygen-17 Solid-State Nuclear Magnetic Resonance Spectroscopy

The structural roles of alkali and calcium cations are important for understanding the physical and chemical properties of aluminosilicate melts and glasses. Recently, oxygen-17 nuclear magnetic resonance (17O NMR) studies of calcium–sodium aluminosilicate glasses showed that these structural roles are not randomly given, but rather each cation has its own preferential role. However, the relationship between cation type and role preference in calcium aluminosilicate glass is not completely understood. In the present study, the structural roles of lithium, sodium, and potassium cations in selected calcium aluminosilicate glasses are investigated using 17O solid-state NMR experiments. Data from these experiments clearly show that potassium cations have a notably stronger tendency to act as charge compensators within the network structure, compared to sodium and lithium cations. The result of 17O NMR experiment also showed that sodium and lithium cations in part act as network modifier alongside with calcium cations.

Effect of additive oxides on the viscosities of CaO-SiO2-Al2O3 and CaO-Fe2O3 melts

The effects of MgO, TiO 2 or Fe 2 O 3 on the viscosity of 40CaO-40SiO 2 -20Al 2 O 3 /mass% slags have been measured by a rotating crucible viscometer. The viscosity of these quaternary slags decreased with increasing the content of additive oxide. At the same content of additive oxide, the viscosity decreases from MgO, TiO 2 to Fe 2 O 3 . In addition, the effects of SiO 2 , Al 2 O 3 or MgO on the viscosity of 26.1CaO-73.9Fe 2 O 3 / mass% (CF) and 14.9CaO-85.1Fe 2 O 3 / mass% (CF 2 ) slags have been measured. Viscosity of calcium ferrite slags increased with increasing SiO 2 , Al 2 O 3 or MgO content. Al 2 O 3 was found to be more effective for increasing the viscosity at the same content of additive oxide.

Oxygen Speciation in Multicomponent Silicate Glasses Using Through Bond Double Resonance NMR Spectroscopy

The description of the structure of aluminosilicate glasses is more often centered on its cationic constituents, and oxygen ions determine their connectivity, directly impacting the physical properties of those disordered materials. A very powerful approach to ascertain this short- to medium-range order is to use 17O NMR, but up to now the speciation of the chemical bonds was only ambiguously achieved for multicomponent glasses. Here, we propose to directly probe the very scarcely explored through-bond correlations using 17O{27Al} and 17O{23Na} solid-state nuclear magnetic resonance (NMR) double-resonance experiments. Our approach allows quantifying the strongly overlapping components of the 17O NMR spectra of a quaternary aluminosilicate glass. We observe a cooperative location of alkali and aluminum ions in the neighborhood of bridging oxygens, which is consistent with the modified random network model where the glass structure is composed of two regions: network structure and breakage region (i.e., channel).

Capacitance measurement of molten calcium silicate under shear stress field

Abstract The effect of shear stress on the crystallization behavior of molten 50CaO-50SiO2 (mol%) slag was investigated by in-situ measurements of its electrical capacitance in wide temperature range including supercooled region. It is well known that the electrical capacitance of liquids should be generally much higher than that of solids because of the differences in their respective polarization mechanisms. The difference was employed as a sensitive indicator of the crystallization of molten silicates in an experimental furnace equipped with an electrical-capacitance measurement system. The system comprised a Pt-based alloy crucible and a rotating rod that allow us to evaluate the effect of shear stress, both connected to a capacitance meter (LCR meter). As expected, at a particular temperature, the electrical capacitance of the molten calcium silicate abruptly decreased by roughly three orders of magnitude, which clearly indicated crystallization confirmed by corresponding microstructural analyses. It was also found that, for the rotating-rod measurements (with shear stress), the temperatures at which the capacitance abruptly dropped were higher than that without the shear stress. This suggests that the agitation effect by the rotating-rod accelerates the crystallization of molten calcium silicate.

Advances in Transient-Liquid-Phase Bonding of Ultra-high Temperature ZrC Ceramics

Abstract Full exploitation of the many attractive engineering properties of ultra-high temperature ceramics (UHTCs) requires that they can be joined. This paper explores progress in identifying joining strategies based on the use of transient liquid phases (TLPs). Wetting studies are used to explore the suitability of specific liquids for joining, while bonding studies provide the ultimate test. Sintering aids in the UHTC provide a major potential obstacle to successful joining, and dissolved impurities in the TLP can also complicate the joining process. Nonetheless, we show that well-bonding interfaces can be achieved when ZrC ceramics are bonded at 1673 K using a Ni/Nb/Ni multilayer interlayer.

Viscosity Estimation of Spherical Particles Dispersed Suspension

The viscosity measurement has been made for suspensions consisting of polyethylene beads and silicone oil matrix as a function of mean diameter of beads and shear rate. The relative viscosity is found to increase with increasing the volume fraction of beads and decrease with the mean diameter of beads and shear rate. We also tested several viscosity equations to reproduce the viscosity values of spherical particle dispersed suspension. However, any equation could not reproduce well the experimental viscosity values of suspension measured under various conditions. Some modification is needed by considering some experimental conditions (volume fraction, mean diameter of beads and shear rate). Then, the modified Einstein–Roscoe equation is recommended for reproducing the viscosity values of suspension under various conditions.

Ultrarapid Transient-Liquid-Phase Bonding of Advanced Ceramics

Interlayer designs and processing conditions that promote rapid and reliable transientliquid- phase (TLP) bonding/joining of Al2O3 and ZrO2-toughened Al2O3 ceramics are presented. The interplay between wetting, roughness, interlayer design and microstructure, and interlayer homogenization is described. The prospects for extending the method to other ceramics, notably the ultrahigh-temperature ceramics (UHTCs) will be discussed.

Joining of UHTC Composites Using Metallic Interlayer

Ultra-high temperatures ceramics (UHTCs) are the subject of intense worldwide research effort, and their stability in severe environments makes them candidates for aerospace, nuclear and solar energy applications. Widespread usage UHTCs requires the development of effective and reliable joining methods that facilitate the fabrication of large, complex-shaped, and potentially multimaterial components and devices. Joining of HfB2 and ZrB2, UHTC diborides, which exhibit outstanding thermo-mechanical and thermochemical properties and good erosion and corrosion resistance, was the focus of the present study. MoSi2 is an effective sintering aid and a composite component for both HfB2 and ZrB2, resulting in dense bulk materials with excellent mechanical properties. HfB2–10 vol.% MoSi2 composites were joined at 1500 °C with a Ni/Nb/Ni interlayer that forms a thin liquid film. Joint-region characterization revealed well-bonded interfaces with interfacial reaction products with the MoSi2. Well-bonded interfaces were also obtained for a ZrB2–10 vol.% MoSi2 composite bonded at 1500 °C with both Ti and Zr interlayers. It was found that the Ti interlayer exhibited more intensive interfacial reaction with ZrB2 composite than the Zr interlayer. Additionally, well-bonded interfaces were also found for a ZrB2–10 vol.% MoSi2 composite bonded at 1500 °C with ZrB2-X vol.% Ni (X = 20, and 40) powder-based interlayer. Joint-region characterization revealed well-bonded interfaces with microstructures strongly dependent on the Ni content.

Effect of Nanosized Particles on the Mechanical Properties of Y2O3

A systematic series of experiments was performed to determine the optimum firing schedule of Y2O3. A two-step sintering with subsequent profile succeeded to fabricate Y2O3 ceramic with the relative density of 97.6% and the average grain size of 0.46 μm: first step and second step temperature of T1 = 1490 °C and T2 = 1350 °C, respectively and second step holding time of t2 = 20 h. After the firing schedule of pure Y2O3 was determined, two types of TiO2/Y2O3 and ZrO2/Y2O3 composites were fabricated for the further improvement of mechanical properties. According to results, ZrO2/Y2O3 composite showed a dramatic increase in strength and toughness as 417 MPa and 4.4 MPa.m1/2, respectively.

Phase Separation Behavior and Coloring of Coating Glasses for Sanitary Ware

We investigated the phase separation behavior of multi-component oxide glasses for coating layer of sanitary wares, and the holding time dependence of the microstructure and the coloring nature of phase separated glasses. Two kinds of multi-component silicate glasses (CaO-SiO2-Al2O3-MgO-ZnO-K2O-Na2O system) were employed, which had different CaO/SiO2 ratio. Glass A has higher CaO/SiO2 ratio, and glass B has lower CaO/SiO2. Quenched glasses that were pre-melted at 1550 °C for 90 min in advance, were isothermally held at 800~1100 °C for 0.5~2 h by the hot-thermocouple. The microstructure of phase-separated glass was observed by using FE-SEM on the polished section. It was found that the glass A and B heat-treated at given temperatures indicated a spinodal and a binodal type phase separation, respectively. Moreover, the glass A was found to have the larger microstructure of phase separation, which caused whitish color. In contrast, the glass B revealed the finer binodal phase separation that resulted in a bluish phase separated glass.