Low Melting Point Oxide Research Articles

Simultaneously enhancing heat resistance and mechanical performance for phthalonitrile through in-situ formation of inorganic protective layer derived from low melting point oxide

Simultaneously enhancing heat resistance and mechanical performance for phthalonitrile through in-situ formation of inorganic protective layer derived from low melting point oxide

Synthesis of low-temperature sintered M-type barium ferrites with enhanced microstructure, magnetic and dielectric properties

M-type barium ferrites (BaM) are utilized in the preparation of ferrite circulators due to their excellent magnetic properties. However, high sintering temperature of BaM is one of the major problems unsuitable for actual production requirements. In this study, Bi3+ ions from the low-melting point oxide bismuth(III) oxide (Bi2O3) were made to substitute Fe3+ ions to reduce the sintering temperature and control the magnetic properties. Addition of an appropriate content of Bi3+ ions at the sintering temperature of 900 °C led to the disappearance of the second phase, and a pure BaBix(CoTi)1.2Fe9.6−xO19 phase was formed. The results exhibited the existence of dense microstructure in BaM ceramics. Moreover, when the x value of Bi2O3 was 0.45, the permeability of the sample increased from 12.59 to 21.6 at 10 MHz, the saturation magnetization reached 3313.34 gauss, and the permittivity increased from 10.75 to 21.24. Permeability and permittivity were found to be approximately equal. Interestingly, addition of excessive Bi2O3 led to the formation of the second phase, and the microstructure exhibited the appearance of abnormal grains. However, BaM still maintained acceptable magnetic properties. The results showed that the addition of Bi3+ ions could reduce the sintering temperature of the ferrite and simultaneously adjust the magnetic and dielectric properties. Therefore, this material may have good performance in the preparation of ferrite circulators.

Ablation Behavior of Zr–Al(Si)–C Layered Carbides Modified 3D Needled C/SiC Composites

3DN C/SiC composites modified through the combined method of slurry impregnation (SI) with reactive melt infiltration (RMI) can obtain obviously improved mechanical properties. However, when used under the oxyacetylene torch ablation environment, metal melt and low melting point oxides usually lead to the low ablative properties. In this paper, Al40Si60 alloy and Si melt are used to infiltrate 3DN C/SiC preforms impregnated with TiC or ZrC powders, respectively. Large amount of Ti3Si(Al)C2 or Zr3Al3C5 (and Zr3[Al(Si)]4C6) with nano‐laminated structure generated in the modification matrix, which not only increase the flexural strength of the composites, but also reduce the content of low melting point phases in the modification matrix. These layered carbides can keep steady under air flow, thus further improve material's ablative properties. Meanwhile, during the ablation of Zr–Al(Si)–C layered carbides modify 3D needled C/SiC, the high melting point layered carbides act synergistically with the high melting point ZrO2 generated. They can block the ZrO2 generated from migrating along with the air flow, so that ZrO2 can effectively act its pinning effect on the oxide melt and finally obtain desirable ablative properties.

Reduction of Intergranular Exchange Coupling for CoPt–B2O3 Granular Media by Employing a RuCoCr-Oxide Buffer Layer With Oxide of Various Melting Points

CoPt-oxide granular films have been widely used for perpendicular magnetic recording media. To further increase recording density of the media, enhancement of magnetocrystalline anisotropy $(K_{u})$ to overcome the thermal stability issue and reduction of media noise to increase signal-to-noise-ratio are essential. The requirements can be realized through the promotion of columnar growth of magnetic grains which are phase separated with oxide boundary material and intergranular exchange decoupling 1), respectively. Generally, for the grain boundary materials of the granular media, oxides with amorphous phase which do not dissolve into CoPt metal have been utilized. The oxide is expected to segregate into the trench of Ru underlayer so that CoPt grains can grow heteroepitaxially on the bump of Ru underlayer. Many authors have proposed various kinds of oxide materials to be segregated into the grain boundaries, like SiO 2 2), TiO 2 3), Ta 2 $\mathrm {O}_{5}^{3)}$, Nb 2 $\mathrm {O}_{5}^{4)}$, WO 3 4), MgO 5), Cr 2 $\mathrm {O}_{3}^{5)}$, and $\mathrm {Y}_{2} \mathrm {O}_{3}^{5)}$. Previously, we had found that a granular medium with high magnetocrystalline anisotropy $(K_{u})$ was successfully realized when B 2 O 3 was applied for the grain boundary material 6). However, the separation between magnetic grains at the initial growth region in the Ru trench by low melting point oxide such as B 2 O 3 is not sufficient 7). Therefore, we have carried out an investigation on the deposition of a buffer layer (BL) with non-ferromagnetic metal and oxides of various melting points $(T_{m})$ on the Ru underlayer to grow the non-ferromagnetic metal and oxide on the Ru bump and trench, respectively, aiming to intergranular exchange decouple the magnetic grains. In this paper, we will discuss about the effect of utilizing BL with oxide of various $T_{m}$ on the intergranular exchange decoupling of CoPt$- \mathrm {B}_{2} \mathrm {O}_{3}$ granular media in relation with magnetic properties.

Design, formation, and property of high emissivity WSi2-Si-glass hybrid coating on fibrous ZrO2 ceramic for reusable thermal protection system

The objective of this research was to develop a high emissivity coating on the low thermal conductive insulation for reusable thermal protection system. The design principles including high emissivity, match of the coefficients of thermal expansion and excellent high temperature stability were proposed for the first time. A novel WSi2-Si-glass hybrid coating with optimized composition was successfully prepared on fibrous ZrO2 ceramic insulation by slurry dipping and subsequent high temperature rapid sintering method. The total emissivity of the as-prepared coating is up to 0.92 in wavelength of 0.3–2.5µm. After oxidation at 1673K for 100h and 1773K for 20h, the total emissivity values of the coatings are still as high as 0.89 and 0.87. A competitive mechanism between the “defects formation” caused by aging stress, the CTE mismatch stress and the volatilization of low melting point oxides and the “defects healing” resulted from self–healing phases during the different oxidizing conditions was discussed.

Effect of basicity and B2O3 on the viscosity and structure of fluorine-free mold flux

The effect of basicity (weight ratio of CaO/SiO2) and B2O3 on the viscosity and structure of Fluorine-free mold flux for the casting of medium carbon steels was conducted in this article, through the rotating cylinder method combined with the Fourier transform infrared (FTIR) spectroscopy. The results showed that, with the increase of basicity, the viscosity of mold flux was attenuated dramatically, and then kept constant or slight increased in the low temperature region. The reason could be explained as the degree of polymerization (DOP) of the network structure was first reduced significantly with the addition of basicity, and then the further depolymerization is less pronounced with the further increase of basicity. Beside the formation of high melting point substance leads to the slight increase of viscosity. Moreover, it suggested that the viscosity of mold flux is decreased with the addition of B2O3 content, due to the fact that B2O3 is a low melting point oxide which could substantially lower the break temperature of mold flux. The result of FTIR indicated B2O3 acts as network former, and tends to form [BO3]-trihedral and [BO4]-tetrahedral structural units, which would connect with each other to form some simple network structure such as diborate or pentaborate. With the addition of B2O3, the free oxygen ions (O2−) would depolymerize the diborate structural unit, and the depolymerized diborate would link again with free [BO3]-trihedral to form complex pentaborate groups. Moreover, the effect of above addition on the apparent activation energy for viscous flow and break temperature of mold flux also were discussed. The results obtained in this paper provide the detailed study of the structure evolution of Fluorine-free mold flux when B2O3 is added.

Effects of Additives Content on the Properties of Porous SiC Ceramics

The porous silicon carbide ceramics were fabricated by adding a variety of low melting point oxides in this paper. The additives were mullite, magnesium oxide, calcium oxide, and vanadium oxide. Effects of the additives content on the properties of porous silicon carbide ceramics were studied. The results showed that, when the additives content was greater than 2.8%, the apparent porosity, the bending strength, the permeability and the pore size were in an inversely proportional relationship with the additives content, while the content was less than 2.8%, proportional relationship was observed. When the additives content reached 2.8%, the porous SiC ceramics showed the best performances.

Magnetic properties and densification of Manganese–Zinc soft ferrites (Mn 1-xZn xFe 2O 4) doped with low melting point oxides

Mn–Zn ferrites have high electrical resistivity, low power loss and high initial permeability up to several MHz range. Oxide additives can greatly affect the magnetic properties of these ferrites. The effects of the additives on the sintering behaviour and magnetic properties of Mn–Zn ferrites are different. Some low melting point additives such as Bi 2O 3 enhance the sintering by forming a liquid phase in the ferrites. The additive V 2O 5 enhances the sintering by increasing bulk diffusion due to the increased vacancy concentration which is accompanied by the solubility of V 5+ in the ferrites. Some additives are cations that are soluble in the host lattice and enter regular positions on the tetrahedral or octahedral sites. This paper investigates the effect of several low melting point oxides on the magnetic properties, microstructure and densification of Mn–Zn soft ferrites.

Deformation and Fracture Behavior of Surface Oxide Scale on Fe-13Cr Alloy in Hot-Rolling Process

The behavior of the surface oxide scale on steel products during hot rolling process influences the surface properties of final products. To investigate the deformation and the fracture behavior of surface oxide scale of Fe-13Cr alloy, a hot rolling test was carried out. The oxide scale rolled out was observed in detail by using TEM. The specimen was hot-rolled after oxidation at 1100 for 90 minutes in air. The hot rolling tests with two conditions (. The hot rolling test of the outer scale {=whole layer scale} , . The hot rolling test of the inner scale that removed the outer scale) were carried out. The rolling reduction rate was 25, 44, 58, and 68%. The outer scale was composed of Fe2O3 and F3O4, and the inner scale was composed of Fe3O4, FeCr2O4, and a small amount of Fe2SiO4. Fe2SiO4 formed along the grain boundaries of the other oxides (Fe3O4, FeCr2O4) was observed by TEM. In the test , Fe2O3 of the outer scale was pulverized to fine particle that looks like red powder, and Fe3O4 of the outer scale was cracked by hot rolling. A ductility-like behavior was observed in the inner scale (Test ). That is, it was found by the SEM observation that porosity and micro cracks of the surface oxide disappeared gradually according to the increase in the rolling reduction. It was thought that the porosity and the micro cracks eased the compression stress caused by hot rolling. In the case of high reduction rate, FeSi2O4 ,which is a low melting point oxide, formed on grain boundary caused grain boundary slipping. When the rolling reduction is very high, plastic deformation by dislocation occurred in Fe3O4 and FeCr2O4. However, these oxides were broken, when their plasticity would not be able to accept considerably high rolling reduction.

Electrical Behavior of BaO-Nd2O3-Sm2O3-TiO2 with Glass/Oxide Additives Analyzed by Impedance Spectroscopy

The electrical properties of BaO-Nd2O3-Sm2O3-TiO2 ceramics doped with low loss glass or low melting point oxide B2O3 are evaluated by impedance spectroscopy. Glass or B2O3 is doped as liquid phase sintering aid. Doping of glass/B2O3 enhances both the growth in the longitudinal direction of the columnar crystal and the preferred orientation of (002). The grain size increases and grain boundary decreases with the increase of dopant. Both the grain and grain-boundary resistivities decrease with the increase of dopant. The grain boundary activation energy for charge transport is larger than that of the grain activation energy. Possible mechanisms for the electrical behavior of the liquid-phase sintered BaO-Nd2O3-Sm2O3-TiO2 ceramics are proposed and discussed.

Influence of Liquid Phase Additives on Structural and Sintering Behaviour of Samarium Modified Lead Titanate Ceramics

The combination of metal oxides Bi2O3:Li2O in a ratio 89:11 gives a eutectic with a melting point of ∼680°C. Such a low melting point oxide combination creates a working liquid phase at a highly favorable temperature for use as a densification aid. A liquid—phase sintering aid incorporating Bi2O3 and Li2O is presented which demonstrates not only a reduction in the required sintering temperature but also shows relatively higher ‘c/a’ ratio (tetragonality) of PbTiO3 ceramics with no fragility of the samples. Detailed dilatometric investigations have been performed in order to study the dominant shrinkage mechanism in the present system. Besides acting as a liquid phase fluxing agent, Bi2O3/Li2O also behave as Curie shifter, which decreases Curie temperature in lead titanate system. The Curie temperature has also been verified from the thermal expansion behavior of sintered specimens. The value of dielectric constant increases after poling which may be due to the dominance of 180° domain wall over 90°.

Solid state reactions in Mg mechanically alloyed with addition of low melting point oxides : A. Yamazaki et al. (Nihon University, Narashino, Japan.) J. Japan Soc. Powder/Powder Metall., Vol 48, No 5, 2001, 397–403. In Japanese

Solid state reactions in Mg mechanically alloyed with addition of low melting point oxides : A. Yamazaki et al. (Nihon University, Narashino, Japan.) J. Japan Soc. Powder/Powder Metall., Vol 48, No 5, 2001, 397–403. In Japanese

Volatile Surfactant-Assisted MOCVD: Application to LaAlO3 Thin-Film Growth

A new approach to the CVD of oxides with kinetically hindered diffusion, called volatile surfactant-assisted (VSA) metal-organic chemical vapor deposition (MOCVD), consisting of film deposition in the presence of a volatile low melting point oxide (Bi 2 O 3 ) has been developed. The process was applied to the deposition of LaAlO 3 films, and a model of the process was proposed. Epitaxial and textured LaAlO 3 films on various substrates were obtained, both by thermal and VSA MOCVD. A marked improvement in crystalline quality and surface morphology was found for the films deposited by VSA MOCVD. LaAlO 3 films obtained in the presence of Bi 2 O 3 did not contain Bi. A significant increase (up to five times) of the deposition rate was observed for LaAlO 3 films deposited by VSA MOCVD compared with that for the films grown by thermal MOCVD.

Monolayer dispersion of MoO 3, NiO and their precursors on γ-Al 2O 3

The dispersion capacities of MoO 3, NiO and their precursors on the surface of γ-Al 2O 3 are studied by XPS and XRD techniques. As a relatively low melting point oxide, MoO 3 gives a dispersion capacity higher than its precursor molybdate based on mole of MoO 3 on γ-Al 2O 3. Dispersion capacities of molybdate on γ-Al 2O 3 depend on the pH of molybdate solution used for impregnation while the dispersion capacity of MoO 3 on γ-Al 2O 3 is independent of its precursors. As a high-melting point oxide, the dispersion capacity of NiO based on mole of NiO is the same as that of its precursor. By one-step impregnation, dispersion capacity of nickel nitrate and its derived NiO on γ-Al 2O 3is larger than that of nickel acetate and its derived NiO. This difference can be attributed to the larger size of nickel acetate molecule. The utmost dispersion capacity of NiO on γ-Al 2O 3 is achieved through one-step impregnation when nickel nitrate is used as the precursor, while the same capacity can only be achieved through multiple impregnation when nickel acetate is used as the precursor.

磁石・磁性材料の化学 Ｉ 低温焼成・無収縮Ｎｉ‐Ｃｕ‐Ｚｎフェライト材料

We have developed a Non-Shrinkage Ferrites “NSF” having near-net-shape by adding metallic Fe and sintered at high temperature (about 1200°C). In this work, we report low temperature (under the melting point of Ag, 960°C) sintered NSF. The control of the degree of NSF shrinkage is possible through utilizing both the expansion caused by the oxidation of metallic Fe and the complex chemical reaction allowed with NiO, ZnO, and CuO during sintering up to 920°C. In the case of low temperature sintering, high density NSF cannot be realized because non-uniform grain caused by the extreme oxidation of metallic Fe remains. It is found that addition of low-melting point oxides to the NSF permits effectively the NSF's microstructure to make uniform and compact. XRD and VSM show these NSF have the complete spinel crystal structure of ferrite. As a result, the shrinkage of low temperature sintered NSF is extremely small (-0.4%) and their magnetic characteristics are actually identical with those of conventional low temperature sintered ferrites.

Low voltage varistors based on SrTiO 3 ceramics

Varistors exhibiting nonlinear resistance at low voltages of 4.5 to 30 V mm −1 have been realised from SrTiO 3 ceramics. These are processed from powders obtained from the gel-crystallite conversion technique. Doping with ≲ 1% Y 3+ enhances the average grain size to over 50,um, when sintered around 1650 K in static air. On annealing the ceramics, in N 2 + H 2 atmospheres, they acquire a low resistivity of 0.4 to 3.7 Ω cm with positive temperature coefficient of resistance. They are painted with low melting point oxide mixtures of PbO + Bi 2O 3 + B 2O 3 and re-annealed. The energy dispersive X-ray results indicate selective melting reactions at the grain boundary layers with higher concentrations of the low melting point oxide constituents. The abnormally high dielectric constants, ε λ = 10 4 to 10 5, point to the prevalence of GBL capacitance in these ceramics. Depending upon the conditions of the second annealing, the breakdown voltage could be adjusted from 0.2 to 1.5 V per grain boundary, without any change in the grain size. The nonlinearity coefficient a ranges from 6 to 15 and the barrier height from 0.15 to 0.3 eV This can be explained on the basis of variable pinning of traps at the interface and also the extent of trap filling.

Carbon oxidation catalyzed by low melting point oxide phases

Carbon oxidation catalyzed by low melting point oxide phases