Effect of Carbothermal Reduction Nitriding of Si/SiO2 Composite Green on Properties of Fused Silica Ceramics

2020 ◽  
Vol 12 (7) ◽  
pp. 934-938
Author(s):  
Liang Tian ◽  
Qinglin Hou ◽  
Yingxia Wang ◽  
Yihui Hou ◽  
Tao Chen
Keyword(s):  
High Temperature ◽  
Carbothermal Reduction ◽  
Fused Silica ◽  
Solid Content ◽  
Nitrogen Compounds ◽  
Green Body ◽  
Nitriding Reaction ◽  
Different Temperatures ◽  
Silica Ceramic

Si/SiO2 composite green body with solid content of 50% was prepared by low toxic gel system and sintered in nitrogen at high temperature. Nitrogen compounds were synthesized in situ on fused silica ceramic substrate. The influence of different temperatures on nitriding reaction was discussed: different temperatures were used for nitriding at 1350 °C, 1400 °C, 1450 °C, 1500 °C. The effect of different nitriding times on nitriding reaction was discussed: different holding times were used for nitriding +1 h, 1.5 h, 2 h and 2.5 h. The best nitriding process was obtained by analyzing the composition, microstructure and properties of the nitrided samples.

Thermodynamic Evaluation for the Synthesis of T2 Phase from Elemental Powders via In Situ Reactively Hot-Pressing

2012 ◽  
Vol 538-541 ◽  
pp. 2082-2085
Author(s):  
Lai Qi Zhang ◽  
Lei Huang ◽  
Yong Ming Hou ◽  
Jun Pin Lin
Keyword(s):  
High Temperature ◽  
Hot Pressing ◽  
Initial Temperature ◽  
Adiabatic Temperature ◽  
Advanced Technology ◽  
Thermodynamic Evaluation ◽  
Temperature Synthesis ◽  
High Temperature Synthesis ◽  
Different Temperatures

T2 phase(Mo5SiB2) is a key component of the two Mo-Si-B tri-phase alloys under hot research. However, there is little research on T2 phase, especially its mechanic characteristics, due to the difficulty of fabrication of pure T2. In this present work, the thermodynamics of an advanced technology to fabricate pure T2 phase i.e. IRHP (In-situ Reactively Hot-Pressing) using elemental powders was analyzed. Formation free enthalpies at different temperatures for the compounds in Mo-Si-B system were calculated. Adiabatic temperatures and molten fractions of T2 phase at different initial temperatures for the reaction of synthesizing T2 phase were evaluated. The results show that it is feasible to in-situ synthesize T2 phase from elemental powders. T2 phase can not be synthesized using SHS(Self-propagating High-temperature Synthesis) mode of combustion. On the contrary, the explosion mode of combustion (IRHP) is receivable. Adiabatic temperature and molten fraction of T2 phase are relevant to initial temperature.

scholarly journals Influence of Al2O3 content on mechanical properties of silica-based ceramic cores prepared by stereolithography

2021 ◽  
Author(s):  
Wen Zheng ◽  
Jia-Min Wu ◽  
Shuang Chen ◽  
Chang-Shun Wang ◽  
Chun-Lei Liu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Flexural Strength ◽  
Room Temperature ◽  
Linear Shrinkage ◽  
Fused Silica ◽  
Al2o3 Content ◽  
High Temperature Mechanical Properties ◽  
Silica Ceramic ◽  
Excellent Chemical

AbstractSilica ceramic cores have played an important part in the manufacture of hollow blades due to their excellent chemical stability and moderate high-temperature mechanical properties. In this study, silica-based ceramics were prepared with Al2O3 addition by stereolithography, and the influence of Al2O3 content on mechanical properties of the silica-based ceramics was investigated. The Al2O3 in silica-based ceramics can improve the mechanical properties by playing a role as a seed for the crystallization of fused silica into cristobalite. As a result, with the increase of Al2O3 content, the linear shrinkage of the silica-based ceramics first decreased and then increased, while the room-temperature flexural strength and the high-temperature flexural strength first increased and then decreased. As the Al2O3 content increased to 1.0 vol%, the linear shrinkage was reduced to 1.64% because of the blocked viscous flow caused by Al2O3. Meanwhile, the room-temperature flexural strength and the high-temperature flexural strength were improved to 20.38 and 21.43 MPa with 1.0 vol% Al2O3, respectively, due to the increased α-cristobalite and β-cristobalite content. Therefore, using the optimal content of Al2O3 in silica-based ceramics can provide excellent mechanical properties, which are suitable for the application of ceramic cores in the manufacturing of hollow blades.

scholarly journals In-Situ Isothermal Crystallization of Poly(l-lactide)

Polymers ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 3377
Author(s):  
Zirui Huang ◽  
Meiling Zhong ◽  
Haibo Yang ◽  
Enqin Xu ◽  
Dehui Ji ◽  
...  
Keyword(s):  
High Temperature ◽  
Nucleation Rate ◽  
Low Temperatures ◽  
Isothermal Crystallization ◽  
The Other ◽  
Wide Angle ◽  
X Ray Diffraction ◽  
X Ray ◽  
Different Temperatures

The isothermal crystallization of poly(l-lactide) (PLLA) has been investigated by in-situ wide angle X-ray diffraction (WAXD) and polarized optical microscopes (POM) equipped with a hot-stage accessory. Results showed that the spherulites of PLLA were formed at high temperature, whereas irregular morphology was observed under a low temperature. This can be attributed to the varying rates of crystallization of PLLA at different temperatures. At low temperatures, the nucleation rate is fast and hence the chains diffuse very slow, resulting in the formation of imperfect crystals. On the other hand, at high temperatures, the nucleation rate is slow and the chains diffuse fast, leading to the formation of perfect crystals. The change in the value of the Avrami exponent with temperature further verifies the varying trend in the morphological feature of the crystals.

scholarly journals High-temperature Fe oxidation coupled with redistribution of framework cations in lobanovite, K2Na(Fe2+ 4Mg2Na)Ti2(Si4O12)2O2(OH)4 – the first titanosilicate case

2019 ◽  
Vol 75 (4) ◽  
pp. 578-590 ◽  
Author(s):  
Elena S. Zhitova ◽  
Andrey A. Zolotarev ◽  
Frank C. Hawthorne ◽  
Sergey V. Krivovichev ◽  
Viktor N. Yakovenchuk ◽  
...  
Keyword(s):  
High Temperature ◽  
Elevated Temperatures ◽  
Iron Oxidation ◽  
Ex Situ ◽  
X Ray Diffraction ◽  
X Ray ◽  
Different Temperatures ◽  
Bond Strengths ◽  
Increasing Temperature

The high-temperature (HT) behaviour of lobanovite, K2Na(Fe2+ 4Mg2Na)Ti2(Si4O12)2O2(OH)4, was studied using in situ powder X-ray diffraction in the temperature range 25–1000°C and ex situ single-crystal X-ray diffraction of 17 crystals quenched from different temperatures. HT iron oxidation associated with dehydroxylation starts at 450°C, similar to other ferrous-hydroxy-rich heterophyllosilicates such as astrophyllite and bafertisite. A prominent feature of lobanovite HT crystal chemistry is the redistribution of Fe and Mg+Mn cations over the M(2), M(3), M(4) sites of the octahedral (O) layer that accompanies iron oxidation and dehydroxylation. This HT redistribution of cations has not been observed in titanosilicates until now, and seems to be triggered by the need to maintain bond strengths at the apical oxygen atom of the TiO5 pyramid in the heteropolyhedral (H) layer during oxidation–dehydroxylation. Comparison of the HT behaviour of lobanovite with five-coordinated Ti and astrophyllite with six-coordinated Ti shows that the geometry of the Ti polyhedron plays a key role in the HT behaviour of heterophyllosilicates. The thermal expansion, geometrical changes and redistribution of site occupancies which occur in lobanovite under increasing temperature are reported. A brief discussion is given of minerals in which the cation ordering (usually for Fe and Mg) occurs together with iron oxidation–dehydroxylation at elevated temperatures: micas, amphiboles and tourmalines. Now this list is expanded by the inclusion of titanosilicate minerals.

A Low-High Temperature Camera for In-Situ X-Ray Diffraction Studies of Catalysts

1983 ◽  
Vol 27 ◽  
pp. 285-291
Author(s):  
J. Pielaszek ◽  
J.B. Cohen
Keyword(s):  
High Temperature ◽  
Porous Silica ◽  
X Ray Diffraction ◽  
X Ray ◽  
Controlled Atmospheres ◽  
Research Areas ◽  
High Temperature Xrd ◽  
Different Temperatures ◽  
Porous Silica Glass

X-Ray diffraction studies of substances under controlled atmospheres and at different temperatures are of great importance in many research areas. This is especially true in the area of catalysis, where the correlation of structural and catalytic properties is needed. The camera described here was made for this purpose although any sample in the powdered form can be studied as well. Many catalysts are in the form of highly dispersed metal deposited on a granulated support. The content of metal may vary from a few tenths to several percent. In a camera used by Janko and Borodzinski a small amount of catalyst was spread out on a porous silica glass sample holder which then was placed in a high temperature XRD camera with flowing gas of controlled composition.

scholarly journals Elevated temperature, but not decreased pH, impairs reproduction in a temperate fish

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Ana F. Lopes ◽  
Ana M. Faria ◽  
Sam Dupont
Keyword(s):  
High Temperature ◽  
Elevated Temperature ◽  
Exposure Period ◽  
Low Ph ◽  
Paternal Investment ◽  
Reproductive Process ◽  
Different Temperatures ◽  
Temperate Fish ◽  
Near Future

AbstractFish reproductive success is linked to the ability of couples to mate and produce clutches that successfully hatch. Environmental stressors like high temperature and low pH can jeopardize this energetically costly process. In this study, exposure to high temperature and low pH was tested on a marine temperate species, Gobiusculus flavescens, to evaluate effects on reproductive performance. Breeding pairs were assigned to different temperatures (+ 0 °C, + 3 °C relative to in situ temperature) and pH levels (8.0, 7.6), in a cross-factorial design for a 3-month period. Reproduction activity, success, and paternal investment were measured throughout the exposure period. Results show reproduction is impaired by elevated temperature, while low pH had little impact. Breeding pairs under high temperature had 3% to 10% hatching success, up to 30% less eggs and eggs up to 20% smaller. Although paternal investment was not affected by tested parameters, males of breeding pairs exposed to elevated temperature had smaller gonadosomatic indexes, which might indicate a lack of investment in the reproductive process. Overall, results show that elevated temperature, expected more frequently in the near future, as a consequence of global warming, may impair key processes like reproduction in temperate fish, with potential consequences for fitness and population replenishment.

Inhibiting crystallization of fused silica ceramic at high temperature with addition of α-Si3N4

2020 ◽  
Author(s):  
Jun Liu ◽  
Qinghu Wang ◽  
Yawei Li ◽  
Xiong Liang ◽  
Xueqing Wang ◽  
...  
Keyword(s):  
High Temperature ◽  
Fused Silica ◽  
Silica Ceramic

The reaction of amorphous Ni-Nb films with Si in the presence of a native SiO2 layer

1990 ◽  
Vol 48 (4) ◽  
pp. 664-665
Author(s):  
N. Rozhanski ◽  
A. Barg
Keyword(s):  
High Temperature ◽  
Crystallization Temperature ◽  
Diffusion Barriers ◽  
Sio2 Layer ◽  
Si Substrate ◽  
Cross Sectional ◽  
Plan View ◽  
Temperature Range ◽  
Sputter Deposited

Amorphous Ni-Nb alloys are of potential interest as diffusion barriers for high temperature metallization for VLSI. In the present work amorphous Ni-Nb films were sputter deposited on Si(100) and their interaction with a substrate was studied in the temperature range (200-700)°C. The crystallization of films was observed on the plan-view specimens heated in-situ in Philips-400ST microscope. Cross-sectional objects were prepared to study the structure of interfaces.The crystallization temperature of Ni5 0 Ni5 0 and Ni8 0 Nb2 0 films was found to be equal to 675°C and 525°C correspondingly. The crystallization of Ni5 0 Ni5 0 films is followed by the formation of Ni6Nb7 and Ni3Nb nucleus. Ni8 0Nb2 0 films crystallise with the formation of Ni and Ni3Nb crystals. No interaction of both films with Si substrate was observed on plan-view specimens up to 700°C, that is due to the barrier action of the native SiO2 layer.

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