scholarly journals Synthesis of Silicon Carbide Powders from Methyl-Modified Silica Aerogels

2020 ◽  
Vol 10 (18) ◽  
pp. 6161
Author(s):  
Kyoung-Jin Lee ◽  
Yanggu Kang ◽  
Young Hun Kim ◽  
Se Won Baek ◽  
Haejin Hwang
Keyword(s):  
Silicon Carbide ◽  
High Purity ◽  
Silica Aerogel ◽  
Carbothermal Reduction ◽  
Single Phase ◽  
Phase Evolution ◽  
Silica Aerogels ◽  
Methyl Groups ◽  
Modified Silica ◽  
Lower Temperature

β-silicon carbide (SiC) powders were synthesized by the carbothermal reduction of methyl-modified silica aerogel/carbon mixtures. The correlations between the phase evolution and morphologies of the SiC powders and the C/SiO2 ratio were investigated. At a C/SiO2 ratio of 3, β-SiC formed at 1425 °C and single-phase SiC powders were obtained at 1525 °C. The methyl groups (-CH3) on the silica aerogel surfaces played important roles in the formation of SiC during the carbothermal reduction. SiC could be synthesized from the silica aerogel/carbon mixtures under lower temperature and C/SiO2 ratios than those needed for quartz or hydrophilic silica. The morphology of the SiC powder depended on the C/SiO2 ratio. A low C/SiO2 ratio resulted in β-SiC powder with spherical morphology, while agglomerates consisting of fine SiC particles were obtained at the C/SiO2 ratio of 3. High-purity SiC powder (99.95%) could be obtained with C/SiO2 = 0.5 and 3 at 1525 °C for 5 h.

Fabrication of SiC by Carbothermal-Reduction Reactions of Sepiolite

2007 ◽  
Vol 555 ◽  
pp. 261-265 ◽  
Author(s):  
A. Devečerski ◽  
A. Radosavljević-Mihajlović ◽  
A. Egelja ◽  
M. Pošarac ◽  
B. Matović
Keyword(s):  
Silicon Carbide ◽  
Carbothermal Reduction ◽  
Phase Evolution ◽  
Reducing Agent ◽  
Phase Content ◽  
Reduction Reactions ◽  
Effective Source

The objective of this manuscript was to investigate the synthesis of SiC by carbothermal– reduction reactions of sepiolite. Sepiolite of Serbian origin and carbon (from various precursors) as a reducing agent were used. The green bodies with various C/SiO2 ratios were carbonized at 1073 K and heattreated at 1673 K in a controlled Ar flow atmosphere. Phase evolution and phase content were followed as a function of C/SiO2 ratio and carbon origin. The starting materials and products were characterized by means of XRD and SEM. The results show that sepiolite can be very effective source for obtaining silicon carbide powders.

Sintering and Microstructural Modification of Seeded and Neodymium Doped Lanthanum Hexaaluminate

2016 ◽  
Vol 835 ◽  
pp. 237-250 ◽  
Author(s):  
P. Jana ◽  
P.S. Jayan ◽  
S. Mandal ◽  
Koushik Biswas
Keyword(s):  
Rare Earth ◽  
Heterogeneous Nucleation ◽  
Single Phase ◽  
Sol Gel ◽  
Phase Evolution ◽  
Neodymium Oxide ◽  
Lower Temperature ◽  
House Structure ◽  
Gel Processing ◽  
Lanthanum Hexaaluminate

The effect of (i) heterogeneous nucleation by seeding or (ii) doping with neodymium on the formation of lanthanum hexaaluminate was studied during sol to gel conversion. The resultant dried gels were calcined at various temperatures starting from 1100°C to 1600°C for 2 h to study the phase evolution and microstructure.The combined effects of advanced sol gel processing and heterogeneous nucleation promoted the formation of lanthanum hexaaluminate phase at lower temperature (1200°C) than the conventional routes (1300°C). Lanthanum hexaaluminate phase was detected at 1200°C and 1300°C in seeded gel (SG) and unseeded gel (UG), respectively. Heterogeneous nucleation of SG decreases the temperature of formation of lanthanum hexaaluminate by 100°C. Single phase lanthanum hexaaluminate was formed at 1600°C in seeded gel whereas trace of lanthanum monoaluminate phase was still present in UG even at 1600°C.On the doped ones, randomly grown platelets of lanthanum magnesium hexaaluminate form a porous interlocking structure. Presence of various percentages of neodymium oxide significantly modifies the porous interlocking microstructure into self-reinforced, card-house like microstructure. Platelets of rare earth rich magnesium hexaaluminate were grown preferentially more than the stoichiometric rare earth magnesium hexaaluminate at elevated temperature greater than 1450°C. Rare earth rich magnesium hexaaluminate platelets formed the skeleton of a card house structure and the tiny platelets of stoichiometric rare earth magnesium hexaaluminate fill the rest. Lattice parameters of the hexagonal unit cell (c and a) decrease, relative density increases and pore size distribution remained almost unaltered with the increment of doping concentration.

scholarly journals Performance of silica aerogels modified with amino functional groups in PB(II) and CD(II) removal from aqueous solutions

2012 ◽  
Vol 14 (1) ◽  
pp. 50-56 ◽  
Author(s):  
Hossein Faghihian ◽  
Heshmatollah Nourmoradi ◽  
Maryam Shokouhi
Keyword(s):  
Aqueous Solutions ◽  
Functional Groups ◽  
Silica Aerogel ◽  
Contact Time ◽  
Silica Aerogels ◽  
Adsorption Behavior ◽  
Modified Silica ◽  
Freundlich Isotherms ◽  
Adsorbate Concentration ◽  
Removal Of Metal Ions

Performance of silica aerogels modified with amino functional groups in PB(II) and CD(II) removal from aqueous solutions The adsorption behavior of Pb(II) and Cd(II) ions in aqueous solutions on silica aerogels modified with amino propyl triethoxysilane was investigated as a function of pH, contact time, adsorbate concentration and adsorbent dose. It was found that maximum adsorption of Pb(II) and Cd(II) ions occurs at pH 6.0 and pH 8.0, respectively. The optimum contact time to obtain equilibrium adsorption with the modified silica aerogel was experimentally found to be around 48h. Adsorption isotherms clearly indicated that the adsorption behavior of metals ions on the modified silica aerogels is fitted well with both the Langmuir and Freundlich isotherms. The maximum adsorption capacities of Pb(II) and Cd(II) on modified silica aerogel were found to be 45.45mg/g and 35.71mg/g, respectively. The results indicated that silica aerogels modified with amino functional groups can be used as an efficient adsorbent in the removal of metal ions such as Pb(II) and Cd(II) from aqueous solutions.

Synthesis of high‐purity high‐entropy metal diboride powders by boro/carbothermal reduction

2019 ◽  
Vol 102 (12) ◽  
pp. 7071-7076 ◽  
Author(s):  
Da Liu ◽  
Honghua Liu ◽  
Shanshan Ning ◽  
Beilin Ye ◽  
Yanhui Chu
Keyword(s):  
High Purity ◽  
Carbothermal Reduction ◽  
High Entropy

EFFECT OF MEAN ION SIZE AND SPATIAL SPIN DISORDERS FOR (La1-xYx)2/3Ca1/3MnO3 MANGANITES

2004 ◽  
Vol 18 (26) ◽  
pp. 3451-3464 ◽  
Author(s):  
JINCANG ZHANG ◽  
YUFENG ZHANG ◽  
SHIXUN CAO ◽  
CHAO JING
Keyword(s):  
Single Phase ◽  
Bond Angle ◽  
Gradual Increase ◽  
High Concentration ◽  
Magnetic Studies ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Average Ionic Radius ◽  
Lower Temperature ◽  
Ion Size

The structure and transport properties of perovskite ( La 1-x Y x)2/3 Ca 1/3 MnO 3 (0≤x≤0.3) systems are systematically investigated. It is found that all the specimens show a single-phase structure and reveal a direct relationship between the Curie temperature Tc and the average ionic radius <rA> of La site. With increasing Y 3+ doped content, the metal-insulator transition temperature T MI (M-I) shifts to lower temperature. While the relevant resistivity peak ρp is sharp increased, for the specimens with large doping content, x=0.3, it has enhanced eight orders of magnitudes larger than the non-doped samples (x=0.0). At high concentration area, that is to say, when x>0.1, magnetic studies show a gradual increase of antiferromagnetic interaction with an increase of x, ultimately leading to a spatial-spin disorders, that is, spin-glass-like state for x=0.2 and x=0.3 compounds at about 35 K. The results show that it has connected a reduction of Tc and an increase in magnetoresistance with a decrease in the microstructural Mn - O - Mn bond angle.

scholarly journals Magnetic properties of the natural and isotope-modified diamond and silicon carbide

2018 ◽  
Vol 185 ◽  
pp. 04007 ◽  
Author(s):  
A.N. Taldenkov ◽  
A.V. Inyushkin ◽  
E.A. Chistotina ◽  
V.G. Ralchenko ◽  
A.P. Bolshakov ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
Magnetic Properties ◽  
Isotopic Composition ◽  
Single Crystals ◽  
High Purity ◽  
Diamagnetic Susceptibility ◽  
Synthetic Diamond ◽  
Paramagnetic Centers ◽  
Natural Isotopic Composition ◽  
Ferromagnetic Component

The magnetic properties of single crystals of synthetic diamond and crystals of silicon carbide were studied. High-purity samples of diamonds synthesized with HPHT and CVD technologies were used. The crystals of silicon carbide were grown by sublimation and industrial technology. Along with samples with a natural isotopic composition, monoisotopic crystals of diamond (99.96% 12C and 99.96% 13C) and silicon carbide (99.993% of 28Si) were studied. On the basis of the data obtained, the diamagnetic susceptibility was determined and the concentration of paramagnetic centers and the content of the ferromagnetic component were evaluated. The results are discussed.

scholarly journals Silica Aerogel Monoliths Derived from Silica Hydrosol with Various Surfactants

Molecules ◽  
2018 ◽  
Vol 23 (12) ◽  
pp. 3192 ◽  
Author(s):  
Dong Chen ◽  
Xiaodong Wang ◽  
Wenhui Ding ◽  
Wenbing Zou ◽  
Qiong Zhu ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Stability ◽  
Silica Aerogel ◽  
Low Cost ◽  
Ambient Pressure ◽  
Silica Aerogels ◽  
Ambient Pressure Drying ◽  
Low Thermal Conductivity ◽  
Silica Hydrosol ◽  
High Production Cost

Owing to their ultra-low thermal conductivity, silica aerogels are promising thermal insulators; however, their extensive application is limited by their high production cost. Thus, scientists have started to explore low-cost and easy preparation processes of silica aerogels. In this work, a low-cost method was proposed to prepare silica aerogels with industrial silica hydrosol and a subsequent ambient pressure drying (APD) process. Various surfactants (cationic, amphoteric, or anionic) were added to avoid solvent exchange and surface modification during the APD process. The effects of various surfactants on the microstructure, thermal conductivity, and thermal stability of the silica aerogels were studied. The results showed that the silica aerogels prepared with a cationic or anionic surfactant have better thermal stability than that prepared with an amphoteric surfactant. After being heated at 600 °C, the silica aerogel prepared with a cationic surfactant showed the highest specific surface area of 131 m2∙g−1 and the lowest thermal conductivity of 0.038 W∙m−1∙K−1. The obtained low-cost silica aerogel with low thermal conductivity could be widely applied as a thermal insulator for building and industrial energy-saving applications.

Sign in / Sign up

Export Citation Format

Share Document