scholarly journals Specific surface area, crystallite size and thermokinetic of oxide formation γ → α-Al2O3 nano powders at 570 – 1470 K

Surface ◽  
2020 ◽  
Vol 12(27) ◽  
pp. 146-152
Author(s):  
V. V. Garbuz ◽  
◽  
V. A. Petrova ◽  
T. A. Silinskaya ◽  
T. F. Lobunets ◽  
...  
Keyword(s):  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
Arrhenius Law ◽  
Aluminum Boride ◽  
Oh Groups ◽  
Nitrogen Desorption ◽  
Α Al2o3 ◽  
Single Heating ◽  
Maximum Content

Powders where the γ≈α-Al2O3-nano phases are the priority precursors for catalysts for heterogeneous catalysis with the maximum content of surface 5-coordinated Al centers for Pt attachment. Hydrogenated nano powders (~8 nm) of γ-, γ '-, θ-, κ-Al2O3 soluble in hydrochloric acid were obtained from the processing of aluminum boride powders with an icosahedral structure. Samples, which underwent a step-by-step and single heating of 50-100K heat treatment for 2 hours at temperatures of 570-1470K, were received in quantity of 34. The specific surface area of SВET, m2g-1 was measured by the thermal nitrogen desorption express method of gas chromatography through the GC-1 device. X-ray (phase and coherent), fluorescence and phase chemical-analytical evaluation of the samples were performed. The thermokinetic characteristics of the processes are calculated using the exponential Arrhenius law. Dimensional characteristics of crystallites (10.4-48 nm); specific surface area of powders (213-8.6 m2g-1, SВET); thermokinetic parameters of α-Al2O3 crystallite growth process (V α-Al2O3 - 1.44 10-3 - 6.67 10-3 nm s-1; E α-Al2O3 = 38.7±2.1kJ mol-1; A0 = 0.16±0.0 s-1 along the temperature line 1220-1470K were determined and calculated. The process of dehydration of two OH-groups occurs in the region 570-720K Ea H2O ↑ = 30.5 ± 0.5 kJ mol-1 A0 = 1.33±0.3 s-1. The last group of OH at temperatures of 820 -1070К and a rate of 2.13 10-4 - 4.93 10-4 mol s-1 Ea H2O ↑ = 13.2 ± 0.8 kJ mol-1 A0 = 16.9 ± 0.9 s-1. The activation energy of the phase transition is Ea., γ → α-Al2O3 = 23.9 ± 1.0 kJ mol-1 A0 = 2.01 ± 0.72 s-1 (770-970K) and Ea., γ → α-Al2O3 = 83.5 ± 0.8 kJ mol-1 A0 =(2,05±0,95) 103 s-1 (1070-1170K). It agrees well with the known heat of conversion Eа, γ→α-Al2O3 = 85 kJ mol-1. The TK of γ≈α-Al2O3-nano phases is at 1170K.

scholarly journals The Influence of Oxygen Concentration during MAX Phases (Ti3AlC2) Preparation on the α-Al2O3 Microparticles Content and Specific Surface Area of Multilayered MXenes (Ti3C2Tx)

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 353 ◽  
Author(s):  
Błażej Scheibe ◽  
Vojtech Kupka ◽  
Barbara Peplińska ◽  
Marcin Jarek ◽  
Krzysztof Tadyszak
Keyword(s):  
Specific Surface ◽  
Surface Area ◽  
Oxygen Concentration ◽  
Specific Surface Area ◽  
High Specific Surface Area ◽  
Max Phase ◽  
Max Phases ◽  
Critical Feature ◽  
Al2o3 Particles ◽  
Α Al2o3

The high specific surface area of multilayered two-dimensional carbides called MXenes, is a critical feature for their use in energy storage systems, especially supercapacitors. Therefore, the possibility of controlling this parameter is highly desired. This work presents the results of the influence of oxygen concentration during Ti3AlC2 ternary carbide—MAX phase preparation on α-Al2O3 particles content, and thus the porosity and specific surface area of the Ti3C2Tx MXenes. In this research, three different Ti3AlC2 samples were prepared, based on TiC-Ti2AlC powder mixtures, which were conditioned and cold pressed in argon, air and oxygen filled glove-boxes. As-prepared pellets were sintered, ground, sieved and etched using hydrofluoric acid. The MAX phase and MXene samples were analyzed using scanning electron microscopy and X-ray diffraction. The influence of the oxygen concentration on the MXene structures was confirmed by Brunauer-Emmett-Teller surface area determination. It was found that oxygen concentration plays an important role in the formation of α-Al2O3 inclusions between MAX phase layers. The mortar grinding of the MAX phase powder and subsequent MXene fabrication process released the α-Al2O3 impurities, which led to the formation of the porous MXene structures. However, some non-porous α-Al2O3 particles remained inside the MXene structures. Those particles were found ingrown and irremovable, and thus decreased the MXene specific surface area.

Alteration of imogolite by dry grinding

Clay Minerals ◽  
1981 ◽  
Vol 16 (2) ◽  
pp. 139-149 ◽  
Author(s):  
Teruo Henmi ◽  
Naganori Yoshinaga
Keyword(s):  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
Layer Silicate ◽  
Oh Groups ◽  
X Ray ◽  
Dry Grinding ◽  
Structure Morphology ◽  
Complete Breakdown ◽  
Water Holding

AbstractThe effects of dry grinding on the structure, morphology and properties of imogolite have been investigated by means of X-ray powder diffraction analysis, IR, DTA, and measurements of CEC and specific surface area. Imogolite is very susceptible to alteration by grinding compared to layer silicate minerals such as halloysite, kaolinite and montmorillonite. In the earlier stages of grinding, the parallel array of imogolite tubular structure units is markedly disturbed. On further grinding, disruption of Si-O-Al linkages, polymerization of the silica component released and loss of structural OH groups proceed simultaneously, these changes eventually resulting in complete breakdown of the structure. Ground imogolite is reaggregated finally into granular particles of irregular shape. All these changes are associated with a decrease in water holding capacity, CEC and specific surface area.

scholarly journals Effect of Ethanol on the Morphology and Textual Properties of ZSM-5 Zeolite

Catalysts ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 198
Author(s):  
Xiuru Liu ◽  
Yiqing Sun
Keyword(s):  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
Crystal Size ◽  
Ethanol Concentration ◽  
Textural Properties ◽  
Oh Groups ◽  
And Diffusion

The morphology of ZSM-5 zeolite impacts the adsorption, separation and diffusion of molecules. The morphology and textural properties of ZSM-5 zeolites were adjusted by regulating the content of ethanol in the synthesis gel. When the ratio of ethanol/SiO2 was lower than 2, the obtained crystals were isolated particles. With higher ethanol concentration, the chainlike zeolite was generated due to the condensation of terminal Si-OH groups. The crystals stacked more and more compactly with the increase in ethanol concentration, resulting in decreased specific surface area, total volume and mesoporous volume. The crystal size increased gradually with the increase in the ethanol concentration. Moreover, some other small molecular alcohols could also induce the formation of chainlike morphology of ZSM-5.

scholarly journals Towards Macroporous α-Al2O3—Routes, Possibilities and Limitations

Materials ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1787
Author(s):  
Simon Carstens ◽  
Ralf Meyer ◽  
Dirk Enke
Keyword(s):  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
Sol Gel ◽  
Surface Areas ◽  
Alumina Membranes ◽  
Sol Gel Process ◽  
Specific Surface Areas ◽  
Α Al2o3 ◽  
Sol Gel Synthesis

This article combines a systematic literature review on the fabrication of macroporous α-Al2O3 with increased specific surface area with recent results from our group. Publications claiming the fabrication of α-Al2O3 with high specific surface areas (HSSA) are comprehensively assessed and critically reviewed. An account of all major routes towards HSSA α-Al2O3 is given, including hydrothermal methods, pore protection approaches, dopants, anodically oxidized alumina membranes, and sol-gel syntheses. Furthermore, limitations of these routes are disclosed, as thermodynamic calculations suggest that γ-Al2O3 may be the more stable alumina modification for ABET > 175 m2/g. In fact, the highest specific surface area unobjectionably reported to date for α-Al2O3 amounts to 16–24 m2/g and was attained via a sol-gel process. In a second part, we report on some of our own results, including a novel sol-gel synthesis, designated as mutual cross-hydrolysis. Besides, the Mn-assisted α-transition appears to be a promising approach for some alumina materials, whereas pore protection by carbon filling kinetically inhibits the formation of α-Al2O3 seeds. These experimental results are substantiated by attempts to theoretically calculate and predict the specific surface areas of both porous materials and nanopowders.

Preparation of Nanoscale High-Purity α-Alumina Powders

2007 ◽  
Vol 336-338 ◽  
pp. 2051-2053 ◽  
Author(s):  
Xiu Lan Wu ◽  
Qiang Ren ◽  
Xuan Meng He
Keyword(s):  
Heat Treatment ◽  
Phase Transformation ◽  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
High Purity ◽  
High Specific Surface Area ◽  
Aluminium Isopropoxide ◽  
Reaction Progress ◽  
Α Al2o3

High-purity nanoscale α-alumina powders with high specific surface area were prepared from boehmite powders synthesized by the method of aluminium isopropoxide hydrolysis. The physiochemical transformation of boehmite powders under heat-treatment was investigated. The results showed that the reaction progress of boehmite under heat-treatment is as follows: AlO(OH) → Al2O3 (amorphous) → γ-Al2O3 → δ-Al2O3 → α-Al2O3. The phase transformation from δ-Al2O3 to α-Al2O3 begins at 1050oC, and the α-Al2O3 grains growth accelerates as temperature increases. High-purity α-Al2O3 nanometer powders with higher specific surface area can be obtained after incineration at 1100oC for 4 h.

Synthesis of rutile and anatase TiO2 nanoparticles from Ti-peroxy compound aqueous solution with polyols

2003 ◽  
Vol 18 (4) ◽  
pp. 797-803 ◽  
Author(s):  
Naofumi Uekawa ◽  
Miki Suzuki ◽  
Takahiro Ohmiya ◽  
Fumihiko Mori ◽  
Yong Jun Wu ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Particle Size ◽  
Ethylene Glycol ◽  
Specific Surface ◽  
Tio2 Nanoparticles ◽  
Surface Area ◽  
Specific Surface Area ◽  
Single Phase ◽  
Anatase Tio2 ◽  
Oh Groups

Ti-peroxy compound was synthesized from Ti(O-iPr)4 and H2O2. Anatase and rutile TiO2 nanoparticles were prepared by heating the Ti-peroxy compound diluted with a polyol aqueous solution at 368 K for 24 h. In this research, ethylene glycol, glycerin, erythritol, and D-mannitol were used as polyols in the diluting solution. The ratio of anatase/rutile of the TiO2 obtained depended on the polyol concentration in the diluting solution. Furthermore, the polyol concentration at which single-phase anatase could be obtained was lowest when the number of OH groups in the polyol molecule was the highest. With increasing polyol concentration, the obtained TiO2 nanoparticles showed increasing specific surface area and decreasing particle size.

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