Metastability of tetragonal ZrO2 derived from Zr-n-propoxide-acetylacetone-water-isopropyl alcohol

1998 ◽  
Vol 13 (8) ◽  
pp. 2174-2183 ◽  
Author(s):  
Zhaoqi Zhan ◽  
Hua C. Zeng
Keyword(s):  
Transformation Temperature ◽  
Isopropyl Alcohol ◽  
Tetragonal Zro2 ◽  
Surface Oxygen ◽  
Crystallite Growth ◽  
Calcination Temperatures ◽  
Work Surface ◽  
20 Nm ◽  
Temperature Time ◽  
Thermodynamic Factors

ZrO2 nanopowders derived from zirconium n-propoxide [Zr(OC3H7)4]-acetylacetone-water-isopropanol have been investigated with respect to their tetragonal metastability on heating-cooling processes. The transformation temperature of metastable tetragonal to monoclinic (t′ → m) phase is found to be governed by ultimate firing temperature, time, and atmospheres employed. Crystallite growth is fastened with increase in calcination temperatures over 1000–1400 °C, and the t′ → m transformation temperature is correlated linearly with crystallite size in the studied range of 12–20 nm. Heating in an oxygen environment increases the size of the final crystallites and hence the rate of the t′ → m transformation. It is revealed that the t′ → m transformation temperature depends largely on the heating atmosphere, but only weakly on the cooling one. Based on the findings of this work, surface oxygen deficiencies are attributed to be responsible for low-temperature tetragonal metastability. A crystallite growth model to explain the decline of t′-ZrO2phase is proposed. Kinetic and thermodynamic factors are also discussed in connection with the existing theories of tetragonal metastability.

The Poisoning Effect of Co3O4 on γ-Al2O3 and MgO Supports During the Decomposition of Isopropyl Alcohol

1995 ◽  
Vol 60 (12) ◽  
pp. 2057-2063 ◽  
Author(s):  
Samih A. Halawy ◽  
Mohamed A. Mohamed ◽  
Suzan F. Abd El-Hafez
Keyword(s):  
Isopropyl Alcohol ◽  
Vapour Phase ◽  
Phase Decomposition ◽  
Surface Oxygen ◽  
Poisoning Effect ◽  
Excess Surface

Catalysts containing 20 wt.% Co3O4 supported on γ-Al2O3 and MgO were prepared. The catalyst precursors were analyzed by TG, DTG and DTA, and the calcined catalysts (400-700 °C) were characterized by XRD. The amount of excess surface oxygen for the catalysts was estimated iodometrically. The vapour-phase decomposition of isopropyl alcohol over these catalysts was studied. Co3O4/γ-Al2O3 catalysts are selective towards propene formation, whereas Co3O4/MgO catalysts are selective towards acetone formation. The poisoning effect of Co3O4 on both supports and the activity of the catalysts is discussed.

Synthesis and Characterization of Stabilized Tetragonal Nano Zirconia by Precipitation Method

2019 ◽  
Vol 56 ◽  
pp. 142-151
Author(s):  
Hassan Shokry ◽  
Marwa Elkady ◽  
Hesham Hamad
Keyword(s):  
Phase Transformation ◽  
Crystallite Size ◽  
Calcination Temperature ◽  
Average Crystallite Size ◽  
Precipitation Method ◽  
Synthesis And Characterization ◽  
Calcination Temperatures ◽  
Ft Ir ◽  
20 Nm

Nano sized ZrO2 nanopowder was synthesized by precipitation method. Phase transformation was investigated as a function of calcination temperature by XRD, SEM , and FT-IR. It is indicated that the thermal anneling from 400 to 800 °C resulted in increasing the average crystallite size from 12 to 20 nm. As the calcination temperature increased, the crystallite size and the agglomeration were increased. The increase in the monoclinic content and grain growth are caused by the calcination temperatures even calcination at 800 °C.

scholarly journals Fabrication and study of Raman signal enhancement of pyramid/nano-Ag structured Silic substrate

2021 ◽  
Vol 4 (1) ◽  
pp. 21-23
Author(s):  
Nguyet Dau Tran Anh ◽  
Hieu Van Vo Kim ◽  
Thanh Van Tran Thi ◽  
Luan Huynh Nguyen Thanh ◽  
◽  
...  
Keyword(s):  
Silicon Substrate ◽  
Enhancement Factor ◽  
Isopropyl Alcohol ◽  
Rhodamine 6G ◽  
Alcohol Concentration ◽  
Raman Signal ◽  
Enhancement Effect ◽  
Optimal Parameters ◽  
Chemical Corrosion ◽  
20 Nm

The pyramid-structured silicon substrate was successfully fabricated by a chemical corrosion method with an average thickness of about 1 - 3 μm with the optimal parameters such as corrosion temperature of 70oC, corrosion time of 5 min, concentration KOH of 3 M and isopropyl alcohol concentration of 1 M. After that, the silver nanoparticles layer (thickness 20 nm) was coated on the silicon substrate by a sputtering method to enhance the SERS signal. The results proved that the Pyramid/nano Ag structure silicon substrate showed the enhancement effect of Raman signal, and Rhodamine 6G pigment in food at low concentration (10-6 M) was detected and the enhancement factor was 9.7 × 102.

Kinetic Studies on Crystallization and Grain Growth of Amorphous Al2O3-ZrO2 Powder

2016 ◽  
Vol 680 ◽  
pp. 120-123
Author(s):  
Xi Qing Xu ◽  
Jia Chen Liu ◽  
Yi Wang
Keyword(s):  
Uniform Distribution ◽  
Grain Growth ◽  
Amorphous Phase ◽  
Kinetic Studies ◽  
Spherical Particles ◽  
Calcination Temperatures ◽  
Sem Micrograph ◽  
Controlled Crystallization ◽  
Average Size ◽  
20 Nm

Nanocrystalline Al2O3-ZrO2 powders were prepared through controlled crystallization of amorphous phase, and kinetic studies on crystallization and grain growth were carried out. Based on Kissinger equation, the activation energies for crystallization were determined to be 981.8 kJ·mol-1 for (Zr0.94Y0.06)O1.88 and 1364.1 kJ·mol-1 for α-Al2O3. Average size of crystallite was obtained by Scherrer equation according to FWHMs in XRD peaks; the grain growth was slow below 1100°C, and turned severe at higher temperatures. The appropriate calcination temperatures was determined to be 1100°C, at which stable phases were formed and further severe grain growth can be restrained. SEM micrograph of Al2O3-ZrO2 powder after calcination at 1100°C revealed uniform distribution of spherical particles with size of about 20 nm, close to that determined by XRD results.

scholarly journals Chế tạo và khảo sát khả năng tăng cường tín hiệu Raman của đế Silic cấu trúc kim tự tháp/nano bạc

2021 ◽  
Vol 4 (1) ◽  
pp. 21-23
Author(s):  
Nguyệt Đậu Trần Ánh ◽  
Hiếu Văn Võ Kim ◽  
Thanh Vân Trần Thị ◽  
Luận Huỳnh Nguyễn Thanh ◽  
◽  
...  
Keyword(s):  
Isopropyl Alcohol ◽  
20 Nm

Đế Silic có cấu trúc kim tự tháp được chế tạo thành công bằng phương pháp ăn mòn hóa học. Mật độ kim tự tháp trên bề mặt đế dày, kích thước trung bình khoảng 1 - 3 μm với các thông số chế tạo tối ưu như nhiệt độ ăn mòn ở 70°C, thời gian ăn mòn là 5 phút, nồng độ dung dịch KOH là 3 M và nồng độ dung dịch isopropyl alcohol là 1 M. Sau đó, lớp nano bạc (bề dày 20 nm) được phủ lên bề mặt đế Silic cấu trúc kim tự tháp bằng phương pháp phún xạ để tăng cường tín hiệu tán xạ Raman bề mặt (SERS). Kết quả cho thấy, đế Silic cấu trúc kim tự tháp/nano Ag cho hiệu ứng tăng cường tín hiệu Raman phát hiện được chất màu Rhoamine 6G trong thực phẩm ở nồng độ thấp (10-6M) và có hệ số tăng cường là 9,7 × 102.

scholarly journals Nanocrystalline zirconia based powders synthesized by hydrothermal method

2012 ◽  
Vol 6 (3) ◽  
pp. 151-157 ◽  
Author(s):  
Viktoria Tsukrenko ◽  
Elena Dudnik ◽  
Alexey Shevchenko
Keyword(s):  
Electron Microscopy ◽  
Nanocrystalline Powders ◽  
Average Particle ◽  
Particle Sizes ◽  
Tetragonal Zro2 ◽  
Xrd Phase Analysis ◽  
Nanocrystalline Zirconia ◽  
20 Nm ◽  
Processing Steps ◽  
Scanning Electron

Nanocrystalline powders in the ZrO2-Y2O3-CeO2-CoO-Al2O3 system with 1 and 10 mol% Al2O3 were prepared via hydrothermal treatment in alkaline medium. The characteristics of nanocrystalline powders after heat treatment in the temperature range from 500 to 1200 ?C were investigated by XRD phase analysis, scanning electron microscopy, petrography and BET measurements. It was found that hydrothermally treated powders contained metastable low-temperature cubic solid solution based on ZrO2 and addition of Al2O3 increased temperature of phase transformation of the metastable cubic- ZrO2 to tetragonal-ZrO2. It was evidenced that both powders remained nanocrystalline after all processing steps with the average particle sizes from 8 to 20 nm. The addition of 0.3 mol% CoO allows one to obtain composites with good sinterability at 1200 ?C.

Macromolecular structures of biological specimens are not obscured by controlled osmium impregnation

1983 ◽  
Vol 41 ◽  
pp. 606-607
Author(s):  
Klaus-Ruediger Peters ◽  
Samuel A. Green
Keyword(s):  
Thin Films ◽  
Electrical Conductivity ◽  
Critical Point ◽  
Metal Films ◽  
High Magnification ◽  
Osmium Impregnation ◽  
Instrumental Resolution ◽  
20 Nm ◽  
Continuous Metal

High magnification imaging of macromolecules on metal coated biological specimens is limited only by wet preparation procedures since recently obtained instrumental resolution allows visualization of topographic structures as smal l as 1-2 nm. Details of such dimensions may be visualized if continuous metal films with a thickness of 2 nm or less are applied. Such thin films give sufficient contrast in TEM as well as in SEM (SE-I image mode). The requisite increase in electrical conductivity for SEM of biological specimens is achieved through the use of ligand mediated wet osmiuum impregnation of the specimen before critical point (CP) drying. A commonly used ligand is thiocarbohvdrazide (TCH), first introduced to TEM for en block staining of lipids and glvcomacromolecules with osmium black. Now TCH is also used for SEM. However, after ligand mediated osinification nonspecific osmium black precipitates were often found obscuring surface details with large diffuse aggregates or with dense particular deposits, 2-20 nm in size. Thus, only low magnification work was considered possible after TCH appl ication.

A scanning electron microscopic study of the veliger larvae of the scallop argopecten purpuratus

1988 ◽  
Vol 46 ◽  
pp. 284-285
Author(s):  
G.C. Bellolio ◽  
K.S. Lohrmann ◽  
E.M. Dupré
Keyword(s):  
Morphological Description ◽  
Electron Microscopic ◽  
Larval Stages ◽  
Scanning Electron Microscopic Study ◽  
The Pacific ◽  
Argopecten Purpuratus ◽  
Veliger Larvae ◽  
20 Nm ◽  
Ethanol Series ◽  
Scanning Electron

Argopecten purpuratus is a scallop distributed in the Pacific coast of Chile and Peru. Although this species is mass cultured in both countries there is no morphological description available of the development of this bivalve except for few characterizations of some larval stages described for culture purposes. In this work veliger larvae (app. 140 pm length) were examined by the scanning electron microscope (SEM) in order to study some aspects of the organogenesis of this species.Veliger larvae were obtained from hatchery cultures, relaxed with a solution of MgCl2 and killed by slow addition of 21 glutaraldehyde (GA) in seawater (SW). They were fixed in 2% GA in calcium free artificial SW (pH 8.3), rinsed 3 times in calcium free SW, and dehydrated in a graded ethanol series. The larvae were critical point dried and mounted on double scotch tape (DST). To permit internal view, some valves were removed by slightly pressing and lifting the tip of a cactus spine wrapped with DST, The samples were coated with 20 nm gold and examined with a JEOL JSM T-300 operated at 15 KV.

Analysis of 2D and 3D defects associated with precipitation of Cu in silicon

1991 ◽  
Vol 49 ◽  
pp. 870-871
Author(s):  
P.M. Rice ◽  
MJ. Kim ◽  
R.W. Carpenter
Keyword(s):  
Colony Growth ◽  
Dark Field ◽  
Dark Side ◽  
Silicide Phase ◽  
Strain Fields ◽  
Near Surface ◽  
Unknown Composition ◽  
Secondary Precipitates ◽  
20 Nm ◽  
2D And 3D

Extrinsic gettering of Cu on near-surface dislocations in Si has been the topic of recent investigation. It was shown that the Cu precipitated hetergeneously on dislocations as Cu silicide along with voids, and also with a secondary planar precipitate of unknown composition. Here we report the results of investigations of the sense of the strain fields about the large (~100 nm) silicide precipitates, and further analysis of the small (~10-20 nm) planar precipitates.Numerous dark field images were analyzed in accordance with Ashby and Brown's criteria for determining the sense of the strain fields about precipitates. While the situation is complicated by the presence of dislocations and secondary precipitates, micrographs like those shown in Fig. 1(a) and 1(b) tend to show anomalously wide strain fields with the dark side on the side of negative g, indicating the strain fields about the silicide precipitates are vacancy in nature. This is in conflict with information reported on the η'' phase (the Cu silicide phase presumed to precipitate within the bulk) whose interstitial strain field is considered responsible for the interstitial Si atoms which cause the bounding dislocation to expand during star colony growth.

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