Evolution of Surface area During the Controlled Growth of Silica Spheres

1990 ◽  
Vol 180 ◽  
Author(s):  
Gregory H. Bogush ◽  
C. J. Brinker ◽  
P. D. Majors ◽  
D. M. Smith
Keyword(s):  
Surface Area ◽  
Growth Process ◽  
Growth Models ◽  
Silica Spheres ◽  
Conventional Model ◽  
Silicon Alkoxides ◽  
Aggregative Growth ◽  
Hydrolysis Of ◽  
Controlled Hydrolysis

ABSTRACTSeveral mechanisms have been proposed for the growth of silica spheres by the controlled hydrolysis of silicon alkoxides, the limiting cases of which are the conventional and aggregative growth models. The evolution of surface area predicted from the two models is substantially different at early times into the reaction. In order to probe the change in surface area during growth, 1H NMR measurements of the solvent were made during the growth process. It has been demonstrated that the spin-spin relaxation time.(T2) for an absorbed phase is less than that of the bulk solvent. Using this principal, the change in surface area can be followed in situ during the reaction. The experimental results were compared to the predictions of the conventional model and found not to be in agreement.

scholarly journals In-situ HRTEM observations of growth process of decagonal quasicrystals

2014 ◽  
Vol 70 (a1) ◽  
pp. C97-C97
Author(s):  
Keisuke Nagao ◽  
Kazue Nishimoto ◽  
Tomoaki Inuduka ◽  
Keiichi Edagawa
Keyword(s):  
Growth Mechanism ◽  
Growth Process ◽  
Structural Information ◽  
Growth Models ◽  
Experimental Studies ◽  
Unit Cell ◽  
Small Scale ◽  
Growth Processes ◽  
Decagonal Quasicrystals

Quasicrystals possess quasiperiodicity, where the structure cannot be described simply by the repetition of unit cell like conventional crystals. This fact raises the question of how quasicrystals grow, i.e., what physical mechanism makes the growth of quasicrystals possible. While crystals can grow by copying a unit cell via local atomic interactions, nonlocal structural information seems to be required in the growth of quasicrystals. This problem has attracted much attention ever since the first discovery of a quasicrystal in 1984, and several theoretical growth models [1] have been proposed. However, no experimental studies have so far been reported, and it is still unclear whether these theoretical growth models apply to real quasicrystals. In the present study, we have conducted in-situ high-temperature electron microscopic (HRTEM: High-Resolution Transmission Electron Microscopy) observations of the growth process of decagonal quasicrystals to elucidate the growth mechanism. The growth processes of a decagonal quasicrystal of Al70.8Ni19.7Co9.5were observed by HRTEM in the temperature range 1073-1173K. Tiling patterns with edge length of about 2nm were constructed from a series of HRTEM images. They were analysed in the framework of the projection method. Here, we followed the procedures in our previous work [2]. We have already reported the results of some observations and analyses elsewhere [3]. However, the growth processes of them were on a small scale, and the results were indefinite. Recently, we have succeeded in observing a growth process on a massive scale. In this paper, we present the results of this observation and subsequent analyses, and discuss the growth mechanism of the quasicrystal.

Synthesis of Submicron, Narrow Size Distribution Spherical Zincite

1986 ◽  
Vol 73 ◽  
Author(s):  
Robert H. Heistand ◽  
Yee-Ho Chia
Keyword(s):  
Size Distribution ◽  
Surface Area ◽  
Systematic Study ◽  
Spherical Particles ◽  
Narrow Size Distribution ◽  
Crystallite Sizes ◽  
Hydrolysis Of ◽  
Controlled Hydrolysis

ABSTRACTZincite has been produced by the controlled hydrolysis of an alkylzinc alkoxide (ethylzinc-t-butoxide) resulting in ∼0.2 μm spherical particles with a narrow size distribution consisting of 150 Å crystallites. The surface area is 30 m2/g. Variation of the concentration of the water drastically affects the particle and crystallite sizes. The results of a systematic study of the hydrolysis parameters are reported here.

Agglomeration of silica spheres under ultrasonication

1997 ◽  
Vol 12 (5) ◽  
pp. 1410-1415 ◽  
Author(s):  
Naoya Enomoto ◽  
Shingo Maruyama ◽  
Zenbe-e Nakagawa
Keyword(s):  
Particle Size Analysis ◽  
Laser Diffraction ◽  
Size Analysis ◽  
Silica Spheres ◽  
Power Ultrasound ◽  
Agglomeration Process ◽  
Transmission Electron ◽  
Rapid Formation ◽  
Hydrolysis Of ◽  
Controlled Hydrolysis

Power ultrasound of 20 kHz was applied to the synthesis of silica spheres via the controlled hydrolysis of tetraethoxysilane (TEOS). Silica spheres of about 0.3 μm were agglomerated to form tolerably uniform, dense particles of about 2 μm through 90 min sonication. This agglomeration behavior was examined by laser diffraction particle size analysis and transmission electron microscopy. It was found that the agglomeration process involves (I) an incubation period in which no agglomeration occurs, (II) rapid formation of ramified particles, and (III) their densification. It was inferred that sonication enhances collision among silica spheres.

INDIREKTE PAPIERCHROMATOGRAPHISCHE METHODE ZUR BESTIMMUNG DER HARNOESTROGENE

1961 ◽  
Vol 38 (4) ◽  
pp. 545-562 ◽  
Author(s):  
L. Kecskés ◽  
F. Mutschler ◽  
I. Glós ◽  
E. Thán ◽  
I. Farkas ◽  
...  
Keyword(s):  
Pregnant Women ◽  
Granulosa Cell ◽  
Iron Content ◽  
List Type ◽  
Granulosa Cell Tumour ◽  
Hydrolysis Of ◽  
Phenol Fraction ◽  
Qualitative Determination

ABSTRACT 1. An indirect paperchromatographic method is described for separating urinary oestrogens; this consists of the following steps: acidic hydrolysis, extraction with ether, dissociation of phenol-fractions with partition between the solvents. Previous purification of phenol fraction with the aid of paperchromatography. The elution of oestrogen containing fractions is followed by acetylation. Oestrogen acetate is isolated by re-chromatography. The chromatogram was developed after hydrolysis of the oestrogens 'in situ' on the paper. The quantity of oestrogens was determined indirectly, by means of an iron-reaction, after the elution of the iron content of the oestrogen spot, which was developed by the Jellinek-reaction. 2. The method described above is satisfactory for determining urinary oestrogen, 17β-oestradiol and oestriol, but could include 16-epioestriol and other oestrogenic metabolites. 3. The sensitivity of the method is 1.3–1.6 μg/24 hours. 4. The quantitative and qualitative determination of urinary oestrogens with the above mentioned method was performed in 50 pregnant and 9 non pregnant women, and also in 2 patients with granulosa cell tumour.

In Situ Microscopy for In-line Monitoring of the Enzymatic Hydrolysis of Cellulose

2013 ◽  
Vol 85 (17) ◽  
pp. 8121-8126 ◽  
Author(s):  
Britta Opitz ◽  
Andreas Prediger ◽  
Christian Lüder ◽  
Marrit Eckstein ◽  
Lutz Hilterhaus ◽  
...  
Keyword(s):  
Enzymatic Hydrolysis ◽  
Enzymatic Hydrolysis Of Cellulose ◽  
Hydrolysis Of Cellulose ◽  
Hydrolysis Of

scholarly journals Permeability of muscle capillaries to small heme-peptides. Evidence for the existence of patent transendothelial channels.

1975 ◽  
Vol 64 (3) ◽  
pp. 586-607 ◽  
Author(s):  
N Simionescu ◽  
M Siminoescu ◽  
G E Palade
Keyword(s):  
Plasma Proteins ◽  
Intercellular Junctions ◽  
Rat Diaphragm ◽  
Enzymic Hydrolysis ◽  
Graphic Analysis ◽  
Heme Peptides ◽  
Future Work ◽  
Hydrolysis Of ◽  
Muscle Capillaries

Two heme-peptides (HP) of about 20-A diameter (heme-undecapeptide [H11P], mol wt approximately 1900 and heme-octapeptide [H8P], mol wt approximately 1550), obtained by enzymic hydrolysis of cytochrome c, were sued as probe molecules in muscle capillaries (rat diaphragm). They were localized in situ by a perixidase reaction, enhanced by the addition of imidazole to the incubation medium. Chromatography of plasma samples showed that HPs circulate predominantly as monomers for the duration of the experiments and are bound by aldehyde fixatives to plasma proteins to the extent of approximately 50% (H8P) to approximately 95% (H11P). Both tracers cross the endothelium primarily via plasmalemmal vesicles which become progressively labeled (by reaction product) from the blood front to the tissue front of the endothelium, in three successive resolvable phases. By the end of each phase the extent of labeling reaches greater than 90% of the corresponding vesicle population. Labeled vesicles appear as either isolated units or chains which form patent channels across the endothelium. The patency of these channels was checked by specimen tilting and graphic analysis of their images. No evidence was found for early or preferential marking of the intercellular junctions and spaces by reaction product. It is concluded that the channels are the most likely candidate for structural equivalents of the small pores of the capillary wall since they are continuous, water-filled passages, and are provided with one or more strictures of less than 100 A. Their frequency remains to be established by future work.

scholarly journals Characterization of Glycoside Hydrolase Family 5 Proteins in Schizosaccharomyces pombe

2010 ◽  
Vol 9 (11) ◽  
pp. 1650-1660 ◽  
Author(s):  
Encarnación Dueñas-Santero ◽  
Ana Belén Martín-Cuadrado ◽  
Thierry Fontaine ◽  
Jean-Paul Latgé ◽  
Francisco del Rey ◽  
...  
Keyword(s):  
Cell Wall ◽  
Schizosaccharomyces Pombe ◽  
Protein Characterization ◽  
Wall Material ◽  
Glycoside Hydrolase Family ◽  
Content Type ◽  
Hydrolysis Of ◽  
Controlled Hydrolysis ◽  
Hydrolase Family

ABSTRACT In yeast, enzymes with β-glucanase activity are thought to be necessary in morphogenetic events that require controlled hydrolysis of the cell wall. Comparison of the sequence of the Saccharomyces cerevisiae exo-β(1,3)-glucanase Exg1 with the Schizosaccharomyces pombe genome allowed the identification of three genes that were named exg1 + (locus SPBC1105.05), exg2 + (SPAC12B10.11), and exg3 + (SPBC2D10.05). The three proteins have different localizations: Exg1 is secreted to the periplasmic space, Exg2 is a membrane protein, and Exg3 is a cytoplasmic protein. Characterization of the biochemical activity of the proteins indicated that Exg1 and Exg3 are active only against β(1,6)-glucans while no activity was detected for Exg2. Interestingly, Exg1 cleaves the glucans with an endohydrolytic mode of action. exg1 + showed periodic expression during the cell cycle, with a maximum coinciding with the septation process, and its expression was dependent on the transcription factor Sep1. The Exg1 protein localizes to the septum region in a pattern that was different from that of the endo-β(1,3)-glucanase Eng1. Overexpression of Exg2 resulted in an increase in cell wall material at the poles and in the septum, but the putative catalytic activity of the protein was not required for this effect.

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