Röntgenographische und kolloidchemische Untersuchungen über Ton

Hofmann, Ulrich; Endell, Kurd; Wilm, Diederich

doi:10.1002/ange.19340473002

Cited by 127 publications

(28 citation statements)

References 25 publications

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“…In the 1930s, studies of the condensation processes of silicic acids, carried out by Hofmann, Endell and Wilm [6], Rideal [7] and Kiselev [8], and slightly later by Carman [9], showed that hydroxyl (silanol) groups, Si OH, should be present on the surface of silicates and silicas. On the basis of measurements of the heat of wetting and a comparison of the adsorption data with the data from chemical analysis and the corresponding results reported in the literature, Kiselev suggested that the water evolved during calcination of silica gel, besides physically adsorbed water, is formed from OH groups that are chemically held on the silica surface.…”

Section: Introductionmentioning

confidence: 99%

The surface chemistry of amorphous silica. Zhuravlev model

Zhuravlev

2000

Colloids and Surfaces A: Physicochemical and Engineering Aspect

2,064

142

1,967

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A review article is presented of the research results obtained by the author on the properties of amorphous silica surface. It has been shown that in any description of the surface silica the hydroxylation of the surface is of critical importance. An analysis was made of the processes of dehydration (the removal of physically adsorbed water), dehydroxylation (the removal of silanol groups from the silica surface), and rehydroxylation (the restoration of the hydroxyl covering). For each of these processes a probable mechanism is suggested. The results of experimental and theoretical studies permitted to construct the original model (Zhuravlev model-1 and model-2) for describing the surface chemistry of amorphous silica. The main advantage of this physico-chemical model lies in the possibility to determine the concentration and the distribution of different types of silanol and siloxane groups and to characterize the energetic heterogeneity of the silica surface as a function of the pretreatment temperature of SiO 2 samples. The model makes it possible to determine the kind of the chemisorption of water (rapid, weakly activated or slow, strongly activated) under the restoration of the hydroxyl covering and also to assess of OH groups inside the SiO 2 skeleton. The magnitude of the silanol number, that is, the number of OH groups per unit surface area, h OH , when the surface is hydroxylated to the maximum degree, is considered to be a physico-chemical constant. This constant has a numerical value: h OH,AVER =4.6 (least-squares method) and h OH,AVER = 4.9 OH nm − 2 (arithmetical mean) and is known in literature as the Kiselev-Zhuravlev constant. It has been established that adsorption and other surface properties per unit surface area of silica are identical (except for very fine pores). On the basis of data published in the literature, this model has been found to be useful in solving various applied and theoretical problems in the field of adsorption, catalysis, chromatography, chemical modification, etc. It has been shown that the Brunauer -EmmettTeller (BET) method is the correct method and gives the opportunity to measure the real physical magnitude of the specific surface area, S Kr (by using low temperature adsorption of krypton), for silicas and other oxide dispersed solids.

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Section: Introductionmentioning

confidence: 99%

The surface chemistry of amorphous silica. Zhuravlev model

Zhuravlev

2000

Colloids and Surfaces A: Physicochemical and Engineering Aspect

2,064

142

1,967

View full text Add to dashboard Cite

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“…Hofmann et al [14] postulated the presence of silanol groups (Si-OH) on the silica surface that causes its hydrophilicity, wherein silanol groups act as binding sites (H + bonds) for water. The protonation and deprotonation of these silanol groups determine the surface charge of silica NP and the extent of the repulsive energy that keep them dispersed in the solution [15].…”

Section: Introductionmentioning

confidence: 99%

Effect of Various Silica Nanofluids: Reduction of Fines Migrations and Surface Modification of Berea Sandstone

Abhishek

Hamouda

2017

Applied Sciences

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This work is aimed at addressing surface modification of berea sandstone by silica nanofluids (NFs). Three types of nanofluids were used: silica/deionized water (DIW), silica in DIW with a stabilizer fluid (3-Mercaptopropyl Trimethoxysilane) and sulfonate-functionalized silica in DIW. Core flood studies showed that application of silica nanoparticles (NPs) improved water injectivity in sandstone. The change in the measured zeta potential indicated surface modification of sandstone by application of NPs. Computation of the surface forces showed that the modified berea sandstone has net attractive potential with fines (obtained from water/rock interaction) leading to reduction of fines migration, hence improvement of water injectivity. It was also observed that the silica NPs have greater affinity to adhere/adsorb on quartz surfaces than kaolinite in berea core. This was confirmed by scanning electron microscope imaging and isothermal static adsorption tests. Although the stabilizing of NFs almost did not reduce the fine migration, as was qualitatively indicated by the pressure drop, it enhanced the NPs adsorption on the minerals as obtained by isothermal static adsorption tests. The reduction of fines migration due surface modification by silica NP suggests that NPs can be utilized to overcome the problem of formation damage induced during low salinity flooding in sandstones.

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“…Interlayer water is weakly bound and, depending on humidity, may be lost at temperatures of 50~ (Hofmann et aL, 1934) or less (D. L. Bish, personal communication, Los Alamos National Laboratory, Los Alamos, New Mexico), yielding a product similar to kaolinite, AlzSi2Os(OH)4. With additional heating to about 600~ halloysite dehydroxylates to a disordered layer-like structure containing some residual hydroxyls (Pampuch, 1966).…”

Section: Introductionmentioning

confidence: 99%

Thermal Stability of Halloysite by High-Pressure Differential Thermal Analysis

Johnson¹,

Guggenheim

Groos

1990

Clays and clay miner.

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Abstract--Platy (Te Puke, New Zealand), cylindrical (Spruce Pine, North Carolina), and spherical (North Gardiner mine, Huron, Lawrence County, Indiana) halloysite samples were analyzed by high-pressure differential thermal analysis (HP-DTA) to determine the effect of morphological and chemical differences on their respective thermal stability. In halloysite, these morphological differences imply structural features. The metastable phase relations of each are analogous to those of kaolinite. At 1 bar, the platy, cylindrical, and spherical samples showed peak temperatures (maximum deflection in the dehydroxylation endotherm) of 560 ~ 578 ~ and 575"C, respectively, whereas at about 600 bars the peak temperatures were 622 ~ 655", and 647~ At low pressures the observed reaction is related to dehydroxylation: halloysite (H) = metahalloysite (MH) + vapor (V), whereas higher pressures produce melting reactions, either H + V = metaliquid (ML) for conditions of P(H20) = P(total), or H + MH = ML for P(H20) < P(total). The PT conditions of the invariant point, H + MH + ML + V, for each system are: Te Puke, 612 ~ + 4"C, 25 _+ 7 bars; Spruce Pine, 657 -+ 2"C, 30 + 7 bars; North Gardiner, 652* _+ 2*(2, 34 _+ 7 bars. The lower thermal stability of the Te Puke sample may be related to its higher iron content, although additional data are necessary to confirm that it is not related also to the platy structure. Furthermore, morphological differences between the cylindrical and spherical varieties appear to have had little effect on the energy required to dehydroxylate these halloysite structures. Exceptionally high values obtained for the dehydroxylation enthalpies using the van't Hoffequation, compared with values derived using other methods, may be explained by a 10-15-bar excess in the intracrystalline H20 fugacity during dehydroxylation.Intracrystalline fugacity is defined here as the H20 fugacity within crystallites and is not related to the partial pressure of H20 around individual particles.

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Röntgenographische und kolloidchemische Untersuchungen über Ton

Cited by 127 publications

References 25 publications

The surface chemistry of amorphous silica. Zhuravlev model

The surface chemistry of amorphous silica. Zhuravlev model

Effect of Various Silica Nanofluids: Reduction of Fines Migrations and Surface Modification of Berea Sandstone

Thermal Stability of Halloysite by High-Pressure Differential Thermal Analysis

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