In Vietnam, Fluvisols are distributed mainly in the agro-economic zones of the Red River and the Mekong River Deltas and consist of some soil units. Clay mineralogy was studied for five pedons of Fluvisols collected in these agro-economic zones: two from the Haiphong coastal plain, one from the Red River plain and one from the Thaibinh River plain of the Red River Delta, and one from the Mekong River plain of the Mekong River Delta.
Mica was a predominant mineral with contents ranging between 21 and 50% in the <2μm clay fraction. Mica, and chlorite and kaolinite with lesser amounts were present in all the pedons examined. Minor amounts of smectite and vermiculite were detected in one pedon of the Red River plain. Two kinds of mixed-layer minerals were identified. The mica/vermiculite/smectite mixed-layer mineral was identified in two pedons of the Haiphong coastal plain. The vermiculite/smectite mixed-layer mineral was identified in two pedons of the Thaibinh River and the Mekong River plains, and chlorite-vermiculite intergrade was present in the top layer of these pedons.
The inherent potentiality of Fluvisols as paddy cultivation was evaluated based on the particle-size distribution and the nature and amount of minerals in the clay fraction. Among the five Fluvisols examined, it was high for Fluvisols of the Mekong River plain, medium for those of the Haiphong coastal plain and the Thaibinh River plain, and low for that of the Red River plain.

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Utilization of common clay in admixtures with various other substances for fabrication of utility goods and art objects are widely in practice. However, slip casting of slurries of such crude materials poses several problems in shaping of green bodies because of poor reproducibility due to lack of sufficient knowledge on the rheological properties of those suspensions. In the present investigation, suspensions containing common clay, quartz and fly ash have been selected for evaluating rheological properties of those suspensions with an ultimate objective of preparing slips with reproducible castability. Newtonianity of those suspensions were evaluated by rotational type viscometer and an attempt was made to explain the behavior of suspensions in terms of Newtonian factor ‘n’ consistency factor ‘k’ and viscosity ‘η’. Different factors responsible for affecting ‘n’, ‘k’ and ‘η’ were analyzed and their inter relationship established. It was found that the suspensions were of pseudo plastic in nature with a marked tendency towards becoming Newtonian. Rheological parameters like ‘n’, ‘k’ and ‘η’ were found to be extremely electrolyte sensitive. The entire phenomenon was explained by assuming floc structure and deflocculations were interpreted in terms of electrolytic as well as mechanical forces. Castability of suspension was found to be related to ‘n’, ‘k’ and ‘η’.

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The intercalation of an amphiphilic cationic azobenzene derivative into the interlayer space of clays has been conducted by the ion exchange reactions between clays and p-(ω-trimethylammoniopentyloxy)-p'-(dodecyloxy) azobenzene bromide. The X-ray diffraction and the elemental analysis results indicated that the dye cations were intercalated into the interlayer space of clays. The spectral properties as well as the X-ray diffraction results have revealed that the adsorbed azo dye cations form J-aggregates in the interlayer space. The intercalated azo dyes exhibit reversible trans-to-cis photoisomerization by UV and visible light irradiation.

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The amount of negative charge (CEC) of allophane increased markedly after the organic compounds adsorption (in NaCl with total [Na⁺] =10mM), except for acetate, while the positive charge decreased significantly for all cases. The CEC of allophane treated by oxalate at initial pH4 was higher than that treated by citrate and acetate. At higher pH, citrate caused increase in CEC more than oxalate and acetate. Because the oxalate adsorbed in binuclear form, increase in the CEC was just through creating the new negative charge on silanol groups. Whereas, citrate adsorbed on allophane in bidendate form, so increase in CEC of allophane-citrate complex may includes negative charge carried by citrate itself. The change in surface charges was divided into two factors: effect of increase in pH and net effect of the organic compounds adsorption. The value of net CEC change tended to decrease with increasing the equilibrium pH. This resulted from decrease in the amount of the OC adsorption with increasing the pH. Based on the H (heat of formation) value, the inductive power of the three organic anions in accelerating deprotonation on silanol groups was estimated as oxalate>citrate>acetate.

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New organophilic smectites were prepared by introducing quaternary ammonium cations containing polyoxyethylene (PEO) group into the interlayer of synthetic smectite (hectorite). The organophilic smectites formed a colloidally stable dispersion in polar organic solvents such as aprotic solvents and fatty alcohols to show high apparent viscosity. The stability of the dispersion of the organophilic smectites arose from the incorporation of the organic solvent molecules to the interlayer gallery of the organophilic smectites. The incorporation of the organic solvent molecules was caused by solvation to oxyethylene (EO) groups and hydroxyl groups in the guest cation and by affinity for the interlayer matrix. In the case of organophilic smectite dispersion in ethanol, the apparent viscosity was enhanced up to several times by the addition of water to the system. Maximal apparent viscosity was obtained at 10 wt.% of water content, where the dispersed particle size was markedly reduced. Consequently these phenomena can be accounted for by the role of water as polar activator in the organophilic smectite dispersion.

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Montmorillonite is noted for its expansive properties and characteristics that whose suspension exhibit a certain yield stress even in dilute state. In general, yield stress is regarded as a criterion whether continuous network of particles arise or not, and its strength is the measure of an interaction between clay particles and their fl ocs.
In this study, flow curves, namely, relationships between shear rates and shear stresses of montmorillonite suspensions were observed with use of cone-plate viscometer. Then a slight yield stress was confirmed for suspension whose solid ratio was 1.0% on the volume basis. When estimating yield stresses τ₀ [Pa] as a function of solid ratio φ_s [%], their dependence proved to be markedly high, and expressed as τ₀ ∝φ_s^7.24. However, usual uniform floc models fail to explain this high dependence, because this model leads to the power law approximately as τ₀ ∝φ_s⁵ at most.
In order to solve this discrepancy, self-similar floc model is newly proposed. This model is based on the assumption that each n th order spherical floc is composed of the same L pieces of (n-1) th order flocs. Here diameter ratio of n th to (n-1) th is m, shown in Fig. 4. When compared with the calculated values on this model, experimental tendencies of yield stresses would be realized by the step up of the order of self-similar degree from two to three, with increase in solid ratio from 1% to 2%.

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Clay mineralogy of Vietnam soils was examined. Surface soils were collected from agricultural land at the sites different in parent rocks in four out of seven agroeconomic zones. The soils derived from alluvium and sandstone were light clay, clay loam or sandy clay loam in texture, and the clay fraction was composed of mica and kaolinite with or without chlorite. In addition, the mica/vermiculite/smectite mixedlayer mineral was found in the soils collected from the Red River Delta region, while vermiculite-chlorite intergrade was detected in the soils collected in the North Midland and Mountainous region. The soils derived from limestone were of heavyclay texture, and the clay fraction consisted predominantly of kaolinite. The soils derived from basalt were of heavyclay texture, and the clay mineralogical composition was different with relief. The clay fraction of Ferralsols on the hillside was composed of kaolinite, whereas that of Luvisols on the terrace comprised smectite and halloysite (7Å).

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The clay mineralogy of bentonite in Balamban, Cebu Province, Philippines was studied. Specimens were randomly collected from lenticular seams of bentonite concordantly intercalated with sequences of calcareous and tuffaceous shale and sandstone of the Middle Miocene Toledo Formation. Multiple analytical techniques of the <2μm size fraction reveal that smectite is the dominant clay constitution of the bentonite. Minor association of mixed-layer kaolinite/smectite, kaolin, and mica is indicative. Diagenetic facies of calcium-rich bentonite and cristobalite-rich bentonite are diagnostic features. Non-phyllosilicate components are mainly quartz, feldspar, cristobalite, calcite, and zeolite. Volcanic glass shards, considered as the precursor material, occur sporadically in the clay-dominated matrix. Calcareous microfossils or nanofossils also exist as subordinate impurities.
Rehydration capacity of the calcium-rich bentonite was observed to be generally greater than the cristobalite-rich bentonite.
Bentonite formation is ascribed to be generated by halmyrolysis of the volcanic glass fragments contained in the vitric tuff exhalative unit of the Toledo Formation. The devitrification and transformation of the glass into nearly pure smectitic clay suite apparently ensued in a marine environment. Diagenetic formation of the calcium-rich facies appears syngenetic with the accumulation of the volcanic ash in saline waters while the cristobalite-rich facies appears authigenic, constituting the silica-rich layers.

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The coprecipitation of various amino acids (phenylalanine: Phe, alanine: Ala, leucine: Leu, tryptophan: Trp, histidine: His and aspartic acid: Asp) into the Zn-Al layered double hydroxide (LDH) was quantitatively investigated at 40°C. When Phe was used as a guest amino acid, the coprecipitation was influenced by the solution pH, Zn/Al/Phe molar ratio and kind of coexisting inorganic ion. The optimum conditions were reaction time: 1h, pH range: 7-9 and Zn/A1/Phe molar ratio: 2-4/0.5-1/1, in which Phe was thought to be intercalated into the Zn-Al LDH precipitates as zwitterion. In the (Cl, Phe)/Zn-Al LDH and Phe/Zn-Al LDH precipitates, the basal spacing of (003) was observed at 7.8Å(using chloride reagent) and 18.8Å(using nitrate reagent), respectively. It suggests that the intercalated Phe was oriented horizontally or vertically for the Zn-Al LDH basal layer, in which the arrangement was dependent on the charge density of coexisting inorganic ions. In the case of various other amino acids, the coprecipitation greatly influenced by the kind of side-chain of the amino acids. The amino acids having hydrophobic side-chain (Leu and Trp) were preferentially intercalated into the LDH interlayer as zwitterion. Moreover, in the deintercalation experiments of Phe from the Phe/Zn-Al LDH precipitate, Phe was easily deintercalated by the ion exchange with CO₃^2- ion.

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