Noncrystalline aluminosilicate gels with Al2O3/(Al2O3 + SiO2) weight ratios from 0.3 to 0.5 were reacted in 0.1 N KOH at temperatures varying from 125° to 175°C. The pH of the solutions dropped sharply with increasing gel:solution ratios, indicating that the coordination number of Al in the products changed from IV to VI. The degree of hydrolysis appeared to be higher with KOH than with NaOH. X-ray powder diffraction and infrared spectroscopy showed that disordered kaolinite was the only crystalline product formed. Thermal data and surface area measurements indicated that the kaolinite was formed by a condensation process.

The most prominent authigenic reaction in Holocene tuffaceous sediments at Teels Marsh, Nevada, is the hydration of rhyolitic glass by interstitial brines and the subsequent formation of phillipsite. This reaction has the form: rhyolitic glass + H2O → hydrous alkali alumninosilicate gel → phillipsite. Phillipsite is the most abundant authigenic phase in the tuffaceous sediments (>95%), analcime is the next most abundant phase, and clinoptilolite occurs as a trace mineral in the <2-mm fraction. Analcime forms by the reaction of phillipsite and Na+. Gaylussite and searlesite also are common authigenic phases at Teels Marsh. The concentration of silica in the interstitial brines is controlled by one or more of the authigenic reactions at less than 100 ppm. A stoichiometric equation for the reaction of phillipsite to analcime at Teels Marsh is:

$$0.43N{a + }\, + {K_{0.43}}N{a_{0.57}}AlS{i_{3.1}}{O_{8.2}}\, \cdot \,3.2{H_2}O\, \to \,NaAlS{i_2}{O_6}\, \cdot \,{H_2}O\, + \,1.1{H_4}Si{O_4}\, + \,0.43{K + }.$$

Sodium and potassium activities of brines associated with both phillipsite and analcime were used to estimate the equilibrium constant for this reaction as 3.04 × 10−5. The ΔG0 value for the reaction is +6.2 kcal/mole at 25°C and 1 atm pressure. The estimated ΔG0 value of phillipsite, using this reaction, is −1072.8 kcal/mole at 25°C and 1 atm.

The osmotic swelling of an n-butylammonium vermiculite in a 0.1 M solution of n-butylammonium chloride has been studied as a function of temperature and hydrostatic pressure by neutron diffraction. On application of a pressure of 1050 bar the vermiculite swelled macroscopically at 20°C, the c-axis spacing changing from 19.4 to 126 Å. The phase transition was completely reversible with respect to both pressure and temperature, and a complete study of the temperature-pressure phase diagram was made at pressures as high as 2000 bar. The heat capacity change with temperature across the swelling transition was measured at atmospheric pressure, and the enthalpy and entropy of the change from crystalline to osmotic phases were found to be, respectively, 5.2 J/g and 0.0183 J/K·g of dry clay. The combination of the entropy change with the gradient of the pressure-temperature phase boundary gave the volume change accompanying the transition. The total volume of the swollen phase was less than that of the crystalline phase plus the appropriate amount of solution, corresponding to a fractional decrease of about 0.1% in the water volume from bulk solution to between the plates.

Cementing materials in the Arahama sand dune, Japan, were studied mineralogically and biogeochemically to gain a better understanding of the cause of hardening. The cementing material is a clay-organic complex composed of noncrystalline gels and a matrix of small, poorly crystalline particles showing 14–16-Å spacings. The gel materials appear to have transformed into the poorly crystalline particles, which have a high carbon content and Al/Si ratios of 2.2 to 2.0. These particles are slightly richer in Si and poorer in Fe than the gel materials themselves. The organic portion of the complex can be removed by H2O2 treatment, leaving a noncrystalline network-structure containing a dispersed granular component. Scanning auger-depth profiles of individual particles show a high surface concentration of C and O and an increase in the Al/Si ratio with depth. The energy-intensity distribution suggests a mixture of carbon compounds having a major core-line binding energy of a hydrocarbon. The gel-cementing materials in the sand dune may have been formed from biochemical weathering products of organic matter, which subsequently controlled the formation of clay-organic complexes.

Poly(ethylene oxides) (PEOs) with sulphonate groups attached at both chain ends (S-PEOs) were strongly adsorbed by dispersed Na- and Ca-montmorillonite particles. The amounts adsorbed were very similar to those of cationic end-capped poly(ethylene oxides). In both cases bilayers of PEO chains were intercalated so that the basal spacing of the particles reached the same plateau values of ~1.73 nm. In contrast, the influence of anionic PEOs on the colloidal behaviour of the Na- and Ca-montmorillonite dispersions was very different from the effect of the cationic PEOs. The shorter chain S-PEOs (S-PEO 1500, 4000) destabilized the Na-montmorillonite dispersions by coagulation due to the Na+ ions introduced as counterions to the S-PEOs. The longer chain S-PEO 20000 and S-PEO 35000 did not coagulate the Na-montmorillonite sols because the corresponding Na+ concentration did not reach the critical coagulation value. The slightly enhanced salt tolerance indicated that the long-chain PEOs exerted a weak steric stabilization. In contrast, bridging of the particles by S-PEO molecules and Ca2+ ions played an important role in destabilizing the Ca-montmorillonite dispersions in the form of flocs and formation of gels.

The colloidal state (sol, flocs, gels) of Na-montmorillonite dispersions (from bentonite from Bavaria, Germany) was adjusted by the addition of poly(ethylene oxides) with terminal trimethylammonium groups. The colloidal state of the dispersions changed with the molar mass of these end-capped poly(ethylene oxides). The sol-gel diagrams (up to 4.5% (w/w) montmorillonite) in the presence of TMA-PEO 1500 and TMA-PEO 4000 (up to 40 g/l) were characterized by large fields of gel whereas TMA-PEO 20000 and TMA-PEO 35000 caused peptization by steric stabilization. Even dispersions with the highest montmorillonite content (4.5%) were peptized by >0.2 g/l TMA-PEO 35000. The critical coagulation concentration of NaCl was increased by the polymer addition, but the increase was modest (from 8-12 mmol/l to 50 mmol/l). The changes of the colloidal state, the flow behaviour and the salt coagulation reveal the sensitive interplay between stabilization mechanisms (electrostatic, steric) and destabilization effects (bridging, charge compensation, depletion flocculation).

The essential oil (EO) of Piper aduncum Linnaeus, known as ‘sireh lada’ to locals Malaysian, has the potential to be used as an alternative to synthetic insect repellents such as N,N-diethyl-meta-toluamide. However, the EO's efficacy as a repellent decreases after application due to the high volatility of its active ingredients. A number of studies have showed that optimizing the formulation of plant-based EOs can improve their efficacy as repellents. The present study sought to evaluate the effectiveness of 10% P. aduncum EO in ethanol and in three different semisolid formulations: ointment, cream and gel. These formulations were tested on Aedes aegypti under laboratory conditions. Each formulation was applied to the subject's hands, which were then inserted into a cage containing 25 nulliparous A. aegypti. The number of mosquitoes landing on or biting each subject's hand was recorded, and the repellency percentage, landing/biting percentage and protection time for each of the formulations were compared. There were no statistically significant differences between the semisolid EO formulations with regards to the repellency percentage and the landing/biting percentage at 4 h post-application. All three semisolid EO formulations were able to repel >65% of the A. aegypti at 4 h post-application. The EO ointment formulation provided a protection time (182.5 ± 16.01 min) that was statistically significantly longer than that associated with the EO gel formulation (97.5 ± 14.93 min). Meanwhile, the EO cream formulation provided a protection time of 162.5 ± 6.29 min. As the EO cream and ointment formulations displayed better repellent properties than the EO gel formulation, they appear to be the most promising P. aduncum EO formulations to be developed and commercialized as alternatives to synthetic repellents.