Hydrated Silica Research Articles

Chemical fog dispersal with ground equipment for mosquito control.

Fogging for mosquito control has long been centered around the thermal fog and non-thermal fog. Recently a new concept in mosquito control called a chemical fog was reported by Stokes (1967, Proc. Calif. Mosquito Contr. Assoc. 35: 122). Stroud & Stevens (1968, Mosquito News 28: 569–71) reported the effectiveness of this method as a ground application with propoxur and fenthion. An aerial application technique and the description of the chemical reaction was described by Knapp (1968, Mosquito News 28: 516–24). Basically, this consists of hydrated silicon dioxide (SiO2) particles impregnated with the insecticides in association with a fog of ammonium chloride (NH4Cl) particles. These 2 products are formed by a chemical reaction resulting from combining silicon tetrachloride (SiCl4) and 5% ammonia water mixed in the atmosphere [SiCl4 + 4NH3 + 2H2O-SiO2(s) + 4NH4Cl(s)].

Incorporation of aluminum and iron into siliceous sinters

The water content of siliceous sinters deposited from the same thermal water can be expressed in terms of their SiO 2 and Me 2O 3 (Me = Al and Fe) contents: ( H 2O )=0.13(SiO 2) + 7.6( Me 2O 3 The content of each constituent being given in m-moles/g, this equation means that each metallic atom is linked by 3.8 molecules of water. The structure of the siliceous sinters is best represented by hydrous silica adsorbing monomeric hydroxo-complexes Me(OH) 3(H 2O) 3 through elimination of water. Boron content of the sinters also favors this structure.

Mechanism of the carbonatation shrinkage of lime and hydrated cement

AbstractCarbonatation of hydrated lime compacts produces shrinkage and changes in mechanical properties comparable with those found in similarly treated compacts of bottle‐hydrated cement and samples of hardened Portland cement paste. From experimental results obtained with the simpler lime system a mechanism for carbonatation shrinkage is proposed that postulates a through‐solution reaction and induced cycles of wetting and drying.Experiments on compacts of bottle‐hydrated cement show that carbonatation of the ‘combined lime’ is at least as rapid and extensive as the carbonatation of the ‘free lime,’ and that contrary to current opinion the former reaction results in even greater carbonatation shrinkage. The mechanism for carbonatation shrinkage of this system is considered to be connected with dehydration and polymerisation of the hydrous silica product of carbonatation.

Pedological Problems concerning Volcanic Ash in Japan

The authors tried to review scientific works on volcanic ash soils in Japan from the pedogenetical point of view.Morphology: The soils consist of the thick humified loose A horizon and brownish structural B to BC horizon, though in younger soils A-C sequence is common, lacking B horizon. Neither any sign of podzolization nor laterization is recognized. Such a normal profile is often disturbed by denudation, accumulation of surface humic soil materials or by successive addition of recent pyroclastic fall.Mechanical, chemical and mineralogical composition: Though younger soils mainly consist of sand and gravel in texture, most of matured soils are so highly weathered that the clay content often amounts to about one-half of the total soil mass. Chemical analysis reveals that matured soils have been suffered from severe weathering which results in marked loss of silica and bases leaving clay complex rich in hydrous sesquioxides. The principal mineral of the clay fraction in volcanic ash soils is allophane with some quantity of various layer silicates, gibbsite and other sesquioxide minerals. Allophane is considered to be formed by co-precipitation of hydrous silica and alumina gels both of which are regarded as end products of severe weathering of volcanic glass and plagioclase dominant in original volcanic ash. The genesis of allophane is mainly conditoned by such peculiar physical properties of the parent material as homogeneous fine grain size, extraordinally broad specific surface area and rapid permeability. And it seems that the genesis is accelerated by the warm and superhumid climate in Japan.Accumulation of humus: The characteristic thick humus layer of volcanic ash soils contains very high amounts of organic carbon (8-30%), and its almost real black colour looks just like as in Chernozem. The raw material must be derived from grass vegetation seeing from the predominace of the phytolith or plantopal in the very fine sand fraction of the humus layer. The chernozemic black colour may be due to highly condensed and polimerized humic acid, which may have been formed in the rather aerobic soil condition of porous volcanic ash materials persisting even under humid monsoon climate. Nevertheless, judging from the fact that more content of the fulvic acid is determined than that of the humic acid in most cases, and that both acids are combined with sesquioxides or allophane and not with Ca, the humus of the soils should have also podzolic character which may be related to superhumid climate and aerobic soil condition. And allophane must be responsible for such a marked accumulation of humus in the volcanic ash soils.Physical and chemical characteristics: The volume of the solid phase of the soils occupies only 20-30% of the whole soil mass, in other words, the porosity and water holding capacity are extremely high and apparent density is very low. It is the main reason why the volcanic ash soils are not only subjected from rapid weathering and specific humification, but also suffered from wind and sheet erosion, as well as frost damage. Clods of the soils are apt to be broken down into water-stable micro-aggregate (0.05-0.02mm in dia.), which is thought to be bound by loose hydrogen bond in the swelling water with Fe or Al bridge. The soils contain a lot of swelling and hygroscopic water, both of which may be mostly combined with allophane. Besides, such structural OH is released continuously by heating or an ion exchange treatments.The reaction of surface horizon of the soils is generally acid based on humic acid, but very weakly acid to nearly neutral in subsoil in which allophane is dominant component in the clay fraction, in spite of extremely low degree of base saturation caused by severe leaching under the superhumid climate. The cation exchange capacity of the soils is rather high, though the determination tends to be ill-reproducible

THE SURFACE ENERGY OF TOBERMORITE

The total surface energy (or surface enthalpy) of a calcium silicate hydrate, tobermorite, having the composition of Ca3Si2O7•2H2O, was determined at 23.5 °C. The tobermorite was obtained from the room-temperature hydration of tricalcium silicate, Ca3SiO5, or β-dicalcium silicate, β-Ca2SiO4, two of the most important constituents of portland cements. The hydration reactions were carried out in three different ways, and 14 preparations were obtained. For each preparation the heats of solution in a mixture of nitric acid and hydrofluoric acid were measured at 23.5 °C, and the surface areas were determined by the B.E.T. method, using water vapor at 25 °C as the adsorbate. The cross-sectional area of the adsorbed water molecule was taken to be 11.4 Å2. The surface energy of tobermorite at 23.5 °C was found to be 386 ± 20 ergs/cm2. It is close to the geometric mean of the surface energies of calcium hydroxide and hydrous amorphous silica, previously reported.Nitrogen adsorption did not measure the true surface area of most tobermorite preparations. This was indicated by negative surface energy values in a number of instances.

Outline of Mineralization in Zoned Granitic Pegmatites

Abstract An introduction to the general problems and procedures of the paper is given, and the background and approach are indicated. Zoned granitic pegmatites are divided into four groups with respect to major constituents. Simple pegmatites, composed mainly of biotite, plagioclase, microcline, and quartz, are distinguished from more complex ones with muscovite, late albite, and lithium minerals respectively. Two types of internal zoning are recognized. They differ in the nature of outer zones, which are made up of granite and graphic granite in one pattern, and of quartz and quartz-muscovite assemblages in the other. The first type is preferentially developed in simple pegmatites, and the other one in more complex deposits. Outer zones of the second type pattern mineralogically resemble inner zones, especially the quartz core and its margin, and therefore this pattern is considered to be reversed, and the pattern of simple pegmatites is chosen as a basis for the later discussion. It is shown that pegmatites crystallized from the walls inward and that internal zoning developed rapidly, and not in response to secular changes in geologic conditions. Internal spatial zones are not accepted as strictly synchronous or paragenetic formations. The following main paragenetical groups are recognized instead: the granitoid, the graphic granite, and the pegmatoid zones, the core margin, alkali replacement, and core margin mica groups, and the quartz core and late alterations. A schematic two-dimensional synopsis of mineralization in pegmatites is given, showing the correlation of minerals with development of pegmatites and paragenetical groups within these. Some features of wall rock alteration and of primary pegmatitic cavities are presented. In the discussion specific genetical problems of pegmatites are indicated, especially those involved in the strong geochemical fractionation, and the formation of the pegmatitic texture, the quartz core, and alkali replacements. For geological reasons a magmatic approach is chosen as a starting point, since it is valid for at least some pegmatites. Claims of a general harmony between mineral association in pegmatites and degree of metamorphism in the surrounding region are rejected and it is shown that they are based on insufficient data and mistakes in reasoning. Interpretation is started with deductions of temperatures, pressures, and gross composition of pegmatite systems. Pegmatitic crystallization is explained as a consequence of low magmatic temperatures, which imply low energy-content and poor nucleation in pegmatite systems. Fractional crystallization is thus the result of heat — and concentration gradients towards the walls and scarcity of growth centres. It is essentially non-eutectic. Scarcity of growth-centres is also the cause of the formation of giant crystals, crystal size being expressed as the mass of crystallized matter divided by the number of available growth centres. Crystallization of quartz is shown to be abnormal by the stop in the formation of graphic granite and the subsequent late formation of the core. After exclusion of alternatives it is explained as being caused by immobilisation of silica due to increased activity of CO2. Muscovite marks increased activity of H2O and CO2, i. e. hydration and extraction of potassium and silica. Alkali replacements are caused by supersaturation (sugary albite) and by changes in stability relations upon the appearance of an aqueous, carbonated phase (cleavelandite, spodumene, petalite), i. e. increased activity of H2O and CO2 and an excess of alkalies over the amount necessary to balance Al2O3. Interpretation is extended to explain reversed (American) zoning and the occurrence of minor minerals. Outer zones rich in quartz and muscovite denote an originally high content of H2O and CO2 whereas the distribution of minor minerals reveals the influence of the same fundamental factors, which ruled the occurrence of major constituents. A special factor is the inactivation and precipitation of core-silica, which raises the concentration of rare constituents in the residual system and favours precipitation of compounds with other anions in the core margin. For a general background brief statements on the mechanisms of the chemical differentiation of pegmatites, and their magmatic and metamorphic genesis are given, along with some comments on the structural behaviour of pegmatites, its relation to metamorphism, and some indications of analogies with other types of rocks and mineral deposits.

THE SURFACE ENERGIES OF AMORPHOUS SILICA AND HYDROUS AMORPHOUS SILICA

The total surface energies (or, more strictly, surface enthalpies) of amorphous silica and hydrous amorphous silica were determined by measuring the heats of solution in a mixture of nitric acid and hydrofluoric acid of samples having differing specific surface areas and bound water contents, and by measuring the surface areas by the B.E.T. method, using nitrogen as adsorbate. The molecular area of nitrogen was taken to be 16.2 Å2 at 77.3 °K. The surface energy of amorphous silica of zero water content (or the energy of the pure siloxane surface) at 23 °C. was found to be 259 ± 3 ergs/cm.2 The heat of hydration by liquid water of the siloxane surface to silanol surface at 23 °C. was found to be 258.6 ± 13.0 cal./gm. of water. From these two values, with the added assumption that the molecular area of bound water was 25 Å2, the surface energy of hydrous amorphous silica with a completely hydrated surface (or the energy of pure silanol surface) at 23 °C. was calculated to be 129 ± 8 ergs/cm.2 This value is only slightly greater than the surface energy of liquid water. Surface area determinations were also made by water vapor adsorption at 25 °C. The packing of physically adsorbed water appeared to be determined by the geometry of the surface. The cross-sectional area of the adsorbed water molecule was found to be 12.5 Å2. The density of amorphous anhydrous silica was 2.28 to 2.29 gm./cc. Silica particles having an average dimension of 37 Å were dehydrated at lower temperatures and sintered at lower temperatures than particles having an average dimension of 64 Å.

A Flaked Flint from the Red Crag

The remarkable specimen which forms the subject of this communication was presented to me by Mr. Reid Moir, who had extracted it with his own hands from the base of the Red Crag exposed in Messrs. Bolton & Laughlin's brick field, near Ipswich.It is a fragment of a nodule of chalk flint, irregularly rhombic in outline, with nearly flat base and a rounded upper surface which slopes away on each side from a medium line (the shorter diameter) joining the two obtuse angles of the rhomb.The upper rounded side formed part of the original surface of the nodule and retains the whitish weathered crust, 8 mm. or more in thickness, which was formed while the nodule lay embedded in the chalk. The exterior of this crust has since been traversed by solutions which have deposited in its pores some silica and ferric hydrate, thus forming a brown superficial layer which is now too hard to be scratched with a knife.

Radium and Geology

AFTER reading Arrhenius's vivid account1 of the bombardment of the earth by electrically charged solar dust, one is prepared to appreciate Prof. Joly's hypothesis as set forth in his letter in NATURE of January 24. On the other hand, Mr. Strutt's analysis of granite affords strong support to the view that the radium it contains is of terrestrial origin. The concentration of this constituent in the biotite might conceivably be due to the absorption of percolating water containing radium in solution, but not in the zircon, a mineral which is as impermeable as quartz. A mineral analysis of Cornish granite from Penrhyn, made by Miss Davies in our geological laboratory, gave the following results:—orthoclase, 24.62 per cent.; albite, 13.42 per cent.; quartz, 40.23 per cent.; muscovite, 10.05 per cent.; biotite, 11.46 per cent.; magnetite and zircon, 0.16 per cent. The heavy portion of the Cornish granite analysed by Mr. Strutts which was insoluble in hydrochloric acid, consisted of silica hydrate and zircon, and if the latter mineral was present to the extent of 0.16 per cent. only, it must have contained, judging from the analysis, 0.637 × 1012 gram of radium per gram, or a little less than was found in crystals of zircon from North Carolina. In the consolidation of granite, the zircon crystallises out first, then the biotite, next the muscovite, afterwards the albite, and, finally, the orthoclase and quartz; but the concentration of radium diminishes in a similar order, a correspondence that can hardly be the effect of chance.