Clay Admixtures Research Articles

A study of the sediments and communities in Lagos Lagoon, Nigeria

Recent increased human pressures on the environment have led to biological consequences in Lagos' coastal waters, notably in the Lagos lagoon and its drainage channel to sea. Two broad surveys were conducted in February and June 1985 and repeated in 1986 to obtain information on the distribution, habitats and communities in the Lagos lagoon in relation to environmental factors. The samples were used for biological, sediment particle size, organic matter, heavy metal and hydrocarbon analyses. A wide variety of sediments occurred throughout the study area. These ranged from fine, medium and coarse sands to admixtures of silt and clay which provided a wide selection of habitats. The western industrialized areas contained high levels of selected heavy metals. Petroleum hydrocarbon contamination was present in most samples. The percentage of total organic matter was closely associated with the sediment types and the influence of waste inputs. The distribution of several species was influenced by the salinity regime and nature of bottom deposits. Benthic macro-infauna was dominated by molluscs, which were most common in the shallow shoal sands of the northeastern portions of the study area. Species characteristic of stressed environments, notably Capitella capitata, Nereis sp. and Polydora sp., were more abundant in the polluted western industrialized portions. Several species showed seasonal population fluctuations. Diversity indices indicated that the communities exhibited high dominance with a small number of species.

The development of soil porosity in experimental sandy soils with clay admixtures as examined by quantimet 720 from besi and by other techniques

For this study thin sections have been prepared of natural and artificial sands mixed with 20% and 40% clay. These and other samples had already been examined using soil physical and soil mineralogical methods for loose samples. Initial thin section studies, with the help of the light microscope alone, have been enlarged upon in this investigation using backscattered electron scanning images and an image analyzer (Quantimet 720). This allowed quantitative information to be obtained on the development of different types of soil porosity patterns using various clay admixtures. Information was also obtained on the influence the form of mineral grains had on the shape of pores in the mixtures of sand and clay. It was also possible to obtain quantitative information on the amount of clays and larger mineral grains in the thin sections. Much of the present data cannot be obtained automatically but must be manually controlled by using the image editor of the Quantimet. This type of work, however, may provide basic data which can subsequently be used to help explain various processes which occur in soils.

Chemical, Physical and Engineering Characterization Of Candidate Backfill Clays and Clay Admixtures for a Nuclear Waste Respository-Part I

ABSTRACTFourteen Canadian clays and clay admixtures were subjected to simulated nuclear waste repository environments. The present work is concerned with the montmorillonite-dominant materials only. The montmorillonite-dominant samples showed significant leaching on interaction with deionized water. On heating the samples at 200°C for 500 hours, montmorillomites lost intermicellar water completely and acquired cusp-like to cylindrical morphologies. The loss of water and the morphological changes in montmorillonites significantly altered the engineering characteristics. Permeability, shrinkage limits, compactability and shear strength varied in response to the dominant exchange cation in the structure of montmorillonites and the presence of other mineral components in the materials. The synthetic granite water reacted with montmorillonites and led to changes in chemical and mineralogical compositions, crystalline state and engineering properties.

Marsh Gases in Muskrat Houses in Winter

Houses in eight different marshes were sampled during the winter. Three of these marshes, located in the Carlos Avery Game Refuge west of Forest Lake, Minnesota, are in an area predominantly of peat soil with an interspersion of small islands of Merrimac loamy fine sand (Smith, Nesom, and Roth, 1918). The vegetation was predominantly cat-tail (Typha latifolia). Other emergent vegetation included rice-cutgrass (Leersia oryzoides), sedges (Carex spp.), cane (Phragmites maxima), bulrush (Scirpus acutus), and wild rice (Zizania aquatica). Aquatic vegetation included pondweeds (Potamogeton berchtoldi, P. zosteriformis, P. natans, P. pectinatus), coontail (Ceratophyllum demersum), star-duckweed (Lemna trisulca), and water moss (Drepanocladus sp.). The other five areas, all in Ramsey County, may be characterized briefly as follows: (1) The southwest bay of Lake Owasso in Rose Township is a peat soil with underlying admixtures of silt and clay (Smith and Kirk, 1916). Again the most abundant vegetation was cat-tail, although sedges, smartweeds (Polygonum spp.), rushes (Eleocharis spp.), and duck-potato (Sagittaria latifolia) were also found. Aquatic vegetation included sago pondweed (Potamogeton pectinatus), yellow water-lily (Nuphar variegatum), and coontail. (2) An extensive marsh in White Bear Township near the junction of U.S. Highway 61 and County Road D had similar soils and vegetation. (3) A small marsh supporting cat-tails north of New Brighton in Mounds View Township lies in a Hinckley loamy fine sand. (4) A marsh on Snelling Avenue in Rose Township had Merrimac loamy fine sands and Miami loams and vegetation that was chiefly river bulrush (Scirpus fluviatilis). (5) Another area on County Road C in Rose Township had similar soils and vegetation.

Ceramic Coatings for Nuclear Reactors A Progress Report

Ceramic coatings were prepared from materials having low absorption coefficients for thermal neutrons. They were specifically designed for application to typical high‐temperature alloy parts for use in nuclear reactors. Best results were obtained with boron‐free coatings of the frit‐refractory type, in which a high‐barium frit containing small amounts of phosphate, beryllia, lime, zinc oxide, and titania was milled with additions of ceria or mixtures of chromic oxide and ceria. Coating compositions and test data are given.Summary and ConclusionsA total of 85 new frits and more than 200 new coatings were prepared and tested in the development of ceramic coatings for the protection of high‐temperature alloys against oxidation in air at elevated temperatures. The coatings which were designed especially for use in nuclear reactors, where only materials of low absorption coefficients for thermal neutrons can be used, may be suitable for more conventional purposes. The development work is still in progress, but the results to date may be summarized as follows:(1) Boron‐free frits have been developed and tested that have average neutron absorption coefficients in the range 0.15 to 0.50 barn, fritting temperatures of 2600°F. or below, and fiber‐deformation softening temperatures of 1450°F. or above.(2) The best frits developed to date are of the barium silicate type and contain small amounts of BeO, CaO, ZnO, and P2O5. Some of them also contain TiO2.(3) Coatings containing these frits, with admixtures of clay and various refractory oxides, have been developed and tested. The firing temperatures of the most promising of these coatings are in the range 1850° to 2250°F.(4) Of the refractory oxides used as mill additions in the coatings, best results were obtained with Cr2O3 and CeO2 and mixtures of the two.(5) The best ratio of frit to refractory oxide for all frits is 65 to 35 parts by weight.(6) Coatings were applied and adhered well to all the following alloys: types 309, 310, and 321 stainless steel, Inconel, Nichrome V, Stellite 25, and S‐816.(7) The protection given to the various coated alloy specimens varied with the composition of the alloys as well as with the composition of the coatings. Type 321 stainless steel was the most difficult to protect, and Nichrome V and Inconel were the easiest to protect. Type 310 stainless steel was relatively easy to protect.(8) The best evaluation of the degree of oxidation of a coated specimen during long‐time heating in air was obtained by microscopic comparison of metallographic sections of tested and untested coated specimens and determinations of the depth of external oxidation, maximum depth of stringer penetration, and number of stringers per inch of specimen.(9) The better coatings reduced greatly both the depth of stringer penetration and number of stringers per inch on type 310 stainless steel tested at 1900°F. for approximately 150 hours.

Building of Mississippi Delta

The delta of Mississippi River seems not to extend much, if any, above Baton Rouge and not to be as old as the Pliocene Citronelle formation. Its coarsest sediments are fine sands with very fine sand, coarse and fine silt, and clay admixtures. Its finest sediments are clays or ultra-clays. With the exception of Old River, through which Mississippi River waters commonly discharge into Atchafalaya River, all the natural distributaries are closed artificially by levees down as far as the Forts. Below the lower ends of the maintained levees there are three distributaries: Batiste Colet's Bayou, the Jump, and Cubit's Gap. At Head of Passes the river breaks up finally to form Pass a Loutre, South Pass, and Southwest Pass. An explanation of the method and rate of delta building s attempted.