Composition Of Amorphous Material Research Articles

Contribution of amorphous material to properties of a laboratory-prepared soil

The presence and the importance of amorphous material are becoming recognized in sensitive soils and have been documented in previous studies. In order to further appreciate the specific contributions and influences of the varying composition of amorphous material to a sensitive soil, it is necessary to obtain a soil system where the individual components can be rigorously controlled and subjected to proper scrutiny. To achieve this, the laboratory-prepared soils were obtained by mixing synthesized amorphous iron–silica mixed hydroxides of varying composition with silt-sized particles of primary materials such as quartz, feldspar, or hornblende.In this study the influence of water content and the amount and composition of amorphous material mixed with nonclay minerals on the resultant sensitivity and basic engineering parameters is investigated.The results indicate that Atterberg limits of the laboratory-prepared sensitive soils are dependent upon the composition of amorphous material and that the trends established are similar to those obtained in similar tests on natural sensitive clays obtained from St. Alban, Outardes, and Gatineau. Similarly, the increase in shear strength and soil suction upon aging of the prepared sensitive soil is dependent upon the composition or molar ratio Fe2O3/(Fe2O3 + SiO2) of amorphous material.

EFFECTS OF SOME CHEMICAL TREATMENTS ON K/Ca CATION EXCHANGE SELECTIVITY OF LAYER SILICATES

The effects of chemical treatments commonly employed to remove amorphous materials, on the K/Ca cation exchange selectivity (CES) of montmorillonite, kaolinite, chlorite, vermiculite, biotite, muscovite, and soil clays were studied. The K/Ca CES values for biotite and muscovite decreased appreciably upon peroxidation. Both the Na–dithionite–citrate–bicarbonate and boiling 0.5 N NaOH dissolution treatments resulted in a substantial increase in the K/Ca CES of biotite and muscovite. This was attributable to increases in the wedge-zone sites resulting from partial K-depletion of these minerals. Furthermore, the release of structural cations and their subsequent precipitation on mineral surfaces appears to have resulted in the "preferential occupation" of Ca-adsorbing sites and thus contributed to the lower selectivity of Ca ions. However, these two treatments affected the K/Ca CES of illite slightly. Acid NH4-oxalate extraction reduced the K/Ca CES values for all layer silicates investigated except chlorite for which the reverse was true. Selectivity of Ca and the CEC of illite were substantially increased by this treatment. The data suggested that the naturally occurring amorphous inorganic and organic constituents may have higher selectivity towards Ca relative to K. However, the degree of variation in the K/Ca CES seems to be further controlled by the amount, nature, and composition of amorphous materials and the mechanisms by which they are associated with the crystalline mineral components.

The nature and composition of amorphous material and free oxides in some temperate region and tropical soils

Abstract Amorphous clay separated from pedons of a highly weathered soil previously classified as Oxisol and an Ultisol of the Southern States and, from the surface horizons of an Oxisol and two Andepts of the tropics were studied by chemical, DTA, infrared and X‐ray analysis. Considerable amounts of amorphous material, 20–37% in temperate region and 29–40% in tropical soils, were extracted by differential dissolution using 0.5 N NaOH. The molar SiO2/Al2O3 ratios of the dissolved material varied from sesquioxidic to siliceous (0.36–9.1) in temperate region soils, whereas those of the Andepts were allophonic (1.5–1.7). DTA and infrared analysis confirmed these results, however the strong gibbsite peaks in the X‐ray analysis of temperate region soils suggested that the aluminum fraction dissolved was in part, if not all, crystalline in nature. Indications were obtained with DTA and infrared that Na‐dithionite treatment might have altered the nature of the clay.

Amorphous Clay Minerals of Recent Volcanic Ash Soils (Part 1) : Contents and Composition of Amorphous Materials and Existence of Discrete Amorphous Silica

Amorphous Clay Minerals of Recent Volcanic Ash Soils (Part 1) : Contents and Composition of Amorphous Materials and Existence of Discrete Amorphous Silica