Papers by Keyword: Clay

Abstract: Natural radionuclides K-40, and Th-232, U-238 (Ra-226) decay chain products contained in building materials are the main source of radiation dose received by population and the only source of indoor radiation exposure. Present work contains results of the study of natural radionuclide activity level in clay, clay ceramics and silica bricks used in Latvia. Obtained data show that radionuclide content in different clay products can differ up to five times. However, determined activity index values for all tested materials, except fireproof bricks, were below radionuclide concentration level permitted by EU and Latvian national regulations. Comparison with analogous data from other North European and Baltic countries shows that average concentrations of natural radionuclides and activity index values for clay and clay bricks used in Latvia are on the same level as in other countries, except Sweden.

Abstract: Conventional processes for manufacturing porous ceramic sometimes provide bodies with low mechanical strength in addition to the high complexity or cost. This work proposes a new porous ceramic processing route: gelatinization, using as raw material clay with low plasticity, water and gelatin. The characterization of the clay was carried out and specimens of various compositions were produced by varying clay content (40, 50, 55 and 60% of solids) and keeping the water and gelatin content constant in the formulation. After cold forming the samples were fired under various conditions: initial temperature of 300 or 600 °C; maximum firing temperature of 800, 900, 1000, 1100 or 1350 °C. After firing, it was obtained the values of the water absorption, bulk density, apparent porosity, linear shrinkage and mechanical resistance. The best results were for samples fired in temperatures lower than 1100 °C and 50% and 55 % of solid content.

Abstract: Clays are materials consisting of clay minerals and non-clay minerals. Some applications allow to use raw clay others require to separate clay minerals from non-clay minerals. Clay mineral fraction is considered to be a nanofraction. Description and characterization of 3 different Latvian clay nanosized minerals from 3 different geological periods (clay Liepa from Devonian period, clay Vadakste from Triassic period and clay Apriki from Quaternary period) are summarized. The main mineral in these clays is illite, however the presence of kaolinite is observed and its quantity depends on geological period in which clays formed. Nanosized clay mineral particles were obtained using sedimentation method. Comparison of mineralogical composition, BET nitrogen adsorption, zeta potential, DTA/TG analysis and FTIR spectra is given. XRD phase analysis results were very close to each other and shows that mineral of illite is more than that of kaolinite. BET nitrogen adsorption data shows that clay minerals of Apriki has the highest specific surface area (81 m²/g), whereas clay minerals of Vadakste has it the lowest (43 m²/g). Zeta potential values for clay minerals Apriki, Liepa and Vadakste are-40.9 mV, -49.6 mV and-43.0 mV, respectively. DTA analysis and FTIR spectra show similar tendencies for all 3 clay minerals.

Abstract: Dolomitic Roman cement was a widely used binder for construction purposes during the late 19^th/ early 20^th century in territory of Latvia. Because of its hydraulic properties and fast setting it was especially favorable for the usage for the cast elements of Art Nouveau style facades. The production of the material was discontinued in the middle of the 20^th century. Nevertheless, there is a need of compatible material for restoration purposes that is not currently commercially available. A compatible binder has been synthesized from mixture of dolomite flour and clay. The research gives an insight of the ongoing chemical processes during the hydration of the cement minerals in the binder. The influence of clay content in compositions and of firing temperature on the physico-chemical properties and mineralogical composition of obtained material is estimated.

Abstract: Polymer nanocomposites using natural clays such as nanofiller have mechanical properties, flame-retardant, the gas barrier improvement compared to polymers without nanoclay. The aim of this work is intercalated molecules between the clay layers and characterize it with a view to its use in polymer nanocomposites. The kaolinite neat and modified used was characterized by fourier transform spectroscopy (FTIR), X-ray diffraction (XDR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetry (TGA). The results showed that kaolinite can be used as a nanofiller in polymer nanocomposites.

Abstract: In this study the objective was to evaluate the properties affected by the incorporation of phyllite and sand as raw materials in the composition of ceramic material for the roofing tiles production with light color using kaolinite clay from Campos dos Goytacazes – RJ, Brazil as main raw material. Specimens were prepared by uniaxial pressing at 20 MPa and fired at 950oC. The determined technological properties were: dry apparent density, linear shrinkage, water absorption and mechanical strength (three point bend test). The results indicated that the incorporation of sand and phyllite improved the dry apparent density, reduced loss on ignition and aluminum oxide content of the pure clay. These factors resulted in a reduced open porosity, improving water absorption and linear shrinkage. However, the mechanical strength was compromised due to the increase of quartz content.

Abstract: For nanocomposite production, montmorillonite clays are often modified with organic surfactants to favor its intermixing with the polymer matrix. In the present study, Na⁺-montmorillonite (Na⁺-MMT) was subjected to organo-modification by cation exchange with protonated 12-aminolauric (ALA). The amount of the amino fatty acid surfactants loaded were 25, 50, 100 and 200% times the CEC of Na⁺-montmorillonite. X-ray diffraction (XRD) analysis revealed the interlayer spacing of the clay increased from 1.25 to 1.82 nm with increasing ALA content. The amino fatty acid chain were considered to be arranged into a flat monolayer structure at low surfactant loading, while they form a bilayered to a pseudotrilayered structure at high surfactant loading. Infrared spectroscopy (FTIR) revealed the alkylchains adopt a gauche conformation indicating their disordered state. Thermogravimetric analyses (TGA) revealed that the surfactant in the clay were thermally stable with T_d ranging from 353 to 417°. The difference in the melting behavior of the pristine fatty amino fatty acids and confined fatty acids in the interlayer galleries of the clay were evaluated differential scanning calorimerty (DSC). The melting temperatures (T_m) of the amino fatty acid in the clay were intitially higher than the free amino fatty acid but decreased with increasing surfactant loading. The amino fatty acid may be tethered to the clay structure via ionic interaction or ion-dipole attraction. Scanning electron microscopy (SEM) revealed that the organo-clays have a disordered and flaky morphology. The present study suggests that 12ALA is a suitable intercalating agent for the production of organophilic clay materials.

Abstract: Glass fiber reinforced unsaturated polyesters were prepared by hand lay-up technique. Effect of clay conditions and loading, as well as mixing time on tensile modulus, flammability, and wear resistance were evaluated. In general, the results showed that there might be two possible structures, dispersed and agglomerated, in the composite samples. The modulus results showed that the effect of clay drying, as well as higher filler loading increase the property. In contrast, the mixing time resulted in negative effect on modulus. The improvement on modulus and flammability might be influenced by clay dispersion due to shear and viscosity change, while the decrease on modulus and wear resistance might be caused by agglomerated structures due to lubrication effect of moisture content, and less crosslink point caused by styrene evaporation.

Abstract: It is estimated that there are about 300,00 products named biomaterials that are used in the area of Health. Although they are widely used they have yet to be optimized for therapeutic use. Hence, the objective of this work was to develop nanocomposites hydrogels with poly (vinyl alcohol) (PVAl), glucantime, chitosan and synthetic clay Laponite RD, processed by gamma irradiation. To compare the behavior of drug release two systems were compared, PVAl / chitosan / clay and PVAl / clay. The morphology of the nanocomposites hydrogel was understood by using characterization techniques: X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy (AFM) and gel fraction. The release kinetics was analyzed at 37 °C for period of 48 hours. It was observed that the slower release of the drug occurs in the delivery system composed by PVAl / chitosan / clay with correlation of the crosslink type formed by chitosan.

Abstract: In this study, test specimens of nanocomposites were produced through Vacuum Assisted Resin Transfer Molding process, VARTM. By using Epoxy as substrate, test specimens of Nanocomposites were prepared as multiple layers of carbon fibers, clay and carbon nanotube. The carbon fibers are featured in high strength and high thermal conductive. Also, the clay and the carbon nanotube have outstanding nature of strength.To explore the hardness, stress, strain and friction of nanocomposites, various experiments were used in this study, including mechanical hardness test, tensile test and pin on disc bench test. With optimized amount of additives, physical properties of the material, including hardness, tensile strength have increased by 94 % and 111 %. Dry friction is also decreased with the increase of mechanical properties.