Clays, clay minerals and cordierite ceramics - a review

The conventional methods for the synthesis of cordierite ceramics include the solid-state sintering of individual oxides of magnesium, aluminium and silicon of the corresponding chemical composition of cordierite, or sintering of the natural raw materials. Clays are used in the ceramics industries largely because of their contribution to the molding and drying properties. The most effective use of clays meets with the problems of the improvement of the working properties of clays and bodies through additions of non-plastic materials or chemicals and the influence of the clay content of ceramic bodies on their behavior during firing. Applicable nomenclatures for clays, clay minerals, ceramic raw materials, cordierite ceramics and characteristic structural properties of the cordierite and cordierite polymorphs are summarized. Selected published data confirmed the fact that identical formulation of clay mineral mixtures led to a variable mineral phases sintered in cordierite ceramics. Among the many factors, important roles play chemical and structural characteristics of individual clay minerals used in the clay mineral mixtures and methodology of processing of the green body and sintering conditions.Web of Science59434033

Structural characteristics of cordierites based on commercial vermiculites in relation to the natural and synthetic cordierites

The preparation and characterization of cordierites based on the commercial vermiculites obtained from the powder pre-ceramic mixtures containing talc, kaolinite and vermiculite in the composition close to the cordierite 2MgO.2Al(2)O(3).5SiO(2) has been reported since 2009. The aim of this paper was to characterize the structural properties of the nine synthetic cordierites sintered from the pre-ceramic mixtures containing commercial vermiculites at 1300 degrees C, in comparison with the orthorhombic natural and synthetic hexagonal cordierites (indialites) selected from literature. The orthorhombic natural cordierites showed the elements Fe and Mn replacing Mg in an appropriate correlation F = (Fe+Mn)/(Fe+Mn+Mg) with the unit cell parameter a, and an inverse correlation with parameter c. The unit cell parameters c calculated for the nine synthetic cordierites based on vermiculites (Ver) were in good linear relation with the F-ver = (Fe/(Fe+Mg)(oct) + (K+Na+Ca)(int)) per formula unit of the corresponding vermiculites in the pre-ceramic mixtures. The structural disorder of cordierites based on vermiculites was determined higher, according to the wide index W1/3 of (211) reflection varying in a narrow range W1/36((211)) from 0.290 degrees to 0.299 degrees 2 theta, in comparison with the W1/3((211))= 0.324 degrees 2 theta of the cordierites based on the alumina.Web of Science60431630

α-Fe2O3 nanoparticles/vermiculite clay material: Structural, optical and photocatalytic properties

Photocatalysis is increasingly becoming a center of interest due to its wide use in environmental remediation. Hematite (-Fe2O3) is one promising candidate for photocatalytic applications. Clay materials as vermiculite (Ver) can be used as a carrier to accommodate and stabilize photocatalysts. Two different temperatures (500 degrees C and 700 degrees C) were used for preparation of -Fe2O3 nanoparticles/vermiculite clay materials. The experimental methods used for determination of structural, optical and photocatalytic properties were X-ray fluorescence (ED-XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS), N-2 adsorption method (BET), diffuse reflectance UV-Vis spectroscopy (DRS), photoluminescence spectroscopy (PL) and photocatalytic reduction of CO2, respectively. The data from XRD were confronted with molecular modeling of the material arrangement in the interlayer space of vermiculite structure and the possibility of anchoring the -Fe2O3 nanoparticles to the surface and edge of vermiculite. Correlations between structural, textural, optical and electrical properties and photocatalytic activity have been studied in detail. The -Fe2O3 and -Fe2O3/Ver materials with higher specific surface areas, a smaller crystallite size and structural defects (oxygen vacancies) that a play crucial role in photocatalytic activity, were prepared at a lower calcination temperature of 500 degrees C.Web of Science1211art. no. 188

Vibrational spectroscopy of acid treated vermiculites

The natural vermiculites from different localities (Bulgaria, Brazil, and South Africa) after acid treatment were used for this study. Differently acidified vermiculite samples were prepared from the natural vermiculite sample using different concentrations of hydrochloric acid (0.5 M and 1 M) and different reaction time (2 h and 4 h) at 80 °C. Natural vermiculites and acid treated vermiculites were analyzed by elemental analysis, X-ray diffraction (XRD) analysis and studied using Fourier transform infrared (FTIR) spectroscopy and dispersive Raman spectroscopy. According to the XRD analysis vermiculites are interstratified structures created in the different two-one-zero sheet hydrated phases. Ratio of intensities of spectrally deconvoluted bands at 1075 cm−1 and 1000 cm−1 (stretching vibration of Sisingle bondO bonds of vermiculites and stretching vibration of Sisingle bondO bonds of amorphous silica, respectively) was used to determine the content of amorphous silica in acid treated vermiculite samples. Study of the infrared and Raman spectra of the acidified vermiculites enable a comparison of these two spectroscopic data that have not yet been performed.Web of Science70696

Vermikulit s Ag a Cu použitý jako antibakteriální nanoplnivo v polyethylenu

Vermiculite (Ver) enriched with silver and copper was used as nanofiller to the polyethylene (PE) matrix. Specifically, the low density polyethylene (LDPE) was chosen as a matrix. The samples Ver-Ag,Cu were prepared by shaking of Ver with the aqueous solutions of silver and copper nitrate. The mixtures of the Ver nanofillers and PE were homogenized by melt compounding technique and further thin plates were pressed from stiff matter of PE with Ver nanofiller. The exfoliation of the powdery Ver nanofillers in PE matrix was characterized by the X-ray diffraction analysis of thin plates. Distribution of Ver nanofiller in PE matrix was observed by Light microscopy. The reinforcing effect of nanofillers onto PE matrix was studied by creep experiment. Antibacterial activity of powder Ver-Ag,Cu samples and surfaces of PE/Ver-Ag,Cu samples was tested on the Gram-positive bacteria Enterococcus faecalis. All tested PE/Ver-Ag,Cu surfaces showed good antibacterial behaviour after 24 h in comparison to pure PE. The number of colonies decreased from the countless number to several hundred colonies.Vermikulit (Ver) obohacený stříbrem a mědí byl použit jako nanoplnivo v polyethylenové (PE) matrici. Konkrétně byl jako matrice vybrán nízko hustotní polyethylen (LDPE). Vzorky Ver-Ag,Cu byly připraveny mícháním Ver s vodnými roztoky dusičnanu stříbrného a měďnatého. Směsi Ver nanoplniv a PE byly homogenizovány postupem míchání taveniny a následně byly ze ztuhnuté směsi PE s Ver nanoplnivem vylisovány tenké destičky. Exfoliace práškového Ver nanoplniva v PE matrici byla hodnocena pomocí Rentgenové difrakční analýzy tenkých destiček. Distribuce Ver nanoplniva v PE matrici byla studována Světelnou mikroskopií. Vyztužující efekt nanoplniv na PE matrici byl studován pomocí krípového experimentu. Antibakteriální působení práškových vzorků Ver-Ag,Cu a povrchů vzorků PE/Ver-Ag,Cu bylo testováno na grampozitivní bakterii Enterococcus faecalis. Všechny testované povrchy PE/Ver-Ag,Cu vykazovaly dobré antibakteriální působení po 24 h oproti povrchu čistého PE. Počet kolonií poklesl z nespočetného množství na několik stovek kolonií

Characterization of two low-charge vermiculites after hydrochloric acid treatment

Two natural vermiculites (Ver) with very similar chemical composition but slightly different low charge on the layers were investigated to find an answer the question, how to change their structural and chemical properties after exposure to different concentrations of HCl solutions. Vermiculite from Bulgaria (Ver-B) with the layer charge 0.47 eq/O10(OH)2 and from Brazil (Ver-SL) with the layer charge 0.36 eq/O10(OH)2 were studied on their particle size fraction less than 40 μm after treatment at different HCl concentrations (0.5 M HCl and 1 M HCl). Both samples represent a mixed-layer structure after incomplete transformation of mica (biotite) to vermiculite. Based on the XRD patterns, Ver-B may be considered as the mixed-layer vermiculite interstratified with small proportion of mica layers and Ver-SL as the mixed-layer mica-vermiculite. The leaching with 0.5 M HCl increased SA of Ver-B from 29.5 m2.g-1 to 261 m2.g-1 at Ver-B05 in comparison with the SA of Ver-SL from 14.0 m2.g-1 to 191 m2.g-1 in Ver-SL05. It can be assumed that the acidification was more effective to: (1) leaching of Mg2+ cations at incomplete vermiculated sample Ver-SL and (2) Fe2+and Fe3+ from octahedra and Al3+ from the tetrahedra at vermiculite sample Ver-B and (3) increasing SA at Ver-B.Web of Science12330629

Crystallization and quantification of crystalline and non-crystalline phases in kaolin-based cordierites

Kaolin is most often used as traditional raw material in ceramic industry. The purpose of the study was to obtain understanding of the structural and chemical variability of cordierite ceramics influenced by chemical and mineralogical properties of six raw kaolins taken from different localities when they are applied in ceramics mixtures with vermiculite and sintered up to 1300 degrees C. The X-ray diffraction and simultaneous thermogravimetric and differential thermal analysis were used to identify and characterize crystalline mineral phases and the course of reactions during the heating. The percentages of the crystalline and non-crystalline phases were newly determined by recalculation of the bulk chemical analyses of kaolins and cordierite ceramics using Chemical Quantitative Mineral Analysis (CQMA) method. Varying amounts of minerals in kaolins: kaolinite from 73.3 to 85.0, muscovite from 4.2 to 9.9, and quartz from 6.0 to 19.5 (mass %) affected amount of cordierite/indialite from 75.2 to 85.1, enstatite from 5.8 to 8.9 (when are calculated as their maximal possible percentages), and non-crystalline phases from 8.8 to 15.1 (mass %) in cordierite ceramics. Regression analysis predicted high relationship between quantity of: (a) kaolinite in kaolins and crystalline cordierite and (b) quartz in kaolins and non-crystalline phases in the ceramics. The migration of potassium from muscovite into the cordierite structure, melting point and crystallization of cordierite/indialite phases and pore size variability in relation to impurity of kaolins are documented and discussed.Web of Science1219art. no. 310

Silver and/or copper vermiculites and their antibacterial effect

Vermiculite (V) from Brazil with aqueous solutions AgNO3 and/or Cu(NO3)2 was used for preparation of nanocomposites V/Ag, V/Cu, V/AgCu and V/CuAg using two procedures and their effect on bacteria was compared. Structural changes were evaluated using X-ray diffraction (XRD) analysis, Infrared spectroscopy (IRS) and Scanning electron microscopy (SEM). Elemental chemical composition was determined using X-ray fluorescence (XRF) analysis and the solutions were analyzed by Atomic emission spectroscopy with inductively coupled plasma (AES-ICP). Antibacterial properties of Ag- and Cu-vermiculites and combined Ag/Cu-vermiculites were tested on two bacteria groups: (1) Gram-positive, G+, (Staphylococcus aureus and Enterococcus faecalis) and (2) Gram-negative, G-, (Pseudomonas aeruginosa and Klebsiella pneumoniae). The samples under antibacterial testing showed different effective times and minimum inhibitory concentration (MIC) values. The Gram-negative bacteria showed higher sensitivity to the prepared samples than Gram-positive bacteria. The combined Cu/Ag vermiculites stopped the bacterial growth at lower MIC value.Web of Science1011049

Graphite an exfoliated and organomodified filler for polymeric nanocomposites

Two types of graphite were processed using mechanical route to obtain the highest possible exfoliated graphite. Using three various media, commercial dishwashing liquid, mixture of defined concentration of 4 ammonium quaternal salts and single salt hexadecyl trimethylammonium bromide with addition of ethylene glycol, the liquid exfoliation shear-forces process was employed. The process provides defined exfoliated particles with small particles size and greater crystallinity compare to original graphite. Exfoliated particles were tested using scanning electron microscopy and atomic force microscopy to explain the shape and morphology changes at shearing forces process. The particles were found as irregular rounded shapes with tiny crystals of used organic matter on the edges of particles. Such modification brings advantage for utilization exfoliated particles in polymeric nanocomposites because they will be more likely interacting with organic substance