Mixed silica and alumina hosted carboxylate oxide for removal of chromium species from wastewater

Increasing in the use of various chromium species over the past few decades has inevitably resulted in an increased flux of their metallic substances in aquatic life. Therefore, experimental work was developed to improve the physical and chemical characteristics of the prepared mesoporous SiO₂–Al₂O₃ mixed oxides via a sol–gel process. The effective key parameter on the properties of the materials was achieved by the addition of carboxylate functional group such as Alph-hydroxyl isobuteric acid (AHIBA) during the gelation process and prior the calcinations step. Better performance of these carboxylate resins are attributed to the complexing ability of the carboxylate groups toward polyvalent chromium species which is added to the normal sorption properties of the oxides. Urea has been used as a means of producing an aluminum precipitate that is easier to filter than that produced by rapid addition of base. Introduction of Al and Si salts together to form mixed oxide modified the way of their substitution in the hosting resin than when they were separately added. The data revealed that mesoporous materials with very narrow pore diameter distribution (micron-sized) and high surface area were obtained. The surface areas and pore size distributions were mainly depend on SiO₂ content. Systematic investigations were carried out on the set of the prepared mixed oxides with different porosity, cross-linking degree and exchange loading to find out the best sorbent for chromium removal. The final objective in all cases was aimed at determining feasible and economically reliable solution to the environmental problems related to the tannery industry.     

Characterization of lead and lead leaching properties of lead glazed ceramics from the Solis Valley, Mexico, using inductively coupled plasma-mass spectrometry (ICP-MS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT)

Ingestion of relatively small amounts of lead is now recognized to cause significant neurological and cognitive effects in humans. Large quantities may be fatal, yet lead poisoning, especially of children, is still a major public health concern in many parts of the world. In rural Mexican communities lead oxide (PbO) is added to ceramic glaze as a fluxing agent, lowering starting firing temperatures to 500 °C. The purpose of this study is to characterize the lead chemical forms in ceramic glazes from the Solis Valley, Mexico, to investigate lead leaching properties of these ceramics, and to demonstrate the applicability of lead isotope signatures as a means of tracing lead source origins. Ceramics were collected from the rural village of Santa Maria de Canchesda, State of Mexico, Mexico. Dried liquid glazes, post-fired glaze material, and pure PbO were analyzed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). Results from DRIFT analysis indicate that PbO (1429 cm⁻¹ band) is the active form of lead found in liquid glazes and ceramics. Some shifting of 1429 cm⁻¹ PbO peak to lower wavenumbers occurs in post-fired ceramics, and this may be due to the formation of lead bisilicate during firing. Ceramics samples were leached in 0.02 M citric acid solution for 1 min, and leached lead concentrations were measured using inductively coupled plasma-mass spectrometry (ICP-MS). Lead concentrations in these leachates varied from 0.4-80.4 μg ml⁻¹, while the control pottery from the US leached only 0.1 μg ml⁻¹ lead. Elemental distributions on glaze surfaces were identified by laser ablation (LA)-ICP-MS. Nitric acid extracts of soils, teeth, and ceramic glazes were analyzed for lead isotope ratios (²⁰⁷Pb/²⁰⁶Pb vs. ²⁰⁸Pb/²⁰⁶Pb) using ICP-MS. Similarities of tooth and ceramic lead isotope ratios indicate that ceramics may be a substantial source of body lead burden in the Solis Valley. This study demonstrates the applicability of lead isotope ratios for lead source identification, and it identifies potential health risks from ceramic use induced lead toxicity within the Solis Valley.     

Influence of the Grain Boundaries on the Heat Transfer in Laser Ceramics

Grain boundaries play a key role in determining several key properties of polycrystalline laser ceramics. Heat transfer measurements at low temperature constitute a good tool to probe grain boundaries. We review the results of heat transfer measurements in polycrystalline Y₃Al₅O₁₂ garnets as well as Y₂O₃ and Lu₂O₃ sesquioxide materials obtained by self-energy-driven sintering of nano-particles. The average phonon mean free path in Y₃Al₅O₁₂ was found to be significantly larger than the average grain size and to scale with temperature as T ⁻² at low temperature. Existing models describing the interaction between phonons and grain boundaries are reviewed. Correct temperature dependence of the mean free path and order of magnitude of scattering rates were found by assuming the existence of a grain boundary layer having acoustic properties different from those of the bulk. A different temperature dependence of phonon mean free path was found for the sesquioxides and was ascribed to the stronger elastic anisotropy of these materials. The thermal resistance associated to the grain boundaries of laser ceramics was found to be lower than in other dense polycrystalline ceramic materials reported in the literature.     

Comparison of Drying Procedures for the Preparation of Alumina Powders with the System Al-Alkoxide/Tertiary Butanol/Water

Two series of alumina gel precursors, obtained from Al sec-butylate, ASB, or Al tert-butylate, ATB, dissolved in tertiary butanol, TB, have been dried according to five procedures, in order to compare their efficiency and the consequences they may have on the structure of the final product. They consist of lyophilization (or freezedrying), evacuation at room temperature (with or without ageing of the gel), drying in an oven at atmospheric pressure, or under hypercritical conditions. Chemical analysis, X-Ray diffraction and spectroscopic characterizations (FTIR and laser Raman) allow the identification of the phases present. The temperature of the drying step, as well as the nature of the alkoxide percursor, considerably affect the final dried products.     

Mass spectrometric analysis of ceramics after decomposition with elemental fluorine

The features of a combustion with elementary fluorine for the case of compact SiC ceramics and model substances for boron containing ceramics (H₃BO₃ and Na₂B₄O₇) were investigated with the aim of their decomposition and analysis. On-line detection of the gaseous decomposition products by quadrupole mass spectrometry using electron impact ionisation was studied. Limitations by blanks and transport interferences were investigated. Standard addition as well as the isotope dilution technique were used for calibration in the case of B, C and W at the trace and major component level.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthdayDeceased May 1995.     

Glycine oligomerization on silica and alumina

Oligomerization of glycine (gly) and diglycine (gly₂) on silica and alumina was observed in experiments simulating wetting-drying cycles at 80°C. Glycine produces less than 1% total yield of gly₂ and diketopiperazine (DKP) after one week. In experiments starting from gly₂, more than 10% DKP is formed. Formation of higher oligomers (gly₃–gly₆) proceeded as well, with 3.8% and 5.1% total yields on silica and alumina surfaces respectively.     

氧化锆陶瓷的摩擦磨损行为与机理

氧化锆陶瓷的工程应用前景广阔，在许多场合都必须与水或水溶液接触，但有关这种陶恣在水中的摩擦磨损行为和机理的研究报道不多见，而且已有的工作也不够深入。因此，对氧化锆陶瓷分别在水润滑和干摩擦下的摩擦学特性及其磨损机理进行了考察。     

（Ca,Mg）—Sialon陶瓷在空气及水润滑条件下的磨损机理研究

利用ＳＲＶ球－盘磨损试验机考察了一种（Ｃａ，Ｍｇ）－Ｓｉａｌｏｎ陶瓷在空气及水中的摩擦学性能，并采用ＥＰＭＡ，ＳＥＭ，ＥＤＡＸ以及ＸＰＳ等分析手段对其磨损机理做了进一步研究。结果表明：（Ｃａ，Ｍｇ）－Ｓｉａｌｏｎ陶瓷在水中比在空气中具有更低的摩擦因数，但具有较高的磨损体积损失。     

ELECTROELASTIC FIELD FOR AN IMPERMEABLE ANTI-PLANE SHEAR CRACK IN A PIEZOELECTRIC CERAMICS PLATE

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