Accurate, precise, and valid organic and elemental carbon (OC and EC, respectively) measurements require more effort than the routine analysis of ambient aerosol and source samples. This paper documents the quality assurance (QA) and quality control (QC) procedures that should be implemented to ensure consistency of OC and EC measurements. Prior to field sampling, the appropriate filter substrate must be selected and tested for sampling effectiveness. Unexposed filters are pre-fired to remove contaminants and acceptance tested. After sampling, filters must be stored in the laboratory in clean, labeled containers under refrigeration (<4 °C) to minimize loss of semi-volatile OC. QA activities include participation in laboratory accreditation programs, external system audits, and interlaboratory comparisons. For thermal/optical carbon analyses, periodic QC tests include calibration of the flame ionization detector with different types of carbon standards, thermogram inspection, replicate analyses, quantification of trace oxygen concentrations (<100 ppmv) in the helium atmosphere, and calibration of the sample temperature sensor. These established QA/QC procedures are applicable to aerosol sampling and analysis for carbon and other chemical components.

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Quality assurance and quality control for thermal/optical analysis of aerosol samples for organic and elemental carbon

Nanostructured ceramic powders by hydrothermal synthesis and their applications

The effects of steam and carbon dioxide on calcite decomposition using dynamic X-ray diffraction

Hydrothermal stability of pure and modified microporous silica membranes

The hydrothermal stability of microporous (0.6 nm) silica membranes prepared by the sol-gel process was studied at 600 and 800 °C in a 50 mol% steam atmosphere. The membranes remained microporous after calcination and hydrothermal treatment at 600 °C for 30 h but a substantial reduction in the specific surface area (48%) accompanied by a 77% decline in the micropore volume was observed. Hydrothermal treatment at 800 °C for 30 h resulted in complete densification of the membranes. The effect of alumina and magnesia on the hydrothermal stability of the membranes was investigated. Both Al2O3 and MgO were introduced into the membranes by doping the starting silica sol with controlled amounts of the corresponding nitrate salts. Alumina did not change the pore structure of the silica membranes which retained a large part of their microporosity after hydrothermal treatment at 600 °C compared to pure silica membranes. Doping with magnesia, however, resulted in lower specific surface areas relative to those of pure and alumina-doped silica membranes after drying and calcination. These effects on the stability of the membranes are explained by assuming structural changes in the membranes catalysed by magnesia.

The effect of sample preparation on the thermal decomposition of CaCO3

A comparative dynamic x-ray diffraction (DXRD) and differential thermal analysis (DTA) study was performed in the investigation of mullite and spinel formation from slowly hydrolyzed single phase gels with Al/Si ratios ranging from 1/1 to 14/1. Both metastable tetragonal mullite and spinel were observed to form at temperatures 1250 °C. As the Al/Si ratio increases, both the tetragonal mullite and spinel formation temperatures decrease while the orthorhombic mullite formation temperature increases. Based on the Al/Si composition where the formation extents of tetragonal mullite and spinel were maximum, their compositions are estimated to be 2Al 2 O 3 · SiO 2 and 6A12 O3 · SiO 2 , respectively.

Mullite formation from nonstoichiometric slow hydrolyzed single phase gels

The effect of steam on the reaction kinetics of both mullite and metastable spinel formation from sol-gel precursors, having an Al/Si atomic ratio of 3/1, was studied using dynamic x-ray diffraction (DXRD) coupled with differential thermal analysis (DTA). Steam was observed to accelerate the nucleation of tetragonal mullite in single phase gels at ~980 °C. When single phase gels are formed with a faster hydrolysis step, the presence of steam also increases the nucleation of metastable spinel at this temperature, possibly due to the in situ formation of boehmite in locally enriched alumina regions at <300 °C. In addition, steam also enhances the decomposition of metastable spinel in single phase gels and transient alumina in the diphasic gel at ~1200 °C, probably as a result of surface interactions of water with spinel or transient alumina grains. There was no observable effect of steam on second stage mullite formation (~1250 °C) in either the single or diphasic gels. This is attributed to the hypothesis that the rate-limiting step at this stage might be the dissolution of alumina into the silica-rich amorphous matrix, a step that is unaffected by the presence of steam.

Yong Wang

Papers

The effect of sample preparation on the thermal decomposition of CaCO3

Mullite formation from nonstoichiometric slow hydrolyzed single phase gels

The influence of steam on mullite formation from sol-gel precursors