Identification and chemical characterization of particulate matter from wave soldering processes at a printed circuit board manufacturing company

In this case study, the elemental composition and mass size distribution of indoor aerosol particles were determined in a working environment where soldering of printed circuit boards (PCB) took place. Single particle analysis using ion and electron microscopy was carried out to obtain more detailed and reliable data about the origin of these particles. As a result, outdoor and indoor aerosol sources such as wave soldering, fluxing processes, workers' activity, mineral dust, biomass burning, fertilizing and other anthropogenic sources could be separated. With the help of scanning electron microscopy, characteristic particle types were identified. On the basis of the mass size distribution data, a stochastic lung deposition model was used to calculate the total and regional deposition efficiencies of the different types of particles within the human respiratory system. The information presented in this study aims to give insights into the detailed characteristics and the health impact of aerosol particles in a working environment where different kinds of soldering activity take place.

Measurement of periapical pressure created by occlusal loading

AIM

To develop an in vitro model in which the pressure in the periapical tissues can be measured during loading.

METHODOLOGY

Extracted human maxillary central incisors were embedded in resin blocks that had physical characteristics similar to those of bone and periodontal ligament. Each tooth was loaded with 20, 40, 50, 60, 75, 85, 100, 200, 300 and 450 N vertical forces from the incisal edge of the crown on three consecutive occasions. A minute resistor embedded in the periapical space was used to detect apical pressure changes during occlusal loading. The ratio of apical pressure changes (DeltaP) to the loading force changes (DeltaF) was calculated.

RESULTS

The periapical pressure detected was in direct proportion to the loading force. The mean value of DeltaP/DeltaF was 5.994 kPa N-1 (SD = 2.04).

CONCLUSIONS

Direct proportionality was found between the coronal loading and the apical hydrostatic pressure. The DeltaP/DeltaF ratio determined in this study makes it easier to estimate the apical hydrostatic pressure values during occlusal loading of single-rooted teeth. In this study, the apical pressure generated under occlusal loading was the same magnitude as that estimated with the finite element method.

Comparative microstructural study of the diffusion zone between NiCr alloy and different dental ceramics

Our knowledge on the bonding mechanisms between the metal and ceramic parts of dental systems is very limited. This work tested the hypothesis that the details of the interface processes can be described in the framework of a chemical diffusion model. The development of interfacial phases was investigated by cross-sectional analytical transmission electron microscopy between a NiCr (Wiron 99) alloy and three different dental ceramics (Carat, Vita VMK 95, and Vision). All systems were investigated at normal firing conditions (suggested by the manufacturer) and at increased firing times as well. The conclusions are based on the results that the formation of a nanocrystalline Cr(2)O(3) layer and amorphous silicon oxide inclusions were detected in the early stage of the firing process in all investigated systems, and that, in the case of Carat and Vision ceramics, formation of complex NiCr and NiCrTi oxides was also observed at longer annealing times.

Silver Nanoparticles by PAMAM-Assisted Photochemical Reduction of Ag(+)

The photochemical synthesis of Ag(0) nanoparticles in the presence of amino- and carboxylate-terminated PAMAM dendrimers is reported. The formation of Ag(0) nanoparticles was followed spectrophotometrically and by transmission electron microscopy (TEM). According to TEM investigations Ag(0) nanoparticles with the average size of about 7 nm in diameter were produced. Based on the present investigation a possible mechanism for the Ag(0) nanoparticles formation is proposed. Copyright 2000 Academic Press.