a new polymorph crystalline silica composition having uniform pore dimensions were synthesized by calcining a crystalline hydrated alkyl-ammonium silicate. the pore dimensions approximately were 6 angstrom for silicalite-1 and 11 angstrom for silicalite-2 units. the silicalite-1 was prepared hydrothermally at a ph of about 10 from a reaction mixture consist of water, amorphous silica and a quat...

A new polymorph crystalline silica composition having uniform pore dimensions were synthesized by calcining a crystalline hydrated alkyl-ammonium silicate. The pore dimensions approximately were 6 angstrom for silicalite-1 and 11 angstrom for silicalite-2 units. The silicalite-1 was prepared hydrothermally at a pH of about 10 from a reaction mixture consist of water, amorphous silica and a ...

Quartz (α-quartz), is the most common crystalline silica polymorph in nature and is the only polymorph found in significant concentrations in coal and in coal ash. Since exposure to quartz is liable to cause lung diseases, it is very important to know the concentration of biologically active quartz in respirable particles in order to evaluate their effect on the workers in contact with them. Th...

Silicon dioxide has eight stable crystalline phases at conditions of the Earth's rocky parts. Many metastable phases including amorphous phases have been known, which indicates the presence of large kinetic barriers. As a consequence, some crystalline silica phases transform to amorphous phases by bypassing the liquid via two different pathways. Here we show a new pathway, a fracture-induced am...

This article reviews the analytical methods for crystalline silica polymorphs and summarizes promising techniques for compliance with health-related regulations. X-ray diffraction analysis appears to be the most promising method of determining quartz and cristobalite content at this threshold in many bulk mineral and chemical systems. Other analytical techniques can be used in some mineral and ...

Melanophlogite, a low-pressure silica polymorph, has been extensively studied at different temperatures and pressures by molecular dynamics simulations. While the high-temperature form is confirmed as cubic, the low-temperature phase is found to be slightly distorted, in agreement with experiments. With increasing pressure, the crystalline character is gradually lost. At 8 GPa, the radial distr...

Silica (SiO2) is one of the most common materials on Earth. The crystalline form α-quartz is the stable silica polymorph at ambient conditions although metastable forms exist. α-quartz is a piezoelectric material, it can be produced artificially and is widely used for example in electronics and the biosciences. Despite the many application areas, the atomic surface structures of silica polymorp...

A Raman microspectroscopic study of several fulgurites has been undertaken. A fulgurite is an amorphous mineraloid, a superheated glassy solid that is formed when a lightning bolt hits a sandy or rocky ground and thermal energy is transferred. The Raman spectra revealed several forms of crystalline and fused silica and also the presence of polyaromatic hydrocarbons found in an interfacial zone ...

Theoretical calculations are performed to study transformations in silica as a function of nonhydrostatic stress. Molecular-dynamics calculations reveal a crystalline-to-crystalline transition from a-quartz to a phase with five-coordinated silicon (Si) at high pressure in the presence of deviatoric stress. The phase, which appears for specific orientations of the stress tensor relative to the c...

the aim of this cross-sectional study was to explore the association of crystalline silica aerosols exposure with malondialdehyde in blood serum and urinary neopterin and explore their potential as biomarkers of their external exposure. nonsmoking and healthy male glass sandblasters and control population were randomly selected for this study. all groups were monitored for their personal exposu...