Purifying by a solution containinghydrofluoric acid: disclosed is a method of purifying a solution containing hydrofluoric acid, nitric acid and at least one silicon impurity by treating the solution with at least one reverse osmosis membrane. According to the method of the present invention, silicon impurities contained in the solution containing hydrofluoric acid and nitric acid can be selectively removed or reduced. This method can be advantageously used in the photovoltaic industry or in the battery component industry.

Underestimation of chromium and zirconium in soils by hydrofluoric acid digestion: The concentrations of chromium (Cr) and zirconium (Zr) in 503 soil samples collected from 78 site in Japan were determined by using two utterly different methods. The first was the relatively widely used inductively coupled plasma-mass spectrometry (ICP-MS) combined with digestion with hydrofluoric acid (HF) and perchloric acid (HClO4). The second was a non-destructive polarizing energy dispersive X-ray fluorescence spectrometric method (EDXRF) using pressed powder pellets. The Cr concentrations obtained by EDXRF were higher than those obtained by ICP-MS in ~75% of the samples.The differences between the two methods were greater for Zr than for Cr. Zirconium concentrations obtained by EDXRF were higher than those by ICP-MS for all samples except three. The difference between the two methods was more pronounced in soils derived from granite that is widespread in western Japan. The EDXRF/ICP-MS ratios for seven soil samples from different horizons at a single sampling site ranged from 4.82 to 6.94 and were generally higher at the A horizon (Apg and Ag) and decreased with depth. Our results indicate that there is a high possibility of underestimation of Cr and Zr contents in soils for a considerable number of samples if determined with ICP-MS, and it could also overlook some important chemical characteristics of soils.

Hydrofluoric acid etching of dental zirconia: among the diverse treatments proposed to promote the osseointegration of zirconia dental implants, hydrofluoric acid (HF) etching appears to be a good candidate. However little is known on the effect of this process on the mechanical properties and long-term reliability. In this work, the surface integrity, the flexural strength and the ageing sensitivity of yttria-stabilized zirconia were assessed after etching in HF 40%. Results show that etching induces an increase of monoclinic phase content and a decrease in flexural strength. The strength decrease is limited to 15% for etching times below 60 min, whereas it reaches 29% after 120 min because of the formation of large etching pits. No substantial change in the ageing sensitivity was evidenced. Within the limits of this study, HF 40% etched zirconia appears to be reliable for long-term implantation provided that the etching duration does not exceed 60 min.