Wet Precipitation Process Research Articles

Pressureless sintering of translucent MgO ceramics

MgO nanocrystalline powders were synthesized via a wet precipitation process. X-ray diffraction analysis of the heat-treated precursor powders shows that a crystalline MgO phase forms at ∼500 °C. Translucent MgO ceramics were prepared by pressureless sintering the nanocrystalline MgO powders at 1400 °C for 2 h under ambient atmosphere. The as-sintered MgO ceramics have a relative density of 98.1% with an average hardness of 6.8 GPa. Scanning electron microscope characterization revealed that the translucent MgO ceramics have an average grain size of ∼6 μm.

Highly photocatalytic activity of metallic hydroxide/titanium dioxide nanoparticles prepared via a modified wet precipitation process

Surface modification is one important approach to increase the photocatalytic activity of TiO 2. By using a modified wet precipitation process, novel M(OH) x /TiO 2 nanoparticles were synthesized, where M(OH) x represents ferric or cupric hydroxide. The prepared M(OH) x /TiO 2 powders were characterized with XRD, FT-IR, BET, UV–vis DRS, and TGA, and were observed to yield high photocatalytic ability by using methyl orange (MO) as a model compound of organic pollutants to be degraded. Due to the accelerating effects of the new photocatalyst, the half-time of MO during its photocatalytic degradation at pH 6.0 over M(OH) x /TiO 2 was decreased from 332 min for unmodified neat TiO 2 to 63 min for Fe(OH) 3/TiO 2 and 65 min for Cu(OH) 2/TiO 2, respectively. The enhancing effects of M(OH) x /TiO 2 was further observed in a wide composition range with various M/Ti atomic ratios in the photocatalysts and in a wide pH range of the MO solution from 3 to 7. This enhancing effect is mainly attributed to the increased trapping of the photogenerated electron by the higher valence sites (Fe(III) or Cu(II)) in the hydroxide layer near the M(OH) x /TiO 2 interface and the enriched surface hydroxyl groups which accept photogenerated holes to yield more hydroxyl radicals.

Synthesis control and characterization of hydroxyapatite prepared by wet precipitation process

Several techniques have been utilized for the preparation of hydroxyapatite (HA) and other calcium phosphates for the development of biomaterials. It is vital to know the reaction kinetics to be able to control the material obtained by the aqueous solution route. In the present work, HA has been produced by different wet precipitation processes and different experimental conditions. Calcium hydroxide, calcium phosphate, ammonium phosphate and phosphoric acid were used as reagents. The precipitate was dried at 100 °C overnight and then some samples were treated at 900 °C for 2 h. The powder samples were characterized by scanning electron microscopy (SEM), X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses. SEM photomicrographs showed an aggregate powder, granular to dense and suggested typical columnar particles. Qualitative XRF showed that the main components of HA powders were calcium and phosphorus. Pure HA and other phases according to processing parameters were observed by XRD analysis.

The wet precipitation process of hydroxyapatite

Stoichiometric hydroxyapatite (HA) powder was synthesized by wet method using orthophosphoric acid and calcium hydroxide, as raw materials. In this regard, the time-depending changes of the precipitated particles and effects of heating on them were investigated. The as-precipitated and heated powder samples were examined using field emission electron microscopy (FESEM), XRD and Raman spectroscopy methods. The results revealed that the morphology and size of the precipitated particles change in each stage of the process. After drying, these nanoparticles tend to form small agglomerates.

Some important factors in the wet precipitation process of hydroxyapatite

The precipitation process considered here, involved the addition of orthophosphoric acid solution to a calcium hydroxide solution. Several parameters such as the effects of atmosphere controlling, pH, adding extra acid solution, the amount of stirring speed, and post-chemical treatment were studied. In order to study the thermal stability of synthesised powders, they were sintered for 2 h at 1200 °C and the as-precipitated and sintered powder samples were examined using SEM, XRD, FTIR and ICP methods. The results clearly revealed that the final precipitated powder is hydroxyapatite (HA) with good purity, stoichiometry and successful thermal stability. SEM high magnification micrographs showed that the precipitated HA consists of small rod-like particles.

Carbonation−Calcination Cycle Using High Reactivity Calcium Oxide for Carbon Dioxide Separation from Flue Gas

This study is focused on improving the reactivity of a CaO sorbent for its use in a reaction-based process for the separation of carbon dioxide (CO2) from flue gas. The separation process consists of cyclical carbonation (of a metal oxide) and calcination (of the metal carbonate formed) reactions to yield concentrated CO2 from flue gas. CaO sorbents synthesized from naturally occurring limestone and dolomite were microporous in nature. Pore filling and pore pluggage of these micropores limited the conversion of CaO in the carbonation reaction to about 45−50% of the stoichiometric limit. A wet precipitation process was tailored to synthesize high-surface-area precipitated calcium carbonate (PCC). The pores of PCC predominantly lie in the mesoporous range (5−20 nm). The CaO sorbent obtained from PCC (PCC-CaO) was less susceptible to pore pluggage and attained over 90% conversion. PCC-CaO was also capable of maintaining its high reactivity (>90%) over two carbonation−calcination cycles.