To enhance the luminous intensity of phosphors containing Tb 3+ , Gd 3+ was used as a sensitizing ion to recombine with Tb 3+ . Gd 3+ and Tb 3+ ions were loaded on the Al 2 O 3 aerogel matrix with nano porous structure via a simple and facile sol‐gel method. After vacuum drying and calcination, Al 2 O 3 : Tb 3+ , Gd 3+ composite aerogel materials were obtained. Al 2 O 3 aerogel matrix has three‐dimensional nanostructure and good chemical stability, which can provide stable crystal field and emission site for the rare earth activated ions. The results indicated that the introduction of Gd 3+ can effectively enhance the luminescence intensity of Al 2 O 3 : Tb 3+ at 543 nm under 260 nm UV excitation. The optimal ratio of Gd 3+ and Tb 3+ was determined to be 1: 1. The mechanism of Gd 3+ sensitization to Tb 3+ can be considered as electric multipole resonance transmission. We expected that this work could provide guidance for the development of enhancing the luminous intensity of green phosphors for lamp.
In this study, the temperature dependence of Cr(VI) formation and reduction in the presence of CaO was examined during the thermal treatment of sludge that contains chromium. thermogravimetry–differential scanning calorimetry and X-ray diffractometry were used to characterize the thermal behavior and phase transformation, respectively. Na2CO3 leaching procedure was employed to determine the amount of Cr(VI). The result showed that CaO promoted Cr(III) oxidation, however, its influence is very dependent on heating temperature, with the extent of the effect varying with temperature. From 200–400°C, the presence of CaO facilitated formation of intermediate product Cr2O3+ x containing Cr(VI) during dehydration of chromium hydrate, while Cr2O3+ x would decompose as temperature over 400°C, accompanied by part of Cr(VI) being reduced to Cr(III). From 500 to 900°C, Cr(III) reacted with CaO to form a leachable CaCrO4 product. This product was stable and a prolonged heating time did not reduce the amount of Cr(VI) significantly. At 1000–1200°C, part of CaCrO4 was reduced to Ca(CrO2)2 in 1h. While extended heating time above 1h resulted in the Ca(CrO2)2 being oxidized reversibly to CaCrO4 at 1200°C. Since CaCrO4 is thermodynamically less stable over 1000°C, MgO could induce CaCrO4 to be reduced into MgCr2O4 at around 900°C, lower than that for the reduction from CaCrO4 into Ca(CrO2)2. It suggested that adding MgO might be a potential approach for inhibiting Cr(VI) formation during heating sludge containing chromium.
A noticeable amount of electroplating sludge, resulting from electroplating and surface treatment industries, may pose serious threat to human health and surrounding environmental without safe treatment. This study examined the feasibility of preparing the fired clay bricks with the addition of electroplating sludge, by evaluating the physical properties and environmental risk of the prepared clay bricks. It was found that the introduction of electroplating sludge reduced the bulk density and compressive strength, and increased the mass loss, linear shrinkage, porosity ratio and water absorption. It was observed compressive strength declined from 23.5 to 15.5 MPa, and water absorption increased from 2.7 to 3.46% with the addition of electroplating sludge up to 10 wt%. Though the introduction of electroplating sludge influenced the mechanical and physical properties, these parameters are enough according to the values required by the standards. Prolonged leaching experiments up to 20 days were carried out to test the whole bricks and brick powder. The results clearly presented the optimum substitution amount of electroplating sludge in clay bricks was less than 8 wt%. Besides, leaching test suggested that though the prepared bricks with the addition of electroplating sludge were abandoned in the surrounding environmental after the use period, the leaching risks of heavy metals released from the bricks still can be reduced substantially, because heavy metals might be incorporated into stable mineral structure during firing process. These results suggested use of electroplating sludge in the production of fired clay bricks or ceramics might be a alternative and reliable method for the disposal of electroplating sludge.
Background Advanced aerogels with lightweight, flame retardant and rapid cooling properties are urgently needed as thermal insulators in harsh environments. Method The Cr2O3−Al2O3 aerogels were fabricated by simple method and freeze-dried process. A large number of pores were produced in the microstructure of samples by carbonization of soluble starch during calcination. Findings The porous structure makes the density of prepared Cr2O3−Al2O3 aerogel as low as 0.0060 g·cm−3 and the thermal conductivity as high as 0.30 W m−1·K−1, which indicates that the sample has good thermal dissipation and rapid cooling performance. The effect of calcination temperature on cooling rate was studied. The results show that material cooling can be divided into two stages, the second stage is the speed control step. With the increase of the calcination temperature, the cooling rate of sample improves and the cooling time decreases. The prepared Cr2O3−Al2O3 aerogels have good flame retardancy and cannot ignite upon exposure to the burner for 2 min. The flame retardancy and rapid cooling mechanism of the sample was also studied. The Cr2O3−Al2O3 aerogels have the advantages of lightweight, flame retardancy and rapid cooling, which has potential application prospects in the field of flame retardant cooling coatings.
The oxidation behavior of Cr(III) during the thermal treatment of chromium hydroxide in the presence of alkali and alkaline earth metal chlorides (NaCl, KCl, MgCl2, and CaCl2) was investigated. The amounts of Cr(III) oxidized at various temperatures and heating times were determined, and the Cr-containing species in the residues were characterized. During the transformation of chromium hydroxide to Cr2O3 at 300 °C approximately 5% of the Cr(III) was oxidized to form intermediate compounds containing Cr(VI) (i.e., CrO3), but these intermediates were reduced to Cr2O3 when the temperature was above 400 °C. Alkali and alkaline earth metals significantly promoted the oxidation of Cr(III) during the thermal drying process. Two pathways were involved in the influences the alkali and alkaline earth metals had on the formation of Cr(VI). In pathway I, the alkali and alkaline earth metals were found to act as electron transfer agents and to interfere with the dehydration process, causing more intermediate Cr(VI)-containing compounds (which were identified as being CrO3 and Cr5O12) to be formed. The reduction of intermediate compounds to Cr2O3 was also found to be hindered in pathway I. In pathway II, the alkali and alkaline earth metals were found to contribute to the oxidation of Cr(III) to form chromates. The results showed that the presence of alkali and alkaline earth metals significantly increases the degree to which Cr(III) is oxidized during the thermal drying of chromium-containing sludge.
The mixing of galvanized sludge in fired clay brick manufacturing has been regarded as an alternative approach for the consumption of galvanized sludge. Decreasing the surface area and porosity of fired brick definitely lowers the risk of heavy metal release. In this study, a novel method is proposed to reduce the surface area and porosity of bricks and promote heavy metal immobilization by adding waste glass. The introduction of waste glass enhanced the physical and mechanical performances of fired clay bricks and resulted in an increase in bulk density and compressive strength and a decrease in water absorption. Microstructure analysis showed that the texture of the bricks turned from porous to smooth and homogeneous due to the introduction of waste glass. Porosity analysis showed that surface area and pore volume of fired brick were substantially reduced. When the added waste glass amount exceeded 15 wt%, the heavy metal concentrations that leached from bricks containing 10 wt% galvanized sludge fired at 950 °C met the regulatory requirement. These results demonstrate that waste glass can be reused to enhance the stabilization/solidification of heavy metals, during the mixing of hazardous waste in bricks and ceramics manufacturing process.
Cement kiln co-processing is a major technique for disposing of hazardous solid wastes, yet the formation of toxic soluble compounds during the process may
