In order to clarify the reaction behavior of phosphorus in the multi phase flux, the solid 2CaO · SiO 2 piece was reacted with the CaO-SiO 2 -FeO x -P 2 O 5 slag for 1 to 180 s at 1 573 or 1 673 K. The interfaces between the original solid and liquid phases were observed and compositions of both phases were analyzed by SEM/EDS.The result shows that P 2 O 5 is condensed at the rim layer of 2CaO · SiO 2 piece very fast in less than 1 s. The P 2 O 5 condensed phases are identified as the mixture of 2CaO · SiO 2 -3CaO · P 2 O 5 solid solution and the surrounding liquid slag. After reaction for longer time, the reaction behavior of P 2 O 5 depends on the reaction temperature and initial slag composition. Reaction temperature and mole ratio of CaO/SiO 2 in the initial slag influence the stability of P 2 O 5 condensed phases. Higher temperature induces the dissolution of P 2 O 5 condensed phases while larger mole ratio of CaO/SiO 2 has the opposite effect.KEY WORDS: multi phase flux; hot metal dephosphorization; dicalcium silicate; P 2 O 5 condensed phase; reaction mechanism.The present study is aimed to clarify the microscopic reaction behavior of phosphorus at the interface between solid 2CaO · SiO 2 and liquid CaO-SiO 2 -FeO x -P 2 O 5 slag on the basis of the previous studies. A solid 2CaO · SiO 2 piece was reacted with the CaO-SiO 2 -FeO x -P 2 O 5 slag with different composition at 1 573 or 1 673 K. The interface between the original solid and liquid phases was observed and analyzed by SEM/EDS. The formation mechanism of P 2 O 5 condensed phase at interface between 2CaO · SiO 2 and the P 2 O 5 containing slag was clarified. The influence of temperature and initial slag composition on the condensation behavior of phosphorus was discussed. ExperimentalThe CaO-SiO 2 -FeO x -P 2 O 5 slag was prepared by mixing the synthesized wustite, CaO obtained by the calcination of reagent grade CaCO 3 , reagent grade SiO 2 and 3CaO · P 2 O 5 . With different FeO x content and CaO/SiO 2 mole ratio, three types of slags were used in the present study as shown in Table 1. The 2CaO · SiO 2 piece was prepared by pressing a mixture of CaO and reagent grade SiO 2 on mole ratio of 2 : 1 at 50 MPa, followed by heating at 1 773 K for 24 h. About 1 mass% of 3CaO · P 2 O 5 was also added into the mixture to prevent the dusting of 2CaO · SiO 2 .Ten grams of slag were charged in an alumina crucible (I.D.: 34 mm, O.D.: 38 mm, height: 45 mm) with the coexistence of solid iron (3 g) and melted in a furnace at argon atmosphere. In the previous study on reaction between CaO and slag at 1 673 K, both the Al 2 O 3 crucible and Fe crucible were used. The results proved that about 15 mass% of dissolved Al 2 O 3 at maximum does not affect the reaction significantly.13) Accordingly, it is supposed that the influence of Al 2 O 3 impurity is also limited in the present study. Solid iron was used to control the oxygen partial pressure determined by the Fe/FeO equilibrium. The solid 2CaO · SiO 2 piece (0.5 to 1 g, f10ϫ1 mm cylinder shape) attached to the ti...

Electrodeposition of Si films from a Si-containing electrolyte is a cost-effective approach for the manufacturing of solar cells. Proposals relying on fluoride-based molten salts have suffered from low product quality due to difficulties in impurity control. Here we demonstrate the successful electrodeposition of high-quality Si films from a CaCl -based molten salt. Soluble Si -O anions generated from solid SiO are electrodeposited onto a graphite substrate to form a dense film of crystalline Si. Impurities in the deposited Si film are controlled at low concentrations (both B and P are less than 1 ppm). In the photoelectrochemical measurements, the film shows p-type semiconductor character and large photocurrent. A p-n junction fabricated from the deposited Si film exhibits clear photovoltaic effects. This study represents the first step to the ultimate goal of developing a cost-effective manufacturing process for Si solar cells based on electrodeposition.

Herein we report the demonstration of electrochemical deposition of silicon p-n junctions all in molten salt. The results show that a dense robust silicon thin film with embedded junction formation can be produced directly from inexpensive silicates/silicon oxide precursors by a two-step electrodeposition process. The fabricated silicon p-n junction exhibits clear diode rectification behavior and photovoltaic effects, indicating promise for application in low-cost silicon thin film solar cells.

Direct electrolytic reduction of SiO 2 was investigated in molten CaCl 2 at 1123 K as a fundamental study to develop a continuous process for solar-grade Si production. Several different types of SiO 2 granules, as well as SiO 2 pellets, were successfully reduced to Si on the bottom cathode of a Si plate. Three parameters were varied in the reduction of SiO 2 granules: electrode potential, layer thickness of the SiO 2 granules, and SiO 2 particle size. The reduction rate was evaluated by the magnitude of the reduction current. The main factor determining the reduction rate was the diffusion of O 2− ions inside the reduced porous Si layer filled with the electrolyte. Another factor which influenced the reduction rate was the contact resistance between Si granules.

Production of silicon film directly by electrodeposition from molten salt would have utility in the manufacturing of photovoltaic and optoelectronic devices owing to the simplicity of the process and the attendant low capital and operating costs. Here, dense and uniform polycrystalline silicon films (thickness up to 60 µm) are electrodeposited on graphite sheet substrates at 650 °C from molten KCl-KF-1 mol% K 2 SiF 6 salt containing 0.020-0.035 wt% tin. The growth of such high-quality tin-doped silicon films is attributable to the mediation effect of tin in the molten salt electrolyte. A four-step mechanism is proposed for the generation of the films: nucleation, island formation, island aggregation, and film formation. The electrodeposited tindoped silicon film exhibits n-type semiconductor behavior. In liquid junction photoelectrochemi cal measurement, this material generates a photocurrent about 38-44% that of a commercial n-type Si wafer.

The electrochemical reduction behavior of stratified SiO 2 granules in molten CaCl 2 at 1123 K (850℃) was investigated to develop a new process for producing solar-grade silicon. The cross sections of the electrolyzed electrode prepared from a graphite crucible filled with SiO 2 granules were observed and analyzed. The visual and SEM observations indicate that the overall reduction proceeds via two different routes. In one route, the reduction proceeds along the granule surfaces from the SiO 2 near the conductor to the distant SiO 2. In the other route, the reduction proceeds from the granule surface to the core of each granule. The reduction along the granule surfaces is faster than that from the surface to the core. Fine SiO 2 granules are expected to be favorable for a high reduction rate.

A highly efficient photoenergy conversion is strongly dependent on the cumulative cascade efficiency of the photogenerated carriers. Spatial heterojunctions are critical to directed charge transfer and, thus, attractive but still a challenge. Here, a spatially ternary titanium-defected TiO2@carbon quantum dots@reduced graphene oxide (denoted as V Ti@CQDs@rGO) in one system is shown to demonstrate a cascade effect of charges and significant performances regarding the photocurrent, the apparent quantum yield, and photocatalysis such as H2 production from water splitting and CO2 reduction. A key aspect in the construction is the technologically irrational junction of Ti-vacancies and nanocarbons for the spatially inside-out heterojunction. The new “spatial heterojunctions” concept, characteristics, mechanism, and extension are proposed at an atomic-/nanoscale to clarify the generation of rational heterojunctions as well as the cascade electron transfer.

Synopsis :It is quite important to reveal the microscopic reaction mechanisms and the role of the solid and liquid phases in the solid CaO coexisting flux in the hot metal dephosphorization process. In the present study, solid CaO piece and FeO x -CaO-SiO 2 -P 2 O 5 slag with various FeO x and P 2 O 5 contents, and CaO/SiO 2 ratios of the slag were reacted at 1573 and 1673K. The interface between solid CaO and molten slag was observed and analyzed by SEM/EDS. Microscopic reaction mechanisms between solid CaO and molten slag was discussed with changing reaction times, slag compositions and temperatures. The CaO-FeO x phase adjacent to solid CaO, and the CaO-SiO 2 or CaO-SiO 2 -P 2 O 5 solid phase coexisting with the FeO x -CaO-SiO 2 liquid slag next to the CaO-FeO x phase were observed for all slag compositions, temperatures and reaction times. Phosphorus was condensed as 2CaO · SiO 2 -3CaO · P 2 O 5 phase more easily in the case of higher CaO/SiO 2 ratio and higher FeO x content in slag. There was a linear relationship between P 2 O 5 content in 2CaO · SiO 2 -3CaO · P 2 O 5 phase and the distance from CaO-FeO x phase to 2CaO · SiO 2 -3CaO · P 2 O 5 phase. The P 2 O 5 content increased from CaO-FeO x boundary toward bulk slag, and P 2 O 5 content in the condensed phase near the CaO-FeO x phase increased with increasing reaction time. This P 2 O 5 concentration gradient tended to diminish. These results suggest that the condensation of phosphorus as 2CaO · SiO 2 -3CaO · P 2 O 5 phase was controlled by P 2 O 5 diffusion from bulk slag to reaction interface, not by absorption of P 2 O 5 into 2CaO · SiO 2 particle.