Solidification and Refining

Solidification involves a phase change from liquid to solid. Most impurities have a lower solubility in solid than in the liquid phase. Consequently, solidification presents an opportunity to refine or purify metals. The redistribution of impurities during freezing (called segregation) also has a considerable influence on the properties of the solidified casting. This chapter deals primarily with three subjects: removal of impurities during solidification; transferral of unwanted elements to parts of the casting where they do not harm the finished product; and grain refinement, where a nucleant is added to achieve a small (refined) grain structure. The segregation coefficient is defined. The mass transfer coefficient of impurities from solid to liquid is considered and used to model macrosegregation. Two important industrial processes are described in detail: the refining of silicon for solar cells, and the grain refinement of aluminium.

Cleaning of humid air from ammonia impurities by UV radiation

The removal of ammonia impurities (100–200 ppm) in a humid air flow with a flow rate of 30–150 m3/h by ultraviolet radiation of an low-pressure amalgam lamp with a wavelength of 185 nm and 254 nm was experimentally investigated. The presence of water vapor is necessary for the effective removal of impurities by UV radiation, since highly active OH and atomic hy-drogen H radicals are formed during the dissociation of water molecules. The presence of water droplets dramatically reduces the efficiency of cleaning. The main reactions of photooxidation are considered. The high efficiency of removing ammonia molecules by one photon of 185 nm is noted.

The Promotor and Poison Effects of the Inorganic Elements of Kraft Lignin during Hydrotreatment over NiMoS Catalyst

One-pot deoxygenation of kraft lignin to aromatics and hydrocarbons of fuel-range quality is a promising way to improve its added value. Since most of the commercially resourced kraft lignins are impure (Na, S, K, Ca, etc., present as impurities), the effect of these impurities on the deoxygenation activity of a catalyst is critical and was scrutinized in this study using a NiMoS/Al2O3 catalyst. The removal of impurities from the lignin indicated that they obstructed the depolymerization. In addition, they deposited on the catalyst during depolymerization, of which the major element was the alkali metal Na which existed in kraft lignin as Na2S and single-site ionic Na+. Conditional experiments have shown that at lower loadings of impurities on the catalyst, their promotor effect was prevalent, and at their higher loadings, a poisoning effect. The number of moles of impurities, their strength, and the synergism among the impurity elements on the catalyst were the major critical factors responsible for the catalyst’s deactivation. The promotor effects of deposited impurities on the catalyst, however, could counteract the negative effects of impurities on the depolymerization.

Effects of Slag Treatment Conditions on Boron Removal from Metallurgical Silicon by United Gas-slag Refining Technology

Impurities in industrial silicon strongly affect the performance and use value of silicon products, so that raw industrial silicon must be refined to reduce the impurity content and improve its quality. In this work, the effect of the conditions of the refining process on the removal of impurities was studied. The slag agent and industrial silicon powder are uniformly mixed, and a mixed gas of Ar-H 2 O-O 2 is blown into the melt for refining experiments when the set refining temperature is reached. 3% mass fraction high-purity boron powder is pre-melted into industrial silicon raw materials to prepare Si-3%B alloy raw materials, and then the Si-3%B alloy raw materials are refined and pickled with CaO-SiO 2 -CaCl 2 . The composition of the slag agent, the slag-agent-to-silicon mass ratio, the refining time, and the refining temperature conditions were explored, and the best efficiency of boron removal was found to be 96.77%, with the boron content in silicon decreased from 22 ppmw to the lowest value of 0.6 ppmw. The boron content in refined silicon shows a clear decrease, demonstrating that slag-making gas blowing refining is effective for the removal of impurities in industrial silicon.

IMPORTANCE OF SHODHANA WITH SPECIAL REFERENCE TO SAMANYA SHODHANA OF TAMRA

Rasa Shastra is a branch of Ayurveda, which deals with the uses of drugs originated mainly from metals and minerals substances like Tamra Bhasma. Raw Tamra may contain impurities, heterogeneous and unwanted qualities. Aim of Shodhana is to make it purified and make it free from toxicity and suitable for the body. In this study Shodhana of Tamra was performed by classical method mentioned in Rasa Ratna Samucchya. In this process for Samanya Shodhana of Tamra. It was heated and after red hot it was quenched for 7 times in Tila Taila, Takra, Gomutra, Kanji and Kulattha kwatha in order. Total weight loss of Tamra after Samanya Shodhana was 13.33%, which shows removal of impurities. Literally, Shodhana is a procedure of elimination of Doshas in a drug. After Shodhana Loss on weight of Tamra, pH and colour changes of all liquid media were observed.

Effect of partially reduced highly fluxed DRI pellets on impurities removal during steelmaking using a laboratory scale EAF

The present work represents a comparative study on the impurities removal from pig iron melt by addition of partially reduced highly fluxed direct reduced iron (DRI) to make steel in a 2 kg capacity electric arc furnace (EAF). Three types of fluxed DRI (30, 50, 80% Reduction (%R) with similar basicity-8) were used to maintain different level of oxidizing potential on the bath for studying the kinetic behaviour of impurities removal from melt. Results showed that the rate of removal of impurities (i.e. C, Si, Mn, P, S etc.) was increased initially up to 5 minutes of reaction time then decreased afterwards. Phosphorus (~64%), sulfur (~16%) and carbon (~94%) were removed simultaneously up to 25 minutes of reaction time using 30%R fluxed DRI. Similarly, phosphorus (~33%), sulfur (~50%) and carbon (~62%) were removed simultaneously using 50%R fluxed DRI while highly reduced (80%R) flux DRI removed sulfur (~58%), carbon (~56%) with a small fraction of phosphorus (~18%) from pig iron. It was observed in all the cases that silicon (>99%) and manganese (>80%) were removed. From the present study, it can be concluded that ~30%R DRI is favorable for effective phosphorus removal whereas ~80%R is favorable for sulfur removal. The significant removal of impurities could be achieved by charging ~50%R fluxed DRI in the pig iron melt.