Peiyang Shi

Development of Glass Ceramics Made From Ferrous Tailings and Slag in China

A great amount of ferrous tailings and slag cause severe damage to the ecological environment, which must be reclaimed and utilized. The composition, type, and characteristics of ferrous tailings and slag in China were introduced. The research status and the application outlook of glass ceramics made from ferrous tailings and slag were discussed. Glass ceramics made from ferrous tailings and slag can be applied to various fields, and it will be environmentally conscious materials in the 21st century.

Sulfuric acid leaching kinetics of South African chromite

The sulfuric acid leaching kinetics of South African chromite was investigated. The negative influence of a solid product layer constituted of a silicon-rich phase and chromium-rich sulfate was eliminated by crushing the chromite and by selecting proper leaching conditions. The dimensionless change in specific surface area and the conversion rate of the chromite were observed to exhibit a proportional relationship. A modified shrinking particle model was developed to account for the change in reactive surface area, and the model was fitted to experimental data. The resulting model was observed to describe experimental findings very well. Kinetics analysis revealed that the leaching process is controlled by a chemical reaction under the employed experimental conditions and the activation energy of the reaction is 48 kJ·mol−1.

Descaling Behavior of 430 Hot-rolled Stainless Steel in HCl-based Solution

Descaling of hot-rolled stainless steel is generally implemented through pickling process in HNO3-HF mixed acids, which induces severe environmental concerns of nitrogen oxide (NOx) gases and nitrites. According to the electrochemical measurement, the mass loss test and the appearance analysis, a new pickling process which employed HCl-based solution was proposed and evaluated to provide theoretical basis for the development of environment-friendly and highly effective pickling process. Under the experimental condition, the HCl-based solution can compete with ordinary HNO3-HF mixed acids in terms of pickling efficiency, surface integrity and the removal of Cr-depleted layer. The descaling process of 430 hot-rolled stainless steel in the HCl-based solution consisted of three steps. The descaling solution penetrated the oxide scales into the underlying metal, dissolving the Cr-depleted layer and part of substrates. The oxide scales peeled off from the stainless steel and a polished and smooth surface was exposed. The descaled stainless steel was dissolved uniformly in the HCl-based solution; therefore, the pickling duration was vital for desired surface integrity. Under the static condition, the appropriate descaling time of 4 30 hot-rolled stainless steel in HCl-based solution was 400 s.

Corrosion of hot-rolled 430 stainless steel in HCl-based solution

The mixtures of hydrochloric acid and hydrogen peroxide were employed as the environmental friendly pickling solution for 430 hot-rolled stainless steel in this study. Increase of HCl concentration accelerates the corrosion rate of base metal, however aggravates the intergranular attack in sole hydrochloric acid solution. Addition of oxidant (H2O2) boosts the corrosion potential of stainless steel significantly resulting in the change of electrode action. At high oxidant content (0.6 mol l−1 H2O2), a corrosion product film accumulates onto the surface and the corrosion is then governed by the mass-transport at the film/stainless steel interface. The random dissolving of metal ions because of the film leads to brightening of stainless steel surface and the local corrosion is suppressed.

Study on mechanisms of different sulfuric acid leaching technologies of chromite

The extraction of chromate from chromite via the sulfuric acid leaching process has strong potential for practical use because it is a simple and environmentally friendly process. This paper aims to study the sulfuric acid leaching process using chromite as a raw material via either microwave irradiation or in the presence of an oxidizing agent. The results show that the main phases in Pakistan chromite are ferrichromspinel, chrompicotite, hortonolite, and silicate embedded around the spinel phases. Compared with the process with an oxidizing agent, the process involving microwaves has a higher leaching efficiency. When the mass fraction of sulfuric acid was 80% and the leaching time was 20 min, the efficiency could exceed 85%. In addition, the mechanisms of these two technologies fundamentally differ. When the leaching was processed in the presence of an oxidizing agent, the silicate was leached first and then expanded. By contrast, in the case of leaching under microwave irradiation, the chromite was dissolved layer by layer and numerous cracks appeared at the particle surface because of thermal shock. In addition, the silicate phase shrunk instead of expanding.

Corrosion Behavior of S450EW Low-alloy Weathering Steel in Cyclically Alternate Corrosion Environments

Weathering steel is widely used in various fields due to its excellent mechanical properties and high corrosion resistance. The effect of chromium content on the S450EW weathering steel in cyclic immersion test was studied. The results indicated that the corrosion resistance of S450EW weathering steel is closely related to chromium content. The addition of chromium significantly inhibited the weathering steel corrosion. The corrosion rate of experimental steel after 96 h immersion was 1.101 g•m−2•h−1. The rust of S450EW weathering steel was mainly constituted of FeOOH and Fe3O4 phase, and the elevation of chromium content promoted the formation of α-FeOOH. The fine precipitates of the two phases contributed to the formation of dense dust layer of test steel. Furthermore, the increase of chromium is beneficial for the cure of original defects and cracks of the rust layer via the enrichment of chromium. The corrosion potential and the resistance of corrosion process were thus increased, protecting the experimental steel from further corrosion. A S450EW steel with corrosion resistance more than 1.5 times of Q450NQR1 steel was prepared.

Kinetics of Passive Film Growth on 304 Stainless Steel in H2SO4 Pickling Solution under Chemical Oxidation

H2SO4-H2O2 mixtures are a promising and environmentally friendly passivation medium for the stainless-steel pickling process. The corrosion behavior of stainless steel is highly dependent on the ki...

Effect of pickling process on removal of oxide layer on the surface of ferritic stainless steel

ABSTRACT Oxide layer formed on stainless steel surface can result in a decrease in surface quality. Thus, it must be removed. In this paper, we investigated the effect of different pickling processes on removal of the oxide layer. Ferritic stainless steel was used as raw material. After it received annealing treatment, the components and structure of the oxide layer formed on its surface were studied. Then, the annealed stainless steel was pickled in hydrochloric acid solution system and mixed acid solution system, respectively. Results are as follows. The oxide layer on stainless steel surface has a thickness of 15–35 μm. With increase in hydrochloric acid concentration in hydrochloric acid pickling solution, the weight loss rate of stainless steel increases and is always greater than that in mixed acid pickling system. In addition, the surface of the stainless steel pickled in hydrochloric acid is smoother than that pickled in mixed acid. Furthermore, compared with channels in the oxide layer created during mixed acid pickling, those created during hydrochloric acid pickling are more, leading to shorter removal time. These results are important for increasing the pickling efficiency and improving the surface quality of stainless steel.

Passivity of stainless steel in sulphuric acid under chemical oxidation

ABSTRACT The main purpose of the present work was to study the passivity of stainless steel in sulphuric acid under chemical oxidation with H2O2 solution. Potentiodynamic polarisation and open circuit potential (OCP) measurements indicated that H2O2 facilitates the increase of OCP of stainless steel which shifts from active region into passive region. The X-ray photoelectron spectroscopy results suggested that a passive film, composed of oxyhydroxides, Cr2O3, Cr(VI) species, NiO, and sulphate (FeSO4, Cr2(SO4)3·xH2O), is achieved after H2SO4–H2O2 passivation. The passive mechanism under H2O2 oxidation was discussed and the corrosion resistance of passive film was compared with that of the passive films produced by HNO3 passivity and H2SO4 potentiostatic passivity. The results of electrochemical impedance spectroscopy, cyclic voltammetry, and anodic polarisation experiments confirmed that the chemical oxidation with H2O2 solution is capable of improving the corrosion resistance of stainless steel significantly and the passive film is more stable than those produced by other passivating methods.

Effects of Different Oxidants on HCl-based Pickling Process of 430 Stainless Steel

To shorten the time required for the pickling process and to enhance the quality of ferritic stainless steel plates, the effects of oxidants including hydrogen peroxide (H2O2), potassium permanganate (KMnO4), and potassium chlorate (KClO3) on the pickling behavior in HCl-based electrolyte as well as the surface quality of hot-rolled and blasted 430 stainless steel (430-SS) were studied. Experiments were conducted using mass-loss tests, micro-structure analyses, potentiodynamic polarization curves, and electrochemical impedance spectroscopy measurements. The results showed that the addition of oxidants substantially accelerated the pickling process of 430-SS by enhancing the cathodic reaction rate and reducing the charge transfer resistance. In electrolytes comprising 5 – 8 mass% HCl at a temperature of 40 – 60 °C and at the same concentration within the range from 0 to 2 mass%, H2O2 was demonstrated to be superior to KMnO4 and KClO3 in accelerating the pickling process. The surface quality of 430-SS pickled in the presence of H2O2 was better than those of specimens pickled in the presence of KMnO4 and KClO3 when the removal of the oxide layer, intergranular corrosion, and surface roughness were collectively considered. When 1 mass% H2O2 was added, the mass loss rate of 430-SS was increased by 629% and no residual oxide layer or intergranular corrosion was observed on the surface of the steel; in addition, the roughness was only 1. 7 µm. H2O2 was determined to be a better oxidant than KMnO4 and KClO3 when the pickling process, surface quality, solution recycling, and environment protection were considered as a whole.