O. P. Sinha

A review on nickel-free nitrogen containing austenitic stainless steels for biomedical applications

The field of biomaterials has become a vital area, as these materials can enhance the quality and longevity of human life. Metallic materials are often used as biomaterials to replace structural components of the human body. Stainless steels, cobalt-chromium alloys, commercially pure titanium and its alloys are typical metallic biomaterials that are being used for implant devices. Stainless steels have been widely used as biomaterials because of their very low cost as compared to other metallic materials, good mechanical and corrosion resistant properties and adequate biocompatibility. However, the adverse effects of nickel ions being released into the human body have promoted the development of nickel-free nitrogen containing austenitic stainless steels for medical applications. Nitrogen not only replaces nickel for austenitic structure stability but also much improves steel properties. Here we review the harmful effects associated with nickel and emphatically the advantages of nitrogen in stainless steel, as well as the development of nickel-free nitrogen containing stainless steels for medical applications. By combining the benefits of stable austenitic structure, high strength, better corrosion and wear resistance and superior biocompatibility in comparison to the currently used austenitic stainless steel (e.g. 316L), the newly developed nickel-free high nitrogen austenitic stainless steel is a reliable substitute for the conventionally used medical stainless steels.

Effect of nitrogen and cold working on structural and mechanical behavior of Ni-free nitrogen containing austenitic stainless steels for biomedical applications

This investigation deals with the evaluation of structural and mechanical behavior of deformed (10% and 20% cold work) and annealed (at 1050°C for 15 min followed by water quenching) Ni-free high nitrogen austenitic stainless steels (HNSs). The microstructure was observed by optical micrograph and the mechanical properties were determined by macrohardness and tensile tests. Both stress strain behavior and work hardening behavior were evaluated. HNSs have smaller grain size as compared to low nitrogen steels and no formation of martensite was observed after 20% cold working. Further, it was found that hardness; yield strength and ultimate tensile strength of the steels linearly increases and elongation decreased with nitrogen content and degree of cold working. The strength coefficient was observed to be higher for the high nitrogen steels; it decreased to some extent with degree of cold working. The work hardening exponent was also observed to decrease with degree of cold working. Influence of nitrogen on mechanical properties was mainly related to its effect on solid solution strengthening. X-ray diffraction analysis of annealed as well as deformed alloys further confirmed no evidence for formation of martensite or any other secondary phases. SEM fractography of the annealed and deformed samples after tensile tests indicates predominantly ductile fracture in all specimens.

Long term and electrochemical corrosion investigation of cold worked AISI 316L and 316LVM stainless steels in simulated body fluid

AISI 316L and 316LVM stainless steels in annealed (solution quenched from 1050 °C) and rolled (10% and 20% cold work) conditions were assessed for their long term and electrochemical corrosion behavior in simulated body fluid (SBF) at 37 °C. The techniques used for the characterization of their corrosion resistance were the weight loss method, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. Scanning electron microscopy (SEM) was used to investigate the surface morphologies of the alloys after the polarization tests. Surface analysis of the films formed on the steels in SBF was carried out using X-ray photoelectron spectroscopy (XPS). The weight loss and corrosion rate decreased with increasing degree of cold working. The resistance of a passive film is directly related to the materials corrosion resistance and increases on cold working, indicating the formation of a larger protective oxide layer on the surface of cold worked samples. The corrosion current density (Icorr) decreased with increasing degree of cold working and, simultaneously, the corrosion potentials (Ecorr) became more positive. On observing the pit morphologies using SEM, shallower and smaller pits were associated with cold worked samples as compared to annealed samples. The XPS results indicated that the main elements in the passive oxide layer were Cr, Fe and Mo. The Cr-oxide (ox)u2006:u2006Cr-hydroxide (hy) ratio and the Fe-oxide (ox)u2006:u2006Fe-hydroxide (hy) ratio were observed to be higher for rolled materials than for annealed materials, indicating that the passive films on rolled materials are more protective and improve the corrosion resistance.

Recovery of Multi-Metallic Components from Bottom Ash by Smelting Reduction Under Plasma Environment

A new concept for maintaining inert atmosphere with high temperature ~1973xa0K (1700xa0°C) inside the furnace during smelting reduction was described, in which recovery of metallic values from wastes was done in the presence of metal bath which acts as a solvent. Nitrogen plasma arc was generated by passing current and nitrogen gas through a hollow graphite electrode. In this way, the heat for reduction reactions and melting of metal and slag phases under inert atmosphere was maintained. The mixture of bottom ash and carbonaceous reducing agent was fed in the form of pellets near the plasma zone above the liquid iron bath, used for the absorption of reduced metals after reduction of oxides present in the wastes. Percent recovery of metallic values and different consumption parameters were calculated. It was observed that aluminum, iron, and silicon could be recovered effectively from the wastes.

Promising in vitro performances of nickel-free nitrogen containing stainless steels for orthopaedic applications

The aim of the present work was to study the in vitro corrosion resistance in Hank’s solution and biocompatibility of indigenized low-cost Ni-free nitrogen containing austenitic stainless steels (HNSs) and to compare with conventionally used 316L and 316LVM. The electrochemical behaviour was assessed using electrochemical impedance spectroscopy, potentiostatic polarization and scanning electron microscopy. The MTT assay [3-(4,5-dimethythiazol 2-yl)-2,5-diphenyltetrazolium bromide] was performed using Dalton’s lymphoma cell line for cytotoxicity evaluation and cell adhesion test. The resistance of surface film was raised by increasing nitrogen content in stainless steel (SS). The corrosion current density was decreased with increase in nitrogen content and corrosion potentials for HNS were observed to be more positive. Shallower and smaller pits were associated with HNS, indicating that nitrogen suppresses the pit formation. The HNS had higher cell proliferation and cell growth and it increases by increasing the nitrogen content. The surface wettability of the alloys was also investigated by water contact-angle measurements. The value of contact angles was found to decrease with increase in nitrogen content. This indicates that the hydrophilic character increases with increasing nitrogen content, which is further attributed to enhance the surface free energy that would be conducive to cell adhesion, which in turn increases the cell proliferation.

In-vitro long term and electrochemical corrosion resistance of cold deformed nitrogen containing austenitic stainless steels in simulated body fluid.

This work was focused on the evaluation of the corrosion behavior of deformed (10% and 20% cold work) and annealed (at 1050 °C for 15 min followed by water quenching) Ni-free high nitrogen austenitic stainless steels (HNSs) in simulated body fluid at 37°C using weight loss method (long term), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. Scanning electron microscopy (SEM) was used to understand the surface morphology of the alloys after polarization test. It has been observed that cold working had a significant influence on the corrosion resistant properties of these alloys. The weight loss and corrosion rates were observed to decrease with increasing degree of cold working and nitrogen content in the alloy. The corrosion resistance of the material is directly related to the resistance of the passive oxide film formed on its surface which was enhanced with cold working and nitrogen content. It was also observed that corrosion current densities were decreased and corrosion potentials were shifted to more positive values. By seeing pit morphology under SEM, shallower and smaller pits were associated with HNSs and cold worked samples, indicating that corrosion resistance increases with increasing nitrogen content and degree of cold deformation. X-ray diffraction profiles of annealed as well as deformed alloys were revealed and there is no evidence for formation of martensite or any other secondary phases.

Production of thermal insulation blocks from bottom ash of fluidized bed combustion system

The issues of disposal and environmental problems are increased by the generation of bottom ash from the thermal power plants day by day; hence, its recycling is required. The present study aimed to make thermal insulation blocks using as raw material bottom ash and iron ore slime as a binder and to characterize their engineering properties. Two different fineness values of bottom ash were considered with varying amounts of iron ore slime (0–10%) to make the blocks. Blocks were dried followed by firing at 1000, 1100 and 1200°C, respectively. Cold crushing strength, density and thermal conductivity of these fired blocks showed increasing behaviour with firing temperature, fineness of bottom ash and iron ore slime content. In contrast, a reverse trend was observed in the case of porosity. With increasing firing temperature, the formation of lower melting phases like iron silicate followed by iron aluminium silicate was observed, which imparts the strength inside the blocks. The coarser particles of bottom ash increase the interparticle spaces, which enhances the apparent porosity, resulting in higher thermal insulation property in the blocks. Blocks having better thermal insulation property could be possible to make effectively from coarse bottom ash by adding iron ore slime as a binder.

Effect of cold working on biocompatibility of Ni-free high nitrogen austenitic stainless steels using Dalton's Lymphoma cell line.

The aims of the present work are to explore the effect of cold working on in-vitro biocompatibility of indigenized low cost Ni-free nitrogen containing austenitic stainless steels (HNSs) and to compare it with conventionally used biomedical grade, i.e. AISI 316L and 316LVM, using Daltons Lymphoma (DL) cell line. The MTT assay [3-(4,5-dimethythiazol 2-yl)-2,5-diphenyltetrazolium bromide] was performed on DL cell line for cytotoxicity evaluation and cell adhesion test. As a result, it was observed that the HNS had higher cell proliferation and cell growth and it increases by increasing nitrogen content and degree of cold working. The surface wettability of the alloys was also investigated by water contact angle measurements. The value of contact angles was found to decrease with increase in nitrogen content and degree of cold working. This indicates that the hydrophilic character increases with increasing nitrogen content and degree of cold working which further attributed to enhance the surface free energy (SFE) which would be conducive to cell adhesion which in turn increases the cell proliferation.

Effective utilisation of waste fines in preparation of high-basicity double-layer DRI pellets for minimisation of sticking

Sinter of high basicity is well known for affecting the permeability of the burden in the lower portion of the blast furnace due to the formation of more viscous slag. The high-basicity pellets possess less weather resistance if hardened below 1200°C due to the presence of free lime particles. When hardened above 1200°C, the weather resistance increases with increasing sticking tendency among the pellets due to the formation of low-melting eutectics. In the present investigation, efforts were made to make composite-coated iron ore-fluxed pellets to minimise the problems mentioned above. Lime addition to the core of pellets varied from 5 to 100%. The composite pellets subsequently were fired at 1150, 1200 and 1250°C for 30u2005min. Increasing lime content in the pellets resulted in increasing crushing and drop strength of the green pellets. The percent of reduction and cold crushing strength were found comparable to the conventional pellets with varying lime content up to 30% (core basicity 4.68). Weathering resistance was also found increasing trends with increasing firing temperature. XRD analysis revealed the presence of free lime particles inside the core of composite pellets with increasing lime content. From the present work, it could be concluded that the composite-fluxed pellet made with 20% lime in the core (core basicity 3.0) has enough physical strength (187u2005kg), a high percentage of reduction (96%) and excellent weather resistance properties.

Smelting of Industrial Solid Waste for Recovery of Aluminum: Effect of Charge Material

The present paper deals with the effect of charge material on the recovery of aluminum from the industrial solid waste. For the efficient recovery of aluminum metal having a lower vaporization temperature, smelting was carried out in the presence of metal (iron) solvent bath inside a graphite crucible. Nitrogen plasma arc was generated by passing the current as well as the nitrogen gas through a hollow graphite electrode. Charge containing bottom ash or a mixture of iron ore slime and bottom ash along with a reductant of different reactivity was used either in the form of powder or pellets. Liquid iron bath below the plasma arc zone was utilized as a solvent for the absorption of reduced metals after reduction of the oxides present in the wastes. The quick absorption of aluminum in the liquid iron bath subsequent to the reduction of oxides under an inert atmosphere minimized the vaporization loss of aluminum. The effects of carbon content and its reactivity, form of charge material, charge-layer thicknesses for different charge compositions on the recovery of aluminum were studied for 30xa0min of plasma exposure times in all cases. Maximum recovery of aluminum was found for the charge in powder form having a mixture of bottom ash and iron ore slime along with the increased carbon content as well as charge-layer thickness, respectively. The recovery of aluminum was found to be up to 40.80% for the powder charge containing 50% bottom ash and 50% iron ore slime with the char in double stoichiometry carbon.