Gas-forming Elements Research Articles

Development of titanium-based certified reference materials

The Institute for Certified Reference Materials (ICRM) issued for the first time certified reference materials (CRM 11777-2021) of the mass fraction of hydrogen, oxygen and nitrogen in titanium-based materials, i.e., titanium alloy 2V (ISO 1-1) and titanium VT 1-00 (ISO 1-2). The finished material is presented in the form of cylinders 2.5 mm in diameter and 5-6 mm height. The mass of a cylinder is about 0.1 g. To certify gas-forming elements, we used the methods of fusion under inert gas flow (hydrogen, oxygen, nitrogen) and high-temperature vacuum extraction with mass spectroscopy (hydrogen). The analyzers were calibrated using CRM, a gas dose (for hydrogen), and a substance of constant stoichiometric composition (potassium nitrate). Conditions for the determination of the mass fraction of hydrogen, oxygen, and nitrogen in titanium and titanium alloys using an ELTRA ONH-2000 gas analyzer in solid materials have been refined in the analytical laboratory ICRM. The accuracy indicators (assigned characteristics) of the measurement procedure were determined using a great bulk of experimental data.

PROVISION OF THE TRACEABILITY OF MEASUREMENT UPON DETERMINATION OF THE GAS-FORMING ELEMENTS IN STEELS

To ensure the traceability of measurements upon determination of carbon, sulfur, nitrogen and oxygen in steels sodium carbonate, sodium sulfate and potassium nitrate, respectively, are used for calibration of automatic analyzers. This approach places the methods of combustion and reductive fusion in the flow of inert gas on a par with the traditional classical chemical methods of determination which include the procedure of calibration by the substance of constant stoichiometric composition. We present the results of participation of the Test Analytical Center of the «Institute for Certified Reference Materials» in the inter-laboratory experiments on analysis of gas-forming elements in standard samples of steels and cast iron EURONORM-CRM.

Effect of Nonmetallic Inclusions and Impurities on the Properties and Quality Characteristics of Round Rolled Product Made of Special Alloyed Steels

It is found from results of studying rolled steel from special alloyed steels of industrial grades 30G1R, 40Kh and laboratory grades 12KhN, 38KhGNM, 41Kh1 that a change in the ratio of Mn:S concentration in the range of 21–620, P content from 0.004 to 0.022 wt.%, non-metallic inclusions up to point 2.5 according to GOST 1778, N up to 0.010%, H up to 0.0005%, with total pressure created by gas-forming elements up to 1.05 atm, are not critical for occurrence of defects and rolling capacity for cold upsetting. Determination of the characteristics of NI, and CANI content in steel 40Kh round rolled product shows that metal corrosion resistance increases by more than a factor of three with a reduction in CANI2 content and inclusions of the system CaO–Al2O3–MgO containing up to 5 wt.% SiO2, and the insignificant effect of other types of inclusions. A study of the metal of high-strength fasteners manufactured by JH (Taiwan), OF, AL (USA) shows that it has a significantly lower content of other types (corundum, calcium, aluminate, sulphide) of inclusions, and conversely better corrosion resistance.

Application of IR and Raman spectroscopy for the determination of the role of oxygen fugacity in the formation of N–С–О–Н molecules and complexes in the iron-bearing silicate melts at high pressures

Large-scale melting of the Earth’s early mantle under the effect of global impact processes was accompanied by the generation of volatiles, which concentration was mainly controlled by the interaction of main N, C, O, and H gas-forming elements with silicate and metallic melts at low oxygen fugacity (fO2), which predominated during metallic segregation and self-oxidation of magma ocean. The paper considers the application of Raman and IR (infrared) Fourier spectroscopy for revealing the mechanisms of simultaneous dissolution and relative contents of N, C, O, and H in glasses, which represent the quench products of reduced model FeO–Na2O–Al2O3–SiO2 melts after experiments at 4 GPa, 1550°C, and fO2 1.5–3 orders of magnitude below the oxygen fugacity of the iron—wustite buffer equilibrium (fO2(IW)). Such fO2 values correspond to those inferred for the origin and evolution of magma ocean. It was established that the silicate melt contains complexes with N–H bonds (NH3, NH2+, NH2-), N2, H2, and CH4 molecules, as well as oxidized hydrogen species (OH– hydroxyl and molecular water H2O). Spectral characteristics of the glasses indicate significant influence of fO2 on the N–C–O–H proportion in the melt. They are expressed in a sharp decrease of NH2+, NH2-(O–NH2), OH–, H2O, and CH4 and simultaneous increase of NH2-(≡Si–NH2) and NH3 with decreasing fO2. As a result, NH3 molecules become the dominant nitrogen compounds among N–C–H components in the melt at fO2 two orders of magnitude below fO2(IW), whereas molecular СН4 prevails at higher fO2. The noteworthy feature of the redox reactions in the melt is stability of the ОН– groups and molecular water, in spite of the sufficiently low fO2. Our study shows that the composition of reduced magmatic gases transferred to the planet surface has been significantly modified under conditions of self-oxidation of mantle and magma ocean.

The powdered calcium hydride TiNi intermetallic compound

A complex investigation of physicochemical properties and structural components of the calcium hydride TiNi intermetallic compound is performed. Peculiarities of the influence of various consolidation types (hot isostatic pressing and hydrostatic pressing with subsequent sintering in vacuum) on the chemical and phase compositions of compacts from studied powders are investigated by optical and scanning electron microscopy, X-ray structural analysis, and analysis of gas-forming elements. It is established that vacuum sintering makes it possible to decrease contents of oxygen, nitrogen, and especially hydrogen.

Effect of the Content and Form of Impurities and Nonmetallic Inclusions on the Metallurgical Quality of Spring Steels

A detailed study is made of the effect of the form and content of impurities and nonmetallic inclusions on the quality characteristics of spring steels of type 60C2XA. It is established that to prevent the formation of “blowhole” defects it is necessary to limit the steel’s content of gas-forming elements as follows: [H] < < 3.5 ppm, [N] < 60 ppm, [O] < 11 ppm, and [C] < 0.54%. It is shown that the hydrogen content of the steel has the strongest effect on the formation of such defects. To make the steel cleaner in terms of its content of nonmetallic inclusions, it is best to make a metallic semifinished product with a high carbon content and a low (200–400 ppm) content of active oxygen, add carbon-bearing materials early during tapping, and proportion the additions of manganese- and silicon-bearing ferroalloys in a regime which leads to the formation of easily removed silicate inclusions. Another effective measure is to use assimilating covering slags composed of two layers in the tundish. To obtain good quality characteristics for rolled products, it is necessary ensure that the combined content of Sn, Pb, and Zn does not exceed 0.008–0.013% and to use a certain temperature-time regime for the casting operation. Here, the optimum degree to which the steel is heated above the liquidus temperature in the tundish is 23–30°C. Experimental results confirmed the adequacy of the principles that were formulated and the effectiveness of the technological measures that were developed.

Effect of the purity of starting materials on the structure and properties of permanent magnets

The need for using pure starting components in the production of Alnico and Nd-Fe-B system alloys for permanent magnets of high quality is substantiated. The content of gas-forming impurities and nonmetallic inclusions was shown to affect substantially the formation of perfect structure of Alnico-type magnets; optimum conditions of preliminary treatment of the melt to decrease the content of gas-forming elements in ingots were determined. The negative effect of the contamination of starting materials with respect to gas-forming elements was determined and correlations between the oxygen content in Nd-Fe-B magnets and their properties were analyzed.

Oxygen fugacity regime in the upper mantle as a reflection of the chemical differentiation of planetary materials

Oxygen fugacity (fO2) in the Earth’s mantle has a bearing on the problems of the chemical differentiation of the Earth’s materials and formation of the chemical and phase state of its shells. This paper addresses some problems concerning changes in the redox state of the upper mantle over geologic time and through its depth and the possible influence of fO2 stratification in the interiors on geochemical processes. Among these problems are the formation of fluids enriched in H2O, CO2, CH4,and H2; the possible influence of reduced fluid migration from mantle zones with low fO2 values on reactions in the lithosphere; and the formation of films of silicate liquids with high H2O and CO2 contents, which could be responsible for metasomatic transformations in rocks. The formation of a metallic core and accompanying large-scale melting of the silicate part of the Earth are the early mechanisms of the chemical differentiation of the mantle that must have had an effect on the redox state and the composition of volatile components in planetary materials. The molten metallic and silicate phases were prone to gravitational migration, which affected the formation of the metallic core. Volatile components had to be simultaneously formed in the zones of large-scale melting of the early Earth. The composition of these volatiles was largely controlled by the interaction of hydrogen and carbon, the two major gas-forming elements in the mantle, with melt under low fO2 values. A remarkable feature is that, despite fairly low fO2 values imposed by the presence of a metallic phase, both reduced (CH4 and H2) and oxidized species of hydrogen and carbon (H2O, OH− and CO 3 −2 ) are stable in the melt. This peculiarity of carbon and hydrogen dissolution in reduced melts may be crucial for the elucidation of mechanisms for the formation of initial amounts of CO2 and H2O connected with incipient melting in the reduced mantle.

Continuum model for predicting microporosity in steel castings

Using a finite element model for simulating dendritic solidification of multicomponent-alloy castings, the pressure and redistribution of gas-forming elements during solidification and cooling in AISI 8620 steel casting alloy were calculated. The model solves the conservation equations of mass, momentum, energy, each alloy component and gas-forming elements (i.e. hydrogen and nitrogen). By solving for the concentrations of hydrogen and nitrogen in the intergranular liquid and comparing the sum of their Sievert's pressures with the local pressure within the mushy zone of the alloy, the model predicts regions of possible formation of porosity. The thermal boundary conditions on test-bar castings were deduced from a thermal calculation performed with a commercial code, ProCAST™. With these realistic thermal boundary conditions, our porosity-simulations were carried out for many cases with combinations of different initial contents of the gas-forming elements: hydrogen in the range of 3–7 ppm and nitrogen in the range of 0–100 ppm. The calculated results are summarized in a plot that separates castings expected to have porosity from those with no porosity. The effect of adding titanium to form TiN inclusions and inhibit the development of porosity during solidification was also investigated.

Simulations of microporosity in IN718 equiaxed investment castings

A finite element model for simulating dendritic solidification of multicomponent-alloy castings has been enhanced to include the calculation of pressure and redistribution of gas-forming elements during solidification and cooling. The model solves the conservation equations of mass, momentum, energy and alloy components, and the gas-forming elements, hydrogen and nitrogen. By solving the transport of gas solutes and comparing their Sievert's pressure with the local pressure, the model can predict regions of possible formation of intergranular porosity. Calculations were performed on equiaxed Ni-base superalloy (IN718) plate castings. The potential to form microporosity was analyzed with different variables including the mass transfer of hydrogen and nitrogen from the casting to the casting/mold gap, the final grain size, a grain-shape parameter and the thickness of the plate casting. The most important factor was found to be the mass transfer coefficient. The results were also affected by the final grain size and grain-shape parameter.

A model for prediction of pressure and redistribution of gas-forming elements in multicomponent casting alloys

A finite element model for simulating macrosegregation in multicomponent alloys is extended to include the calculation of pressure and redistribution of gas-forming elements during solidification. The model solves the conservation equations of mass, momentum, energy, and alloy components, including gas-forming elements such as hydrogen and nitrogen. The results of transport calculations are contrasted with thermodynamic equilibrium conditions to establish the possible formation of pores, assuming that there is no barrier to nucleation of the pores. By solving the transport of gaseous solutes and comparing their Sievert’s pressure with the local pressure, the new mode can predict regions of possible formation of intergranular porosity. Simulations were performed for a nickel-base alloy (INCONEL 718) in plate castings with equiaxed structure, and the evolution of microporosity for different initial concentrations of hydrogen and nitrogen was analyzed. The simulations showed that during solidification and cooling, a large fraction of the hydrogen escapes and a smaller fraction of nitrogen escapes from the casting. The initial gas concentration is an important factor in porosity formation, but the pressure drop due to shrinkage flow is not very significant. The resulting gas porosity is rather insensitive to initial nitrogen concentration, but sensitive to the concentration of hydrogen.

Spectral-isotopic method of determination of gas-forming elements in organic and inorganic substances

A review is given of the latest papers on the application of the spectral-isotopic method of determination of gas-forming impurities in organic and inorganic materials. Main attention is paid to a new kind of investigation, i.e. the development of spectroscopic methods for isotopic analyses of nitrogen, carbon, oxygen, and hydrogen in biological objects for use in analytical monitoring in biological experiments with “tracers”. A universal method is described for the preparation of natural samples, for the separation of the gases to be analyzed from the sample, and for their purification from the impurities. The main characteristics are given of the methods for individual determination of the above elements and for joint analyses of some elements (N 15-C 13-H 2) in one analytical cycle (spectrum excitation conditions, isotope concentration calculations, etc.). The characteristics of the methods have been compared with the results of other researches and the scope of our method for applications in biological investigations with tracers has been defined. The main results of spectral-isotopic method development in the traditional direction, i.e. for quantitative analysis of impurities in solid inorganic materials and for gas analysis, are produced.

Effects of Hydrogen in Aluminium, Magnesium, Copper, and Their Alloys

The nature of hydrogen solutions in metals and the evidence for physical and chemical hydrogen traps are examined as a prerequisite for interpreting and evaluating experimental observations and information from manufacturing operations. The sources, distribution, control, and effects of hydrogen are then considered for the metals and alloys under review. For aluminium and its alloys, unsoundness in castings, mechanical weaknesses generated by hydrogen, and blistering in wrought products are discussed in terms of the redistribution of hydrogen which occurs in the metal as it solidifies during casting. The arguments are extended to the formation and distribution of microporosity in magnesium alloy castings, taking account of the more dominant role of solidification contraction. Reference is also made to effects of an entirely different character which occur with magnesium alloys containing elements which form stable hydrides. The effects in copper are reviewed with emphasis on interactions between hydrogen and other gas-forming elements, notably oxygen, which may also be present. The topics considered are the control of pitch in fire-refined tough-pitch copper, the evolution of gases in copper alloy castings, steam embrittlement of oxygen-bearing copper annealed in reducing atmospheres, and hydrogen blistering in some self-deoxidizing copper alloys in wrought form. The removal of hydrogen from liquid metals is an important element in controlling the effects described and so the various techniques available are described and evaluated where appropriate, including modern practices such as ‘in-line’ degassing for aluminium and its alloys.