Effect of Holding Time on Populations of Microparticles in Spheroidal Graphite Irons

Non-metallic microparticles in spheroidal graphite irons are a product of the inoculation and the Mg-treatment of the liquid melt. Besides the influence on the mechanical properties of these iron–carbon–silicon alloys, they are also responsible for the nucleation and the morphology of the graphite phase. The present investigation is undertaken to study holding time effects of a (Ba, Ca, Al)–ferrosilicon (called Ba-inoculant) and (Ca, Al)–ferrosilicon (called Ca-inoculant) inoculants on the overall distribution of microparticles. Using the 2D to 3D conversions method, which is typically used for graphite nodules, the non-metallic microparticles’ statistical parameters, such as size distributions and number densities, are quantified. The total number of particles is similar after Mg-treatment and inoculation for Ca-inoculant but not for Ba-inoculated samples, which lose approximately 25 pct of microparticles after 1 minute of holding time. Iron treated with the Ca-inoculant loses about 37 pct of its nodules after 5 minutes, while the Ba-inoculated melts maintain their performance even after 10 minutes. Based on extrapolating the trend of the undercooling, Ba-inoculated samples would reach the uninoculated undercooling values in 48 minutes, while Ca-inoculated samples in only 11 minutes. By evaluating the size distributions of the non-metallic microparticles, the Ostwald ripening hypothesis or particle aggregation can be verified. The results suggest that sulfides are more critical for graphite nucleation since they can be correlated with the graphite number densities. However, due to the small difference in the microparticle population of the uninoculated sample with Ca-inoculated samples, other aspects of the fading mechanism need to be considered, such as transient metastable states, since the central hypothesis of loss of inclusions cannot alone explain the decrease in the nucleation frequency of graphite.

Формирование состава и характеристик поверхности хромоникелевой стали 12Х18Н10Т при лазерном модифицировании в слое экспериментальной легирующей обмазки

The results of an experimental study of laser pulsed modification of the surface of stainless steel 12CR18NI10T in a layer of alloying compound made of graphite paste and nanodispersed titanium dioxide powder (anatase) and without coating are presented. A comparative analysis of the effect of the coating on the elemental and phase compositions, morphological characteristics and microhardness of the modified surface is carried out. It was found that as a result of the treatment, the processes of cementation and oxidation of the surface occur, which made it possible to obtain a mixture of iron carbide and high-strength oxides in the surface layer of steel. In the samples that underwent laser treatment in the coating layer, an increase in the intensity of the diffraction peaks of the graphite phase and the formation of iron oxides Fe3O4 and chromium Cr2O3 with the presence of titanium dioxide TiO2 were revealed, which created a mixed heterophase metal oxide structure with increased mechanical strength. An increase in the microhardness of the modified surface after laser pulsed scanning in the layer of the experimental alloying compound is established.

Atomistic Evidence of Nucleation Mechanism for the Direct Graphite-to-Diamond Transformation

The direct graphite-to-diamond transformation mechanism has been a subject of intense study and remains debated concerning the initial stages of the conversion, the intermediate phases, and their transformation pathways. Here, we successfully recover samples at early conversion stage by tuning high-pressure/high-temperature conditions and reveal direct evidence supporting the nucleation-growth mechanism. Atomistic observations show that intermediate orthorhombic graphite phase mediates the growth of diamond nuclei. Furthermore, we observe that quenchable orthorhombic and rhombohedra graphite are stabilized in buckled graphite at lower temperatures. These intermediate phases are further converted into hexagonal and cubic diamond at higher temperatures following energetically favorable pathways in the order: graphite -> orthorhombic graphite -> hexagonal diamond, graphite -> orthorhombic graphite -> cubic diamond, graphite -> rhombohedra graphite -> cubic diamond. These results significantly improve our understanding of the transformation mechanism, enabling the synthesis of different high-quality forms of diamond from graphite.

Preparation of Graphite Phase Bismuth Carbon Nitride Vanadate Composites and Experimental Analysis of Free Radical Capture

Photocatalysts are mainly divided into two categories: one is that they have good response to sunlight and visible light, such as BiVO4 and Fe2O3; One is that it has its own defects and can not make full use of the energy converted by visible light. In recent years, a class of oxides have attracted much attention because of their good performance of visible light photocatalytic degradation of pollutants. People also have a strong interest in the research of compound oxides in pollutant degradation. In order to further clarify the photocatalytic mechanism of GCB composite samples, different capture agents were added to determine the main active species in the photocatalytic process. Only through the method of modification, the synergistic effect can enhance its photocatalytic activity. 1% g-C3N4/BiVO4(GCB) sample, drhb = 90.4%, the photocatalytic activity did not change significantly after adding IPA. After adding EDTA and VC, the photocatalytic activity decreased, drhb = 32.6% and drhb = 51%. Therefore, the experiments show that h+ and ·O2- are active species of GCB catalytic system, O2 is more important for RHB degradation.

Possibilities of Graphitization of Unburned Carbon from Coal Fly Ash

The paper presents the characteristics of products annealing at the temperatures of 2400 and 3000 °C of unburned carbon from coal fly ash in terms of its possible use as a starting material in the graphitization process. An amorphous substance (organic substance) with an admixture of some minerals has been found in samples subjected to graphitization. However, the graphite phase is dominant in products subjected to graphitization. Studies have also shown a diverse grain morphology in individual samples. The presence of plate-shaped and tube-shaped grains was found. As the graphitization temperature of the starting material increases (2400 and 3000 °C), the specific surface area in the graphitization products decreases. The total pore volume in the samples after the graphitization process was significantly lower than the pore volume of active carbons produced from other unburned carbon. Average pore diameter is similar to the pore diameter in active carbons. The reflectance value of the matrix for the sample graphitized at 3000 °C is characteristic for graphite. Unburned carbon from Polish fly ash can be used as the starting material for graphitization.

DETERMINATION OF THE DIMENSIONAL AND TOPOLOGICAL PARAMETERS OF THE GRAPHITE PHASE IN CAST IRON BY FRACTAL ANALYSIS OF IMAGES OF ITS MICROSTRUCTURE

The basics of metallography and modern systems used for studying and analyzing the structures of materials are described. Special attention is paid to the techniques of quantitative microscopy, as a kind of ancestress of modern microstructure analysis systems. The analysis of modern computer programs used to analyze images of microstructures obtained from digital microscopes is presented. The basics of fractal analysis as a highly effective tool for calculating numerical values of parameters of geometrically complex objects are outlined. Using the example of the analysis of graphitized cast iron structure, the application of the fractal analysis method to determine such characteristics of the graphite phase as the shape of graphite inclusions and their distribution in the alloy volume is demonstrated. As part of the study, various classes of cast iron have been studied, such as graphitic pig iron with flaked graphite, cast iron with vermicular graphite, and high-grade cast iron with spheroidal graphite. To determine the shape of graphite inclusions, a fractal dimension has been proposed to be used, and the unevenness of the distribution has been estimated using such a function as lacunarity. The individual stages of determining these characteristics using a specialized FracLac module applied in the structure of the ImageJ program are presented. The obtained results showed high adequacy. Despite positive assessment, the shortcomings identified during the research on the use of fractal analysis methods for identifying geometrically complex dimensional and topological parameters inherent in the graphite phase in cast iron are noted. The ways for further improvement of these methods for solving a wide range of problems in metallography of alloys are proposed.

Facile Synthesis of Metal Doped Graphite Carbon Nitride for Photocatalytic Degradation of Tetracycline Under Visible Light Irradiation

Using semiconductor photocatalysts for antibiotic contaminants degradation under visible light has become a hot topic in recent years. Herein, a novel cadmium doped graphite phase carbon nitride (Cd/g-C3N4) photocatalyst was successfully constructed via 60 °C oil bath method to degrade tetracycline. Experimental and characterization results revealed that cadmium was well doped at g-C3N4 surface and exhibited high intercontact with g-C3N4. Meanwhile, Cd/g-C3N4 presented excellent electrical conductivity and inhibited the recombination of electron-hole pairs. The introduction of cadmium significantly improved the photocatalytic activity and the degradation efficiency of 10 Cd/g-C3N4 reached to 89.09%, which was exceeded 2.0 times than pure g-C3N4 (43.99%). Additionally, the quenching experiments and electron spin-resonance tests exhibited holes (h+), hydroxyl radicals (•OH) and superoxide radicals (•O2−) were dominated active species in TC degradation. Furthermore, the effects of various conditions on the reaction process, such as different pH, initial TC concentrations and catalyst dosage, were also researched. This work gives a reasonable point to synthesize high-efficiency and economic photocatalysts.

Kajian Pengaruh Temperatur Sintering terhadap Peningkatan Derajat Kristalinitas Karbon dari Limbah Kulit Kemiri

Allotropes of carbon has advantages in the ability to intercalate ions, atoms or molecules that potentially to apply in various technological applications. Graphite one of allotrope carbon which has well intercalation and ion transport capabilities. In case, the synthesis of activated carbon made from candlenut shell was carried out with carbonization temperatures at 700C and used a chemical activator in form of 30% KOH. After the activation process, given the sintering treatment for activating carbon with temperature of 950C and 1000C, respectively, which this process is expected to increase the crystalline phase of activated carbon close to the graphite phase. The result showed that dominantion of the structures were amorphous, with varying degrees of crystallinity ranging 35.23% and 35.44%, respectively, and the degrees of graphitization 36% and 37% for the vertical and horizontal directions, respectively. The treatment of the sintering process with a temperature of 1000C has the highest degree of crystallinity, 35.44%. This indicates that the sintering process has an effect on the activated carbon