Growth-sector dependence of morphological, structural and optical features in boron-doped HPHT diamond crystals

Semiconducting boron-doped diamond single crystals of cubo-octahedral habit with prevalent development of octahedron {111} faces and insignificant area of cube {001}, rhombo-dodecahedron {110} and tetragon-trioctahedron {311} faces were obtained using solution-melt crystallization at high pressure 6.5 GPa and temperatures 1380…1420 °C. Using the Fe-Al solvent, which allows controlled incorporation of boron dopant between 2·10–4…10–2 at.% made it possible to vary the electro-physical properties of the crystals. Methods of micro-photogrammetry, atomic force microscopy, and micro-Raman spectroscopy were applied to reveal sectorial inhomogeneity of impurity composition and morphology of different crystal faces. The obtained crystals were shown to have high structural perfection and boron concentration ranging approximately from 1·1017 up to 7·1018 cm–3. An increase in boron concentration increases the area of {111} faces relatively to the total crystal area. Nanoscale morphological features like growth terraces, step-bunching, dendrite-like nanostructures, columnar substructures, negative growth pyramids on different crystal faces are shown to reflect peculiarities of carbon dissolution at high pressures and temperatures. The changes in the crystals’ habit and surface morphology are discussed in relation to inhomogeneous variation of thermodynamic conditions of crystal growth and dissolution at different boron concentrations.

Iron Carbon Masteralloy as Sintering Activator for Low Alloy Powder Metallurgy Steels

In real industrial environment there is always a difference between ideal theoretical condition and real production condition which bears the risk of producing defective or low quality parts. Getting closer to this ideal situation requires more effort and investment which tends to increase the production cost. In the P/M production lines, the sintering stage is one of the most critical processes. Maintaining an open continuous sintering furnace in an ideal condition is a challenge, and this issue gets more pronounced when using alloy powder containing oxygen-sensitive elements such as Cr or Mn which provide good hardenability at low cost but on the other hand form stable oxides that weaken the sintering contacts if they are not reduced properly. In the present study, using a carbon master alloy as a sintering enhancer in the sintering process of Cr-Mo alloyed powder compacts has been investigated. For clearly depicting the effect of carbon master alloy addition on carbon dissolution and deoxidation, sintering was done in argon as inert atmosphere to avoid other reducing agents such as H2. The physical and mechanical properties of the sintered specimens were investigated, and thermal chemical analysis by DIL/MS and carbon/oxygen measurements were performed. The experiments showed that adding iron-carbon masteralloys promote the sintering processes such as reduction of oxides and carbon dissolution in the early stages of sintering, resulting in better properties after final sintering.

Factors influencing dissolution of carbonaceous materials in liquid Fe–Mn

Carbon dissolution from four types of metallurgical cokes and graphite was investigated by using immersion rods in a resistance furnace to clarify the influence of factors governing the rate of carbon dissolution from carbonaceous materials into Fe–Mn melts at 1550 °C. The factors studied were the microstructure of carbonaceous materials, roughness, porosity and the wettability between carbonaceous materials and the melt. Carbon/metal interface was characterised by scanning electron microscopy accompanied with energy-dispersive X-ray spectrometry to investigate the formation of an ash layer. The results showed that coke E had the highest dissolution rate. Surface roughness and porosity of the carbonaceous materials seemed to be dominant factors affecting the dissolution rates. Further, crystallite size did not have a significant effect on the dissolution rates. Solid/liquid wettability seemed to affect the initial stage of dissolution reaction. The dissolution mechanism was found to be both mass transfer and interfacial reactions.

A Microscopic Numerical Simulation of Carbon Dissolution in Different Coke Shapes in the Dripping Zone of Blast Furnace

The carbon dissolution of coke pieces in hot metal mainly influences the carbon content and carbon saturation temperature in the ironmaking process. The liquid metal and slag start to drop down in the dripping zone (DZ) which is located the lower part of blast furnaces. The dissolution of carbon in liquid metal and slag droplets passing the stagnant hot gas flow in the fixed coke bed of the dripping zone were observed by a multi-droplet model based on the Computational Fluid Dynamics (CFD) method. The uniform-coke pattern was set in the model following the preferred distribution of a one-layer packed bed from a water droplet experiment. The different coke shapes relating to the shape factor from 0.75-1.0 were observed in a 40mm-coke bed. For one-time drainage, the carbon dissolution slightly increased after flow in the coke bed zone and showed a high percentage on the coke surface. The concavity and convexity of coke pieces have more effect on the interaction between liquid and coke surface. Besides, the carbon dissolution can be investigated to approach the coke consumption in one coke channel and estimate the carbon content and carbon saturation temperature of liquid metal after draining.

Транспортные процессы с участием атомов углерода между поверхностью и объемом родия при образовании и разрушении графена

Equilibrium transport of atomic carbon between Rh surface and bulk has been studied. This transport controls the kinetics of the phase transition resulting in graphene growth or destruction. The difference ΔE=0.7 eV has been measured between the activation energy of atomic carbon dissolution E1s and that of its segregation from the bulk to the surface E1s. The temperature dependence of chemisorbed carbon critical cover Neq = Neq(T) has been measured, that is the cover when 2D phase transition takes place and graphene islands start to grow. E.g., Neq = 7.7•1014 cm-2 at T = 1800 K, and Neq = 3.1•1014 cm-2 at T = 1000 K.

Isothermal growth and stacking evolution in highly uniform AB-stacked bilayer graphene

Controlling the stacking order in bilayer graphene (BLG) allows realising unique physical properties. In particular, the possibility of tuning the band gap in AB-stacked BLG (AB-BLG) has a great technological importance for electronic and optoelectronics applications. Most of current methods to produce AB-BLG suffer from inhomogeneous layer thickness and/or coexistence with twisted BLG. Here, we demonstrate a method to synthesise highly pure large-area AB-BLG by chemical vapour deposition (CVD) using Cu-Ni films. Increasing the reaction time resulted in a gradual increase of the AB stacking, with the BLG eventually free from twist regions for the longer times (99.4 % of BLG has AB stacking), due to catalyst-assisted continuous BLG reconstruction driven by carbon dissolution-segregation processes. The band gap opening was confirmed by the electrical measurements. The concept of the continuous reconstruction to achieve highly pure AB-BLG offers a new strategy to control the stacking order of catalytically grown two-dimensional materials.

Isothermal growth and stacking evolution in highly uniform AB-stacked bilayer graphene

Controlling the stacking order in bilayer graphene (BLG) allows realising unique physical properties. In particular, the possibility of tuning the band gap in AB-stacked BLG (AB-BLG) has a great technological importance for electronic and optoelectronics applications. Most of current methods to produce AB-BLG suffer from inhomogeneous layer thickness and/or coexistence with twisted BLG. Here, we demonstrate a method to synthesise highly pure large-area AB-BLG by chemical vapour deposition (CVD) using Cu-Ni films. Increasing the reaction time resulted in a gradual increase of the AB stacking, with the BLG eventually free from twist regions for the longer times (99.4 % of BLG has AB stacking), due to catalyst-assisted continuous BLG reconstruction driven by carbon dissolution-segregation processes. The band gap opening was confirmed by the electrical measurements. The concept of the continuous reconstruction to achieve highly pure AB-BLG offers a new strategy to control the stacking order of catalytically grown two-dimensional materials.