Oleg I. Lomovsky

Solid state synthesis of tungsten carbide in an inert copper matrix

Abstract A copper–tungsten–carbon system was chosen to study the possibility of synthesis of tungsten carbide phases from elements in an inert matrix. Copper played the role of the inert matrix and the composition W 50 C 50 was investigated. A planetary type mill with ball acceleration up to 600 m s −2 was used as an activator for mechanical treatment. Thermal annealing at 820–940°C was carried out in an argon atmosphere. The influence of the initial Cu–W–C mixture content and preliminary mechanical treatment time on the final product phase content and grain size was studied. High tungsten content is found to retard WC synthesis and W 2 C is obtained as the dominating product. Low tungsten content leads to the enhancement of WC in the products. A decrease in product grain size down to the submicron level with an increase of preliminary mechanical treatment time is demonstrated for Cu 94 W 3 C 3 composition, as an example.

Steady state products in the Fe–Ge system produced by mechanical alloying

Abstract Prolonged mechanical alloying of elemental blends and mechanical milling of individual intermetallics of the same chemical composition in the Fe–Ge system lead to the same steady state. The phase composition of this steady state was investigated in the entire composition range using a conventional XRD technique. A map reflecting the steady-state phase composition for the different chemical composition was constructed. Mechanical alloying and grinding form products of the following composition (in sequence of increasing Ge content): α (α 1 ) bcc solid solution, α+β-phase (Fe 2− x Ge), β-phase, β+FeGe(B20), FeGe(B20), FeGe(B20)+FeGe 2 , FeGe 2 , FeGe 2 +Ge, Ge. The incongruently melting intermetallics Fe 6 Ge 5 and Fe 2 Ge 3 decompose on milling. Fe 6 Ge 5 produces a mixture of the β-phase and FeGe(B20) while Fe 2 Ge 3 produces a mixture of the FeGe(B20) and FeGe 2 phases. These facts are in good agreement with a model that implies local melting as mechanism for new phase formation during mechanical alloying. The stability of the FeGe(B20) phase, which is also an incongruently melting compound, is explained as a result of the highest density of this phase in the Fe–Ge system.

Formation of nanocrystalline structures in a Co–Al system by mechanical alloying and leaching

Abstract Phase composition of the materials obtained by mechanical alloying of system Co–Al (Al concentration ranges from 50 to 70 at.%) and removal of aluminum from such alloys was investigated by differential dissolution, X-ray phase analysis and TEM with a resolution of 0.4 nm. The intensive mechanical alloying provides formation of the nanocomposite material containing both amorphous phase Co2Al5 and nanocrystalline particles of phase CoAl. Leaching of amorphous phase Co2Al5 results in the amorphous cobalt containing admixtures of alumina and hydroxide. Nanocomposite amorphous phase Co2Al5 and CoAl convert into nanocomposite amorphous Co and b.c.c. Co.

Ti3SiC2-Cu composites by mechanical milling and spark plasma sintering: Possible microstructure formation scenarios

We present several possible microstructure development scenarios in Ti3SiC2-Cu composites during mechanical milling and Spark Plasma Sintering (SPS). We have studied the effect of in situ consolidation during milling of Ti3SiC2 and Cu powders and melting of the Cu matrix during the SPS on the hardness and electrical conductivity of the sintered materials. Under low-energy milling, (3–5) vol.%Ti3SiC2-Cu composite particles of platelet morphology formed, which could be easily SPS-ed to 92–95% relative density. Under high-energy milling, millimeter-scale (3–5) vol.%Ti3SiC2-Cu granules formed as a result of in situ consolidation and presented a challenge to be sintered into a bulk fully dense sample; the corresponding SPS-ed compacts demonstrated a finer-grained Cu matrix and more significant levels of hardening compared to composites of the same composition processed by low-energy milling. The 3 vol.% Ti3SiC2-Cu in situ consolidated and Spark Plasma Sintered granules showed an extremely high hardness of 227 HV. High electrical conductivity of the Ti3SiC2-Cu composites sintered from the granules was an indication of efficient sintering of the granules to each other. Partial melting of the Cu matrix, if induced during the SPS, compromised the phase stability and uniformity of the microstructure of the Ti3SiC2-Cu composites and thus it is not to be suggested as a pathway to enhanced densification in this system.

Studies of X-ray amorphous phase in mechanochemical synthesis of iron silicides from elements

Iron disilicide synthesis was developed by means of mechanochemical activation under intensive mechanical treatment. The X-ray amorphous phases formed during mechanical treatment of initial iron and silicon were investigated. The methods of the differential dissolution, differential thermal analysis and X-ray phase analysis were used. The formation of supersaturated amorphous solid solution of silicon in iron with limited concentration 17 at.% Si takes place during the initial period of activation. Primary phase obtained in this system is iron monosilicide formed in the decomposition of amorphous supersaturated solution.

INVESTIGATION OF THE REACTION ZONE STRUCTURE UNDER MECHANOCHEMICAL SYNTHESIS OF METAL DISILICIDES BY A METHOD OF LOCAL DIFFRACTOMETRY

Abstract The structure of layers of treatment material on milling bodies in processes of mechanochemical synthesis of metal silicides are investigated. Samples of metallographic specimen of layer on sphere are scanned with step 50 μm. The thickness of layer is 150–250 μm. The layer consists of plastic component (metal) of mix initial products and compound appearing in result of mechanochemical reaction. The less plastic component (silicon) not detected in layers. Two types of distribution of phases in layers on milling sphere are revealed.

Cold and detonation spraying of TiB2-Cu nanocomposites

TiB2-43vol.%Cu nanocomposite powders with titanium diboride particle size 50-100 nm were cold and detonation sprayed in order to fabricate coatings on a copper substrate. The powders were produced by self-propagating high-temperature synthesis (SHS) followed by mechanical milling. The temperatures during spraying were calculated and the change in the nanostructure of the powders during spraying was studied: in cold sprayed coatings the size of TiB2 particles was well retained, in detonation sprayed coatings the growth of the particles was observed, the mode of spraying greatly affecting the microstructure and the size of the particles. The hardness of cold sprayed coatings was higher compared to detonation sprayed coatings. This research shows the future potential for development of coatings with submicron and nanostructure by cold and detonation spraying of powders produced by mechanical milling.

Detonation Spraying of Ti–Al Intermetallics: Phase and Microstructure Development of the Coatings

The goal of this work was to study the phase and microstructure changes involved in the process of coating formation by detonation spraying of Ti3Al, TiAl, and TiAl3 intermetallics. The O2/C2H2 ratio was varied between 1.1 and 2.0, and the explosive charge was 30–40% of the barrel volume. In most experiments air was used as a carrier gas; selected experiments were performed with argon. We found that depending on the spraying parameters, TiAl3 essentially retains in the coatings or partially decomposes forming TiAl and Ti3Al as minor phases. Detonation sprayed Ti3Al reacts with nitrogen and oxygen partially transforming into titanium nitrides TiN/Ti2N and titanium oxynitrides TiNxOy. TiAl partially decomposes forming Ti3Al, which further reacts with oxygen and nitrogen as the particle temperature and the content of oxygen in the explosive mixture increase. The in situ formed titanium nitrides and oxynitrides show a reinforcing effect increasing the hardness of the coatings.

Prediction of higher heating values of plant biomass from ultimate analysis data

For natural plant raw materials and for artificial mixture samples with different lignin content, a comparison between empirical equations for the calculation of higher heating values was carried out relying on the data of ultimate analysis. Selection of tested equations from already known was carried out according to the criteria: equations should be intended for work with plant raw materials; the range of used materials should be rather wide; the data on element content (C, H, N, S) obtained experimentally and in routine mode, as well as ash value of the material, should be variables; ambiguous equations should be excluded. Only 8 from more than 150 published equations were chosen for testing, and 3 of these provide calculation of higher heating values with a less than 5–6% deviation from reference values obtained by means of combustion in an adiabatic calorimeter.

Mechanochemical solid acid/base reactions for obtaining biologically active preparations and extracting plant materials

ABSTRACT Mechanochemically assisted extraction involves the mechanical treatment of powder mixtures of plant materials and convenient reagents in special mill-activators to solubilize the biologically active substances. The reactions of the solid hydroxides, carbonates, and hydrocarbonates of alkali metals are the subject of this paper. During mechanochemical treatment, insoluble biologically active substances are transformed into water-soluble or highly reactive mechanocomposites. The types of reagents used depend on the chemical nature of the biologically active substance and the possible chemical reactions between the substance and reagents. Solid-state mechanochemical reactions between active acids and solid bases and between biogenic amines and acids and the formation of soluble complexes of biologically active substances with water-soluble and insoluble polymers were explored in this study. The advantages of using these reactions in mechanochemically assisted extraction are presented in this review. GRAPHICAL ABSTRACT