Jerzy Lis

Solid combustion synthesis of Ti3SiC2

Abstract Using powders of Ti and Si and carbon black as reactants, a material composed mainly of the ternary compound Ti 3 SiC 2 and of minor amounts of TiC was synthesized by the method of solid combustion. Following ignition at 1050°C, complete conversion of the reactants to the products was observed in a time of 2 to 5 s. The product obtained from the molar composition 3Ti:Si:2C has properties similar to the CVD-derived polycrystalline Ti 3 SiC 2 , which is a ‘soft’ ceramic material capable of being shaped by metalworking methods and shows a high resistance to oxidation and to aggressive environments.

New ceramics based on Ti3SiC2

Abstract Dense polycrystalline Ti 3 SiC 2 -based materials in the form of large shapes were obtained by ceramic processing starting with SHS-derived Ti 3 SiC 2 -based powders. Their high Youngs and shear moduli and chemical resistance classified them as a covalent ceramic material. However, their relatively low hardness and ratio of high Youngs modulus to hardness are close to those of ductile metals.

Microstructure of Ti3SiC2-based ceramics

Abstract The Ti 3 SiC 2 -based ceramic produced by self-propagating high-temperature synthesis (SHS) has been investigated by means of analytical electron microscopy (AEM). The observations have proved that the elongated slabs with rounded corners of well fused Ti 3 SiC 2 grains form a matrix within which some rounded TiC and less frequent angular SiC inclusions are present. A TiSi 2 phase filling up a remaining free space between carbide grains, has been also detected. The Ti 3 SiC 2 grains are characterised by a high density of dislocations, while the TiC ones contain mostly stacking faults. Cracks forming in the material are situated predominantly at the Ti 3 SiC 2 TiC interface.

SHS Synthesis of the Materials in the Ti-Al-C-N System Using Intermetallics

Materials in the Ti-Al-C-N system due to their specific heterodesmic structure show pseudo-plastic properties. Direct synthesis of these compounds from respective elements requires high-temperature and long-lasting reaction. Presented work shows attempts to prepare some ternary compounds using self-propagating high-temperature synthesis (SHS). Intermetalic precursors, TiAl and Ti3Al, were used to synthesize fine and sinterable powders of 211 and 312 complex structure materials.

Stability of a-C:N:H Layers Deposited by RF Plasma Enhanced CVD

A series of amorphous hydrogenated carbon layers doped with nitrogen (a-C:N:H) was deposited on Si (001). The synthesis was performed from gaseous N2/CH4 mixture using PE CVD (RF CVD technique; 13,56 MHz). An influence of the processing conditions on layer-growth rate was analysed. Thickness of the layers deposited during 1 hour at various temperatures, pressures and RF powers were taken as a basis. It has been proved that the substrate temperature is a key parameter for the layer formation. Temperature rise results in the deposition rate decrease. This unfavourable effect may be reduced by application of increased gas pressure and/or higher plasma RF generator power. At optimal conditions (46 oC; 0,8 Tr; 60 W) the deposition rate reaches up to 600 nm/hour. FT-IR spectra of the layers were measured within 1250 - 4000 cm-1 and discussed with regard to the atomic structure. The intensities of the characteristic absorption bands were compared. The results show that the layers have various N/C ratios according to the applied processing conditions.

Ceramic Pigments with Perovskite Structure

The results of preliminary investigation on preparation of perovskite pigments by solid state reaction are presented. The effects of different raw materials used as component carriers on formation of colored pigments were examined. Pigment composition, optimum chromophore addition, type of mineralizer and the conditions of synthesis were determined experimentally as well as the resulting color, phase composition and morphology of powders. The wet method of preparation of starting mixtures was also analyzed.

Diffusion Rates of51Cr,54Mn and 59Fe in MnCr2O4 and FeCr2O4 Spinels

As the result of oxidation of Cr-Mn steels in SO2 the three layer scale is formed. The intermediate layer of this scale is composed mainly of MnCr2O4 spinel whereas FeCr2O4 spinel is present in small amount. MnO dominates in the outer layer. The inner, very thin scale layer contains oxides/sulfides mixture. The aim of this study was to examine self-diffusion processes in both spinels by multitracer method of diffusion measurements to know which of the transport processes during oxidation is the smallest one and deciding on the corrosion rate. In diffusion experiments the radioisotopes 54Mn, 51Cr and 59Fe were used. The serial sectioning method was applied to simultaneous evaluation of diffusion rates of chromium, manganese and iron in both spinels at 1073 K and 1173 K under the pressure of 105 Pa in SO2 containing 10 Pa O2. These spinels were obtained by modified sol-gel method from nitrates. Structures of the spinels were examined by X-ray spectrometry. It was found, that the diffusion rates of metals are higher in MnCr2O4 spinel. Moreover the dominant mechanism of manganese transport (the highest one) in studied samples is the volume diffusion while chromium and iron are transported mainly through the high diffusivity paths.

Supersaturated solid solutions of boron in SiC by SHS

Abstract Sintering of dense silicon carbide products requires specially prepared starting powders with a small grain size, high purity, and appropriate contents of sintering activators. A method for the preparation of such powders with boron dopant by self-propagating high-temperature synthesis (SHS) is described. Supersaturated solid solutions of boron in βSiC with a boron content of up to 20 wt% were synthesized. Such powders were sintered to high densities by pressureless sintering at relatively low temperatures in a range of 2050–2150°C.

Sintering and Hot-Pressing of Ti2AlC Obtained by SHS Process

Some of ternary materials in the Ti-Al-C system are called MAX-phases and are characterised by heterodesmic layer structure. Their specific structure consisting of covalent and metallic chemical bonds influence its semi-ductile features locating them on the boundary between metals and ceramics, which may lead to many potential applications, for example as a part of a ceramic armour. Ti2AlC is one of this nanolaminate materials. Self-propagating High-temperature Synthesis (SHS) was applied to obtain sinterable powders of Ti2AlC Utilization of heat produced in exothermal reaction in adiabatic conditions to sustain process until all substrates are transformed into product is one of the advantages of the method that result in low energy consumption and low cost combined with high efficiency. Different substrates were used to produce fine powders of ternary material. Phase compositions of obtained powder were examined by XRD method. Than selected powders were used for sintering in various temperature both in a presureless sintering and hot-pressing in argon atmosphere. Properties and phase composition of obtained products were examined.

Investigation of γ-Alon Structural Evolution during Sintering and Hot-Pressing

Dense polycrystalline aluminium oxynitride with spinel structure, -alon, is noted for its excellent thermal properties, high-temperature mechanical properties, low dielectric constant, thermal expansion coefficients and intrinsic transparency extending from ultraviolet to mid-infrared wavelengths. The dense materials were made by reactive pressureless sintering or hot-pressing of the SHS derived powders. Powders were synthesized from mixtures of aluminium and corundum powders of different proportions. The products of the SHS synthesis were composed mostly of -alon and in lesser extend of aluminium nitride. Ground powders were pressureless sintered at temperatures of 1800-2100°C for 2-6hs as well as hot-pressed at 1750-1950°C for 1 h under 25 MPa in nitrogen flow. The present work is focused on phase evolution of -alon materials during pressureless sintering and hot-pressing. The structural changes of -alon, a Al2O3 and AlN were also examined.