Evaluation of crack-Growth resistance curve for a particulate ceramic–Metal composite

A technique is described to evaluate the crack growth resistance behaviour in brittle ceramic-base materials. In this method, the crack increment measurements during the stable crack propagation process are not required. The crack growth resistance curves are studied for a particulate ceramic–metal composite in the system lanthanium chromite–chromium. Experiments were performed with standard fracture mechanics single-edge notched beam specimens in a temperature range from room temperature up to 1100°C. Effect of temperature on crack growth resistance behaviour is discussed.     

High-carbon binders in refractories and corrosion-resistant ceramics technology

The authors review the literature sources and patents of foreign companies in the field of application of high-carbon organic binders for refractories, composites and technical ceramics. The review reveals the advantages of the new generation of binders with improved properties and describes binders meeting contemporary environmental requirements and not containing free phenol and other carcinogenic and toxic components. Translated from Steklo i Keramika, No. 5, pp. 12 – 15, May, 1998.     

Synthesis of pigments based on perovskite

The results of synthesis of pigments based on perovskite (CaTiO₃) are presented. Differential thermal and x-ray phase analysis methods are used to study the processes occurring in heat treatment and to determine the phase composition of the yellow pigment based on nickel titanate. The expediency of producing this pigment by the precipitation method is demonstrated. The color characteristics of the pigment and the area of application are indicated.     

Local compaction areas in sintering of ceramics and structural reproducibility

An analysis of fracture surfaces is suggested for assessment of local compaction areas in non-fired and sintered preforms. The analysis of samples made of highly disperse aluminum oxide by extrusion, plastic molding, and casting and heat-treated at different temperatures indicated that local compaction areas are formed in the molding stage, and the nature of the fractures remains similar until a high density of the material is reached. In the context of synergetics, the phenomenon of inherited structure in ceramics is attributed to the controlling effect of internal factors (of the previous structure) at the points of bifurcation on the system’s evolution. A hypothesis is put forward that levelling of the fracture relief in sintered samples corresponds to the temperature region of bifurcation of the sintered system.     

Development of rugged and crack-resistant structures in ceramics (review)

The paper considers methods for increasing crack resistance in ceramics, including microcracking in local stress areas, reorientation of crack movement, polymorphous martensite transition in partly stabilized zirconium dioxide, and bridging of cracks with a plastic phase or crystals with highly nonisometric shape (plates, needles, fibers) in the context of the irreversibility and nonequilibrium, producing self-organization, and a synergetic approach. The possibility of increasing crack resistance due to diffuse polymorphous transitions, twinning, and mechanochemical reactions is discussed.     

N,N-bis (2-hydroxyethyl) fatty amide as novel environmentally friendly crosslinking agent for acid functional acrylic copolymer resin

N,N-bis (2-hydroxyethyl) fatty amide (HAFA) derived from dehydrated castor oil (DCO) has been employed as a curing agent for a carboxylic acid functional acrylic resin (AAR). Coating compositions with a varying AAR/HAFA ratio have been prepared and their various film properties have been studied and compared with the conventional butylated melamine formaldehyde (MF) based systems. The study reveals that HAFA can be used successfully as a crosslinking agent for AAR in baking systems. In addition to other technical advantages, the use of HAFA is environmentally friendly as no toxic volatiles are evolved during curing reaction, unlike in MF-cured systems. Department of Industrial Chemistry, Vallabh Vidyanagar, Gujarat 388 120 India. Hyderabad, India.     

Modeling of the Low-Frequency Noise in Thermal Lens Spectrometry

The low-frequency noise observed in thermal lens spectrometry (TLS) can be modeled by assuming that the heated region, constituted by the thermal lens gradient and associated convective stream, behaves as a weakly damped harmonic oscillator with a natural frequency, v_o, which is forced to move at an externally imposed pump frequency, v_p. Out-of-phase lower-frequency oscillations of the TLS signal can be produced both by transient events, such as the beginning of the TLS experiment and small changes in the pump beam stability, and by drift of boundary conditions, such as the temperature of the surroundings. A model is developed and checked using 1-(2-pyridylazo)-2-napthol (PAN) solutions in silicone oil. Consequences of analytical interest are drawn; e.g., the signal-to-noise ratio of the TLS experiments is improved by pumping at the resonance frequency, where v_p = v_o.