Fracture Resistance of Ceramics upon Edge Chipping

Modern methods of determining fracture resistance are analyzed. The necessity of developing a crucially new method based on edge chipping of a brittle material is shown. The results of experimental studies are presented. The applicability of the method to the comparative fracture resistance evaluation of ceramics is substantiated.     

Synthesis of reagents for inhibiting the growth of sulfate-reducing bacteria in petroleum production

Quaternary ammonium salts were synthesized on the basis of hexamethylenetetramine and piperylene hydrochloride. Conditions for the synthesis of mono-, di-, tri-, and tetraalkenylhexamethylenetetrammonium chlorides in aqueous solutions were optimized. The main physicochemical characteristics of the synthesized compounds were determined and the structures were established. The suppression of the growth of sulfate-reducing bacteria was studied.     

Fracture behaviour of Y-TZP ceramics: New outcomes

Modern approaches to fracture resistance estimation of Y-TZP ceramics are critically analyzed. It is shown that fracture toughness test methods do not produce data that are reliable enough. The present investigation makes use of the edge fracture (EF) test method based on flaking the rectangular specimen edge. Chip scars formed on specimen edges after the Rockwell indentation were examined. It is established that not the chip scar shape but its surface area is decisive for the fracture resistance of these ceramics. The influence of indenter sharpness on fracture resistance estimates was elucidated: Rockwell indenter, 400-μm tip radius conical indenter, and Vickers indenter were used. The EF method ensures simultaneous determining a fracture resistance characteristic and plotting an FR-line some equivalent to a conventional R-curve. Therefore, such economically feasible tests, easily realizable in a conventional mechanical laboratory, provide quite exhaustive information on the fracture behaviour of ceramics. The proposed method of evaluating the fracture resistance of Y-TZP ceramics may be useful in materials science practice.     

Fracture barrier estimation by the edge fracture test method

Known methods for determining the fracture resistance of brittle materials by indentation flaking of the rectangular specimen edge are compared. The edge fracture (EF) test method was chosen as an optimum one. The investigations demonstrated that silicon carbide ceramics, submicrometre alumina, and glasses possessed fracture resistance (F_R) values that can be located above the baseline in the EF base diagram. These results emphasize that the above materials display a higher resistance to the onset of fracture (fracture barrier). This barrier can be estimated by comparing EF test data resulting from Rockwell and Vickers indentations.     

A digital microfluidic method for in situ formation of porous polymer monoliths with application to solid-phase extraction

We introduce the marriage of two technologies: digital microfluidics (DMF), a technique in which droplets are manipulated by application of electrostatic forces on an array of electrodes coated by an insulator, and porous polymer monoliths (PPMs), a class of materials that is popular for use for solid-phase extraction and chromatography. In this work, circular PPM discs were formed in situ by dispensing and manipulating droplets of monomer solutions to designated spots on a DMF device followed by UV-initiated polymerization. We used PPM discs formed in this manner to develop a digital microfluidic solid-phase extraction (DMF-SPE) method, in which PPM discs are activated and equilibrated, samples are loaded, PPM discs are washed, and the samples are eluted, all using microliter droplets of samples and reagents. The new method has extraction efficiency (93%) comparable to that of pipet-based ZipTips and is compatible with preparative sample extraction and recovery for on-chip desalting, removal of surfactants, and preconcentration. We anticipate that DMF-SPE may be useful for a wide range of applications requiring preparative sample cleanup and concentration.     

Fracture resistance estimation of elastic ceramics in edge flaking: EF baseline

The fracture resistance of single-phase oxide and nonoxide ceramics was studied in flaking the specimen edge with a Rockwell indenter (EF test method) and in bar flexure (SEVNB method). The fracture resistance F_R and fracture toughness K_Ic are shown to be proportional, the plot with the F_R–K_Ic coordinates is termed the EF base diagram, in which the EF baseline is constructed. It was revealed that the fracture resistance of ceramics was not influenced by chip scar shapes on the specimen edge. The data points for inelastic ceramics with a lower EF barrier to the onset of fracture lay below the EF baseline in the base diagram, while the data points for glasses and ceramics with a higher barrier were located above it.The EF test method is appropriate for comparative evaluation of fracture resistance of ceramics and verification of estimates obtained by other methods.     

Glass fracture in edge flaking

Fracture resistance of technical quartz and normal window glasses was investigated in testing polished rectangular parallelepipeds by edge flaking their long edges with Rockwell and Vickers indenters (EF method) and by scratching the specimen surface with a Rockwell indenter followed by flaking its edge (S+EF method). It was established that the fracture of those glass specimens in their edge flaking with a Rockwell indenter was started with the formation of a Hertzian ring crack and their corresponding chip scars had the form of Hertzian “quasi-cones.” Fractographic data were used in analysis of test results. __________ Translated from Problemy Prochnosti, No. 6, pp. 103–112, November–December, 2007.     

Fracture resistance of technical and optical glasses: edge flaking of specimens

We present the results of fracture resistance tests for technical and optical glasses performed by indentation flaking of the rectangular specimen edge. The features of crack propagation in these glasses are analyzed during chipping fracture caused by indentation with blunt and sharp diamond indenters. By comparative analysis of the values for resistance to edge flaking and those for fracture resistance, new data on the mechanical behavior of the above glasses in fracture are obtained. In particular, it is shown that these glasses, along with ceramic materials used to produce armor, have an enhanced resistance to the onset of fracture.