Influence of the material removal mechanisms on hole integrity in ultrasonic machining of structural ceramics

Micro-chipping via micro-cracks, due to rapid mechanical indentations by abrasive grits, is the fundamental mechanism of material removal during ultrasonic machining (USM) of hard-brittle materials like ceramics and glass. This study aims mainly to investigate the adverse effects of this inherent removal phenomena on the hole integrity such as entrance chipping, wall roughness and subsurface damage. It also presents the material removal mechanism happens in the gap between the tool periphery and the hole wall (called ‘lateral gap’). To do so, experiments were conducted for drilling holes on three advanced structural ceramics, namely, silicon carbide, zirconia, and alumina. Earlier published basic studies on the initiation of different crack modes and their growth characteristics are employed to explain the experimental findings in this USM study. It is realized that the radial and the lateral cracks formed due to adjacent abrasives, which are under the tool face, extends towards radial direction of the hole resulting in entrance chipping. Additionally, the angle penetration and the rolling actions of the abrasives, which are at the periphery of the tool, contribute to the entrance chipping. Later on, in the ‘lateral gap’, the sliding (or abrasion) and the rolling mechanisms by the larger abrasives take part to material removal. However, they unfavorably produce micro-cracks in the radial direction resulting in surface and subsurface damages, which are ultimately responsible for higher wall-surface roughness. Since the size of micro-cracks in brittle materials is grit size dependent according to the earlier studied physics, it is realized that such nature of the hole integrity during USM can only be minimized by employing smaller grit size, but cannot fully be eliminated.     

Synthesis of 2-Arylpyrimido[4,5-b]porphyrins via Cyclization Reaction with Ammonia

A facile synthetic strategy for the synthesis of a new series of β,β’-fused 2-arylpyrimido[4,5-b]porphyrins has been developed by using condensation cyclization reaction with ammonia. 2-Aroylamino-3-formylporphyrins were synthesized from 2-aroylaminoporphyrins under Vilsmeier–Haack reaction conditions, which were then efficiently converted to the corresponding 2-arylpyrimido[4,5-b]-5,10,15,20-tetrakis(4-chlorophenyl)-porphyrins via a condensation cyclization reaction. The nickel(II), copper(II), free-base and zinc(II) analogues of 2-arylpyrimido[4,5-b]porphyrins were successfully synthesized in 65–72 % yields and structurally characterized on the basis of spectral data analysis. On photophysical evaluation, 2-arylpyrimido[4,5-b]porphyrins demonstrated a 12–19 nm bathochromic shift in their electronic absorption spectra and up to 10 nm red shift in their emission spectra as compared to the simple meso-(tetrakis(4-chlorophenyl))porphyrins due to the extended π-conjugation.     

Study of Scaling Exponents of the Surface Evolved in 2 + 1 Dimension through Competitive Growth between Random Deposition and that with Surface Relaxation

Rough surface develops through computer simulation by competition between growth mechanism random deposition (RD) with a probability of occurrence p and growth mechanism random deposition with surface relaxation (RDSR) with a probability of occurrence 1 − p, on L × L square plane for system size L to record the statistical average of time variation of surface roughness W(L, t) and average height H(t) for the model for specific values of L and p. Other than the pure RD model, the entire evolution may be divided into three regions separated by two specific cross-over times t_x and t_sat. The value of interface width at saturation W_sat depends on both L and p. The first growth exponent β₁ increases exponentially with an increase in p and does not depend on L. The values of the second growth exponent β₂, roughness exponent α, dynamic exponent z( = α/β₂ ), and α + z are 0.0234 ± 0.0008, 0.0506 ± 0.0065, 2.1577 ± 0.0073, and 2.2083 ± 0.0138 respectively and they show no dependence on L and p values. Value of the first cross-over time t_x increases exponentially with an increase in p and does not depend on L. Value of the second cross-over time t_sat increases with an increase in both p and L values. The average growth velocity is unity for the model and is independent of both L and p. For the model, the growth velocity is unity and the fractional porosity is zero. The scaling exponents show some deviation from the relevant universality classes and depend on competitive growth probability for this model. No finite-size effect is present in the model.