Microhardness studies on as-grown faces of NaClO3 and NaBrO3 crystals

Abstract

Single crystals of NaClO 3 and NaBrO 3 are grown from their aqueous solutions at a constant temperature of 35°C by slow evaporation by using good quality seed crystals. Systematic microhardness studies are made on as-grown faces of these crystals at various loads. Typical cracks are observed at the corners of the impressions in NaClO 3 whereas in addition to the cracks at the corners microcracks also appeared in NaBrO 3 crystals around the impressions. The impressions formed in NaBrO 3 are not very clear as in NaClO 3 , a possible mechanism for it is discussed. The work hardening index number (n) for both these crystals is around 1⋅ ⋅6 suggesting that these are moderately harder samples. The hardness studies point out that NaBrO 3 is harder than NaClO 3 (∆ ∆H ≈ ≈ 100 kg/mm 2), this could be due to strong inter ionic forces acting between Na-Br in NaBrO 3 crystals. Using Gilman's empirical relation, hardness values are calculated from the values of elastic constants (C 44) and are found to be close to the experimental results.

Microhardness studies on as‐grown (111) faces of some alkaline earth nitrates

“…The results show that the maximum number lie in the range of 86 for Sr(NO 3 ) 2 , 62 for Ba(NO 3 ) 2 and 60 for Pb(NO 3 ) 2 crystals, suggesting that they are the most possible values for these crystals. Similar variation in hardness was also observed in our earlier studies on NaClO 3 and NaBrO 3 crystals [9]. To understand the reason for such a variation of hardness, number of indentations are made on few samples from one end to the other.…”

“…www.crt-journal.org [13,14] and on alkali halates [9]. This type of behaviour is due to normal Indentation Size Effect (ISE), where size of the indentation d increases with applied load.…”

“…In the recent period considerable amount of work has been reported from this laboratory on hardness studies on a number of crystals like lithium niobate [6], rare earth garnets [7], ammonium and cesium halides [8], NaClO 3 and NaBrO 3 [9], also on some rare earth HCP metals [10]. In continuation of our programme on growth and characterization of crystals, we have undertaken studies of growth and hardness on some alkaline earth nitrate crystals belonging to m3 point group.…”

Studies on conventional and Sankaranarayanan–Ramasamy (SR) method grown ferroelectric glycine phosphite (GPI) single crystals

“…4(b) and (c). It has been already reported that higher hardness crystals develop more cracks around the indentation mark [24]. This is the probable reason for higher reduction of hardness above 100 g of load in SR method grown GPI crystal.…”

Growth, Structural, Optical, Mechanical and Dielectric Characterization of Diammonium Hydrogen Phosphate (DAHP) Single Crystals

“…Indentations were made for various loads from 20 g to 160 g. Several trials of indentation were carried out and the average diagonal lengths were measured for an indentation time of 10 seconds. The Vickers micro hardness number was calculated using the relation H v = 1.8544 P/d kg/mm 2 where P is the applied load and d is the diagonal length of the indentation impression [15].…”