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1.
Optical study of mechanical response indicated by Knoop indentation of cleavage faces of synthetic sodium nitrate crystal based on MEYER 's Law/KICK 's Law (P = adn) and also on modified KICK 's Law {(P — W) = bd2} expressing relations between applied load P and diagonal length d is made. The Newtonian resistance pressure W is finite and positive. The value of standard hardness (a and b), exponent n are calculated. It is found that W and b are almost contant and independent of thermal treatment and of the indenter orientation with respect to direction [100] on cleavage plane (100) of sodium nitrate crystals. Since they are independent of indenter orientations, they are not associated with crystal anisotropy. 相似文献
2.
D. R. Joshi 《Crystal Research and Technology》1993,28(1):111-117
The variation of hardness of rhombohedral single crystals of calcite with orientation of longer diagonal of Knoop indenter with respect to direction [100] on a cleavage plane (100) is studied. The Knoop hardness number H which has a constant value in the range of high loads (40–80 g) varies with orientation A and quenching temperature. By following phenomenological approach, an empirical relation √HA = mA + C is developed from these studies. The effects of crystal anisotropy and thermal treatment of specimens after indentation are also discussed. 相似文献
3.
K. Sangwal 《Crystal Research and Technology》2009,44(10):1019-1037
Indentation size effect, indentation cracks and microhardness measurement of some brittle crystals are reviewed against the background of the existing concepts of indentation deformation of crystalline solids. Several approaches reported in the literature devoted to relationships between applied indentation test load P and indentation diagonal length d are applied to analyze the experimentally observed normal and reverse indentation size effect (ISE) in brittle compounds. Using typical examples of normal and reverse ISE it is shown that the indentation induced cracking model does not give load‐independent hardness and the final expression describing the experimental data for various compounds is essentially another form of the Meyer law. Analysis of experiment data on crack lengths and indentation diagonals for different indentation loads suggests that the origin of ISE is associated with the processes of formation of indentation cracks following the general concepts of fracture mechanics. The load‐independent hardness H0 may be determined reliably from plots of P /d against d of the proportional resistance model or of HV against 1/d as predicted by strain gradient plasticity theories. It was found that the load‐independent hardness of depends on crystal orientation and state of the indented surface. Finally, some comments on determination of fracture toughness and brittle index of crystals are made. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
4.
The hardness of NaCl crystal in the presence of mono, divalent and polyvalent ions were measured. Measurements were made in the indentation load range from 5 x 10‐3 to 20 x 10‐3 N. The measured data showed that there is an indentation size effect. Classical Meyer's law was used for the characterization of crystal hardness f NaCl. The Meyer index was found to be smaller than 2 indicating brittle material characteristic. The PRS model was also used for the determination of the load‐independent microhardness value. It was found that the crystal hardness of NaCl is chancing depending on the type of impurity and the concentration. 相似文献
5.
P. V. Raja Shekar D. Nagaraju V. Ganesh K. Kishan Rao 《Crystal Research and Technology》2009,44(6):652-656
Single crystals of Sr(NO3)2, Ba(NO3)2 and Pb(NO3)2 are grown from their aqueous solutions at a constant temperature of 35 °C by slow evaporation technique. Crystals of size 8 to 10 mm along one edge are obtained in a period of 10 days. Chemical etching technique has been employed to study the dislocations in these crystals. The dislocations are randomly distributed and the dislocation density is about 104 to 105 /cm2. Microhardness studies are made on as–grown (111) faces of these crystals upto a load of 100 g. The hardness of the crystals increases with an increase in load and thereafter it becomes independent of the applied load. These results are discussed on the basis of reverse indentation size effect. Meyer index number n for these crystals is estimated at both low and high load regions. An analysis of hardness data of these crystals as well as some other cubic crystals like alums and alkali halates are discussed using Gilman–Chin parameter Hv/C44, where Hv is the microhardness and C44 is the shear constant. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
6.
The deformation characteristics of KClO4 single crystals have been studied by the methods of static and dynamic indentation on (001) plane. The cracks produced by the dynamic indentation have been interpreted in terms of slip-twin interactions. Also, the load dependence of Vickers microhardness and its anisotropy in this crystal are reported. The observed hardness anisotropy has been used to confirm the indices of the slip system 〈101〉 〈111〉 operative in this crystal at ordinary temperatures. 相似文献
7.
C. C. Desai 《Crystal Research and Technology》1987,22(4):585-590
Single crystals of ammonium hydrogen tartrate AHT NH4HC4H4O6 have been grown employing the controlled reaction between NH4Cl and (CHOHCOOH)2 by slow diffusion process in silica gels. The variation in the microhardness of AHT crystals has been determined using Vicker's microhardness indentor. The effects of annealing and quenching on the mechanical properties of these crystals have been studied. It is observed that: (i) irrespective of the relative orientation of the indentor and the crystal, the median vents initiated at the sharp indentation edges, (ii) the microhardness of the crystals depends on the applied load, (iii) the microhardness of the crystal is independent on the duration of loading, and (iv) maximum plasticity is observed in quenched crystals. The implications of this behaviour are discussed. 相似文献
8.
The effects of x‐beam irradiation with different doses on microhardness and its related physical constants on [Ky(NH4)1‐y]2ZnCl4 mixed crystals with concentrations, y equals 0.000, 0.232, 0.644, 0.859 or 1.000 has been studied. The tests were performed for x‐doses from 0.2 kGy up to 1.6 kGy for loads from 20 to 160 g. The variation of hardness on (010) faces of orthorhombic [Ky(NH4)1‐y]2ZnCl4 mixed crystals with load were studied. The experimental results showed that, the hardness decreased as the x‐doses increased. Variation of the microhardness follows the normal ISE trend for low x‐doses and un‐irradiated crystals, then follows the reverse ISE trend for high x‐doses. Analysis of the experimental results revealed that: the radial cracks length, indentation size and applied indentation load are mutually related, and these dependences related with fracture mechanics are the basis of Meyer's empirical law. Indentation size effect (ISE) can be explained satisfactory by Hays‐Kendall's approach and proportional specimen resistance model. Brittleness of two cracks system are applicable for characterizing cracks around indentation impression (i.e. radial cracks) and another is (lateral cracks) for [Ky(NH4)1‐y]2ZnCl4 mixed crystals, crystals in the load range 60 – 160 g. It is shown that indentation induced microhardness decreases, whereas the length of radial cracks induced on indentation increases with the increase of x‐doses. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
9.
B. Wierzbowska K. Piotrowski J. Koralewska A. Matynia N. Hutnik K. Wawrzyniecki 《Crystal Research and Technology》2008,43(4):381-389
The experimental results concerning continuous mass crystallization process in L(+)‐ascorbic acid – water system are presented and discussed. Influence of L(+)‐ascorbic acid concentration in a feeding solution and mean residence time of suspension in laboratory DT MSMPR crystallizer on product crystal size distribution as well as nucleation and growth kinetics were determined. Kinetic parameter values were evaluated on the basis of size–independent growth (SIG) kinetic model (McCabe's ΔL law). It was observed, that within the examined range of crystallizer productivity (120–1600 kg LAA crystals m–3h–1) crystal product population of mean size Lm from 0.2 to 0.3 mm and CV from 66.6 to 49% is withdrawn. Linear growth rate values present decreasing trend (from ca. 7 · 10–8 to ca. 6 · 10–8 m s–1) with the productivity increase (assuming constant mean residence time of suspension τ = 900 s). Occurrence of secondary nucleation within the circulated and mixed suspension, resulting from crystal attrition and breakage, was observed. The parameter values in design equation connecting linear growth rate and suspension density with nucleation rate were determined. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
10.
N. L. Sizova N. E. Novikova V. L. Manomenova E. B. Rudneva A. E. Voloshin 《Crystallography Reports》2016,61(3):443-448
The microhardness on the (010) and (001) planes in K2Co(SO4)2 · 6H2O crystal has been measured by the Vickers indentation method. Its values are, respectively, 11500 and 1300 MPa. No microhardness anisotropy of the first kind is revealed on either plane. The fracture geometry under indentation by a spherical indenter and Vickers and Knoop indenters is studied. The crystal has lower brittleness than the isomorphic Cs2Ni(SO4)2 · 6H2O crystal. 相似文献
11.
Polycrystalline disc-like pellets of Al2O3 are moulded superficially and then cooled down at different velocities. In this way areas of single crystal character are created. The angle ϑ measuring the inclination of the crystallographic c-axis against the pellet's normal proves to be a statistical quantity. Nevertheless it will be shown that the probability distribution of this angle is differnt for slow and fast cooling rates. In both cases the anisotropy of the crystallization process uniquely represented by a suitable factor k(ϑ) exhibits a remarkable relationship to some stable faces of natural grown single crystals of corundum. Furthermore, the importance of the mean value ϑ and of the variance σ is discussed in detail. 相似文献
12.
N. L. Sizova A. E. Voloshin V. L. Manomenova E. B. Rudneva A. A. Lomov 《Crystallography Reports》2012,57(3):410-414
The microhardness of the (010), (100), and (001) planes in the Cs2Ni(SO4)2 · 6H2O crystal and the geometry of destruction of the (010) plane around impressions of different (spherical, Vickers, and Knoop) indenters has been studied using Vickers indentation. It is shown that the crystal under study is characterized by enhanced brittleness and that the cleavage along the (201) plane is highly imperfect. The maximum microhardness (H = 1140 MPa) is characteristic of the (001) plane under a load of 20 g. 相似文献
13.
The basis material for high sensitive infrared-photo-conductive cells today is often cadmium-mercury telluride (CdxHg1−xTe). In order to get CdxHg1−xTe-infrared detectors with nearly constant elektrical properties a good homogeneity of the material has to be demanded. This can't be achieved by conventional methods of crystal growing (f. i. Bridgman technique). But the technique of high-speed quenching of the melt offers good results. 相似文献
14.
Optical absorption, transport properties and EPR of K2CuCl4 · 2H2O single crystals have been studied. The optical absorption in UV, and visible region are characterized by a charge transfer band, and in the near infrared region at 3998, 4336, and 4480 cm−1 are attributed to transitions between the stark levels of copper(II) ion in an extended octahedral crystal field. An anisotrophic ‘g’ value was observed with g∥ = 2.12 and g∥ = 2.24 by EPR method. The spin orbit coupling constant is found to be 500 cm−1. D.C. electrical conductivity measurements with temperature reveal an anisotropy characteristic of a two-dimensional layered structure and exhibit a first order irreversible structural phase-transition at 377 K, i.e. from tetragonal to monoclinic crystal system. X-ray diffraction studies and density calculations from the crystal structure data in both the phases suggest that the first order irreversible transition occurs following the loss of the two water molecules of hydration. 相似文献
15.
D. Iwanov 《Crystal Research and Technology》1990,25(3):237-244
The effect of diffusion in the vapour phase on the kinetics of growth of zinc single crystals in the presence of argon has been studied. The shift of the basal face in normal direction as a function of the time has been measured at constant temperature and supersaturation and argon pressures varying within the range 5–250 Torr as well as in vacuum 1 × 10−6 Torr. It has been established that the crystal size R changes with the time t following a linear and a parabolic law in the kinetic and the diffusion regimes, respectively. The kinetic critical size Rk for the transition from a kinetic to a diffusion regime has been experimentally obtained. A relatively good agreement is found between the experimentally established and theoretically calculated values of the critical size. The problems related to the transition of the basal faces of zinc single crystals from a kinetic to a diffusion growth mode is discussed. 相似文献
16.
β-BaB2O4 (BBO) crystals with well-defined morphology have been grown from Na2O solutions using the top seeded solution growth (TSSG) method. The crystal morphology in relation to its structure and growth conditions has been studied in detail on the basis of crystallography and crystal chemistry. It is found that the morphological characteristics are related to the orientations of structural unit (B3O6)3— anion rings in the crystal. On the other hand, the growth parameters may greatly affect the appearance of faces of the crystal, but the crystals still generally take trigonal in outline and have a diagnostic character of point group 3m. The observed morphology is in disagreement with BFDH and PBC analyses and is explained from the incorporation of the growth units on the faces and facets. Since the incorporation rates of the growth units are different on different faces, the boule habits with well-defined morphology are formed. 相似文献
17.
Qinhua Wei Hongsheng Shi Xiaofeng Cheng Laishun Qin Guohao Ren Kangying Shu 《Journal of Crystal Growth》2010,312(11):1883-1885
The growth and scintillation properties of the Na2W2O7 crystal are reported. The solid reaction between Na2CO3 and WO3 is used to synthesise the Na2W2O7 material. The Na2W2O7 single crystal has been grown by the Bridgman method. And the Na2W2O7 single crystal with sizes 14×7×6 mm3 has been achieved. The transmission spectra, the Ultraviolet fluorescence spectra and the X-ray excited luminescence spectra of the Na2W2O7 crystal are measured. The measurement results show that the Na2W2O7 crystal is a promising intrinsic scintillator. 相似文献
18.
G. Zahn B. A. Merisov G. Klss G. Ya. Khadshaj S. Müller O. A. Gavrenko P. Paufler 《Crystal Research and Technology》1988,23(4):509-515
The thermal conduction of a sulphur-doped single crystal plastically deformed by bending at 963 K was measured between 2 and 50 K. The thermal resistivity W at temperatures > 14 K is practically independent on deformation. At lower temperatures W is found to be proportional to AT−3 before and to AT−3 + BT−2 after deformation. A is due to boundary scattering, B due to dislocations. 相似文献
19.
Thermal expansion of the monoclinic nonlinear optical crystal BiB3O6 (bismuth triborate) was measured by dilatometry within the temperature range from 173 K to 573 K using single crystal samples of dimensions ∼7 x 7 x 8 mm3. The four independent tensor coefficients are given and the calculated loci of zero thermal expansion of BiB3O6 are related to the loci of phase matching for second harmonic generation. Characteristic features of the crystal structure are taken to discuss the marked anisotropy of thermal expansion of BiB3O6. 相似文献
20.
Vickers microhardness measurements were performed on single crystals of compounds Tl3BX4 (B = V, Nb, Ta; X = S, Se). The anisotropy of the hardness on the (111)-plane was beyond the standard deviation. Besides the load-dependent Vickers hardness HV, the corrected, load-independent hardness HVc was determined. Tl3VS4 showed the highest value of hardness (HV = 66 kp/mm2 at 15 p load), the othe compounds differ only slightly in hardness. 相似文献