Exaggerated Texture and Grain Growth in a Supperplastic SiAlON

A fine-grained superplastic β'-silicon nitride solid solution (SiAlON) was found to develop elongated grains and a pronounced texture during tensile deformation at 1550°C. The texture development is well-described by a geometrical model of grain rotation in accordance with the strain field. Once aligned, grains can then grow with little constraint due to impingement and often coalesce into each other. With the above microstructural development, the stressstrain curve displayed unusually strong strain hardening characteristics due to a fiber–reinforcement effect of the aligned silicon nitride grains on the glass–containing matrix. By extending the rheological model of Chen and Yoon and considering these microstructural evolutions, we are able to simulate the deformation behavior.     

Orientation and Crystallinity Measurements in Film Casting Products

Summary Film casting experiments were carried out with iPP under processing conditions causing the crystallization process to occur under orienting flow. Draw ratio and cooling rates were changed by varying mass flow rates and die thickness. The effect of processing conditions on film crystallinity was investigated by combining WAXS and FT-IR transmission methods, while orientation of both phases was measured by IR dichroism (according to Fraser's method) and successfully compared to birefringence measurements on final films. Crystallinity appears to be almost insensitive to draw ratio and cooling rate. Moreover the crystallinity profile turned out to be also constant along the transverse film direction. Phases orientation were found relatively low and no dependence on draw ratio was detected.     

Orientation and Crystallinity Measurements in Injection Moulded Products

Summary Orientation and crystallinity of isotactic polypropylene moulded products have been investigated by means of infrared microscopy. The experimental techniques are described elsewhere [ 1-31]. The previous application to film casting products and the application in this work to injection-moulded products confirms their usefulness in polymer science. Orientation and crystallinity distributions obtained for different samples are reported and briefly discussed.     

Mechanism of Grain Orientation During Hot-Pressing of Bismuth Titanate

Grain-oriented Bi₄Ti₃O₁₂ ceramics have been prepared by hot-pressing. Platelike grains align during hot-pressing; the long-axis direction perpendicular to the crystal c axis is oriented perpendicular to the pressing direction. The effects of hotpressing conditions such as temperature, pressure, time, and type of filler on the density, orientation degree, and deformation of hot-pressed compacts were examined. Sharp increases in the density, deformation, and grain orientation occurred during the early stage; the density decreased, and the latter two incresed on prolonged hot-pressing. The grain orientation is closely related to the deformation in the radial direction. The grain-orientation mechanism is discussed referring to mechanisms proposed for high-temperature deformation in ceramics. The compact is deformed by two processes: one accompaines grain orientation, and the other does not. Grain-boundary sliding is proposed for the former process. The contribution of grain-boundary sliding to the deformation increases with increasing temperature and pressure. The filler also influences the contribution. The decrease in density is caused by cavity formation during prolonged hot-pressing.     

Determination of Fume State Parameters from Expansion Measurements of Metal Tubes

In cylinder tests, the time progression of the radial deflection of metal tubes as a result of fume (detonation products) expansion are measured. The parameters of the relevant, analytical curves obtained can be determined via a fitting process, from which the expansion velocities of the cylinder wall are obtained through differentiation. In conjunction with conservation propositions for the gas flow in cylinders of varying cross-sections, the course of an expansion process can be calculated iteratively. By taking the JWL curve representation as a basis, the parameters in this context may also be determined by fitting. In this way, the basis for calculation of all types of terminal ballistic data or a splinter picture of the cylinder wall can be given. In the tests, a total of 17 explosives were included with their initial data known from literature, in order to obtain in this way a comparison with those evaluation procedures for cylinder tests which have been in use up to present.     

Preferred Grain Orientation Relationships in Sintered Perovskite Ceramics

Sintered BaTiO₃, SrTiO₃, and Pb(Zr _x Ti_{1− x} )O₃ ceramics were examined using orientation imaging microscopy (OIM^TM), which is a system for the automated measurement of grain orientations by evaluating electron backscatter diffraction patterns in scanning electron microscopy. As expected for sintered materials, none of the three materials exhibited a pronounced texture. However, analysis of the orientation relationships (ORs) between adjacent grains revealed a statistically significant preference of Σ= 3 ORs. Accordingly, the boundaries between grains with a Σ= 3 OR were particularly important for the macroscopic properties of the materials in question.     

Influence of Orientation on Properties of Grain Boundaries in NaCl

Simple (100) tilt, twist, and double-tilt bicrystals of NaCl, grown by the Kyropoulos technique from melts of high-purity NaCl, alone and with controlled impurity additions, were examined for mechanical strength and structure of the grain boundaries. Grain boundary fracture strengths, measured in three-point bending, showed that high-purity bicrystals with simple tilt orientations were stronger than those with simple twist at high mismatch angles (37° to 45°). The results did not show a functional dependence of strength on angle of mismatch in either tilt or twist bicrystals. Pips observed on parted grain boundaries of high-purity NaCl (100] twist and double-tilt bicrystals were believed to represent regions of continuity across the boundary. This feature was rare in similar-purity NaCl (100) tilt bicrystals. Separate additions of 100 ppm SiO₂, CaCl₂, FeCls, and KCl to the melt had no apparent effect on the character of the grain boundary. However, an addition of 1000 ppm CaCl₂ nearly doubled the strength of a (1001) 30° twist bicrystal, whereas the same addition weakened a (100) 45° tilt bicrystal. Sodium chloride (100) tilt grain boundaries, examined in situ under dark-field illumination, showed randomly distributed spots, believed to be impurity segregations, with their maximum density at the boundary. The spot densities increased with increasing tilt angle for angles of 15° and greater. The spots were not observed in the low-angle tilt boundaries (<15°) and were seen only in intermittent clusters in the few twist bicrystals examined.     

Grain Boundary Sliding Microdisplacement Measurements During the Creep of Alumina

Grain boundary sliding (GBS) is thought to be the principal driving force for the nucleation, growth, and coalescence of grain boundary cavities during compressive creep of polycrystalline ceramics. It has been shown theoretically that stochastic GBS gives rise to continuous cavity nucleation and transient cavity growth and coalescence, eventually leading to crack formation and failure. This paper will show through experimental measurements, using stereoimaging techniques, that GBS is in fact stochastic. Also, mode II GBS, in-plane grain rotation, and in-grain shear displacements, strains, and strain rate measurements during creep of Lucalox Al₂O₃ will be presented. These displacements, measured on a machine vision system, will be presented in terms of the surrounding microstructural constraint and their lack of angular relation to the compressive load axis.     

Thick Nb-Doped Bismuth Titanate Film with Controllable Grain Orientation

In the current work, we reported a potential approach to obtain thick ceramic films with controllable grain orientation based on magnetic alignment and polymerization techniques. The slurry containing 40 vol% Bi₄Ti_2.96Nb_0.04O₁₂ (BINT) ceramic powder, monomer, initiator, and catalyst was drop coated on a Pt substrate and then moved into a vertical 10 T magnetic field. In 1–2 min, the ceramic particles were aligned by a strong magnetic force in slurry and then in situ locked by polymerization on the substrate. After sintering at 1000°C, a BINT ceramic film (50–80 μm in thickness) with a highly a / b plane orientation was obtained. Theoretically, the grain orientation in the films can be easily controlled by adjusting the magnetic field direction. This approach is readily applicable to other materials with a non-cubic structure and is expected to facilitate the fast preparation of grain-oriented thick films.     

Improved Determination of Bimodal Size Distributions from Measurements with Diffusional Size Classification

The size distribution of the unattached fraction of the short-lived radon progeny is reported in the literature to have a bimodal structure. Due to the weak size resolution of diffusional size classification, a wide variety of bimodal size distributions yields similar measurement results, obstructing the reconstruction of size distribution parameters from measured data. For example, it could be shown that although 2 of the commonly used nonlinear approximation algorithms per formed well for the reconstruction of a monomodal size distribution, the reproduc tion of parameters of a bimodal size distribution was unsatisfactory. In conse quence, a "random walk" approach is presented. The basic idea for this approach consists of probing the complete parameter space as an ideal method for locating the best set of parameters. Additionally, 2 steps are introduced for the reduction of computation time to render the ideal approach to an applicable method. The range of geometric standard deviations for the calculation was restricted to values between 1 and 5. The range of median diameters was limited according to the penetration functions of the diffusional samplers. This restricted volume of param eter space was subdivided into 10⁴ cells. During the calculation, cells with exceptionally large values of the minimization functional were eliminated from further computation. Compared to the results of EM and Simplex algorithms, this ''random walk'' method was able to retrieve parameters of both monomodal and bimodal size distributions with improved accuracy.     

Grain Boundary Sliding Measurements during Tensile Creep of a Single-Phase Alumina

The grain boundary sliding (GBS) behavior of a single-phase (relatively coarse-grained) alumina material was studied after tensile creep experiments were performed at 1500°C at stress levels of 20 and 35 MPa. Specimens tested at 35 MPa exhibited a number of modes of GBS, including Mode II (shear) displacements, Mode I (opening) displacements, out-of-plane sliding displacements, and in-plane grain rotation. Strains in the grain boundaries due to Mode II GBS ranged from 940% to 4400%. Average Mode II GBS displacements ranged from 0.08 to 0.29 µm in samples tested for 120 and 480 min, respectively, at 35 MPa. The GBS displacements were shown to fit a Weibull distribution. Tensile creep under a 35 MPa stress yielded a GBS rate of 9.5 10^-6µm/s, while the 20 MPa stress resulted in a GBS rate of 2.2 10^-6µm/s. The average Mode II GBS displacements increased linearly with specimen strain, suggesting that GBS may play an important role in creep cavitation during tensile creep. The data also revealed that compatibility and constraint rules appear to govern GBS behavior during tensile creep. GBS behavior during compressive creep will be compared to the tensile creep GBS measurements presented.     

Grain Orientation Dependence of the PTCR Effect in Niobium-Doped Barium Titanate

The positive temperature coefficient of resistivity (PTCR) effect is directly measured in single grain boundaries in 0.1-mol%-Nb-doped BaTiO₃ with 1 mm coarse grains. The PTCR effect largely depends on grain boundary structure. Random grain boundaries exhibit the PTCR effect as in polycrystalline samples, but the PTCR effect does not appear in highly coherent boundaries such as small-angle boundaries, twin boundaries, and coincidence site lattice (CSL) boundaries with low Σ values. For Σ= 3 boundaries, the resistance increase above the Curie temperature is a function of deviation angle. A small PTCR effect is observed in Σ= 3 boundaries with a deviation angle of about 9° in contrast with ideal Σ= 3 boundaries and boundaries with a deviation of about 4°.     

Texture Development by Templated Grain Growth in Liquid-Phase-Sintered α-Alumina

The distribution and orientation of platelet-shaped particles of α-alumina in a fine-grained alumina matrix is shown to template texture development via anisotropic grain growth. The textured microstructure ranges from 4 wt% oriented platelet particles in calcined samples to nearly 100% oriented α-Al₂O₃ grains after sintering at 1400°C. A CaO + SiO₂ liquid phase creates favorable thermodynamic and kinetic conditions for anisotropic grain growth and grain reorientation during sintering. Important criteria for templated grain growth include (1) anisotropic crystal structure and growth, (2) high thermodynamic driving force for template grain growth, and (3) modification of diffusion in the system to continuously provide material to the anisotropically growing template grains.     

粮食中蛋白质含量的测定

蛋白质是评价粮食的重要指标。本实验用凯氏定氮法和双缩脲法分别对大米、小米、小麦粉、荞麦粉进行蛋白质含量的测定,结果显示为大米中含量最高可达10.03%,小麦粉中含量次之,大米中含量最低为7.61%。同时对两种测量方法进行比较,得出双缩脲法可用于需要快速,但并不需要十分精确的蛋白质测定,凯氏定氮法用于标准蛋白质含量的准确测定。     

Determination of Moisture Diffusion Coefficient of Concrete at Early Age from Interior Humidity Measurements

The moisture diffusion coefficient of concrete is critical for moisture distribution calculation in concrete members. This article aims at building an experimental model to solve the moisture transfer coefficient of early age concrete and investigating its variation law with age as well. The model is based on experimental measurements on the interior humidity of concrete specimens under fully plastic sealing and environmental drying conditions. The model results show that the moisture diffusion coefficient of concrete at an early age is significantly dependent on age. The coefficient may vary from 10^?8 to 10^?10 from 3 to 28 days starting from concrete casting. The variation law of the coefficient with age can be described as a rapidly decreasing stage within 7 to 10 days from concrete casting followed by a slow decreasing stage. This obvious two-stage variation law may principally due to the change of the continuity of liquid and/or vapor phases during drying, which reflects the transformation of the moisture removal mechanism from liquid flow to vapor diffusion. High-strength concrete has a lower moisture diffusion coefficient than that of normal strength concrete under the same curing period.     

Modeling the Influence of Orientation Texture on the Strength of WC–Co Composites

Two-dimensional finite element simulations were used to study the effects of orientation texture on the transverse rupture strengths of WC–Co composites. The model incorporates observed microstructural geometries, anisotropic thermal and elastic properties, and a fracture criterion that reproduces the strengths of known specimens. The results show that the greatest potential for increasing the strength occurs when the [001] axes of the carbide grains are orientated perpendicular to the sample loading direction. Furthermore, the strength increases in proportion to the degree of texture, and the texture-derived strength enhancement is greater in microstructures with a larger contiguity.     

Crystallographic Texture Development in Bismuth Sodium Titanate Prepared by Reactive-Templated Grain Growth Method

Bi_0.5Na_0.5TiO₃ (BNT) and 0.94Bi_0.5Na_0.5TiO₃·0.06BaTiO₃ (BNT–BT) bulk ceramics with extensive 〈100〉 texture were prepared by the reactive-templated grain growth method, using platelike Bi₄Ti₃O₁₂ (BIT) particles as templates for BNT. Calcined compacts were composed of matrix grains with random orientation and 〈100〉-oriented grains transformed from aligned BIT particles, and the texture developed by the growth of oriented grains during sintering. Ceramics with extensive texture were obtained by using the starting mixture containing the maximum concentration of platelike BIT to form the maximum volume fraction of oriented grains.     

Residual Stress Determination Using Strain Gage Measurements

A strain gage technique, which relates the prior residual stress state in a material to the strain data obtained by fixing a strain gage on one surface and grinding off the other, has been proposed previously. In the current work, a generalized solution for obtaining an arbitray residual stress profile from strain gage data is presented. Numerical analysis using the solution indicates that the formulation is insensitive to random errors of 10% or less in the experimental data. Based on the results of the analysis, a procedure for determining stress profiles from strain gage data is outlined. Experimental data for tempered glass was analyzed using the technique proposed. The stress profiles predicted are in good agreement with independent observations using indentation and strength data.     

Determination of Resistivity of Lossy Materials from Dielectric Measurements, Making Use of Interfacial Polarization

It is a well-known fact that the phenomenon of interfacial polarization complicates dielectric measurements at low frequencies. This effect leads to a pseudo-Debye relaxation process in a frequency or temperature spectrum of dielectric constant and loss, with the relaxation time determined by the physical dimensions of the barrier layer and by the resistivity of the bulk material. Use of this effect has been made to determine the resistivity of glass by purposely introducing a barrier of known dimensions, in the form of a thin sheet of mica. Values of resistivity and activation energy obtained by this method agree with values obtained by direct-current measurements.