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We refer to this approach as chemical grain refining.
To measure accurately the as-cast grain size, a colour etching technique for Mg alloys developed in house was used to reveal the grain structure.
The TP1 sample cast at 650°C without shearing (Fig. 1a) has an average grain size of 700µm, while the TP1 sample with melt shearing cast at the same temperature has a grain size of 180µm (Fig. 1b).
Fig. 3 Variation of grain size of AZ91D alloy as a function of relaxation time.
[7] Standard Test Procedures for Aluminium Alloy Grain Refiner: TP-1.

The more diamond grains are produced, the thinner battens of metal carbides in catalyst disc are formed.
For the different content of boron-carbon added to catalysts, the numbers of diamond grains synthesized are different.
The number of diamond grains in 1 # and 3 # samples are more than that in 2 # and 4 # samples.
The battens around the diamond grains are thinner, as shown in Figure 4a, b.
Synthetic diamond grains are embedded in the catalyst disc.

But a large number of surface acidic sites of Pd/γ-Al2O3 are covered by highly fragmented Pd-grain, it causes DME selectivity reduced.
The internal heat of the catalysts was uneven, it casese a large number of cracks during the heating in muffle.
And more Pd loading makes larger Pd grains increase and worse Pd dispersion.
The author learns that when the loading is within 2%, the reduction of surface acid is mainly because of acidic sites covered by Pd metal; when the loading is between 2% and 3%, the dispersion of Pd drops severely, the grain particle size increases slightly and the number of grain nearly unchanged, the covered area just increases slightly, therefore the amount of surface acid reduces slightly; but when the loading is more than 3%, some γ-Al2O3 pores are blocked by the excessive metal Pd grains, it makes that the amount of acid in pore can not be detected, and the amount of surface acid reduces significantly again.
Besides, a large number of Pd grains have spread and mounted to the pore of γ-Al2O3 carrier, it leads to that the Pd activity surface and the acid activity surface of catalyst reduce simultaneously, and finally leads to the activity of catalyst reduced.

Generally the grain size should be ≤10µm.
Some coarse-grained alloys can also present superplasticity except fine-grained structural superplasticity.
Recrystal grains grown obviously, grain boundary is distinct owing to high tensile temperature and long tensile time.
The formation of finer grain consumes distortion energy, reduces dislocation density, loosens stress concentration caused by grain-boundary sliding, provides new, slidable, large angle grain boundaries and benefits grain-boundary sliding [4~5].
The grains are finer and the fracture is even.

A number of studies have been done to clarify the fatigue crack generation and growth mechanisms for high strength alloys [2].
The microcrack growth and/or coalescence model can excellently explain for a formation process of Stage I crack with a critical size where a process of microcrack growth involves a large number of cycles and not by its instantaneous spread.
The coplanar arrays developed in a grain under the cyclic softening impinge the grain boundary and produce steps and/or protrusions, which produces a strain-gradient in the neighboring grain as shown in Fig. 2. [8] Thus the strain incompatibility containing shear strain field at the grain boundary is believed to be developed and to act shear stress and tensile stress to the grain boundary plane, since the grain boundary plane is inclined to the applied stress axis.
In order to relax the internal stress due to strain incompatibility, therefore, a deformation or microcracking must occur between the neighboring grains, i.e. deformed grain, neighboring grain or grin boundary.
The multiple slips that developed in a considerable number of grains may promote homogeneous and multidirectional plastic deformation; further, the localized deformation and strain incompatibility at grain boundaries were believed to decrease as a result of the treatment.

The grains in the heat-affected zone were relatively coarse.
It is seen that the microstructures of AZ31B magnesium alloy were mainly fine dynamic recrystallization grains, and there were small amount of coarse grains and elongated grains (Fig. 1 (a)).
Therefore, the crystal grains in the HAZ were relatively coarse (Fig. 1 (b)).
It is seen that there were a large number of dimples on the fracture surface of base metal, and the fracture mode belongs to the ductile fracture (Fig. 3 (a)).
The grains in the heat-affected zone were coarser, and the grains in the thermo-mechanical affected zone were relatively small and deformed.

Figure 1 (a) is a photograph of the sample sintered at a temperature of 450 ℃, it can be seen , the number of small second phase , the formation of voids at the grain boundaries more loose tissue of the large particles and between the particles the binding force is not high .
Figure 1 (b) is a photograph of the sample sintered at a temperature of 500 ℃, it can be seen, significantly increased the number of the second phase, a continuous distribution on the grain boundaries, but still significant voids phenomenon, which may be due to sintering temperature slightly above the eutectic temperature of the material, there eutectic liquid, appear transient liquid phase sintering, the grain boundary diffusion is not fully, resulting sintered structure is not dense.  
Figure1 (c) photograph of the sample sintered at a temperature of 550 ℃, it can be seen, the second phase the number continues to grow, there is almost no voids exist, the higher the density of the material.
Most La and Al react to form Al11La3 who looks like the needle, in turn, increases dispersion of the grain boundary phase; Needle (Al, Mg) 11 la3 phase forming nucleation first , adsorbs on α- Mg , stopping α- Mg grain's growth due to its pinning effect, and then we get fine grains and reinforced matrix.
This is consistent with strengthening mechanism of refining the grain of the magnesium alloy at room temperature, also can use Hall-Petch formula (1) to explain, namely, grain size, the greater the compressive strength is smaller, the smaller the grain size, grain diameter, the greater the compressive strength

Useful data were obtained on the impact of grain position in the ore particle and voidage on leachability.
A number of studies in agricultural soils found that X-ray μCT scanning at low energy doses (80-120 kV) has negligible influence on archaea and bacteria [9].
Exposure to 120 and 150 kV X-rays for 1 h, however, influenced the microbial growth rate compared to the control, while the maximum cell number was still reached.
On depletion of the metabolic energy source following exposure to X-rays, decreased cell numbers result.
Effect of X-ray irradiation on cell number counts of inoculated vials.

(2) where Γ is the Gibbs-Thomson coefficient, R is the dendrite tip radius, Pei is the Peclet number for i, mi is the liquidus slope, C0,i is the initial concentration for i, ki is the partition coefficient for i, ζc(Pei) is a function of the Peclet number, Iv(Pei) is the Ivantsov solution and Ghkl is the average temperature gradient near dendrite tip
Material and Experiment Procedure The dimensions of each small-scale plate are 30mm (length) ×15mm (width) ×5mm (thickness) for a number of bean-on-plate laser welding.
This location is contributory factor of problematic stray grain formation.
This phenomenon explains why (001)/[110] welding configuration more easily initiates stray grain formation.
This location overwhelms stray grain growth and essentially facilitates single- crystal γ-dendrite growth.

Zn grain boundary diffusivity P = s δ Db (s - segregation factor, δ - grain boundary width and Db - diffusion coefficient in grain boundary) was also determined and it was found that it obeys the Arrhenius law P = 7.2 × 10 -15 × exp (-46 kJ mol-1 /RT) m3 s-1.
The final mean grain size is listed in Table 1.
This is, most likely, caused by the partial (grain boundary) pre-melting.
Grain boundary diffusivity shows no significant dependence on Al concentration.
Acknowledgements The work was supported by the Czech Science Foundation - contract number 106/05/2115 and by the Academy of Sciences of the Czech Republic - number of the project AV0Z20410507.