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The permeability values obtained for this reason was correlated with the pore size and number of pores per square centimeter.
The explanation would be that in the mixing and pressing processes, it is possible that two grains of NaCl to come in contact, and so to make pore sizes bigger than that of NaCl grain size.
The maximum number of pores/cm2 was achieved at samples obtained with smaller NaCl powder size.
When using NaCl with a smaller grain size are obtained smaller pores but double in number of pores/cm2 than in previously case.
The grain size of NaCl powder also influences the permeability.

The grain growth mechanism appears to relate to lattice or surface diffusion.
The production of HA with improved mechanical properties has led to a number of different studies with regard to HA composites with other ceramic [8], glass [9] or polymer additions [10].
Whilst there was a range of grain sizes observed in the microstructures after the various sintering times, no evidence of the exaggerated grain noted by Thangamani et al. [2] and Yeong et al. [13] was observed.
For the sake of interest, the grain growth exponent was extracted using the relationship (D-D0) = ktn, where D is the measured grain size after time t, D0 the average grain size after 0 minutes and k the rate constant.
A slow grain growth rate was observed but did not seem to have any significant effect on the microhardness.

The microstructure of the wheel steel was composed of fine-grained ferrite and pearlite and carbides distributed along the ferrite grain boundaries.
In simple ferritic steels, D corresponds to the mean grain size of polygonal ferrite.
That is to say, when the effective grain size is smaller, impact toughness is better.
Fig. 4(b) shows the nano-scale precipitate of experimental steel, a large number of <10nm nano-scale precipitates were obtained.
Conclusions (1) The microstructure of hot-rolled 590MPa grade wheel steel was composed of fine-grained ferrite and pearlite, and carbides distributed along the ferrite grain boundaries.

The rate of annihilation is determined as the change in the number of dislocations of the same sign N depending on time: .
Pearlite grains (about 30%) consist of cementite and ferrite interlayers.
This can be explained, taking into account that the microhardness of pearlite grains is about a third higher than that of ferrite grains.
Using a model crystal with a size of 1000 b, the dependencies in the variation of the number of dislocations and strain in a pile-up on time were analyzed.
Rybin, Grain Boundaries in Metals, Metallurgy, Moscow, 1980.

Fig.2. a) 20x photos of the layers on the bearing end: (1) babbit lining Cerrox (babbit); (2) copper-based material (copper); (3) interlayer chamfer; (4) steel shell; (5) chamfer of the outer side of the shell; (6) the drill. b) Samples of abrasive cloths in 200x blowup: (1) AC80, 0.2 mm grain; (2) AC150, 0.1 mm grain; (3) AC230, 0.055 mm grain; (4) AC320, 0.045 mm grain; (5) AC600, 0.025 mm grain; (6) an abrasive cloth glued to the shaft.
Figures 1…7 correspond to the numbers of formulas (1) … (7) in Table 1.
Deviation of MSVs in dependence to abrasive grain sizes AC on the Fig. 4 proves this conclusion.
The lowest values of WI are typical for AC600 with the grain size of 0.025, and the highest values occur in the case of AC80 the grain size amounting to 0.2.
Features of Wear of Abrasive Grains Depending on Microcutting Speed of Steels.

In the role of the main characteristics that define the operation of magnetron coatings were adopted: the coating microhardness Hμ, grain size d, wear resistance I.
(1) Where S - discharge rate (the number of atoms ejected by one ion); Δm - mass loss of spray material, mcg; j - ion current (mA); τ - time (h); K - coefficient depending on the choice of units; A - mass number of the atoms.
Influence of technological factors on microhardness: discharge power and grain size in magnetron sputtering TiNi - (a); discharge power and pressure in the chamber - b); discharge current and grain size - c); dependence of durability: the discharge power and microhardness - d) The remaining process parameters were assumed constant based on published data and experience.
Posed a series of experiments planned on the basis of plans uniforms-rotatable second order allowed with a minimum number of experiments to make a statistical model magnetron sputtering process alloys with shape memory 321H steel thickness up to 3 mm.
(5) Where Нμ - coating hardness, GPa; I - wear resistance in mg/m; N - discharge power, kW; d - grain size, nm; I - discharge current, A.

The high angle of misorientation between a and b grains can be attained already after a single ECAP pass.
Another method of SPD applied to refine a grain structure was accumulative roll-bonding (ARB) process, carried out in the 70/30 brass alloy sheet on up to six cycles to obtain nano-grains [3].
After six cycles, texture intensity reduces slightly, which can be explained by nano-grain formation.
No grain refinement can be seen, only growth of dislocation density and a single twin can be observed.
The microstructure studies show that the dislocation density is relatively high after both modes of deformation, while after additional groove pressing increases number of deformation twins and fraction of high angle grain boundaries and decreases grain size.

The results showed that the nano-WO3 particles were mainly distributed in the grain boundary of Cu2SnSe3 matrix, and the grain growth of Cu2SnSe3 was inhibited.
It can be observed that the grain size distribution of Cu2SnSe3 matrix phase is about 3 um, and the grain boundary is clearly visible after sintering, showing that the particles have a perfect binding.
Fig. 2(c)-(f) shows the nano-WO3 particles are mainly distributed on the grain boundaries and with the grain size of the matrix is obviously smaller the increasing of nano-WO3.
The introduction of nano-WO3 produced a large number of defects within the crystal, therefore increasing the phonon scattering at the grain boundary.
Nano-WO3 particles were mainly distributed in the grain boundary of Cu2SnSe3 matrix, and the grain growth was inhibited.

The in-line transmission increases with a decrease in grain size.
Ceramics are polycrystalline materials composed of crystallized grains.
It is thought that the existence of grain boundaries has little relationship to light scattering or the scattering at grain boundaries can be neglected [10].
The scattering coefficient of birefringence is given as follows [11]: (13) Here, Ngr is the number of grains, rgr and Qgr are the radius and scattering efficiency factor of a grain.
Effect of grain size on in-line transmission at wavelength λ= 0.5μm.

For Si content ≥10.7%, grain sizes gradually reduced with annealing temperature increasing.
As Si content increased (CrAlSi3.7N, Fig. 1(b)), the size of and number of micro-hole reduced.
When the Si content ≥ 6.3%, the micro-hole basically disappeared and the grain distributed uniformly.
The effect of annealing temperature on grain size of CrAlSi8.6N and CrAlSi10.7N coatings are shown in Fig. 2.
The grain size of CrAl(Si)N coatings gradually decreased with Si content increasing.