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. %) 5 10 15 Average pore diameter (um) 39 41 50 During heating in air, SiC grains combine with graphite particulates, these particulates burn out, leaving pores in the porous ceramics.
Hence, the pore size can be directly controlled by the number of the pore-forming agents.
Such a highly porous structure cannot be achieved by a conventional process.� To achieve strong and reliable porous ceramics, a homogenous microstructure with fine grains and enhanced necks is expected.
Since no continuous interconnection was observed between graphite-derived pores due to a homogeneous dispersion of graphite particles in the powder compacts, the porosimetry results in Fig.6 actually reflect the size and distribution of pore channels between SiC grains.

In recent years, a number of researches on porous HA have been made in the field of biomedical materials, because the reticulated structure of porous HA allows cell attachment, proliferation and provides pathways for interstitial fluid.
Materials and Methods HA powder, with average grain size of 0.3µm, was prepared by neutralization in the laboratory.
In this study, after addition of 6wt% BG, the glass phase tended to gather near the grain boundaries (Fig.3c), which inhibited the growth of crystal grains, thus the average compressive strength of porous ceramics reached 2.3MPa.

The incorporation of fine grain (~5 µm) alumina particles improved both densification and mechanical properties markedly with increasing alumina content.
A number of parameters defined by Hasselman [9] can be used to predict the thermal shock behaviour of a material.
Y is a dimensionless number, which is dependent on the geometry of the loading and the crack configuration with L/D ≈ 8, A0=+1.96, A1=-2.75, A2=+13.66, A3=-23.98, A4=+25.22 [17].
The pores around the fine alumina particles were homogeneously distributed, and they were rarely observed in the microstructure, indicating a high packing of fine alumina particles amongst the coarser grains (Fig. 1a).
Microcracks were observed between coarse alumina and mullite grains, due to the thermal expansion mismatch, where the crack propagation was arrested by the large scale of pores (Fig. 1-b).

Hard rock is a heterogeneous material in nature, and consists of different grains and cementing materials in which internal stiffness and strength show a significant variation.
Moreover there are always a great number of pre-existing micro-cracks present in rock.
Lajtai et al.[10] mentioned that in the case of Lac-du-Bonnet granite, the initiation of micro-cracks starts at stress levels of 0.2-0.5 UCS and mostly at the grain boundaries and is directed parallel to the maximum principal stress.
The most frequently applied mechanisms are stress concentrations around pores[12], elastic mismatch between grains[13], Hertzian contact between grains[14], and sliding along pre-existing cracks[15].
As the number of propagating fractures multiply, damage can be viewed as accumulative and can be correlated to observed decreases in the elastic stress and cohesive strength of the material.

When the Sn content was 1%, the grain size of the alloy was at the minimum size.
The grain size was small and its shape was equiaxial.
The grain size for as-rolled samples was bigger than that for extrusion alloys.
The alloy grain size increased, leading to a decline in its plasticity too.
The fracture microstructure of the as-extruded alloy was composed of a large number of small dimples.

It can be seen that the number of the second phase decreases compared with as-extruded.
From Fig. 4 (a), the water-quenched alloy, it can be seen that there exists very little second phase in the matrix and the grain boundary is clean.
From the microstructure of the oil-quenched alloy, there is some little α-Mg phase and second phase precipitating from β-phase grain boundary.
From Fig. 4(c), the air-quenched alloy, it can be seen that the β-phase grain boundary becomes vague and there appears much tiny dot-like precipitation in the β matrix.
When the temperature increases to 673K，the β phase grain becomes larger in size and leading to the hardness decreases slightly.

The primary mechanism of damage in ceramic is widely reported to be micro-cracking along grain boundaries.
The causes of micro-cracking have been discussed , starting with the initial processing or the thermal anisotropy of the grains and the glass phase and dislocation pileups at a triple point[2].
The average grain size is 8um.
So damage scalar is measured in terms of a dimensionless parameter , where 3 D Na= (3) Where N is the number of cracks per unit volume which is variable ; a is the crack size which is favorable to grow.
With the new micro-cracks nucleating and the micro-cracks extending, D is due to increase in crack size and number of cracks.

In the arc of the contact, several abrasive grains participate in cutting at the same time, the temperature of the cutting point for single grain is extremely high, and the heat must diffuse as quickly as possible, so that relatively lower macroscopic temperature will be formed in grinding contact zone.
In fact, the forming of the metamorphic layer on the working surface is not for the temperature of the cutting point for single grain, but for the macroscopic temperature in grinding contact zone, especially for the temperature of the contact surface.
workpiece, z (refers to Fig.1) is the distance between the isothermal surface and the surface of the workpiece in the arc of the contact, A=vl/2a ( eld= ∆ is the length of the arc of contact, Δis the depth of cut corresponding to the radial amount of feed per revolution of the workpiece, de is the equal diameter), and q is the average intensity of the thermal resource can be express as follows: wtfRFv q Jlb = (2) where Rw=Qw/Qz (Qw is the heat quantity inputted to the workpiece, Qz is the total heat quantity formatted in the working), vf is the velocity of cross feed, J is the heat equivalent of work, b is the grinding width, and according to the references [2], the tangential grinding force Ft is: 1 21 22 te v Fkb ()d V εε − −ε −ε =ω∆ (3) where k is a constant relating to the material of the workpiece, ωis available interval between the grains
The Eq.6 can also be express as: ∆+++==θ= lnzVlnyvlnxKln)0z(lnY c max (7) k=165[kg/mm] Rw=0.8 λ=42[kJ/(m 2h0C)] J=4.2 de=51.6[mm] w=0.4[mm] a=0.05 ε=0.25 v=0.25[m/s] V=33[m/s] Δ=0.02[mm/r] Kc=839.5 0 1 200 300 400 500 600 700 0 200400 600 z(µm) Simulating curve Experimental curve θ (oC) Fig.2 The grinding temperature of different isothermal surface Table 2 L9(3,4) Orthogonal Layout Testing Data v [m/s] V [m/s] ∆ [mm] Grinding parameters Numbers Level Value Level Value Level Value θ (Z=0)[ 0C] 1 L 0.13 L 8.9 L 0.005 247 2 L 0.13 M 17.2 M 0.01 417 3 L 0.13 H 33 H 0.02 702 4 M 0.18 L 8.9 M 0.01 419 5 M 0.18 M 17.2 H 0.02 706 6 M 0.18 H 33 L 0.005 325 7 H 0.26 L 8.9 H 0.02 711 8 H 0.26 M 17.2 M 0.01 327 9 H 0.26 H 33 L 0.005 550 L-Low M-Middle H-High If sets:          + − −∆ = + − − = + − − = 1 005.0ln02.0ln )02.0ln(ln2 X 1 9.8ln33ln
Table 3 The Parameters of Equation 11 Numbers X1 X2 X3 Y 2 1X 2 2X 2 3X X1X2 X2X3 X3X1 X1Y X2Y X3Y 1 -1 -1 -1 5.5431 1 1 1 1 1 1 -5.5413 -5.5431 -5.5413 2 -1 0 0 6.0497 1 0 0 0 0 0 -6.0497 0 0 3 -1 1 1 6.5582 1 1 1 -1 1 -1 -6.5582 6.5582 6.5582 4 0 -1 0 6.0707 0 1 0 0 0 0 0 -6.0707 0 5 0 0 1 6.5793 0 0 1 0 0 0 0 0 6.5793 6 0 1 -1 5.7869 0 1 1 0 -1 0 0 5.7869 -5.7869 7 1 -1 1 6.5999 1 1 1 -1 -1 1 6.5999 -6.5999 6.5999 8 1 0 -1 5.8081 1 0 1 0 0 -1 5.8081 0 -5.8081 9 1 1 0 6.3172 1 1 0 1 0 0 6.3172 6.3172 0 ∑ 0 0 0 55.311 6 6 6 0 0 0 0.5768 0.4504 2.6011 Conclusions This paper has built the thermal model, which works on different isothermal surfaces and the highest temperature on the grinding contact surface in grinding contact zone.

Crack A propagates from one grain to another during growth and changes its direction depending on grain orientation.
Crack C is a set of three mutually parallel cracks within a grain, indicating that these cracks appear to be crystallographic in nature.
Within the large grain, there are two main parallel cracks with a short vertical segment connecting them, and a nonparallel segment attaching to one of the parallel cracks and making an angle of approximately 66 deg with it.
The bigger number of transmitted X-rays that passed through the cracks makes darkcoloured lines in the film.
From the X-ray photograph it was found that a large number of pores marked by arrows are present in the path of the crack, which suggests that the crack is travelling from pore to pore.

Study has shown that S application in the soil can induce the formation of iron plaque outside roots, and with the increase of soil sulfur, the numbers of iron plaque also increase in the roots [3].
Therefore the research of selenium supply in soil has influences on the iron plaque number of rice root and the effects on cadmium absorption under controlled conditions can be expected to provide theoretical guidance for the safe production of rice.
As the selenium treatment concentration increased, the cadmium content of rice roots, stems, leaves, husks and grains significantly decreased.
The decreasing of cadmium accumulation in stems, leaves, husks and grains were higher than in roots.
With the increasing of Se treatment concentration, the Cd content of roots, stems, leaves, rice husks and grains significantly decreased.