Diamonds concentrations

Diamond wheel specifications show diamond concentration in the grinding rim a concentration of 100 equals 25 vol % diamond. Most wheels have diamond concentrations in the range of 50 to 200 and selection depends on use. Lower concentrations work best on wide contact surfaces higher concentrations work best on narrow edge widths (47). 

Deep cones having a 70° apex angle are normally used in drill bits to give built-in stability and to obtain greater diamond concentration in the bit-cone apex. 

The gangue is separated by mechanical methods and the diamonds concentrated by processes which permit... 

Additional demands are made to the production of multi-layered diamond-containing and functionally gradient materials with a gradually from layer-to-layer changing diamond concentration. Those demands include the increase of a material impact resistance and strength, reduction of the expensive diamond powder input, the increase of the expensive diamond powder input, the increase of the diamond boundary concentration in the working layer. 

The SHS-method allowed to produce 6-layer composites with (Ti,Mo)C ceramic binder and from layer-to-layer changing diamond concentration from 0 to 12 % with a step of 3 % and from 0 to 25 % with a step of 5 %. 

Nine compositions with the diamond concentration of 3, 5, 7, 9, 10, 12, 15, 20, 25 mass % were mixed with the charge Ti-C-Mo to produce multi-layered semi-products. The ready mixtures were placed layer-by-layer into a pressform in the following order diamondless layer weighing 25,5 g 3 mass % diamond layer, weighing 10 g 5 % layer -10 g 7 % layer - 10 g 9 % layer - 9,9 g 12 % layer - 9,9 g. After densification pellets were obtained 48 mm in diameter with the thickness of the layers 5.0, 2.0, 2.0, 2.0, 2.0, 2.0 mm correspondently. Multilayered pellets with the diamond concentration from layer to layer as much as 0, 5, 10, 15, 20, 25 % mass were prepared similarly. The final pellet was placed into a reactional mold. An SHS reaction was initiated from the lateral face of the cylindrical pellet by a tungsten spiral. After accomplishment of the combustion reaction and propagation of the combustion synthesis wave, the hot SHS-products were compacted in a hydraulic press at P > 400 MPa for no more than 10 s. The time of exposure to pressure was chosen dependent on the combustion temperature and reology of the products, e.g., on their plasticity and the amount of the liquid phase formed. Usually this time is 0.5 -4 2 sec. SHS-products were cooled at the room temperature. 

Figure l,a and b present the distribution profiles of diamond concentration and strength through the thickness of multilayered samples. The figure shows that the diamond strength grows from 3 % layer to 12 % layer (fig. I a) and is the maximum one in the layer with the diamond concentration equal to 15-20 % (fig.lb). 

One of the peculiarities of the natural diamond is a considerably lower content of admixtures Ni, Mn, oth. as compared to the synthetic diamond. It is this feature that determines its raised resistance to the action of high temperature in the combustion wave. Figure 3 shows the dependencies of the recuperated synthetic and natural diamond strength on the mass proportion of the charge layers mi/m2 with diamond concentration equal to 25 % vol. on the example of the bi-layered composite with the ceramic binder (Ti,Mo)Ca. The strength of diamond grains is also affected by mi/m is the composites with the binder of NiAl, TiB+Ti, TiC-l-TiAl, TiB2+Si. 

Fig. 2. Time series of the alkalinity (Aik, solid diamonds) and dissolved inorganic carbon (DIC, dotted diamonds) concentrations of the culture system water during the 2001 experiment (a) and 2002 experiment (b). Samples for Alk/DlC titrations were not collected until the second half of the 2001 experiment.

The chemistry of the process is presented in Figure 9.1, whereas the mechanism of the process is presented in Figure 9.2. The rate of bond metal dissolution is highest at the metal-diamond interface particles in other words, the tendency of electrolytic dissolution is to expose the diamond particles (Chen and Li I, 2000). In addition, the metal dissolution rate increases with diamond concentration particles (Chen and Li 1,2000). 

For a fixed gap and applied voltage, the current density does not change much with the diamond concentration particles (Chen and Li I, 2000). Hence, to maintain a constant rate of metal removal, the applied electric field should be lower for a higher diamond concentration tool and vice versa. This electric field concentration effect is greatly reduced when the diamond particle is half exposed (Chen and Li II, 2000). This effect sharply decreases from its highest value near the diamond-metal boundary to a... 

Figure 6.9. Activation energy of the PPS crystallization vs. nano-diamond concentration. [Data from Deng, S ...

Test results (Pig.I) show that the second lot composite with diamond strength measure 82 H and diamond concentration 18.7% exhibits the highest fatigue life, the lowest fatigue life is exhibited by the first lot composite with diamond strength measure 32 H and diamond concentration 25%, the ratio with respect to durability (in the case of 50% risk of rupture) being about 65 1. 

Changing the diamond grits strength measure from 32 H to 82 H at constant diamond concentration results in 20-fold increase in fatigue life of the composite. At the same time the decrease in synthetic diamond concentration from 37 5% down to 18.7%, the other parameters being constant, results in 8-fold increase in a number of fatigue cycles to failure of DCM specimens. 

The computer-assisted numeric simulation has shown that the increase in the diamond concentration in the DCM entails an increase in the tensile residual stresses in the matrix... 

Figure 2, The dependence of the second phase particle damage parameter on the grade of diamonds, the reduced diameter value and the diamond concentration in the composite.

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