1、Hydrophobicity
Diamond is not wet with water,but it is prone to sticking to oil.This hydrophobic and lipophilic characteristic is determined by the nature of the non polar bonds of diamond sp3 impurities.This characteristic not only suggests that people can use oil to extract diamonds,but also suggests using organic compounds containing lipophilic genes as diamond wetting agents when manufacturing diamond grinding tools.
2、Chemical stability at room temperature
At room temperature,diamond exhibits inertness towards all chemical reagents such as acids,bases,and salts,and aqua regia cannot react with it.Under heating conditions(below 1000℃),it is not corroded by other chemical reagents except for some oxidants.By utilizing the chemical stability of diamonds,they can be purified using acids and alkalis.
3、Oxidability at high temperatures(thermal stability)
At high temperatures of several hundred degrees,certain oxidants,such as KNO3 and perchlorate,can react with diamonds.Reagents such as NaNO3 can corrode diamonds in a molten state.
In pure oxygen,above 600°C,diamonds begin to lose their luster and form a black skin,which is called incineration.Starting combustion at 700~800℃,reaction formula:C+O2→CO2.
In the air,artificial diamonds begin to oxidize at temperatures ranging from 740 to 840℃,and some products can oxidize at around 600℃.In the air,the starting combustion temperature is 850~1000℃.The thermal stability depends on the integrity of the diamond crystal.
4、Graphitization phenomenon of diamond(thermal stability in non oxygen media)
When heated to a certain temperature in a vacuum or inert atmosphere,diamond undergoes graphitization:
C diamond→C graphite
At 1500℃,surface graphitization can be detected.As the temperature increases,the graphitization rate accelerates,and the entire crystal rapidly graphitizes at 1600-1900℃.At 2100℃,a 0.1 carat octahedral diamond is completely reduced to ashes within 3 minutes.
When even a small amount of oxygen is present,graphitization begins at a lower temperature(below 1000℃).The presence of transition metals will accelerate the graphitization process.
5、Chemical Interaction between Diamond and Transition Metals
Some transition metals can react chemically with diamonds,promoting their disintegration.These metals are divided into two categories.One type is the VII B and VIII group metals in the periodic table,such as Fe,Co,Ni,Mn,and Pt series metals.In the molten state,they are solvents for carbon,which can cause diamond to undergo solvation at high grinding temperatures.Another type is metals that are prone to generating stable carbides,including the IV B,V B,and VI B groups,such as W,V,Ti,Ta,Zr,etc.They have stronger affinity with diamonds and can react chemically with them at high temperatures to produce corresponding stable carbides.
6.Hardness:
Diamond is the hardest substance known to exist naturally,with a Mohs hardness of 10,a new Mohs hardness of 15,and a microhardness of 10,000kg/mm2.The microhardness is1,000 times higher than quartz and150 times higher than corundum.
7.Density and transparency:
The density of colorless,transparent and pure diamond is 3.52g/cm3.When it contains inclusions,the density is 3.44~3.53g/cm3.Both colorless and light-colored diamonds are transparent,while the transparency of dark-colored diamonds and frosted glass diamonds is reduced and appears translucent.
8.Stability:
The ignition point of diamond is 720800℃in pure oxygen and 8501000℃in air,and it is non-conductive.
Generally speaking,diamond has stable chemical properties and has the characteristics of acid and alkali resistance and corrosion resistance.
The interaction between diamond and transition metals is the chemical essence of the tool sticking phenomenon that occurs when machining these materials,which also determines the range of use of diamond tools.