Diamond is a mineral that is almost entirely 96-99% carbon and occurs as eight- (octahedron) and twelve-faced (dodecahedral) crystals, often with rounded faces. Diamond is usually colorless and similar to several other colorless minerals like quartz, topaz, or zircon and has the highest hardness on the Mohs scale with an index of 10.
Diamonds are formed at high pressure of 45,000 to 60,000 atmospheres, at depths of 125 to 200 kilometers at high temperatures. These conditions form a mineral with a cubic crystal lattice. Natural diamond age is estimated at an average of 900 million to 4.25 billion years and can be found on all continents.
Since ancient times, diamond has been considered a gemstone of the highest grade and is now recognized as the most valuable of gems. However, only a small portion is used for jewelry making, while the rest is used in the manufacturing of various cutting, grinding, and polishing tools.
Scientists have been researching and studying the properties of diamonds since the end of the 17th century, but it was only in the early 19th century that they could prove that diamonds are chemically similar to coal and graphite.
This fact has spurred the development of methods to produce synthetic diamonds to cover the growing demand for efficient abrasives and large-scale applications.
Modern knife sharpening products use artificial diamond powders, which are analogous to natural diamonds in their chemical composition and structure, as they have the same crystal lattice and consist of the same natural material.
The principle of diamond synthesis and the development of diamond synthesis technology on an industrial scale were established in several developed countries only in the middle of the last century.
There is one low-cost diamond synthesis method that involves heating with induction or direct flow of electric current. During the process, in a chamber pressurized at 50 x 102 MPa, the reaction mixture undergoes recrystallization of the graphite crystal lattice into a cubic diamond structure with the growing pressure. This method is called high pressure high temperature - «HPHT» and is the most popular due to the homogeneity of the result.
To obtain different fractions of diamond crystals, they change the synthesis time. Synthesis allows the production of strong crystals of artificial diamonds with a size of 500 to 800 microns. All fractions of large sizes have rather low physical and mechanical properties.
Later on, they developed methods that allow synthesis at a lower pressure of only 10 x 102 MPa, but with a slower crystal growth rate.
The development of industrial diamond synthesis methods does not slow down and large companies are working on developing and improving methods to increase the efficiency and optimize the costs of production.
The industrial use of diamonds is directly related to their physical and chemical properties, primarily hardness and wear resistance. Diamonds serve for the production of various cutting tools, while diamond abrasive powders are used for the production of polishing pastes and sharpening stones.
Diamond has twice the abrasive power of boron carbide and five times the abrasive power of silicon carbide. This is why high-quality diamond abrasives, though costly, are the most effective sharpening accessories thanks to their features.
One of the important characteristics of a diamond sharpening tool is the type of bond in the diamond-bearing layer of the stone.
Today, you can find the following types of bonds used in the production of diamond sharpening stones: electroplating, metallic bond, organic bond, and polymer bond.
Originally, the electroplated bond was designed for the production of consumables in the form of diamond wheels for use with industrial equipment for the treatment of complicated surfaces of hard materials such as ceramics, glass, natural stones, and of course hardened steels and carbides.
Picture 1. Sharpening stone with coated diamonds (electroplating)
Electroplating involves embedding diamond crystals under high temperatures into a metal base consisting of nickel. Another feature of electroplated stones is a rather thin layer of diamond powder.
During the production process, diamonds are embedded to a depth of about 60-70% and are securely held in place by the bond. This allows such stones to remove metal aggressively, making them suitable for coarse processing and profiling of cutting edges with significant damage.
However, you should note that such stones wear out rather quickly due to the thin layer of diamonds. In addition, even among branded stones, you may find pieces with much larger diamond grit than indicated in the product specification, which in turn can lead to undesirable and large sharpening scratches.
This type of stone does not need to be prepared for operation or breaking in and can be used without cooling liquids.
For these reasons, diamond stones tend to wear faster when used on softer steels with a hardness of up to 58 HRC, compared to their use on harder steels. Occasionally, some manufacturers offer diamond-coated stones with more than one layer to extend the life of the stones.
This type of bond is made with a combination of copper and tin. The main difference compared to electroplated stones is that the diamond particles are mixed with a bond to form a relatively homogeneous material, which is then shaped like a stone. Sometimes manufacturers add additional abrasive powders to increase efficiency.
Picture 2. Sharpening stone with metallic (copper-tin) bond.
Such stones are used for grinding various products with hard surfaces, and stones of a certain size can be used for knife sharpening.
Compared to all existing bonds and even other types of abrasive grit, copper-tin bonded stones are considered a kind of super abrasive. There are several reasons for this. Diamond stones of this type are no less effective than diamond stones based on cubic boron nitride and are generally less expensive. Diamond sharpening stones with coarse and medium grits are particularly effective.
It should be noted that they are quite durable and should only be flattened when you notice a decrease in their effectiveness. Flattening (and grit renewal - conditioning) is done with tempered glass with silicon carbide powder of approximately 60-100 FEPA F grit.
Organic bonded diamond stones are a fairly good and high-quality sharpening solution.
Picture 3. Sharpening stone with organic (bakelite) bond.
This bond is based on powder bakelite (phenol-formaldehyde resin). As with the copper-tin bond, the abrasive base layer and diamond particles form one material, which is then attached to the backing plate.
Diamond particles mixed with organic bonds wear down slower than those made on hard bonds. If you use them properly, you will find that the service life of these abrasives is significantly long. Also, these stones are easy to break in and do not require conditioning, because they keep the same grit, unlike natural stones.
The results of using such abrasives are somewhat lower in efficiency, but the finishing of the cutting edge is much better than that of other bonds. It is best to use such bars from medium grit to fine grit level. You can use water as a cooling liquid.
This type of bond is not very common, but it is worth mentioning anyway because it is available in some shops that sell sharpening supplies and is used by master sharpeners. This organic bond variation is different from other bond types mainly because it does not include boron carbide, which is often found in others. Plus, it is softer than the rest. Diamond powder for this bond is meticulously controlled, particularly when used on fine-grit stones for which this bond was designed and provides a very clean edge finish.
Picture 4. Sharpening stone with OSB bond.
In terms of surface finishing, this bond can only be surpassed by polymer-bonded or very good sharpening stones made of natural shale rock. They can work with water or oil for cooling.
For several reasons, polymer-bonded abrasive stones cannot be considered a widely popular sharpening solution.
Picture 5. Sharpening stone with polymer bond.
The bonding of this type of abrasive can be classified as oligomeric synthetic compounds that include epoxy groups for strong fixation of diamond grits. The result is an abrasion-resistant substance with a certain plasticity. Due to these properties, diamond grits effectively work on the cutting edge surface, making it extremely sharp while maintaining a good grit renewal rate.
The quality of the bond and diamonds can lead to varying results within similar grit sizes. When used correctly with oil, high-quality abrasives can provide an exceptionally fine finish and create a remarkably sharp edge. A rather important aspect of these stones is their relatively low metal removal rate.
Most existing diamond abrasives can be categorized not only by bond types but also by their sizes: full-size, Apex-type, pocket-sized sharpening rods, and other diamond sharpening tools.
Stones in this category are mainly about 20 cm in length and 5-8 cm in width.
Picture 6. Full-size stone (benchstone)
The main purpose of such stones is to work with long and large blades. Galvanic bond is most commonly used due to its low cost. Other bond stones may also be available, but they typically come at a significantly higher cost.
This form factor is primarily designed for use with guided sharpeners from various manufacturers.
Picture 7. Apex type sharpening stones.
Usually, the size ranges about 15 cm in length and 2.5 cm in width. This is probably the most common size of sharpening stones. Diamond coated abrasives of such type are included in TSPROF sharpening kits: Other similar abrasive holder systems differ from the dovetail concept, but they are not as widely spread.
Pocket bars are designed for portable use and are typically around 10-13 centimeters in length.
Picture 8. Pocket stones.
They can be used in combination with compact manual sharpening systems or independently.
There is also a range of various diamond sharpening tools that are components of different brand sharpeners. You can also use them independently to hone knife blades.
Picture 9. Other diamond abrasives
There is no single answer to this question since there is no universal bond suitable for all sharpening tasks.
Many brands frequently offer diamond sharpening stones as part of their kits. Most diamond abrasives are single-sided, but some manufacturers offer double-sided stones for easy use. Similar sharpening stones are available in our online store.
If you visit the section "Sharpening Stones" in our store, you will find a set of diamond coated bars of 5 different grit sizes, as well as a set of 4 diamond plates with a three-layer coating.
Expert sharpeners with high work volumes and varying knife qualities and conditions may have their solutions, but for home use, it is best to base your choice on personal needs and/or your knife collection.
We recommend using resin bonded diamond sharpening stones. They provide amazing surface finish and are incredibly wear resistant. In our online store you can find TSPROF Alpha Resin bonded diamond sharpening stones, available as individual stones in blister packs or a set of 7 pieces of varying grits for all knife sharpening stages.
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