About superabrasive diamonds
Diamond is carbon in its most concentrated form. Except for trace impurities like boron and nitrogen, diamond is composed solely
of carbon, the chemical element that is fundamental to all life.
But diamond is distinctly different from its close cousin the common mineral graphite which is also carbon. Why is diamond the
hardest surface known while graphite is exceedingly soft? Why is diamond transparent while graphite is opaque and metallic black?
What is it that makes diamond so unique?
The key to these questions lie in diamondīs particular arrangement of carbon atoms or its crystal structure -- the feature that defines any mineralīs fundamental properties. In graphite, each carbon atom bonds to only 3 of its 4 valence electrons with neighboring carbons. The resulting structure of these bonds is a flat sheet of connected carbon atoms. Though individually strong, these layers are only weakly connected to one another, and the ease with which they are separated is what makes graphite so slippery. In diamond however, every carbon shares all 4 of its available electrons with adjacent carbon atoms, forming a tetrahedral unit. This shared electron-pair bonding forms the strongest known chemical linkage, the covalent bond, which is responsible for many of diamondīs superlative properties. The repeating structural unit of diamond consists of 8 atoms which are fundamentally arranged in a cube.
Hardness is not the only property of diamond that makes it so important in industry and technology. Its extraordinary thermal conductivity, low-friction surface, and optical transparency put diamond into cutting-edge applications. Many new products, like compact electronic devices, windows for optical devices in demanding environments, and "no-wear" bearings, such as in the space shuttle, utilize diamond. For these applications, a synthetic form leads the way. This is CVD, so-named for the growth technique chemical vapor deposition.
Diamond has three primary roles in the super abrasive industry: it is used as a cutting tool, it is imbedded in another material and used as a tool or abrasive, and it is turned to powder or paste for grinding and polishing. However, for applications involving the processing of iron alloys, diamond is not used. Apparently, because of a high temperature reaction between iron and carbon, diamond abrades quickly. Although diamond is twice as hard CBN (Cubic Boron Nitride) CBN is a better choice in this case.
Diamond is selected for such uses where its hardness and resistance to abrasion - its long working life and fast cutting action - outweigh its costs. Moreover, diamondīs resistance to wear enables it to cut reproducibly time after time, - a requirement of automated production. Diamond machining tools for turning, milling, and boring are preferred where finely finished surfaces of high precision are needed.
Both natural and synthetic diamonds are used with their own respective applications. For some applications natural diamonds are preferable but synthetic diamonds are probably more useful in terms of their scope, availability and uniformity. They can be tailor made and produced in a large range of shapes and sizes with specific applications in mind. Regular diamond crystal morphology falls between a near cube and an octahedron. Shapes ranging between the two are combinations of cubic and octahedral faces. Blocky or dodecahedral crystals are probably the toughest but friable irregular shapes that fracture and continuously provide sharp edges are more suited for polishing. The resistance to fracture of a saw diamond is a key parameter in saw blade performance, particularly in high impact applications. Size and quality grading is critical and diamond powders need to be sieved and sorted for shape before they are sold for commercial applications. Properly sized diamonds will enhance performance by producing even surfaces without large scratches or grooves which take time to remove. Sizing and sorting are key to performance and few organizations can do it well, especially in the smallest sizes. |
