Controlling the surface chemistry of micron and submicron particles is critical during the manufacturing process
Ron Abramshe, PhD., Warren/Amplex Superabrasives.
Engineers, designers, production managers and purchasing professionals should be informed of the processes used to manufacture the materials used in their respective applications. These applications include but are not limited to:
• Micron diamond used in slicing and dicing wheels for silicon wafer production
• Submicron diamond used in the lapping and polishing of GMR read-write heads in computer hard drives
• Micron and submicron diamond used in polishing laser and LED caps
• Calcium bifluoride crystals for detectors
• And micron/submicron diamond used in polishing aluminum oxide and zirconium oxide hip-replacement joints and dental prostheses
This article is also appropriate for the application of high-performance ceramic materials such as alpha aluminum oxide for slip casting of ceramic parts as hip-replacement joints; titanium dioxide used in paints; or wherever other micron and submicron particles are needed in a state where their surfaces represent the material and not a conglomerate of base material and surface impurities.
It is critical to control the surface chemistry of the particles during the manufacturing process of micron and submicron material. Commonly, feed materials have been processed using a number of aggressive chemical techniques. The precipitation of alumina requires acidic conditions. Synthetic diamond also requires extensive treatment with both alkalis and acids. All of these processes leave residual anions and cations on the surface of the particles. Surface cleaning during processing of the initial material is done to meet effluent standards or post-processing treatment of the water, not necessarily for cleanliness of the product.
When producing high-quality new products, it is vital to control the surface chemistry during processing of micron and submicron materials. Customers can be concerned about agglomeration or cross-contamination in their end product. Hence, reducing or eliminating this concern within their specific chemistry process is a desirable characteristic.
When considering the size separation of micron and submicron particles, it is essential to control the incoming feed.
Elutriation is the process of grading micron and submicron sizes (usually less than 60 μm) into equal distributions that are normally distributed (see Fig. 1). Normal distribution exists when there is a mean, mode and median to the number of particles in the population of material being graded. The population of particles will follow the Gaussian form of:
Since the population follows a normal distribution, the control (or standardization) of micron material lends itself very well to Statistical Process Control.