Chemical Engineering Term Paper

Aluminum oxynitride (Al2ONs), generally called ALON, represents a polycrystalline ceramic containing aluminum, nitrogen, and oxygen (Thornhill 113). Under electromagnetic spectrum, this cubic-spinel crystal structure becomes transparent in visible, infrared, and the near ultraviolet (NUV) regions. Presently, the widespread method of producing ALON comprises the sintering of aluminum nitride and aluminum oxide as raw materials. However, this method of production is expensive, complex, and results in products with low transparency and high porosity. In this project, a team of three members prepared ALON using an alternative approach described by Lee et al. (2016). The method was preferred because it is less expensive and decreases the porosity, resulting in better and transparent ceramic.

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Through the experiment of chemical equation used by Lee et al. (2016) in producing ALON, the three members followed a six-step process. In the first step, raw materials (aluminum nitride, 0.08 wht% yttrium oxide, and 0.15 wht% magnesium oxide) in powder mixture were added into a ball mill. Using anhydrous ethanol as a solvent, the mixture was milled together for 48 hours. Ethanol as an ideal solvent because of its ability to prevent intermediate low-temperature aluminum compounds associated with the hydroxyl group from forming during the experiment (Galakhov et al. 270).

In the second step, the powder was dried using a rotary evaporator drier and ethanol was recovered before being purified for future use. The rotary evaporator was chosen because of its speed and capability to process large volumes of solvent. The dried powders were then shaped into disks with diameters of 20.0 mm and a thickness of 3.0 mm using a dry uni-axial press. Thereafter, they were cold isostatically pressed at a pressure of 275 MPa.

During the third step, the specimens in disk forms were sintered under a nitrogen atmosphere of 0.3 MPa inside an electric furnace with high temperatures. The flow rate of nitrogen into the high-temperature furnace was held at 50 standard cm³ per min/per gram of ALON generated inside the reactor. The first sintering process was done at a temperature of 1660° centigrade for 10 hours, while the second process was undertaken at a temperature of 1970° centigrade for 2 hours. Afterward, the specimens were ground into two flat Surfaced shapes. The surfaces were polished with the help of diamond pastes with sizes of 3.0 um.

In the fourth step, the crude ALON was ground into discs measuring 1.5 mm in thickness before being surface polished. By grinding and polishing the specimens, their transparency was being improved. However, this process also introduced damages and compromised the structural integrity of the specimens. Thereafter, using Varian Spectrophotometer an in-line transmittance of specimens was measured within 200-2500 nm range of wavelength.

During the fifth step, the grounded and polished specimens were sintered for the second time at temperatures of 1970⁰ centigrade for 2 hours, inside an inert nitrogen environment at pressures of 0.3 MPa. The nitrogen flowing into the high-temperature furnace was held at 50 standard cm³ per minute/ per gram of ALON. Later, the temperature was increased at a rate of 20°centigrade per minute until it reached 1500° centigrade. The second sintering process was needed to reinforce the ceramic and further boost its relative density (Vlasova et al. 390).

In the final step, the inerting nitrogen was recovered before being purified for future use. The resulting product was aluminum oxynitride with reduced porosity (less than 5%) and improved relative density (more than 95%).

Works Cited
Galakhov, A. B., et al. “Synthesis of Aluminum Oxynitride from Starter Organic            Compounds.” Refractories and Industrial Ceramics, vol. 53, no. 4, 2012, pp. 269–271.
Lee et al. “Method for Preparing Polycrystalline Aluminum Oxynitride Having Enhanced       Transparency.” United States Patent, 2016, pp. 1–16.
Thornhill, T. F. “Polycrystalline Aluminum Oxynitride Hugoniot and Optical            Properties.” AIP Conference Proceedings, 2006, p. 113
Vlasova, M., et al. “Synthesis of Composite AlN-AlON-Al2O3 Powders and Ceramics         Prepared by High-Pressure Sintering.” The science of Sintering, vol. 42, no. 3, 2010,          pp. 283–295.