A conventional approach to making miniature or microscale gas chromatography (GC) components relies on silicon as a base material and MEMS fabrication as manufacturing processes. However, these devices often fail in medium-to-high temperature applications due to a lack of robust fluidic interconnects and a high-yield bonding process. This paper explores the feasibility of using metal additive manufacturing (AM), which is also known as metal 3D printing, as an alternative platform to produce small-scale microfluidic devices that can operate at a temperature higher than that which polymers can withstand. Binder jet printing (BJP), one of the metal AM processes, was utilized to make stainless steel (SS) preconcentrators (PCs) with submillimeter internal features. PCs can increase the concentration of gaseous analytes or serve as an inline injector for GC or gas sensor applications. Normally, parts printed by BJP are highly porous and thus often infiltrated with low melting point metal. By adding to SS316 powder sintering additives such as boron nitride (BN), which reduces the liquidus line temperature, we produce near full-density SS PCs at sintering temperatures much lower than the SS melting temperature, and importantly without any measurable shape distortion. Conversely, the SS PC without BN remains porous after the sintering process and unsuitable for fluidic applications. Since the SS parts, unlike Si, are compatible with machining, they can be modified to work with commercial compression fitting. The PC structures as well as the connection with the fitting are leak-free with relatively high operating pressures. A flexible membrane heater along with a resistance-temperature detector is integrated with the SS PCs for thermal desorption. The proof-of-concept experiment demonstrates that the SS PC can preconcentrate and inject 0.6% headspace toluene to enhance the detector’s response.

Binder jet printing (BJP), one of the early metal 3D printing technologies, has distinct advantages over the other 3D printing processes that employ locally melting or welding to build 3D parts. Some of the advantages of BJP include printed parts free of residual stresses, build plate not being required, and less powder usage. However, the BJP technology has been adopted only in limited applications such as prototyping and sand molding because of its difficulty in achieving full-density parts. Based on our previous work on stainless steel (SS) 420, the same BJP protocol was used to attain full-density parts made of SS 316L. The effect of the particle size, mixture ratio, and sintering additives on the densities of printed and sintered parts is investigated for SS 316L powder. Three distinct sizes of SS 316L powders are mixed to improve the packing density. A systematic study of the binder burn-out procedure is conducted using thermogravimetric analysis, leading to a complete removal of binder phase without oxidizing SS 316L powder. The optimal sintering condition for some powder mixtures is determined to obtain the maximum density with the addition of small amounts of boron compounds as sintering additives. The quality of the fully-sintered SS 316L parts is evaluated using the various measurements including density, microstructure, hardness, and surface roughness. As we did with SS 420, the relative density of 99.6% is obtained for SS 316L without structural distortion. This is the first demonstration of such density for SS 316L using the BJP technology without any infiltration.

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