A Binder Jet Printed, Stainless Steel Preconcentrator as an In-Line Injector of Volatile Organic Compounds

Abstract

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.

Recent developments and trends in miniaturized gas preconcentrators for portable gas chromatography systems: A review

“…Huang et al [16] printed a stainless steel PC using jet binder printing (BJP) technique (see Figure 2c).…”

“…Moreover, since most adsorbents have a low thermal conductivity, these structures serve also to promote a more efficient heat transfer through the adsorbent bed [16].…”

“…However, the problems related to the fluidic interfacing and the need for cleanrooms for their development has brought researchers to adopt new approaches for PC miniaturization. Recently, 3D printing [16] or milling [4] have been employed as alternative fabrication techniques in the fabrication of miniaturized PC. At present, these techniques do not have the features to create microstructures with the same accuracy as microfabrication techniques, but they enable easier fluidic interfacing and may reduce the costs of the prototyping process.…”

3D Printed MEMS Technology—Recent Developments and Applications

“…Since silicon-based microfluidic devices are often problematic at high temperatures where fluidic interconnects may be leaking, they used binder jet printing, which is a form of metal additive manufacturing. While such metal objects are usually highly porous and thus not suitable for application in microfluidics, the addition of boron nitride supported the sintering process and thus reduced the porosity, resulting in leak-free fitting even at high operating pressures [50].…”

Gas Detection Using Portable Deep-UV Absorption Spectrophotometry: A Review

“…The collected molecules are then released instantaneously using a thermal heater. The release of molecules at a small volume and short time leads to 10 3 –10 5 folds amplification of concentration level at the cost of longer response time [103,104,105].…”