Measurement of Outgassing Rates of Steels

Summary

A protocol for the measurement of outgassing rates of hydrogen from ordinary steel vacuum chambers using the rate-of-pressure rise method is presented.

Abstract

Steels are commonly used materials in the fabrication of vacuum systems because of their good mechanical, corrosion, and vacuum properties. A variety of steels meet the criterion of low outgassing required for high or ultrahigh vacuum applications. However, a given material can present different outgassing rates depending on its manufacturing process or the various pretreatment processes involved during the fabrication. Thus, the measurement of outgassing rates is highly desirable for a specific vacuum application. For this reason, the rate-of-pressure rise (RoR) method is often used to measure the outgassing of hydrogen after bakeout. In this article, a detailed description of the design and execution of the experimental protocol involved in the RoR method is provided. The RoR method uses a spinning rotor gauge to minimize errors that stem from outgassing or the pumping action of a vacuum gauge. The outgassing rates of two ordinary steels (stainless steel and mild steel) were measured. The measurements were made before and after the heat pretreatment of the steels. The heat pretreatment of steels was performed to reduce the outgassing. Extremely low rates of outgassing (on the order of 10⁻¹¹ Pa m³ sec⁻¹ m⁻²) can be routinely measured using relatively small samples.

Introduction

Steels are routinely used in construction because of their good mechanical properties. Certain steels (ferrous steels, in particular) are preferred materials for applications involving vacuum. Depending on the type and grade, these steels have sufficiently low outgassing rates essential for high vacuum (HV, 10⁻⁷ < p < 10⁻⁵ Pa) or ultrahigh vacuum (UHV, 10⁻¹⁰ < p < 10⁻⁷ Pa) systems. Further, extensive research has been conducted toward the development of special pretreatment procedures that reduce outgassing^1-3. The pretreatm....

Protocol

Caution: Please follow all appropriate safety practices while assembling the equipment and sample chambers. Please wear personal protective equipment (safety glasses, gloves, safety shoes, etc.).

1. Fabrication of a Sample Vacuum Chamber

1. Design and fabrication of the vacuum chamber
   1. Prepare and submit design drawings to a commercial vendor or an in-house machine shop for manufacturing the sample vacuum chamber. A representative example of the design drawing for a vacuum chamber made of S20C steel is shown in Figure 1. The chamber designed in this experiment is very basic and ....

Results

As expected, the residual gas after the bakeout was mostly hydrogen.⁷ The pressure rise measured using the SRG was linear over a long period of time (Figure 5). Thus, the readsorption effect might be negligible and the intrinsic outgassing rate (q) for the steels tested in this study can be evaluated using the RoR method.¹⁰ The measured pressure rise data was analyzed using the linear least squares fitting method. The outgassing rates of the.......

Discussion

Numerous methods for the measurement of outgassing rates have been reported in the literature. Experimental methods include the throughput, conductance modulation, two-path, RoR, and variations of these methods. However, no one method is ideal for obtaining the necessary outgassing data.¹⁰ The RoR method using SRG, however, became the method of choice for measurement of low outgassing materials.^11-13 SRG¹⁷ is often used as a secondary standard in high vacuum systems without erroneous pump.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Sample chamber
Stainless steel, 304	POSCO (www.posco.co.kr)
Mild steel, D3752	Xiangtan Iron&Steel co.,LTD (http://www.hnxg.com)
Mild steel, D3752	SeAh Besteel (www.seahbesteel.co.kr)
Name	Company	Catalog Number	Comments
Cleaning
Cleaning bath	Samill IDS		Ultrasonic cleaning, heating, timer, concentration control
Acetone	Samchun Chemical (www.samchun.com)	A1759	HPLC grade (99.7%)
Tekusolv	NCH Co.        (www.nch.com)	0368-0058J	Solvents
BN cleaner	Henkel surface technologies (na.henkel-adhesives.com)	6610263775	Alkaline, pH 13
Ethanol	Fisher Scientific (www.fishersci.com)	A995-4	HPLC Reagent (99.9%)
Deionized water (Electro deionizer SYSTEM)	A.T.A        (www.atagroup.co)	EDI SYSTEM
Liquid N2 gas	Hanyoung (www.gasmaster.co.kr)	B/T 176 L	LN2 dewar, purity 99.999%
Name	Company	Catalog Number	Comments
Welding
Tungsten Inert Gas wedling machine	Thermal Arc (www.victortechnologies.com/thermalarc)	400GTSW	Ar gas preflow and postflow 8 L/min, backflow 5 L/min
turning jig	Vactron (www.vactron.co.kr)	Made to order	Made to order
Ar gas	Lindekorea (www.lindekorea.com)		Purity 99.999%
Name	Company	Catalog Number	Comments
Leak test
Leak detector	Adixen (www.adixen.fr/en/)	ASM380	Pumping Speed (air): 9.7 L/sec
He gas	Lindekorea (www.lindekorea.com)		Purity 99.999%
Name	Company	Catalog Number	Comments
Vacuum equipment
Spinning rotor gauge	MKS Instruments (www.mks.com)	SRG-3	Controller, head, and thimble set
Oscilloscope	Tektronix (www.tek.com)	TDS2012B
Residulal gas analyser	Balzers	QMA200	m/e 0-100
TMP (HiPace 80)	Pfeiffer Vacuum (www.pfeiffer-vacuum.com)	PMP03941	Pumping Speed (N2): 67 L/sec
Scroll pump	Anest Iwata (www.anest-iwata.co.jp)	ISP 90	Pumping Speed (Air): 1.8 L/sec
All-metall easy close angle valve (CF35)	VAT Inc. (www.vatvalve.com)	54032-GE02-0002	Rotatable flange
Angle valve (KF25)	MDC Vacuum Inc. (www.mdcvacuum.com)	KAV-100
Name	Company	Catalog Number	Comments
Temperature control
Chiller	JEIO Tech (www.jeiotech.com)	RW-2025G
Cooling line	LS Metal (www.lsmetal.biz)	C1100	Level Wound Coil, Diameter 10 mm
Heater controllers	HMT	Made to order	Bakeout program controller
Electrical heater tapes	Brisk heat (www.briskheat.com)	BIH101080L
Thermocouple (K type)	miraesensor (www.miraesensor.com)	MR-2290
Handheld multimeter	Saehan (www.saehan.co.kr)	3234
Data recorder (Temp.)	Yokogawa (www.yokogawa.com)	GP10-1E1F-UC10