- •Contents
- •Foreword
- •Preface
- •1 Materials in the Lab
- •2 Measurement
- •3 Joints, Stopcocks, and Glass Tubing
- •4 Cleaning Glassware
- •5 Compressed Gases
- •6 High and Low Temperature
- •7 Vacuum Systems
- •8 The Gas-Oxygen Torch
- •APPENDIX
- •Appendix A Preparing Drawings for a Technician
- •Index
- •Foreword
- •Preface
- •For the Second Edition
- •Please note:
- •1 Materials in the Lab
- •1.1 Glass
- •1.1.1 Introduction
- •1.1.2 Structural Properties of Glass
- •1.1.3 Phase Separation
- •1.1.4 Devitrification
- •1.1.5 Different Types of Glass Used in the Lab
- •1.1.6 Grading Glass and Graded Seals
- •1.1.7 Separating Glass by Type
- •1.1.9 Stress in Glass
- •1.1.11 Tempered Glass
- •1.1.13 Limiting Broken Glass in the Lab
- •1.1.14 Storing Glass
- •1.1.15 Marking Glass
- •1.1.16 Consumer's Guide to Purchasing Laboratory Glassware
- •1.2 Flexible Tubing
- •1.2.1 Introduction
- •1.2.2 Physical Properties of Flexible Tubing
- •1.3 Corks, Rubber Stoppers, and Enclosures
- •1.3.1 Corks
- •1.3.2 Rubber Stoppers
- •1.3.3 Preholed Stoppers
- •1.3.4 Inserting Glass Tubing into Stoppers
- •1.3.5 Removing Glass from Stoppers and Flexible Tubing
- •1.3.6 Film Enclosures
- •1.4 O-Rings
- •1.4.2 Chemical Resistance of O-Ring Material
- •1.4.3 O-Ring Sizes
- •2 Measurement
- •2.1 Measurement: The Basics
- •2.1.1 Uniformity, Reliability, and Accuracy
- •2.1.2 History of the Metric System
- •2.1.3 The Base Units
- •2.1.4 The Use of Prefixes in the Metric System
- •2.1.5 Measurement Rules
- •2.2 Length
- •2.2.1 The Ruler
- •2.2.2 How to Measure Length
- •2.2.3 The Caliper
- •2.2.4 The Micrometer
- •2.3 Volume
- •2.3.1 The Concepts of Volume Measurement
- •2.3.2 Background of Volume Standards
- •2.3.4 Materials of Volumetric Construction #1 Plastic
- •2.3.5 Materials of Volumetric Construction #2 Glass
- •2.3.6 Reading Volumetric Ware
- •2.3.7 General Practices of Volumetric Ware Use
- •2.3.8 Calibrations, Calibration, and Accuracy
- •2.3.9 Correcting Volumetric Readings
- •2.3.10 Volumetric Flasks
- •2.3.11 Graduated Cylinders
- •2.3.12 Pipettes
- •2.3.13 Burettes
- •2.3.14 Types of Burettes
- •2.3.15 Care and Use of Burettes
- •2.4 Weight and Mass
- •2.4.1 Tools for Weighing
- •2.4.2 Weight Versus Mass Versus Density
- •2.4.3 Air Buoyancy
- •2.4.5 Balance Location
- •2.4.6 Balance Reading
- •2.4.7 The Spring Balance
- •2.4.8 The Lever Arm Balance
- •2.4.9 Beam Balances
- •2.4.10 Analytical Balances
- •2.4.11 The Top-Loading Balance
- •2.4.12 Balance Verification
- •2.4.13 Calibration Weights
- •2.5 Temperature
- •2.5.1 TheNature of Temperature Measurement
- •2.5.2 The Physics of Temperature-Taking
- •2.5.3 Expansion-Based Thermometers
- •2.5.4 Linear Expansion Thermometers
- •2.5.5 Volumetric Expansion Thermometers
- •2.5.7 Thermometer Calibration
- •2.5.8 Thermometer Lag
- •2.5.9 Air Bubbles in Liquid Columns
- •2.5.10 Pressure Expansion Thermometers
- •2.5.11 Thermocouples
- •2.5.12 Resistance Thermometers
- •3.1 Joints and Connections
- •3.1.1 Standard Taper Joints
- •3.1.2 Ball-and-Socket Joints
- •3.1.3 The O-Ring Joint
- •3.1.4 Hybrids and Alternative Joints
- •3.1.5 Special Connectors
- •3.2 Stopcocks and Valves
- •3.2.1 Glass Stopcocks
- •3.2.2 Teflon Stopcocks
- •3.2.3 Rotary Valves
- •3.2.4 Stopcock Design Variations
- •3.3.1 Storage and Use of Stopcocks and Joints
- •3.3.2 Preparation for Use
- •3.3.3 Types of Greases
- •3.3.4 The Teflon Sleeve
- •3.3.5 Applying Grease to Stopcocks and Joints
- •3.3.6 Preventing Glass Stopcocks and Joints from Sticking or Breaking on a Working System
- •3.3.7 Unsticking Joints and Stopcocks
- •3.3.8 Leaking Stopcocks and Joints
- •3.3.9 What to Do About Leaks in Stopcocks and Joints
- •3.3.10 General Tips
- •3.4 Glass Tubing
- •3.4.1 The Basics of Glass Tubing
- •3.4.2 Calculating the Inside Diameter (I.D.)
- •3.4.3 Sample Volume Calculations
- •4 Cleaning Glassware
- •4.1 The Clean Laboratory
- •4.1.1 Basic Cleaning Concepts
- •4.1.2 Safety
- •4.1.3 Removing Stopcock Grease
- •4.1.4 Soap and Water
- •4.1.5 Ultrasonic Cleaners
- •4.1.6 Organic Solvents
- •4.1.7 The Base Bath
- •4.1.8 Acids and Oxidizers
- •4.1.9 Chromic Acid
- •4.1.10 Hydrofluoric Acid
- •4.1.11 Extra Cleaning Tips
- •4.1.12 Additional Cleaning Problems and Solutions
- •4.1.13 Last Resort Cleaning Solutions
- •5 Compressed Gases
- •5.1 Compressed GasTanks
- •5.1.1 Types of Gases
- •5.1.2 The Dangers of Compressed Gas
- •5.1.3 CGA Fittings
- •5.1.4 Safety Aspects of Compressed Gas Tanks
- •5.1.5 Safety Practices Using Compressed Gases
- •5.1.6 In Case of Emergency
- •5.1.7 Gas Compatibility with Various Materials
- •5.2 The Regulator
- •5.2.1 The Parts of the Regulator
- •5.2.2 House Air Pressure System
- •5.2.4 How to Use Regulators Safely
- •5.2.6 How to Purchase a Regulator
- •6 High and Low Temperature
- •6.1 High Temperature
- •6.1.1 TheDynamics of Heat in the Lab
- •6.1.2 General Safety Precautions
- •6.1.3 Open Flames
- •6.1.4 Steam
- •6.1.5 Thermal Radiation
- •6.1.6 Transfer of Energy
- •6.1.7 Hot Air Guns
- •6.1.8 Electrical Resistance Heating
- •6.1.9 Alternatives to Heat
- •6.2 Low Temperature
- •6.2.1 TheDynamics of Cold in the Lab
- •6.2.2 Room Temperature Tap Water (=20°C)
- •6.2.8 Safety with Slush Baths
- •6.2.9 Containment of Cold Materials
- •6.2.10 Liquid (Cryogenic) Gas Tanks
- •7 Vacuum Systems
- •7.1 How to Destroy a Vacuum System
- •7.2.1 Preface
- •7.2.2 How to Use a Vacuum System
- •7.2.4 Pressure, Vacuum, and Force
- •7.2.5 Gases, Vapors, and the Gas Laws
- •7.2.6 Vapor Pressure
- •7.2.7 How to Make (and Maintain) a Vacuum
- •7.2.8 Gas Flow
- •7.2.9 Throughput and Pumping Speed
- •7.3 Pumps
- •7.3.1 The Purpose of Pumps
- •7.3.2 The Aspirator
- •7.3.3 Types and Features of Mechanical Pumps
- •7.3.4 Connection, Use, Maintenance, and Safety
- •7.3.5 Condensable Vapors
- •7.3.6 Traps for Pumps
- •7.3.7 Mechanical Pump Oils
- •7.3.8 The Various Mechanical Pump Oils
- •7.3.9 Storing Mechanical Pumps
- •7.3.11 Ultra-High Vacuum Levels Without Ultra-High
- •7.3.12 Diffusion Pumps
- •7.3.13 Attaching a Diffusion Pump to a Vacuum System
- •7.3.14 How to Use a Diffusion Pump
- •7.3.15 Diffusion Pump Limitations
- •7.3.17 Diffusion Pump Maintenance
- •7.3.18 Toepler Pumps
- •7.4 Traps
- •7.4.1 The Purpose and Functions of Traps
- •7.4.2 Types of Traps
- •7.4.3 Proper Use of Cold Traps
- •7.4.4 Maintenance of Cold Traps
- •7.4.5 Separation Traps
- •7.4.6 Liquid Traps
- •7.5 Vacuum Gauges
- •7.5.2 The Mechanical Gauge Family
- •7.5.4 The Liquid Gauge Family
- •7.5.5 The Manometer
- •7.5.6 The McLeod Gauge
- •7.5.7 How to Read a McLeod Gauge
- •7.5.8 Bringing a McLeod Gauge to Vacuum Conditions
- •7.5.10 The Tipping McLeod Gauge
- •7.5.11 Condensable Vapors and the McLeod Gauge
- •7.5.12 Mercury Contamination from McLeod Gauges
- •7.5.13 Cleaning a McLeod Gauge
- •7.5.14 Thermocouple and Pirani Gauges
- •7.5.15 The Pirani Gauge
- •7.5.16 Cleaning Pirani Gauges
- •7.5.17 The Thermocouple Gauge
- •7.5.18 Cleaning Thermocouple Gauges
- •7.5.19 The lonization Gauge Family
- •7.5.20 The Hot-Cathode Ion Gauge
- •7.5.21 Cleaning Hot-Cathode Ion Gauges
- •7.5.24 The Momentum Transfer Gauge (MTG)
- •7.6 Leak Detection and Location
- •7.6.1 AllAbout Leaks
- •7.6.3 False Leaks
- •7.6.4 Real Leaks
- •7.6.5 Isolation to Find Leaks
- •7.6.6 Probe Gases and Liquids
- •7.6.7 The Tesla Coil
- •7.6.8 Soap Bubbles
- •7.6.9 Pirani or Thermocouple Gauges
- •7.6.10 Helium Leak Detection
- •7.6.11 Helium Leak Detection Techniques
- •7.6.13 Repairing Leaks
- •7.7 More Vacuum System Information
- •7.7.1 The Designs of Things
- •8 The Gas-Oxygen Torch
- •8.1.2 How to Light a Gas-Oxygen Torch
- •8.1.3 How to Prevent a Premix Torch from Popping
- •8.2.2 How to Tip-Off a Sample
- •8.2.3 How to Fire-Polish the End of a Glass Tube
- •8.2.4 Brazing and Silver Soldering
- •Appendix
- •A.2 Suggestions for Glassware Requests
- •B.1 Introduction
- •B.2 Polyolefins
- •B.3 Engineering Resins
- •B.4 Fluorocarbons
- •B.5 Chemical Resistance Chart
- •C.1 Chapter 1
- •C.4 Chapter 4
- •C.5 Chapter 5 & Chapter 6
- •C.6 Chapter 7
- •C.7 Chapter 8
- •D.1 Laboratory Safety
- •D.2 Chemical Safety
- •D.3 Chapter 1
- •D.4 Chapter 2
- •D.5 Chapter 3
- •D.6 Chapter 4
- •D.7 Chapter 5 and the Second Half of Chapter 6
- •D.8 Chapter 7
- •D.9 Chapter 8
- •Index
428 |
Vacuum Systems |
leads and running a Tesla coil on the gauge. However, it is best to simply replace the gauge.60
7.5.21 Cleaning Hot-Cathode Ion Gauges61
The cleaning technique used for hot-cathode ion gauges depends on the shape, structure, and composition of the gauge. Hot-cathode gauges are so sensitive that any cleaning will alter or damage the sensitivity of the gauge. You can minimize gauge damage if the cleaning is performed by electrical heating while the gauge is in a high-vacuum condition. This heat cleaning or baking out can be done by grounding the ion collector and applying a Tesla coil to each of the electrodes within the gauge. Important: Be sure that the controller is off when doing this operation. Otherwise the charge from the Tesla coil may destroy the controller.
Chemical cleaning requires the removal of the gauge from the system and a general (gentle) rinsing with distilled water. If the gauge has a deposit that is blue or silver gray, the contamination is probably tungsten oxide or molybdenum oxide. This deposit can be cleaned as follows:
1.Soak the gauge in a 10-20% sodium carbonate solution. Gently heating the solution to 30°C will accelerate the cleaning process, which should take about 15 minutes.
Table 7.13 Thermionic Ionization Gauge Sensitivity/'
Relative to that for Nitrogen*
Hydrogen |
0.47 |
|
0.53 |
Helium |
0.16 |
Neon |
0.24 |
Nitrogen |
1.00 |
Argon |
1.19 |
Carbon monoxide |
1.07 |
Carbon dioxide |
1.37 |
Water vapor |
0.89 |
Oxygen |
0.85 |
Krypton |
1.9 |
Xenon |
2.7 |
Mercury vapor |
3.4 |
Narcoil-40 vapor |
13 |
° True gauge sensitivity is typeand model-specific. Accurate sensitivity tables for your gauge should be supplied by the manufacturer. This table is supplied for reference only.
* Reprinted from Vacuum,Vol. 13, H.A. Tasman, A.J.H. Boerboom, and J. Kistemaker, "Vacuum Techniques in Conjunction with Mass Spectrometry," © 1963, p. 43. with kind permission from Elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington OX5 1GB, UK.
Vacuum Gauges 7.5 |
429 |
2.Rinse with copious amounts of water, then let the gauge soak for about a half-hour filled with distilled water. Repeat the distilled water soak two more times.
If the deposit is brown, the offending contamination is probably cracked hydrocarbon vapor. This deposit can be cleaned as follows:
1.Soak the gauge in a 10% solution of potassium hydroxide and let it stand for about a half-hour. This soaking may have to be repeated with a fresh potassium hydroxide solution.
2.If there is a discoloration of the electrodes, gently shake some hydrogen peroxide in the gauge until the discoloration disappears.
3.Water spots can be removed with an oxidizer such as any substitute for chromic acid (see Sec. 4.1.9). Do not use chromic acid because it is a toxic waste.
4.Rinse with copious amounts of water, then let the gauge soak for about a half-hour filled with distilled water. Repeat the distilled water soak two more times.
7.5.22The Cold-Cathode Ion Gauge
The cold-cathode [a.k.a. Penning gauge, Philips gauge, or PIG (Philips ionization gauge)] requires a high-potential field for removing electrons from the (cold) cathode. This same principle is used in the magnetron and the inverted magnetron. In the cold-cathode gauge, the center loop is an anode (see Fig. 7.49) and it is maintained at a very high electrical potential (2-10 kV). The two plates are cathodes and are grounded. Electrons travel from the cathodes to the anode, ionizing molecules on their way. A U- or circular-shaped magnet is placed over the cathodes. The magnetic field formed by the magnets forces the electrons to take a longer route than they otherwise would.* Thus, they come into contact with a greater number of gas molecules and create a greater number of ions.
Magnetic
field
H
\7
Fig. 7.49 Basic electrode layout of the Penning gauge. From Fundamentals of Vacuum Science and Technology, by G. Lewin McGraw-Hill, New York, 1965 (Fig. 5-4), reproduced with permission.
* At 10~10 torr, it can require 20 minutes for an electron to travel from the cathode to the anode.
430 |
Vacuum Systems |
The range of the cold-cathode gauge is about 10"2 to 10"10 torr. Initiating the discharge within the cold-cathode gauge at lower vacuum ranges (>106 torr) is typically fast, within seconds. However, at lower pressures (10~8 to 10"10 torr) it can take hours for the discharge to begin. You may wish to start your cold-cathode gauge at higher pressures and leave it on as the pressure drops to maintain the discharge.
The cold-cathode gauge can act like a sputtering ion pump just as the hot-cath- ode gauge. However, it can pump nitrogen 10-100 times faster than a hot-cathode gauge. A cold-cathode gauge can pump nitrogen at rates of 0.1-0.5 liters/sec. Thus, if the connection tube to the gauge is too small in diameter, the gauge will remove the nitrogen from the area of the gauge faster than the system can equilibrate. The gauge will then read a greater vacuum than actually exists within the system.
Like a hot-cathode gauge, the cold-cathode gauge can be maintained longer between cleanings if a cold trap is placed between the gauge and the system. However, the gauge will indicate pressures lower than really exist within your system due to the cryogenic pumping capabilities of the cold trap. In addition, it will also slow the speed required for the system and the gauge to come to equilibrium. When installing the gauge, do not position the opening of the gauge to face the cold trap because momentary warming of the trap will cause evaporating frozen material to contaminate the gauge. When mounting the gauge on a vacuum system, be sure to angle the gauge so that the opening faces down. This angling will prevent particulate matter from falling into the gauge.
Do not leave the gauge on for extended periods of time, especially when the pressure is only about 10~2 torr. Otherwise the gauge can contaminate quickly. Likewise, do not let the gauge run continuously while the system is roughing down. Brief use will limit the effects of the pumping action of the gauge.
7.5.23 Cleaning Cold-Cathode Ion Gauges63
Some cold-cathode gauges can be taken apart. If you have one of these gauges, it is possible to carefully sand any surface contamination off the grid with a finegrade glass-sanding paper (do not use a metal file that could leave metal filings within the gauge. These filings can cause major problems during use). The gauge should then be rinsed with appropriate solvents followed by rinses of distilled water and then methanol. After the gauge is reassembled, be prepared to realign the magnet (follow the manufacturer's guidelines).
If your gauge is glass-bodied, it cannot be taken apart and you are limited to the chemical cleaning processes mentioned for the hot-cathode ion gauge.
7.5.24 The Momentum Transfer Gauge (MTG)
The momentum transfer gauge (MTG) was first developed as a lab curiosity in 1962. It uses the principle of gas viscosity to slow a spinning ball bearing that is