The measurement of the outgassing characteristics of materials is important in the construction of many delicate devices. Aboard satellites and other spacecraft, lenses, filters, windows, and other optical components must remain clean. Contamination of these components can be caused by outgassing of volatile materials from nearby parts. For example, plastics and lubricants are known to outgas in vacuum. The outgassed materials are deposited on nearby surfaces. The deposited materials damage components with sensitive surfaces. Therefore, it is desirable to minimize the amount of material outgassed in proximity to sensitive components. The amount of outgassing present is usually limited by cleaning parts and by carefully selecting the materials of which the satellite is made.
Computer hard drives can also be damaged by outgassing and recondensation of volatile materials. Volatile materials outgassed from internal hard drive components recondense on the magnetic data storage surfaces. These contaminants can be swept up by the slider that carries the read-write head, causing it to crash into the disk surface, resulting in failure of the drive and loss of data. The contaminants can also alter the frictional forces between the disk and the slider, possibly preventing the disk from rotating. Therefore, it is desirable to minimize the amount of outgassed volatile materials in the drive. This is accomplished by only using low-emission materials in the manufacturing of parts and by carefully cleaning parts prior to assembly. In selecting the materials and/or parts that can be used in the hard drive, it is necessary to measure the outgassing characteristics of candidate parts and materials.
Measurement of outgassing characteristics has typically been performed by placing the part in question in a vacuum chamber and evacuating the chamber. A pressure or mass detector is also placed within the chamber. Material outgassed from the part is detected by the sensor. A disadvantage of measuring outgassing in a vacuum is that it is time consuming to measure outgassing of many different objects because the vacuum must be reestablished each time a different object is placed within the vacuum chamber.
A problem with other techniques for measuring outgassing is that they do not intrinsically integrate the quantity of outgassed material. They must electronically integrate signals to obtain the total amount of outgassed material, which is less accurate. Further, they do not provide a sample of the outgassed material for chemical or physical analysis. These problems are present in outgassing detectors that detect the concentration of outgassed material in the vapor or gas phase and do not collect the outgassed material.
U.S. Pat. No. 4,561,286 to Sekler et al. discloses a piezoelectric contamination detector that compensates for changes in temperature that can otherwise interfere with contamination measurements. Sekler does not disclose the use of the device in a chamber for measuring the amount of material outgassed from an object.
U.S. Pat. No. 4,735,081 to Luoma et al. discloses a detector for detecting vapors in gaseous fluids, such as air. The air is passed over a detector having a crystal oscillator with a coating selected to absorb the vapor of interest. Luoma does not disclose the measurement of outgassed materials from an object in a closed chamber.
U.S. Pat. No. 5,408,864 to Wenman discloses a method of measuring the amount of gas desorbed from a solid. The solid is placed in a chamber with a specially designed gas. The pressure in the chamber is measured as a function of temperature. The absorptive properties of the solid are then determined from this measurement. Wenman's method requires accurate measurement of pressure inside the chamber. Wenman's method does not use condensed material detectors.
U.S. Pat. Nos. 4,781,358 and 4,719,073 to Langan disclose an apparatus and method for monitoring parts in a sintering furnace. Langan monitors the outgassing of the parts as they are being sintered. Langan flushes the furnace with gases as the parts are sintered.
U.S. Pat. No. 5,287,725 to Zhao et al. discloses an apparatus for detecting volatile material on the surface of a semiconductor wafer. The wafer is placed in a vacuum chamber and heated while the walls of the chamber are cooled. The apparatus is rather inefficient, detecting only a small portion of the material evaporated from the wafer.