Particle contamination

Solution Filtration. The polymer solution, free of unacetylated ceUulose, rigid particle contaminants, and dirt, must pass through spinnerets with holes of 30—80 ]lni diameter. Multistage filtration, usuaUy through plate-and-frame filter presses with fabric and paper filter media, removes the extraneous matter before extmsion. Undesirable gelatinous particles, such as the hemiceUulose acetates from ceUulose impurities, tend to be sheared into smaller particles rather than removed. The solution is also aUowed to degas in hoi ding tanks after each state of filtration. 

Particle Contamination. In assembling large, high voltage equipment such as coaxial lines, contamination by metal particles may occur which may decrease the dielectric strength under various conditions by 5 to 10-fold (44—45). Metal needles are the worst contaminants and electrostatic traps or adhesive areas have been designed to cope with them (46). 

The purpose of open unidirectional airflow benches is to protect products from particulate contaminants by creating a controlled environment. These benches are used, for example, in electronic, biological, pharmaceutical, and food industries. It should be mentioned that within pharmaceutical production, aseptic sterile processes must be carried out in a Class 100 environment (U.S. Federal Standard 209 E, Airborne Particulate Cleanliness Classes in Cleanrooms and Clean Zones). To avoid particle contamination in the bench, horizontal or vertical airflow with high-efficiency particulate air (HEPA)-filtered air is used. The air velocity is normally 0.4-0.5 ra s". Some examples of typical arrangements of open unidirectional airflow benches are shown in Fig. 10.51. 

In some cases, the parts to be coated (such as semiconductor silicon wafers) are stacked vertically. This minimizes particle contamination and considerably increases the loading capacity (as opposed to horizontal loading). 

Exposure of hot particle contaminated soil (sampled 15 km north of the Chernobyl Nuclear Power Plant) to film X, Y and Z of a Differential Autoradiographic Imaging Sandwich. The original film size is 85 x 10 x 10 mm, exposure time was 14 days. Area (a) shows irradiation from a 90Sr dominated hot particle whereas irradiation in area (b) is caused by a 137Cs dominated hot particle. 

Particle contamination, in ion implantation, 14 445-446 Particle counters, 13 466 18 139 Particle counting... 

The rate of primary nucleation and width of the associated metastable zone are difficult to measure with precision in the laboratory, because of their dependence on environmental factors. Dust particles contaminating a solution, and imperfections on the surface of the crystallizer and agitator are often... 

Manufacturing processes are well developed for silicon wafers. To avoid particle contamination, compact clusters of processing units operate in 100-level clean rooms, which for small companies are often rented in larger complexes at approximately 400/ft2-yr. 

Contaminants may reach the subsurface in a gaseous phase, dissolved in water, as an immiscible hquid, or as suspended particles. Contaminant partitioning in the subsurface is controlled by the physicochemical properties and the porosity of the earth materials, the composition of the subsurface water, as well as the properties of the contaminants themselves. While the physicochemical and mineralogical characteristics of the subsurface sohd phase define the retention capacity of contaminants, the porosity and aggregation stams determine the potential volume of liquid and air that are accessible for contaminant redistribution among the subsurface phases. Enviromnental factors, such as temperature and water content in the subsurface prior to contamination, also affect the pollution pattern. 

A typical example of this is the procedure known among practitioners as IMEC, in which there is sequential removal of organic and particle contamination followed by a metal-removing step, usually by the use of diluted HF followed by drying. It should be noted that this sequence is far more environmentally friendly than the typical RCA-clean sequence, as it uses less deionized water or chemicals. The chemicals used do not need to be as clean as those in the RCA-sequence. 

Provisions for reducing room particle count during manufacture operations should be provided through careful dilution of particle-contaminated room air with particle free supply. 

Particle Contamination of Ampules and Vials during Filling Procedure... 

Rodgers et al. [85] identified soil surface-bound polycyclic aromatic hydrocarbons through the use of real-time aerosol mass spectrometry in two NIST standard research material soils (Montana SRM 2710 and Peruvian SRM 4355), each contaminated separately with three common petroleum hydrocarbons (diesel fuel, gasoline and kerosene). This method required no sample preparation. Direct laser desorption/ionisation mass spectrometric analysis of individual soil particles contaminated with each of the petroleum hydrocarbons at three different contamination levels (0.8,8, and 80 ppth (wt/wt)) yielded detectable polycyclic aromatic hydrocarbon cation distributions that ranged from m/z 128 to 234, depending on the fuel contaminant. The same analysis... 

An electrical resistance heater with more turns at the tube ends (to compensate for heat losses) surrounds each tube. There is a vertical laminar flow hood over the loading area to minimize particle contamination of the wafers being loaded. As we can see, there are temperature controls for the furnace tubes, and a power module to provide the electrical power. When operated as a LPCVD system, a unit including both the gas flow and vacuum systems is positioned on the right side. Such a unit is shown in Figure 8. Here we can see the vacuum pumps on the left, and the mass flow controllers on the right. The vacuum pump oil recirculation systems are shown in the slide out drawers. As can be seen in Figure 9, this system, as well as most current similar systems, operate under computer control. 

As in the LPCVD reactor discussed earlier, allowing the electrode structure to touch the tube wall as it is inserted leads to considerable particle contamination. Therefore, cantilever loaders are available here also, and a typical unit on an ASM reactor is shown in Figure 23. Again, in contrast to the AMP-3300, this system is operated under computer control. Automated handling of wafers is more difficult to achieve, and is not generally available. 

By performing the synthesis of the membranes under cleanroom conditions later, De Vos [48,49] showed the influence of particle contamination on the integrity of silica membrane layers. Furthermore, the firing temperature of the silica was increased to 600°C, which resulted... 

Magill, P. L. and E. D. Lumpkins "Distinguishing Skin Scale Particles," Contamination Control, October, 1966. 

Ordinarily, present within the preparation area are localized areas of ISO 5 unidirectional airflow (Class 100) utilized to protect washed components prior to sterilization and/or depyrogenation. These areas are not aseptic and should not be subjected to the more rigorous microbial expectations of aseptic processing. They are designed to reduce/eliminate the potential for particle contamination of unwrapped washed materials. Operators accessing these protective zones wear gloves at all times when handling materials. 

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