Coating problems encountered

One of the major sources of problems encountered in spin-coating hardware is the dispensing equipment. Frequently it has been recommended that the resist be dispensed directly from the bottle thereby avoiding all mechanical pumps, syringes, or additional filtering equipment. Provided the resist solution has been adequately filtered prior to dispensing, direct application from the bottle should yield the lowest defect films possible. 

One of the problems encountered in the entrapment of activated charcoal in a polymer matrix is the blinding-off of the pores of the charcoal, thus inactivating it. Because the pores of the carbon are responsible for its ability to adsorb organics, any pores that are filled or coated with a polymer matrix reduce its effectiveness. Conventional treatments involve blending the carbon into an acrylic latex and then applying the slurry to a reticulated foam. Upon drying, a coalescence encapsulates the carbon. 

The final application of FTIR to be discussed is the analysis of microsamples. A major problem encountered in the infrared examination of microsamples is the reduction in energy reaching the detector (3). The sensitivity of FTIR proved beneficial in work performed in support of metabolite studies of thiofanox. Samples were prepared by dissolving the compound in a small amount of solvent (10-20 pi), followed by withdrawing the solution into a syringe. The tip of the syringe was coated with a small amount of KBr, and the solution was slowly released... 

Lubricants and Coatings. Most of the lubrication problems encountered in the laboratory can be solved with SAE 10 or SAE 20 machine oil, except for ball bearings subject to heavy loads, for which cup grease should be used. 

Developing a reactor for a luminous chemical vapor deposition (LCVD) operation to deal with large numbers of materials to be coated, probably the most difficult problem encountered is how to hold the substrates, place them in appropriate position, and move them in the luminous gas phase. In order to coat large number of substrate uniformly, the movement of substrate within the luminous gas phase is a mandatory requirement, with the exception of direct current (DC) cathodic LCVD. The difficulty progressively increases as the size of the substrate decreases, and it becomes virtually impossible to hold as the size reaches millimeters or less. For instance, the surface of small particulate matters cannot be treated or coated by the conventional modes of LCVD in which substrates are held by some kind of holder. 

One of the major problems encountered in this field concerns the extremely poor reproducibility of the photochemical properties of semiconductor powders and colloids prepared in different laboratories. Often, the materials are badly characterized and any pretreatment is inadequately described. The source, crystal structure, surface contamination, and pretreatment are all critical in determination of the photoactivity of a semiconductor, and until attention is given to these factors the subject will suffer from irreproduci-bUity. These problems become magnified when the semiconductor is doped or coated with a noble metal. 

One of the problems encountered in gas chromatographic separation even with capillary columns is the coelution of some components by one or the other stationary phase. In an experiment studying the mixture shown in Table 3 a 30 m X 0.32 mm ID column coated with I.O fim DB-I (J W) could not separate compounds 8 and 9 whereas they were separated by a DB-I70I (J W)... 

The major problems encountered in the fabrication procedures in the present study are the techniques of both coating the matrix and opening the cavity uniformly. The development of a technique for opening the hole on the flat face of the hemisphere Is very critical to achieve reproducibility. Besides the methods practiced In these studies. Improved techniques to create holes on the flat face of the hemisphere shaped device should be explored. Techniques such as computer aided drilling may prove useful In future studies. 

The main problem encountered with PFT with a neutral selector remains the prevention of the chiral selector from entering the ionization source. This problem becomes particularly important at a high pH where EOF is important. Therefore, an acidic buffer pH or a coated capillary to minimize EOF is of the utmost importance. In addition, it has to be noted that the electrospray ionization process is pneumatically assisted when a sheath-liquid interface is used. The coaxial sheath gas induces an aspirating phenomenon in the capillary which may considerably affect the separation quality. This can be due to the decrease in interaction between analytes and the chiral selector and to a hydrodynamic flow induced by the Venturi effect at the capillary end [33, 34]. 

Microreaction technology allows for better temperature control, and a safer provision and handling of H P both within and outside the range of explosive mixtures with propene and PO. To minimize the decomposition of H P during the evaporation phase, a microstructured falling-film evaporator is used, placed below the mixing device and reaction zone. The reaction is carried out with an excess of propene, at temperatures below 160 °C and a pressure below 1.5 atm. Por a propene conversion of 5-20%, the selectivity for PO obtained is around 90%, but the selectivity with respect to HP is 25%. The catalyst is coated onto the reactor module, forming a layer several hundred micrometers thick. One problem encountered was the slow accumulation of deposits on the catalysts, which were derived from the formation of by-products. 

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