Compatibility problems

Wang and Chen [41] studied the compatibility problems of incompatible NBR-PVC blends. Poly(vinyl-idene chloride-covinyl chloride) is reported to act as an efficient interfacial agent. Blends of PVC, NBR, and the copolymer were prepared by the solution casting technique using THE as a solvent. Improvement in mechanical properties can be achieved in NBR-PVC blend by the addition of different types of rubbers [42]. Different rubbers include NR, styrene butadiene (SBR) and butadiene (BR). Replacement of a few percent of NBR by other rubbers will improve the mechanical properties and at the same time reduce the cost of the blend. 

To avoid compatibility problems, compatibility tests under conditions typical for the planned application are performed. From their results suitable material combinations are selected. Figure 110 shows a compatibility test for metals in contact with inorganic PCM. Test tubes containing both materials (center) are kept in a controlled environment for a fixed time (left) and later effects on the metal are analyzed (right). 

Many other products can be used as softeners but are less important commercially because of greater cost and/or inferior properties. Examples are anionic surfactants such as long-chain (C16-C22) alkyl sulphates, sulphonates, sulphosuccinates and soaps. These have rather low substantivity and are easily washed out. Nonionic types of limited substantivity and durability, usually applied by padding, include polyethoxylated derivatives of long-chain alcohols, acids, glycerides, oils and waxes. They are useful where ionic surfactants would pose compatibility problems and they exhibit useful antistatic properties, but they are more frequently used as lubricants in combination with other softeners, particularly the cationics. 

The intermolecular Heck reaction of halopyridines provides an alternative route to functionalized pyridines, circumventing the functional group compatibility problems encountered in other methods. 3-Bromopyridine has often been used as a substrate for the Heck reaction [124-126]. For example, ketone 155 was obtained from the Heck reaction of 3-bromo-2-methoxy-5-chloropyridine (153) with allylic alcohol 154 [125]. The mechanism for such a synthetically useful coupling warrants additional comments oxidative addition of 3-bromopyridine 153 to Pd(0) proceeds as usual to give the palladium intermediate 156. Subsequent insertion of allylic alcohol 154 to 156 gives intermediate 157. Reductive elimination of 157 gives enol 158, which then isomerizes to afford ketone 155 as the ultimate product This tactic is frequently used in the synthesis of ketones from allylic alcohols. 

The uncontrolled variation in the gypsum-hemihydrate or soluble anhydrite ratio (G-H or A) that occurs during production, storage and transportation of cement can cause compatibility problems with certain superplasticizers, particularly a reduction in workability. The extent of the reduction on workability properties is dependent on the G-H ratio (ranging from 80 20% to 20 80%), level of C3A and alkalis present in the cement and the fineness of... 

When confronted with cement-SP compatibility problems, the following action could be taken to identify whether the problem is primarily due to the reactivity of the cement or the poor performance of the admixture [125, 140] ... 

UNDERWATER CONCRETE - COMPATIBILITY PROBLEMS WITH VISCOSITY... 

DAMP-PROOF CONCRETE (COMPATIBILITY PROBLEMS WITH WRA/DAMP-... 

Very fine filters are recommended for ethanol dispensers to ensure that waterborne solids do not contaminate vehicle filters or fuel injectors. Dispensing hoses delivering ethanol and other alcohol fuels to vehicles may be green or blue in color to signify their compatibility with alcohol fuels. Also, blending ethanol with conventional fuels helps to minimize compatibility problems with existing fuel system components. 

Solvent-polymer compatibility problems are often encountered in industry, such as in the selection of gaskets or hoses for the transportation of solvents. A rough guide exists to aid the selection of solvents for a polymer, or to assess the extent of polymer-liquid interactions. A semi empirical approach has been developed by Hildebrand based on the principle of like dissolves like. The treatment involves relating the enthalpy of mixing to a solubility parameter, S, and its related quantity, 8, called the cohesive energy density. 

Aluminum is used as the material of construction for some aerosol drug products. Also a three-piece tin-plated steel container finds use in topical pharmaceutical aerosols, and to decrease the compatibility problems, an internal organic coating is often used [90]. 

Kim and Park subsequently reported that ruthenium pre-catalyst 2 racemizes alcohols within 30 min at room temperature [53]. However, when combined with an enzyme (lipase) in DKR at room temperature, very long reaction times (1.3 to 7 days) were required, in spite of the fact that the enzymatic KR takes only a few hours (Scheme 5.24). Despite these compatibility problems, their results constituted an important improvement, since chemoenzymatic DKR could now be performed at ambient temperature to give high yields, which enables non-thermostable enzymes to be used. More recently, we communicated a highly efficient metal- and enzyme-catalyzed DKR of alcohols at room temperature (Scheme 5.24) [40, 54]. This is the fastest DKR of alcohols hitherto reported by the combination of transition metal and enzyme catalysts. Racemization was effected by a new class of very... 

Although blending with other coating resins provides a variety of ways to improve the performance of alkyds, or of the other resins, chemically combining the desired modifier into the alkyd structure eliminates compatibility problems and gives a more uniform product. Several such chemical modifications of the alkyd resins have gained commercial importance. They include vinylated alkyds, silicone alkyds, urethane alkyds, phenolic alkyds, and polyamide alkyds. 

Cost factors of expl tagging will be considered in the next section. In view of the above discussion, recalling that there can be serious compatibility problems of currently preferred taggants and expls, and considering that detection tagging is still in its infancy, it seems that immediate or near-future Congressional action to make tagging mandatory would be premature... 

While fuels are usually the source of materials compatibility problems, they also can provide some of the solutions through the use of additives. Additives from several manufacturers are available to help prevent corrosion of fuel system components and to stabilize fuel properties from oxidation. While fuel additives are helpful, they can rarely do it all themselves and must be developed in concert with knowledge of fuel system materials properties. 

The following sections address materials compatibility for alternative fuels. In many cases, alternative fuels bring unique materials compatibility problems. Users of alternative fuel vehicles should be aware of these problems to help prevent mistakes in setting up refueling systems and to recognize and identify materials compatibility problems as they occur. 

The fuel lines onboard flexible fuel vehicles using ethanol will typically be designed to accommodate methanol fuels and should be more than adequate for ethanol. Most fuel system components designed for gasoline are likely also to be compatible with ethanol. In a test of a 1994 model fuel injected vehicle, only slight stiffening of the fuel line was observed [3.11]. No other materials compatibility problems were observed in the fuel system. 

CNG fuel systems can thus be subjected to compressor oil and condensed water vapor that would not occur otherwise if the gas had not been compressed. The compressor oil is probably more of an operating problem than a materials compatibility problem, though new CNG vehicle fuel systems that use multi-point fuel injectors may encounter some problems. 

Even if water vapor does not condense in CNG systems under static condition, some water vapor may condense in the portions of the system where pressure is reduced. The combination of water vapor and sulfur compounds has been known to cause the formation of hydrates, which are crystalline in structure (similar to snow) and which can cause operational and materials compatibility problems. Ways to prevent hydrate formation include limiting water vapor and sulfur in the natural gas, and through good system design. 

Being very clean and pure minimizes the materials compatibility concerns for LNG. However, LNG presents a new materials compatibility concern operation at cryogenic temperatures.3 For LNG fuel tanks, stainless steel is the preferred material and instances of materials compatibility problems are rare. Aluminum also has been used as a tank material without materials compatibility problems. Carbon steels are not used since their performance at low temperatures is questionable, i.e., they become susceptible to brittle fractures. While tanks are usually made from stainless steel or aluminum, LNG fittings may use some nickel alloys, brass, and copper, in addition to stainless steel and aluminum. 

The materials in compressors are primarily cast iron, steel, and aluminum. The quality of the natural gas in the distribution system is such that materials compatibility problems are few. If a dryer is included in the system, materials compatibility concerns should be essentially non-existent. 

CNG dispensers typically incorporate stainless steel for the flowpath of the natural gas, and no materials compatibility problems are likely. CNG dispensers do not typically incorporate filters—if filtering is deemed necessary, it is usually done at the outlet of the compressor before the CNG enters the storage system. 

CNG dispensing nozzles are made from aluminum and stainless steel and no materials compatibility problems have been noted. The mechanical action of fastening the CNG nozzle appears to be the limiting factor in CNG nozzle life, not deterioration due to corrosion from the natural gas. CNG dispensing nozzles have a finite lifetime typically characterized by the total number of refuelings completed. Nozzles should be replaced at the end of their useful life to prevent inadvertent failure. 

LNG tanks are designed for fairly low pressures, typically less than 1.72 MPa (250 psi), otherwise their advantage over storing natural gas as CNG would be lost. As LNG warms, vapor is produced that builds up pressure in the tank. To protect the tank from rupture due to over-pressure, vent valves are included that will release some vapor when the maximum set pressure is reached. Vent valves come in two types those that reseat when the pressure in the tank falls below the maximum, and those that don t. The second type is used only to protect the tank from over-pressure rupture, while the first type is used to control the pressure in the tank. Often they are used together in the same tank. Both types of vent valves may be made from stainless steel, brass, and aluminum materials compatibility problems are rare because of the cleanliness of LNG. 

The uncontrolled variation in the gypsum-hemihydrate or soluble anhydrite ratio (G-H or A) that occurs during production, storage and transportation of cement can cause compatibility problems with certain superplasticizers, particularly a reduction in workability. The extent of the reduction on workability properties is dependent on the G-H ratio (ranging from 80 20% to 20 80%), level of C A and alkalis present in the cement and the fineness of the cement. For the most reactive type of cement with a high content of both C A and alkalis, a reduced G-H or A ratio affects the yield stress, while piastre viscosity is not much affected. These effects are much less pronounced for a less reactive cement, but with the lowest G-H or A ratio, false set can occur [130-132], An increased fineness of cement increases the effect of the G-H or A ratio. The effect has been found to be most pronounced with melamine-based superplasticizers [130, 133],... 

When confronted with cement-SP compatibility problems, the following action... 

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