Contact time behaviour

Temperature effects may also be used in test methods and notably for assessing the effects of inhibitors in acid solutions. The technique is based on that first proposed by Mylius which records the temperature-time behaviour associated with the exothermic reaction resulting from the initial contact of a metal with a corrosive acid solution. The effectiveness of inhibitors may then be determined from their effects on the temperaturetime behaviour. ... 

Ludwig investigated carefully the behaviour of spores under different conditions of HPT [19, 20] and introduced the cycle-type treatment that proved to be more efficient than the double level treatment [21-23], Particularly studied was how the treatment time and pressure influenced the cycle processes. Furthermore, it was noted that the temperature, pressure, contact time under pressure, and average time of treatment were fundamental parameters in the optimization of germination. 

A set of ODH experiments was carried out at the lower space velocity of 36 ml min g in order to study the effect of contact time on the selectivity behaviour. Acrolein was detected among the reaction products of some catafysts, the highest selectivity value of 8% being achieved with the 1 1 5 Nb-V-Si catalyst prepared via the non-hydrolytic method at 500°C. 

In water several types of materials may affect the bioavailability, such as dissolved organic carbon (DOC), particulate organic carbon (POC), etc. In sediment and soil, other factors affect the bioavailability of organic compounds, such as the hydrophobicity of the contaminant, the contact time between contaminant and soil/sediment, the nature and amount of organic carbon and other soil/sediment characteristics, the behaviour of soil/sediment organisms, etc. [85]. Bioavailability may thus lead to an apparently lower BCF. 

PP/silver nanocomposite fibres were prepared with the aim of achieving permanent antibacterial activity in a common synthetic textile. The fibres were melt-spun by coextmsion of PP and PP/silver masteibatches using general conjugate spinning. Masteibatches were made up of a mixture of PP chips and nano-sized silver powder. The antibacterial efficacy of spun fibres was high when the masteibatch was used as the sheath rather than the core. The antibacterial activity of nano-silver in fibres was evaluated after a certain contact time and calculated by percent reduction of two types of bacteria. Staphylococcus aureus and Klebsiela pneumoniae. DSC and wide-angle X-ray diffraction were used for analysis of stractuie, thermal properties and crystallisation behaviour of the spun fibres. SEM was carried out in order to observe particle distribution on the nanocomposite fibres. 17 refs. (2nd International Conference on Polymer Fibres, Manchester, UK, July 2002)... 

The effect of temperature, contact time and reactant concentration on the reaction rate/conversion and products of the of the C3H -N0-02 and C3H6-NO-O2 reactions over 1% Pt/Al203 are given in Fig. 1-11. It is clear that there are a number of differences in behaviour dependant on whether an C3Hg or CgHe is used as the reductant, viz.,... 

Rheology is concerned with the flow and/or deformation of matter under the influence of externally imposed mechanical forces. Two limiting types of behaviour arc possible. The deformation may reverse spontaneously (relax) when the external force is removed this is called elastic behaviour and is exhibited by rigid solids. The energy used in causing the deformation is stored, and then recovered when the solid relaxes. At the other extreme, matter flows and the flow ceases (but is not reversed) when the force is removed this is called viscous behaviour and is characteristic of simple liquids. The energy needed to maintain the flow is dissipated as heat. Between the two extremes arc systems whose response to an applied force depends on the lime-scale involved. Thus pitch behaves as an elastic solid if struck but flows if left for years on a slope. Similarly, a ball of Funny Putty , a form of silicone rubber, bounces when dropped on a hard surface, when the contact time is a few milliseconds, but flows if deformed slowly on a time-scale of seconds or minutes. Systems of this kind are said to be visco-elastic. The precise nature of the observable phenomena depends on the ratio of the time it takes for the system to relax to the time taken to make an observation. This ratio is called the Deborah number (De) ... 

The extrapolation of the curves at zero contact time shows that propene is the primary product. Acrolein and acrylic acid appear at non zero contact time which indicates that these compounds are secondary products. Their selectivities present a maximum with contact time, which shows that they are further transformed to COx. The variations of acetic acid formation show that it is a secondary product formed by another route than acrolein and acrylic acid. COx products show behaviour of typical end products, which are formed from the C-C cleavage of propane and the further total oxidation of acetic and acrylic acids. Thus, a reaction scheme can be proposed... 

E may be aetirmined from the intersection of this asymptote with the C -axis. In addition, the relaxation time T can be estimated as illustrated in Figure 9 Although the deformation model shown in Figure 9 is extremely simplified and neglects some important factors (e.g. the fact, that instead of a single relaxation time a complicated relaxation spectrum may be valid), the model may serve as a basis for the discussion of the contact deformation behaviour of polymers. 

Fig. 7. Idealized behaviour of the carbon magnetization as a function of the experimental contact time in the cross-polarization experiment.

Control of pH, especially when using alum is of great importance as the behaviour of alum changes with pH (see Fig. 5.3). If the pH increases to 6.0, the charge on the alum decreases towards zero. It is important to add the size and the alum as late as possible, in order to decrease the contact time of the alum with the stock. This should ensure that the alum remains in its AP " cationic form for a long enough time to fix the rosin size to the fibre. 

Another important feature of radiocesium partitioning in sediments is its apparently irreversible behaviour. It has generally been observed that Kd increases, and the exchangeability of radiocesium bound to aquatic particles decreases, with increasing contact time between the radionuclide and the particles (e.g. 1,2 J3). This observation has been interpreted as a slow migration of radiocesium from the frayed edge sites towards the deeper interlayer spaces between the illite layers, from where it cannot easily be released (3,14). It is, therefore, important to obtain rate parameters for this process in order to enable prediction of the long-term availability of radiocesium to the aqueous phase, and thus for further transport and uptake in the aquatic food chain. 

The aim of this report is to present the results of the experimental work done recently in our laboratories to study both the surface and the bulk mebrane processes to demonstrate the importance of one over the other in the potential response function. The short time behaviour of model membranes was studied by response time measurements, while the transport processes within the membranes were followed under in situ conditions by means of FTIR-ATR-spectrometry and ion-chromatography. In situ conditions means that the membranes remained in contact with aqueous K" "-containing solutions throughout the FTIR-ATR-measurements simulating normal operating conditions of the electrode membranes. Prior to... 

The relative rate of the different reactions occurring dining cracking, depend, besides on the reaction conditions, i.e., temperature, partial pressure and contact time, on the zeolite physicochemical characteristics. In the case of Y zeolite, the final catalytic behaviour will depend on frameworic and extrafiamework composition, and site accessibility (78). 

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