Under-liquid sensing

Fig. 10 Electrical equivalent circuit for under-liquid sensing with a rigid coating...

The frequency signal is coupled out via DT2 and buffer 2, amplified and adapted to the coaxial cable impedance. The circuit is adjusted to a resonance frequency near/r. However, driving the quartz crystal at a phase of - 40° has been found to be optimal for under-liquid sensing [44]. Temperature dependence of the circuit is essentially due to the temperature dependence of the quartz crystal. Dependence on voltage supply of approximately 20 Hz has been found for a quartz crystal in air and 80 Hz in water [45]. Thus common stabilizing methods for current supply are sufficient. 

Barnes C 1991 Development of quartz crystal for under-liquid sensing Sensors... 

Studies on fundamental interactions between surfaces extend across physics, chemistry, materials science, and a variety of other disciplines. With a force sensitivity on the order of a few pico-Newtons, AFMs are excellent tools for probing these fundamental force interactions. Force measurements in water revealed the benefits of AFM imaging in this environment due to the lower tip-sample forces. Some of the most interesting force measurements have also been performed with samples under liquids where the environment can be quickly changed to adjust the concentration of various chemical components. In liquids, electrostatic forces between dissolved ions and other charged groups play an important role in determining the forces sensed by an AFM cantilever. 

Figure Bl.27.8. Schematic view of Picker s flow microcalorimeter. A, reference liquid B, liquid under study P, constant flow circulating pump and 2, Zener diodes acting as heaters T and T2, thennistors acting as temperature sensing devices F, feedback control N, null detector R, recorder Q, themiostat. In the above A is the reference liquid and C2is the reference cell. When B circulates in cell C this cell is the working cell. (Reproduced by pemiission from Picker P, Leduc P-A, Philip P R and Desnoyers J E 1971 J. Chem. Thermo. B41.)...

Liquid Fabric Softeners. The principal functions of fabric softeners are to minimize the problem of static electricity and to keep fabrics soft (see Antistatic agents). In these laundry additives, the fragrance must reinforce the sense of softness that is the desired result of their use. Most fabric softeners have a pH of about 3.5, which limits the materials that can be used in the fragrances. For example, acetals cannot be used because they break down and cause malodor problems in addition, there is the likelihood of discoloration from Schiff bases, oakmoss extracts, and some specialty chemicals. Testing of fragrance materials in product bases should take place under accelerated aging conditions (eg, 40°C in plastic bottles) to check for odor stabiUty and discoloration. 

A number of types of bituminous material exist and terminology is still somewhat confusing. The term bitumens in its widest sense includes liquid and solid hydrocarbons but its popular meaning is restricted to the solid and semisolid materials. The bitumens occur widely in nature and may be considered to be derived from petroleum either by evaporation of the lighter fraction under atmospheric conditions or by a deeper seated metamorphism. The purer native bitumens are generally known as asphaltites and include Gilsonite, extensively used for moulding, which occurs in Utah. 

Perikinetic motion of small particles (known as colloids ) in a liquid is easily observed under the optical microscope or in a shaft of sunlight through a dusty room - the particles moving in a somewhat jerky and chaotic manner known as the random walk caused by particle bombardment by the fluid molecules reflecting their thermal energy. Einstein propounded the essential physics of perikinetic or Brownian motion (Furth, 1956). Brownian motion is stochastic in the sense that any earlier movements do not affect each successive displacement. This is thus a type of Markov process and the trajectory is an archetypal fractal object of dimension 2 (Mandlebroot, 1982). 

The situation is confused, however, by the case of certain chemicals. Styrene, for example, was known from the mid-nineteenth century as a clear organic liquid of characteristic pungent odour. It was also known to convert itself under certain circumstances into a clear resinous solid that was almost odour-free, this resin then being called metastyrene. The formation of metastyrene from styrene was described as a polymerisation and metastyrene was held to be a polymer of styrene. However, these terms applied only in the sense that there was no change in empirical formula despite the very profound alteration in chemical and physical properties. There was no understanding of the cause of this change and certainly the chemists of the time had no idea of what had happened to the styrene that was remotely akin to the modem view of polymerisation. 

A further conclusion, however, remains to be drawn which is less familiar. The effect of the mutual attraction between molecules must be the same as that of a pressure existing in the liquid, and this is called the intrinsic pressure. A liquid must, therefore, oppose a resistance to forces tending to enlarge its volume or, in other words, must possess cohesion or tensile strength. We habitually overlook this fact, only because we handle liquids almost exclusively under conditions which change their shape, but do not alter their volume. If, however, we attempt to do the latter, the existence of cohesion or intrinsic pressure is easily demonstrated, and some experiments in this sense will be referred to below. 

Newton s law states that for a liquid under shear, the shear stress T is proportional to the shear rate. In this sense, most of the unpigmented vehicles used in the paint and printing ink industries are considered ideal or Newtonian liquids. The ratio of the shear stress t to the shear rate D is thus a constant t), dependent only on temperature and pressure. This is not true for specialized gel varnishes and thixotropic systems, which are designed to have special rheological properties. 

The HF tester is a commercial safety tool for sensing whether an unidentified liquid contains HF [2], It shows in an exemplary way how the electrochemical properties of a silicon electrode, namely its I-V curve in HF, can be applied for sensing. The ability to dissolve an anodic oxide layer formed on silicon electrodes in aqueous electrolytes under anodic bias is a unique property of HF. HF is therefore the only electrolyte in which considerable, steady-state anodic currents are observed, as shown schematically in Fig. 3.1. This effect has been exploited to realize a simple but effective safety sensor, which allows us to check within seconds if a liquid contains HF. This is useful for safety applications, because HF constitutes a major health hazard in semiconductor manufacturing, as discussed in Section 1.2. 

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