Concentration of zinc oxide

A 100 mL bottle of skin lotion contains a number of solutes. One of these solutes is zinc oxide, ZnO. The concentration of zinc oxide in the skin lotion is 0.915 mol/L. What mass of zinc oxide is present in the bottle ... 

Metal fume fever has been observed in humans who inhaled high concentrations of zinc oxide fumes. Metal fume fever is believed to be an immune response characterized by increased body temperature, impaired lung function, increased number of leukocytes in the blood, and bronchoalveolar lavage fluid. Similar effects were observed in animals. Metal fume fever has been observed after acute, intermediate, and chronic inhalation exposures to zinc oxide. 

There has been a history of tight supply situations with the availability of zinc oxide. Forty years ago when the price of ZnO was relatively cheap, larger concentrations of zinc oxide were used in rubber compounds. However, over the years with tight supply and rising prices for ZnO, the average concentration has dropped to a lower level. This makes the rubber industry even more vulnerable to the next shortage period because the rubber fabricators have little flexibility in cutting back any further in the zinc oxide concentrations in their recipes. 

Figure 3.5. Variations in defect concentrations of zinc oxide doped with potassium...

A.cidSolutions. DHute sulfuric acid is the most important solvent for oxide ore and for dead roasted sulfide concentrates. For instance, the leaching of zinc oxide, described by the foHowing equation, can be written as foHows ... 

Initially, vulcanization was accomplished by heating elemental sulfur at a concentration of 8 parts per 100 parts of rubber (phr) for 5 h at 140°C. The addition of zinc oxide reduced the time to 3 h. Accelerator in concentrations as low as 0.5 phr have since reduced time to 1-3 min. As a result, elastomer vulcanization by sulfur without accelerator is no longer of commercial significance. An exception is the use of about 30 or more phr of sulfur, with httle or no accelerator, to produce molded products of hard mbber called ebonite. 

When a zinc strip is dipped into the solution, the initial rates of these two processes are different. The different rates of reaction lead to a charge imbalance across the metal-solution interface. If the concentration of zinc ions in solution is low enough, the initial rate of oxidation is more rapid than the initial rate of reduction. Under these conditions, excess electrons accumulate in the metal, and excess cationic charges accumulate in the solution. As excess charge builds, however, the rates of reaction change until the rate of reduction is balanced by the rate of oxidation. When this balance is reached, the system is at dynamic equilibrium. Oxidation and reduction continue, but the net rate of exchange is zero Zn (.S ) Zn (aq) + 2 e (me t a i)... 

To dissociate molecules in an adsorbed layer of oxide, a spillover (photospillover) phenomenon can be used with prior activation of the surface of zinc oxide by particles (clusters) of Pt, Pd, Ni, etc. In the course of adsorption of molecular gases (especially H2, O2) or more complex molecules these particles emit (generate) active particles on the surface of substrate [12], which are capable, as we have already noted, to affect considerably the impurity conductivity even at minor concentrations. Thus, the semiconductor oxide activated by cluster particles of transition metals plays a double role of both activator and analyzer (sensor). The latter conclusion is proved by a large number of papers discussed in detail in review [13]. The papers cited maintain that the particles formed during the process of activation are fairly active as to their influence on the electrical properties of sensors made of semiconductor oxides in the form of thin sintered films. 

To resolve the problem applying methods of collimated atom beams, equilibrium vapour as well as radioactive isotopes, the Hall effect and measurement of conductivity in thin layers of semiconductor-adsorbents using adsorption of atoms of silver and sodium as an example the relationship between the number of Ag-atoms adsorbed on a film of zinc oxide and the increase in concentration of current carriers in the film caused by a partial ionization of atoms in adsorbed layer were examined. 

It was first shown in study [37] that adsorption of N-atoms on films of zinc oxide reduces its conductivity to a certain stationary value which depends, as with oxygen atoms, both on the stationary concentration of particles in the volume adjacent to the sensor s film and on the temperature. 

Stationary concentration of adsorbed acceptor particles of O- and N-atoms on a film of zinc oxide is attained for the most part due to the competition between the chemisorbtion of particles and their interaction, i. e. mutual recombination on the adsorbent surface, and with free atoms attacking the adsorbed layer of the adsorbent from outside. 

Our comments on adsorption of oxygen and nitrogen atoms lead to conclusion that practically under all conditions the initial rate of variation of conductivity of zinc oxide film due to adsorption of acceptor particles discussed in this section is proportional to the concentration of particles in the space adjacent to the surface of oxide film. This is similar to the case of donor particles. This means that the following equation is applicable ... 

In a review of the course and mechanism of the catalytic decomposition of ammonium perchlorate, the considerable effects of metal oxides in reducing the explosion temperature of the salt are described [1], Solymosi s previous work had shown reductions from 440° to about 270° by dichromium trioxide, to 260° by 10 mol% of cadmium oxide and to 200°C by 0.2% of zinc oxide. The effect of various concentrations of copper chromite , copper oxide, iron oxide and potassium permanganate on the catalysed combustion of the propellant salt was studied [2], Similar studies on the effects of compounds of 11 metals and potassium dichromate in particular, have been reported [3], Presence of calcium carbonate or calcium oxide has a stabilising effect on the salt, either alone or in admixture with polystyrene [4],... 

At the same time Markham and Laidler (70) and also Veselovsky and Shub (71, 72) have shown that the photocatalytic activity of zinc oxide diminishes as a result of the calcination of specimens at high temperatures (around 1000°C) in the reduced atmosphere (such pretreatment results in an increase of the concentration of superstoichiometric zinc in the specimen). In other words, a donor impurity (zinc in excess of stoichiometry) retarded the reaction. 

Zinc ligands are soluble in neutral and acidic solutions, so that zinc is readily transported in most natural waters (USEPA 1980, 1987), but zinc oxide, the compound most commonly used in industry, has a low solubility in most solvents (Elinder 1986). Zinc mobility in aquatic ecosystems is a function of the composition of suspended and bed sediments, dissolved and particulate iron and manganese concentrations, pH, salinity, concentrations of complexing ligands, and the concentration of zinc (USEPA 1980). In freshwater, zinc is most soluble at low pH and low alkalinity 10 mg Zn/L of solution at pH 6 that declines to 6.5 at pH 7, 0.65 at pH 8, and 0.01 mg/L at pH 9 (Spear 1981). Dissolved zinc rarely exceeds 40 pg/L in Canadian rivers and lakes higher concentrations are usually associated with zinc-enriched ore deposits and anthropogenic activities. Marine... 

The influence of ZnCFO concentration (3,0 5,0 7,0 phr) on formation of properties complex of the unfilled rubber mixes and their vulcanizates on the basis of isoprene rubber of the following recipe, phr isoprene rubber - 100,0 sulfur - 1,0 di - (2-benzothiazolyl) -disulfide - 0,6 N, N -diphenylguanidine - 3,0 stearic acid - 1,0, was carried out in comparison with the known activator - zinc oxide (5,0 phr). The analysis of Rheometer data of sulfur vulcanization process of elastomeric compositions at 155°C (fig. 5) shows, that on crosslink density and cure rate, about what the constants of speed in the main period (k2) testify, they surpass the control composition with 5,0 phr of zinc oxide. Improvement of the complex of elastic - strong parameters of rubbers with ZnCFO as at normal test conditions, and after thermal air aging (tab. 1), probably, is caused by influence of the new activator on vulcanization network character. So, the percent part of polysulfide bonds (C-Sx-C) and amount of sulfur atoms appropriating to one crosslink (S atoms/crosslink) in vulcanizates with ZnCFO are decreased, the percent part of disulfide bonds (C-S2-C) is increased (fig. 62). 

The comparative estimation of efficiency of zinc oxide and ZnCFO similar concentrations (3,0 5,0 7,0 phr) as the agents of metaloxide vulcanization system was carried out on example of modelling unfilled elastomeric compositions from chloroprene rubber of recipe, phr chloroprene rubber - 100,0 magnesium oxide - 7,0. Kinetic curves of rubber mixes curing process at 155°C are shown on fig. 8. The analysis of the submitted data testifies, that at increase of zinc oxide contents vulcanization kinetics is changed as follows the scorch time and optimum cure time are decreased, the cure rate is increase. Vulcanization... 

Fig. 5-63. Flat band potential of two n-type semiconductor electrodes of zinc oxide in 1 M KCl (pH 8.5) as a function of donor concentration A= surface finished in 85 % H3PO4 B = surface finished in 2 M KOH = donor concentration. [From Dewald, I960.]...

Fig. 8-90. Normalized cathodic cur> rent of redox reactions of hydrated redox particles as a function of standard redox potential at n-type electrodes of zinc oxide / (n, cqx) = normalized cathodic reaction current n, = concentration of interfacial electrons Cqx = concentration of oxidant particles au = arbitrary unit. [From Morrison, 1969,1980.]...

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