First published 13 15 17 16 0 2 4 6 8 10 9 7 5 3 1. Published by. Macmillan South Africa (Pty) Ltd. Private Bag X Northlands. Gauteng. Platinum Natural Sciences Grade 9 Learner's Book (CAPS). Superior CAPS coverage – written for the new curriculum by expert authors. • Superior illustrations and activities to improve results and.
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Platinum Natural Sciences Grade 9 Learner's Book ePDF (1-year licence) PDF. Superior CAPS coverage – written for the new curriculum by. Technology (Gr 4–6) and Natural Sciences (Gr 7–9) deals with the characteristics of a force. The formal definition of “force” is mentioned for the first time in Grade. A World Without Boundaries. Na tural Scienc es. Grade 9-A. L earner's W orkbook. Natural Sciences. Grade 9-A (CAPS). EXPLORE. A World Without Boundaries.
Home Page Digital textbooks platinum natural sciences grade ebooks. What makes the Platinum Natural Sciences course unique? Its superior quality will guarantee exam successs! It is the number one choice of textbook for Natural Science teachers. Learners are given the opportunity to practice each new skill that is precribed by CAPS through the focus pages that cover process skills. The authors are experts in Natural Science education and they have taken care to expertly cover all aspects of the CAPS curriculum.
Considering that almost two thirds of all the energy produced is discharged as waste heat, technologies are critically needed that can effectively convert this low-grade heat to useful electrical energy. Thermoelectric TE devices have extensively been studied in the past decades 4 , 5 , 6 to convert the waste heat to electric energy.
The TE devices do provide an effective means of converting waste heat to electricity. Rarity of the TE raw materials and the corresponding high unit cost of electric power, however, hampered its practical and large-scale deployment 7 , 8.
Other routes to utilizing waste thermal energy include thermoelectrochemical cells TECs 12 , 13 , 14 , 15 , 16 , 17 , 18 , thermally regenerative electrochemical cells TRECs 19 , 20 , 21 and thermo-osmotic energy conversion TOEC 22 , Among these, TECs or thermocells have received much attention due to the advantages of direct conversion of thermal to electrical energy and continuous direct current DC voltage generation without consuming materials or producing emissions.
A TEC is a non-isothermal electrochemical cell with a simple structure of an electrolyte sandwiched between two non-active electrodes subjected to different temperatures.
With the efforts on developing inexpensive but highly efficient electrodes and high-performance electrolytes, remarkable advances have been made in the TEC performance, which render TEC technologies commercially attractive 25 see Supplementary involving recent advances in thermocell performance.
As being analogous to a commercial thermoelectric module utilizing p-type and n-type thermoelectric materials, an array of p-type and n-type thermocell elements has been demonstrated using electrolytes with opposite temperature coefficients. This provides a sign convention which is consistent with thermoelectrics for n-type and p-type elements in TECs, providing negative and positive temperature coefficients, respectively. Although exciting recent progress has been realized for the TEC array with series and parallel interconnection, the output performance from the TEC array was found to be mainly limited by a relatively low performance of n-type electrolytes, compared to that of p-type electrolytes, at the use of same cross-sectional areas and electrode materials of both n-type and p-type elements.
For direct comparisons between electrolytes, we adopt the typical measures of performance of thermoelectrics for the electrolytes such as power factor and figure of merit. The intrinsic quantities pertaining to these measures are temperature coefficient of redox potential, ionic conductivity, and thermal conductivity.
To deliver high electrical power, it is desirable for an electrolyte to have the high temperature coefficient, high ionic conductivity, and low thermal conductivity. We determine experimentally these quantities and compare the proposed perchlorate electrolyte against the benchmark cyanide electrolyte in terms of the ionic power factor and figure of merit. We then compare the thermocell device performance.
Results and Discussion One of the favorable factors for choosing the iron perchlorate electrolyte was that the high solubility of iron perchlorate salts in water 28 such that its use can increase the output current of the TEC and at the same time decrease the thermal conductivity of electrolyte.
The non-volatile and stable nature of the perchlorate anion is another favorable factor, while highly toxic hydrogen cyanide gas can evolve from the cyanide electrolyte when decomposed thermally or under acidic conditions Because of these favorable factors, iron perchlorate electrolyte was chosen for the investigation in this work. An optical image of each electrolyte is shown in the right panel in the figure. Full size image The redox reactions leading to the generation of electricity have to be reversible for continuous operation of the TEC.
Cyclic voltammetry CV was used to check the reversibility of electrochemical reactions of the perchlorate electrolyte with platinum as the electrode. The cyclic voltammograms of the electrolyte solutions of 10 mM K4Fe CN 6 and Fe ClO4 2, obtained with the conventional three electrode configuration, are compared in Fig. S1a,b in Supplementary Information. The relationship between the scan rate square-rooted and the pick current density is highly linear for both electrolytes, implying that the redox reactions are limited by free diffusion in the reaction.
Therefore, it is concluded from the CV analysis that the redox reaction of the perchlorate electrolyte appears to be quasi-reversible and self-regenerative that the reaction product formed at one electrode becomes a reactant at the other electrode, as with the cyanide electrolyte. As shown in Fig. Comparison of b ionic and c thermal conductivity of the electrolytes.
It is clear from the eq. Actually, the non-covalent interactions between redox-counter ions and solvent molecules, and those among solvent molecules affect the solvation structures and correspondingly result in the changes of reaction entropy of redox couples It should be noted in this regard that perchlorate ion is known as a strong water structure breaker 38 , 39 in the electrolyte.
The ionic and thermal conductivities of both electrolytes are compared in Fig. It seems unlikely that the measured ionic conductivity directly corresponds to the conductivity of TEC device because of irreversible voltage losses occurred during TEC operation.
The voltage loss is generated by three primary internal overpotentials, such as activation, ohmic and mass transport overpotentials. Discussion on the conductivity of TEC device is provided in Supplementary Information in conjunction with the internal resistance extracted from the current-voltage curves of TECs.
Since the output voltage of TEC is proportional to the temperature difference between the two electrodes, a lower thermal conductivity of electrolyte is highly desirable to lower the heat transport losses through the TEC, thereby enhancing the conversion efficiency of TEC. As shown in the figure, the thermal conductivities of both electrolytes decrease with increasing concentration.
For the purpose, one can adopt the performance measures of TE materials for the evaluation of TEC electrolytes, particularly in view of the fact that TEC has the same equivalent circuit as TE. A higher PFe would indicate a larger electrical power, but not necessarily a better efficiency for the energy conversion. This energy conversion efficiency of a given electrolyte would be represented by the ionic figure of merit.
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