This article is the third of the four parts of the 15th William Blum Lecture republished at the 61st AES Annual Meeting in Chicago, Illinois on June 17, 1974. Dr. George Dubpernell reviewed the history and scope of commercial electroplating, and then delved into the science of electrochemistry, including potential, overvoltage, and connection to electronic devices. #电子学#Research
Winner of the William Bloom Prize in 1973
Editor's Note: Originally published as Electroplating and Surface Treatment, 62 (6), 573-580 (1975), this article is the third part of the four parts of the 15th William Bloom Lecture, in the 61st AES The presentation was held on June 17, 1974 in Chicago, Illinois. Click here for a printable PDF version of Part 3. A printable PDF version of the complete 44-page paper is available here.
The hydrogen overvoltage of the base metal to be plated is usually the main factor in electroplating from acid and alkaline solutions, and may even determine whether to obtain any plating. For example, the surface of cast iron, malleable cast iron, or high carbon steel may become difficult or impossible to electroplate after being cleaned and pickled for electroplating, because the resulting surface has a lower hydrogen overvoltage. The surface of this acid-washed or acid-leached cast iron or high-carbon steel is comparable to the platinum surface used for hydrogen electrodes in terms of low hydrogen overvoltage, making it easy for hydrogen evolution at low potential and difficult to deposit many metals.
Alkaline zinc cyanide solution is usually not used for electroplating cast iron or malleable cast iron parts, because it will only produce hydrogen precipitation, or the coverage rate is poor at best. 104,105 One way to solve this problem is to add a small amount of mercury to the plating solution, or to immerse the parts in an acid mercury-containing immersion solution before plating to increase the surface overvoltage. This procedure has been patented. 106-108 also found that treating such surfaces in a boiling hot concentrated cyanide solution for 5 to 30 minutes would increase their overvoltage and allow them to be galvanized. 109 Sometimes the only remedy is to grind or polish the low overvoltage surface, or to coat it with a thick layer of another metal primer, such as copper or cadmium. Two recent references indicate that this behavior is still a problem. 110,111
Chrome plating uses a very strong acid bath, usually only on bright, dense, highly polished surfaces (with relatively high hydrogen overvoltage). Haring and Barrows clearly recognized this in 1927.112. If the nickel surface is "passive", it may not be chrome-plated. This can happen in many ways. Anode alkaline cleaning tends to oxidize nickel and “passivate” it and should be avoided. Poorly covered zinc die castings may have dim, streaks, and dark nickel deposits in the grooves. These deposits are difficult to cover with chromium and often even hinder the coverage of the surrounding area. The use of black nickel plates to produce low overvoltage electrodes has been patented. 113
A bright nickel plate from a solution containing an excessive amount of brightener may be "passive" and chrome plating is impossible, even if it looks satisfactory. Under cathodic reduction conditions, a very small amount of invisible nickel compounds on the surface may be sufficient to provide low overvoltage conditions. Similarly, Raney nickel powder is a catalyst for hydrogenation, and a very small amount is effective.
The electrodeposition theory of chromium itself may be closely related to the hydrogen overvoltage theory. The black powdered chromium coating may have a lower overvoltage and tend to inhibit further chromium deposition and promote hydrogen evolution. The success of the hexavalent chromium electroplating solution may be due to the ability of chromate to complex or otherwise make impurities such as iron, copper, zinc, nickel, and lead harmless.
This impurity is difficult to control in the trivalent chromium bath. Removal of lead is a clear step in the operation of the ammonium chromium sulfate plating bath used for electrolysis of metals, 114,115. If the bath is shut down for more than a few minutes, the cathode chromium surface will produce low overvoltage conditions. This may take several hours of electrolysis to overcome . This period of electrolysis is probably due to the nature of electrolysis purification, and it needs to be carried out in a new electrolytic cell before the current efficiency reaches the normal level of about 50% or higher.
The current efficiency in chromium deposition is closely related to the hydrogen overvoltage on the surface and the simultaneous hydrogen evolution, although 10% or 20% or more may be lost in side reactions, such as the reduction of hexavalent chromium to trivalent chromium, or the reduction of trivalent chromium For the second price. If the temperature of the solution increases, the current efficiency will usually be greatly affected.
Figure 23 from the NE Ryan116 report shows the typical behavior of a 300 g/L chromic acid solution catalyzed by the addition of sulfate and fluoride and electrolyzed at a rate of over 1000 A/ft2 to produce chromium. It seems that the low current efficiency of heavy deposits in hot sulfate boiling solutions is due to low overvoltage conditions, while maintaining a cleaner, more oxide-free surface in the fluoride catalytic solution may have a higher overvoltage and provide more High current efficiency. Shluger and Mikhailova117 showed that the oxide film on sulfate-catalyzed chromium deposits proportionally contains more sulfate than the solution, while Shluger and Osbenkova118 believe that there is no oxide film on fluoride-catalyzed chromium deposits at all.
Figure 23-Ryan curve of current efficiency for chromium deposition at high temperature using sulfate catalyst and fluoride catalyst. Reprinted with permission from the Australian Federal Aviation Research Laboratory Melbourne.
In all cases of chrome plating, low overvoltage is not necessarily a problem or difficulty. Therefore, Bedi119 uses platinum or palladium impregnated deposits on steel to ensure low overvoltage conditions to prevent etching in the low current density areas in the fluoride catalytic bath, while Bedi and Dubpernell120 use the same surface treatment and even etch cast iron 121. Prevent chromium from depositing at high current densities for stopping purposes. Glover122 reported an investigation of chromium plating on cast iron, and he found that high phosphorus seems to be more important than carbon, making it difficult to plate cast iron.
In the trivalent solution, Jangg and Burger123 used a mercury cathode in a pH 3.2 ammonium chromium sulfate solution to obtain a current efficiency of up to 68%. However, in many tests, they obtained low current efficiency due to the formation of black sponge-like deposits with low overvoltage. Some of their results on chromium sulfate and chromium chloride are given in Figures 1 and 2. Figures 24 and 25 also show the rather unusual results of decreasing current efficiency as the concentration increases. This can probably be explained by the fact that impurities cause lower overvoltage deposits in more concentrated solutions, but have less effect in more dilute baths.
Figure 24-Jangg and Burger's measurement of the chromium deposition current efficiency of a chromium sulfate solution on a mercury cathode. Drawing with permission from Pergamon Press.
Figure 25-Jangg and Burger's measurement of the chromium deposition current efficiency of a chromium chloride solution on a mercury cathode. Reprinted with permission from Pergamon Press.
JE Bride and colleagues have obtained a number of patents on chromium plating from trivalent solutions. These patents show the main effects of impurities and overvoltage in these solutions, especially if the reported plating speed results are recalculated as current efficiency. Figure 26 shows some results of one of the patents 124, indicating that three hypothetical solutions tested at slightly different temperatures and prepared at different times lack reproducibility. This may be due to different impurity effects and the resulting different overvoltages, as well as the decrease in current efficiency with current density. Another argument may be that depending on the details of the procedure and the exact organic additives used, potentially harmful impurities are compounded to varying degrees.
Figure 26-Huba and Bride measured the current chromium deposition efficiency of three newly formulated same trivalent chromium baths at different temperatures.
Contact potential-Volta potential-Electrostatic surface potential
From the Volta era to today, for about 180 years, there has been a continuous debate in the name of "contact potential." Patai and Pomerantz125 and Langmuir126 pointed out that Volta first discovered and measured this effect in 1797. When Volta published the voltaic stack in 1800 (Reference 1, page 42), the title of his paper was "On the Electricity Excited by the Mere Contact Different Kinds of Conductive Materials." Volta hoped he had discovered A perpetual motion machine, but time has not proven him. From another source (Ref. 127, pp. 133-134), both Volta and Pfaff calculated the first element table in 1793 based on their ability to stimulate electricity.
The name "contact potential" seems a bit of a misnomer, because the metal first contacts and then separates in order to measure the contact potential or volt potential in a thin, dry gas space or vacuum. For this reason, the name "electrostatic surface potential" contained above is more descriptive. It is used by WA Zisman and seems to be worth using in the future (Reference 128, pages 1-9, "Solid/liquid interface-an important and active scientific frontier").
Some confusion related to contact potential is related to its size. This is usually considered to be in the μV range, or a few mV at most, so it is not important in most jobs. It is easy to see from Figure 27 that this is not true. Figure 27 shows the change in the surface potential of mercury in dry nitrogen after adding 2 ppm of zinc (Ref. 92, pages 219-226, AH Ellison, GA Lyerly and EW Otto The paper on "The influence of impurities on the surface potential and the diffusion of liquids on mercury"). In about a minute, zinc appeared on the surface of mercury and changed about 0.80V relative to the surface potential of gold. When the surface of mercury is swept, it wrinkles and is cleaned by removing the surface film, because the surface potential changes greatly in the direction of cleaning the mercury.
Figure 27-Ellison, Lyerly and Otto's measurement of the change in mercury surface potential after adding 2 ppm of zinc. Reprinted with permission from Marcel Dekker, Inc.
The contact potential is quite reproducible in many dry gases and vacuum, and the exact distance between the electrodes is not important. Usually, they are first separated by 0.5 mm (0.0156 inches), and then further separated during the measurement process. Measuring the potential of a single electrode is very similar to that of a reference electrode, and the electrolyte in the middle is replaced by dry gas or vacuum.
Lord Kelvin (Lord Kelvin) reviewed the previous controversy in 1897-1898129, pointed out that a contact potential measurement of up to nearly 4 V had been carried out, and described a reliable measurement method. Figure 28, taken from Zisman130, shows the type of equipment used. If A is far away from B, it will cause the quadrant electrometer to deflect. If a potential is applied to balance the contact potential, a point is reached where moving A away from B no longer causes the electrometer to deflect, thereby determining the contact potential of A relative to B measured as the reference electrode.
Figure 28-Zisman diagram of the most commonly used method of measuring contact potential difference. Reprinted with permission from "Scientific Instruments Review".
A. Dravnieks (Reference 131, pp. 236-239) has recently conducted a good review of contact potential measurement. Dravnieks discussed the difficulties of these measurements and the choice of reference electrodes. He gave an interesting table of values based on Michaelson's 132 work function measurement table. This is reproduced in Table 1, which contains the work function in the vacuum from which it was derived, with the addition of the sodium and potassium values from the same source. The contact potential is calculated by using gold as the best reference electrode, and by subtracting the work function of gold from the work function of each other metal. Compare the familiar electric series. It is difficult to avoid the conclusion that these are just two different methods of measuring the same amount. Using gold as a reference electrode for the contact potential will tilt the noble metal end of the ruler by about one volt or more, but the close relationship is still obvious.
Although the measurement of contact potential is usually not very accurate and repeatable, the electric potential of the electric series has some similar backgrounds, mainly calculated based on the thermodynamic properties of the material, rather than the measured value (Reference 51, p. 88; References. 68). The contact potential or electrostatic surface potential is very sensitive to the adsorption layer on the clean metal surface, and this characteristic has led to their use in adsorption studies, such as the study by Zisman and his collaborator 128.
Fort and Wells133 found that it is possible to perform stable and easily reproducible contact potential difference measurements in saturated non-polar organic liquid environments (such as cyclohexane or benzene) instead of using vacuum or dry gas. Using electrodes immersed in this medium, they were able to study the effect of the separation distance between the electrode and the gold reference electrode. They found that the measurement accuracy of the contact potential in organic liquids can reach ±0.001 V.
Steinrisser and Hetrick found that ±0.000001 V is more accurate in semiconductor work,134 using low-voltage electron beam technology to determine the photovoltage or photoemission of cadmium sulfide exposed to intermittent light beams in high vacuum.
Langmuir126 is convinced that the contact potential and the electromotive force series are closely related, and pointed out that "the volt series of an element is determined by the magnitude of ϕ, and the electron affinity" (electronic work function). Based on the limited data he obtained in 1916, he concluded: "...The contact electromotive force can only account for about half of the observed cell electromotive force." One might say that the most recent measurements given in Table 1 indicate Better relevance.
Many later workers have studied this relationship, but it always seems impossible to conclude that the two potentials are the same attributes of the elements obtained through different measurement or calculation methods. In 1932, Gurney 135 proved the parallelism between the electrochemical series and the Volta contact potential series on the basis of general theoretical and mathematical considerations, and concluded that the interface potential is caused by electrons at the metal-metal junction. The Nernst solution's theoretical metal pressure is incorrect. He continued these same ideas in a later book (Ref. 136, pp. 33-38, 192-200).
Klein and Lange137-139 performed their own measurement of the voltaic potential of mercury as a reference electrode in an argon atmosphere. However, they did not seem to compare these measurements with the electric series, but instead focused on the measurement of the contact potential between mercury and aqueous solutions. Even in a book from 1962, 140 had a chapter devoted to volt potential, without discussing any possible relationship with electrodynamic series.
Butler141 compared zinc as the zero reference electrode in 1951 and concluded that the metal contact potential difference is a large part of the electromotive force of the battery. He doesn't seem to think that these forces are exactly the same, but "...the electromotive force usually exhibits a fairly close parallelism with the contact potential."
According to the theory proposed in this article, when metal sheets are pressed together in a good electrical contact in an external circuit, the "contact potential" or electrostatic surface potential seems to be largely eliminated. All the metal pieces in the external circuit are grouped together as if they are made of one piece of metal; the conductive electrons of each piece of metal can circulate freely between all the metal pieces and establish their own balance. Now only the outer surface of each piece of metal can freely express the inherent "contact potential" of the metal, and it is best to think that this "contact potential" has been basically eliminated at or near the point where the metal fragments are located. The metals are pressed together. At or near the point where these metal sheets are pressed together, there is only a small potential difference, such as contact resistance (IR voltage drop), thermoelectromotive force, etc.
The high conductivity of metals obviously does not mean that all points in a given piece of metal are at the same potential. A common observation is that a piece of chrome-plated metal may only be plated on the protruding part, while the low current density area may not be chrome-plated at all. This means that, at least during the current flow, the protruding area is at a higher cathode potential, while the groove is at a lower cathode potential at the same time.
It is not a good practice to electroplate articles made up of many different metal sheets stamped or welded together. If you must do this, you must first find a solution, perhaps copper cyanide, which will cover all the metals in the combination with a good coating of a single metal (such as copper). Thereafter, the part can be easily electroplated as a single piece of metal. If this is not possible, people will encounter difficulties around the joints and welds between different metals, or part of the component may be easily electroplated while other parts are not at all.
It seems that any metal coated with its oxide exhibits electrode potential behavior that is sensitive to acid and alkali, and can be used to measure acidity and alkalinity in a specific pH range. Such responses are indicated in Figure 1 and Figure 3. 5, 6 and 7 represent tin, chromium and platinum. The others are shown in Figure 4. Sometimes antimony and palladium are used. The glass electrode may be considered a silicon oxide electrode. The mercury-mercury oxide electrode is used to accurately measure the pH value in alkaline solutions.
Bates (Ref. 142, pages 304-306) describes many other "hydrogen ion electrodes" including tungsten, tellurium, bismuth, iridium, rhenium, osmium, ruthenium, and manganese dioxide. Ives and Janz (Reference 143, pages 116-117) also discuss hydrogen electrodes based on other metals, including many of the metals mentioned above, including gold, rhodium, nickel, and selenium. New hydrogen electrodes are patented from time to time. A recent patent describes uranium oxide, 144 and another palladium oxide. 145
Many electrodes are far away from the hydrogen electrode, but respond well to pH. The mercury-mercury oxide electrode and the silver-silver oxide electrode are 0.926 and 1.17 V higher than the hydrogen electrode, respectively, and can be used in alkaline solutions (Ref. 143, pages 334-335). Cahoon 146 found that the manganese dioxide electrode is about 1.07 V higher than the hydrogen electrode and gives an accurate pH response in the range from pH 0 to pH 11.5. Obviously, it can be used outside this range. Cahoon also wrote a practical article on using reference electrodes. 147
Although the operation of the platinum hydrogen electrode and a few similar electrodes generally uses a hydrogen atmosphere, most of the other metal-metal oxide reference electrodes mentioned above are used in the air, and there is no special requirement.
In 1928, French and Kahlenberg 148 and Closs and Kahlenberg 149 published two noteworthy studies containing a wealth of information on the above-mentioned issues. -In each case, when oxygen, nitrogen or hydrogen is bubbled through the solution, a saturated standard potassium chloride solution. Nitrogen and hydrogen generally have similar effects, and air and oxygen generally have similar effects. Other gases studied in some cases are carbon monoxide, methane, and helium. The effects of stirring and complete immersion were also checked. Generally speaking, gas has a very significant effect on the potential of metals.
In the second paper, Closs and Kahlenberg149 showed that a variety of metals can be used instead of hydrogen electrodes to potentiometric titration of acids and bases, especially molybdenum, tungsten, arsenic, antimony and bismuth, as well as tin and aluminum. Although metals have different potentials at the beginning, they all give the same end point in acid-base titration, and then perform potentiometric titration. In the discussion of this paper, Professor Kahlenberg said: "I think the other electrodes mentioned here are as repeatable as hydrogen electrodes. They can be calibrated and used, any of them, especially those that are not under attack. I don’t believe we need a hydrogen electrode at all;..."
The author will conclude from the widely varying potentials in the above work that the so-called hydrogen electrode is just one example of many electrodes that exhibit similar behavior, and its potential seems to be at all.
Dr. Blum described Kahlenberg’s work well in one of the above discussions, saying (Ref. 148, p. 194) “Dr. Kahlenberg has a faculty member — I don’t know if I would call it a happy faculty member — Many unexplainable facts have developed. I will not try to explain them."
Nernst theory of ion electromotive force
Arrhenius put forward the theory of electrolysis dissociation in 1883-1887, and Nernst put forward the theory of electrokinetic activity of ions in 1889.150. Both theories seem to have been overused, and it seems that it is time to seriously reconsider and reconsider. Evaluate. Opposition seems to be most often ignored, ignored and ignored.
Glasstone (Ref. 151, pp. 18-20, 321-322) briefly reviews some of the objections to the theory of electrolytic dissociation. In September 1903, at the Fourth Meeting of the American Electrochemical Society in Niagara Falls, New York, a timely and fairly comprehensive seminar was held on the subject. Bancroft gave a good summary of this situation, 151a and then extensive discussions.
One of the strongest opponents is Professor Louis Cullenberg (1870-1941) of the University of Wisconsin. Curiously, Kullenberg studied in Leipzig's Ostwald laboratory, where he received his doctorate. In 1895. He was an enthusiastic supporter of these new theories at first, until he discovered that they were inconsistent with many experimental facts, and strongly opposed them from about 1900. 152
A comprehensive bibliography of Kahlenberg and colleagues' publications is available. 153 A few years later, in addition to many research reports, Kahlenberg's position became clear, and it was clarified in four articles from 1901-1905 and 154-157. A notable feature of his research reports is that many of them were published in the Journal of Physical Chemistry, even though his editor WD Bancroft (1867-1953) was dedicated to the theory of electrolysis dissociation. Lincoln 152 quoted Bancroft writing to Cullenberg: "You are right, Cullenberg, but you will find that you cannot convince people with facts."
Obviously, it turns out that this is true. On the occasion of the 25th anniversary of the birth of the electrolysis dissociation theory, GN Lewis158 discussed many facts that showed that the theory is poorly based, but still based on the "applicability" of the theory to draw conclusions that support the theory.
Callumberg practiced what he preached. He wrote a general chemistry textbook and did not use ion theory. Instead, the solution was the concept of compounds with variable proportions. His textbooks are very popular, have been used for a long time, and have gone through several editions. Callumberg has established an enviable reputation as an excellent teacher.
However, Cullenberg's opposition to the electrolysis dissociation theory was largely futile at the time. Lewis45 improves the activity coefficient, which leaves some leeway for the behavior of individual ions, but not enough for much improvement, as already discussed (sometimes called the trash factor because it includes many errors and variables) . The Debye-Huckel inter-ion attraction theory was introduced in the 1920s to expand the concentration range covered by the electrolysis dissociation theory, but it did not extend to high concentrations or make extensive changes to the situation. Kahlenberg said desperately in a 1927 discussion of LaMer's paper: "The problem is that we don't pay enough attention to Epsom salt!" Unfortunately, this expressive comment was played down in the print discussion. 160
The same volume traded by the Electrochemical Society includes a paper by Bancroft 161, which reviews some of the difficulties of Nernst and Arrhenius. What is outstanding is his comment that the measured pH of the solution does not necessarily show any information about the actual concentration of hydrogen ions. Bancroft gave an example, adding enough sodium chloride to 0.1N HCl to make the apparent hydrogen ion concentration equal to 0.5N HCl, which would correspond to 300% or more dissociation, which is of course absurd. This effect is still under study. 162,163
At this point, one might say, for example, what about the emerging field of ion selective electrodes described by Frant, 164? Generally, these electrodes are not used to directly determine a given ion in the electroplating bath. Usually, the desired ion is very widely diluted in a medium with a constant background composition and pH value, and the desired ion itself may change in the process. Superb skills and extraordinary manipulation changes have been used to find "Nernst" conditions and responses in this field of development, but it is clear that the electrode potential is often not Nernst's. European workers 165 expressed a preference for the term "ion sensitive" rather than "ion specificity" or "ion selectivity."
Probey Potential-pH Figure 166 provides a useful method for studying and recording thermodynamic data. If it is considered that the ions in the solution do not have an electromotive force or a determining potential, but at most only modify the pre-existing electrode potential, which is an inherent characteristic of the electrode material, then check the most common potential-pH diagram. Figure 29 is such a diagram (reference 167, page 112; also reference 166, page 100 and reference 168, page 36). Line "a" is the potential of the hydrogen electrode, which is also the basis of pH (Figures 2 and 3), and line "b" is the oxygen electrode. The potential above the line "b" corresponds to the anode reaction, and the potential below the line "a" corresponds to the cathode reaction. These reactions can be produced by chemical and electrolytic methods, for example, by using hexavalent chromium, permanganate, hydrogen peroxide, fluorine or other oxidants to obtain oxidation or anode effects; and divalent chromium, dithionite, hypophosphorous acid Salt, metal sodium or other reducing agents to achieve reduction or cathodic effect.
Figure 29-Pourbaix diagram of the electrochemical equilibrium in water containing acid, alkali, oxidizing and reducing media. Reprinted with permission from Plenum Publishing Corp.
If the potentials in the graph are not a measure of ion concentration, then the factors that determine them become a problem. Are we measuring the concentration of two different electrical carriers at the interface, namely electrons and holes? It seems that acids and bases are involved in the presence or absence of excess electrons, the presence or absence of oxidation and reduction holes, and vice versa. Jorgensen48 believes that acid-base balance is related to proton activity, and redox balance is related to electronic activity. Someone would like to know whether acidity and alkalinity are just a special form of oxidation and reduction, or are there four different current carriers?
Electrochemistry is at least partly a product of electrophysiological research, and electrochemists have been fascinated by the obvious importance of the inherent electrical phenomena in living organisms. According to Motte-lay (Ref. 169, pp. 298-300), the study of electric fish and eels was carried out in the 16th, 17th and 18th centuries. Galvani's "Animal Electricity" work was first published in 1791.1, 170, and John Hunter was an outstanding Scottish surgeon who received the Copley Medal of the Royal Society in 1775 for his work on dissecting electric fish. 171 Hunter found as many as 1182 "pillars" or individual layers ("electroplaques" or "electroplates" in French) in a 1.3 m (4.5 ft) long, 33 kg (73 lb.) oversized fish. In each of the two electrical organs (Ref. 169, pp. 240-241).
It was the background of Galvani and Ritter 2's work that prompted Volta to discover the voltaic stack or battery. Volta doesn't like to source electricity from animals, and shows that it can be produced by the contact of metals with salt solutions.
It is said that the electric eels of the Amazon River can provide electric shocks of up to 600 V and 1 A or higher in the process of killing or stunning their prey for a few milliseconds (again, ref. 175, p. 157). The source and processing of so much electricity in nature does not seem to be adequately explained.
Beutner 176, 177 proposed a theory based on the contact potential difference on both sides of the biofilm, which seems to have its advantages. Grundfest (Ref. 175, pp. 141-166) believes that the source of biopotential is located in the membrane itself.
Dr. GW Crile (1864-1943) was a pioneer surgeon who was very concerned about the electrical properties of life. It is said that he and his colleagues dissected about 3734 animals of various sizes and breeds. 178 He has published many books and articles, but the titles of two of them seem to be particularly enlightening. 179,180
Many articles have been published in this general field, and it is impossible to conduct a comprehensive review in this article. A few additional titles seem to be particularly noteworthy. 181,182
The Electrochemical Society continues its activities in this field, and recently published a seminar. 183 The first article of this seminar is AA Pilla's noteworthy review of electrochemical events in tissue growth and repair (Ref. 183, p. 1-16). Pilla drew attention to RO Becker's excellent work in stimulating bone growth through a very low current density cathodic treatment similar to electroplating, but with very low current density. 184 Figure 30 shows Dr. Becker's test results within 7 days.
Figure 30-Becker stimulated the growth of leg bones in amputee rats 7 days later. This line shows the approximate level of the original amputation. A is the control, and D shows the growth due to the very low current density as a cathodic stimulus. Reprinted with permission from Macmillan Journals Limited.
Many relationships with electronic products are already obvious. In 1796, (Reference 185, p. 4) Volta named all dry conductors as the first type of conductors, and all wet or liquid conductors as the second type of conductors. He apparently came up with this term a few years ago (Reference 127, pages 132-133) when describing the table of metals and other conductors of the first type, in order of their ability to excite electricity.
The first use of the term "semiconductor" is particularly interesting. In 1792, (Ref. 127, p. 5), when repeating Galvani’s frog leg experiment, Volta was able to pass various nominally non-conductive materials (such as ice, damp wooden or marble tabletops, people, or damp wall hangings). , And call these “semiconductors.” In 1805, (Reference 186, p. 79) Ritter believed that Volta used the term “semiconductor” for the above-mentioned materials. However, further (Reference 186, p. 225-239) In a more realistic discussion of semiconductors, Ritter pointed out that Walter calls these substances "semi-insulators", but he prefers to call them "semiconductors." He doesn't have many examples, but mentions alcohol, ethers, and cycloalkanes. And metal oxides and their compounds.
If an electrode reaction is observed, it does not seem necessary to classify conduction as "electrolysis". Once the current passes through the anode or cathode interface through the electron transfer reaction, conduction through the medium is indistinguishable from metal conduction, and Ohm's law is obeyed. This view that electrolysis and electron conduction are fundamentally indistinguishable has been expressed by some electrochemists, but their views rarely attract attention.
Therefore, JW Richards187 reviewed Marvin's early work on induced currents in electrolytic conductors and showed that they behave in exactly the same way as metal conductors with the same resistance. Richards concluded from this and his own experiments that solutions are simple conductors with the same properties as metal conductors.
Kahlenberg188 reviewed this issue and agreed with the view that the conduction in the electrolyte is the same simple conduction as in the metal, and the reaction on the electrode is a secondary phenomenon.
Lukens 189 conducted a painstaking study of the current distribution in metals and solutions through equipotential lines, and concluded that these lines are the same as the metal conductors in all aspects of the solution.
Compared with electrolysis using electrodes, Brenner190 conducts current induction experiments in electrolytes containing dyes without using electrodes. The difficulty of this type of experiment is obvious. Brenner concluded that it supports the migration of ions in the electrolyte, but this conclusion seems to be more representative of his belief than the clear results of the experiment.
Rosenberg and Postow (Reference 191, pp. 161-190, an article on "Semiconductors in Proteins and Lipids") reported on the electron conduction in hemoglobin, reaching about 20% hydration, and the presence of more water Under electrolysis and ion conduction.
Putting the most important information about the resistivity of different materials and media in a chart for reference may help explain these and other facts. This is done in Figure 31, which shows the resistivity from the best insulators (such as polystyrene and mica) to the resistivity of superconductors at near absolute zero temperature. Interestingly, molten salt has such a narrow range of resistivity.
Figure 31-The resistivity chart of various media and materials at various temperatures.
This is one of the longest scales of any single property. One drawback is that it tends to ignore the effects of temperature changes. Therefore, at a temperature of zero Kelvin, the metal may appear as a superconductor at the right-hand end of the scale, but as the temperature rises to room temperature, it moves up to the middle of the scale and enters the range indicated by the metal.
On the other hand, as the temperature increases, the semiconductor moves in the opposite direction and exhibits a reduced resistivity. The same is true for the aqueous solution we are mainly concerned with-the resistivity decreases as the solution is heated. From this perspective, solutions can be considered liquid semiconductors, and there seems to be no reason not to treat them as liquid semiconductors. Their resistivity is in the middle of the semiconductor range. The presence of barriers at the electrodes and electrolytic rectification are commonplace. The occurrence of electrode reactions at the electrodes may prove that this is the only way current can pass through the interface.
The research on "amorphous" or liquid semiconductors has developed into a broad field of research. Gubanov192 did not discuss the issue of ion conduction in liquid electrolytes, but did come to the conclusion that there is no fundamental difference between liquid crystal electronic conductors and liquid crystal electronic conductors, and the mechanism of electron movement in liquids and crystals has the same properties.
The electronic properties of metal surfaces are of concern to solid-state physicists. A noteworthy comment is HJ Juretschke (Ref. 90, pp. 38-53), who drew attention to a fictitious or man-made metal called "colloid metal" proposed by C. Herring 193. Metal glue may be thought of as a positively charged jelly or a uniformly positively charged medium where electrons move. These considerations obviously help to discuss the properties of metal surfaces. The author was unable to obtain the latest comments from Boudreaux and Juretschke194.
Bogenschütz (Ref. 195, pp. 319-368) has conducted an excellent review of electronic devices based on electrochemistry, and the number of them is staggering. Some of these materials also appeared earlier in several magazines. 196 There are coulomb counters and micro coulomb counters, as well as electrochemical timers. There are 11 pages dedicated to the electrolysis information storage unit. Devices based on redox reactions include electrolytic analog transistors, Solion, and vibration sensors. Conductivity cells appear in multiple devices. Electrolytic rectifiers and capacitors are of course old equipment. The other devices mentioned are gastrointestinal transmitters, electrolytic respirometers, and stabilization cells. It also briefly introduces dry batteries, storage batteries, fuel cells and pyrogen batteries.
Therefore, it is clear that the electronics industry has a close relationship with electroplating and electrochemistry, and is free to use these in its device technology. It should be mentioned that Vijh197's book is also very helpful.
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