标题: 如何让铜金粉耐高温? [打印本页] 作者: 秀逗★恶魔 时间: 2008-9-19 13:22 标题: 如何让铜金粉耐高温? 目前我正在做一项实验,就是通过一些化学试剂使铜金粉表面处理一下,在300度的温度下只能放置5分钟,时间再长点粉就烧掉了,没有达到我预计的效果,请问我该怎么办作者: funnnd 时间: 2008-9-19 23:29 http://www.cqvip.com/QK/97035A/2007001/24032427.html
这里有一篇文章
但是看不了，你自己找找看。作者: wyj7506 时间: 2008-9-20 10:32
Oxidation Resistance of Copper-Aluminum Alloys at Temperatures up to 1,000°C,
In this study, the high-temperature oxidation resistance of copper and copper-aluminum alloys in air was investigated using thermo-gravimetric analysis. Upon heating in air, copper starts to noticeably oxidize at temperatures above 400°C. It was found that as the temperature increased, more aluminum was required in order to protect the copper. Alloying with 4 wt.% aluminum leads to a remarkable improvement in oxidation resistance. The atmosphere used to heat the samples to the required test temperatures had a noticeable impact on the subsequent oxidation rates. When heated in argon before being oxidized, copper alloys with 3 wt.% and 4 wt.% aluminum showed excellent oxidation resistance with rates 1,000 times less than that of pure copper at 1,000°C. However, when these alloys were heated in air, they were much less effective at providing oxidation resistance.
INTRODUCTION
For the protection and cooling of high-temperature metallurgical reactors, various copper cooling devices are employed, including water-cooled copper fingers, panels, and tapholes. 1 The main purpose of the cooling devices is to extract sufficient heat through the wall they are protecting so a shell of frozen slag or some other frozen material is formed on the inside surface. The formation of such a frozen layer should stop or minimize reactions and erosion of the walls, extending the service life and reliability of the reactors. However, such cooling devices have problems and experience failures. One potential problem is the oxidation of the hot face of the copper cooler, leading to decreased reliability and potential failure. Failures of the cooling system may lead to run outs of molten slag, matte, or copper, causing spectacular explosions. These situations lead to lost production, expensive repairs, and dangerous working conditions. The objective of this study is to determine if the oxidation resistance of copper at high temperatures can be improved by alloying with small amounts of aluminum.2
Whittle3 established that with oxidation-resistant alloys, a surface scale forms immediately after exposure to the oxidizing gas. Upon initial exposure, the oxide of each reactive alloy component is formed in proportion to the bulk composition. Further reactions either involve outward diffusion of one of the alloying elements or inward diffusion of oxygen. Oxides with high intrinsic growth rates such as NiO, FeO, CoO, and Cu^sub 2^O, may overgrow slower-growing oxides such as Al^sub 2^O^sub 3^ and Cr^sub 2^O^sub 3^. While this overgrowth is taking place, the more stable oxides grow from isolated nuclei laterally to the point at which they may come in contact, developing a dense continuous layer.
After the initial transient stage, the overall oxidation rate becomes controlled by diffusion of a particular species through the growing oxide layer within the scale. As a consequence, the oxidation rate is often closely described by the parabolic rate law. This stage cannot last indefinitely, since at least one of the alloy components is being removed selectively and will eventually be completely oxidized.3-5 With time, scale spalling may also take place, leading to further corrosion of the alloy and the eventual need for replacement since the alloy would not be able to withstand the chemical attack of the surrounding atmosphere.
Tests on Fe-Al, Co-Al, and Ni-Al alloys5 showed that at high temperatures (T>900°C) and high (above 5 wt.%) aluminum contents, it is easy to form highly protective layers of α-Al^sub 2^O^sub 3^. However, the alumina layers spall as the temperature increases. Wood and Stott5 observed that, depending on the temperature and the aluminum content, the morphology of the oxide layers varies (see Figure 1) and can be summarized as follows:
* A compact alumina layer surrounds the alloy core, preventing further outward diffusion of the alloy components and stopping oxygen penetration
* A compact alumina layer surrounds the alloy core as in the preceding example, but the alumina layer is not as dense, and thus some oxides are randomly precipitated just beneath the Al^sub 2^O^sub 3^ layer
* A thick external oxide scale forms, made up of the host metal oxides (FeO, NiO, or CoO) followed by a layer made of a mixture of different oxides (NiO or FeO or CoO + Al^sub 2^O^sub 3^). Beneath this layer there is a region depleted in the alloying element (aluminum)
This investigation was conducted to determine if this behavior also occurred in the Cu-Al system. See the sidebar for experimental procedures.
RESULTS AND DISCUSSION
To establish under which conditions the various copper-aluminum alloys start to oxidize, using a thermogravimetric analyzer (TGA), a series of samples were heated in dry air up to 1,000°C at a heating rate of 10°C/min. As seen in Figure 2, the samples start to slowly oxidize at around 300°C. Pure copper oxidizes the fastest, and the 4 wt.% aluminum alloy the slowest. Up to about 400°C, the addition of aluminum does not significantly lower the oxidation rate. It is further observed that the 2 wt.% aluminum alloy oxidizes slower than pure copper from about 400°C to 700°C, but then reacts nearly at the same rate as copper when the temperature is increased to above 800°C. On the other hand, the 2.25 wt.% and 2.5 wt.% aluminum alloys behave in these tests very similarly to the 4 wt.% alloy, and appear to provide reasonable resistance to oxidation.
To investigate the detailed oxidization behavior of these alloys, a series of isothermal oxidation tests were carried out in the TGA. In these tests, the samples were heated in argon until temperature stabilization had been reached. After about 2 min. to 4 min. at the test temperature, air was introduced to the sample and the mass gain was recorded. The mass gain during oxidation at 800°C and 1,000°C are shown in Figure 3. As seen in Figure 3a, at 800°C the 2 wt.% aluminum alloy oxidizes at approximately the same rate as pure copper. This is very similar to the behavior shown in Figure 2 upon continuous heating in air for temperatures at and above 800°C. On the other hand, the isothermal oxidation rate at 800°C of the 4 wt.% aluminum alloy is three orders of magnitude lower than that of copper. Figure 3b compares the rates of oxidation in air of several Cu-Al alloys at 1,000°C. It is observed that alloys with 2 wt.% aluminum and less oxidize at a rate very similar to that of pure copper while the 3 wt.% and 4 wt.% aluminum alloys improve the oxidation resistance by three and four orders of magnitude, respectively. Figure 3 clearly shows that to promote good oxidation resistance at 800°C to 1,000°C, it is necessary to use at least 3 wt.% aluminum in the alloy.
One noticeable difference between the results obtained during continuous heating in air (Figure 2) with those obtained during the isothermal oxidation (Figure 3) was that when the 4 wt.% aluminum alloy was heated in air it oxidized noticeably fester than when heated first in argon before air was introduced. It is suggested that this is caused by segregation of aluminum to the surface of the alloy during heating in argon, allowing for the formation of a more dense and protective alumina layer. When heated in air, copper oxide is formed in addition to alumina since the diffusion of aluminum to the surface is slow at low temperatures. This copper oxide layer may retard the subsequent formation of a dense and protective alumina layer.
To determine how much of the actual experimental weight gain is due to the formation of alumina relative to copper oxide, after being heated in air to 1,000°C, the alloys were cooled in argon and then reduced in 80%H^sub 2^-20% Ar gas at 600°C. Since at 600°C hydrogen will not reduce Al^sub 2^O^sub 3^, any mass loss is assigned to the reduction of copper oxide. It was found that for the 2 wt.% aluminum alloy, the most oxidized alloy, the mass loss during reduction was nearly identical to the mass gain during oxidation. This means that nearly all the mass gain during the oxidation process was due to Cu^sub 2^O with basically no Al^sub 2^O^sub 3^ formation. This is reasonable since the experimental mass gain of 4.3 wt.% corresponds to a dense Cu^sub 2^O layer of about 70 µm while the maximum calculated by the diffusion of aluminum to form Al^sub 2^O^sub 3^ is only 0.6 µm. This confirms that the penetration of oxygen and the diffusion of copper outward are faster than the diffusion of aluminum toward the surface.作者: wyj7506 时间: 2008-9-20 10:35
For alloys with 2.25 wt.% aluminum or more, the mass loss during hydrogen reduction corresponded to between 40% and 50% of the gain during the previous oxidation. This suggests that during oxidation upon heating to 1,000°C at 10°C/min., slightly more than 50% of the mass gain is due to oxidation of aluminum. Thus, during heating in air, the aluminum provides these alloys some oxidation resistance but a single dense layer is not formed and mixed oxidation takes place.
To confirm and extend the oxidation rates obtained in the TGA apparatus, other tests were conducted with larger samples exposed to air for extended periods of time in a muffle furnace. At 800°C, the 1 wt.% aluminum alloy oxidizes at a rate comparable to that of pure copper, while the 2 wt.% aluminum alloy has a rate of oxidation five times slower than pure copper. This lower rate appears to contradict the results from the TGA, showing that the 2 wt.% aluminum alloy oxidizes at about the same rate as copper. However, in the early oxidation stage, the 2 wt.% aluminum alloy oxidizes similarly to copper, just as in the TGA. This initial rate increment may be due to the development of the internal oxidation layer. Once such a layer has formed, the alumina that has precipitated may serve as a diffusion barrier, nearly stopping the further oxidation.
At 1,000°C, the 1 wt.%, 2 wt.%, and 2.5 wt.% aluminum alloys are unable to prevent copper oxidation. Indeed, the rates of oxidation of the 1 wt.% and 2 wt.% aluminum alloys are faster than that of pure copper. The 2.5 wt.% aluminum alloy has a rate comparable to pure copper, but as more aluminum is added to the copper, the oxidation rate decreases drastically. Both the 3 wt.% and 4 wt.% aluminum alloys oxidize at a rate three orders of magnitude slower than pure copper.
The parabolic rate constants for the different alloys tested were determined by plotting the square of the mass gained versus the time and fitting the data with the least squares method. The slopes of the resulting straight lines represent the corresponding parabolic rate constants shown in Figure 5. In order to illustrate what aluminum content is required to satisfactorily protect copper, three distinct zones of rate constants were defined. The first zone is for excellent protection. The 3 wt.% and 4 wt.% aluminum alloys fall in this category since they oxidize at an extremely slow rate at every test temperature. In addition, microscopic investigations show that no major oxidation products were formed. Other alloys that present limited excellent protection are the 2.25 wt.% aluminum up to 850°C and the 2.5 wt.% aluminum alloy up to 900°C. Up to about 700°C, the 2 wt.% aluminum alloy also provides excellent oxidation resistance. The un-alloyed copper and the 1 wt.% aluminum alloy are both basically unsuitable for any application at or above 500°C.
In the case of rate constants that are greater than 10 mg^sup 2^/cm^sup 4^/h, excellent regression was obtained with the regression coefficient R^sup 2^ above 0.95. On the other hand, for small values of the rate constants, the fit was significantly poorer. This means that with insufficient aluminum for protection, oxidation is described well by the standard diffusion barrier of the oxide layer formed. However, when sufficient amounts of aluminum are added this is no longer the case. It is proposed that as the oxidation proceeds, aluminum from the bulk region inside the oxide layer has time to diffuse outward toward the oxidizing front. This will effectively increase the local aluminum concentration and therefore also the oxidation resistance. The enrichment of aluminum may also lead to the exchange of copper oxide with aluminum to form alumina and metallic copper. In this manner, the oxidation process will deviate negatively from the parabolic rate law and instead follow more closely a cubic or logarithmic rate behavior. The concentration profiles of aluminum through the 2 wt.% and 2.25 wt.% aluminum alloys, both oxidized at 850°C during 21 h, are shown in Figure 6. Such concentration profiles confirm that when the alloy surface is enriched with aluminum, the oxidation resistance improves.
At temperatures greather than 800°C, the 1 wt.% and 2 wt.% aluminum alloys exhibited a thick external oxide scale. This scale consisted mainly of Cu^sub 2^O, and some CuAlO^sub 2^ dispersed in the external scale near to the alloy core. Some traces of CuO also were detected. This means that, at these temperatures, there is insufficient aluminum in the alloy to form a protective alumina layer, allowing copper to diffuse outward. Alloys with less than 3 wt.% aluminum will fail rapidly if they are exposed to oxidizing environments at or around 1,000°C.
The 2 wt.% aluminum alloy showed the existence of the three cases of microstructural features previously illustrated in Figure 1. At the lowest test temperature (500°C), type I morphology was present, while at 700°C, type II morphology was evident.
Finally, at and above 800°C, the third kind of microstructure was present as seen in Figure 7 for a 2 wt.% aluminum alloy oxidized at 850°C for 21 h. As the temperature increased, more copper oxide precipitates were present throughout the alloy and the thickness of the different layers contained in the oxidized samples increased. Copper oxide forms an external oxide layer beyond the alumina-rich layer. Due to insufficient aluminum, the alumina layer is not capable of preventing the continuous diffusion of copper outward to form a growing oxide layer. In the case of the 4 wt.% aluminum alloy, it basically exhibited the first and the second type of morphologies. However, the sample oxidized at 1,000°C in pure oxygen showed a small external scale without any of the other oxide layers previously cited. Such morphological features are summarized in Table I. Also shown in this table are the phases detected after performing x-ray diffraction on the oxidized samples.
ACKNOWLEDGEMENTS
Funding for this project from CONA-CyT (México) and NSERC (Canada) is greatly appreciated.
For more information, contact Gabriel Plascencia, University of Toronto, Materials Science & Engineering Department, 184 College St., Toronto, ON, Canada, M5S 3E4; (416) 978-0912; fax (416) 978-4155; e-mail g.plascencia@utoronto.ca.
References
1. J. Merry, J. Sarvinis, and N. Voerman, "Designing Modern Furnace Cooling Systems," JOM, 52 (2) (2000), pp. 62-64.
2. G. Plascencia (Ph.D. thesis, University of Toronto, Toronto, Canada, April 2004).
3. D.R Whittle, Oxidation Mechanisms for Alloys in Single Oxidant Gases," Proceedings of the High Temperature Corrosion Conference, ed. R.A. Rapp (Houston, TX: NACE, 1981), pp. 171-183.
4. G.G. Wood, "High Temperature Oxidation of Alloys," OxW. Metals, 2(1) (1970), p. 11.
5. G.G. Wood and RH. Stott, "The Development and Growth of Protective α-Al^sub 2^O^sub 3^ Scales on Alloys," Proceedings of the High Temperature Corrosion Conference, ed. R.A. Rapp (Houston, TX: NACE, 1981), pp. 227-249.
Gabriel Plascencia, Torstein Utigard, and Tanai Marín are with the Materials Science & Engineering Department at the University of Toronto in Toronto, Canada.
Copyright Minerals, Metals & Materials Society Jan 2005
Provided by ProQuest Information and Learning Company. All rights Reserved作者: slglnfs 时间: 2008-12-11 23:06
7506版主写的都是英文看不懂呀？！作者: SLS20002003 时间: 2008-12-13 15:05
抗氧化铜铝合金在温度高达1000摄氏度，
在这项研究中，高温抗氧化铜和铜合金在空气中进行了使用热重分析。加热后在空气中，铜开始明显氧化在温度超过400摄氏度结果发现，随着温度的增加，更需要铝，为了保护铜。合金4重。 ％铝导致了显着的改善，抗氧化。这里的气氛用来加热样本测试所需的温度有明显影响随后的氧化率。当加热的氩气被氧化，铜合金， 3重。 ％和4重。 ％铝展示了优异的抗氧化率1000倍小于纯铜在1000摄氏度然而，当这些合金在空气中加热，他们更有效地提供抗氧化。