Nano copper

Scientifically, the term ultrafine powder or ultrafine particles is used to describe solid products in which the particle sizes are no greater than 100 nm. The ultrafine white carbon black to be discussed in this chapter is the product of particles of a smaller size than those in common products, i.e., ultrafine here is not a scientific but a commercial term. The ultrafine powders in the scientific sense, e.g., nano copper, nano TiO and nano hydroxyapatite, and related topics will be discussed in later chapters. Nevertheless, the principles involved in the preparation of ultrafine white carbon black by impinging stream reaction-precipitation are very similar to those involved in the preparation of the nano powders mentioned above. Therefore this topic is discussed here under the overall title Preparation of ultrafine powders . 

PREPARATION OF ULTRAFINE POWDERS BY REACTION-PRECIPITATION IN IMPINGING STREAMS II NANO COPPER AND ITS SURFACE IMPROVEMENT... 

This chapter introduces investigations into the preparation of nano copper and its surface improvement together with the major results the preparation of the other two nano materials, Titania and hydroxyapatite, will be discussed in later chapters. 

Nano copper powder has important applications in the following fields ... 

Electro-conductive rubber material Because of its great strength and much lower price than such expensive metals as silver and palladium, nano copper or copper-silver double metal powder can be used in the electronics industry to take the place of those expensive metals for the preparation of electro-conductive rubbers [191], electro-conductive slurry, and electrode materials etc. in addition, the copper-silver double metal powder has the characteristic of antibiosis. For such use nano copper or copper-silver powder should be needle-like crystalline the nano copper powders of sphere-like crystalline has very low electro-conductivity. 

Chemical reactions in preparation of nano copper by reduction-precipitation... 

The experimental equipment system for the preparation of nano copper powder by reduction-precipitation is shown in Fig. I4.l, where the submerged circulative impinging stream reactor (SCISR) has the same structure as was used in the investigations described in the previous chapters in Part II of this book, with the same effective volume of 3.6x10 3 m it is also operated without the top cover but is made of titanium for anti-corrosion of Cl-. 

The make-up of the reactant solutions is an important link in the preparation of nano copper by reduction-precipitation affecting the efficiency of the process. The procedures for the two solutions are as follows ... 

Figure 14.4 Nano copper of needle-like form obtained in the feeding mode III. 14.4.2.2 Influence of CuCI2 concentration...

Figure 14.7 TEM photo of nano copper obtained under the optimized conditions.

Comparison is always of interest. Table 14.3 gives a comparison between the mean sizes of nano copper powders prepared with various technologies, different reaction agents and in various reactors. It appears that the SCISR has significant superiority for the preparation of nano materials by liquid reaction- precipitation. 

A comparison of average sizes of nano copper products obtained by various technologies and... 

SURFACE IMPROVEMENT OF NANO COPPER PREPARATION OF CU-AG DOUBLE METAL POWDER... 

Surface improvement is a very important link between preparation and application of nano materials the specific method employed for the surface improvement is closely related to the occasion where the nano material is to be used. For nano copper powder the main problem is its easy oxidation, i.e., it has no anti-oxidation nature at room temperature. The partial replacement of Cu by Ag to transform the nano copper powder into the Cu-Ag double metal powder is one of the most feasible methods for the surface improvement of nano copper, because the nano Cu-Ag double metal can meet the requirement of anti-oxidation at room temperature also the latter can be used in the preparation of electro-conductive materials and electro-conductive rubbers etc. to replace some expensive metals such as silver and palladium. 

There are two methods for the preparation of Cu-Ag double metal powder by replacement reaction. One is to react nano copper with silver nitrate solution directly in the existence of polymer protecting agent to produce Cu-Ag double metal powder, which, by TEM determination, appears usually in the form of twigs. In the other method, an Ag(NH i) + solution is used to replace the AgNOj solution to take part in the replacement reaction, and with the other conditions being the same as those in the former method, sphere particles can normally be obtained. The present study is aimed at the preparation of nano particles of sphere form, and so the second method is employed. 

It is clear from Table 14.4 that in both the mean size and the anti-oxidation nature, among the five Cu-Ag double metal powders listed in this table, the one prepared with the nano copper powder produced in the SCISR is the best. 

Reducing agent and/or equipments for nano copper Average size of nano Cu Ag amount Average size of covered Cu-Ag particles %mass Anti-oxidation nature at room temperature Ref. 

The repeated experimental operation under the optimal conditions described in Item (1) can yield a stable nano copper product average-sized 5 to 10 nm with a narrow size distribution and a high content of the simple substance copper. 

The pH of the reaction solution has an important influence on the properties and appearance of the nano copper product the escape of ammonia in the form of bubbles during and after the reaction favors the dispersity of the particles the rotary speed of the propellers has no significant influence on the particle size in the product in the range of speed tested. 

With the nano copper produced in the SCISR the Cu-Ag double metal powder is prepared by the replacement reaction with AgN03 as the reactant. The TEM-determined results show that the product of Cu-Ag double metal powder prepared consists of particles sized 5 to 30 nm and their clumps after storage for one month at room temperature no change in the color of the Cu-Ag double metal powder has been found, suggesting the product has anti-oxidation nature at room temperature. 

The rotary speed of the propellers exhibits a turning influence on the average size of the product this is similar to the results obtained by Chen et al. [165] in their investigation on an analogous problem in a stirred tank reactor and also similar to the results on the preparation of nano copper described in the previous chapter. It results from the mutual effect between macro- and micro-mixing, as mentioned before. 

Wang, yanni and Zhang, Zhikun (1995). Growth scheme of polymerized ethyne on the surface of nano copper particles. Functional Materials, supplement issue, 501-502 (in Chinese). 

Chen, Zhen (2004). Preparation of nano copper powder by impinging stream reaction-precipitation. ME thesis, Wuhan Institute of Chemical Technology, Wuhan, China (in Chinese). 

Zhang, Zhimei, Han, Hongxi and Sun, Miaoxin (2000). Preparation of nano copper powder. Fine Chemicals Industry, 17(2) 69-71 (in Chinese). 

Yuan, Wei and Jin, Xin (1997). Methods for preparation of nano copper powder. Chinese Patent app. No 97100501.X. 

Liu, Zhijie, Zhaobin, Zhang, Zongtao and Hu Liming (1996). A study on the surface improvement of nano copper powder and its anti-oxidation nature. J. Eastern China University of Technology, 22(3) 270-275 (in Chinese). 

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