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power flow controller with small impedances in 5. Fikret Caliskan. Robust quadratic stable dynamic power flow analysis // Electrical Engineering. output compensator // Electrical Engineering. 2006. V. 89. P. 1-9. 2008. V. 90. P. 181-187.
He Bolin, Yu Yingxia, Li Qiuping УДК 669.7/.8
PREPARATION OF THE POROUS CERAMICS OF AI2O3-TIB2 SYSTEM BY SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS METHOD
The porous ceramics is a new kind of functional material. These ceramic materials have many good properties and been attracted great interest for wide application in many fields such as chemical industry, information technology, biomaterial engineering, environmental protection and so on[1-3]. There are many homogeneous porosity which dispersed in base ceramic materials. They have the advantages of lower density, the BET surface area, physical surface characteristics, selecting permeability for liquid and gas, energy absorbing, damping, and so on. Forthmore, the porous ceramic materials have high temperature corrosion resistance, higher chemical stability and size stability. By making advantages of homogeneous porosity, the porous ceramics can be manufactured into filters, separating equipment, etc. By making advantages of energy absorbing property, they can be used for sound absorbing materials, shock absorption materials. By making advantages of high value of the BET surface area, they can be used for porous electrode, catalyst supports, heat exchanger, gas sensor. By making advantages of lower density and heat conductivity, they can be used as heat-insulation material and light structural materials.
Self-propagating High-temperature Synthesis
Today, the methods preparing porous ceramics are appending producing pore techniques, froth techniques, organic forth-dipping techniques, and sol-gel method [4,5]. Self-propagating high-temperature synthesis (SHS) is developed from Russia [6,7]. The method is based on the use of the heat released during exothermic reactions in order to preheat raw materials and to obtain a self-sustained system.
In this paper self-propagating high-temperature synthesis method is carried out to fabricated the porous ceramics and Al2O3-TiB2system is used for research object by adjusting the state of reaction mate-
rials, including raw materials chemistry composition, reaction materials grain size, raw sample density and so on. Many porous ceramic products with different shapes such as circle plate, and cylinder, etc, have been fabricated by author with porosity of 45%-68%, and pore sizes of 1-400 ^m. 1 Experiment conditions and process
1.1 Reaction system
10Al + 3TiO2 + 3B2O3 ^ 5Al2O3 + 3TiB2.
For the porous ceramics of Al2O3-TiB2 system, the range of porosity and pore size is great. The porosity and pore size are easy alternated and controlled. In the Al2O3-TiB2 system, high combustion temperature is one of features during the combustion process. The highest temperature in Al2O3-TiB2 system is 223 0oC and higher than the melting point of Al2O3. The Al2O3 and TiB2 in the system can be thoroughly sintered. Another feature is that the combustion materials are easy formed in the combustion process. The combustion materials are not easy dela-minated and can be ignored easily. It does not effect the ignore point to add different kind and quantity of additions and the system can combusted thoroughly. It gives the convinince to alternate and control the pore size by adding some additions.
1.2 Raw materials
Al powder: industrial, grain size 45-175 ^m; TiO2 powder: industrial, rutile, grain size smaller than 45^m; B2O3 powder: industrial, grain size smaller than 175^m.
1.3 Raw materials
The raw materials are mixed according to chemical mole ratio of the composite system for 4 hours, and some additive is added. After being sieved, mixed and dried, the reactive mixtures were filled up the stainless steel die by pressing or librating to shape.
МЕХАНИКА. ТРАНСПОРТ. МАШИНОСТРОЕНИЕ. ТЕХНОЛОГИИ
1.4 Raw sample and products measurement
The calculating formula of raw sample density
is:
Pr = m / V. (1)
In the formula, m is the mass of raw sample; V the volume.
Products density is measured by GB/T 19661996.
Pp = mipw /(m2-ms), (2)
where m1 is the sample dry mass; m2 is the mass with full of water in the air; m3 is the mass with full of water in the water; pw is the water density.
1.5 The visible porosity measurement
The visible porosity of cermet composite was calculated according to the following equation[8]:
0v = [( m2 - mi ) / ( m2 - m3 )] x 100%. (3)
1.6 The total porosity calculation
The total porosity of cermet composite was calculated according to the following equation[8]:
0t = ( 1 - Ps / p0 ) x 100%, (4)
where p0 is the produce academic density. In the reaction system, p0 is 4.06 g/cm3. the formula is as fol-lows[8]:
_ m(Al2O3) + m(TiB2) _ p0 _ _
m( Al2O3) m(TiB 2) d (Äl2O3) + d (TiB2) mol (Al2O3) x M (Al2O3) + mol (TiB2) x M (TiB2) mol(Al2O3) xM(Äl2O3) mol(TiB2) xM(TiB2)'
(5)
d (Al2O3) d (TiB2)
Notes: the density of Al2O3 is 3.9 g/cm3; TiB2 is 4.5 g/cm3.
1.7 The closed porosity calculation
The closed porosity is calculated by using the following formulor:
0c = 0t - 0v. (6)
1.8 Experimental equipment
The experimental equipment include pressure die which is made by ourselves, mechanical press with the force of 250KN, oxy-acetylene flame, JA1103N type electronic balance with the precision of 0.0001g, scanning electron microscope, graphite crucible, etc.
1.9 The compressive strength measurement
The compressive strength is measured by using the formula o = P/S on all-purpose material tester with cylinder 920mm x 20mm according to GB/T 19641996.
1.10 Manufactory process of porous ceram-
ics
All the raw materials were weighed out according to the ratio Al:TiO2:B2O3=9:8:7 and mixed homo-genously. Some additive such as Al2O3 and SiC is added to the reaction system. In order to compare the experimental results, the specimen is shaped by using pressing and hand. The pressed samples which are put in the graphite crucible are ignored by using oxy-acetylene flame.
2 Experimental results and analysis
2.1Effect of additive on pore size and porosity
Generally, additives don't take part in chemistry reaction. So additive of Al2O3 and SiC are choozed. The raw materials are added some additive. The results are listed in Table 1, Table 2 and Fig. 1.
Table 1
Additive/ % Actul densit У theoretic al density visible porosit У total porosit У closed porosit У
0 1'28 4'06 57 62 5
10 1'31 4'03 62 67 5
20 1'39 4'03 59 66 7
Table 2
Additive/ % Actul densit У theoretic al density visible porosit У total porosit У closed porosit У
0 1'29 4'06 59 64 5
10 1'32 4'03 63 68 5
20 1 '41 4'03 61 67 6
Pore size is decreasing obviously when the content of Al2O3 and SiC is increased, but effect on porosity is little. This is because that Al2O3 and SiC don't take part in high chemistry reaction. But it obstructs reaction. The one it obstructs melt Al reuniting at the igniting, and fills in primary pores; the other is combustion temperature decreasing depreciations pore size enlarging. In addition, effect of different Al2O3 and SiC content on product actual density and academic density is little.
2.2 Effects of pressure on porosity and compressive strength
This research analyzed the effect of form pressure on porosity and compressive strength with shape by pressing and hand. The results are shown in Fig.2 and Fig.3.
-c LD
20 -15 -10 -
5
Shape by hand
shape by Press
Fig. 2. Relation between shape pressure and compressive strength
b. shape by pressing Fig. 3. The SEM micrographs of composite with different pressure
Effect of form press on pore size is obvious. The porous ceramic which is pressed by hand is larger than that of pressing by machine,see Fig.2 and Fig.3. The press can only decrease the pore sizes. It can not increase the porosity ratio. The compressive strength ob is increased by increasing the form press. Grain contact area is smaller and integrate between grains, more consolidate while composite compressive strength is higher when shaped by pressure. 2.3 Properties measurement The research has indicated porous ceramics products with different shapes such as circle plate and cylinder, etc. the properties are following.
Composite pore sizes are 1-400^m; compressive strength is larger than 12MPa; visible porosity is about 45%-68%; the acid and alkali resistance is very good (mass losing < 2%).
Filtration capability by measured liquid passing is a means token filtration precision in this paper. Sample size is choose cylinder ^30mm*40mm. The liquid for filtration is composed with TiC powder weight 1g, grain size 3^m and distilled water 1000ml. The experimental result analyzed by using grain size analysis instrument is showed that the filtration capability of sample with additive 20% Al2O3 and SiC is 90%, 94%, respectively. 3 Conclusions
(1) Porosity and pore size of Al2O3-TiB2 system porous ceramic are easy to change and control by alternating the content of additive of Al2O3 and SiC. The filtration capability of the porous ceramic with additive 20% A^ and 20%SiC is 90%, 94%, respectively.
(2)Effect of form press on pore size is obvious. The pore size of porous ceramic which is pressed by hand is larger than that of pressing by machine. (3)The additive of Al2O3 and SiC can greatly decrease the pore size and its effect on porosity is little.
REFERENCES
1. Liu Fude, Chen Senfeng, Zhang Shuzheng. Materials Review. 2000. Vol. 14. 33 p. (In Chinese).
МЕХАНИКА. ТРАНСПОРТ. МАШИНОСТРОЕНИЕ. ТЕХНОЛОГИИ
2. Wang Yaoming, Cai Weiqing. Jiang Su Ceramics. 2003. Vol. 36. 19 p. (In Chinese).
3. She J. H, Ohji T. Mater Chem and Phy. 2003. Vol. 80. 610 p.
4. Zhu Xinwen, Jiang Dongliang, Wang Tan Shou-hong // Journal of Ceramics. 2003. Vol. 24. 40 p. (In Chinese).
5. Ma Wen, Shen Weiping, Dong Hongying. Powder Metallurgy Technology. 2002. Vol. 20. 365 p. (In Chinese).
6. He Bolin, Li Shuzhen. Journal of East China Jiao-tong University. 2003. Vol. 20. 98 p. (In Chinese).
7. Mezhanov A. G. International Journal of Self-propagating High-temperature Synthsis. 1997. Vol. 16. 119 p.
8. Su Juan, Qian Donghao, Zhou Xiaoxin. Powder Metallurgy Technology. 2006. Vol. 24. p. (In Chinese).
Wu Cai-bin, Xiang Su-lin, Dong Zhong-zhen, Bu Jing-jing
Y^K 669.2/.8
THE EXPERIMENTAL RESEARCH OF VALUABLE METALS' RECOVERY FROM WASTE PRINTED CIRCUIT BOARDS
1. Introduction
The waste printed circuit board s(PCBs) is enough rich in noble metal, nonferrous metals, ferrous metal, rare earth metal and so on, therefore it has become a research focus. A lot of researches show that metal grades in the waste PCBs are better than industrial products of natural ore, the prospect of recovery is better as well. As a rule, the PCBs are referred to as secondary resources.
In PCBs waste resources development, its utilization technology mainly related to mechanical treatment, hydrometallurgy, hydrometallurgy, the recent emergence of the biological method and so on. At present, mechanical treatment has the characteristics of less pollution and resource comprehensive utilization so it has been used widely [1,2]. Wang Hui, studies on the crushing performance of PCBs employing several crushers such as jaw crusher, roller crusher, disk crusher, vibration grinding [3]. However, on separation, a company in Germany developes a separation of metal and plastic electrostatic separator, it can be separated from the particle size of less than 0.1mm, or even be able to recover the precious metals from the dust under some control conditions. Usually the dust in other processes could be treated as hazardous
The elment
waste [4]. The methods of airflow-classifier and eddy current separator could be wide-spreadly applied to concentrate the PCBs [5-8]. For example, Shunli Zhang and others use a newly developed eddy current separator and recycling aluminum from the computer circuit board waste. The grate of aluminum metal enrichment is up to 85%, the recovery could reach 90% [9]; J.M. Krowinke and others use eddy separator could get 76% aluminum, 16% other non-ferrous metals and a small amount of glass, plastic, metal-rich collective, the recovery of aluminum could reach 90% [10].
2. Experimental
2.1 Materials
The waste PCBs are obtained from the discarded computer motherboards. The main components are shown in table 1. It is artificial pretreatment into 20 x 20mm x mm size before the crusher.
2.2 Flowsheets
The experimental flowsheets employed are presented in figure 1.
Table 1
in PCBs
Components Cu Zn Mn Ni Fe Al Cr Mg Sn Ti SiO2 C Ag Au
Contents /% 26.8 1.5 0.47 0.47 5.3 4.7 0.05 1.9 1.0 3.4 15 9.6 3300g/t 80g/t
