, 2004, 46, . 4 Chemical mechanical modification of nanodiamond in aqueous system,, Y.W. Zhu, X.Q. Shen, B.C. Wang, X.Y. Xu, Z.J. Feng Department of Precision Instruments & Mechanology, Tsinghua University, Beijing 100084, China China R&D Center, Changsha Research Institute of Mining and Metallurgy, Hunan 410012, China China Department of Materials Science and Technology, Jiangsu University, Jiangsu, 202013 China E-mail: y.w.zhu@63.net The effect of Chemical Mechanical Modification (CMM) on the -potential and size distribution of nanodiamonds was studied. Results show significant change in the functional groups on its surface after the CMM treatment by the anionic surface modifier DN-10. The amount of hydroxyl groups decreases and two peaks connected with the stretching vibration of carboxylate appear instead of those of carbonyl. The -potential goes up significantly and the size drops to some extent. If treated further with CMM1, a new absorption peak 1382.19 cm-1 connected with the vibration of some distinctive functional groups which cause the increase in the -potential and the decrease in size appears.

1. Introduction This paper presents some results about the effect of CMM on the surface functional groups, -potential and size distribution of nanodiamonds.

Owing to its excellent mechanical, medical, and electronic characteristics, nanodiamond has been applied in the fields of run-in oil of engine, wear-resistant plating layer of 2. Experimental parts, and wear-resistant alloying parts to some extent.

It has a great application potential in such sectors, as A grey powder of the nanodiamond sample L (produced ultra-fine polishing of silicon wafers and other man-made by a Chinese corporation Lingyun Nano-materials Co., Ltd) crystals, modification of plastics and rubber magnetic was investigated. Before measuring the -potential, an memory devises and cold cathode display [14]. In these adequate amount of the nanodiamond powder should be applications, dispersion and stability of nanodiamond in dispersed into deionized water to get its suspension. If there various suspensions are the decisive preconditions of its is precipitation, the supernatant could be used to measure its application. When used for ultra-fine polishing of crystals, -potential, as the -potential is independent on the particle size. All the -potential and most of size distribution meaaggregates may cause nicks on the surface of a work-piece.

surements were conducted by ZETASIZER3000HS, other When used for electroplating or non-electrolytic plating, size measurements were conducted by small angle X-ray aggregates result in the inadequate particle distribution and scattering (SAXS) and CILAS 1064 Liquid. The primary a decrease in the wear-resistant properties.

size distribution was studied by SAXS, which ran at 35 kV In aqueous systems, a particle always carries electric and 30 mA. The X-ray source was generated by Co K and charges because of ionization, absorption of ions or prethe filter was iron. The size parameters such as the mean ferential substitution of ions [5]. The -potential of an size, the median size and the distribution can be obtained ultra-fine particle is often used to evaluate the variety and from the SAXS results. The CMMs of nanodiamond intensity of charge, and it is a very important index that were carried out in a stirring mill. In the process of reflects the repulsive force intensity among particles and stirring, the anionic surfactant DN-10 was added into the the dispersion stability. There exist such functional groups mill to modify its surface characteristics. The mass ratio as COOH, OH, NH2, and the like on the surface of of DN-10 to nanodiamond was 5 : 100 and the peripheral nanodiamond [6]. The kinds and intensity of functional velocity of the stirring vane was about 4.5 m/s. CMM1 is groups affect its sorption behavior and ionization properties.

a further treatment after CMM, which employs the same The status of charge exerts great influence on the stability equipment as CMM and an more acidic environment. The of nanodiamond suspensions. infrared spectrum analysis in this work was conducted using Nexus 470.

It was pointed out in [4] that the -potentials for different fractions of ultradispersed diamond were different.

The Chemical Mechanical Modification (CMM) treat3. Results and Duscussions ment is a kind of process, which involves particle fragmentation and surface modification at the same time. Good results 3.1. -pot ent i al of sampl e L. The -potential with were achieved by the CMM treatment of calcium carbonate the pH curve for sample L was presented in Fig. 1 (see CaCO3 and wollastonite [7,8]. curve a). Its Isoelectric Point (IEP) was found to be at 4.3.

666 Y.W. Zhu, X.Q. Shen, B.C. Wang, X.Y. Xu, Z.J. Feng neutral water system. With the rise of pH, the intensity of charge is reinforced because of absorption of OH- and the -potential becomes more negative. With the decrease of the pH value, the -potential became more positive until it showed electropositive at the pH = 4.3 as a result of the absorption of H+.

3.2. CMMs of Nanodi amond. The -potential versus pH curve after the CMM treatment by DN-10 for sample L was presented by the curve b in Fig. 1. The curve c in Fig. 1 represented that of chemical mechanical modified sample L by further CMM1 treatment. CMM1 is also a kind of CMM, the purpose of which is to change its surface functional groups.

After sample L treated with CMM and CMM1, the -potential with the pH curve goes up and the IEP shifts to Figure 1. The -potential of nanodiamond before and after the right. The -potential of nanodiamond boosts a lot in treatments. a Sample L, b after CMM treatment, c after the acid range. And it is more than 30 mV in the pH range CMM1 treatment.

of 3-5 for sample treated with CMM1. As a result, the stability of nanodiamond suspension in this range improves greatly. So, the suspension in the above pH range could be kept for a long time without obvious precipitation.

After the CMM treatment, the absorption peaks at 1629.29 and 1764.89 cm-1 of carbonyl for sample L disappear, substituted by peaks at 1611.74 and 1324.48 cm-caused by the stretching vibration of carboxylate. The intensity of absorption peak locating at 1117.43 cm-decreases obviously and it shifts to the lower wave number values by 30 cm-1. And this peak is connected with the stretching COH and CN vibration. The intensity of absorption peak at 3405.94 cm-1 also decreases obviously.

The CMM treatment exerted little influence on CNgroups, Figure 2. Infrared spectra before and after treatment. a Sampbut it could make it easily for some functional groups to be le L, b after CMM treatment, c after CMM1 treatment.

linked to the COH groups. It suggests that the amount of COH bonds on the nanodiamond surface drops. It is the drop of the amount of OH groups that causes the decrease of intensity of absorption peak. The changes mentioned The -potential is positive in the pH range of 3-4.3, and above are the main reasons why the -potential for sample negative in the range of 4.3-11. Its absolute value is more CMM shifts upper in the acid range. The absorption peaks than 30 mV the pH range between 7 and 11, which ensures of stretching vibration of carboxylates for sample CMMstable suspension without coarse particles.

disappears completely, and substituted by peaks of carbonyl Infrared spectrum of sample L (see curve a Fig. 2) reveals again. Compared with sample L, a new absorption peak a very strong absorption peak located at 1117.43 cm-1. It at 1382.19 cm-1 for sample CMM1 appears, in connection may be connected with the stretching COH vibration of with the stretching vibration of some distinctive functional hydroxyl or / and CN vibration of amine on the nanodiagroups, which causes the rise of the -potential.

mond surface. It could be reinforced by the absorption of 3.3. Ef f ect of CMM on t he Si ze Di st ri but i on.

(SO4)- or (ClO4)- during its purification. The absorption After CMM and further treatment (CMM1), the size dispeak at 1764.89 cm-1 may be connected with distinctive tribution of sample L changes markedly (listed in Table 1).

absorption of carbonyl for carboxyl. There is a very strong Before the CMM treatment, the fraction of particles less absorption peak around 3450 cm-1, it may be induced by than 100 nm for sample L is only 0.77 wt.%, and the average the stretching OHor / and NH vibration. Absorption peak size is 2 260 nm and the maximal size is 12 000 nm. Here, locating at 1629.29 cm-1 may be due to the combinational the particle size refers to the one of the secondary particle, action of I C = O and II NH + CN. It also may i. e., the aggregate particle size because of various kinds of be induced by the functional group CN = O. It can be forces. The results of the SAXS of sample L (listed in suggested from the above analysis and the comparison in Table 2) show that the mean size of primary particles is absorption intensity among the peaks that there are less only 12 nm and all the particles are less than 60 nm. Here, NH2 groups and more COOH groups on the nanodiamond we refer the particle before aggregation (measured SAXS) surface. As a result, the particles showed electronegative in to the primary particle. The mean size of the secondary , 2004, 46, . Chemical mechanical modification of nanodiamond in aqueous system Table 1. Size distribution of nanodiamond before and after Under usual stirring grinding conditions, smaller particles treatments are formed due to the media grinding and shearing action.

But those smaller particles easily congregate to be larger Mass fraction Mean size, Maximum ones as a result of the demand of reducing the free energy Samples (< 100 nm), % nm size, nm of the system once the stirring stops. So, usual stirring Sample L 0.77 2.260 12.000 grinding has little effect on the decrease of the size for ultraAfter CMM 7.57 670 3.fine particles. The reason why the nanodiamond aggregates After CMM1 81.6 95.6 205.can be effectively crushed during CMM process may be attributed to the combinational action of mechanical grinding and chemical absorption during the stirring grinding. With the addition of DN-10 in the process of stirring grinding, Table 2. Results of SAXS for sample L smaller aggregates form due to the grinding of media and shearing action, and at the same time the temperature of Size interval, nm Mass fraction, % Cumulative, % the nanodiamond aggregate surface rises and its activity 1-5 20.1 20.improves, which results in the reaction between DN-5-10 43.0 63.molecules and the active spots on nanodiamond aggregates.

10-18 25.2 88.The surface electrical properties change markedly because 18-36 4.7 93.of the chemical absorption of DN-10. The -potential 36-60 7.0 of nanodiamond particles increases a lot in the pH range between 3 and 7, and the enforced repulsive forces among particles protect them from aggregating. As a result, the Table 3. Size distributions after the addition of gallic acid mean size of nanodiamonds drops.

After sample L treated with CMM and further treatment Size range, nm Volume, % Number, % CMM1, its particle size could be further reduced with the 17.8-21.8 0 addition of 0.5 mg gallic acid per liter. Table 3 presents 21.8-26.6 3.2 10.its size distribution. No particles with the size more than 26.6-32.5 10.6 22.88.5 nm are found. The mean volume size of nanodiamond 32.5-39.7 19.8 28.is 52 nm. And the suspension can be used for ultra-fine 39.7-48.5 24.3 21.polishing of crystals and composite electro-less plating and 48.5-59.3 23.0 11.electroplating of parts.

59.3-72.5 16.6 5.72.5-88.5 2.5 0.88.5-108.5 0 4. Conclusions 1) After treated with CMM, the amount of OH groups decreases, if further treated with CMM1, a new absorption particle measured by ZETASIZER3000HS is 100200 times peak at 1382.19 cm-1 appears which is connected with coarser than that of SAXS, namely, the index of aggregation some distinctive groups. The -potential goes up in the of nanodiamond sample L is 100200.

acid range, and the stability of its suspension improves a lot.

The formation and properties of nanodiamond aggregates 2) After treated with CMM and CMM1, the average are very complicated. Some are soft aggregates caused volume size drops from 2260 to 95.6 nm. If further by van der Waals forces among particles, some are hard dispersed with the addition of 0.5 mg gallic acid per liter, ones caused by chemical bonds among particles. It is the mean volume size reaches 52 nm.

very difficult to disperse them, especially for the latter.

Detonation is a very complicated transit high pressure References high temperature process involved many chemical reactions.

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to lower the free energy of the system, the fine particles [4] V.Yu. Dolmatov. Russian Chem. Rev. 70, 7, 607 (2001).

congregate to aggregates with a large size spontaneously.

[5] F.S. Li. Technologies for Ultra-fine Particles. Changsha: NaThe obvious improvement of the nanodiamond size distri- tional Industrial Publishing, House (2000). P. 7.

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