CN100516855C - A powder metal resistivity measuring device - Google Patents

Abstract

The invention relates to new type powder metallic material resistivity testing method and device. It feature is that it measures the resistivity for the measured powder material with different density, calculates out the corresponding resistivity and conductivity to gain the curve described powder material electricity performance. The testing device is made up of pressure mechanism, micro displacement testing device, rigid bridge, and sample box. The pressure mechanism is used to change the powder material volume in the sample box. The micro displacement measuring device is used to record the change in real time. The rigid bridge is used to record corresponding powder resistance value. This measuring method and device can be used in nickel powder resistivity measuring, other metallic or non metallic powder material, nanometer material resistivity and conductivity measuring. Thus it will play an important role in materials, electronic technology etc.

Description

A powder metal resistivity measuring device

technical field

The invention relates to a measuring device for resistivity or conductivity of powder metal materials. The device uses pressure to act on the sample of the powder material to be tested, and changes the density of the powder material without changing the microscopic appearance of the powder material to be tested. By measuring the corresponding resistance and density, the resistivity and conductivity are calculated.

Background technique

Resistivity and conductivity are important electrical performance parameters of electronic materials. For common bulk materials, there are international and domestic norms and standards for the measurement of resistivity, and the resistivity and conductivity of many commonly used materials have been compiled into relevant data sheets for query. But for powder materials and nano-powder materials, due to the localized characteristics of electrons and the surface potential and interface potential of powder particles, their resistivity and conductivity are different from those of bulk materials. For example, the resistivity of nickel bulk material is 6.97×10 ^-6 Ωcm at 20°C under normal pressure, while the resistivity of nickel powder is at least four orders of magnitude higher than that of bulk material, and it is also related to the production process of nickel powder, Storage state, powder surface oxidation state and so on. The same material has different porosity, and its resistivity is also different; the resistivity of powder metals of different specifications composed of the same element produced by different manufacturers cannot compare their electrical properties.

In recent years, the rapid development of industries involving powder metal materials such as battery technology and low-cost electronic thin film technology has directly promoted the development of powder metal production technology and driven the market demand for powder metal materials. Material manufacturers hope to be able to produce materials with different electrical properties to meet the increasingly expanding application requirements; if the electrical properties of materials can be scientifically evaluated, the production process can be adjusted according to material properties, and powder metal materials of different specifications can be produced . Users of materials also hope to be able to use electrical performance parameters as one of the basis for selecting materials, so as to achieve scientific and rational use of materials. Therefore, enterprises involved in the production and application of materials all hope to scientifically evaluate the electrical properties of powdered metal materials, and the demand for scientific evaluation methods of powdered metal materials is becoming increasingly urgent.

According to the survey, at present, there are no specifications and standards for testing the electrical properties of metal powder materials, either internationally or domestically. In the conductive adhesive and electrostatic shielding industries, powdered metal materials are mixed into colloids, and some people have studied the electrical property measurement methods in this case. However, producers and users of materials want to know the electrical properties of metal materials in powder state. The Institute of Optoelectronics of Shenzhen University and Shenzhen Zhongjin Lingnan Nonferrous Metals Co., Ltd. conducted a cooperative research on the conductivity of fibrous nickel powder, and summarized a set of test methods for powder metal. According to this method, the powder metal It is possible to evaluate the electrical conductivity of materials including nanometer materials, which provides a basis for the comparison of electrical conductivity of powder materials. The present invention is produced on this basis.

Contents of the invention

The invention provides a method for testing the resistivity and conductivity of powder metal, which can scientifically evaluate the conductivity of powder metal materials. The feature of this method is to apply pressure to a certain amount of powder material sample in a continuous increasing manner, so that the density of the sample material changes, and record the corresponding pressure, resistance and characteristic size of the sample at the same time, and then calculate according to the various parameters recorded The resistivity and conductivity of the material.

In our research on the conductivity of fibrous nickel powder, we found that when the pressure is continuously increased for a certain mass of nickel powder, the resistance of the nickel powder first decreases rapidly, that is, the change rate of resistivity with pressure is very large; after that, the resistivity It begins to decrease slowly; as the pressure increases further, the resistivity changes more and more slowly; when the pressure increases to a certain extent, the resistivity is close to the resistivity value of the bulk material (see Figure 1). The function of the pressure is to change the volume of the material sample. When the quality of the sample remains unchanged, the function of the pressure is to change the density of the powder sample. Therefore, the change of resistivity with density follows the same trend as that with pressure (see Figure 2). By measuring the resistivity at different densities, the electrical conductivity of powder materials can be compared. This is the basis of the present invention.

Based on the above method, the present invention provides an example of a measuring device. The measuring device is composed of pressure device, micro-displacement testing device, precision electric bridge, sample box and so on. Among them, the pressure device provides the sample with continuously changing pressure and can accurately measure and display the provided pressure. It can be manual, electric, or provide pressure through hydraulic pressure; the micro-displacement test device is used for Record the displacement of the material in the sample box along the pressure direction under pressure; the precision electric bridge is used to measure the resistance of the sample under pressure; the sample box provides a cylindrical or rectangular space for powder materials, it It consists of upper and lower electrodes and an insulating sleeve. The electrodes can slide along the sleeve wall in the sleeve, and the sliding length is recorded by the micro-displacement test device.

Based on the above measuring method and device, the present invention provides a simple pressure generating device. The mechanism for generating pressure is mechanical screw precession, which can not only provide pressure, but also maintain the provided pressure for a long time to meet different testing requirements.

Based on the above measurement method and device, the present invention provides a simple micro-displacement measuring device. When one electrode of the sample box is fixed, it can accurately measure the displacement of the other electrode of the sample box under the action of pressure, thereby determining the displacement of the sample box. The volume change of a material under pressure.

The invention also provides the structural design and manufacture of a powder material sample box. The space it provides for containing samples should have a simple and regular geometry, and at the same time be able to withstand high pressure. The electrodes of the sample box should have good electrical conductivity, and the sleeve should have high electrical insulation.

Description of drawings

Accompanying drawing 1 resistivity changes curve with pressure.

Accompanying drawing 2 resistivity changes curve with material density.

Accompanying drawing 3 is the scanning electron micrograph of nickel powder in a natural state without any external pressure.

Accompanying drawing 4 is the scanning electron micrograph of nickel powder after 400 Newton pressure.

Accompanying drawing 5 is a schematic diagram of a powder metal material resistivity measuring device.

Accompanying drawing 6 is a schematic diagram of the structure of the sample box.

Accompanying drawing 7 is the schematic structural diagram of the pressure device.

In the accompanying drawings, 510 sample box, 520 pressure device, 530 micro-displacement test device, 531 vertical ruler, 532 slider, 533 rigid straight rod, 540 test bridge, 611 upper electrode, 612 insulating sleeve, 613 sample, 614 lower electrode, 721 rigid fixed block, 722 support, 723 screw rod, 724 slide block, 725 pressure gauge, 726 pressure transmission block, 727 handle wheel, 728 base.

Detailed ways

The method for measuring resistivity and conductivity provided by the invention is suitable for electrical performance evaluation of powder metal materials. The powdered metal material here refers to the smallest unit of the material—the characteristic size of the powder particles is in the range of nanometers to submillimeters, and the typical characteristic size is several microns. The shape, surface state and material density of these micron-sized particles directly affect the resistivity of the powder material. This makes it difficult to measure and evaluate the electrical properties of powder metal materials, and the conventional bulk material resistivity measurement methods and standards are no longer suitable for powder materials. The rapid development of powder technology and nanomaterial technology requires electrical performance testing methods suitable for their own characteristics. Through the test and research on the electrical properties of nickel powder, we propose that the use of resistivity-density curves can not only describe the electrical conductivity of nickel powder objectively, but also facilitate comparison. The present invention is produced on this basis, therefore, the measurement of resistivity-density curve is the core of the present invention.

When powdered metals are used, they are generally dispersed in colloids or other reagents or materials, and their particle morphology should remain unchanged. Therefore, various external effects applied to the sample when measuring its conductivity should ensure that the microscopic particle shape of the sample remains unchanged. This is a fundamental constraint of the measurement method provided by the present invention. In the present invention, the change of the sample density depends on the external pressure. We found in the test and research on the electrical properties of nickel powder that the pressure applied to the sample is within 400 Newtons, and the microscopic particle morphology of the sample does not change much. There are knots in some samples. group phenomenon. Figure 3 is a scanning electron micrograph of nickel powder in a natural state without any external pressure, and Figure 4 is a scanning electron micrograph of a sample of the same specification after being subjected to a 400 Newton pressure and then the external force is removed. Through a lot of comparison and observation, we determined the upper pressure limit used in the nickel powder resistivity test method to be 400 Newton. Figure 1 is the resistivity-pressure curve of nickel powder, and Figure 2 is the corresponding resistivity-density curve. It can be seen from the figure that the resistivity changes very slowly when the pressure is greater than 200 Newton, which shows that our pressure range is reasonable.

Fig. 5 is an example of a measuring device provided by the present invention, which consists of four parts such as a sample box (510), a pressure device (520), a micro-displacement testing device (530) and a test bridge (540). The sample box is the core component of the measuring device, which is used to place the measured powder metal sample. Figure 6(A) is a schematic diagram of its structure. It consists of an upper electrode (611), a lower electrode (614), an insulating sleeve (612) and a sample (613). The structures and materials of the two electrodes are the same, and they are processed into the shape shown in Figure 6(B) with a copper rod with good electrical conductivity. The cylindrical electrode has the same diameter as the inner diameter of the sleeve and slides freely within the sleeve. The disc of the electrode is mainly used to withstand and transmit pressure, and its diameter is not strictly regulated, generally the same as the outer diameter of the sleeve, and the thickness of the disc is preferably more than 10mm. The difference between the two electrodes is only the length of the electrode column. The electrode column length of the electrode (614) below is short, and the size can be taken as about 1/4 of the sleeve length; the electrode column of the upper electrode (611) is longer, and its The length is 0.8-1.2 times of the sleeve length. In fact, there are no strict regulations on the length of the electrode columns of the two electrodes, but the sum of the lengths of the two electrode columns should not be less than the length of the sleeve. The sleeve of the sample box can be made of ceramic or plastic with good insulating properties, and its shape is shown in Figure 6(C). The size of the inner and outer diameters of the sleeve can be selected according to the test needs. In this example, the inner diameter is selected as 10mm, and the outer diameter is selected as 30mm. The length of the sleeve is also determined according to the test needs, in this example, it is selected as 80mm. The sample to be tested (613) is placed between the upper and lower electrodes in the sleeve.

The pressure device (520) in FIG. 5 is used to provide pressure to the sample, and its structural schematic diagram is shown in FIG. 7 . It consists of a rigid fixed block (721), a bracket (722), a screw rod (723), a slider (724), a pressure gauge (725), a pressure transmission block (726), a handle wheel (727) and a base (728), etc. composition. The rigid fixed block and the bracket are rigidly fixed together, the helical shaft is helically connected with the slide block (724) through the rigid fixed block, and the handle wheel is rigidly connected with the helical shaft. The pressure gauge is rigidly connected with the slide block, and the pressure transmission block is rigidly connected with the pressure gauge telescopic rod. Turn the handle wheel, and the screw shaft will rotate accordingly, driving the slider to slide on the two vertical rods of the bracket. The pressure gauge moves up and down together, and the pressure is transmitted to the pressure transmission block through the expansion rod of the pressure gauge, and then acts on the sample box. When the handle wheel is turned to reach the desired pressure value, the pressure can be maintained all the time.

The micro-displacement testing device (530) in Fig. 5 is used to measure the displacement of the electrodes on the sample box. It consists of two parts, namely a vertical ruler (531) and a slide block (532) that can slide on the ruler, and the base (534), the pressure device and the sample box are rigidly fixed on the same base plate. A displacement sensor, a liquid crystal display (LCD) and operation buttons are arranged in the slider. A rigid straight rod (533) rigidly connects the sliding block and the telescopic rod of the square meter in the pressure device together. Any slight movement of the powder sample in the sample box under pressure (accuracy can reach 1 micron, in this case the precision is 10 microns) can be transmitted to the telescopic rod of the pressure gauge through the upper electrode of the sample box, and then rigidly driven The slider (532) of the displacement device moves to display on the LCD display. The micro-displacement testing device can also be any electronic or mechanical displacement testing device that meets the above requirements.

The resistance measuring instrument (540) in Fig. 5 is a precision electric bridge. It is any single or double arm DC bridge that meets the test accuracy requirements. The bridge in this example is a single and double arm DC bridge with an accuracy of 0.05. The two electrodes of the sample box are connected to the measuring terminal of the bridge, and the resistance of the connecting wire should be as small as possible.

The process of measuring the resistivity of the powder metal material with Fig. 5 measuring device provided by the invention is as follows:

1) After scrubbing the sample box (including electrodes and sleeves) with alcohol, short-circuit the two electrodes (do not put any sample in the sample box), and connect the connection with the bridge;

2) Adjust the pressure device so that the pressure at this time is at the critical point of zero pressure; adjust the displacement test device so that the displayed position reading is zero;

3) Change the pressure continuously, record the corresponding resistance value and the position coordinates of the upper electrode;

4) Release the pressure and take out the sample box;

5) Use a precision balance to weigh the mass of the powder sample to be tested, put the sample into the sample box, insert the upper electrode, and then put it on the pressure device;

6) Repeat step 3);

7) Data processing.

The above narration is only an exemplary implementation example of the present invention. It should be noted that the basic ideas and basic methods in the present invention can have multiple changes, and each change can be implemented, and they should be limited by the claims of the present invention .

Claims (1)

1. powder metallic resistance rate measurement mechanism, this measurement mechanism comprises: pressure apparatus, pressure gauge, test electric bridge and sample box are formed, be provided with upper and lower electrode in the sample box, top electrode transmits piece, manometric expansion link through pressure and is connected successively along axis with screw rod in the pressure apparatus, it is characterized in that:

A. set up the micro displacement testing device of forming by vertical ruler (531), slide block (532), rigidity straight-bar (533), base (534) (530) on the described measurement mechanism:

B. described slide block (532) is provided with displacement transducer, LCDs (LCD) and operation knob:

C. described base (534) is fixed on the base (728) of measurement mechanism, and slide block (532) is slidingly connected with vertical ruler (531), fixedlys connected with slide block (532) with manometric expansion link respectively in rigidity straight-bar (533) two ends.

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