Powder sintered metallic porous body, filter element and method for improving permeability thereof

Abstract

Disclosed are a powder sintered porous metal with better comprehensive properties, especially with good corrosion resistance to hydrofluoric acid, and a filter element using same. The powder sintered porous metal of the present invention has a porosity of 25-60%, an average pore diameter of 0.5-50 m and a weight loss rate of at most 1% after being immersed into a hydrofluoric acid solution with a mass fraction of 5% at room temperature for 20 days; and the powder sintered metal porous body consists of Cu accounting for 23-40 wt %, Si accounting for 0-5% and the balance of Ni, based on the weight of the powder sintered metal porous body. The powder sintered porous metal of the present invention has good mechanical properties and machinability, and excellent corrosion resistance in acid mediums, especially in hydrofluoric acid mediums. In particular surprisingly, when Cu and Ni are introduced into the powder sintered porous metal by Cu element powders and Ni element powders doped in the raw material powders, the powder sintered porous metal has significantly improved permeability and backflushing regeneration property.

Claims

1. A powder sintered porous metal: formed by sintering 23-40 wt % of elemental Cu powder together with 0-5 wt % of elemental Si powder and elemental Ni powder as the remaining at a temperature above a melting point of elemental Cu but below a melting point of elemental Ni so that the sintered porous metal has grains of elemental Ni sintered together by melted elemental Cu, the powder sintered porous metal having a porosity of 40-60% and an average pore diameter of 0.5-50 m; which is characterized in that, the powder sintered metal porous body consists of 23-40 wt % of elemental Cu powder, 0-5 wt % of elemental Si powder, and elemental Ni powder as the remaining, which has a weight loss rate of at most 1% after being immersed into a hydrofluoric acid solution with a mass fraction of 5% at room temperature for 20 days; and which has a tortuosity factor of 1.02-1.25, wherein the tortuosity factor is calculated using the formula $=\frac{D^2}{32KL},$ where represents the tortuosity factor, represents an open porosity of the porous body, D represents an average pore diameter, K represents a permeability, represents a fluid viscosity, and L represents a thickness of the porous body.

2. The powder sintered porous metal according to claim 1 is characterized in that, the powder sintered porous metal consists of 23-40 wt % elemental Cu powder and elemental Ni powder as the remaining, wherein the crystalline phase of the powder sintered metal porous body is a (Cu, Ni) solid solution.

3. The powder sintered porous metal according to claim 1 is characterized in that, the powder sintered porous metal contains 0.5-4 wt % of elemental Si powder.

4. The powder sintered porous metal according to claim 1 is characterized in that, the tortuosity factor of the powder sintered porous metal reaches at most 1.10.

5. The powder sintered porous metal according to claim 1 is characterized in that, the average pore diameter of the powder sintered porous metal is 1-20 m.

6. A method of making the sintered porous metal of claim 1, the method comprising: (a) mixing 23-40 wt % of elemental Cu powder of 250-+400 mesh, 60-77 wt % of elemental Ni powder of 200-+300 mesh, and up to 5 wt % of elemental Si powder with a particle size of 3-10 m to form a mixed powder; (b) granulating and drying the mixed powder at a drying temperature of 40-60 C. for 4-8 hours to form a dry mixed powder; (c) pressing the dry mixed powder with a pressure of 100-200 MPa for 20-80 seconds to obtain a compact sheet; (d) sintering the compact sheet in a sintering furnace in three stages: (i) a first stage comprising sintering at 400-450 C. for 120-180 minutes, with a first rate of temperature change being 5-10 C./min; (ii) a second stage comprising sintering at 750-850 C. for 120-240 minutes, with a second rate of temperature change being 5-10 C./min; (iii) a third stage comprising sintering at 1000-1200 C. for 180-300 minutes; with a third rate of temperature change being 3-5 C./min; (e) to form a sintered sheet; and (f) cooling the sintered sheet to form the sintered porous metal, wherein the sintered porous metal has a porosity between 40-60% and an average pore diameter of 0.5-50 m.

7. The method for making a sintered porous metal of claim 6 wherein the metal is resistant to corrosion, characterized by a weight loss of at most 1% after being immersed into a hydrofluoric acid solution with a mass fraction of 5% at room temperature for 20 days.

8. The method for making a sintered porous metal of claim 6 wherein the metal has a tortuosity factor of 1.02-1.25, wherein the tortuosity factor is calculated using the formula $=\frac{D^2}{32KL},$ where represents the tortuosity factor, represents an open porosity of the porous body, D represents an average pore diameter, K represents a permeability, represents a fluid viscosity, and L represents a thickness of the porous body.

9. The method of making a sintered porous metal of claim 8 wherein the metal has a tortuosity factor of at most 1.10, wherein the tortuosity factor is calculated using the formula $=\frac{D^2}{32KL}.$

10. The method of making a sintered porous metal of claim 6 wherein an average pore diameter of the sintered porous metal is 1-20 m.

11. A sintered porous metal comprising: 23-40 wt % of elemental Cu powder; 60-77 wt % elemental Ni powder; with a porosity between 40-60 wt %; and an average pore diameter of 0.5-50 m, wherein the sintered porous metal includes grains of elemental Ni powder sintered together by melted elemental Cu.

12. The sintered porous metal of claim 11 wherein the metal consists of 23-40 wt % of elemental Cu powder, 0.5-5 wt % of elemental Si powder, and 59.5-76.5 wt % elemental Ni powder.

13. The sintered porous metal of claim 12 wherein the metal is resistant to corrosion, characterized by a weight loss of at most 1% after being immersed into a hydrofluoric acid solution with a mass fraction of 5% at room temperature for 20 days.

14. The sintered porous metal of claim 11 wherein an average pore diameter of the powder sintered porous metal is 1-20 m.

Description

DETAILED EMBODIMENTS

(1) Hereinafter, the method for preparing the powder sintered metal porous body and the powder sintered metal porous body obtained by these methods are described in detail through experiments. Through these descriptions, a person skilled in the art can clearly recognize the prominent features owned by the powder sintered metal porous body of the present application. The numbers of experimental examples referred to hereinafter are in accordance with the numbers of the corresponding compacts and samples.

(2) 1 Materials Preparing Process

(3) As shown in Table 1, in order to describe the powder sintered metal porous body of the present invention and the preparation for same, the following two classes of experiments, that is, Experiment Class A and Experiment Class B, are prepared. Experiment Class A is divided into three groups of experiments, that is, A1, A2 and A3, and Experiment Class B is also divided into three groups of experiments, that is, B1, B2 and B3. The ratios of Cu to Ni are same in the raw materials of Experiment A1 and Experiment B1, and the difference is that, Experiment A1 adopts Cu element powders and Ni element powders, whereas Experiment B1 adopts CuNi alloy powders; the ratios of Cu, Ni and Si are same in the raw materials of Experiment A2 and Experiment B2, and the difference is that, Experiment A2 adopts Cu element powders, Si element powders and Ni element powders, whereas Experiment B2 adopts CuNi alloy powders and Si element powders; and similarly, the ratios of Cu to Ni are same in the raw materials of Experiment A3 and Experiment B3, and the difference is that, Experiment A3 adopts Cu element powders and Ni element powders, whereas Experiment B3 adopts CuNi alloy powders. In order to accurately reflect the value of the tortuosity factor of the powder sintered porous metal obtained by Experiment Class A, Experiment A1 includes three parallel experiments, that is, A1-1, A1-2 and A1-3, and the tortuosity factor of Experiment A1 will take the average value of the samples A1-1, A1-2 and A1-3; Experiment A2 includes three parallel experiments, that is, A2-1, A2-2 and A2-3, and the tortuosity factor of Experiment A2 will take the average value of the samples A2-1, A2-2 and A2-3; and similarly, Experiment A3 includes three parallel experiments, that is, A3-1, A3-2 and A3-3. As adopted in Table 1, the particle size of Cu element powders is 250+400 mesh, the particle size of Ni element powders is 200+300 mesh, the particle size of the Si element powders is 3-10 m, and the particle size of CuNi alloy powders is 200+300 mesh.

(4) TABLE-US-00001 TABLE 1 The components and content of the raw materials adopted in the experiments Experiment Class B Experiment Class A Materials Materials components components Experiment Cu element Si element Ni element Experiment CuNi alloy Si element Number powders powders powders Number powders powders A1 A1-1 25% x 75% B1 100% x A1-2 25% x 75% A1-3 25% x 75% A2 A2-1 30% 4% 66% B2 96% 4% A2-2 30% 4% 66% A2-3 30% 4% 66% A3 A3-1 40% x 60% B3 100% x A3-2 40% x 60% A3-3 40% x 60% Note: x represents free of the component.

(5) The raw materials of the experiments are mixed respectively according to that listed in Table 1. After thoroughly mixing, in order to prevent segregation, the raw material powders of each other experiments except Experiments B1 and B3 are granulated and then dried with a drying temperature set at 55 C. and drying time set for 6 hours. Next, the raw material powders of each experiment are respectively filled into isostatic pressing molds with a unified specification. Then, these molds are respectively positioned in a cold isostatic pressing machine and kept under a pressure of 100 MPa for 60 seconds, and the tubular compacts with corresponding numbers are then prepared after demolding. Next, these compacts are filled into sintering boats respectively, and these sintering boats are positioned into the sintering furnace for sintering and furnace cooled after sintering, and finally, the samples with corresponding numbers are taken out from each sintering boat.

(6) 1.1 the Sintering Schedule of Experiment Class A

(7) The sintering schedule of Experiment Class A includes the following three stages: the first stage: raising the sintering temperature from room temperature to 400-450 C., controlling the temperature-rising rate at 5-10 C./min, and keeping temperature at 400-450 C. for 120-240 minutes; the second stage: raising the sintering temperature to 750-850 C., controlling the temperature-rising rate at 5-10 C./min, and keeping temperature at 750-850 C. for 90-180 minutes; and the third stage: raising the sintering temperature to 1000-1200 C., controlling the temperature-rising rate at 3-5 C./min, and keeping temperature at 1000-1200 C. for 180-300 minutes. The powder sintered porous metal is then obtained by furnace cooling after sintering, wherein, the main purpose of the first stage is to degrease; the second stage is a medium temperature solid solution stage, and the main purpose is to promote the solid solution reaction between the elements; and the third stage is a component homogenization stage, and the main purpose is to obtain structure uniformity and final properties. The sintering procedure stated above can adopt inert gas-protecting sintering or vacuum sintering.

(8) The sintering process parameters of the three stages in the sintering schedule of Experiment Class A are shown in Table 2 in detail. In Table 2, the unit of temperature-rising rate is C./min, and the unit of sintering time is minute.

(9) TABLE-US-00002 TABLE 2 the sintering schedule of Experiment Class A The first stage The second stage The third stage Raising Time for Raising Time for Raising Time for Experimental temperature- temperature holding temperature- temperature holding temperature- temperature holding Number rising rate to ( C.) temperature rising rate to ( C.) temperature rising rate to ( C.) temperature A1 5 450 120 5 800 180 3 1150 120 A2 5 450 120 5 800 180 3 1150 120 A3 5 450 120 5 800 180 3 1150 120

(10) 1.2 the Sintering Schedule of Experiment Class B

(11) The sintering schedule of Experiment Class B is relatively simpler (due to adopt the alloy powders), and is specifically gradually raising the sintering temperature from room temperature to 1200 C., controlling the temperature-rising rate at 5 C./min, and keeping temperature at 1200 C. for 2 hours.

(12) 2 Materials Properties Measurements

(13) All of the crystalline phases of Sample A1 (comprising A1-1, A1-2 and A1-3), Sample A2 (comprising A2-1, A2-2 and A2-3), Sample A3 (A3-1, A3-2 and A3-3), Sample B1, Sample B2 and Sample B3 are (Cu, Ni) solid solutions. Si is interstitially solid dissolved in the CuNi alloy. Thus, the tensile strength of these samples is higher, and can substantially reach at least 80 MPa.

(14) The pore structure measurement results of these samples stated above are shown in Table 3. In Table 3, the unit of thickness is mm, the unit of open porosity is %, the unit of average pore diameter is m, the unit of porosity is %, and the unit of permeability is (10.sup.5.Math.m.sup.3.Math.m.sup.2.Math.s.sup.1.Math.Pa.sup.1). The measurements of the porosity, the open porosity, and the average pore diameter of the materials adopt the bubbling method; and the permeability specifically is nitrogen (20 C.) flux on a filtering area of 1 square meter under a filtration pressure difference of 1 pa for 1 second.

(15) <As for Tortuosity Factor>

(16) 1) The definition of the tortuosity factor:

(17) $\begin{array}{cc}=\frac{L^{}}{L}& \left(1\right)\end{array}$

(18) wherein, L is the material thickness, L is the shortest distance through which the fluid flows over the porous medium.

(19) 2) The Characterization Means for the Tortuosity Factor:

(20) On the basis of the Darcy law, Kozeny law and Hagen-poiseuille law, it is concluded the quantitative relationship between the tortuosity factor and the relevant pore structure parameters (laminar flow process):

(21) $\begin{array}{cc}K=\frac{D^2}{32L},& \left(2\right)\end{array}$

(22) thereby obtaining

(23) $\begin{array}{cc}=\frac{D^2}{32KL}& \left(3\right)\end{array}$

(24) wherein, is the open porosity of the porous material (%), D is the average pore diameter (m), K is the permeability (m.sup.3.Math.m.sup.2.Math.s.sup.1.Math.Pa.sup.1), L is the material thickness, and is the fluid viscosity (Pas).

(25) The data of the thickness, open porosity, average pore diameter, permeability and fluid viscosity are obtained, and then the tortuosity factor can be obtained according to the equation (3). The fluid viscosity is calculated according to Nitrogen fluid viscosity at 20 C.

(26) TABLE-US-00003 TABLE 3 the measurements of the pore structures of the samples Experiment Class A Experiment Class B Average Average Item Thick- open pore Perme- Tortuosity Item Thick- open pore Perme- Tortuosity Number ness porosity diameter Porosity ability factor Number ness porosity diameter Porosity ability factor A1 A1-1 1.33 33.7 12.33 45 5.58 1.23 B1 1.68 27.5 12.3 35 3.18 1.67 A1-2 1.57 33.9 13.67 48 6.49 1.10 A1-3 1.60 33.5 11.80 43 4.63 1.13 A2 A2-1 1.73 38.5 12.93 51 5.71 1.13 B2 1.75 28.2 11.8 36 3.44 1.58 A2-2 1.84 39.0 11.53 52 5.78 1.12 A2-3 1.99 37.0 12.1 50 5.50 1.13 A3 A3-1 2.15 43.6 12.3 56 6.47 1.11 B3 1.60 26.8 13.2 34 3.19 1.62 A3-2 2.29 44.5 12.7 57 6.60 1.12 A3-3 1.81 42.7 12.42 55 6.33 1.14

(27) All of the corrosion resistance measurement results of Sample A1 (comprising A1-1, A1-2 and A1-3), Sample A2 (comprising A2-1, A2-2 and A2-3), Sample A3 (comprising A3-1, A3-2 and A3-3), Sample B1, Sample B2 and Sample B3 are shown in Table 4, wherein, the corrosion resistance 1 is specifically characterized by the weight loss rate after being immersed into a hydrofluoric acid solution with a mass fraction of 5% at room temperature for 20 days; and the corrosion resistance 2 is specifically characterized by the weight loss rate after being immersed into a hydrofluoric acid solution with a mass fraction of 5% (further containing 0.1-0.5 mol/L of Fe.sup.3+ in the solution) at room temperature for 20 days.

(28) TABLE-US-00004 TABLE 4 the corrosion resistance measurement results of the samples Experiment Class A Experiment Class B Item Item Corrosion Corrosion resistance Corrosion resistance Corrosion Number 1 resistance 2 Number 1 resistance 2 A1 A1-1 0.73 0.83 B1 0.76 0.85 A1-2 0.72 0.85 A1-3 0.74 0.88 A2 A2-1 0.55 0.54 B2 0.56 0.55 A2-2 0.53 0.52 A2-3 0.52 0.55 A3 A3-1 0.75 0.85 B3 0.77 0.87 A3-2 0.72 0.84 A3-3 0.73 0.86

(29) As shown in Table 4, the weight loss rates of all samples after being immersed into the hydrofluoric acid solution with the mass fraction of 5% at room temperature for 20 days are below 1%; and when the sample contains Si, not only are better properties exhibited by the indicator of corrosion resistance 1, but also excellent properties are exhibited by the indicator of corrosion resistance 2 (oxidizing medium system). The present invention suggests that the preferable Si content should be 2%, 2.5%, 3% or 4%.