RU2311470C2 - Method of production of high-porous nickel and its alloys - Google Patents

Abstract

FIELD: powder metallurgy; production of high-porous permeable cellular materials.

SUBSTANCE: proposed method includes preparation of nickel powder suspension or mixture of powders for production of alloy in aqueous solution of polyvinyl alcohol. This suspension is applied on substrate made from porous polymer material for forming the blank which is dried and subjected to heat treatment at temperature not below 160°C. Blank is placed in between non-conducting shields and electrochemical deposition of nickel from electrolyte is carried out by reversing the current. Polyvinyl alcohol and substrate are removed by thermal destruction. Blank is sintered during period of time ê_s³1.08(θd)²/D, where ê_s is sintering time, h; 1.08 is constant; θ is relative density of high-porous alloy thus produced; d is average diameter of cells of porous polymer material, mm; D is diffusion coefficient of powder mixture component which possesses minimum fluidity in galvanically deposited metal at sintering temperature, cm²/s.

EFFECT: high porosity of material and homogeneous structure in area and in depth.

5 cl, 3 dwg, 1 tbl, 1 ex

Description

The invention relates to metallurgy, in particular to methods for producing highly porous permeable cellular materials (HPMP) or alloys having specific properties inherent in these alloys.

Currently, there are five fundamentally different methods for producing HPLM with a porosity of 80-99% using polyurethane foam (PPU) substrates as a primary basis: foundry, gas-phase, chemical, galvanic, suspension (slip) using suspensions of dispersed metal powders.

The essence of the galvanic method of producing HPLM consists in the electrolytic reprecipitation of metal from compact metal anodes onto prepared polyurethane foam plates with a previously created conductive layer. The galvanic method of producing HPLM is one of the most economical and productive. Therefore, it is most common. The advantages of the method should also include the possibility of obtaining plates of HPLM large area, with a thickness depending on the diameter of the cells of the foam. The disadvantages of the method include the impossibility of directly producing alloys of a given composition, the heterogeneity of the coating thickness both in the thickness of the HPLC sheet (in the inner parts the density is less than in the outer ones) and in area (on the peripheral parts the density is greater than in the central regions of the plates).

A known electrochemical method for producing porous cellular nickel and its alloys (USSR Author's Certificate No. 1366294, class B22F 5/00, dated 1986), comprising applying a thin layer of nickel to a substrate of a porous polymeric material to form a preform, deposition on it by the electrochemical method nickel or another metal to obtain an alloy, by cyclically alternating the processes of deposition and dissolution of this metal, while the current is reversed at a ratio of the deposition current density to the dissolution current density I am as 0.3 ÷ 0.5 and with a ratio of the duration of the precipitation process to the duration of the dissolution process as 5 ÷ 7.

The advantage of the known method is that the use of a current reverse reduces the density heterogeneity of porous nickel and its alloys along the depth of the obtained plate, however, even with a tight fit of the HPLM blank to the walls of the galvanic bath, an increased density at the edges of the formed nickel plate is obtained and, as a result , uneven distribution of pores over the area and volume of the plate.

Closest to the proposed invention is a method for producing highly porous material (RF Patent No. 2002580, class B22F 3/10, dated 1993), comprising preparing a suspension of metallic nickel powder in an aqueous solution of an organic substance - polyvinyl alcohol, applying the suspension to a substrate from a porous polymeric material to form a preform, drying the resulting preform, its subsequent heat treatment at a temperature of at least 160 ° C, applying to it by electrochemical deposition of nickel or rugogo metal if necessary alloying, subsequent thermal degradation to remove the organic substance and the substrate, and sintering.

However, this known method does not ensure the production of nickel and its alloys with a high degree of homogeneity, since the density distribution of the galvanic deposit and all the resulting HPLC over the area and depth of the plate is not uniform. In addition, the known method does not allow to obtain high-quality HPLC with a larger cell size.

The technical result achieved by the invention is to increase the uniformity of the obtained material, namely nickel and its alloys, in density and composition, as well as in area and depth, while ensuring the production of porous material with increased porosity.

The specified technical result is achieved by the proposed method for producing highly porous alloys by preparing a suspension of metal powder — nickel, in an aqueous solution of an organic substance — polyvinyl alcohol, applying the suspension to a substrate of porous polymeric material to form a preform, drying the resulting preform, and subsequent heat treatment at a temperature not lower than 160 ° C, applying to it by electrochemical deposition of nickel or another metal, if necessary irradiation of the alloy, followed by thermal degradation to remove organic matter and the substrate, and sintering, while new is that before the electrochemical deposition of the workpiece is placed between current-conducting screens, and deposition of nickel or another metal on the workpiece by electrochemical deposition of the nickel or other metal is carried out by reversing the current, while sintering is not less than the value calculated by the formula

τ _c = ≥1.08 (θd) ² / D, where

τ _s - sintering-homogenization time, h;

1.08 is a constant,

θ is the relative density of the obtained highly porous alloy;

d is the average cell diameter of the PUF, mm;

D is the diffusion coefficient of the least mobile component of the powder mixture of the workpiece in a galvanically deposited metal at a sintering-homogenization temperature, cm ² / s.

As the substrate of a porous polymeric material, a substrate of polyurethane foam is used.

The mass ratio of the mass of metal powder in suspension and Nickel or other metal deposited on the workpiece by electrochemical deposition is 1: 1.

As non-conductive screens, plastic U-shaped screens are used.

The current is reversed at a ratio of the deposition current density to the dissolution current density of 0.5 ÷ 0.75 and with a ratio of the duration of the deposition process to the duration of the dissolution process as 6 ÷ 7.5.

Due to the fact that before the electrochemical deposition, the workpiece is placed between the current-conducting screens, which can be made in the form of ordinary plates or U-shaped plates, the excessive supply of metal to the workpiece is prevented, which means that its uneven density at the edges of the highly porous material is eliminated.

Due to the fact that electrochemical deposition is carried out by reversing the current, an increase in the uniformity of the resulting material in density and composition is achieved.

Due to the fact that the sintering time is not less than the value calculated by the formula τ _c = ≥1.08 (θd) ² / D, the process of homogenization of the material in the entire volume is completed, which means that it will be characterized by uniformity both in depth and by area.

Due to the fact that during the implementation of the proposed method, the workpiece is subjected to reverse current in the presence of non-conductive screens that provide a kind of protection both to the ends of the workpiece and partially to the upper and lower parts of the workpiece adjacent to the ends, it is possible to obtain homogeneous nickel or its alloys even when using a highly porous substrate (with an average cell diameter of more than 1 mm).

Due to the fact that the current is reversed at a ratio of the deposition current density to the dissolution current density of 0.5–0.75 and with a ratio of the deposition process duration to the duration of the dissolution process of 6–7.5, a more uniform galvanic deposit is formed on the formed plate by area and depth. These parameters are optimal, the method is feasible with other values.

Due to the fact that a substrate of polyurethane foam is used as a substrate of a porous polymeric material, the formation of pores of a given size (diameter) is achieved.

Due to the fact that the mass ratio of nickel and metal deposited on the workpiece by electrochemical deposition is 1: 1, the optimum performance of the resulting material in terms of uniformity, area and depth is ensured.

When implementing the proposed method, the following operations are performed in the specified sequence:

- prepare a suspension of nickel powder in an aqueous solution of an organic substance - polyvinyl alcohol;

- apply a predetermined amount of the specified suspension on a substrate of a porous polymeric material, for example, polyurethane foam;

- dry the resulting workpiece;

- the dried billet is thermally treated at a temperature not lower than 160 ° C;

- carry out the activation of the workpiece;

- then an electroconductive layer is created on it by chemical deposition;

- place the workpiece between the non-conductive screens, which use either ordinary or U-shaped screens made of a polymeric material, for example, plexiglass, so that they are in contact with the ends of the workpiece;

- correlate by weighing the mass of nickel and metal (it may be nickel or another metal, if an alloy is obtained) applied to the workpiece by electrochemical deposition, so that this ratio is 1: 1,

- another metal is deposited onto the workpiece by electrochemical deposition by reversing the current, with a ratio of the deposition current density to the dissolution current density of 0.5 ÷ 0.75 and with a ratio of the duration of the deposition process to the duration of the dissolution process as 6 ÷ 7.5;

- produce thermal degradation, while removing the substrate;

- calculate the sintering time according to the formula τ _c = ≥1.08 (θd) ² / D,

- and produce sintering, as a result of which material of a given composition (nickel and its alloys) is obtained.

The proposed method is illustrated by drawings, where figure 1 shows the layout of the screens relative to the workpiece; figure 2 is a three-dimensional graph of the distribution of electrolytic nickel in width and height of the HPMP plate obtained by a method known in the prior art; figure 3 is a three-dimensional graph of the distribution of electrolytic Nickel in width and height of the HPM plate obtained by the proposed method.

The proposed method was tested in experimental production.

An example of obtaining a highly porous alloy of nichrome X25H75.

First, a suspension of a given relative density of 0.07-0.1 is prepared from a mixture of chromium powder of the PHS-1 brand and carbonyl nickel powder in a 1: 1 weight ratio in a 7% solution of polyvinyl alcohol based on the content of the powder mixture in the workpiece by weight of component 1 / 2 finished product.

Put on a substrate (polyurethane foam with an average cell diameter of 0.85-3.2 is used as an organic cellular substrate) a predetermined amount of suspension, the amount of which is controlled by weighing the substrate when applying the suspension. Get the workpiece for further processing. Next, the resulting preform is dried in a heating cabinet at a temperature of 160 ° C for 30-60 minutes. The dried preform is cooled at room temperature. Then the preform is immersed for 15 min at room temperature in an activation solution containing:

PdCl ₂ - 0.5 g / l

HCI - 5.0 ml / L.

The subsequent imparting electrical conductivity to the activated billet is carried out by deposition on it for 30 minutes a thin (1 μm) layer of nickel from a chemical nickel plating solution of the following composition, g / l:

NiSO ₄ · 7 H ₂ O - 28 Na ₄ P ₂ O ₇ · 10 H ₂ O - fifty NH ₄ OH - twenty NaH ₂ PO ₂ · H ₂ O - 25

Next, the workpiece 1 (according to figure 1) is placed between the non-conductive screens 2, for example, U-shaped, so that these screens, made, for example, of plexiglass, touch the ends 3 of the workpiece 1. But at the same time, the U-shaped edges of the screens overlap ("cover") the edges of the workpiece with indentation from it with shelves 4 approximately 1.5-3.0 cm

The required amount of Nickel, calculated from the need to obtain a nichrome alloy containing 25 wt.% Chromium, is deposited on a workpiece surrounded by current-conducting screens from an electrolyte containing, g / l:

NiCl ₂ · 6 H ₂ O - 160 NaCI - 120 NH ₄ CI - thirty H ₃ IN ₃ - 28

Electrochemical deposition is carried out at an overall deposition current density of 1.5 A / dm ² , with a cyclic alternation of the deposition and dissolution of the metal coating by reversing the current at a ratio of the deposition current density to the dissolution current density of 0.5 ÷ 0.75 and with respect to the duration the precipitation process to the duration of the dissolution process of 6 ÷ 7.5.

The removal of organic matter and the substrate is carried out by gradually heating, for 3 hours, the specified preform in a furnace with a hydrogen atmosphere to 650 ° C, with exposure at this temperature for 30 minutes.

Sintering of the alloy is carried out by gradually heating, for 3 hours, the workpiece in a vacuum furnace to a temperature of 1250 ° C, with exposure at this temperature for a sintering time corresponding to that calculated by the formula τ _c = ≥1.08 (θd) ² / D, Where

τ _c - sintering-homogenization time, h;

1.08 is a constant,

θ is the relative density of the obtained highly porous alloy;

d is the average cell diameter of the PUF, mm;

D is the diffusion coefficient of the least mobile component of the billet powder mixture in a galvanically deposited metal at a sintering-homogenization temperature, cm ² / s (the values of the diffusion coefficients of the alloying elements from the powder layer into the galvanically deposited matrix metal layer are calculated using reference data).

Data on the homogeneity of highly porous nichrome obtained by the proposed and known methods are shown in the table.

The results shown in the table show that

- the proposed method (examples 1, 3, 4) allows to obtain a homogeneous Nickel alloy, which is characterized by high uniformity in area and depth; and at the same time, a high porosity of the obtained alloy is ensured (average cell diameter up to 3.2 mm);

- analysis of the microstructure and ferromagnetism showed that the obtained nichrome alloy, according to both the proposed method and the one known from the prototype, corresponds to the electrical conductivity and scale resistance of nichrome and there are no sections with a chromium content of less than 6-7% (in which the alloy becomes non-ferromagnetic);

- HPLC from examples 2 (without using screens) and 5 (sintering time does not correspond to the calculated one, but is lower) do not have the properties of nichrome and they do not have homogeneity.

Thus, after analyzing the manufacturing results of the inventive method of highly porous nichrome shown in the table, we can conclude that a positive result, i.e. the homogeneity of the nickel alloy is achieved when the actual sintering time corresponds to the calculated one, as in examples 1, 3 and 4 of the table, and during all operations in the stated sequence.

A comparison of the structure homogeneity of highly porous nickel obtained by various methods is shown in FIG. 2 and FIG. 3. Figure 2 shows a three-dimensional graph of the distribution of electrolytic nickel in width and height of the HPMP plate obtained by a method known in the prior art; figure 3 is a three-dimensional graph of the distribution of electrolytic Nickel in width and height of the HPM plate obtained by the proposed method. It is obvious that the nickel obtained by the proposed method is characterized by the uniformity of the structure, including along the edges and in volume.

Thus, highly porous nickel and its alloys obtained by the proposed method meet all the requirements for HPLC.

Table
Data on the homogeneity of highly porous nichrome obtained by the proposed and known methods (preparation of a highly porous nichrome alloy (Cr 25%, Ni 75%), Cr diffusion coefficient in Ni at 1250 ° С D _Cr-Ni = 4.97 · 10 ^-10 cm ² / s; at 1200 ° С 2.39 · 10 ^-10 cm ² / s K = 1.08) Example Number Relative density, θ The average cell diameter d, mm Sintering temperature T _cn ° C The diffusion coefficient of Cr in Ni D _Cr-Ni , cm ² / s Sintering time T, hour Estimated sintering time τ ₁ · hour Alloy homogeneity one 0,07 3.2 1250 4.97 · 10 ^-10 3.0 2,8 + 2 0.10 3.2 1250 4.97 · 10 ^-10 3.0 5.71 - 3 0.10 3.2 1250 4.97 · 10 ^-10 6.0 5.71 + four 0,071 1,2 1250 4.97 · 10 ^-10 0.5 0.405 + 5 0,071 1,2 1250 4.97 · 10 ^-10 0.25 0.405 - Known method 0,071 0.85 1200 2.3910 ^-10 3.0 0.423 +

Claims (5)

1. A method of producing highly porous nickel or an alloy thereof, comprising preparing a suspension of a metal powder in an aqueous solution of polyvinyl alcohol, applying a suspension to a substrate of porous polymeric material to form a preform, drying, heat treatment at a temperature of at least 160 ° C, electrochemical deposition of nickel from an electrolyte thermal degradation to remove polyvinyl alcohol and the substrate and sintering, characterized in that in the preparation of the suspension as a metal powder using a powder nickel or a mixture of powders to obtain an alloy preform prior to electrochemical deposition screens placed between non-conducting, electrochemical deposition is carried out by reversing the current, and sintering is carried out for a time determined by the formula τ _s ≥1.08 (θd ² ) / D, where τ _s is the sintering time, h; 1.08 is a constant; θ is the relative density of the obtained highly porous alloy; d is the average cell diameter of the porous polymeric material, mm; D is the value of the diffusion coefficient of the least mobile component of the powder mixture in a galvanically deposited metal at a sintering temperature, cm ² / s. 2. The method according to claim 1, characterized in that polyurethane foam is used as the porous polymeric material. 3. The method according to claim 1, characterized in that the amount of nickel is deposited on the preform so that the mass ratio between it and the amount of metal powder in the suspension is 1: 1. 4. The method according to claim 1, characterized in that as a non-conductive screens use plastic plate U-shaped. 5. The method according to claim 1, characterized in that the current is reversed when the ratio of the deposition current density to the dissolution current density is 0.5-0.75 and the ratio of the duration of the deposition process to the duration of the dissolution process is 6-7.5.

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