The present invention belongs to the field of preparing metal porous materials. It provides a new process for preparing hollow nickel fiber mats with high porosity.
A new method of preparing hollow nickel fiber mat
Metal porous materials are usually made of metal powder by pressing (rolling) and sintering. However, due to the few contact points between the powders, making a high porosity material leads to relatively low mechanical properties. In order to produce highly porous metal materials with good mechanical properties. A variety of processes for making porous materials from metal fibers have been developed in recent years. As a result of using microfine metal fibers to make porous materials, the mechanical properties of porous materials can be improve by increasing the contact points between the independent components of the materials. The key to solving this problem is the development of technically feasible. And economically inexpensive processes for preparing metal fibers. and for felting the fibers by rational molding and sintering.
The current methods of producing metal fibers are drawing, extrusion, grinding (Japanese patent Akira 47-37804), spinning (Japanese patent Akira 47-26980) and vibration cutting. All of these methods are more complex in process. And having higher energy consumption, or are difficult to produce uniform metal fibers of micron diameter. Thus limiting the application of fiber porous metal materials to some extent.
The purpose of the present invention is to overcome the shortcomings of the existing technology. And develop a new method for preparing nickel composite fibers and making high porosity nickel fiber mats suitable for industrial production.
To achieve the above purpose, the invention puts the natural (or artificial) fiber in NH3-(NH4)2SO4-NiSO4-H2O system, carries on the hydrogen reduction under pressure, deposits the metallic nickel on the fiber to make the nickel composite fiber. Then uses the organic binder to bond the nickel composite fiber to make the blank. After decarburization, rolling (or pressing), sintering to make the nickel felt.
The natural (or artificial) fibers are place in NH3-(NH4)2SO4-NiSO4-H2O system. In which the nickel concentration is controll to be 10-120 g/L, ammonium sulfate concentration to be 100-200 g/L, [NH3]:[Ni++] ≥ 2.0-2.2:1, temperature 140°-180°C. Hydrogen partial pressure 15-40 kg/cm2, stirring speed 300-600 rpm. And then hydrogen reduction was carry out to reduce the nickel-ammonia complex ions in the solution to metal deposited on the fibers.
When the concentration of nickel ions in the system is too high, the viscosity of the liquid phase is too high, which is not conducive to the uniform deposition of metallic nickel on the fiber. Too low concentration makes the process inefficient. Free ammonia and nickel ions to form nickel-ammonia complex ions to facilitate the smooth progress of the reduction reaction. Too much ammonia, the reaction process, NH3/Ni++ ratio increases. And finally the reduction reaction is terminate and the reaction is incomplete; such as when the amount of ammonia is not enough, the reaction process. The system PH value drops too much, and finally the reduction reaction is also terminated and the reaction is incomplete.
In order to speed up the reaction speed of hydrogen reduction and control the free nickel powder as well as the uniformity of the nickel layer on the surface of the composite fiber. Nucleating agents (or surface activators) such as Fe++, Cr++, Sn++, Pd++, etc. are used to treat the fiber. The amount of which depends on the activity of the fiber surface on the hydrogen reduction reaction, usually in the range of 0.01-1.0%.
What is the composit of nickel fibers?
The nickel composite fibers are modulat with organic binder into a slurry and made into nickel felt blanks by decompression settling method or centrifugal settling method, etc. The polymer binder can be hydroxymethyl cellulose, polyvinyl alcohol, starch, etc.
In order to make a pure nickel felt, the binder and the chemical (or natural) fibers in the composite fiber need to remove, therefore, the blanks need to be decarburized by high-temperature gasification in the range of 450-1100°C for 60-240 minutes.
In order to achieve the desired porosity and thickness, a pressing or rolling process required. Felt that has been roll (or pressed) has nickel fibers intermittently increasing many contact points. To increase the mechanical strength of the nickel fiber mats, sintering in a reducing atmosphere is required at temperatures of 1000-1220°C for 30-60 minutes. The porosity of the produced nickel mat is in the range of 50-94%.
A new type of metal porous material
Nickel metal fiber mat is a new type of metal porous material, which can be further alloy into nickel alloy fiber mat. Nickel and its alloy fiber mats have special applications in the aerospace and aviation industries. They can be manufactured for high, medium. And low temperatures and different types of heat pipe pistons. They can be manufacture for gas turbine engine turbine radial clearance, compressor blade tip gap wear sealable bushings. And other parts of the sealing material. Thereby improving engine performance.
These materials are very compatible with each other in terms of ligation, erosion resistance and wearability. High porosity nickel fiber mats can be use as electrode substrates to develop alkaline batteries with light mass, high specific energy. And long cycle life, especially Ni-Cd, Ni-H2 batteries are ideal for power supply in aerospace technology. It can also be use to manufacture filters, catalysts, catalyst carriers, self-lubricating bearings. And heat and sound insulation materials at high temperatures.
This process can produce nickel composite fibers with diameters of several microns (or tens of microns). And prepare hollow nickel fiber mats with thicknesses of 0.5-4.0 mm and porosity of 50-94%.
How to make:
60 g of degreased chemical fiber, aqueous sensitization with SnCl2 hydrochloric acid and activation with 120 mg of PdCl2 ammonia solution. Weigh 1620 g of nickel sulfate, 900 g of ammonium sulfate, dissolve with 4.5 liters of pure water. Adding 910 ml of concentrated ammonia, put together in a pressurized reactor. And at a temperature of 155-160°C, pH 225-30 kg/cm2, stirring speed 450- 500rpm.
And the reaction was carry out for 35 minutes under the conditions to obtain nickel composite fiber.
The prepared nickel composite fibers were blend with 1% hydroxymethyl cellulose aqueous solution to form a slurry. Made into pre-determined area of felt blanks by the reduced pressure settling method. It left to dry and then placed in a sintering furnace for decarburization. Heated under hydrogen atmosphere at 1050°C for 200 minutes.
The decarburized nickel felts are roll to the desired thickness. Then placed in a furnace with pure hydrogen atmosphere and sintered at 1100°C for 40 minutes. Hollow nickel fiber mats with 85% porosity, 1.0 mm thickness and 110-120 kg/cm2 tensile strength were produce.