JPS5993867A - Production of needle iron - Google Patents

Abstract

PURPOSE:To produce needle iron which has high saturation magnetization and coercive force, is highly resistant to weather and is easy to handle by flowing a gaseous mixture composed of FeCl3 and H2 heated to evaporate under the reduced pressure over a substrate and depositing needle Fe. CONSTITUTION:FeCl3 is put in the boat 5 in a furnace core tube 2 for reaction and the boat is placed in the place corresponding to a heater 3. A substrate 6 made of Mo for deposition is placed in the place corresponding to a heater 4, and the air in the tube 2 is discharged by using a rotary pump 7. The heater 3 is heated to 300-500 deg.C and the heater 4 to 600-1,200 deg.C, respectively. The valve 8 of a hydrogen supply cylinder 1 is opened to flow gaseous hydrogen, so that the decomposition reaction for depositing needle iron is induced over the substrate 6. The valve of the pump 7 is regulated during the reaction to maintain the reduced pressure in the tube 2. The heaters 3, 4 are switched off upon ending of the reaction, and the substrate 6 is removed after the furnace temp. is lowered. The deposited iron whiskers are recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing needle iron capable of high-density recording.

Conventional groove formation and its problems Most magnetic powders for magnetic tapes and magnetic disks currently in practical use use acicular particles of γ-Fe2O3 (maghemite). However, in recent years, as magnetic recording and reproducing equipment has become smaller and lighter, demands for higher performance recording media have been increasing. In other words, high-density recording,
Improvements in commercial strength and frequency characteristics are required.

In order to satisfy the above requirements in a magnetic recording medium, the characteristics of a magnetic material required are large saturation magnetization and high coercive force. By the way, in addition to the above-mentioned γ-Fe2O3 (maghemite), magnetic materials conventionally used in magnetic recording media include magnetic powders such as magnetite (Fe304) and chromium dioxide (Cr02). The magnetization (C5) is at most gOemu/y and the coercive force (HC) is at most 5000e (Oersted), which limits the reproduction output and recording density in magnetic recording media using these magnetic powders.

Furthermore, the Co-γ-Fe203 magnetic powder containing C9 has a high coercive force (Hc) of 8000e, but the saturation magnetization (C5) is low at 60 to 80 emu/p, which also affects the reproduction output and This puts a limit on recording density. Recently, there has been active development of magnetic particles having characteristics suitable for Takada power and high-density recording, that is, magnetic powders having large saturation magnetization and high coercive force. As a material having such characteristics, there is an acicular magnetic powder mainly composed of iron (Fe). For FeO acicular magnetic powder, C5 is 150 emu
/f and Hc of about 12000c can be obtained, making it possible to create a medium with high reproduction output and high recording density. F
Conventionally used methods for obtaining acicular particles of e are as follows: (1) Iron oxide reduction method, that is, a method in which acicular iron oxide powder is reduced in a reducing gas to obtain iron powder.

(b) Borohydride method, a method in which iron salts (e.g. ferrous sulfate) are reduced in an aqueous solution using sodium borohydride as a reducing agent.

etc. The magnetic powder obtained by these conventional methods has the following drawbacks. All iron particles obtained by these methods are susceptible to oxidation. In particular, if the powder after the reaction is suddenly taken out into the air, it may react with oxygen in the air and cause a fire. It must be mixed and dispersed with resins, higher fatty acids, etc., without coming into contact with them. In addition, the iron particles obtained by this method have various defects introduced during the reduction of iron oxide and the precipitation process in an aqueous solution, resulting in an iron particle of 150 emu//, which is lower than the theoretical saturation magnetization of iron σs-5-218e//cc.
. . It's only about 12 ooo
The weather resistance is also poor (σS in the moisture resistance test).
(mainly due to oxidation).

Purpose of the Invention The present invention solves the above-mentioned conventional drawbacks.The present invention has acicular shape of particles, has high saturation magnetization and high coercive force, has few defects, is highly weather resistant, and can be easily immersed in air. The purpose is to provide a method for producing reusable magnetic powder (acicular iron).

Structure of the Invention In order to achieve the above object, the method for producing needle iron of the present invention involves heating and vaporizing a mixed gas of iron chloride and hydrogen at 800'0-500'C in reduced pressure at 600'GK]200
After the iron is poured onto a substrate heated with C to precipitate needle-shaped iron, the needle-shaped iron is recovered from the substrate.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on the drawings. The present invention aims to obtain acicular iron powder by a gas phase method. That is, iron needle crystals (whiskers) are precipitated on a substrate by the following chemical reaction, and then the iron needle crystals are collected to form magnetic powder.

2FeC7?3+ 8H2-> 2Fe+ 6l-IC
! ! -■Here, FeC1!3 is ferric chloride (FeC1!
2 is also possible), H1! Is hydrogen, HCJ? is hydrogen chloride. This reaction usually occurs at normal pressure and at a temperature of 600°C or higher, and various crystal forms can be obtained depending on the flow rate of FcCJ3 or IH2, the atmospheric pressure of the entire reactor, the temperature of the substrate, etc. The reaction involved is a reduction-precipitation reaction of chloride, resulting in highly pure crystals with few defects. In particular, whiskers are said to be nearly defect-free. Next, an example of the basic structure of an apparatus for producing acicular iron powder will be explained with reference to the drawings. In the figure, (1) is a hydrogen supply cylinder, (2) is a reactor core tube (made of quartz), (3) is a heater for FeC1!2 evaporation, (April, heater for iron needle crystal precipitation reaction, (5) contains FeC1!3 board 1- (manufactured by Imo), (6
) is a substrate for acicular iron precipitation, (7) is a rotary pump for exhaust and pressure adjustment, and (8 is a valve.) First, FeCl3 is poured into the boat (5) in the reaction furnace tube (2). is placed in the heater (3).Next, the molybdenum precipitation substrate (6) is placed in the heater (4), and the rotary pump (7) is used to pump the inside of the reaction furnace tube (2). Exhaust the air and turn the heater (3) to 800℃~550''O.
4) respectively to 600'C to 1200'0, open the valve (8) of the hydrogen supply cylinder (1) and add hydrogen to 100C.
C/min to xt/min to cause a precipitation and decomposition reaction of needle iron on the substrate (6). During the reaction, adjust the valve (8) of the rotary pump (7) to a pressure of 10 Torr to 20 Torr.
Set it to 0 Torr. Heater after reaction (3) (4)
8oo and remove the base (6) after the temperature of the furnace has decreased.
Below ``C, the vapor pressure of FeC1!3 is low, so Fe
Cl! This is because the flow rate of No. 3 is low and iron is difficult to precipitate on the substrate (6). Also, the temperature below 550”C is 55
When the temperature exceeds 0℃, FeCl! This is because the amount of evaporation of 3 becomes too large, making it difficult to obtain needle-shaped crystals on the substrate (6).
(prone to granular FC). Hydrogen flow rate 100Cc/
1 t/min is F for 100 ccZ min or less.

This is because the precipitation rate of II! This is because it is difficult to obtain high-quality acicular crystals when the heating time exceeds 1/min (grainy Fe tends to form). Set the temperature of the heater (4) to 600°C to 1200'
C! This is because acicular iron does not precipitate below 600°C, and above 1200υ the substrate and precipitated iron react, making it impossible to obtain good magnetic properties. Furthermore, the pressure during the reaction was increased from 10 Torr to 200 Torr.
I made it below LO'rorr ('I Qmm
This is because at temperatures below 200 Torr, the number of gas molecules is small and the precipitation rate is slow, and at temperatures above 200 Torr, the degree of supersaturation is thermodynamically low and granular or powder (spherical) iron is more likely to precipitate than acicular iron ( With pressure writing, the degree of supersaturation is low and it is difficult to become needle-like).

Specific examples will be described below. First, a molybdenum plate (substrate) with a width of 8α, a length of 2CCIIL, and a thickness of 8cm is placed in the reaction zone in the furnace core tube1), then FeC73100fr
It was placed on a boat made of Fe and placed in the evaporation zone.

The air is then pumped out using a rotary pump and placed in the evaporation zone (
The reaction zone (where the molybdenum plate was placed) was set at 300°C (where the FeC13 was placed) and 600°C (where the molybdenum plate was placed), and hydrogen (H
2) was flowed at a rate of 100 CC for 7 minutes, the valve was adjusted so that the pressure in the furnace was 10'rorr, and the reaction was carried out for about 30 minutes. Next, turn off the heater in each zone until the temperature reaches 100.
Hydrogen is continued to flow until the temperature falls below 100°C, and when the temperature falls below 100°C, air is introduced to take out the molybdenum substrate, and the acicular iron crystals deposited thereon are brushed off and collected. When this powder was observed with an electron microscope, the axial ratio (major axis/minor axis) was about 40 and the length of the major axis was 1.0 μm. Next, the saturation magnetization σ8 and coercive force H of this acicular powder were measured and the results were 1,5==185 em+i/c c, Ho=125
It was 00e. Next, as a weather resistance test, this acicular powder was left at 60°C and 590% relative humidity (RH) for 7 days, and then the C5 was measured, and the change was -2,596.
There was a decrease in The results are shown in sample number 1 in the following table.

In the following margins, Fe was deposited on a molybdenum substrate in the same manner as in the above specific example. At that time, the temperature of the evaporation zone, the temperature of the reaction zone, the flow rate of hydrogen, the form of precipitated crystals, σ, ,
HC1 moisture resistance (σ after being left for 7 days at 60°C and 90%RH)
The rate of change in S) is shown in sample numbers 2 to 8.

Comparative examples (sample numbers 17 to 18) with sample numbers 9 to 16 and other needle iron manufacturing methods in which the above temperature conditions and pressure conditions are outside the range of the present invention are also shown.

Effects of the Invention As described above, according to the present invention, the following effects can be obtained. As can be seen by comparing the examples (sample numbers 1 to 8) and comparative examples (sample numbers 9 to 18) in the table above, needle iron produced using a gas phase reaction in the process of producing needle iron The powder has high saturated sulfidation (σ3) and high coercive force, and has excellent weather resistance (moisture resistance). In particular, the evaporation temperature of FeCZ3 is soo'o-550°C, the temperature of the 1 minute precipitation reaction is 600'C!~1200'O, and the flow rate of hydrogen is xoo
cc15. ) to 100 OC and the furnace pressure is in the range of 10 to 200 Torr, better properties can be obtained.

[Brief explanation of the drawing]

The drawing is an explanatory diagram showing the basic structure of an apparatus for producing needle iron. (1) Hydrogen supply cylinder, (2) Reaction core tube, (3) Evaporation heater, (4) Precipitation reaction heater, (5) Boat , (6)... Substrate for precipitation, (7)... Rotary pump, (8)... Valve agent Yoshihiro Morimoto

Claims (1)

[Claims] 1. A mixed gas of iron chloride and hydrogen heated and vaporized at 300'C)-500°C under reduced pressure at 600'O to 1200
A method for producing acicular iron, in which the acicular iron is poured onto a substrate heated at °C to precipitate the acicular iron, and then the acicular iron is recovered from the substrate. 2. The method for producing needle iron according to claim 1, wherein the hydrogen flow rate is 100 cc/min to 1000 cc/molecule. 8. The method for producing needle iron according to claim 1, wherein the reduced pressure is 10 Torr to 200 Torr.