CN1007257B - Solid electrolyte for protecting cathode of overhead metal pipe and its process - Google Patents

Abstract

The present invention relates to solid electrolyte sodium beta-A2O3 powder suitable for the cathodic protection of overhead metallic conduits and a preparation method thereof, which belongs to the field of general electrochemical corrosion resistance. The powder is characterized in that the powder is prepared from the mixture of beta' and beta and contains 7.5 to 9.5 wt% of Na2O, 0.3 to 0.85 wt% of Li2O or 2 wt% of MgO or 0.7 wt% of Li2O, 0.4 wt% of MgO and balance of Al2O3 trace impurity. The powder is prepared by the distribution of particles of 40 to 200 meshes. The powder is prepared from industrial alumina sold in the market by a wet mixing and grading heat preservation method.

Description

Solid electrolyte for protecting cathode of overhead metal pipe and its process

The invention relates to the solid electrolyte sodium Beta-Al that protecting cathode of overhead metal pipe is used ₂O ₃Powder material and preparation method thereof belongs to general electrochemical anti-corrosive erosion field.

Sodium Beta-Al ₂O ₃, since 1916 are found, only be made into molten-cast brick as the refractory material of some special occasions, until U.S. Ford in 1967 reported it brilliance ionic conductance and announce first sodium Beta-Al ₂O ₃Pottery can be used as solid electrolyte and is used for making and just is subjected to common concern after the sodium-sulphur battery.The research of nearly one, 20 year this material and preparation technology thereof development is very rapid, and the method that is used to prepare forerunner's powder of this pottery at present roughly has electric smelting method, secondary synthetic zeta law, spray-drying process and gel method etc.But with the fine grained reactive powder of present prior art preparation, be that fine and close sodium Beta-Al is produced in that do not synthesize, semi-synthetic or synthetic all only being applicable to ₂O ₃Ceramic material and do not conform with the requirement of protecting cathode of overhead metal pipe coating.

As with existing fine grained sodium Beta-Al ₂O ₃Powder, as the solid electrolyte of the cathodic protection of overhead metal pipe, not only cost is high but also in the coated process metallic conduit is had obvious corrosion behavior, and the polarization behavior of cathodic protection is also unstable.An obvious example is that the people such as the Chen Li of Inst. of Physics, CAS spring had once studied " the fast-ionic conductor anticorrosive paint is to the protection of 16 manganese steel ", the solid electrolyte β " Al that adopts ₂O ₃, be to prepare ceramic explained hereafter according to external zeta law, prepared powder material has obvious corrosivity to metal before implementing coating process and in the implementation process.This is because of Na in its prescription ₂The cause of O too high levels.They will pay usefulness by the product that ceramic process is produced behind pulverizing and jevigating, and Li in the prescription ₂The O consumption is again bigger, and this certainly will will make product cost improve.

The object of the present invention is to provide a kind of be suitable for that protecting cathode of overhead metal pipe is used, almost do not have good solid electrolyte sodium Beta-aluminum oxide powder material of the ionic conductivity of electronic conduction and chemical stability and preparation method thereof.This powder material allows with the appropriate means coated in claimed metallic surface; form the solid electrolyte layer with the sole plate metal mortise, add suitable electric field can in the atmospheric environment under-10 ℃～300 ℃ temperature or the metal in acid, alkalescence and the marine atmosphere implement corrosionproof protection.

Specifically, sodium Beta-Al provided by the invention ₂O ₃The component feature of solid electrolyte powder material is 7.5～9.5(wt) %Na ₂O and 0.3～0.85(wt) %Li ₂O or 2(wt) %MgO or 0.7(wt) %Li ₂O and 0.4(wt) %MgO, all the other are Al ₂O ₃And micro impurity element.One of principal character of this powder material is to be β " with the mixing of β mutually, " relative amount of phase is 65～90% to β, does not contain α-Al ₂O ₃Phase, ionic conductivity is good; Two of feature is Na of the powder material of use ₂O content is lower, does not contain rich sodium phase, and chemical stability is good; Three of feature is that particle size distribution is 40～200 orders, and wherein the content between 40～100 orders is 30～80%(accumulating weight), be convenient to impregnation and coated.

" and β powder mix material is to adopt following simple process and cheap feedstock production to β provided by the invention.The raw material that adopts is Li, the Na that commercially available technical pure aluminum oxide, lithium hydroxide and sodium hydroxide or other can be water-soluble, the salt of Mg.Can use not treated commercially available aluminium hydroxide, r-Al ₂O ₃Or α-Al ₂O ₃, or among the three any two make raw material, by a certain percentage the batching, such as Li ₂O: Na ₂O: Al ₂O ₃=0.8: 9.5: 89.7(wt).Take an amount of water as medium, or with ball mill or with Y type batch mixer or even with the wet mixing of will preparing burden of general cement batch mixer, or make dry powder with spray drying process or with the rotary drying method or 110 ℃ of oven dry.The control of wet mixing moisture content adapts with drying means, and moisture content is controlled at 25%～40%(wt) when oven dry or rotary drying, and moisture content should be controlled at 45%～65%(wt) when adopting spraying drying.Powder is the step heat preservation calcining in common High Temperature Furnaces Heating Apparatus or tunnel furnace, and for example 1150～1450 ℃ of insulations 1～2 hour, insulation is 15 minutes to 2 hours in 1500～1600 ℃ of scopes.

Sodium Beta-Al by the present invention's preparation ₂O ₃Solid electrolyte is applicable to protecting cathode of overhead metal pipe, and one of feature is that sodium content is low, does not contain rich sodium phase, in the work progress metallic conduit is not had obvious corrosiveness; Two of feature is that crystal grain physically well develops, and transformation fully neither contains rich sodium and also do not contain mutually α-Al mutually ₂O ₃Phase; Three of feature is β " with β mixture mutually, has taken into account electrical conductivity height, two requirements that sodium content is low; Four of feature is that particle size distribution is convenient to the impregnation coated; Five of feature is cheap.

Sodium Beta-Al provided by the invention ₂O ₃Solid electrolyte; show through coated test of polarization potential and current relationship on 16 manganese steel; current potential can increase take place with polarization current that forward moves or negative sense moves; especially the cathodic polarization curve that moves at the current potential negative bias finds that an obvious flat region is arranged, and this shows that solid electrolytic confrontation overhead metal pipe provided by the invention has good cathodic protection effect.

One of embodiment of the invention is: take by weighing 235 gram lithium hydroxides and (contain Li ₂O34.4%), 1251 gram NaOH (contain Na ₂O75.4%) and 9163 gram purity be industrial α-Al of 99% ₂O ₃Add water 11 liters mix grinding in the corundum ball mill and made moisture about 55% mud in 2 hours, make dry powder with spray drying process and enter the stove calcining.Earlier respectively be incubated 1 hour, rise to 1570 ℃ of insulations 1 hour then at 1350 ℃ and 1450 ℃.

Two of the embodiment of the invention be with 116 the gram lithium hydroxides and 1224 the gram NaOH be dissolved in 4500 ml waters, with 9446 the gram purity be 98% commercially available r-Al ₂O ₃Fully evenly mixed, enter stove through 110 ℃ of oven dry, by the calcining of example one condition.

Three of the embodiment of the invention is, take industrial aluminium hydroxide, NaOH and magnesium nitrate as raw material by MgO: Na ₂O: Al ₂O ₃(wt)=and 2: 9.5: 88.5 ratio batching, about 1.5 kilograms (pure-oxide total amounts) add 1300 milliliters in water, process by example one same method.

The product that makes by example one, example two and example three is β " to be mixed mutually with β, not to contain α-Al ₂O ₃Mutually with other rich sodium mutually, " content is greater than 65% for β.Product grains is grown intact, does not harden easily to pulverize.Cross 40 mesh sieves after product is pulverized and to pay usefulness.

Four of the embodiment of the invention is the solid electrolyte sodium Beta-Al that make with said method ₂O ₃Powder material and adhesive are made into coating, and coated is answered Anodic on overhead metal pipe, and Cathodic Protection is carried out in polarization take metal tube as cathodal closing.Test specimen is under 50 ℃ of simulated environment temperature, through 30 μ A/m ²The current density test, protection potential reaches-1.1 volts, and the protection electrical parameter is more satisfactory.Test through half a year more; to no coating test specimen, coating no power test specimen is arranged and coating is arranged and the test specimen of switching on is surveyed sample; discovery has only and scribbles the coating that the invention provides the powder material and the polar test specimen of switching on does not have signs of corrosion fully; test specimen smooth finish still with not test (N.T.) before identical, so protected metal specimen is had significant anticorrosion ability.

Claims (5)

1, a kind of solid electrolyte sodium Beta-Al that is applicable to that protecting cathode of overhead metal pipe is used ₂O ₃The powder material is characterized in that:

(1) solid electrolyte powder material is by β " Al ₂O ₃And β-Al ₂O ₃The mixing phase composition;

(2) contain 7.5～9.5 (Wt) %Na ₂O and 0.3～0.85%Li ₂O or 2 (Wt) %MgO or 0.7 (wt) Li ₂O and 0.4 (wt) %MgO, all the other are Al ₂O ₃With other impurity elements;

(3) size distribution is 40～200 orders.

2, the relative content of " and in the mixed phase of β, β " is 65～90% by the described powder material of claim 1, to it is characterized in that described β.

3, by the described powder material of claim 1, it is characterized in that powder material size distribution accounts for 30～80%(accumulating weight between 40～100 orders).

4, be suitable for the solid electrolyte sodium Beta-Al that protecting cathode of overhead metal pipe is used a kind of the preparation ₂O ₃The method of powder material comprises batching, wet mixing and drying, burns till, and it is characterized in that:

(1) control of wet mixing moisture content and drying means adapt, and moisture content should be controlled at 25～40(weight when adopting oven dry with rotary drying) %, moisture content should be controlled at 45～65(weight when adopting spraying drying) %;

(2) firing condition is to be incubated 1～2 hour at 1150～1450 ℃ earlier, and then is warmed up to 1500～1600 ℃, is incubated 15 minutes to 2 hours.

5, by the described preparation method of claim 4, can adopt not treated commercially available aluminium hydroxide or γ-Al when it is characterized in that preparing burden ₂O ₃Or α-Al ₂O ₃Or arbitrarily the two mixing among the three.