JP5164072B2 - Manufacturing method of vanadate glass - Google Patents

Description

【Technical field】
[0001]
  The present invention relates to a method for producing a vanadate glass suitably used as an electrode material or the like.
[Background]
[0002]
  Conventionally, vanadate glass containing vanadium as a main component or a subcomponent has been developed as a glass semiconductor used as a thermistor or the like. Vanadate glass consists of vanadium oxide, diphosphorus pentoxide, alkali metal oxides such as potassium oxide and sodium oxide, alkaline earth oxides such as barium oxide, cerium oxide, tin oxide, lead oxide, and copper oxide. In addition, those that are vitrified are known. Vanadate glass has a relatively high electrical conductivity because it exhibits electronic conductivity, unlike ordinary ion-conducting oxide-based glasses, but vanadium oxide, phosphorous pentoxide, alkaline earth oxidation When glass is produced by a normal method of rapidly cooling a melt such as a product, the electrical conductivity at room temperature is 10^-5S · cm^-1Only a moderate amount was obtained. Therefore, vanadate glass has been applied only to specific applications such as thermistors and heaters.
  Therefore, the present inventor aims to improve the electrical conductivity at room temperature of the vanadate glass, “after heating and melting a mixture containing vanadium oxide and then rapidly cooling to obtain a glass composition, A method for producing a vanadate glass that is maintained at a temperature of an annealing treatment not lower than the glass transition temperature and not higher than the crystallization temperature for a predetermined time was developed and patented (Patent Document 1).
[Patent Document 1]
Japanese Patent Laid-Open No. 2003-34548
DISCLOSURE OF THE INVENTION
[Problems to be solved by the invention]
[0003]
  However, the invention described in Japanese Patent Application Laid-Open No. 2003-34548 (Patent Document 1) has room for improvement in the following points.
(1) The electrical conductivity at room temperature of the vanadate glass produced by the technique disclosed in Patent Document 1 is 10^-4-10^-1S · cm^-1In order to expand the application to electrode materials etc.^-1S · cm^-1A vanadate glass having the above high electric conductivity has been demanded.
(2) Since the electrical conductivity of the vanadate glass may vary depending on the holding time at the annealing treatment temperature, stable production can be achieved with little fluctuation in the electrical conductivity even if the holding time at the annealing treatment temperature varies. There has been a demand for vanadate glass having excellent properties.
(3) In order to increase the production stability of the vanadate glass having high electrical conductivity and increase the product yield, the electrical conductivity of the vanadate glass is set to 10^-4S · cm^-1There has been a demand for a technique for designing and controlling with high accuracy in the above-described region.
[0004]
  The present invention satisfies the above requirements, and at room temperature 10^-1S · cm^-1The vanadate glass having the above high electrical conductivity can be produced, and the electrical conductivity can be drastically increased even if it is kept in the predetermined temperature range for a short time of about 30 minutes. Even when the holding time varies, the electrical conductivity does not vary so much and the production stability and quality stability are remarkably excellent. Furthermore, the electrical conductivity at room temperature is 10^-4S · cm^-1An object of the present invention is to provide a method for producing a vanadate glass that can be designed and controlled with high accuracy in the above-described region and can increase the product yield.
Means for solving the problem
[0005]
  In order to solve the above conventional problems, the method for producing vanadate glass of the present invention has the following configuration.
  The method for producing a vanadate glass according to claim 1 of the present invention is a method for producing a vanadate glass containing vanadium as a main component or a subcomponent, and includes vanadium., Barium and ironVitrification step of producing an oxide glass by vitrifying the composition containing the oxide glass, and the oxide glass is the highest exothermic peak temperature among the exothermic peaks of crystallization by differential thermal analysis (DTA) of the oxide glass. And a reheating step of maintaining in a temperature region exceeding the melting point for a predetermined time.
  With this configuration, the following effects can be obtained.
(1) Since the oxide glass is provided with a reheating step for maintaining the oxide glass in a temperature range exceeding the highest heat generation peak temperature of the oxide glass and below the melting point for a predetermined time, the electrons in the oxide glass are energetically high. 10 levels at room temperature.^-1S · cm^-1The vanadate glass having the above high electrical conductivity can be produced, and the electrical conductivity can be dramatically increased even if it is kept in a predetermined temperature range for a short time of about 30 minutes. Even if the holding time varies, the electric conductivity does not vary and the production stability is remarkably excellent.
(2) By changing the heating time and holding time in the reheating step, the electric conductivity of the vanadate glass at room temperature is set to 10^-FourS · cm^-1It is possible to design and control with high accuracy in the above region, and to increase the product yield.
(3) A glass skeleton in which atoms of vanadium, barium, and iron are three-dimensionally related can be formed, and high electrical conductivity by electron hopping can be expressed.
(4) Since tetravalent and pentavalent vanadium and trivalent iron can be arranged in the glass skeleton, the probability of electron hopping is increased and the electrical conductivity can be increased.
[0006]
  Here, as vanadate glass, in addition to vanadium, one or more of alkali metals such as potassium and sodium, alkaline earth metals such as barium and magnesium, cerium, tin, lead, copper, iron and the like A known glass having the following constituent atoms is used. In a vanadate glass that is a glass semiconductor, conductivity is exhibited by electrons hopping between transition metal ions such as vanadium and iron.
  In the reheating step of the present invention, the oxide glass is held in a temperature range higher than the crystallization temperature and lower than the melting point, whereas in the annealing process of Japanese Patent Laid-Open No. 2003-34548 (Patent Document 1), the oxide glass Is maintained at the glass transition temperature or more and the crystallization temperature or less, the heat energy given to the oxide glass in the reheating step of the present invention is the heat given to the oxide glass in the annealing treatment of (Patent Document 1). Greater than energy. Therefore, the electrons in the oxide glass are distributed in a high energy level, and the thermal energy (activation energy) necessary for hopping the electrons can be made smaller than in the case of (Patent Document 1). I guess that the electrical conductivity can be increased. Further, in the reheating step, by holding for a predetermined time at a temperature higher than the crystallization temperature of the oxide glass, the distortion of the glass skeleton is removed as in (Patent Document 1), and the activation energy (band gap) at which electrons hop is obtained. Since it can be made smaller, it is presumed that as a result, the electrical conductivity can be increased.
  In addition, when the crystal of the vanadate glass is insulative, the electrical conductivity decreases when the vanadate glass is crystallized. For this reason, in the reheating process, if the oxide glass is kept at a temperature higher than the crystallization temperature for a long time, an insulating crystal is precipitated and the electrical conductivity is gradually lowered. Therefore, in the reheating step, it is necessary to cool to below the crystallization temperature before the vanadate glass crystals are precipitated and the electrical conductivity is lowered.
[0007]
  The crystallization temperature and melting point can be determined by actually measuring the oxide glass by differential thermal analysis (DTA), differential scanning calorimetry (DSC), or the like. Moreover, it can also obtain | require by performing the thermodynamic calculation etc. using the state diagram of the estimated component.
  When the crystallization temperature is determined by differential thermal analysis (DTA), the temperature at the central point or the bottom side temperature of the exothermic peak of crystallization is defined as the crystallization temperature. Moreover, when calculating | requiring melting | fusing point by a differential thermal analysis (DTA), let the temperature in the center point of the endothermic peak in higher temperature than crystallization temperature be a melting | fusing point.
[0008]
  As a means for vitrifying the composition in the vitrification step, a composition such as a mixture of crystalline solids can be converted into a liquid or gas, and then an oxide glass that is a solid having a glass transition temperature or lower can be obtained without crystallization. If it is, it will not be restrict | limited in particular. For example, an oxide glass can be obtained by heating and melting a composition such as a mixture of crystalline solids, followed by rapid cooling. Alternatively, an oxide glass can be obtained by once putting a composition such as a mixture of crystalline solids into a vapor state by vapor deposition, sputtering, glow discharge, or the like. The oxide glass can also be obtained by passing through a gel such as a sol-gel method.
[0009]
  As a means for maintaining the temperature range below the melting point and exceeding the crystallization temperature in the reheating process of the oxide glass, for example, an electric furnace or the like is set to the reheating temperature in advance and the temperature in the furnace becomes constant. By the way, put the oxide glass into the furnace, and immediately after the target time has passed, remove the oxide glass from the electric furnace, etc., fluid such as air, water, ice water, cooled copper plate or stainless steel plate, copper or stainless steel, etc. What is cooled by a member such as a roller is used. Alternatively, after the oxide glass is reheated in a furnace such as an electric furnace for a certain period of time, the temperature in the furnace is gradually lowered or gradually moved away from the heating source in the furnace, and the oxide glass is allowed to cool in the furnace. What to do is used. The inside of the furnace for reheating can be an inert gas atmosphere such as air, nitrogen, or argon.
[0010]
  The holding time in the reheating step can be appropriately set to an optimal time so that the electric conductivity of the oxide glass that has undergone the reheating step is increased. The holding time varies depending on the composition, heat capacity, and reheating temperature of the oxide glass, but is set to 1 to 180 minutes, for example. When the holding time is shorter than 1 minute, the thermal energy given to the oxide glass is small, so the rate of increase in electrical conductivity is small, and variation in the rate of increase is seen, and when longer than 180 minutes, crystals are precipitated. Since melting may cause a decrease in electrical conductivity and productivity, neither is preferable.
[0011]
  When the heating temperature in the reheating step is equal to or lower than the crystallization temperature of the oxide glass, since the thermal energy given to the oxide glass is small, the rate of increase in electrical conductivity is small, and the rate of increase may vary. If the heating temperature is equal to or higher than the melting point of the oxide glass, melting of the oxide glass and precipitation of crystals are promoted, and the electrical conductivity is lowered.
[0012]
  The electrical conductivity of an oxide glass (vanadate glass) at room temperature of 25 ° C. is, for example, that after applying a silver paste to a sample made of a glass piece having a thickness of 1 mm or less and drying, an electrode using silver-containing solder And can be obtained by a DC two-terminal method or a DC four-terminal method.
[0013]
  Thus, the electrical conductivity in 25 degreeC of the oxide glass (vanadate glass) before the reheating process calculated | required is 10^-8-10^-4S · cm^-1Preferably 10^-6-10^-4S · cm^-1It is preferable that it exists in the range. Electrical conductivity is 10^-6S · cm^-1As it becomes lower, it tends to become difficult to improve the electrical conductivity to a practical level even after the reheating step.^-8S · cm^-1A lower value is not preferable because this tendency becomes remarkable. The electrical conductivity of the oxide glass before the reheating step is 10^-4S · cm^-1A higher value is not preferable because the composition of the glass oxide and the temperature history of the vitrification process are restricted, resulting in poor productivity and poor production stability.
  The electrical conductivity of the oxide glass (vanadate glass) that has undergone the reheating step is 10 at room temperature of 25 ° C.^-4~ 1S · cm^-1Preferably 10^-3~ 1S · cm^-1The range can be improved. Electrical conductivity is 10^-3S · cm^-1As vanadate glass is applied to thermistors and heating elements, power consumption increases and energy saving tends to be lost as it becomes smaller. There is a tendency for the effect to decrease, and further, when applied to a plasma discharge electrode, there is a tendency that it is difficult to discharge. In particular, the electrical conductivity is 10^-4S · cm^-1A smaller value is not preferable because these tendencies become remarkable.
[0014]
  Vanadate glass is composed of AgI, NaI, Ag, Ag.₂O, In₂O₃, SnO, SnO₂It may be added with additives such as. This is because the electrical conductivity can be increased by the effect of the additive. In addition to AgI, NaI, Ag, etc., CeO₂An anti-reduction agent such as Thereby, it can prevent that additives, such as AgI, NaI, Ag, are reduced, and can maintain high electrical conductivity.
[0016]
  Here, barium oxide (BaO), vanadium oxide (V₂O₅), Iron oxide (Fe₂O₃) Ratio is not particularly limited as long as an oxide glass exhibiting a glass transition phenomenon can be obtained. In particular, the molar ratio of barium oxide (B) in the oxide glass to vanadium oxide (V) is not limited. The ratio (B: V) is preferably 5:90 to 35:50.
  Thereby, the following actions are obtained.
(1) Since a three-dimensional glass skeleton having vanadium as the main skeleton can be formed in the vitrification step, the electrical conductivity can be dramatically increased in the reheating step.
(2) Since there is less variation in the electrical conductivity of the oxide glass before the reheating step and it is difficult to crystallize in the reheating step, the electrical conductivity of the oxide glass after the reheating step can be kept within a predetermined range. Excellent production stability.
  Here, when the molar ratio (B: V) is smaller than 5:90, it becomes difficult to form a glass skeleton having a three-dimensional structure, and it becomes difficult to obtain a homogeneous oxide glass. ) Greater than 35:50 is not preferable because vitrification becomes difficult and crystallization is likely to occur in the reheating step, and good conductivity is not exhibited.
[0017]
  The molar ratio (F: V) of iron oxide (F) to vanadium oxide (V) in the oxide glass is preferably 5:90 to 15:50.
  Thereby, the following actions are obtained.
(1) Since a three-dimensional glass skeleton having vanadium as the main skeleton can be formed in the vitrification step, the electrical conductivity can be dramatically increased in the reheating step.
(2) Since optical properties such as light transmittance are maintained to some extent, it can be used as an optical element by forming a thin film or fiber.
  Here, when the molar ratio (F: V) is smaller than 5:90, it becomes difficult to vitrify, and when the molar ratio (F: V) is larger than 15:50, the optical characteristics such as light transmittance are deteriorated and uniform. Since it becomes difficult to obtain oxide glass, neither is preferable.
[0018]
  In addition, vanadium oxide (V₂O₅), Barium oxide (BaO), iron oxide (Fe₂O₃) Vanadium oxide (V₂O₅) Is 40 to 98 mol%, preferably 60 to 85 mol%. As it becomes less than 60 mol%, it tends to be difficult to maintain a glass skeleton having vanadium as the main skeleton, and it is difficult to obtain high electrical conductivity. In particular, since the content of subcomponents is reduced, adjustment functions such as electrical conductivity and mechanical properties due to the subcomponents tend to be reduced. In particular, when the amount is less than 40 mol% or more than 98%, these tendencies are remarkable, which is not preferable.
  The barium oxide (BaO) in the three-component system in the oxide glass is 1 to 40 mol%, preferably 10 to 30 mol%. As the amount becomes less than 10 mol%, homogenous vitrification tends to be difficult, and as the amount exceeds 30 mol%, mechanical strength decreases and vitrification tends to become difficult. In particular, when the amount is less than 1 mol% or more than 40 mol%, these tendencies are remarkable, which is not preferable.
  Iron oxide (Fe in the ternary system in oxide glass)₂O₃1) to 20 mol%, preferably 5 to 20 mol%. As the content becomes less than 5 mol%, the contribution to the electron hopping by the valence electrons of iron tends to be reduced, and the electrical conductivity tends to be difficult to improve. On the other hand, if it exceeds 20 mol%, the optical properties such as light transmission properties are significantly lowered, which is not preferable.
  In particular, vanadium oxide (V₂O₅), Barium oxide (BaO), iron oxide (Fe₂O₃) In the range of 60 to 85 mol%, 10 to 30 mol%, and 5 to 20 mol%, respectively, the electrical conductivity at room temperature is increased by several orders of magnitude by reheating the oxide glass. Let 10^-1S · cm^-1Thus, excellent characteristics can be exhibited as a thermistor, a heating element, various electrode materials, an antistatic material, and the like.
[0019]
  Of the present inventionClaim 2The invention described in claim 1 is the method for producing the vanadate glass according to claim 1, wherein the composition is a mixture containing vanadium oxide, barium oxide and iron oxide, and the oxide glass is The mixture is obtained by heating and melting and then rapidly cooling.
  With this configuration, in addition to the operation obtained in the first aspect, the following operation can be obtained.
(1) Since a mixture containing vanadium oxide, barium oxide and iron oxide is heated and melted and then rapidly cooled to obtain an oxide glass, it can be mass-produced at low cost and has excellent productivity.
[0020]
  Here, as vanadium oxide, vanadium monoxide (VO), divanadium trioxide (V₂O₃), Vanadium dioxide (VO)₂), Divanadium pentoxide (V₂O₅In particular, divanadium pentoxide (V₂O₅) Is preferably used. This is because a glass skeleton having a three-dimensional structure is easily formed by adding barium oxide.
  As barium oxide, barium oxide (BaO), solid solution barium oxide containing excess oxygen, barium peroxide, or the like is used, but barium oxide (BaO) is generally used. In addition, when barium carbonate, barium oxalate, or the like is used, it is decomposed by heating and melting, and BaO remains in the oxide glass to serve as network modifying ions.
  As iron oxide, iron monoxide (FeO), ferric trioxide (Fe₂O₃), Triiron tetroxide (Fe₃O₄) Etc. are used.
[0021]
  In addition to vanadium oxide, barium oxide, and iron oxide, rhenium oxide (ReO) is used as the second component.₃), Silver (Ag), etc. can also be added. Thereby, electrical conductivity can be further improved. The addition amount of the second component such as rhenium oxide is preferably 15 parts by mass or less with respect to 100 parts by mass of the mixture. This is because if the added amount of the second component exceeds 15 parts by mass, a glass skeleton having vanadium as a main skeleton cannot be formed.
Effect of the invention
[0022]
  As described above, according to the method for producing the vanadate glass of the present invention, the following advantageous effects can be obtained.
  According to the invention of claim 1,
(1) Since an oxide glass having a glass transition temperature or lower is maintained for a predetermined time in a temperature region higher than the highest exothermic peak temperature of the oxide glass and lower than the melting point of the oxide glass, a reheating step is provided.^-1S · cm^-1The vanadate glass having the above high electrical conductivity can be produced, and the electrical conductivity can be dramatically increased even if it is kept in a predetermined temperature range for a short time of about 30 minutes. Even if the holding time varies, it is possible to provide a method for producing a vanadate glass with little fluctuation in electrical conductivity and remarkably excellent production stability.
(2) By changing the heating time and holding time in the reheating step, the electric conductivity of the vanadate glass at room temperature is set to 10^-FourS · cm^-1It is possible to provide a method for producing a vanadate glass that can be designed and controlled with high accuracy in the above-described region and can increase the product yield.
(3) It is possible to provide a method for producing a vanadate glass capable of forming a glass skeleton in which atoms of vanadium, barium, and iron are three-dimensionally related and exhibiting high electrical conductivity by electron hopping.
(4) Since tetravalent and pentavalent vanadium and trivalent iron can be arranged in the glass skeleton, it is possible to provide a method for producing a vanadate glass capable of increasing the probability of electron hopping and exhibiting high electrical conductivity.
[0024]
  Claim 2According to the invention described in claim 1, in addition to the effect of claim 1,
(1) Since a mixture containing vanadium oxide, barium oxide and iron oxide is heated and melted and then rapidly cooled to obtain an oxide glass, a method for producing a vanadate glass capable of mass production at low cost and excellent in productivity is provided. it can.
[Brief description of the drawings]
[0025]
[FIG. 1] Differential thermal separation results of oxide glasses of Experimental Examples 1 to 3
FIG. 2 is a plot of electrical conductivity before and after reheating of the oxide glasses of Experimental Examples 1 to 3 cooled to a glass transition temperature or lower.
FIG. 3 is a graph showing the relationship between reheating temperature, reheating time and electrical conductivity of the oxide glass of Experimental Example 2
BEST MODE FOR CARRYING OUT THE INVENTION
[0026]
  Hereinafter, the present invention will be specifically described by way of examples. The present invention is not limited to these examples.
  (Experimental example 1)
  10 mol% of barium oxide (BaO), divanadium pentoxide (V₂O₅) 80 mol%, ferric trioxide (Fe₂O₃) Weighed each reagent grade reagent so that the total amount is 10 g, mixed in an agate mortar, put in a platinum crucible, and the mixture placed in the platinum crucible was heated to 1000 ° C. It was melted by heating in the atmosphere for 90 minutes. The melt was poured out on a stainless steel plate having a thickness of 10 mm and rapidly cooled to below the glass transition temperature, whereby the oxide glass of Experimental Example 1 was obtained.
  (Experimental example 2)
  20 mol% of barium oxide (BaO), divanadium pentoxide (V₂O₅) Is 70 mol%, ferric trioxide (Fe₂O₃) Was 10 mol% and the total amount of the reagent was weighed so that the total amount of the reagent was 10 g. In the same manner as in Experimental Example 1, an oxide glass of Experimental Example 2 was obtained.
  (Experimental example 3)
  30 mol% of barium oxide (BaO), divanadium pentoxide (V₂O₅) 60 mol%, ferric trioxide (Fe₂O₃) Was 10 mol% and the total amount of the reagent was weighed so that the total amount of the reagents was 10 g. In the same manner as in Experimental Example 1, an oxide glass of Experimental Example 3 was obtained.
[0027]
  (Results of differential thermal analysis of oxide glasses of Experimental Examples 1 to 3)
  The differential thermal analysis (DTA) of the oxide glasses of Experimental Examples 1 to 3 was performed. The conditions for differential thermal analysis (DTA) were α-alumina used as a reference material and a heating rate of 10 ° C./min in a nitrogen atmosphere.
  FIG. 1 shows the results of differential thermal analysis of the oxide glasses of Experimental Examples 1 to 3.
  From FIG. 1, as the molar ratio of barium oxide increases and the molar ratio of divanadium pentoxide decreases, the glass transition temperature (Tg) and the crystallization temperature (Tc) increase. 362 ° C., 392 ° C. in Experimental Example 2 (the highest exothermic peak temperature was about 470 ° C.), and 433 ° C. in Experimental Example 3. The sharp endothermic peak observed in the temperature range exceeding the crystallization temperature (Tc) indicates the melting point, which is 600 ° C. or higher in Experimental Example 1, 540 ° C. in Experimental Example 2, and 563 ° C. in Experimental Example 3. It was.
[0028]
  (Relationship between reheating temperature and electrical conductivity)
  The oxide glasses of Experimental Examples 1 to 3 cooled to the glass transition temperature or lower were reheated at 350 ° C., 400 ° C., 500 ° C., and 550 ° C. for 1 hour in the atmosphere. The electrical conductivity at 0 ° C. was measured by a DC four-terminal method.
  FIG. 2 is a graph plotting the electrical conductivity before and after reheating of the oxide glasses of Experimental Examples 1 to 3 cooled to the glass transition temperature or lower. In FIG. 2, the horizontal axis represents the reheating temperature (° C.), and the vertical axis represents the electrical conductivity σ (S · cm at 25 ° C.^-1).
  From FIG. 2, when the oxide glass of Experimental Example 1 is reheated at 500 to 550 ° C., which is a temperature higher than the crystallization temperature (362 ° C.) and lower than the melting point (600 ° C. or higher) for 1 hour, the electric conduction at 25 ° C. The degree could be increased by about 4 orders of magnitude compared to before reheating.
  In FIG. 2, the electric conductivity when reheated at 400 ° C. for 1 hour was the same as before reheating, but by reheating at 400 ° C. for 2 hours, the electric conductivity at room temperature (25 ° C.) was 10^-3S · cm^-1It was able to be about. In the oxide glass of Experimental Example 1, it is considered that the holding time when the reheating temperature is 400 ° C. was short at 1 hour.
  Further, from FIG. 2, when the oxide glass of Experimental Example 2 is reheated at 400 to 500 ° C., which is a temperature exceeding the crystallization temperature (392 ° C.) and not higher than the melting point (540 ° C.) for 1 hour, Conductivity of 10^-3S · cm^-1The above high electric conductivity could be achieved. In particular, when reheating at 500 ° C., which is higher than the highest exothermic peak temperature (about 470 ° C.), 10^-1S · cm^-1The above high electrical conductivity could be realized. In addition, when it reheated at 550 degreeC higher than melting | fusing point (540 degreeC) for 1 hour, a part crystallized.
  From FIG. 2, when the oxide glass of Experimental Example 3 is reheated at 500 ° C. which is a temperature exceeding the crystallization temperature (433 ° C.) and not higher than the melting point (563 ° C.), the electrical conductivity at 25 ° C. is 10^-2S · cm^-1The above high electric conductivity could be achieved.
In addition, when it reheated at 550 degreeC close | similar to melting | fusing point (563 degreeC) for 1 hour, since one part crystallized, the electrical conductivity of the oxide glass reheated at 550 degreeC is not plotted. This is probably because the molar ratio of barium oxide to divanadium pentoxide was increased. By shortening the holding time and reheating at 550 ° C. for 0.5 hour, the electric conductivity at 25 ° C. is reduced to 10 without crystallization.^-2S · cm^-1It was able to be about.
  From the above, the electrical conductivity at room temperature (25 ° C.) is drastically achieved through a reheating step in which the oxide glass (vanadate glass) is maintained in a temperature range exceeding the crystallization temperature and not higher than the melting point. It became clear that it could be increased. In addition, it was found that the electrical conductivity improves as the reheating temperature increases within a temperature range in which crystal precipitation and melting do not occur remarkably. It has also been found that the retention time may be shorter as the reheating temperature increases. From these phenomena, it is considered that the mechanism by which the electric conductivity is improved by reheating above the melting point and exceeding the crystallization temperature is due to the activation energy of electrons.
[0029]
  In addition to these experimental examples, vanadium oxide (V₂O₅), Barium oxide (BaO), iron oxide (Fe₂O₃), Various oxide glasses are prepared so that the molar ratios are in the range of 40 to 98 mol%, 1 to 40 mol%, and 1 to 20 mol%, respectively, and the crystallization temperature and melting point of each are determined and reheated. When the electrical conductivity at room temperature before and after the process was measured, it was confirmed that the electrical conductivity increased by going through the reheating process as in these experimental examples.
  Vanadium oxide (V₂O₅), Barium oxide (BaO), iron oxide (Fe₂O₃As well as oxide glass produced by melting and cooling the mixture of Vanadium oxide (V₂O₅), Diphosphorus pentoxide (P₂O₅), Oxide glass produced by melting and cooling a mixture of barium oxide (BaO), vanadium oxide (V₂O₅), Potassium oxide (K₂O), iron oxide (Fe₂O₃It was also confirmed that even in the oxide glass produced by melting and cooling the mixture of), the electrical conductivity increased through the reheating step.
  From the above, it can be said that the production method of the present invention can be widely applied to vanadate glass containing vanadium as a main component or a subcomponent and has high versatility.
[0030]
  (Relationship between reheating time and electrical conductivity)
  Example 1
  The oxide glass of Experimental Example 2 cooled to below the glass transition temperature was reheated in the atmosphere at 500 ° C., which is higher than the highest exothermic peak temperature (about 470 ° C.) and below the melting point (540 ° C.). Were taken out at regular intervals and the electrical conductivity at 25 ° C. was measured.
  (Example 2)
  The oxide glass of Experimental Example 2 cooled to the glass transition temperature or lower is reheated in the atmosphere at 400 ° C., which is a temperature exceeding the crystallization temperature (392 ° C.) and not higher than the melting point (540 ° C.). The electrical conductivity at 25 ° C. was measured.
  (Comparative Example 1)
  The oxide glass of Experimental Example 2 cooled to the glass transition temperature or lower is reheated in the atmosphere at 350 ° C., which is the glass transition temperature (328 ° C.) or higher and the crystallization temperature (392 ° C.) or lower, and is constant from the furnace. The electrical conductivity at 25 ° C. was taken out every hour. This reheating condition is the annealing condition described in Japanese Patent Application Laid-Open No. 2003-34548 (Patent Document 1) (a condition in which the temperature is maintained in the temperature range of the glass transition temperature to the crystallization temperature).
[0031]
  FIG. 3 is a graph showing the relationship between the reheating temperature and reheating time of the oxide glass of Experimental Example 2 and electrical conductivity. In FIG. 3, the horizontal axis represents the holding time at the reheating temperature, and the vertical axis represents the electrical conductivity σ (S · cm at 25 ° C.^-1).
  In Examples 1 and 2, in which the oxide glass of Experimental Example 2 cooled to below the glass transition temperature was reheated in the atmosphere at a temperature higher than the crystallization temperature (392 ° C.) and lower than the melting point (540 ° C.), It was confirmed that the electrical conductivity can be improved by 3 digits or more by reheating, and the electrical conductivity hardly fluctuates even if the reheating is continued. In addition, it was confirmed that Example 1 having a higher reheating temperature than Example 2 can increase electrical conductivity.
  On the other hand, in Comparative Example 1, which was reheated at a temperature not lower than the glass transition temperature (328 ° C.) and not higher than the crystallization temperature (392 ° C.), the electrical conductivity increased as the holding time at the reheating temperature increased, and 180 minutes or longer. It was confirmed that the electrical conductivity could not be kept constant unless it was maintained. Moreover, it was confirmed that the electrical conductivity of the comparative example 1 is one digit or more lower than the electrical conductivity of Example 1 and 2. FIG.
  From the above, according to the present embodiment, the electric conductivity does not vary depending on the time of holding at the reheating temperature, and the electric conductivity is drastically increased even if it is held for a short time of about 30 minutes in a predetermined temperature range. Further, it was revealed that even when the holding time varies, the electric conductivity does not vary and the production stability is remarkably excellent. Further, by changing the heating time in the reheating step, the magnitude of the electrical conductivity of the vanadate glass at room temperature is set to 10^-4S · cm^-1It has become clear that it is possible to design and control with high accuracy in the above-mentioned area.
[Industrial applicability]
[0032]
  The present invention relates to a method for producing a vanadate glass suitably used as an electrode material or the like.^-1S · cm^-1The vanadate glass having the above high electrical conductivity can be produced, and the electrical conductivity can be dramatically increased even if it is kept in a predetermined temperature range for a short time of about 30 minutes. Even if the holding time varies, the electrical conductivity does not fluctuate and the production stability and quality stability are remarkably excellent, and the product yield can be increased. Not only thermistors, heating elements and antistatic materials, but also SED -Conduction Electron-emitter Display (SCE) Surface-conduction electron-emitter (SCE), which is most suitable for commercialization of various electrode materials such as electron emission electrodes and discharge electrodes. A method for producing a vanadate glass can be provided.

Claims (2)

A method for producing a vanadate glass containing vanadium as a main component or a subcomponent,
A vitrification step of vitrifying a composition containing vanadium, barium and iron to produce an oxide glass, and the oxide glass, among the exothermic peaks of crystallization by differential thermal analysis (DTA) of the oxide glass, And a reheating step of maintaining for a predetermined time in a temperature range exceeding the highest temperature exothermic peak temperature and not higher than the melting point, a method for producing a vanadate glass. Wherein the composition is a mixture containing vanadium oxide, barium oxide and iron oxide, claim 1, wherein the oxide glass, characterized in that said mixture is obtained it is rapidly cooled after melted by heating The manufacturing method of vanadate glass as described in any one of.

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