538014 A7 〜^ -B7____ 五、發明說明（'） t明背景 發明領域 (請先閱讀背面之注意事項再填寫本頁) 本發明係關於具有保護塗層之含碳耐火物件。更特別地, 本發明敘述減少碳氧化之保護塗層。 先行技藝說明 耐火物.件，其用於鋼之連續鑄製，經常包括耐火氧化物及 大量之元素碳。碳在接觸熔化之鋼時可改良物件到熱化學 及熱機械應力之抗性。例如，中間平巷圍板（SES)將熔化之 鋼由澆注盤轉移至模，而且經常包括5-40重量％之石墨。 碳易於氧化，其可嚴重地損壞耐火物件之性能。高溫加速 氧化且至少在燃燒、預熱及鑄製操作時發生。含碳物件經 常在還原、井氧化氣氛中燃燒，使得然後無法發生氧化。相 反地，在預熱.鑄造操作時還原氣氛是不實際的。爲了抑制 氧化，經常以相當不透氣之保護塗層覆蓋物件。保護塗層可 由熔融形成保護性、氧屏障之固體或液體。重要地，保護塗 層應”濕潤”及完全塗覆物件而無缺陷或”針孔”。保護塗層 中之針孔使氧接觸及氧化含碳耐火物件。不幸地，碳本身因 保護塗層而抑制濕潤。 經濟部智慧財產局員工消費合作社印製 不只設計用於含碳耐火物件之塗層亦嘗試減少針孔及改 良濕潤。例如，Akhtar之美國專利5,01 3,697教示用於半導 體工業之密封玻璃，其使用達30重量％之氧化鉍將熔融溫 度降低至400°C以下，並且改良釉在陶瓷基質上之濕潤力，特 別是塗覆金屬之陶瓷。密封玻璃將兩個陶瓷表面黏合在一 起而形成抗破裂及破壞之煉金上密封容器。降低之熔融溫 本紙張尺度適用中國國家標準（CNS)A4規格（210 X 297公釐） 538014 A7 B7 五、發明說明（> ) 度減少對半導體之損壞。Akhtar並未教示用於含碳基質，針 孔減少，或在高溫應用之用途之保護塗層。 (請先閱讀背面之注意事項再填寫本頁) EP-A-02 5 262 1專利確實敘述用於含碳耐火物件之保護塗 層。此塗層包括用於電弧爐石墨電極之固態粒狀釉。該釉 包含20-40重量％之經石墨濕潤可熔融材料、35-70重量％ 之耐火塡料、及10-25重量％之金屬或類金屬，其可在電極 爲高溫時氧化成耐火氧化物。該經石墨濕潤之可熔融材料 爲硼化合物或含硼玻璃，如硼矽酸鹽玻璃。該金屬或類金屬 較佳爲鋁，而且意圖在氧到達耐火物件之前與任何氧反應。 在熱電極上噴灑及熔融固態粒狀釉。包括鹼與硼氧化物之 類似之固態組成物亦由DE-A1 -42 1 6934專利之文件得知。 這些組成物被塗抹、搗平或噴灑。噴灑、塗抹或搗平無法 容易地及快速地塗覆複雜之幾何圖或孔穴，例如，其包括澆 注管之孔。 其他亦包括氧化硼之保護組成物揭示於美國專利 3,460,987。然而，這些組成物無法直接用於含少於5%之氧 化硼之基質，因此無法用在大部份用於玻璃或金屬工業之含 碳耐火物件。 申請人在此倂入Buchanan之美國專利5,856,0 1 5的參考 經濟部智慧財產局員工消費合作社印製 資料，其教示用於含碳物件之保護塗層。此保護塗層爲包括 黏土、玻璃玻料、鋁、矽或其合金之粉末及抑制劑之水性 懸浮液。該玻料爲具有低於600°C之軟化點之硼矽酸鹽、 硼磷酸鹽或磷酸鹽玻璃。該粉末敘述爲抗氧化劑，其抑制碳 之氧化。該抑制劑敘述爲降低粉末對水之反應性。抑制劑 ^ -4- 本紙張尺度適用中國國家標準（CNS)A4規格（210 X 297公釐） 538014 A7 B7 五、發明說明（4 ) (請先閱讀背面之注意事項再填寫本頁) 與水之間之反應散逸氫氣而在塗層造成氣泡及針孔。該抑 制劑包括多種酸與鹽，而且較佳爲三磷酸鈉。其益處爲包括 改良之儲存壽命及促進更平均之保護塗層。 儘管有濕潤助劑與抑制劑的加入，在含碳耐火物件上仍發 生針孔及生成氧化，特別是更包括氧化鋁、氧化鎂與氧化锆 之物。仍持續有在高溫減少含碳耐火物件上之針孔，並且在 預熱及鑄製操作時保護物件免於氧化之保護塗層之需求。 發明槪耍 本發明係關於具有保護物件免於氧化之塗層之含碳耐火 物件。在廣義狀態中，此物件包括一種形式之碳，較佳爲石 墨，及至少一種其他耐火成分，例如，如氧化物，碳化物或氮化 物。保護塗層包括二氧化矽、氧化硼、氧化鋁及濕潤助劑。 或者，氧化鈣或氧化鎂可取代所有或部份之氧化鋁。 最常爲含碳耐物件敘述爲在鑄製時接觸熔化金屬流之物 件，例如，圍板、噴嘴、單塊或塞焊。或者，物件可爲坩堝或 其他容納或接觸熔化金屬之耐火物件。 經濟部智慧財產局員工消費合作社印製 該保護塗層敘述爲對於濕潤耐火組成物之困難特別有效， 如包括氧化鎂及氧化锆之物件。該濕潤助劑敘述爲在高溫 降低保護塗層之表面能量，因而改良濕潤及減少含碳耐火物 件之針孔及氧化。在一種狀態中，該濕潤助劑敘述爲選自 砷、鍊、鉍、錫、釩及錯之金屬構成之金屬氧化物。較佳 爲，金屬氧化物爲氧化鉍且以1 0重量％或更少而存在。 在本發明之進一步具體實施例中，保護塗層亦包括助熔劑， 其改良保護塗層之流動性。助熔劑可爲鹼金屬之氧化物，而 本紙張尺度適用中國國家標準（CNS)A4規格（210 X 297公釐） 538014 A7 B7 五、發明說明（斗） 且較佳爲鋰、納或鉀之氧化物。 (請先閱讀背面之注咅？事項再填寫本頁) 本發明之其他細節與優點隨以下實行本發明之較佳方法 之說明而變爲明顯的。 發明詳細說明 本發明係關於具有保護塗層之含碳耐火物件。該耐火物 件包括在對物件性能有重大影響之碳氧化量之任何含碳之 物件。一般而言，該耐火物件包括2_40重量％之碳，而且碳 爲石墨之形式。此種物件亦經常爲碳鍵結且意圖直接接觸 熔化之金屬。除了碳，物件包括至少一種耐火成分，例如，耐 火氧化物、碳化物或氮化物。此種耐火成分之選擇對熟悉 此技藝者爲已知的技術。耐火物件之實例包括沈沒中間噴 嘴、沈沒中間平巷、滑閘板、塞桿、石墨電極、坩堝及其 他用於鋼與冶金工業之組件。耐火物件亦可包括”單塊”物 件，其爲包括堅定地固定於管之滑閘板單片，如噴嘴或圍 板。 經濟部智慧財產局員工消費合作社印製 保護塗層包括小部份之高溫濕潤助劑，及包括適合氧化物 之主要部份，如氧化矽、氧化硼、及鋁、鈣或鎂之氧化物。 本發明之主要部份實質上敘述於美國專利5,856,0 1 5,其教 示申請人在此倂入作爲參考。此主要部份由耐火氧化物之 顆粒形成，特別是包括硼矽酸鹽、硼磷酸鹽或磷酸鹽之無紿 及無鋇玻璃，其具有低於60(TC之熱膨脹軟化點。此主要部 份具有40-80重量％之氧化矽、5-20重量％之氧化硼、及5-20 重量％之至少一種選自包括氧化鋁、氧化鈣與氧化鎂之耐 火氧化物。此外，此主要部份可具有至多4重量％之氧化鈷。 -6- 本紙張尺度適用中國國家標準（CNS)A4規格（210 X 297公爱） 538014 A7 B7 五、發明說明（r ) 此主要部份通常以至多約99重量％存在於保護塗層中。 (請先閱讀背面之注音？事項再填寫本頁) 此主要部份亦包含在耐火物件中之元素碳之前犧牲氧化 之抗氧化劑。該抗氧化劑之包含物可推薦抑制劑之使用，其 可延遲抗氧化劑之氧化。抗氧化劑及抑制劑可包括主要部 份至多約30重量％。適合之抗氧化劑包括金屬、類金屬、 碳化物、氮化物之粉末或其組合。該詞”粉末”包括粉末及 屑狀材料。粉末較佳爲具有1至250微米，而且最佳爲10 至50微米範圍之粒度。在需要較厚保護塗層時，較大之粒 度較佳。常用之抗氧化劑包括鋁、鎂、硼、鈣、矽及矽、 鈣、銷、硼、鉅與鈦之碳化物。 經濟部智慧財產局員工消費合作社印製 高溫濕潤助劑在高於約300°C之溫度改良含碳耐火物件 上之保護塗層濕潤。改良之濕潤減少針孔及增加保護塗層 保護物件免於氧化之能力。不意圖受此解釋限制，濕潤助劑 可降低保護塗層之表面能量，因而改良濕潤，減少針孔及氧 對含碳耐火物件之擴散。濕潤助劑包括選自砷、銻、鉍、 錫、釩與鉛之金屬之氧化物。氧化鉍作爲濕潤助劑特別有 用。應了解，這些金屬經常以其還原狀態及氧化物而存在。 含碳耐火物件在還原氣氛中之燃燒有助於還原金屬之存 在。如此工業所習知，還原金屬之存在以如同其爲氧化物之 重量％報告。 存在足量之濕濕助劑以改良濕潤及減少針孔。有效含量 視特定之條件而定，例如，耐火材料之組成物，保護塗層之厚 度、及熔融溫度。在濕潤助劑之量損壞主要部份之屏障性 質及使氧擴散通過塗層至含碳耐火物件時存在上限。較佳 -7- 本紙張尺度適用中國國家標準（CNS)A4規格（210 X 297公釐） 538014 Α7 Β7 i、發明說明（h ) 爲，濕潤助劑之量在保護塗層之0.5至1 0重量％之範圍。 (請先閱讀背面之注音？事項再填寫本頁) 保護塗層亦可包括在高溫降低保護塗層黏度之助熔劑。 較低之黏度增加流動性且使保護塗層更易於密封塗層中之 少量缺點。助熔劑不應有害地與保護塗層之其他成分反應， 特別是抗氧化劑。助熔劑加成之含量視所需之特定性質而 定，而且易由熟悉此技藝者決定。鹼金屬（如鋰、鈉與鉀）之 氧化物及氟化物爲特別有用之助熔劑。助熔劑在至多約5 重量％之範圍最有效；雖然可使用至多約20重量％。 保護塗層可藉任何適合之塗佈方法塗佈於耐火物件，例如， 其包括滑鑄、浸漬、乾或濕噴、或膠合。視方法而定，可能 需要液體載體及流變調節劑之添加劑。此方法影響所需添 加物之型式及量。較佳爲，濕潤助劑及主要部份懸浮於液體 載體中。可使用流變調節劑將液體載體中之懸浮液增稠及 安定之，因而利於懸浮液在耐火物件上之塗佈。液體載體最 常爲水，但是可爲其他適合之液體，如醇及其他有機溶劑。 需要足量之液體載體以懸浮濕潤助劑、主要部份、及流變 調節劑，使得保護塗層可塗佈於耐火物件上。液體載體與流 變調節劑之量可藉由組合保護塗層之其他成分，直到得到所 需之稠度而實驗地決定。 經濟部智慧財產局員工消費合作社印製 實1拒例 製造具有保護塗層之碳鍵結塞桿。塞桿主體爲碳鍵結且 包括氧化鋁及至少20重量％之石墨。塞桿之鼻包括氧化鎂 及至少20重量。/〇之石墨。保護塗層本質上包括以下之組成 物： 本紙張尺度適用中國國家標準（CNS)A4規格（210 X 297公t ) 538014 A7 ---B7 _ 五、發明說明（7 ) 材料 重量％ 氧化矽 62 (請先閱讀背面之注意事項再填寫本頁) 氧化硼 13 氧化銘 1 氧化鉀 2 氧化鈉 6 氧化鋰 2 氧化鈣 3 氧化鋁 9 氧化鉍 2 將保護塗層以水性懸浮液在超過800°C之氧化氣氛中加熱 之前塗佈於塞桿。保護塗層顯然完全濕潤塞桿且未觀察到 針孔。在空氣中將具有保護塗層之塞桿加熱至1100 °C 90 分鐘之時間。未注意到有氧化或去碳。相對地，無加護塗層 之塞桿呈現廣泛之氧化且因碳鍵結退化而變脆。 顯然地，本發明之許多修改及變化爲可能的。因此，應了 解在以下申請專利範圍之範圍內，可未如特別地敘述而實行 本發明。 經濟部智慧財產局員工消費合作社印製 本紙張尺度適用中國國家標準（CNS)A4規格（210 X 297公釐）538014 A7 ~ ^ -B7 ____ V. Description of the invention (') Background of the invention (please read the precautions on the back before filling this page) The present invention relates to carbon-containing refractory articles with protective coatings. More specifically, the present invention describes a protective coating that reduces carbon oxidation. Description of prior art refractories. Pieces used in the continuous casting of steel, often including refractory oxides and large amounts of elemental carbon. Carbon improves the resistance of objects to thermochemical and thermomechanical stresses when in contact with molten steel. For example, the middle runway siding (SES) transfers molten steel from the casting pan to the mold, and often includes 5-40% by weight of graphite. Carbon is susceptible to oxidation, which can severely damage the performance of refractory objects. High-temperature accelerated oxidation occurs at least during combustion, preheating, and casting operations. Carbonaceous objects are often burned in a reducing, well-oxidizing atmosphere, so that oxidation cannot then occur. In contrast, it is not practical to reduce the atmosphere during the preheating. Casting operation. To suppress oxidation, objects are often covered with a fairly air-impermeable protective coating. Protective coatings can be formed by melting to form a protective, oxygen barrier solid or liquid. Importantly, the protective coating should be "wet" and fully coated with no defects or "pinholes". Pinholes in the protective coating allow oxygen to contact and oxidize carbon-containing refractory objects. Unfortunately, carbon itself inhibits wetting due to the protective coating. Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs. Not only coatings designed for carbon-containing refractory objects, but also attempts to reduce pinholes and improve wetting. For example, U.S. Patent No. 5,01 3,697 to Akhtar teaches sealing glass for the semiconductor industry, which uses up to 30% by weight of bismuth oxide to reduce the melting temperature to below 400 ° C, and improves the wetting force of the glaze on the ceramic substrate. It is a metal-coated ceramic. Sealed glass glues two ceramic surfaces together to form a sealed container on an alchemy that resists cracking and destruction. Reduced melting temperature This paper is sized for China National Standard (CNS) A4 (210 X 297 mm) 538014 A7 B7 V. Description of the invention (>) Reduces damage to semiconductors. Akhtar does not teach protective coatings for carbonaceous substrates, pinhole reduction, or applications in high temperature applications. (Please read the precautions on the back before filling out this page) EP-A-02 5 262 1 The patent does describe a protective coating for carbon-containing refractory objects. This coating includes solid granular glazes for electric arc furnace graphite electrodes. The glaze contains 20-40% by weight of a graphite wettable meltable material, 35-70% by weight of a refractory material, and 10-25% by weight of a metal or metal-like material, which can be oxidized to a refractory oxide when the electrode is at a high temperature . The graphite wettable fusible material is a boron compound or a boron-containing glass, such as a borosilicate glass. The metal or metalloid is preferably aluminum and is intended to react with any oxygen before it reaches the refractory. Spray and melt solid granular glaze on the hot electrode. Similar solid compositions including bases and boron oxides are also known from DE-A1 -42 1 6934. These compositions are smeared, smoothed or sprayed. Spraying, smearing, or smoothing cannot easily and quickly coat complex geometries or cavities, for example, it includes holes for a pouring tube. Other protective compositions that also include boron oxide are disclosed in U.S. Patent 3,460,987. However, these compositions cannot be used directly on substrates containing less than 5% boron oxide, and therefore cannot be used on most carbon-containing refractory articles used in the glass or metal industry. The applicant hereby incorporates reference from US Patent No. 5,856,0 15 of Buchanan, printed by the Consumers ’Cooperative of the Intellectual Property Bureau of the Ministry of Economics, which teaches protective coatings for carbonaceous objects. The protective coating is an aqueous suspension including powders and inhibitors of clay, glass frit, aluminum, silicon or alloys thereof. The frit is a borosilicate, borophosphate or phosphate glass with a softening point below 600 ° C. The powder is described as an antioxidant, which inhibits the oxidation of carbon. The inhibitor is described as reducing the reactivity of the powder to water. Inhibitors ^ -4- This paper size is in accordance with Chinese National Standard (CNS) A4 (210 X 297 mm) 538014 A7 B7 V. Description of the invention (4) (Please read the precautions on the back before filling this page) and water The reaction between them dissipates hydrogen and causes bubbles and pinholes in the coating. The inhibitor includes a variety of acids and salts, and is preferably sodium triphosphate. The benefits include improved shelf life and promotion of a more even protective coating. Despite the addition of wetting aids and inhibitors, pinholes and oxidation have occurred on carbon-containing refractories, especially those that include alumina, magnesia, and zirconia. There continues to be a need for protective coatings to reduce pinholes in carbonaceous refractory articles at high temperatures and to protect articles from oxidation during preheating and casting operations. The invention relates to a carbonaceous refractory article having a coating that protects the article from oxidation. In the broad state, the object includes one form of carbon, preferably graphite, and at least one other refractory component, such as, for example, an oxide, carbide, or nitride. Protective coatings include silicon dioxide, boron oxide, aluminum oxide, and wetting additives. Alternatively, calcium oxide or magnesium oxide may replace all or part of the alumina. Carbon-containing refractory items are most often described as items that come in contact with molten metal flow during casting, such as enclosures, nozzles, monoliths, or plug welds. Alternatively, the object may be a crucible or other refractory object containing or contacting molten metal. Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs This protective coating is described as particularly effective against the difficulties of wetting refractory compositions, such as objects including magnesia and zirconia. The wetting additive is described to reduce the surface energy of the protective coating at high temperatures, thereby improving wetting and reducing pinholes and oxidation of carbon-containing refractory parts. In one state, the wetting aid is described as a metal oxide composed of a metal selected from the group consisting of arsenic, chain, bismuth, tin, vanadium and metal. Preferably, the metal oxide is bismuth oxide and is present at 10% by weight or less. In a further embodiment of the invention, the protective coating also includes a flux, which improves the fluidity of the protective coating. The flux can be an oxide of an alkali metal, and this paper size applies the Chinese National Standard (CNS) A4 specification (210 X 297 mm) 538014 A7 B7 V. Description of the invention (bucket) and preferably lithium, sodium or potassium Oxide. (Please read the note on the back? Matters before filling out this page) Other details and advantages of the present invention will become apparent with the following description of the preferred method of implementing the present invention. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a carbon-containing refractory article having a protective coating. The refractory article includes any carbonaceous article in the amount of carbon oxidation that has a significant effect on the performance of the article. Generally, the refractory article includes 2 to 40% by weight of carbon, and the carbon is in the form of graphite. Such objects are also often carbon-bonded and intended to be in direct contact with molten metal. In addition to carbon, the article includes at least one refractory component, such as a refractory oxide, carbide, or nitride. The choice of such refractory ingredients is known to those skilled in the art. Examples of refractory objects include sunk intermediate nozzles, sunk intermediate tunnels, slides, plugs, graphite electrodes, crucibles, and other components used in the steel and metallurgical industries. Refractory articles may also include "monolithic" articles, which are monolithic pieces including a slide plate firmly fixed to a tube, such as a nozzle or a fence. Printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs. The protective coating includes a small amount of high-temperature wetting aids, and includes major parts suitable for oxides, such as silicon oxide, boron oxide, and aluminum, calcium, or magnesium oxides. A substantial portion of the present invention is described substantially in U.S. Patent No. 5,856,0 15, which teaches applicants to incorporate herein by reference. This main part is formed of particles of refractory oxide, especially thorium-free and barium-free glass including borosilicate, borophosphate or phosphate, which has a thermal expansion softening point lower than 60 ° C. This main part 40-80% by weight of silicon oxide, 5-20% by weight of boron oxide, and 5-20% by weight of at least one selected from refractory oxides including alumina, calcium oxide, and magnesium oxide. In addition, this main part May have up to 4% by weight of cobalt oxide. -6- This paper size applies to the Chinese National Standard (CNS) A4 specification (210 X 297 public love) 538014 A7 B7 5. Description of the invention (r) This main part is usually up to about 99% by weight is present in the protective coating. (Please read the note on the back? Matters before filling out this page.) This main part also contains the antioxidants that sacrifice oxidation before the elemental carbon in the refractory. This antioxidant contains The use of inhibitors can be recommended, which can delay the oxidation of antioxidants. Antioxidants and inhibitors can include up to about 30% by weight. Suitable antioxidants include metal, metalloid, carbide, and nitride powders The combination. The term "powder" includes powder and crumb-like materials. The powder preferably has a particle size in the range of 1 to 250 microns, and most preferably 10 to 50 microns. When a thicker protective coating is required, a larger particle size Better. Commonly used antioxidants include aluminum, magnesium, boron, calcium, silicon and silicon, calcium, pin, boron, giant and titanium carbides. The high-temperature wetting additive printed by the Consumer Cooperative of the Intellectual Property Bureau of the Ministry of Economic Affairs is higher than A temperature of about 300 ° C improves the wetting of the protective coating on carbon-containing refractory objects. The improved wetting reduces pinholes and increases the ability of the protective coating to protect the object from oxidation. It is not intended to be limited by this explanation, and wetting additives can reduce protection The surface energy of the coating improves wetting, reducing pinholes and oxygen diffusion to carbon-containing refractory objects. Wetting additives include oxides of metals selected from arsenic, antimony, bismuth, tin, vanadium and lead. Bismuth oxide is used as wetting Additives are particularly useful. It should be understood that these metals often exist in their reduced state and oxides. The combustion of carbonaceous refractory objects in a reducing atmosphere helps to reduce the presence of metals. As is known in the industry The presence of reduced metal is reported as if it were an oxide in weight percent. A sufficient amount of wet and wet additives are present to improve wetting and reduce pinholes. The effective content depends on specific conditions, such as the composition of refractory materials, protective coatings Layer thickness and melting temperature. There is an upper limit when the amount of wetting additive damages the barrier properties of the main part and allows oxygen to diffuse through the coating to the carbon-containing refractory. CNS) A4 specification (210 X 297 mm) 538014 A7 B7 i. Description of the invention (h) is that the amount of wetting aid is in the range of 0.5 to 10% by weight of the protective coating. (Please read the note on the back first? Please fill in this page again) The protective coating can also include a flux that reduces the viscosity of the protective coating at high temperatures. The lower viscosity increases flowability and makes the protective coating easier to seal small defects in the coating. Fluxes should not adversely react with other components of the protective coating, especially antioxidants. The amount of flux addition depends on the specific properties required and can easily be determined by those skilled in the art. Oxides and fluorides of alkali metals such as lithium, sodium and potassium are particularly useful fluxes. Fluxes are most effective in a range of up to about 5 weight percent; although up to about 20 weight percent can be used. The protective coating may be applied to the refractory article by any suitable coating method, including, for example, slip casting, dipping, dry or wet spraying, or gluing. Depending on the method, additives for liquid carriers and rheology modifiers may be required. This method affects the type and amount of additives required. Preferably, the wetting aid and the main part are suspended in a liquid carrier. The rheology modifier can be used to thicken and stabilize the suspension in the liquid carrier, thus facilitating the coating of the suspension on the refractory. The liquid carrier is most often water, but may be other suitable liquids, such as alcohols and other organic solvents. A sufficient amount of liquid carrier is needed to suspend the wetting aid, the main part, and the rheology modifier so that the protective coating can be applied to the refractory article. The amount of liquid carrier and rheology modifier can be determined experimentally by combining other ingredients of the protective coating until the desired consistency is obtained. Printed by the Consumer Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs. Example 1 Refusal Manufacture of carbon-bonded plugs with protective coatings. The plug body is carbon-bonded and includes alumina and at least 20% by weight of graphite. The nose of the stem includes magnesium oxide and at least 20 weights. / 〇 的 Graphite. The protective coating essentially includes the following components: The paper size is applicable to the Chinese National Standard (CNS) A4 specification (210 X 297 g t) 538014 A7 --- B7 _ V. Description of the invention (7) Material weight% Silicon oxide 62 (Please read the precautions on the reverse side before filling out this page) Boron oxide 13 Oxide oxide 1 Potassium oxide 2 Sodium oxide 6 Lithium oxide 2 Calcium oxide 3 Alumina 9 Bismuth oxide 2 Protective coating in an aqueous suspension at more than 800 ° C Apply to the plug before heating in an oxidizing atmosphere. The protective coating clearly wets the plug stem completely and no pinholes are observed. Heat the plug with a protective coating in air to 1100 ° C for 90 minutes. No oxidation or decarbonization was noted. In contrast, plugs without a protective coating exhibit extensive oxidation and become brittle due to carbon bond degradation. Obviously, many modifications and variations of the present invention are possible. Therefore, it should be understood that the present invention may be practiced without being specifically described within the scope of the following patent application. Printed by the Employees' Cooperatives of the Intellectual Property Bureau of the Ministry of Economic Affairs This paper is sized to the Chinese National Standard (CNS) A4 (210 X 297 mm)