TWI758224B - Method of fabricating modified ferrite magnetic powder and ferrite magnet - Google Patents
Method of fabricating modified ferrite magnetic powder and ferrite magnet Download PDFInfo
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本發明係關於一種磁粉與磁石的製造方法，特別是關於一種改質鐵氧體磁粉的製造方法及改質鐵氧體磁石的製造方法。The present invention relates to a method for manufacturing a magnetic powder and a magnet, in particular to a method for manufacturing a modified ferrite magnetic powder and a method for manufacturing a modified ferrite magnet.
近年來，隨著電子零部件的小型化、輕量化以及高性能化，對於由氧化物構成的永磁鐵氧體磁體，也不斷要求具有較高的磁氣特性。作為永磁鐵氧體磁體的磁氣特性之指標一般以剩磁(B r)以及矯頑磁力( iH c)作為指標。一直以來，為了達到高剩磁與高矯頑磁力的特性，永磁鐵氧體磁體中的元素成份組成之探討一直在進行著。 In recent years, with the reduction in size, weight, and performance of electronic components, permanent ferrite magnets composed of oxides have been increasingly required to have higher magnetic properties. As indicators of the magnetic properties of permanent ferrite magnets, remanence ( Br ) and coercive force ( iHc ) are generally used as indicators. For a long time, in order to achieve the characteristics of high remanence and high coercivity, the elemental composition of permanent ferrite magnets has been studied.
另外，永磁鐵氧體磁體除了具有高剩磁與高矯頑磁力之外，矩形度(Sauareness ratio)也要盡可能的高(矩形度為：在90%的B r的時候，其磁場值(H k)相對於 iH c之比例。即，如果H k/ iH c高的話，則由外部磁場和溫度變化所引起的退磁(Demagnetization)就會比較小，也代表磁體本身的磁場配向度較高，因此能夠得到更穩定的磁氣特性。除此之外，另一個永磁鐵氧體磁體生產上的指標則是需達到減少磁體於磁場成型後之生胚產生裂紋或是燒結製程中磁體出現缺陷機率，以進一步提高永磁鐵氧體磁體量產之良率。然而，現有的永磁鐵氧體磁體的製造方法並無法同時達成上述對於磁氣性質與量產良率的要求。 In addition, in addition to high remanence and high coercivity, permanent ferrite magnets should also have a Sauareness ratio as high as possible (the Sauareness ratio is: at 90% of B r , its magnetic field value ( The ratio of H k ) to i H c . That is, if H k / i H c is high, the demagnetization (Demagnetization) caused by the external magnetic field and temperature changes will be relatively small, which also represents the magnetic field alignment of the magnet itself higher, so more stable magnetic properties can be obtained. In addition, another indicator for the production of permanent ferrite magnets is to reduce the cracks in the green embryo after the magnet is formed in the magnetic field or the magnet during the sintering process. Defect probability occurs to further improve the mass production yield of permanent ferrite magnets. However, the existing manufacturing methods of permanent ferrite magnets cannot simultaneously meet the above requirements for magnetic properties and mass production yield.
故，有必要提供一種改質鐵氧體磁粉及磁石的製造方法，以解決習用技術所存在的問題。Therefore, it is necessary to provide a manufacturing method of modified ferrite magnetic powder and magnet to solve the problems existing in the conventional technology.
本發明之一目的在於提供一種鐵氧體磁粉及磁石的製造方法，其係利用特定的細粉碎步驟及混合步驟，以使兩種不同平均粒徑的細粉碎顆粒混合，進而降低小於0.1微米的超細微粒(相對於單次細粉碎形成相近粒徑的細粉末而言)，以避免或減少鐵氧體磁石中不利於磁特性的非磁性相的生成，並且可增加鐵氧體磁石的良率，進而減少生產成本。One object of the present invention is to provide a method for manufacturing ferrite magnetic powder and magnet, which utilizes a specific fine pulverizing step and a mixing step to mix two fine pulverized particles with different average particle sizes, thereby reducing the particle size smaller than 0.1 micron. Ultrafine particles (compared to fine powders with similar particle size formed by single fine crushing) can avoid or reduce the formation of non-magnetic phases that are unfavorable for magnetic properties in ferrite magnets, and can increase the good quality of ferrite magnets. rate, thereby reducing production costs.
為達上述之目的，本發明提供一種改質鐵氧體磁粉的製造方法，其包含步驟：提供一混合物，其中該混合物包含一氧化鐵粉及一鍶化物；進行一煅燒步驟，對該混合物以1260至1300℃之間的溫度持溫達50至70分鐘之間，以形成一前處理物；對該前處理物進行一粗粉碎步驟，以形成多個粗粉碎顆粒，其中以使該些粗粉碎顆粒的一平均粒徑介於2.5至2.7微米之間； 對該些粗粉碎顆粒進行一細粉碎步驟，其中該細粉碎步驟分別將該些粗粉碎顆粒粉碎成第一細粉碎顆粒及第二細粉碎顆粒，其中該第一細粉碎顆粒的一平均粒徑介於0.9至1微米之間，以及該第二細粉碎顆粒的一平均粒徑介於0.5至0.6微米之間；以及混合該第一細粉碎顆粒以及該第二細粉碎顆粒以獲得該改質鐵氧體磁粉，其中該改質鐵氧體磁粉的一平均粒徑介於0.7至0.8微米之間。In order to achieve the above object, the present invention provides a manufacturing method of modified ferrite magnetic powder, which comprises the steps of: providing a mixture, wherein the mixture comprises iron oxide powder and a strontium compound; performing a calcination step, the mixture is The temperature between 1260 and 1300° C. is maintained for 50 to 70 minutes to form a pretreatment; a coarsely pulverizing step is performed on the pretreatment to form a plurality of coarsely pulverized particles, wherein the coarsely pulverized particles are formed. an average particle size of the pulverized particles is between 2.5 and 2.7 microns; a fine pulverizing step is performed on the coarsely pulverized particles, wherein the fine pulverizing step pulverizes the coarsely pulverized particles into first fine pulverized particles and second fine pulverized particles respectively finely pulverized particles, wherein an average particle size of the first finely pulverized particles is between 0.9 and 1 micron, and an average particle diameter of the second finely pulverized particles is between 0.5 and 0.6 microns; and mixing the first finely pulverized particles a finely pulverized particle and the second finely pulverized particle to obtain the modified ferrite magnetic powder, wherein an average particle size of the modified ferrite magnetic powder is between 0.7 and 0.8 microns.
在本發明之一實施例中，該前處理物的一分子式係SrO．nFe 2O 3，其中n介於5至6之間。 In one embodiment of the present invention, a molecular formula of the pretreatment is SrO. nFe 2 O 3 , where n is between 5 and 6.
在本發明之一實施例中，該混合物更包含一鈷化物及一鑭化物中的至少一種。In one embodiment of the present invention, the mixture further comprises at least one of a cobalt compound and a lanthanide compound.
在本發明之一實施例中，該前處理物的一分子式係(Sr 2+ 1-xLa 3+ x)O．n(Fe 3+ 1-yCo 2+ y) 2O 3，其中n介於5至6之間，x介於0.25至0.3之間，以及y介於0.01至0.02之間。 In one embodiment of the present invention, a molecular formula of the pretreatment product is (Sr 2+ 1-x La 3+ x )O. n(Fe 3+ 1-y Co 2+ y ) 2 O 3 , where n is between 5 and 6, x is between 0.25 and 0.3, and y is between 0.01 and 0.02.
在本發明之一實施例中，在提供該混合物的步驟中，更包含：提供一添加劑，其中該添加劑包含碳酸鈣、氧化矽、五氧化二磷以及氧化硼中的至少一種。In one embodiment of the present invention, in the step of providing the mixture, it further comprises: providing an additive, wherein the additive comprises at least one of calcium carbonate, silicon oxide, phosphorus pentoxide and boron oxide.
在本發明之一實施例中，該添加劑包含碳酸鈣及氧化矽，並且以該混合物的一總重為100重量份計，碳酸鈣係介於0.5至1.5重量份之間；以及氧化矽係介於0.2至0.8重量份之間。In one embodiment of the present invention, the additive comprises calcium carbonate and silicon oxide, and based on a total weight of the mixture as 100 parts by weight, the calcium carbonate is between 0.5 and 1.5 parts by weight; and the silicon oxide is an intermediate Between 0.2 and 0.8 parts by weight.
在本發明之一實施例中，該添加劑包含碳酸鈣、氧化矽、五氧化二磷以及氧化硼，並且以該混合物的一總重為100重量份計，碳酸鈣係介於0.5至1.5重量份之間；氧化矽係介於0.2至0.8重量份之間；五氧化二磷係大於零且小於等於0.1重量份；以及氧化硼係大於零且小於等於1重量份。In one embodiment of the present invention, the additive comprises calcium carbonate, silicon oxide, phosphorus pentoxide and boron oxide, and based on a total weight of the mixture as 100 parts by weight, the calcium carbonate is between 0.5 and 1.5 parts by weight The silicon oxide is between 0.2 and 0.8 parts by weight; the phosphorus pentoxide is greater than zero and less than or equal to 0.1 parts by weight; and the boron oxide is greater than zero and less than or equal to 1 part by weight.
在本發明之一實施例中，在提供該混合物的步驟之後以及進行該煅燒步驟之前更包含對該混合物進行一脫水步驟，其中經該脫水步驟處理後的該混合物的含水率係介於18%至24%之間。In an embodiment of the present invention, after the step of providing the mixture and before the step of calcining, the mixture further includes a dehydration step, wherein the moisture content of the mixture after the dehydration step is between 18% to 24%.
在本發明之一實施例中，以該改質鐵氧體磁粉的總重為100wt%，該第一細粉碎顆粉係介於59.5wt%至60.5wt%之間，以及該第二細粉碎顆粒係介於39.5wt%至40.5wt%之間。In one embodiment of the present invention, the total weight of the modified ferrite magnetic powder is 100wt%, the first finely pulverized particles are between 59.5wt% and 60.5wt%, and the second finely pulverized powder is between 59.5wt% and 60.5wt%. The particle system is between 39.5 wt % and 40.5 wt %.
為達上述之目的，本發明提供一種改質鐵氧體磁石的製造方法，其包含步驟：提供一改質鐵氧體磁粉，其中該改質鐵氧體磁粉係通過如上任一實施例所述之改質鐵氧體磁粉的製造方法所製成；對該鐵氧體磁粉進行一磁場配向成型步驟，以形成一胚體，其中該磁場配向成型步驟的一配向磁場強度係介於1.3至1.7特斯拉之間，一成型壓力係介於3至4噸/平方公分之間，以及一成型時間係介於90至110秒之間；以及進行一燒結步驟，對該胚體以介於1220至1240℃之間的溫度持續燒結達50至70分鐘之間，以製得一鐵氧體磁石。In order to achieve the above-mentioned purpose, the present invention provides a method for manufacturing a modified ferrite magnet, which comprises the steps of: providing a modified ferrite magnetic powder, wherein the modified ferrite magnetic powder is produced by the method described in any of the above embodiments. The invention is made by the manufacturing method of the modified ferrite magnetic powder; a magnetic field alignment molding step is performed on the ferrite magnetic powder to form a green body, wherein an alignment magnetic field strength of the magnetic field alignment molding step is between 1.3 and 1.7 Between Tesla, a molding pressure is between 3 and 4 tons/cm 2 , and a molding time is between 90 and 110 seconds; The sintering is continued at a temperature between 1240°C for between 50 and 70 minutes to produce a ferrite magnet.
為了讓本發明之上述及其他目的、特徵、優點能更明顯易懂，下文將特舉本發明較佳實施例，並配合所附圖式，作詳細說明如下。再者，本發明所提到的方向用語，例如上、下、頂、底、前、後、左、右、內、外、側面、周圍、中央、水平、橫向、垂直、縱向、軸向、徑向、最上層或最下層等，僅是參考附加圖式的方向。因此，使用的方向用語是用以說明及理解本發明，而非用以限制本發明。In order to make the above-mentioned and other objects, features and advantages of the present invention more clearly understood, the preferred embodiments of the present invention will be exemplified below and described in detail in conjunction with the accompanying drawings. Furthermore, the directional terms mentioned in the present invention, such as up, down, top, bottom, front, rear, left, right, inner, outer, side, surrounding, center, horizontal, lateral, vertical, longitudinal, axial, Radial, uppermost or lowermost, etc., are only directions with reference to the attached drawings. Therefore, the directional terms used are for describing and understanding the present invention, not for limiting the present invention.
請參照第1圖所示，本發明一實施例之改質鐵氧體磁粉的製造方法10主要包含下列步驟11至15：提供一混合物，其中該混合物包含一氧化鐵粉及一鍶化物(步驟11)；進行一煅燒步驟，對該混合物以1260至1300℃之間的溫度持溫達50至70分鐘之間，以形成一前處理物(步驟12)；對該前處理物進行一粗粉碎步驟，以形成多個粗粉碎顆粒，其中以使該些粗粉碎顆粒的一平均粒徑介於2.5至2.7微米之間(步驟13)；對該些粗粉碎顆粒進行一細粉碎步驟，其中該細粉碎步驟分別將該些粗粉碎顆粒粉碎成第一細粉碎顆粒及第二細粉碎顆粒，其中該第一細粉碎顆粒的一平均粒徑介於0.9至1微米之間，以及該第二細粉碎顆粒的一平均粒徑介於0.5至0.6微米之間(步驟14)；以及混合該第一細粉碎顆粒以及該第二細粉碎顆粒以獲得該改質鐵氧體磁粉，其中該改質鐵氧體磁粉的一平均粒徑介於0.7至0.8微米之間(步驟15)。本發明將於下文逐一詳細說明實施例之上述各步驟的實施細節及其原理。Referring to FIG. 1, a
本發明一實施例之改質鐵氧體磁粉的製造方法10首先係步驟11：提供一混合物，其中該混合物包含一氧化鐵粉及一鍶化物。在本步驟11中，該氧化鐵粉例如可以是一市售產品，亦可以是一鋼鐵製程中所產生的副產品，例如鋼鐵在進行熱加工時需將鐵表面所生成的鐵銹去除，而該鐵銹可作為該氧化鐵粉的來源。在一實施例中，該鍶化物例如可包含碳酸鍶。值得一提的是，所提供的該混合物主要用於生成鍶系鐵氧體磁粉。The
在一實施例中，在提供該混合物的步驟11中，還可提供一添加劑，其中該添加劑包含碳酸鈣(CaCO
3)、氧化矽(SiO
2)、五氧化二磷(P
2O
5)以及氧化硼(B
2O
3)中的至少一種。以下說明各種添加劑的效果，其中所涉及的重量百分比皆是以該混合物的總重為100重量份計為基準。在一實施例中，該添加劑可在粉碎步驟中加入至球磨機中。
In one embodiment, in the
碳酸鈣是一種用於促進晶粒成長的元素，於本發明中碳酸鈣之添加量例如介於0.5至1.5重量份之間，當碳酸鈣添加量過多的時候(例如大於1.5重量份)，後續形成鐵氧體磁石所進行的燒結步驟中，會發生過量的晶粒增長，而導致矯頑磁力的降低。另一方面，當加入的碳酸鈣之添加量過少的時候(例如小於0.5重量份)，晶粒增長的現象會被過度抑制，進而導致與晶粒增長同時發生的取向的提高不足，最終導致剩磁(B r)低落。 Calcium carbonate is an element used to promote the growth of crystal grains. In the present invention, the amount of calcium carbonate added is between 0.5 and 1.5 parts by weight. During the sintering step performed to form ferrite magnets, excessive grain growth occurs, resulting in a decrease in coercivity. On the other hand, when the amount of calcium carbonate added is too small (for example, less than 0.5 parts by weight), the phenomenon of grain growth will be excessively suppressed, resulting in insufficient improvement of orientation that occurs simultaneously with grain growth, and ultimately leads to residual Magnetic (B r ) drops.
氧化矽之添加則是用來消除燒結時的晶粒增長，本發明中之氧化矽的添加量例如介於0.2至0.8重量份之間。當加入的氧化矽過少時(例如小於0.2重量份)，在燒結階段會發生過量的晶粒增長，而導致矯頑磁力降低。當加入的氧化矽過多時(例如大於0.8重量份)，在燒結階段之晶粒增長會過度消除，而導致與晶粒增長同時發生的取向之改進不足，最終而導致剩磁(B r)的下降。 The addition of silicon oxide is used to eliminate grain growth during sintering, and the added amount of silicon oxide in the present invention is, for example, between 0.2 and 0.8 parts by weight. When too little silicon oxide is added (eg, less than 0.2 parts by weight), excessive grain growth will occur in the sintering stage, resulting in a decrease in coercivity. When too much silicon oxide is added (for example, more than 0.8 parts by weight), the grain growth in the sintering stage will be eliminated excessively, resulting in insufficient improvement of the orientation that occurs simultaneously with the grain growth, and finally leads to the remanence (B r ) of the decline.
五氧化二磷之添加可提高矩形度(H k/ iH c)、剩磁(B r)及矯頑磁力( iH c)。本發明中之五氧化二磷的添加量例如可以是大於零且小於等於0.1重量份。若是未介於前述範圍，則無法提高前述的磁力性質。 The addition of phosphorus pentoxide can improve squareness (H k / i H c ), remanence (Br ) and coercivity ( i H c ). The amount of phosphorus pentoxide added in the present invention may be, for example, greater than zero and less than or equal to 0.1 part by weight. If it is not within the aforementioned range, the aforementioned magnetic properties cannot be improved.
氧化硼之添加是為了可降低在製得由永磁鐵氧體磁體構成的燒結磁體時之燒結溫度且同時能提高剩磁(B r)、矯頑磁力( iH c)，本發明中之氧化硼添加量例如是大於零且小於等於1重量份。若是未介於前述範圍，則無法提高前述的磁力性質。 The addition of boron oxide is to reduce the sintering temperature when making sintered magnets composed of permanent ferrite magnets and at the same time to improve the remanence ( Br ) and coercive force ( iHc ). The addition amount of boron is, for example, greater than zero and less than or equal to 1 part by weight. If it is not within the aforementioned range, the aforementioned magnetic properties cannot be improved.
在一實施例中，該添加劑包含碳酸鈣及氧化矽，並且以該混合物的一總重為100重量份計，碳酸鈣係介於0.5至1.5重量份之間；以及氧化矽係介於0.2至0.8重量份之間。在另一實施例中，該添加劑包含碳酸鈣、氧化矽、五氧化二磷以及氧化硼，並且以該混合物的一總重為100重量份計，碳酸鈣係介於0.5至1.5重量份之間；氧化矽係介於0.2至0.8重量份之間；五氧化二磷係大於零且小於等於0.1重量份；以及氧化硼係大於零且小於等於1重量份。In one embodiment, the additive comprises calcium carbonate and silicon oxide, and based on a total weight of 100 parts by weight of the mixture, the calcium carbonate is between 0.5 and 1.5 parts by weight; and the silicon oxide is between 0.2 and 100 parts by weight. Between 0.8 parts by weight. In another embodiment, the additive comprises calcium carbonate, silicon oxide, phosphorus pentoxide and boron oxide, and based on a total weight of the mixture as 100 parts by weight, the calcium carbonate is between 0.5 and 1.5 parts by weight ; Silicon oxide is between 0.2 and 0.8 parts by weight; phosphorus pentoxide is greater than zero and less than or equal to 0.1 parts by weight; and boron oxide is greater than zero and less than or equal to 1 part by weight.
本發明一實施例之改質鐵氧體磁粉的製造方法10接著係步驟12：進行一煅燒步驟，對該混合物以1260至1300℃之間的溫度持溫達50至70分鐘之間，以形成一前處理物。在本步驟12中，該煅燒步驟主要用於使該混合物在高溫反應，進行使該前處理物符合鍶系鐵氧體磁粉的分子式。在一實施例中，該前處理物的一分子式係SrO．nFe
2O
3，其中n介於5至6之間。在另一實施例中，進行該煅燒步驟處理時的一氣氛係包含5%的氧氣。
The
在一實施例中，該混合物還可包含一鈷化物及一鑭化物中的至少一種。具體而言，鈷化物中的鈷元素或是該鑭化物中的鑭元素，其皆有助於改質鐵氧體磁粉所製成的永磁鐵氧體磁石得到更高的剩磁(B r)、矯頑磁力( iH c)和矩形度(H k/ iH c)。在一範例中，該鈷化物例如是氧化鈷(Co 3O 4)。在另一範例中，該鑭化物例如是氧化鑭(La 2O 3)。在本實施例中，該混合物經煅燒步驟後所形成的該前處理物的一分子式係(Sr 2+ 1-xLa 3+ x)O．n(Fe 3+ 1-yCo 2+ y) 2O 3，其中，其中n介於5至6之間，x介於0.25至0.3之間，以及y介於0.01至0.02之間。在一實施例中，鈷化物可在後述的粉碎步驟中加入。 In one embodiment, the mixture may further include at least one of a cobalt compound and a lanthanide compound. Specifically, the cobalt element in the cobalt compound or the lanthanum element in the lanthanide compound helps the permanent ferrite magnet made from the modified ferrite magnetic powder to obtain higher remanence (B r ) , coercivity ( i H c ) and squareness (H k / i H c ). In one example, the cobalt compound is, for example, cobalt oxide (Co 3 O 4 ). In another example, the lanthanide compound is, for example, lanthanum oxide (La 2 O 3 ). In this embodiment, a molecular formula of the pretreatment product formed after the calcination step of the mixture is (Sr 2+ 1-x La 3+ x )O. n(Fe 3+ 1-y Co 2+ y ) 2 O 3 , wherein n is between 5 and 6, x is between 0.25 and 0.3, and y is between 0.01 and 0.02. In one embodiment, the cobalt compound may be added during the pulverization step described later.
在一實施例中，在提供該混合物的步驟11之後以及進行該煅燒步驟12之前更包含對該混合物進行一脫水步驟，其中經該脫水步驟處理後的該混合物的含水率係介於18%至24%之間。In one embodiment, after the
本發明一實施例之改質鐵氧體磁粉的製造方法10接著係步驟13：對該前處理物進行一粗粉碎步驟，以形成多個粗粉碎顆粒，其中以使該些粗粉碎顆粒的一平均粒徑介於2.5至2.7微米之間。在本步驟13中，將該前處理物粉碎至平均粒徑約達2.6微米左右。The
本發明一實施例之改質鐵氧體磁粉的製造方法10接著係步驟14：對該些粗粉碎顆粒進行一細粉碎步驟，其中該細粉碎步驟分別將該些粗粉碎顆粒粉碎成第一細粉碎顆粒及第二細粉碎顆粒，其中該第一細粉碎顆粒的一平均粒徑介於0.9至1微米之間，以及該第二細粉碎顆粒的一平均粒徑介於0.5至0.6微米之間。在本步驟14中，主要是將該些粗粉碎顆粒粉碎成兩種不同的平均粒徑。具體的，第一細粉碎顆粒之功能性在於能夠儘可能地降低混合後之整體瓷漿內部粒子徑＜0.1μm之過細磁粉比例，有助於提升濕式磁場成型所需瓷漿之成型性、成型良率及整體良率。第二細粉碎顆粒有別於第一細粉碎顆粒，其功能在於能進一步提升燒結後磁石內部之單磁區晶粒比例，對於磁石整體磁特性可起到明顯助益。The
在一實施例中，第一細粉碎顆粒例如是球磨機(Ball Mill)以料球重量比為1:12，磁粉漿料固含量約35~37%，轉速約為40rpm，濕式研磨3~4小時，進一步細化後出料得到第一細粉碎顆粒，以使第一細粉碎顆粒的平均粒徑(或稱平均磁粉粒度(D 50))達到0.95±0.05μm (例如可通過市售的費氏粒徑分析儀測得之窄單峰粒徑分佈。其中，鋼球可以是約為直徑Φ4.76mm的無鉻軸承鋼球。 In one embodiment, the first finely pulverized particles are, for example, a ball mill (Ball Mill) with a material-to-ball weight ratio of 1:12, a solid content of the magnetic powder slurry of about 35-37%, a rotational speed of about 40 rpm, and a wet grinding of 3-4 After further refining, the material is discharged to obtain the first finely pulverized particles, so that the average particle size of the first finely pulverized particles (or the average particle size of magnetic powder (D 50 )) reaches 0.95±0.05 μm (for example, it can be obtained by a commercially available fee. Narrow unimodal particle size distribution measured by a particle size analyzer, wherein the steel ball can be a chromium-free bearing steel ball with a diameter of about Φ4.76mm.
在一實施例中，第二細粉碎顆粒例如是球磨機(Ball Mill)以料球重量比為1:12，磁粉漿料固含量約35~37%，轉速約為40rpm，濕式研磨9~10小時，進一步細化後出料得到第一細粉碎顆粒，以使第二細粉碎顆粒的平均粒徑(或稱平均磁粉粒度(D 50))達到0.55±0.05μm (例如可通過市售的費氏粒徑分析儀測得之窄單峰粒徑分佈。其中，鋼球可以是約為直徑Φ4.76mm的無鉻軸承鋼球。 In one embodiment, the second finely pulverized particles are, for example, a ball mill (Ball Mill) with a material-to-ball weight ratio of 1:12, a solid content of the magnetic powder slurry of about 35-37%, a rotational speed of about 40 rpm, and a wet grinding of 9-10 After further refining, the material is discharged to obtain the first finely pulverized particles, so that the average particle size of the second finely pulverized particles (or the average particle size of magnetic powder (D 50 )) reaches 0.55±0.05 μm (for example, it can be obtained through a commercially available fee. Narrow unimodal particle size distribution measured by a particle size analyzer, wherein the steel ball can be a chromium-free bearing steel ball with a diameter of about Φ4.76mm.
本發明一實施例之改質鐵氧體磁粉的製造方法10接著係步驟15：混合該第一細粉碎顆粒以及該第二細粉碎顆粒以獲得該改質鐵氧體磁粉，其中該改質鐵氧體磁粉的一平均粒徑介於0.7至0.8微米之間。在本步驟15中，主要是通過混合的方式來形成平均粒徑介於0.7至0.8微米之間的改質鐵氧體磁粉。在一實施例中，以該改質鐵氧體磁粉的總重為100wt%，該第一細粉碎顆粉係介於59.5wt%至60.5wt%之間，以及該第二細粉碎顆粒係介於39.5wt%至40.5wt%之間。The
這種作法不同於傳統方法。具體而言，傳統方法通常是使用經細粉碎步驟的單一種平均粒徑的鐵氧體磁粉，例如，單純將粗粉碎顆粒直接研磨至平均粒徑介於0.7至0.8微米之間的細粉碎顆粒。這種作法雖然可以得到目標平均粒徑，但是這種作法會導致超微細粉(例如小於0.1微米的粒徑)的增加，反而導致產品的良率下降，並且產品的磁特性差(相關的實驗佐證在後面段落描述)。反之，本發明是利用混合的方式來將兩種粒徑的細粉碎顆粒形成改質鐵氧體磁粉，其可具有較少的超微細粉(相關的實驗佐證在後面段落描述)。This approach differs from traditional methods. Specifically, the conventional method usually uses a single average particle size ferrite magnetic powder that has undergone a fine pulverization step, for example, simply grinding the coarsely pulverized particles directly to finely pulverized particles with an average particle size between 0.7 and 0.8 microns . Although this method can obtain the target average particle size, this method will lead to the increase of ultra-fine powder (for example, the particle size of less than 0.1 microns), which will lead to the decrease of the yield of the product and the poor magnetic properties of the product (related experiments). The corroboration is described in the following paragraphs). On the contrary, the present invention uses a mixing method to form finely divided particles of two particle sizes into modified ferrite magnetic powder, which can have less ultrafine powder (relevant experimental evidence will be described in the following paragraphs).
這邊要提到的是，一般而言，該改質鐵氧體磁粉的平均粒徑越小，磁氣特性越佳。但是，該改質鐵氧體磁粉中粒徑過小的部分(即上述的細微顆粒)反而有害於磁氣特性與成型良率。具體而言，粒徑過小的部分的該改質鐵氧體磁粉容易在後續燒結步驟中產生非磁性相，進而有害於磁氣特性。另一方面，在後續磁場配向成型步驟中通常會使用一模具，以使該改質鐵氧體磁粉形成預定的形狀。該模具上通常會開設有多個小孔洞，以使該改質鐵氧體磁粉中的水份在加壓時流出。然而，該改質鐵氧體磁粉中粒徑過小的部分會在加壓過程中阻塞該些小孔洞，導致需以更大的壓力才能完成磁場配向成型步驟，導致胚體中形成較大的應力進而產生裂紋或是於燒結後產生缺陷。因此，通過上述特定參數的細粉碎步驟及混合步驟，進而減少或避免上述的問題。It should be mentioned here that, generally speaking, the smaller the average particle size of the modified ferrite magnetic powder, the better the magnetic properties. However, the portion of the modified ferrite magnetic powder with too small particle size (ie, the above-mentioned fine particles) is detrimental to the magnetic properties and the molding yield. Specifically, a portion of the modified ferrite magnetic powder with an excessively small particle size is likely to generate a non-magnetic phase in the subsequent sintering step, thereby detrimental to the magnetic properties. On the other hand, in the subsequent magnetic field alignment forming step, a mold is usually used to form the modified ferrite magnetic powder into a predetermined shape. The mold is usually provided with a plurality of small holes, so that the water in the modified ferrite magnetic powder can flow out when pressurized. However, the portion of the modified ferrite powder with too small particle size will block the small holes during the pressurization process, resulting in the need to use a higher pressure to complete the magnetic field alignment forming step, resulting in the formation of a larger stress in the embryo. Cracks or defects occur after sintering. Therefore, the above-mentioned problems can be reduced or avoided by the fine pulverization step and the mixing step of the above-mentioned specific parameters.
請參照第2圖，本發明另一實施例提出一種改質鐵氧體磁石的製造方法20，其包含步驟21至23：提供一改質鐵氧體磁粉，其中該改質鐵氧體磁粉係如上所述任一實施例的改質鐵氧體磁粉的製造方法所製成(步驟21)；對該改質鐵氧體磁粉進行一磁場配向成型步驟，以形成一胚體，其中該磁場配向成型步驟的一配向磁場強度係介於1.3至1.7特斯拉之間，一成型壓力係介於3至4噸/平方公分之間，以及一成型時間係介於90至110秒之間(步驟22)；以及進行一燒結步驟，對該胚體以介於1220至1240℃之間的溫度持續燒結達50至70分鐘之間，以製得該鐵氧體磁石(步驟23)。Referring to FIG. 2, another embodiment of the present invention provides a
本發明將於下文逐一詳細說明實施例之上述各步驟的實施細節及其原理。The present invention will hereinafter describe in detail the implementation details and principles of the above steps in the embodiments.
本發明一實施例之改質鐵氧體磁石的製造方法20首先係步驟21：提供一改質鐵氧體磁粉，其中該改質鐵氧體磁粉係如上所述任一實施例的改質鐵氧體磁粉的製造方法所製成。在本步驟21中，通過上述的改質鐵氧體磁粉的製造方法10製成該改質鐵氧體磁粉。The
本發明一實施例之改質鐵氧體磁石的製造方法20接著係步驟22：對該改質鐵氧體磁粉進行一磁場配向成型步驟，以形成一胚體，其中該磁場配向成型步驟的一配向磁場強度係介於1.3至1.7特斯拉之間，一成型壓力係介於3至4噸/平方公分之間，以及一成型時間係介於90至110秒之間。在本步驟22中，主要是提供成型壓力與配向磁場，以使該改質鐵氧體磁粉成型為預定的形狀並且具有預定的磁場方向。這邊要提到的是，由於使用改質鐵氧體磁粉的製造方法10製成的該改質鐵氧體磁粉，故可使用較低的成型時間即可成型為胚體，並且具有較高的良率。The
本發明一實施例之改質鐵氧體磁石的製造方法20最後係步驟23：進行一燒結步驟，對該胚體以介於1220至1240℃之間的溫度持續燒結達50至70分鐘之間，以製得該鐵氧體磁石。在本步驟23中，主要是通過燒結步驟以使該胚體中的水份去除以製得一鐵氧體磁石。The
這邊要提到的是，由於本發明實施例之改質鐵氧體磁石的製造方法20使用本發明實施例之改質鐵氧體磁粉的製造方法所製得的改質鐵氧體磁粉，其中該改質鐵氧體磁粉中的粒徑過小的部分較少。因此，在燒結步驟中不易產生非磁性相，並且在磁場配向成型步驟中也不易產生阻塞的問題，故可提高磁氣性質以及良率。It should be mentioned here that, since the
以下舉出數個實施例與比較例，以說明本發明實施例之改質鐵氧體磁粉的製造方法及本發明實施例之改質鐵氧體磁石的製造方法所製得的鐵氧體磁石確實具有上述的效果。Several examples and comparative examples are given below to illustrate the ferrite magnets obtained by the method for manufacturing the modified ferrite magnet powder according to the embodiment of the present invention and the method for manufacturing the modified ferrite magnet according to the embodiment of the present invention. It does have the above effect.
實施例1Example 1
首先，將主原料氧化鐵粉(Fe 2O 3)與另一種主原料碳酸鍶(SrCO 3)以SrO·nFe 2O 3(n=5.9)之基本組成進行配料，另同時加入4.9wt%的微量添加劑La 2O 3及水進行混合後，以料球重量比為1:5的市售球磨機(Ball Mill)混磨2小時後出料得到漿料狀態的混合物，鋼球為直徑3/16英吋的無鉻軸承鋼球。接著，將上述的混合物以市售空氣壓濾機進行脫水，脫水後的混合物的含水率約21±3%。 First, the main raw material iron oxide powder (Fe 2 O 3 ) and another main raw material strontium carbonate (SrCO 3 ) were prepared with the basic composition of SrO·nFe 2 O 3 (n=5.9), and 4.9wt% of After the trace additive La 2 O 3 and water were mixed, the mixture was milled for 2 hours with a commercially available Ball Mill with a weight ratio of 1:5 to obtain a mixture in a slurry state, and the steel balls were 3/16 in diameter. inch chrome-free bearing steel balls. Next, the above-mentioned mixture was dehydrated by a commercial air filter press, and the water content of the dehydrated mixture was about 21±3%.
接著，將脫水後的混合物進行煅燒步驟。以一市售烘乾機對該混合物進行預熱，其中烘乾機之溫度為300±10 oC，持溫時間為30至40分鐘，經過烘乾後的混合物含水率小於2%。之後，將該混合物放入一市售旋窯進行煅燒以形成一前處理物，煅燒溫度為1280±20 oC，煅燒時間為1小時，且煅燒時旋窯內之氧氣含量約5%。 Next, the dehydrated mixture is subjected to a calcination step. The mixture is preheated with a commercial dryer, wherein the temperature of the dryer is 300±10 o C, the temperature is maintained for 30 to 40 minutes, and the moisture content of the dried mixture is less than 2%. After that, the mixture was calcined in a commercial rotary kiln to form a pretreatment. The calcination temperature was 1280±20 oC , the calcination time was 1 hour, and the oxygen content in the rotary kiln was about 5% during calcination.
將經過旋窯煅燒之前處理物通過與旋窯相連結的溜管送入冷卻桶中進行冷卻。在前處理物的溫度降至90 oC以下時，通過裝置有旋風收集器之風選功能的松永式球磨機(Roller Mill)進行粗粉碎步驟，以使該些粗粉碎顆粒的平均粒徑約為2.5~2.7微米(例如約2.6微米)之窄單峰粒徑分佈。 The processed material before being calcined in the rotary kiln is sent to the cooling barrel for cooling through the chute connected with the rotary kiln. When the temperature of the pre-treatment material drops below 90 o C, the coarse pulverization step is carried out through a Matsunaga ball mill (Roller Mill) equipped with a cyclone collector, so that the average particle size of the coarsely pulverized particles is about Narrow unimodal particle size distribution of 2.5 to 2.7 microns (eg, about 2.6 microns).
之後，以上述的該混合物的總重為100重量份計，再加入各個組成物，包含1.5重量份的Co 3O 4、1.0重量份的CaCO 3、0.4重量份的SiO 2、0.03重量份的P 2O 5及0.05重量份的B 2O 3至球磨機中，於球磨機(Ball Mill)以料球重量比為1:12，磁粉漿料固含量約35~37%，轉速約為40rpm，鋼球是約為直徑Φ4.76mm的無鉻軸承鋼球，並分別以濕式研磨3~4以及9~10小時進行細粉碎步驟，以分別得到第一細粉碎顆粒及第二細粉碎顆粒，其中第一細粉碎顆粒的平均粒徑(或稱平均磁粉粒度(D 50))達到0.95±0.05μm (例如可通過市售的費氏粒徑分析儀測得之窄單峰粒徑分佈)，第二細粉碎顆粒的平均粒徑(或稱平均磁粉粒度(D 50))達到0.55±0.05μm (例如可通過市售的費氏粒徑分析儀測得之窄單峰粒徑分佈。之後，再將第一細粉碎顆粒及第二細粉碎顆粒混合以形成該改質鐵氧體磁粉，其中以該改質鐵氧體磁粉的總重為100wt%，該第一細粉碎顆粉係介於59.5wt%至60.5wt%之間，以及該第二細粉碎顆粒係介於39.5wt%至40.5wt%之間，該改質鐵氧體磁粉的平均粒徑約為0.7至0.8微米之間(例如約0.75微米)。 Then, based on the total weight of the above mixture as 100 parts by weight, each composition was added, including 1.5 parts by weight of Co 3 O 4 , 1.0 parts by weight of CaCO 3 , 0.4 parts by weight of SiO 2 , and 0.03 parts by weight of P 2 O 5 and 0.05 parts by weight of B 2 O 3 are put into the ball mill, the weight ratio of material to ball is 1:12 in the ball mill, the solid content of the magnetic powder slurry is about 35~37%, the rotation speed is about 40rpm, the steel The ball is a chromium-free bearing steel ball with a diameter of Φ4.76mm, and the fine pulverization step is carried out by wet grinding for 3~4 and 9~10 hours respectively, so as to obtain the first finely pulverized particles and the second finely pulverized particles, wherein The average particle size of the first finely pulverized particles (or the average magnetic particle size (D 50 )) reaches 0.95±0.05 μm (for example, the narrow unimodal particle size distribution can be measured by a commercially available Fisher particle size analyzer), and the second The average particle size of the two finely pulverized particles (or the average particle size of magnetic powder (D 50 )) reaches 0.55±0.05 μm (for example, a narrow unimodal particle size distribution that can be measured by a commercially available Fisher particle size analyzer. The first finely pulverized particles and the second finely pulverized particles are mixed to form the modified ferrite magnetic powder, wherein the total weight of the modified ferrite magnetic powder is 100wt%, and the first finely pulverized particles are between 59.5 Between wt % and 60.5 wt %, and the second finely divided particles are between 39.5 wt % and 40.5 wt %, the average particle size of the modified ferrite magnetic powder is between about 0.7 and 0.8 microns (for example, about 0.75 microns).
接著，進行(濕式)磁場配向成型步驟，使用市售的25噸之半自動濕式磁場成型機，對該改質鐵氧體磁粉進行20顆胚體的磁場配向成型，配向磁場強度為1.5特斯拉(Tesla)，成型壓力為3.5噸/平方公分(Ton/cm 2)，成型胚件尺寸為Φ26.5、厚度約13mm之圓胚。於實施例1中，經成型20顆胚體之平均所需濕式磁場成型時間為72秒，胚體之平均良率為97%。 Next, a (wet) magnetic field alignment molding step is performed, and a commercially available 25-ton semi-automatic wet magnetic field molding machine is used to perform magnetic field alignment molding of 20 embryos of the modified ferrite magnetic powder, and the alignment magnetic field strength is 1.5 tex Tesla, the molding pressure is 3.5 tons/square centimeter (Ton/cm 2 ), the size of the molding blank is Φ26.5, and the thickness is about 13mm. In Example 1, the average required wet magnetic field molding time for 20 embryos was 72 seconds, and the average yield of the embryos was 97%.
最後，進行一燒結步驟，對該胚體以介於1220至1240℃之間的溫度持續燒結達60分鐘，以製得實施例1之該鐵氧體磁石。Finally, a sintering step was performed, and the green body was continuously sintered at a temperature between 1220 and 1240° C. for 60 minutes to obtain the ferrite magnet of Example 1.
比較例1至3Comparative Examples 1 to 3
比較例1至3大致上相同於實施例1，唯其不同之處在於細粉碎步驟不同，並且不具有混合步驟。具體地，比較例1至3的細粉碎步驟皆各自形成單級平均粒徑的細粉碎顆粒，例如比較例1是單級球磨得到平均粒徑約為0.95微米的細粉碎顆粒；比較例2是單級球磨得到平均粒徑約為0.55微米的細粉碎顆粒；以及比較例3是單級球磨得到平均粒徑約為0.75微米的細粉碎顆粒，如下表一所示。Comparative Examples 1 to 3 are substantially the same as Example 1, except that the fine pulverization step is different, and there is no mixing step. Specifically, the finely pulverizing steps of Comparative Examples 1 to 3 each form finely pulverized particles with a single-stage average particle size. Single-stage ball milling obtained finely pulverized particles with an average particle size of about 0.55 microns; and Comparative Example 3 was single-stage ball milling to obtain finely pulverized particles with an average particle size of about 0.75 microns, as shown in Table 1 below.
表一
接著，利用市售儀器(中國計量科學研究院NIM-2000型 B-H Loop Tracer)量測各實施例與比較例中，各自的20顆鐵氧體磁石的各種磁氣性質，並且平均值計算，列於上表一。Next, the various magnetic properties of each of the 20 ferrite magnets in each of the examples and comparative examples were measured with a commercially available instrument (the NIM-2000 B-H Loop Tracer of the China Institute of Metrology), and the average value was calculated, as shown in the following table: in Table 1 above.
依據日本TDK FB9B，其規格中值分別為：B r=4500G； bH c=4300Oe； iH c=4500Oe；(BH) max=4.9MGOe。若是低於上述的規格中值，則表示該鐵氧體磁石未達商用標準。因此，由上表二可知，比較例1至3並未達到日本TDK FB9B規格中值的要求，而實施例1達到日本TDK FB9B規格中值的要求。 According to Japan's TDK FB9B, the median values of its specifications are: B r =4500G; b H c =4300Oe; i H c =4500Oe; (BH) max =4.9MGOe. If it is lower than the median value of the above specification, it means that the ferrite magnet does not meet the commercial standard. Therefore, it can be seen from Table 2 above that Comparative Examples 1 to 3 do not meet the requirement of the median value of the Japanese TDK FB9B standard, while Example 1 meets the requirement of the median value of the Japanese TDK FB9B standard.
然而，比較例1至3的成型時間不僅高於實施例1之外，比較例1至3的成型良率也低於實施例1。就一般工業考量，成型時間需小於120秒，並且良率需達75%以上才屬合格製程。另外值得一提的是，由於粒徑大於0且小於等於0.05微米的細微顆粒係與成型時間有正相關，故可知實施例1中的細微顆粒的含量少於比較例1至3的細微顆粒的含量。However, the molding time of Comparative Examples 1 to 3 is not only higher than that of Example 1, but also the molding yield of Comparative Examples 1 to 3 is lower than that of Example 1. For general industrial considerations, the molding time should be less than 120 seconds, and the yield should be more than 75% to qualify as a process. It is also worth mentioning that since the fine particles with a particle size greater than 0 and less than or equal to 0.05 μm are positively correlated with the molding time, it can be seen that the content of the fine particles in Example 1 is less than that of the fine particles in Comparative Examples 1 to 3. content.
實施例1可同時達到較高的整體磁特性以及較短的成型時間、較高的成型良率，其原因主要是: 因為實施例1中，取60±0.5%之「第一細粉碎顆粒」與40±0.5%之「第二細粉碎顆粒」，進行混合級配成實施例1之改質鐵氧體磁粉，其磁粉粒徑分佈窄且均勻(如第3圖所示)。微粉碎後的粒徑分佈若過大，容易於引起明顯的不連續晶粒成長，從而造成整體磁特性變差。反之，若粒度分佈愈窄，即瓷漿中磁粉的顆粒尺寸愈均勻，愈有利於後續濕式磁場成型與燒結。 由第3圖能明顯觀察到實施例1之磁粉粒徑分佈＜0.1μm之超微細粉的比例明顯降低，可改善其成型性。另一方面，其整體磁粉粒徑峰值降至0.75±0.05μm，可提升其燒結後永磁鐵氧體磁石微觀組織中之單磁區晶粒比例，有助於提升其整體磁特性。以實施例1之分級混合級配球磨技術所得到之瓷漿，因最長球磨時間僅9~10小時，整體球磨時間短，有利於永磁鐵氧體磁石之大批量生產。Example 1 can achieve higher overall magnetic properties, shorter molding time, and higher molding yield at the same time. The main reasons are: Because in Example 1, 60±0.5% of the "first finely pulverized particles" were taken. The modified ferrite magnetic powder of Example 1 was mixed and graded with 40±0.5% of "second finely pulverized particles", and the particle size distribution of the magnetic powder was narrow and uniform (as shown in Figure 3). If the particle size distribution after micro-pulverization is too large, it is easy to cause obvious discontinuous grain growth, thereby causing the overall magnetic properties to deteriorate. On the contrary, if the particle size distribution is narrower, that is, the particle size of the magnetic powder in the porcelain slurry is more uniform, which is more conducive to the subsequent wet magnetic field forming and sintering. From Fig. 3, it can be clearly observed that the proportion of ultrafine powder with particle size distribution <0.1 μm of the magnetic powder in Example 1 is significantly reduced, which can improve its formability. On the other hand, the peak particle size of the overall magnetic powder is reduced to 0.75±0.05 μm, which can increase the proportion of single magnetic domain grains in the microstructure of the permanent ferrite magnet after sintering, which helps to improve its overall magnetic properties. The ceramic slurry obtained by the grading, mixing and grading ball milling technology of Example 1 is beneficial to the mass production of permanent magnet ferrite magnets because the longest ball milling time is only 9-10 hours, and the overall ball milling time is short.
另要需要詳細說明的是，比較例3之作法有別於實施例1，其中比較例3直接以「單級」球磨，以使瓷漿於微粉碎後平均磁粉粒度(D 50)達到0.75±0.05μm (利用費氏粒徑分析儀測量)之作法，其內部磁粉中所含＜0.1μm之超微細粉的比例相對於實施例1仍然偏高(可從良率得知)，因此比較例3相對於實施例1之作法對於提升瓷漿之成型性幫助甚低。 It should be noted in detail that the method of Comparative Example 3 is different from that of Example 1, in which Comparative Example 3 is directly milled with a "single-stage" ball, so that the average particle size (D 50 ) of the magnetic powder after the micro-grinding of the ceramic slurry reaches 0.75± 0.05μm (measured by Fisher particle size analyzer), the proportion of ultrafine powder <0.1μm contained in the internal magnetic powder is still higher than that of Example 1 (it can be known from the yield), so Comparative Example 3 Compared with the method of Example 1, it is very less helpful for improving the formability of the porcelain paste.
綜上所述，本發明實施例之改質鐵氧體磁石的製造方法可節省成型所需時間，並且良率大於75%(甚至達97%)，並且對於永磁鐵氧體磁體的剩磁、矯頑磁力、矩形度以及磁場配向度也起到顯著提升的效果。To sum up, the manufacturing method of the modified ferrite magnet according to the embodiment of the present invention can save the time required for forming, and the yield rate is greater than 75% (even up to 97%), and the remanence, Coercive force, squareness and magnetic field alignment also play a significant role in improving.
雖然本發明已以較佳實施例揭露，然其並非用以限制本發明，任何熟習此項技藝之人士，在不脫離本發明之精神和範圍內，當可作各種更動與修飾，因此本發明之保護範圍當視後附之申請專利範圍所界定者為準。Although the present invention has been disclosed with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the present invention The scope of protection shall be determined by the scope of the appended patent application.
10:方法
11~15:步驟
20:方法
21~23:步驟10:
第1圖是本發明一實施例之改質鐵氧體磁粉的製造方法之流程方塊圖。 第2圖是本發明一實施例之改質鐵氧體磁石的製造方法之流程方塊圖。 第3圖是實施例1、比較例1及比較例2的細粉碎顆粒的粒徑分布圖。 FIG. 1 is a flow block diagram of a method for manufacturing modified ferrite magnetic powder according to an embodiment of the present invention. FIG. 2 is a flow chart of a method for manufacturing a modified ferrite magnet according to an embodiment of the present invention. FIG. 3 is a particle size distribution diagram of finely pulverized particles of Example 1, Comparative Example 1, and Comparative Example 2. FIG.
10:方法 10: Methods
11~15:步驟 11~15: Steps
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| TW202041468A (en) * | 2019-05-10 | 2020-11-16 | 中國鋼鐵股份有限公司 | Method of fabricating modified ferrite magnetic powder and ferrite magnet |
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| TWI728886B (en) * | 2020-07-30 | 2021-05-21 | 中國鋼鐵股份有限公司 | Method of evaluating moldability of ferrite magnetic powder |
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| JP2004296514A (en) * | 2003-03-25 | 2004-10-21 | Minebea Co Ltd | Ferrite magnet and its producing process |
| US9552910B2 (en) * | 2012-09-12 | 2017-01-24 | Lg Electronics Inc. | Ferrite magnet with salt and manufacturing method of the same |
| TW202041468A (en) * | 2019-05-10 | 2020-11-16 | 中國鋼鐵股份有限公司 | Method of fabricating modified ferrite magnetic powder and ferrite magnet |
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