Calcium hexaborate (also known as calcium borate) is a compound of calcium and boron, with the chemical formula of CaB6. It has excellent conductivity, high hardness, chemical stability and high melting point. It is a gray black solid, shiny and inactive powder with low density. It has a typical cubic structure of metal boride and is composed of octahedral units of 6 boron atoms and calcium atoms. CaB6 and lanthanum doped CaB6 show weak ferromagnetism, No.: 12007-99-7, and the microhardness is 27gpa. The relative density is 2.33, the melting point is 2200 ℃, the Knoop hardness is 2600kg / mm2, the young's modulus is 379gpa, and the pure crystal resistivity is greater than 2.10 10 Ω· M. CaB6 is a semiconductor having an energy gap of about 1.0 electron volts. It is stable at high temperature in the air, insoluble in hydrochloric acid and dilute sulfuric acid, does not react with water, can be eroded by strong oxidants such as chlorine, fluorine, nitric acid and hydrogen peroxide, and reacts slowly with alkali.

1. Structural information: the crystal structure of calcium hexaborate is a cubic lattice, the center of the crystal cell is calcium, and the apex is a three-dimensional boron network formed by a tight regular octahedron of boron atoms connected by boron boron bonds. Each calcium has 24 nearest boron atoms. The calcium atoms are arranged in a simple cubic stack, so there are holes between the eight calcium atoms located at the apex of the cube. The simple cubic structure is expanded by introducing octahedral B6 groups, which are filled with calcium and hexaboride groups. Another way to describe calcium hexaborate is CSCL type structure with metal B6 2-octahedral polymeric anions, where calcium atoms occupy CS sites and B6 octahedron is at CL sites. The CA-B bond length is 3.05 Å and the BB bond length is 1.7 Å.

The nuclear magnetic resonance (NMR) data of 43Ca contained -56.0 ppm δ Peak and at -41.3 ppm δ Different, wherein δ The maximum peak width is 0.85, and the negative shift is due to the high coordination number.  

Raman data: since the active modes are a1g, eg and t2g respectively, there are three Raman peaks at 754.3, 1121.8 and 1246.9cm-1 for calcium borate.  

Properties: CaB6 has been studied for its special physical properties, such as superconductivity, valence fluctuation and Kondo effect. However, the most remarkable characteristic of CaB6 is its ferromagnetism. It appears unexpectedly at high temperature (600 K) and low magnetic moment. The source of this high-temperature ferromagnetism is the connection between the ferromagnetic phase of the diluted electron gas and the assumed exciton state in the calcium borate or the external impurities on the sample surface. Impurities may include iron and nickel and may come from boron used to prepare samples.

2. Preparation method: evenly mix and dry calcium oxide and boron powder, and put them into high-temperature reaction furnace; Vacuum treatment shall be conducted before heating treatment in high-temperature reaction furnace; Calcium oxide and boron powder are reacted at high temperature under vacuum and inert gas; The calcium hexaborate ceramic powder was separated and purified; The separated and purified calcium hexaborate ceramic powder was ball milled to obtain uniformly dispersed calcium hexaborate ceramic powder. The method of the invention is simple and easy to realize, and the manufacturing cost is low. The prepared calcium hexaborate ceramic powder has small particles and uniform dispersion.

3. Typical application products:

◆ used as a boron containing additive for oxidation resistance, corrosion resistance and improving thermal strength of dolomite carbon and magnesium dolomite carbon refractories. CaB6 can improve the strength and bulk density of castable after treatment at various temperature stages

CaB6 can promote the high-temperature densification of the castable, so that the castable can obtain better oxidation resistance, higher high-temperature bending strength and erosion resistance. CaB6 can obviously improve various properties of castable for iron hook. When 0.5% calcium borate is added, the castable has better comprehensive properties.

◆ used as deoxidizing and degassing agent for high conductivity red copper to improve conductivity and strength.

◆ used as a new material for neutron protection in the nuclear industry.

◆ used as a new semiconductor material in spin electronic components with a Curie temperature of 900K. CaB6 has excellent conductivity and low work function, so it can be used as hot cathode material.

◆ used as raw material for manufacturing boron trichloride (BCl3) and amorphous boron.

◆ used as raw material for manufacturing high-purity metal borides (TiB2, ZrB2, HfB2, etc.) and high-purity boron alloys (Ni-B, Co-B, cu-b, etc.). Other borides, such as hexagonal boron nitride and superconducting MgB2, were prepared using CaB6 as raw material.

◆ it is used to produce the mixture of calcium boron nitride (ca3b2n4) and hexagonal boron nitride containing catalyst and to produce crystalline cubic boron nitride with excellent performance.

◆ used as desulfurizing, deoxidizing and boron increasing agent for boron alloy cast iron.

◆ used as desulfurizing, deoxidizing and boron increasing agent for boron steel.

◆ it is used as deoxidizer for metal smelting. It is an excellent deoxidizer for oxygen-free copper. The comparison test results show that calcium hexaborate deoxidizer is higher than copper boron alloy and phosphorous copper, and has purification effect on copper liquid, strengthening effect on copper matrix, and no pollution on copper liquid. When the content of calcium hexaborate is more than 0.60%, the oxygen content of copper liquid can be reduced to < 20 × 10-6, reaching the domestic first-class oxygen free copper standard. Calcium hexaborate has little effect on the conductivity of copper. The relative conductivity of copper is in the range of 88% ~ 91.6% when the amount of calcium hexaborate is in the range of 0.69% ~ 1.12%. With the increase of calcium hexaborate content, the tensile strength of copper continued to increase, and the elongation first increased and then decreased, and reached the maximum when the calcium hexaborate content was 0.88%.

◆ micro powder and additives for engineering ceramics

Application of CaB6 as a special ceramic and special ceramic additive: CaB6 can be used as an additive in the sintering process of some boride and carbide ceramics, on the one hand, it can improve various physical and chemical properties of ceramics. For example, taking ultrafine TiB2 as the matrix and adding CaB6 as the second phase, after hot pressing, the dissolution of Ca prevents the growth of grain, so that this kind of material has extremely high microhardness and bending strength. Calcium hexaborate has excellent properties such as extremely high melting point, hardness, strength, chemical stability, good electromagnetic performance and strong neutron absorption capacity, which makes it widely used in refractory and wear-resistant materials, composite materials, ceramic materials, semiconductor materials and nuclear control materials. Coating additives and aluminum magnesium alloys added with CaB6.

◆ calcium borate is used to produce boron alloy steel and oxygen-free copper as deoxidizing agent. The latter has higher conductivity than conventional phosphorus deoxidized copper due to the low solubility of boron in copper. CaB6 can also be used as high-temperature materials, surface protection, abrasives, tools and wear-resistant materials.

◆ CaB6 is also a promising candidate for n-type thermoelectric materials because its power factor is not less than that of common thermoelectric materials Bi2Te3 and PbTe.

4. Precautions: calcium borate is irritating to eyes, skin and respiratory system. Proper protective glasses and protective clothing shall be used when handling this product. Do not pour calcium borate into the drain pipe or add water to it.