The crystal structure of titanium

Titanium with two different allotropic forms, low (< 882.5 C) stable state for alpha and dense row of the six party system; high temperature stable state for beta type. Body centered cubic.

  The lattice parameter alpha -Ti, 25 DEG,Ca＝2.9503±0.0004Å，c＝4.6832
±0.0004Å，c / a=1.5873±0.0004. Because the ratio of c/a alpha -Ti less than ideal spherical 1.633 axle ratio, so ti is malleable metal. The impurities present alpha in -Ti have a significant impact on the lattice structure of trace oxygen, the presence of nitrogen makes lattice growth along the c axis, cause the increase of C value and a value, in fact almost does not change.

Clinical application hindering of pure titanium prosthesis

In the roasting temperature casting shrinkage crystal transition volume change larger material can compensate the pure titanium, but easy to molten titanium reacts, the fouling layer formation of thick, affect the physical and mechanical properties of titanium prosthesis.

  At present can not only solve the titanium restoration precision, but also can reduce the pollution of Titanium casting has not been reported buried materials package, so about titanium casting investment research and development work is still a hot spot.

  In addition, the current commercial better performance of several ti investments are expensive, the manufacturers instructions also require the use of casting system of the factory matching (Titanium alloy valve, titanium), this has to some extent increased titanium restoration cost, finally make titanium restorations be roughly the same price with the use of expensive metal material prices.

  This hinders widely used in clinical application of pure titanium prosthesis.

Titanium casting Condensing shrinkage

Although Japan through years of research, introduced the Titanium 
 -vest, Titanium-vest-D (Ohara Co.), Selevest-DM, Selevest-D (Center for rotating, the United States has Noyes Vinh phuc) Tycast Mold (Pentron Co.), Germany Tancovest (Bego Co.), Rematitan plus (Dentaurum Co.) and other commercial products, although all have their own advantages, but also the existence of their own shortcomings, such as the pollution layer too thick and lack of precision castings.

  Theory and molten titanium oxide was blunt in calcination temperature shape variables are not large, can not be compensated completely condensed shrinkage Titanium casting process

Precision casting of titanium denture

Titanium alloy valve resources in China ranks first in the world, for dental titanium denture to provide the most favorable conditions. Currently the most common titanium denture processing technology, is still using the method of precision casting, and PFM crown and bridge can be made into various bracket and titanium removable denture fixed denture base crown.

  However, molten titanium precision casting and oxygen, nitrogen, hydrogen and other elements, oxides, chlorides, fluorides are able to react strongly, resulting in Ti investments (mold material selection very difficult).

Titanium denture success

Gold titanium check valve is suitable for making dentures, but the price is expensive, difficult to widely used. Cobalt chromium, nickel chromium alloy although cheap, but because of containing Ni, Cr, Co and other harmful elements, so not ideal material for making dentures.

  Therefore, the developed countries from the 80's of the last century began to study the Titanium alloy valve restorations, both the processing technology of titanium teeth or with matching equipment, equipment, have made gratifying achievements.

How to maintain the accuracy of the castings

In order to avoid too fast reaction speed to make Titanium castings dissolved amount of difficult to control, not conducive to maintaining the precision of castings, and if the hydrogen permeation increases, also will make the mechanical properties of castings variation.

  In the practical application, the use of lower concentrations of HF and HNO3 mixed acid to remove surface contamination layer is Aerospace titanium castings suitable.

Complete removal of surface contamination layer of titanium castings

Experiments have confirmed the elevated HF concentration, the reaction is speeded up obviously, and the 0.6MPa pressure blasting test pieces in a concentration of 1mol:5mol mixed acid solution soak for 60sec can be completely remove surface contamination layer.

  Therefore, the use of high pressure blast Titanium castings soaked in low concentration of HF and HNO3 mixed acid solution in 60sec can achieve the purpose of complete removal of surface contamination layer.

The dissolved amount of titanium

The concentration of titanium alloy casting in HF and HNO3 in the mixed solution with HF and HNO3 dissolved quantity related, the former molar concentration is high, dissolving capacity of the latter molar concentration is low.

  Lower concentration of HF on the dissolution of Titanium  amount is small, but can get the surface is smooth, and easy to master the dissolved quantity.

Acid pickling of pure titanium castings

The dissolved quantity of HF solution at room temperature for titanium is far greater than the HCL and H2SO4 solution, and low concentration of HF can be 1.5% or 2.5% make Titanium  bulk dissolved in a very short period of time, the rapid improvement of surface roughness, surface hardness is decreased.

  For the titanium and its alloys in HF solution at room temperature can be a lot of soluble H2 (analytic 6HF+2Ti=2TiF3+3H2 arrow), and a passivation reaction in HNO3 solution,the chemical properties of the surface of the passivation layer is extremely stable.

  Visiblly, the corrosion rate of HNO3 solution is added into the HF solution can not only control of titanium, but can be significantly reduced due to Titanium casting surface hydrogen permeation and lead to the risk of hydrogen embrittlement, acid wash so experiment using mixed acid solution of HF and HNO3 of pure titanium castings.

How to overcome the uniform mechanical grinding removal

Because the thickness of contaminated layer of pure titanium surface with Titanium casting system for casting is about 75 mu m, and uniform thickness, so the removal of pollution layer of pure titanium surface with uniform removal method when the surface layer microstructure is more suitable .

  The industry usually uses acid dissolving and removing contaminated metal surface layer(Suan Xi), its purpose is to make the metal surface and evenly dissolved, removal of oxide skin, can effectively uniform removal of pollution layer of cast pure titanium  surface, to overcome the mechanical grinding removal amount is not uniform.

The first domestic dental titanium casting machine

Although the The Fourth Military Medical University and Henan Luoyang Jianxi light industry general machinery factory jointly developed the first domestic dental Titanium alloy valve, and in the domestic sales of 23 units, and laid a solid foundation for Titanium  denture in China extensively,

   But due to the Department of Stomatology crowns and bridges of the high accuracy requirement, the internal (shaft wall) fit < 73µm, marginal fit < 100 µm, there is no domestic embedding material can meet this demand.

Experimental study on pure titanium castings surface nitriding treatment

Surface modification of pure titanium castings for this study, in order to enhance its wear resistance and corrosion resistance, improve the surface color, so as to improve the performance and aesthetic effect of titanium prosthesis.

   Plasma nitriding of pure titanium casting experiment of puretitanium TA2 conventional  casting,

 mechanical polishing and then exposed to plasma nitriding furnace, glow plasma nitriding treatmentin ammonia atmosphere, glow voltage 700V, current of 13 ~ 15A, 150Pa vacuum nitriding furnace,temperature 700 C, permeability nitrogen time 1 ~ 4h, the study of plasma nitriding the pure titaniummicro hardness, wear resistance and corrosion resistance effect.

Pure titanium castings surface nitriding

Ti has good mechanical properties, chemical stability and biocompatibility, have been widely used in aerospace, marine, military and biomedical fields. Pure titanium in oral medicine is mainly used for making denture, crown and fixed bridge, orthodontic bracket,implant and titanium porcelain etc..

  Titanium  is self passivation of metal, a layer of stable and dense oxide film formed surface at room temperature, so it has good corrosion resistance. But pure titanium low hardness, wear resistance is poor, pure titanium prosthesis to function in oral BOC,titanium oxide films on the surface of friction force, shearing force under stress, prone to scratches and wear, dental caries preventive agents such as fluoride toothpaste, gel on the film also has a certain role in bad breaking.

Effects of fluoride on the corrosion resistance of pure titanium castings

Pure titanium due to good biocompatibility is widely applied in the field of oral medicine, such as titanium, titanium porcelain crown bridge bracket and titanium implant etc.. Its good biocompatibility because the pure titanium surface with a layer of compact oxide film, good chemical stability, so as to protect the pure titanium substrate from being corrosion preventing precipitation of titanium ion.

  But co existed in the fluoride ion and hydrogen ion condition, the surface of pure titanium oxide film is dissolved, the decrease of the corrosion resistance,resulted in the precipitation of titanium ion, likely to cause adverse effects on the surrounding tissue and human body.

Effects of titanium nitride coating on corrosion resistance of pure titanium castings

Pure titanium as a biological material, low density, good mechanical performance, strong corrosion resistance, good biology compatibility, so it is widely used in the field of oral medicine. However, pure titanium as the material of denture, poor wear resistance, color appearance, susceptible to fluoride corrosion.

  The academic topic related research has been conducted on the plasma nitriding / titanium nitride coating composite surface treatment, surface properties of titanium castings of biological safety, fungal adhesion properties and clinical application effect, experiment is mainly through the potentiodynamic polarization technique and ion release experiment was conducted to observe the effect of composite surface treatment of titanium castings in corrosion resistance of fluorine environment the application of dynamic.