Abstract:
A method for preparing a hybrid inorganic-organic nanostructured inhibitive pigment, includes premixing a first stock solution containing one or more cations and a second stock solution containing one or more oxoanions to form a premixture under pH control in the presence of polymers as surface modifiers. The premixture is then reacted to form a slurry. The slurry is then quenched to separate nanoparticles from the slurry, followed by surface functionalization in organic inhibitors.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of provisional application Ser. No. 62/019,918, filed Jul. 2, 2014. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to corrosion inhibitors and, more particularly, to a method for preparing a hybrid inorganic-organic nanostructured inhibitive pigment. 
         [0003]    Metallic components, achieve higher strengths through inclusion of alloying elements. However, the presence of these alloying elements tends to make the alloy vulnerable to corrosion. 
         [0004]    Corrosion inhibitive pigments provide a necessary function in protective coatings in the prevention of metal and alloy corrosion. The majority of high-performance pigments are currently based on hexavalent chromate chemistry. Hexavalent chromium may be relatively toxic such that alternatives are in demand. Conventional individual candidates proposed as alternatives to chromate, include rare earth metal cations: Ce 3+ , Y 3+ , La 3+ , Pr 3+ ; transition metal oxoanions: VO 3   − , MoO 4   2− , WO 4   2− , transition metal oxides: ZrO 2 , TiO 2 , NbO x , ZnO 2 , CoO x ; non-metal oxoanions: PO 4   3− , SiO 3 , B 2 O 4   2− ; and organic inhibitors of O, N, and S-containing organic molecules. However, none of these have been shown to be as effective as chromate. 
       SUMMARY 
       [0005]    A method for preparing a hybrid inorganic-organic nanostructured inhibitive pigment according to one disclosed non-limiting embodiment of the present disclosure includes premixing a first stock solution containing one or more cations and a second stock solution containing one or more oxoanions to form a premixture in the presence of polymers as surface modifiers; reacting the premixture to form a slurry; quenching the slurry; and separating nanoparticles from the slurry after the quenching. 
         [0006]    A further embodiment of the present disclosure includes, wherein the first stock solution includes a Zn 2+  citric complex solution (1:1). 
         [0007]    A further embodiment of any of the foregoing embodiments of the present disclosure includes wherein the first stock solution includes a Ce 3+  EDTA complex solution (1:1). 
         [0008]    A further embodiment of any of the foregoing embodiments of the present disclosure includes wherein the first stock solution includes a Pr 3+  tartaric complex solution (1:1). 
         [0009]    A further embodiment of any of the foregoing embodiments of the present disclosure includes wherein the second stock solution includes a MoO 4   2− , PO 4   3− , SiO 3− , mixed with 1-2 w % polymers as surface modifiers. 
         [0010]    A further embodiment of any of the foregoing embodiments of the present disclosure includes controlling the pH of the premixture between 8-10 pH. 
         [0011]    A further embodiment of any of the foregoing embodiments of the present disclosure includes wherein reacting the premixture to form the slurry is performed as a hydrothermal process. 
         [0012]    A further embodiment of any of the foregoing embodiments of the present disclosure includes wherein quenching the slurry includes cooling with distilled water. 
         [0013]    A further embodiment of any of the foregoing embodiments of the present disclosure includes wherein separating the nanoparticles from the slurry is performed with a membrane filter followed by surface functionalization in organic inhibitors. 
         [0014]    A further embodiment of any of the foregoing embodiments of the present disclosure includes washing the nanoparticles with distilled water. 
         [0015]    A further embodiment of any of the foregoing embodiments of the present disclosure includes dispersing the nanoparticles in organic inhibitors for surface functionalization after washing. 
         [0016]    A further embodiment of any of the foregoing embodiments of the present disclosure includes wherein the cations include at least one of a rare earth and transition metal cations. 
         [0017]    A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the oxoanions includes at least one of a transiton metal and a nonmetal. 
         [0018]    A further embodiment of any of the foregoing embodiments of the present disclosure includes wherein the polymer includes at least one of a polyacrylic acid (PAA) and a polyvinyl alcohol (PVA). 
         [0019]    A hybrid inorganic-organic nanostructured inhibitive pigment, according to another disclosed non-limiting embodiment of the present disclosure includes two or more corrosion inhibitive species in an inorganic core, organic shell nanoparticle from a metal-ion-ligand/complex-polymer based precursor solution. 
         [0020]    A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the metal ions complexed with a chelating agent. 
         [0021]    A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the chelating agent include an organic amines. 
         [0022]    A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the organic amines include diethanolamine (DEA). 
         [0023]    A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the organic amines include triethanolanine (TEA). 
         [0024]    A further embodiment of any of the foregoing embodiments of the present disclosure includes, wherein the chelating agent includes an organic acid. 
         [0025]    The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation of the invention will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be exemplary in nature and non-limiting. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
           [0027]      FIG. 1  is a schematic of a hydrothermal process for hybrid inorganic-organic nanostructured inhibitive pigments; and 
           [0028]      FIG. 2  is a schematic of the synthesis of inorganic (core) and organic (shell) nanostructures for preparing a hybrid inorganic-organic nanostructured inhibitive pigment. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]      FIG. 1  schematically illustrates a hydrothermal process  10  for preparation of a hybrid inorganic-organic (core-shell) nanostructured inhibitive pigment  100  ( FIG. 2 ). The preparation of the hybrid inorganic-organic nanostructured inhibitive pigment  100  is via a chemical precipitation process, in combination with in-situ follow-up surface modification processes, i.e. polymer surfactants, pH control and organic inhibitors that provide an effective chromate alternative. 
         [0030]    Initially, at least a first stock solution  20 , such as, for example only, zinc (Zn 2+ ) citric complex solution (1:1), cerium (Ce 3+ ) EDTA complex solution (1:1), or praseodymium (Pr 3+ ) tartaric complex solution (1:1) is premixed with a second stock solution  30 , as an example, such as molybdate (MoO 4   2− ) , phosphate (PO 4   3− ), silicate (SiO 3   − ), added with 1-2 w % polymers, such as polyacrylic acid (PAA) and Polyvinyl alcohol (PVA). The precursor solutions include the desired metal ions complexed with a chelating agent, and metal-oxide anions dispersed in polymer/surfactants (surface modifiers). The chelating agents include organic amines such as diethanolamine (DEA), and triethanolanine (TEA), as well as organic acids such as citric/oxalic/tartaric acid, etc. That is, two or more corrosion inhibitive species (i.e. Ce 3+ , Pr 3+ , Zn 2+ , VO 3   − , MoO 4   2− , PO 4   3− , SiO 3   −  and organic molecules, etc.) are incorporated in the form of the inorganic (core)-organic (shell) nanoparticles as inhibitive pigments, prepared from metal-ion-ligand/complex-polymer based precursor solutions. 
         [0031]    The first stock solution  20  and the second stock solution  30  are, for example, communicated through respective high pressure pumps,  22 ,  32  to premix at a controlled pH  40 . In this disclosed non-limiting embodiment, the flow rate is about 10-15 ml/min flow at 20° C. such that the pre-mixture is at 20° C., 25-50 MPa with the pH controlled to about 8-10 pH. 
         [0032]    The premixed solution is then reacted in a heated and pressurized reactor  50 . In this disclosed non-limiting embodiment, the premixed solution is heated and pressurized with distilled water  52  at about 300° C.-400° C., 25-50 MPa to generate a hydrothermal process at a supercritical condition. The distilled water  52  is communicated through a high pressure pump  60  which, in this disclosed non-limiting embodiment, is at about 300° C.-400° C. at a flow rate of about, 50-70 ml/min. 
         [0033]    The reacted premixed solution produces a reaction product slurry  70  that is quenched and cooled by the distilled water  52 . In this disclosed non-limiting embodiment, the distilled water is supplied at about 20° C., 25-50 MPa. 
         [0034]    The nanoparticles are then separated by a membrane filter, washed with distilled water, then dispersed in organic inhibitors for surface functionalization to provide the hybrid inorganic-organic nanostructured inhibitive pigment  100  ( FIG. 2 ). A back-pressure regulator  90  may be utilized to control the separation. 
         [0035]    The chemical nature of the polymer/surfactant modified inorganic precursor core  108  with the organic porous polymer shell  110  ( FIG. 2 ) composites allows combination with organic inhibitor additives  102  ( FIG. 2 ) to produce the hybrid inorganic-organic nanostructured inhibitive pigment  100 . The organic inhibitor additives include amphiphilic molecules composed of a hydrophilic or polar moiety known as head  104  and a hydrophobic or nonpolar moiety known as tail  106 . 
         [0036]    Example organic inhibitor additives include, but are not limited to: 4,5-Diamino-2,6-dimercaptopyrimidine (C 4 H 6 N 4 S 2 ); 4,5-Diaminopyrimidine (C 4 H 6 N 4 ); Sodium diethyldithiocarbamate ((C 2 H 5 ) 2 NCSSNa); 2-Mercaptopyridine (C 5 H 5 NS); Thiophenol (C 6 H 5 SH); 4-mercaptobenzoate (C 7 H S O 2 S); 2-mercaptobenzoate (C 7 H S O 2 S); 6-Mercaptonicotinate (C 6 H 5 NO 2 S); 2-Mercaptonicotinate (C 6 H 5 NO 2 S); 2-mercaptosuccinate (C 4 H 4 O 4 S); mercaptoacetate (C 2 H 3 O 2 S); Sodium-mercaptopropionate (C 3 H 5 NaO 2 S). 
         [0037]    Example polymers/surfactants include: acetylacetone polyacrylamide (PAM); phosphonate-polyethlene glycol (PEG); and polyacrylic acid (PAA), propylamine phosphonate-polyethlene glycol (PEG); sulfonated acylate copolymer; polyvinyl pyrrolidone (PVP); and hydroxypropylcellulose (HPC). 
         [0038]    The hydrothermal process  10  provides one approach to synthesize a hybrid inorganic-organic nanostructured inhibitive pigments, having multiple corrosion protection modes for use as a chromate replacement. The nano-sized pigments reduce costs and improve coating performance as one challenge in applying nano-sized particles as pigments is the strong aggregation during their synthesis process commonly observed in nanoparticles that have been produced from the liquid phase. This agglomeration is, readily resolved by use of the disclosed in-situ surface modification technique during the pigment synthesis process. 
         [0039]    Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure. 
         [0040]    The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.